FIELD OF INVENTION

The present invention relates to a pharmaceutical composition comprising zebularine (l-(P-D-ribofuranosyl)-2( 1 H)-pyrimidinone) and/or a pharmaceutically acceptable salt thereof and at least one pharmaceutically acceptable carrier and/or diluent.

The invention furthermore relates to the use of the composition as a medicament for promoting regeneration and/or treatment of wounds resulting from mechanical and/or chemical and/or radiation and/or thermal injuries and/or surgical operations and/or other pathological conditions.

In addition, the present invention provides a method for promoting regeneration and/or wound healing, which comprises administering a therapeutically effective dose of a pharmaceutical composition as defined above.

In addition, the present invention relates to a use of zebularine or a combined use of zebularine and retinoic acid for the manufacture of medicaments for promoting regeneration and/or treatment of wounds.

BACKGROUND OF THE INVENTION

Regeneration limits in mammals

Regeneration is the ability to restore lost or damaged tissues and organs, which involves the restoration of original function and structure. In scarring, which is another response to wounding, fibrous connective tissue replaces the damaged structures. Regenerative capability in mammals is known to decrease with development. Adult mammalians exhibit physiological regeneration such as that of liver, epidermis, intestine epithelium but are regarded as incapable of epimorphic regeneration.

A decrease of regenerative and wound healing abilities manifested as non-healing and chronic wounds (Frykberg and Banks 2015) could be a side-effect of radiotherapy (Gieringer et al. 2011), chemotherapy (Falcone and Nappi 1984), as well as other conditions, in particular cancer (McCaw 1989, Rybinski et al. 2014), diabetes, and ischemia (Brem et al. 2003, Blakytny and Jude 2006).

Scarless skin wound healing observed in foetuses (Podolak-Popinigis et al. 2016) in different mammalian species, perfect heart repair following partial resection in reported murine neonates (Porrello et al. 201 1) and functional regeneration of spinal cord after complete transection found in opossum pups (Fry et al. 2003) are the spectacular phenomena which imply that mammals have huge regenerative potential repressed in adulthood. Ear pinnae-injury model

Making 2 mm holes in the ear pinnae is a method for permanent marking of laboratory mice. As the result of healing, the holes made in the centre of ear pinnae decrease in size but remain for life. In contrast to the majority of murine strains, the MRL/MpJ mouse has been observed to close ear holes within 30 days after injury (Clark et al. 1998). The closure involves the restoration of complex tissue architecture including not only skin, but also blood vessels, muscles, cartilage, and peripheral nerves (Buckley et al. 201 1) and it seems related to enhanced regenerative responses in other tissues including heart (Leferovich et al. 2001), digit stumps after amputation (Chadwick et al. 2007), retina (Xia et al. 201 1), cornea (Ueno et al. 2005), spinal cord (Thuret et al. 2012), tendons (Lalley et al. 2015), articular joints (Fitzgerald et al. 2008). Therefore, the phenomenon of ear pinnae hole closure could be regarded as an indicator of regenerative capability in the whole organism. In laboratory mice, which show no ability to close ear holes spontaneously, ear pinnae regeneration could be induced pharmacologically. Ear hole closure after topical delivery of an immunophilin ligand GM284 was described in a patent pending submitted by D.E. Weinstein (US2009/0093528A1 2009). Later studies reported partial ear hole closure induction using Wnt pathway inhibitor XAV-939 (Bastakoty et al.

2015) and a prolyl hydroxylase inhibitor 1,4-DPCA (4-oxo-lH-l,10-phenanthroline-3 -carboxylic acid) (Zhang et al. 2015).

Epigenetic basis of regeneration

Organism and organ development depends on epigenetic regulation. More than that, a number of epigenetic characteristics determine the pluripotency induction in somatic cells. Epigenetic basis of regenerative potential (Gomikiewicz et al. 2013, Gomikiewicz et al. 2016, Podolak-Popinigis et al.

2016) and the involvement of epigenetic mechanisms in regeneration processes have been reported in several studies (Yakushiji et al. 2007, Powell et al. 2013, Sim et al. 2015). However, the attempts to use epigenetic agents in order to stimulate regeneration processes met with limited success (Wang et al. 2010, Tan et al. 2015).

