The present description refers to a method and a kit for the in vitro prediction and/or monitoring of chemoresistance of leukemic forms through the detection of the hERG1 channel on the plasma membrane of leukaemia cells and the expression thereof in terms of median fluorescence index (MFI).

STATE OF THE ART

Leukaemia is a general term which encompasses a wide spectrum of diseases: a first distinction is between acute and chronic forms. Moreover, the pathology can be divided into lymphoblastic (lymphoid) leukaemias and myeloid leukaemias, which can show either acute or chronic forms in the adults and acute forms in children, hence we can refer to either paediatric leukaemias or adult leukaemias. The combination of the two classification criteria leads to the identification of four main forms of leukaemia: Acute lymphoblastic leukaemia (ALL); Chronic lymphoid leukaemia (CLL); Acute myeloid leukaemia (AML); Chronic myeloid leukaemia. ALL is the most common leukemic form in children, but can affect also adults, older than 65 years. Standard treatments include chemotherapy and radiotherapy. Survival varies depending on patients' age: it is 70-80% in children, 50% in adults. CLL mainly affects adults, males, over 55 years old, and is never in children. Five years survival is around 75%. AML more frequently affects adults, more rarely children, and five years survival of this leukaemia form is around 40%. Also in this case, the elected treatment is chemotherapy, and, sometimes, bone marrow transplantation. CML affects mainly adults, and only in a small percentage children. The elected treatment includes a targeted inhibitor, i.e. Imatinib (Gleevec), which inhibits the bcr/abl protein. Five year survival is around 80%.

In the last years, acute leukaemia survival and, particularly, acute leukaemia survival, has greatly improved. Despite this fact, recurrence still occurs in a high percentage of children and/or adults affected by this disease. These failures of chemotherapy lead to the suggestion of bone marrow transplantation, having a strong impact not only on the patient, but also on the health services, due to the high costs of transplants. The main cause of the treatment failure is due to mechanisms of intrinsic or acquired drug resistance. One of the major causes of chemoresistance lies in the protective effect exerted by the bone marrow microenvironment, and in particular by bone marrow stromal cells. It has been shown that bone marrow stromal cells provide a refuge for some leukemic cell populations, in particular for stem cell populations that are responsible for the development and maintenance of the leukemic disease, and that can escape the apoptotic death induced by chemotherapy and can acquire a treatment-resistant phenotype (Konopleva, M et al. Stromal cells prevent apoptosis of AML cells by up-regulation of anti-apoptotic proteins. Leukemia 16: 1713-1724 (2002).

The protection mechanisms mediated by stromal cells involve complex reciprocal interactions between stroma-derived factors, in particular the SDF-1 a chemokine (stroma-derived factor 1 a) and its receptor CXCR4 (Zeng , Z et al . Inhibition of CXCR4 with the novel RCP168 peptide overcomes stroma-mediated chemoresistance in chronic and acute leukaemias. Mol. Cancer Ther. 5: 31 13-3121 (2006)). A further mechanism by which stromal cells confer protection to leukemic cells, involves the interaction between adhesion receptors (in particular the VLA4integrin), expressed on leukaemia cells, and adhesion molecules, su ch as fibronectin, displayed on the surface of marrow stromal cells (Tabe, Y et al. Activation of integrin-linked kinase is a critical prosurvival pathway induced in leukemic cells by bone marrow-derived stromal cells. Cancer Res. 67: 684-694 (2007)). Recent data highlight how integrins can trigger survival signals inside cells, through the assembly of macromolecular complexes with different proteins present on the plasma membrane. One of the partners involved in these complexes is represented by ion channels. The channel protein is not only a passive interactor, but often feed backs by controlling integrin activation and downstream signalling (Arcangeli, A Becchetti, A. Complex functional interaction between integrin receptors and ion channels. Trends Cel. I Biol. 16: 631 -639 (2006)). These mechanisms can provide a molecular confirmation to the recent demonstration that ion channels, mainly K ⁺ channels, mark and regulate specific steps of neoplastic progression, and may hence represent novel targets for antineoplastic therapy (Arcangeli, A et al. Targeting ion channels in cancer: a novel frontier in antineoplastic therapy. Cur. Med . Chem. 16(1 ): 66-93 (2009)). Among ion channels, hERG1 channels (also known as KCNH2 or Kv1 1 .1 , Gene Bank AAH01914.2), encoded by the et er-a-go-go-related gene 1, represent a relevant example of how this kind of K ⁺ channel is capable form multi- protein complexes on the plasma membrane of tumour cells (Arcangeli, A Becchetti, A. Complex functional interaction between integrin receptors and ion channels. Trends Cel. I Biol. 16: 631 -639 (2006)). Moreover, hERG1 channels represent an important pharmacological target for antineoplastic therapy, as already hypothesized and reported in the literature published by the inventors (5), and as demonstrated by the fact that drugs that can block hERG1 (that we shall call from now on "hERG1 blockers") inhibit neoplastic growth and progression, both in vitro and in vivo (Arca ngel i , A et a l . Targeti ng ion cha n nels i n ca ncer: a novel frontier i n antineoplastic therapy. Cur. Med. Chem. 16(1 ): 66-93 (2009).