DNA methyltransferase inhibitors

DNA methylation is a fundamental epigenetic mechanism of gene expression regulation and it plays important roles in a number of biological processes such as development, organogenesis, aging, differentiation and de-differentiation. Impaired DNA methylation first found in neoplasms, later, was reported in a number of other malignancies. As a principle, DNA methylation of promoter regions results in repressed gene expression. The inhibition of DNA methyltransferase leads to passive demethylation during successive rounds of DNA replication, thus allowing the activation of genes silenced by DNA methylation. As DNA methylation-mediated gene repression is found in different pathologies, DNA methyltransferases inhibitors are investigated as drug candidates in different cancers, in addition to immunological disorders and neurodegenerative diseases. The inhibitors of DNA methyltransferases could be divided into the nucleoside and nonnucleoside ones. The first are the analogues of natural nucleosides and they are incorporated into DNA during replication. Binding of the modified nucleosides incorporated into DNA leads to irreversible inactivation of DNA methyltransferases. The non-nucleoside inhibitors of DNA methyltransferase exert their action without incorporation into DNA, so they could block DNA methyltransferases in non-dividing cells. Once incorporated into DNA, the nucleoside inhibitors are possible to retain in cells longer than the non-nucleoside ones.

Two inhibitors of DNA-methyltransferase, 5-aza-2’-deoxycytidine and 5-azacytidine are used in anticancer therapies to treat myelodysplastic syndromes and acute myeloid leukaemia. The anticancer activity is explained by cytotoxic and demethylating effects, and the latter one is thought to activate cell differentiation.

Zebularine - uses and mechanism of action

Zebularine is a cytidine analog lacking the amino group at C-4. As a nucleoside, zebularine has to be incorporated into DNA to act as a DNA methyltransferase inhibitor. This incorporation is preceded by metabolic activation: phosphorylation to zebularine monophosphate by uridine-cytidine kinase and further phosphorylation to diphosphate by nucleoside-phosphate kinase followed by the reduction to deoxyzebularine diphosphate by ribonucleotide reductase and subsequent phosphorylation to triphosphate by nucleoside-diphosphate kinase (Ben-Kasus et al. 2005). Deoxyzebularine triphosphate is utilized during DNA synthesis as a substrate of DNA polymerase. Zebularine incorporated mainly in the place of cytidine mispairs with adenine (Lee et al. 2004). Zebularine incorporated into DNA forms a stable covalent adduct with DNA methyltransferase (but unlike 5-aza- 2’-deoxycytidine it is not methylated in the course of inhibition). This leads to depletion of DNA methyltransferases and DNA hypomethylation (Cheng et al. 2004). Intracellular zebularine uptake is dependent on active transport that is counter-acted by efflux through protein transporters (Arimany- Nardi et al. 2014). Oxidation to uridine by liver aldehyde oxidase in the cytosol and RNA incorporation challenge zebularine conversion to deoxyzebularine triphosphate, the substrate for DNA incorporation. In addition, the RNA incorporation is estimated to be 7-fold higher than that to DNA (Ben-Kasus et al. 2005). Further, zebularine phosphorylation can be inhibited competitively by cytidine (Ben-Kasus et al. 2005).

In contrast to two known epigenetic drugs, 5-azacytidine and 5-aza-2’-deoxy cytidine, zebularine displays high stability in water with a half-life of 508 h at 37°C, at pH 7.4 (Cheng et al. 2003) and very low toxicity as observed in cell culture (Ben-Kasus et al. 2005) and animal models. No toxic effects were found in mice after treatment with 400 mg/kg body weight of intraperitoneally delivered zebularine for 78 consecutive days (Herranz et al. 2006). The impediments in metabolic activation are probably responsible for the requirement of high zebularine doses (several hundred mg/kg body weight), but, on the other hand, its low toxicity. Low zebularine toxicity may be also explained by the fact that zebularine metabolites are endogenous substances (Beumer et al. 2006). In addition to unusually excessive doses, the use of zebularine could be complicated by its inhibitory action on thymidylate synthase and cytidine deaminase (Yoo et al. 2008). Because of these drawbacks, zebularine, though showing interesting properties, has never entered either medical use or clinical trials. Nevertheless, zebularine was tested for potential medical applications, primarily, as an anticancer drug in cell culture and animal models (Herranz et al. 2006, Tan et al. 2013, Yang et al. 2013). Zebularine was reported to show antineoplastic activity in different cancers either used alone or as a chemosensitizer (Andrade et al. 2014). Certain studies indicate other possible medical uses of zebularine. Zebularine was found to exert an anti-immunogenic effect, probably mediated through indolamine-2, 3 -deoxygenase induction in spleen (Liu et al. 2007), which could be used to treat autoimmune diseases or prevent immune rejection of transplants (Nittby et al. 2013). Local zebularine delivery directly before brain injury was demonstrated to exert neuroprotective action in a stroke model in the rat (Dock et al. 2015). Zebularine was also shown to potentiate transdifferentiation of mesenchymal stem cells into cardiomyocytes (Naeem et al. 2013).