Pillozzi S et al , 2002 (Pillozzi S., et al. HERG potassium channels are constitutively expressed in primary human acute myeloid leukemias and regulate cell proliferation of normal and leukemic haemopoietic progenitors. Leukemia, 16, 1791 -1798, (2002)) and Pillozzi S et al, 2007(Pillozzi S, et al. VEGFR-1 (FLT-1 ), βΐ integrin and hERG K ⁺ channel form a macromolecular signalling complex in acute myeloid leukemia: role in cell migration and clinical outcome. Blood, 1 10: 1238- 1250, (2007)), and the already cited Arcanqeli A et al., 2009 (Arcangeli, A et al. Targeting ion channels in cancer: a novel frontier in antineoplastic therapy. Cur. Med. Chem. 16(1 ): 66-93 (2009)), highlight the important role of the hERG1 channel in the leukaemic disease. In the first paper it is described how hERG1 activity is related with proliferative mechanisms and with cell cycle progression, both in AML cell lines and primary samples. Differently from normal hematopoietic progenitor cells, hERG1 resulted as constitutively expressed in leukaemic cells and is necessary for their progression into the cell cycle. The cited papers show how the administration of "hERG1 blockers" (class III antiarrhythmic drugs, such as E4031 or Way 123,398), impairs cellular growth.

Finally, in the publication Arcangeli, A et al. Targeting ion channels in cancer: a novel frontier in antineoplastic therapy. Cur. Med. Chem. 16(1 ): 66-93 (2009), the authors have provided several experimental evidences not only to the fact that hERG1 plays a fundamental role in the control of different aspects of neoplastic progression, both in leukaemias and in human solid cancers; but also to the fact that it represents an excellent pharmacological target for antineoplastic therapy. In fact, in the literature, but also on the pharmaceutical market, many drugs exist capable of blocking the hERG1 channel ( "hERG1 blockers"). In the publication (5) the authors show numerous evidences, both in vitro and in vivo, that some "hERG1 blockers" (in particular class I II anthyarrhythmics, such E4031 and Way 123,398) behave as potential antineoplastic drugs.

The failure of chemotherapy due to the onset of chemoresistant leukaemic forms leads to the need of identifying methods that allow predicting and/or monitoring chemoresistance with the aim to identify the most suitable treatment for treating the leukaemia from of interest.

SUMMARY OF THE INVENTION

The present description refers to a method and a kit for the in vitro prediction and/or monitoring of chemoresistance or drug-resistance of leukaemic forms. As shown by the state of the art, it is not possible at present to predict or monitor chemoresistance of leukaemic forms due to the lack of methods which use specific molecular markers. The authors found that the expression level, per se, of the ion channel hERG1 on the plasma membrane of leukaemic cells can be transformed i nto a n i n d ex th at a l l ows the prediction of the possible development of chemoresistance or the monitoring of the level of chemoresistance itself, e.g. after the application of particular therapeutic protocols.

The method and the kit of the invention allow the identification a numerical value that is directly correlated to the expression of the hERG1 allowing establishing unambiguously whether the leukaemic form under analysis will develop or not chemoresistance (or pharmacoresistance).

The present description therefore refers to a method and/or a kit for the in vitro prediction and/or monitoring of chemoresistance of the analysed leukaemic forms, based on the median fluorescence index (MFI) value that is a value identified for the first time in the present description that is correlated with the expression level of hERG1 on the plasma membrane of leukaemic cells. The MFI value allows a classification of the sample under analysis into: a leukaemic form that will develop chemoresistance or a leukaemic form that will not develop chemoresistance.

Object of the present description are:

- an in vitro method for the prediction and /or monitoring of chemoresistance of leukemic forms, comprising the following steps:

a) incubating a sample x of primary leukemic cells from a patient, with a anti- hERG1 monoclonal antibody, specific for the external portion of said ion channel;

b) incubating the cells obtained in step a) and a sample y of primary leukemic cells from the same patient that were not previously incubated with said primary antibody, with a fluoroch rome-labelled secondary antibody, specific for the primary antibody;

c) evaluating the fluorescence of both samples by flow cytometry;

d) calculating the MFI value, determined as the ratio between the fluorescence displayed by the sample x and the fluorescence displayed by sample y; wherein a MFI value equal or greater than 25 is predictive of chemoresistance in the analysed sample x, or indicates an already existing chemoresistance;

Steps a), b), c) and d) may also be carried out on a control sample, consisting of mononuclear cells isolated from the peripheral blood of a healthy donor. The M FI value of the control sample may represent a negative control for the method. - a kit for the in vitro prediction and/or monitoring of chemoresistance of leukemic forms comprising on e or m ore al iq u ots of a primary anti-hERG1 monoclonal antibody, specific for the external portion of the above-mentioned ion channel, and instructions for MFI calculation.

GLOSSARY

hERG1 . In the present description "hERG1 " indicates the potassium channel encoded by the human gene KCNH2 (or Kv1 1 .1 , Gene Bank AAH01914.2) in all its possible isoforms; where "hEGV is indicated in the text, it is possible to read it also as "the mammal homologue" of hERG1 .

Chemoresistance. To the aims of the present description, the term chemoresistance, or more generally pharmacoresistance (drug resistance), means a reduction or a l a ck of res po n s iveness to one or more drugs, such as chemotherapeutic d rugs used alone or in combination, also with drugs commonly used in antineoplastic therapies (such as, for example, antibiotics, corticosteroids etc).

Leukemic cells. In the present description the term "leukemic cells" means cells directly derived, or manipulated, from biological samples of leukemic forms.