Zebularine as a potential pro-regenerative agent

D A demethylation leads to re-activation of silenced genes, including those which induce cell pluripotency and may lead to cell transdifferentiation. Zebularine is listed among other DNA methyltransferase inhibitors in a number of patent applications as one of demethylating agents for pluripotency induction (US201 10076678 A 1 2011) or cell transdifferentiation (US201 10206644A1 2013). A Regarding the mechanism of pro-regenerative action, it should be considered that zebularine was found to have not only demethylating but also neuroprotective, cytotoxic to selected cell subsets and immunomodulatory effects.

Zebularine is a nucleoside inhibitor of DNA methyltransferases as well as cytidine deaminase and thymidylate synthase known under several names including: l-(P-D-ribofuranosyl)-2(l H)-pyrimidinone, pyrimidin-2-one b-D-ribofuranoside, 4-deoxyuridine, 1- (b-D-Ribofuranosyl) -l,2-dihydropyrimidin-2-one, 2-Pyrimidone-l^-D-riboside.

Though it has been considered in cell-based therapies, zebularine has not been reported to be effectively applied to induce regeneration in an animal organism to date. SUMMARY OF THE INVENTION

The object of the present invention is the first example of successful epigenetic regenerative therapy observed in a mammalian organism under zebularine treatment.

In one aspect, a novel medical use of zebularine for promoting wound healing and complex tissue regeneration is provided.

In another aspect, the use of compositions comprising zebularine and retinoic acid for promoting wound healing and complex tissue regeneration is provided.

DETAILED DESCRIPTION OF THE INVENTION

In one aspect, methods for promoting wound healing and regeneration in a subject are provided, the methods comprising: administering a therapeutically effective amount of zebularine or zebularine compositions or zebularine compositions with retinoic acid.

In one aspect, provided herein are methods for promoting wound healing and regeneration of complex tissue based on the delivery of compositions comprising zebularine or zebularine and retinoic acid.

In this aspect, zebularine as a cytidine analogue can be incorporated into newly synthesized DNA strand and act as a DNA methyltransferase inhibitor.

There are four bases that constitute DNA molecule: cytosine, guanine, adenine and thymine. Cytosines in CpG dinucleotides can be methylated to form 5-methylcytosine. Such modifications within gene promoter regions typically result in its silencing. After DNA replication, said DNA consist of two strands, one methylated (template strand), and one unmethylated (daughter strand) and it is referred to as hemimethylated DNA. After DNA methyltransferases inhibition, the replication machinery itself would produce daughter strands that remain unmethylated and, over time, would lead to passive loss of methylation.

In a related aspect, the methods and compositions provided herein promote extensive regeneration of complex tissue following wounding in a subject. In another manner, use of compositions provided herein may inhibit DNA methylation as well as may modulate response from immune system during early stages of wound healing.

In another aspect, zebularine mediated DNA demethylation may lead to activation of repressed genes including those which promote wound healing and regeneration such as pluripotency genes.

In another aspect, zebularine can increase production of indoleamine-2, 3 -di oxygenase (IDO), which is a natural immunosuppressive molecule. Indoleamine 2,3-dioxygenase (IDO) degrades the indole moiety of tryptophan and initiates the production of neuroactive and immunoregulatory metabolites, collectively known as kynurenines. The immune suppressive action of IDO may be explained by: (i) starvation of tryptophan; (ii) direct toxic effects of the aforementioned metabolites/catabolites which induce apoptosis of immune cells; (iii) stimulation of differentiation of T helper cells to immunosuppressive regulatory cells.