Leukemic forms. The term "leukemic forms", in the present description, means a group of malignant diseases characterized by an uncontrolled, hence neoplastic, proliferation of hematopoietic cells.

Responsiveness. For the purposes of the present description, the term "responsiveness" means the ability of a cell and/or more generally of a patient, to respond as desired by the researcher/clinician in a particular therapeutic treatment; responsive cells and/or patients are those on which the therapeutic treatment operates in a curative manner; on the contrary, non-responsive cells and/or patients are, in the present description, cells and/or patients on which a cancer treatment is ineffective because of the chemoresistance of the treated leukaemia form.

MFI: this term means the mean fluorescence intensity of the sample labelled firstly with a primary anti-hERG1 antibody and subsequently with a fluorochrome- labelled secondary antibody specific for the primary antibody, referred to the fluorescence intensity of a sam ple of the same cells label led on ly with the fluorochrome-labelled secondary antibody. In this particular case, it is an indirect, semi-quantitative, index of the amount of hERG1 protein present on the plasma membrane of the cells under study. DETAILED DESCRIPTION OF THE FIGURES

Figure 1. Effect of hERG1 inhibitor drugs on apoptosis induced by Doxorubicin in human leukemic cells, cultured in vitro in the absence or in the presence of marrow stromal cells (MSC), and treated with E4031 , Erythromycin, Sertindole and Way (indicated with +) or not treated (indicated with -). A, B) 697 cells; C) ALL Cells (3), ALL(4) e ALL(6). Aliquots of 1 x10 ⁵ cells have been centrifuged at 1 100 rpm for 5 minutes (min) and washed in PBS 1X before incubation at room temperature for 15 minutes with the primary antibody (murine monoclonal anti hERG1 antibody, produced in our laboratory, which recognizes an extracellular portion of the channel, diluted 1 :50). At the end of incubation, washes in PBS 1 X are performed, followed by a 15 min incubation with the secondary antibody (anti-mouse IgG FITC (1 μg 10 ⁶ cells)). The pellet is washed twice in PBS and re-suspended in 500 μΙ of 1 % formalin in PBS solution. The analysis is carried out with the FACScan flow cytometer (Becton Dickinson). We standardized a method that allows expressing in absolute quantitative terms the expression of hERG1 at the level of the cell plasma membrane, regardless of the flow cytometer used, of the voltage of photomultiplier and of the user. The detection of the analysed antigen is obtained by using fluorescent tracers that generate a signal which is translated in terms of intensity of fluorescence. The Mean Fluorescence Index (MFI) is defined as the ratio between the mean fluorescence of the sample under analysis and the fluorescence of a sample incubated only with the secondary antibody (that is fluorescent and hence shows a signal which is not due to the direct antigen- antibody binding). In other words, such index can be calculated as the ratio between the specific signal of the sample which labelled both with the primary and secondary antibody (mean fluorescence of the sample = FC) and the aspecific signal obtained in the same sample labelled only with the secondary antibody (mean fluorescence of the control = Fc), multiplied by 100: hence MFI = FC/Fc 100. The values obtained, expressed in a percentage scale, provide an estimate which is independent of the fluorophore bound to the secondary antibody (in fact one can use Cy3, Cy5, Alexa 488, PE, other than FITC) and of the flow cytometer which has been used.

DETAILED DESCRIPTION OF THE INVENTION

As previously indicated, the presence of hERG1 ion channels on the plasma membrane of leukemic cells and their ability to form macromolecular complexes with different membrane proteins plays a relevant role in triggering molecular signals responsible for the survival of leukemic cells inside the bone marrow.

It is indeed the survival of these cells inside the bone marrow that is responsible for the chemoresistance observed in some patients. The need of selectively targeting these chemoresistant (or drug-resistant) leukemia cells is to be considered a primary objective in order to avoid to the patient exhausting, but unfortunately ineffective, treatments. The medical staff, nowadays, has no valuable tools allowing to determ i ne i n adva nce wh eth er th e patient wi l l devel op chemoresistance (or pharmacoresistance), and hence to decide which treatment protocol would be more suitable. Unfortunately, only the course of the disease is able to indicate the effectiveness or ineffectiveness of the treatment that has been carried out, with obvious negative implications, both clinical and psychological, for the patient when the disease recurs.

There is therefore an urgent need, in the state of the art, of identifying a priori the patient that will develop or not develop chemoresistance in order to establish the most appropriate therapeutic protocol.

The present description, therefore, provides an in vitro method for the prediction and/or monitoring of chemoresistance in leukemic forms, comprising the following steps:

a) incubating a sample x of primary leukemic cells from a patient, with an anti-hERG1 monoclonal antibody, specific for the external portion of the ion channel;

b) incubating the sample obtained after incubation of step a) and a sample y of primary leukemic cells from the same patient, not previously incubated with the primary antibody, with a fluorochrome-labelled secondary antibody, specific for the primary antibody,;

c) evaluating the fluorescence of both samples by flow cytometry;

d) calculating the MFI value as the ratio between the fluorescence displayed by the sample x and the fluorescence displayed by sample y: a MFI value equal or greater than 25 is predictive of chemoresistance in the analysed sample x under, or is an index of already-existing chemoresistance;

Steps a), b), c) and d) may also be applied to a control sample, consisting of mononuclear cells isolated from the peripheral blood of a healthy donor. The MFI value of said control sample will represent a negative control for the procedure.