In another aspect, zebularine can exert cytotoxic effects on selected cell subsets in the injury area. In this manner zebularine may eliminate cells responsible for harmful inflammation and those involved in scar formation, thus promoting regeneration.

The objective of the invention herein is to provide novel compositions ad methods that could be applied for wound healing and/or regeneration of complex tissue. The above problem has been unexpectedly solved to a significant degree in the present invention.

The subject of the invention is a novel pharmaceutical composition comprising zebularine and/or its pharmaceutically acceptable salt or at least one pharmaceutically acceptable carrier and/or diluent.

A composition that additionally comprises retinoic acid and/or its metabolites and/or pharmaceutically acceptable salts thereof.

A composition that promotes regeneration or healing of wound resulting from mechanical injuries, chemical injuries, radiation injuries, bums, surgical operations or pathological conditions.

Use of a composition as defined above as a therapeutic agent for regeneration or healing of wounds resulting from mechanical injuries, chemical injuries, radiation injuries, bums, surgical operations or pathological conditions.

Use where the therapeutic agent has demethylating activity.

Use where the therapeutic agent has the effect of activating silenced genes, preferably pluripotency genes.

A method of promoting wound healing and regeneration, comprising administering a therapeutically effective dose of a pharmaceutical compositions as defined above.

A method where the pharmaceutical composition is followed by the regeneration and healing of chronic and non-healing wounds, especially in the case of pressure ulcers, wounds resulting from diabetic complications and / or complications of peripheral arterial disease.

A method where the regeneration of complex tissues involves neurons, blood vessels, muscles, cartilage, skin and epidermis, hair follicles and hair, and sweat glands. Use of zebularine for the manufacture of medicaments for promoting tissue regeneration or healing of wounds resulting from mechanical, chemical, thermal, radiation, surgical or pathological conditions.

Combined use of zebularine and retinoic acid for the manufacture of medicaments for promoting tissue regeneration or healing of wounds resulting from mechanical, chemical, thermal, radiation, surgical or pathological conditions.

Use of zebularine and retinoic acid for the manufacture of medicaments in the form of ointments, creams, sprays, injections or tablets.

The following terms used in the description and claims shall have the following meanings:

It is to be understood that the term“wound” encompasses any injury of living tissue caused by impact, pressure and other mechanical factors, heat, cold, radiation, chemical agents, ischemia, and other biological agents. In particular the term“wound” encompasses skin lesions but also lesions of other tissues and organs.

As used herein the term“wound healing” refers to a post injury repair process which involves debridement of foreign bodies and necrotic tissues within the wound area and cell proliferation leading to the restoration of tissue continuity with or without scar formation.

As used herein the term“regeneration” refers to a process of restoration of lost tissues, structures and appendages that occurs either spontaneously or under pharmacological treatment.

As used herein the term“complex tissue” refers to a tissue containing at least two different cell types which function together.

As used herein the term“chronic wound” or“non-healing wound” refers to a wound that does not fully heal in the amount of time considerably exceeding that predicted for normal healing; typically wounds that do not heal within 3 months are considered chronic. Chronic wounds or non-healing wounds are often ischemic wounds and ulcers, those of diabetic patients, but are not limited to those.

The term“CpG sites” or”CpG” refers to a DNA sequence where a cytosine nucleotide is followed by a guanine nucleotide along its 5' ® 3' direction

The term“DNA methyltransferase” or“DN T” refers to the DNMT1 , DNMT3A and DNMT3B proteins. DNMT1 is a maintenance methyltransferase that is responsible for copying DNA methylation patterns to the daughter strands following DNA replication, whereas DNMT3A and DNMT3B are thought to be de novo methyltransferases that set up DNA methylation patterns early in development.

As used within the term“IDO” refers to three different proteins that can catabolize tryptophan: IDO-1 , IDO-2 and TDO.

In one embodiment, zebularine is administered at early stage of wound healing. It is to be understood that the term“early stage” of wound healing can encompass immunological response from

immediately after wounding.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1. presents the representative photographs of ear pinnae hole closure 42 days post injury in the zebularine treated and vehiculum (saline) administered control mice.