The term "leukaemic forms", in the present description, indicates a group of malignant diseases characterized by an uncontrolled, and hence neoplastic, proliferation of hematopoietic cells. On the basis of the hematopoietic lineage, myeloid or lymphoid, involved, we can distinguish a myeloid leukaemia (ML) and a lymphoblastic leukaemia (LL). Moreover, on the basis of the clinical course, we can distinguish acute leukaemic forms and chronic leukaemic forms. Therefore, it is possible to distinguish different types of leukaemic forms, namely: acute lymphoblastic leukaemia, acute myeloid leukaemia, chronic lymphoid leukaemia, and chronic myeloid leukaemia. Such leukaemia forms can develop, as already described, both in adult and paediatric subjects, although with different clinical courses and percentages of success.

For the purposes of the present description, the term chemoresistance, or, more generally, pharmacoresistance (drug resistance), means a reduction or a lack of responsiveness to one or more drugs, such as chemotherapeutic drugs used alone or in combination, also with drugs commonly used in antineoplastic therapies (as, for example, antibiotics, corticosteroids etc).

The method herein described has the aim of predicting whether leukaemic forms selected in the group comprising both adult and paediatric leukaemias, as for example the acute lymphoblastic leukaemia (both paediatric and of the adults), the acute myeloid leukaemia (both paediatric and of the adults), the chronic lymphoid leukaemia of the adult and the chronic myeloid leukaemia of the adults, will develop or will not develop chemoresistance or, in other terms, whether said forms will prove to be responsive to particular chemotherapy drugs. In particular, the method herein claimed is an important tool available to the person skilled in the art, because it allows to establish a priori whether a particular patient will develop chemoresistance (or drug resistance), thus allowing the identification of the most appropriate therapy. Moreover, such meth od a lso a l lows to mon itor, i.e. to verify course of chemoresistance in time with the aim, for example, of identifying the effectiveness of a particular therapeutic protocol.

The information regarding the prediction and/or the monitoring of the course of chemoresistance through the time, will be obtained by an analysis and elaboration of the data obtained on the expression levels of the ion channel hERG1 on the plasma membrane of leukaemic cells.

The leukaemic cells to be analyzed will be cells obtained by biological samples of leukaemic forms selected in the group comprising adult and paediatric leukaemias, such as for example the acute lymphoblastic leukaemia, both paediatric and of the adults, the acute myeloid leukaemia, both paediatric and of the adults, the chronic lymphoid leukaemia of the adult and the chronic myeloid leukaemia of the adult.

The biological sample from which the leukaemic cells will be obtained, may be any sample, fresh or frozen, from which it is possible to isolate said cells; in particular, it will be e.g. possible to use blood and tissue samples. By way of example and without limitation of the scope of this description, the tissue samples that can be used are fresh or frozen samples obtained from lymph node biopsies taken from leukaemic patients. Further biological samples usefu l to isolate leukaemic cells are represented by bone marrow aspirates or peripheral blood collection of leukaemic patients.

The biological samples may be used either fresh or not fresh. The skilled person does not need in this description any further information on the various techniques for the storage of biological material since he will be able to choose, with no inventive effort, the most suitable technique for his needs taking into account the detailed information provided in any laboratory manual.

The isolation of the leukaemic cells, starting from the set of cells of different nature present in the biological sample, can be performed using conventional techniques, e.g. by using any one of the molecular features that biochemically define said leukemic cells.

In a particular embodiment, the leukaemic cells can be isolated by density gradient centrifugation (Ficoll-Hypaque (d = 1077 g/ml)) (as indicated in the protocol in RA Abrams icoll-Hypaque separation of bone marrow cells". Blood 1 985; 66:472:473). In general, any method known by the skilled person, allowing the isolation of the population of leukem ic cells to analyse from a cells pool, is considered suitable for the scopes of this description.

The leukaemic cells to be analyzed according to the method herein described, will be incubated at suitable temperatures and for suitable times, with a monoclonal antibody specific for the extracellular portion of the hERG1 channel, re- suspended at suitable concentrations into a suitable buffer, e.g. PBS.

For the purposes of the present description, a monoclonal antibody specific for the extracellular portion of the hERG1 channel means any monoclonal antibody capable of selectively binding to the hERG1 channel only when it is present on the extracellular side of the plasma membrane, with the aim to identify only the hERG1 channel present on the external face of the plasma membrane.

The ionic channel hERG1 is a K ⁺ channel that, as already outlined, it can form multi-protein complexes on the plasma membrane of tumour cells and can regulate specific steps of neoplastic progression.

The hERG1 channel shows an extracellular portion of about 100 amino acids that ca n be u sed to identify recognition epitopes that can be used for the development of antibodies. The extracellular portions of said channel suitable for making epitopes may be, for example, the S1 -S2 portion, the S3-S4 portion, the S5- Pore portion. It is worth noting that the S1 -S2 portion is particularly suitable for the development of antibodies specific for the extracellular portion of the hERG1 channel.

For the purposes of the present invention any of such epitopes or any extracellular suitable region of the channel, may be used for the development of an anti-hERG1 monoclonal antibody, following what is known to the skilled person. The development of monoclonal antibodies is now carried out by conventional techniques, taught in laboratory manuals, and it is also carried out as a service by a number of biotech companies. Further details will therefore not be necessary in this description for the creation of antibodies that can also be ordered from the appropriate companies.