The ear pinnae of the mouse receiving zebularine in intraperitoneal injections was almost completely closed within approximately 30 days post injury, while in the saline administered control, the ear pinnae hole was only slightly decreased as compared to the initial excision of 2 mm diameter. Zebularine was administered 7 times (1000 mg/kg body weight): on the day of injury directly after excision and 1 , 2, 3, 4, 7, and 10 days after injury.

Figure 2. presents the results of ear pinnae healing for 47 zebularine treated (n=94 ears) and 48 control mice (n=95 ears) expressed as the percentage of ear hole closure area on the day 42 after injury.

Zebularine was administered 7 times (1000 mg/kg body weight): on the day of injury directly after excision and 1, 2, 3, 4, 7, and 10 days after injury

Statistical significance was determined using heteroscedastic two tailed Student’s t-test. The differences with p-values lower than 0.001 are marked with triple asterisks (***).

Figure 3. presents the timeline of ear pinnae hole closure detennined by the ear hole area measured directly after injury and 7, 14, 21, 28, 35 and 42 days after injury for 47 zebularine treated (n=94 ears) and 48 control mice (n=95 ears).

The mean ear hole sizes in the zebularine treated and control mice remained similar during the initial several days after injury. On the 14 day post injury, the mean ear hole area was a little bigger, while from the day 21 post injury, it was recorded to be significantly smaller in the zebularine treated animals as compared to the control ones. The maximal closure was recorded from the day 35 post injury. Zebularine was administered 7 times (1000 mg/kg body weight): on the day of injury directly after excision and 1, 2, 3, 4, 7, and 10 days after injury.

Statistical significance was determined using two-tailed Mann- Whitney test. The differences with p- values lower than 0.001 are marked with triple asterisks (***).

Figure 4. presents the distributions of ear pinnae healing results for 47 (n=94 ears) zebularine treated and 48 (n=95 ears) control mice 42 days after injury.

Each dot represents the area of a single ear pinnae hole.

Zebularine was administered 7 times (1000 mg/kg body weight): on the day of injury directly after excision and 1, 2, 3, 4, 7, and 10 days after injury.

Statistical significance was determined using two-tailed Mann-Whitney test. The differences with p- values lower than 0.001 are marked with triple asterisks (***).

Figure 5. presents zebularine dose-effect on regenerative ear hole closure.

Mean ear pinnae hole sizes on the day 42 post injury examined for 200, 500 and 1000 mg/kg body weight.

Zebularine was administered 7 times: on the day of injury directly after excision and 1, 2, 3, 4, 7, and 10 days after injury.

Statistical significance was determined using two-tailed Mann-Whitney test. The differences with p-values lower than 0.001 are marked with triple asterisks (***).

Figure 6. presents the effect of subcutaneous and intraperitoneal zebularine delivery on regenerative ear hole closure.

Mean ear pinnae hole sizes were examined on the day 42 post injury.

Zebularine was administered 7 times (1000 mg/kg body weight): on the day of injury and 1, 2, 3, 4, 7, 10 days after injury.

Statistical significance was determined using two-tailed Mann-Whitney test. The differences with p-values lower than 0.001 are marked with triple asterisks (***).

Figure 7. presents the gene expression changes observed for selected pluripotency, developmental and cell cycle genes under zebularine treatment in the injury/regeneration area.

Relative gene expression was determined using qPCR with Tbp and beta-actin ( Actb ) as the reference transcripts. Mean transcript levels were calculated for six animals (n=8 ears) at each time point. Statistical significance was determined using two-tailed Mann-Whitney test. The significant results (p< 0.05) are marked with an asterisk (*). Figure 8. presents the decrease in DNA methylation expressed as 5-methyl-cytosine content in the injury/regeneration area under zebularine treatment.

Mean CpG methylation levels were determined for six animals (n=8 ears) at each time point. Statistical significance was determined using heteroscedastic two tailed Student’s T-test. The result lower than 0.001 is marked with a triple asterisk (***).

Figure 9. presents the representative photographs of complete regenerative ear hole closure under synergistic action of zebularine and retinoic acid.