In order to develop a monoclonal antibody any standard technique for the development of primary antibodies will be suitable: it is herein briefly reminded that any specific antibody, recognising a specific antigenic determinant (epitope), is produced by a specific B lymphocyte. The isolation and culture in vitro of a cell capable of producing a single antibody represents a source of monoclonal antibodies (mono-specific). However, B lymphocytes, when cultured in vitro, die after a short time, and hence cannot be a source for the long term production of antibodies.

The technology of monoclonal antibodies comprises the isolation of these B lymphocytes e their subsequent fusion with transformed cells (myeloma cells), useful for their characteristics of higher proliferation and survival. Many of the resulting hybrid cells (or hybridomas), that are cultured in vitro, will maintain their immortality, in addition to producing large amounts of the mono-specific antibody.

The fusion between B lymphocytes (obtained from the spleen and lymph nodes of an immunized animal) and the murine myeloma cells (mouse is the most used animal), is obtained by the participation of a membrane fusion promoter, such as Polyethylene glycol.

The medium in which hybridomas are cultured is a selective medium, known as HAT that, due to its composition, inhibits the growth of both myelomas and non- fused spleen cells, but not of the hybridoma cells which complement the two parental cells.

Hybridomas are submitted to a screening for the identification of the desired specific antibodies and the selected ones are then initiated to storage or mass production.

Furthermore, monoclonal anti-hERG1 antibodies, which are specific for epitopes present on the extracellular portion and can be utilized in flow cytometry, are also commercially available (e.g. ALX-804-652-R300, from Alexis-Biochemical or ABIN195450 from Antibodies on-line) and may be used for the purposes of the present invention, without providing any further detail in this description.

The details on protocols for the incubation with the primary antibody are well known to the person skilled in the art and, when commercially available antibodies are used , such details are reported in the manufacturer's instructions. Such incubation protocols imply the use of appropriate buffers, such as, e.g., PBS (phosphate buffer saline) or, when commercially available antibodies are used, buffers specifically suggested by the manufacturer. The dilution of the antibody, taking into account the cytofluorimetric technique used, can be in the range between 1 :20 and 1 :200, including the extremes of the range and, in case of commercially available antibodies, the suitable dilution to be applied will be clearly indicated in the manufacturer's instructions. The incubation time of the primary antibody with a sample x of primary leukaemic cells of a patient shall be sufficient, as well known to the skilled person, to guarantee the binding between the antigenic determinant and the antibody, and, for such purpose, can be, for example, a minimum incubation time of 15 min or maximum of 48 hours. If commercially available antibodies are used, the incubation time is, once again, indicated by the supplier.

For mere illustrative purposes, as reported in the example described above, if the antibody which is utilized is developed against the epitope comprised between residues 575-588 of the hERG1 channel (accession N° NM 000238 pubmed), it will be possible to carry out an incubation at room temperature for 1 5 min with an antibody dilution of about 1 :50.

The detection of the primary monoclonal antibody, can be carried out by using any fluorochrome-labelled secondary antibody capable of selectively recognizing such primary antibody. As known in the literature, a secondary antibody is specific for the constant region, also known as Fc region, of the primary antibody, which in turn depends on the animal species used for the development of the primary antibody itself. In other words, it is the type of the animal used for the immunization with the epitope of interest (primary antibody), which determines the kind of secondary antibody; therefore, for example, if the immunized animal is a rabbit, the secondary antibody will be anti-rabbit; if the immunized animal is a sheep, the secondary antibody will be anti-sheep, if the immunized animal is a goat, the secondary antibody will be anti-goat, if the immunized animal is a horse, the secondary antibody will be anti-horse etc. In a particular embodiment in which the primary antibody is developed in the mouse, the secondary antibody, as well known by the skilled person, will be a secondary anti-mouse antibody.

The method herein described can be carried out with any flow cytometer since the inventors have found the possibility of expressing in absolute quantitative terms the expression of h ERgl at the level of the cellular plasma membrane, through a value, indicated as MFI as described in details below, independently of the fluorochrome or the flow cytometer employed. For this reason, the secondary antibody must be labelled with a fluorochrome. The secondary antibody may be labelled with any fluorochrome commonly used for the labelling of secondary antibodies and in particular a fluorochrome selected in the group comprising: idrossicumarine, aminocumarine, metossicumarine, Cascade Blue®, Pacific Blue™, Pacifc Orange™ , Lucifer Yellow, NDB, phycoerythrin (PE), PE conjugates, Texas Red®, Peridinin chlorophyll (PerCP), TruRed, FluorX, fluorescein, BODIPY-FL, TRICT, X-rodamine, allophycocyanine (APC), APC conjugates, Alexa Fluor®, FITC, Cy3, Cy5, Cy2, Cy7 may be used.

The technical details on the incubation of the labelled secondary antibody are well known to the skilled person and are widely reported in laboratory manuals or also, in the case of commercially available antibodies, are supplied by the manufacturer. The dilution buffers and also those for the incubation can be simple buffers such as, for example, PBS or any other buffer known to be suitable for such steps. For commercially available antibodies, all the experimental conditions, as buffers , d i l uti on s , i n cu bation ti m e a n d tem peratu re a re reported i n the manufacturer's instructions. For the sake of example, as reported in the example below, if a secondary anti-mouse IgG FITC antibody is employed, the buffer used will be PBS, the antibody concentration 1 μg/10 ⁶ cells and the incubation will be carried out at room temperature for 15 min in the dark.

The detection of the antigen of interest under examination can be obtained thanks to the fact that the fluorescent tracers generate a signal which is translated, for the first time in the present description, in terms of median fluorescence intensity (MFI). The translation of the signal into MFI makes it possible to define a value that, independently of the flow cytometer employed, of the voltage of the photomultipliers and of the user, defines the expression level of the hERG1 channel on the plasma membrane.

The Mean Fluorescence Index (MFI) is defined as the ratio between the mean fluorescence of an aliquot of the sample under analysis incubated with a primary antibody and subsequently with a secondary, fluorochrome labelled, anti- primary antibody and the fluorescence of a control aliquot of the same sample incubated only with the secondary antibody (that is fluorescent and hence the sample shows a signal which is not due to the direct antigen-antibody binding "background"). In other words, such index can be calculated as the ratio between the specific signal of the sample labelled with a primary and a secondary antibody (mean fluorescence of the sample=FC) and the non specific signal (background) obtained from the same sample labelled solely with the secondary antibody (mean fluorescence of the control = Fc) and multiplied by 100: that is MFI= FC/Fc 100. The values thus obtained, reported on a percentage scale, allow having an assessment which is independent of the fluorochrome linked to the secondary antibody and of the flow cytometer used.

Studies performed by the inventors on primary leukaemia cells from patients affected by leukaemia, have shown how it is possible to establish a MFI value beyond which it the development of chemoresistance can be predicted. In particular, the analysis of samples comprising leukaemic cells from patients affected by leukaemia, has emphasized that, already before the onset of chemoresistance, it is poss i b l e to e l a bo rate d ata ca pa b l e of p red i cti n g th e d evel op m en t of chemoresistance.

The authors have analyzed primary leukaemia cells from patients, whose clinical course has subsequently indicated the development of chemoresistance, before the developments thereof, and have discovered that a MFI value higher than 25 in the samples examined before treatment, corresponded to a subsequent development of chemoresistance in the same patients. In other words, a MFI value higher than 25 has been detected in samples of leukaemic cells from patients, before the clinical course confirmed the real development of chemoresistance.

Furthermore, the authors have developed an in vitro culture method that mimics, in a surprisingly effective manner, the development of chemoresistance in leukaemic cells which occurs in vivo. Such in vitro culture method consists of carrying out a co-culture of leukaemic cells and stromal cells, which reproduces the protective effects as well as the induction of chemoresistance, in the leukaemic cells, that can be observed in the bone marrow.

The method, applied on several samples of primary leukaemic cells, from patients whose clin ical course is known, has shown the development of chemoresistance in vitro only in the co-cultures of primary leukaemic cells from those patients that have indeed development a chemoresistant leukaemia, whereas no in vitro chemoresistance has been detected in the cells from those patients whose clinical course has indicated no development of chemoresistance.

Also the in vitro co-culture method leads to the development of chemoresistance in those primary cells that, a priori, show a MFI value higher than 25.

In particular, the studies carried out by the authors have allowed to define an MFI value which is predictive of chemoresistance development or useful for the monitoring of chemoresistance itself before, after or during a particular therapeutic protocol. Therefore, as indicated above, an MFI value higher than or equal to 25 is an index that is predictive of chemoresistance development and, if monitored during treatment, of persistence of chemoresistance.

The table below exemplifies some cases in which the MFI value (column 7 in the table) (Cases 3,4, and 6 are reported in Figure 1 ) calculated in the sample under study, and the clinical course of the disease, as detected in the patient from whom the sample had been obtained, have been related.

Table 1

Legend

Index 1 : index of in vitro chemoresistance

Index 2: index of the bypass of in vitro chemoresistance

Index 3 (MRD (+78)): index of in vivo chemoresistance

The belonging to group SR, M R or H R is defined at day +78 from the beginning of therapy, and provides an indication on the minimal residual disease (MRD). It is calculated after evaluating several clinical parameters and allows stratifying patients into three risk groups: High, Medium and Standard.

Index 1 represents the ratio between the percent of apoptotic leukaemia cells after treatment with doxorubicin in cultures in the absence of bone marrow stromal cells (MSC) versus the % of apoptotic cells after treatment with doxorubicin in cultures in the presence of MSC. Such index represents an index of the capacity of leukaemia cells to be chemoresistant.

Index 2 represents the ratio between the percent of apoptotic leukaemia cells cultured on MSC and treated with doxorubicin and a hERG1 blocker (such as E4031 ) versu s the % of apoptotic cel ls cu ltu red on MSC a nd treated with doxorubicin alone. Such index represents an index of the capacity of overcoming chemoresistance induced by MSC in leukaemia cells.

Index 3 represents an index of chemoresistance in vivo. It provides an indication about the minimal residual disease (MRD) at day +78 from the beginning of therapy and is calculated evaluating a series of clinical parameters that allow stratifying the patients into three risks groups: high, medium and standard.

Patients with a hERG1 MFI value≥ than 25 have a mean value of index 1 equal to 2.85+/-0.2835, whereas patients with a hERG1 MFI value lower than 25 have a mean index 1 value = 1 .46+/-0.023 (P=0.00313); these data indicate that patients with a high hERG1 expression display a higher protection by the marrow stroma, that is statistically significant compared to patients with low hERG1 expression.

Patients with a hERG1 MFI value≥ 25 have a mean value of index 2 of 2.03+/-0.42, whereas patients with a hERG1 MFI value lower than 25 have a mean value of 1 .02+/-0.04 (P=0.07498): patients with a high hERG1 show ha higher capability of overcoming doxorubicin-induced chemoresistance with respect to the other patients.

Moreover, patients with a hERG1 MFI value≥25 belong to the medium risk group (MR), while patients with a hERG1 MFI value lower than 25 belong to the standard risk group (SR).

The belonging to group SR, MR or HR is determined at day +78 from the beginning of therapy, and provides an indication of the minimal residual disease (MRD). It is calculated by evaluating a series of clinical parameters that allows stratifying patients in three risk groups, high, medium and standard.

To predict the development of chemoresistance it will be necessary to consider that the threshold value of 25 indicated for the MFI has been obtained through the statistical analysis of the data obtained by the samples of different leukaemic patients and therefore there could be possible gray areas where the correlation between the value of MFI and chemoresistance mig ht n ot be so straightforward.

Object of the present invention is also a kit for the in vitro prediction and/or monitoring of chemoresistance of leukaemic forms. For the first time, hence, a practical tool is provided, that can be used to identify patients who will develop chemoresistance (Pharmacoresistance) and/or to monitor the course of the disease in the light of a specific treatment protocol.

The kit will contain, in its simplest form, one or more aliquots of an anti hERG1 monoclonal antibody specific for the extracellular portion of such channel and an accompanying documentation as, for example, sheets containing the instructions for the calculation of MFI . For the purposes of the present description any monoclonal antibody capable of specifically binding the extracellular portion of the hERG1 channel may be comprised in the kit claimed herein. In particular, therefore, the kit may contain one or more monoclonal anti hERG1 antibodies, each developed for an epitope selected among the S1 -S2, S3-S4 or S5-PORE of the hERG 1 channel. The kit may possibly imply the use of commercially available monoclonal anti hERG1 antibodies (such as the antibody supplied by Alomone Labs, which is directed against the residues 430-445; accession number Q12809 ). The kit may also include some accompanying sheets. Such sheets may indicate the components of the kit, the protocol recommended by the manufacturer that may also include instructions for calculating MFI that will lead the skilled person to determine the MFI value indicating the specific formula for obtaining it and indication on the data to be used for the calculation. In particular, as already said above, the MFI is calculated according to the following formula:

MFI= FC/Fc 100

wherein

FC= mean fluorescence of the sample and Fc= mean fluorescence of the control.

Moreover, the instructions may also contain information on the interpretation of the MFI value obtained on the sample under analysis and in particular it will be highlighted that a value higher or equal than 25 is a predictive index for the development of chemoresistance and, in the case of monitoring during treatment, it is an index of the persistence of chemoresistance.

The kit may further contain one or more aliquots of a fluorochrome-labelled secondary antibody, specific for the primary antibody. Such secondary antibody, as it known by the skilled person, will be capable of specifically recognising the constant portion of the monoclonal antibody used, and because of this, the choice of the secondary antibody to be used will depend on the animal species that has been immunized with the epitope of interest. So by way of example and not limiting of the present description, if the immunized animal is a rabbit, the secondary antibody will be anti-rabbit; if the immunized animal is a sheep, the secondary antibody will be anti-sheep, if the immunized animal is a goat, the secondary antibody will be anti- goat, if the immunized animal is a horse, the secondary antibody will be anti-horse.

The use of a fluorochrome-labelled secondary antibody strictly depends on the definition, provided for the first time in the present description and as reported above, of the MFI.

The secondary antibody may be labelled with any fluorochrome commonly used for the labelling of secondary antibodies and in particular it will be possible to use any fluoroch rome selected in the group comprising: idrossicumarine, aminocumarine, metossicumarine, Cascade Blue®, Pacific Blue™, Pacifc Orange™, Lucifer Yellow, N DB, phycoerythrin (PE), PE conjugates, Texas Red®, Peridinin chlorophyll (PerCP), TruRed, FluorX, fluorescein, BODIPY-FL, TRICT, X-rodamine, allophycocyanine (APC), APC conjugates, Alexa Fluor®, FITC, Cy3, Cy5, Cy2, Cy7.

The kit may further comprise one or more aliquots of reagents for the detection of the hERG1 channels on the plasma membrane.

The negative control is any sample comprising cells which do not express on the plasma membrane the hERG1 channel and on which, therefore, the detection of a fluorescent signal is to be interpreted as a signal due to an aspecific binding of the primary and/or secondary antibody that has been used. In a particular embodiment, th e n egative control m i g ht be represented by a sa m pl e com pri si n g non chemoresistant leukaemic cells that, according to what stated above, are characterized by the lack of the hERG1 channel on the cellular plasma membrane.

The positive control will allow testing the correctness of the procedure carried out and the possible validity of the means used as it may contain a sample including any type of cells expressing the hERG1 channel on the plasma membrane and on which, by definition, it must be possible to detect emission of fluorescence. I n particular, the most appropriate positive control, but not limitative of the invention, will be a chemoresistant leukemic cell sample. This sample may eventually also be defined by a known MFI value in order to exclude, e.g., any operator errors during sample analysis.

I n a parti cu la r em bodiment, chemoresistant and non chemoresistant leukaemic cells are selected in the group comprising: adult and paediatric leukaemias as for example the acute lymphoblastic leukaemia (both paediatric and of the adults), the acute myeloid leukaemia (both paediatric and of the adults), the chronic lymphoid leukaemia of the adults and the chronic myeloid leukaemia of the adults.

The kit might additionally comprise one or more aliquots of reagents apt to detect the presence of hERG1 channels on the cell membrane. Such reagents consist of any solution useful for carrying out the different steps leading to the identification of the MFI value of the sample analyzed. In particular, buffer solutions can be used, by way of example and not limiting, here is reported the PBS buffer (phosphate buffer saline), containing potassium chloride, sodium chloride, sodium phosphate, potassi um phosphate; blocking solutions, as for example P BS complemented with bovine serum albumin at different concentrations, for a more or less intense blocking step.

Examples are reported below with the aim of better illustrating what reported in the present description; such examples are in no way to be considered as a limitation of the above description and following claims. EXAMPLES

Example 1

Evaluation and determination of MFI

Effects of hERG1 blockers on apoptosis induced by doxorubicin in human leukemic cells cultured in vitro in the absence or in the presence of marrow stromal cells (MSC), and treated (indicated with +) or not (indicated with -) with E4031 , Erythromycin, Sertindole and Way. A, B) 697 cells; C) Cells ALL(3), ALL(4) and ALL(6).

Aliquots of 1 x10 ⁵ cells were centrifuged at 1 100 rpm for 5 minutes, washed with PBS 1X before the incubation at room temperature for 15 minutes with the primary antibody (mouse monoclonal, anti hERG 1 , access number pubmed N M 000238) specific for an extracellular portion of the channel, and diluted 1 :50). At the end of the incubation washes with PBS 1 X and staining for 15 minutes with the secondary antibody (anti-mouse IgG FITC (1 μg 10 ⁶ cells)) are carried out. The pellet is washed twice with PBS 1 X and re-suspended in 500 μΙ of a 1 % formalin in PBS solution. The analysis is performed with the flow cytometer FACScan (Becton Dickinson). We standardized a new method for the detection and quantification of the hERG1 channel on the plasma membrane regardless of the flow cytometer used, of the voltage of photomultiplier and of the user. The detection of the antigen investigated is obtained by using fluorescent tracers that generate a signal which is translated in terms of intensity of fluorescence. The Mean fluorescence intensity (MFI) is defined as the ratio between the average fluorescence of the sample and the fluorescence displayed by the sample incubated with the secondary antibody (that is fluorescent and hence the sample shows a signal which is not due to the direct antigen-antibody binding). In other words, such index can be calculated as the ratio between the specific signal of the sample labelled with both the primary and secondary antibody (mean fluorescence of the sample = FC) and the aspecific signal obtained in the same sample labelled only with the secondary antibody (mean fluorescence of the control = Fc) and multiplied by 100: hence MFI = FC/Fc 100. The values obtained, expressed in a percentage scale, allow the provision of an estimate which is independent of the fluorophore conjugated to the secondary antibody (can also be used Cy3, Cy5, Alexa 488, PE, other than FITC) and of the flow cytometer which has been used.

From data obtained on samples of primary leukaemic cells, from patients whose clinical course has become known, it has been shown that an MFI value > 25 is an index of presence or of future development of chemoresistance. Example 2

Co-culture of stromal cells and leukaemic cells

The stromal cells used in the experiments have been obtained and amplified from al iq uots of a marrow stromal cell line. Cells were re-suspended at a concentration of 2 X 10 ⁶ /ml in RPMI-1640, 10% foetal bovine serum (FCS, Hyclone), 2 mmol/l of L-glutamine (Euroclone), 1 % of penicillin-streptomycin (Euroclone) and 10 ^"6 mol/l of hydrocortisone (Sigma, St Louis, MO, USA). Stromal cells were incubated at 37° C, 5% C0 ₂ and 90% humidity and after the formation of confluent and adhering fibroblast layer, about after one week of culture, have been detached and used for experiments of co-culture with leukaemia cell lines in 96-well plates.

The day before the experiment, the wells were coated with 0,1 % fibronectin (Sigma) at the final concentration of 1 μg well to allow the adhesion of stromal cells to the well bottom. 10 μΙ of fibronectin (diluted in PBS) were added in each well and plates left open overnight, in a laminar flow hood, to air dry.

The day after, the media that was in the stromal cells flask has been removed and the cells washed with PBS and incubated for about two minutes in the incubator, to allow a partial detachment from the bottom. Subsequently PBS has been removed and 5 ml trypsin (Euroclone) were added incubating at 37°; after about one minute the flask was vigorously shaken, until complete detachment of the cells. Next, cells were washed once with RPMI-1640 with 10%Fetal Bovine Serum, 2 mmol/l of L-glutamine (Euroclone), 1 % of penicillin-streptomycin (Euroclone) and re-suspended in fresh culture medium containing 10 ^"6 mol/l of hydrocortisone (Sigma) and seeded in 96-weii plates 200 μΙ/well.

The day after cell counting has been carried out on cells to plated on stroma, about 20 μ I of cells were drawn from the flask in which they were cultured and adding 20 μΙ of Tripan Blue (ratio 1 :1 ) were added.

The count of viable cells has been carried out using a Burker chamber.

After removal of the culture medium, by removal of 50% of culture medium, and re-infusion of an equal volume of fresh medium without hydrocortisone (step repeated seven times), the cell suspension has been plated at 100.000 a cells/well concentration, after centrifuge at 1200 rpm for 5 minutes and re-suspension in AIM- V medium (Gibco). For each cell line wells containing stromal cells and leukaemic cells were set, as well as wells containing leukaemic cells only. REFERENCES

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