Complete ear hole closure was observed in mice receiving zebularine and retinoic acid in intraperitoneal injections within 21 days post injury. Zebularine (1000 mg/kg body weight) was administered 7 times: on the day of injury and 1, 2, 3, 4, 7, 10 days after injury. Retinoic acid, RA, (16 mg/kg body weight) was administered 6 times: on the day of injury and 2, 4, 7, 9 and 11 days after injury weight. The vehiculum administered controls showed no significant ear hole closure, while partial closure was observed in the mice treated with RA alone.

Figure 10. presents the potentiation of zebularine pro-regenerative activity by synergistic action of retinoic acid (RA).

Timeline of ear pinnae hole closure was determined directly after injury and 7, 14, 21, 28, 3,5 and 42 days after injury for 12 mice (n= 24 ears) receiving combined zebularine and RA treatment (ZEB+RA), 6 mice (n=12 ears) receiving RA alone (RA), 6 mice (n=12 ears) receiving 4-keto-retinoic acid (4-keto-RA), and 12 mice (n=24 ears) administered with vehiculum (ZEB+RA contrl). The timelines were juxtaposed to that for zebularine delivered alone (ZEB, Figure 3). Complete ear hole closure was recorded on the day 21 after injury in the mice receiving the combined treatment with zebularine and RA.

Figure 11. presents 5-azacytidine effect on ear hole closure.

5-azacytidine (5-azaC) (0.25 mg/kg body weight) was delivered intraperitoneally 7 times: on the day of injury and 1, 2, 3, 4, 7, 10 days after injury. Mean ear pinnae hole area was measured on the day 42 after injury. The results were compared to those for the mice treated with zebularine (1000 mg/kg body weight) and saline according to the same schedule. Statistical significance was determined using two-tailed Mann- Whitney’s test. The differences with p-values lower than 0.001 are marked with triple asterisks (***).

Figure 12. presents the effect of topical zebularine treatment on dorsal skin wound healing.

Wound closure was determined directly after injury and 2, 4, 7, 1 1, 14 and 18 days after injury for 6 zebularine treated (n=12 wounds) and 6 control mice (n=T2 wounds). Error bars show SEM. Statistical significance was determined using two-tailed Mann- Whitney’s test. The differences with p-values lower than 0.005 and 0.001 are marked with double (**) and triple asterisks (***), respectively.

Figure 13. presents the representative photographs of dorsal skin wounds in the mice receiving zebularine topically for five days following injury and the controls. The initial wound diameter was 6 mm. The wound treated with zebularine displayed complete closure 11 days after injury. The same wound of the same individual is shown throughout all time points.

EXAMPLES

The invention is further illustrated by the following non- limiting examples.

Example 1

Determining the effect of zebularine on complex tissue regeneration

In order to evaluate the regenerative effect of zebularine, through-and-through holes of 2 mm diameter were made in the ear pinnae of the BALB/c 2-month-old female mice using scissor style ear punch. The mice were randomly divided into two groups consisting of six individuals each. The mice of one group were intraperitoneally injected with 7 doses of zebularine dissolved in saline (50 mg/ml), 1000 mg/kg body weight, on the day of injury directly after punching, and 1, 2, 3, 4, 7, 10 days after injury. The second, control group, was administered with saline.

The animal study protocols were approved by the Local Ethics Committee for Animal Experimentation at the University of Science and Technology in Bydgoszcz, Poland (Permit No. 50/2016).

The ears were photographed every 7 days, for 42 days, and ear hole closure was tracked by determining the area using computer-assisted image analysis. The experiment was repeated 8 times. Collectively, the experiment was performed for 47 zebularine treated and 48 saline ( vehiculum ) administered control mice. While minor effects of ear hole closure were recorded in the control groups, similar to those reported in the literature, extensive ear pinnae restoration was observed in the zebularine treated animals, which was manifested by broad rings of newly formed tissues surrounding the injury area as demonstrated in the representative photographs (Figure 1). The mean ear hole areas determined on the day 42 post injury were 0.53+/-0.3 and 1.77+/-0.48 sq mm for zebularine treated and saline controls, respectively. The results expressed as percentage of wound closure correspond to 83.2% and 43.6% for the zebularine treated and control group, respectively (Figure 2).The timeline of regeneration process is presented in Figure 3. Significantly better ear hole closure under zebularine treatment was recorded from the day 21 after injury, while maximal closure on the day 35. The distributions of ear hole areas on the day 42 after injury were plotted as dot diagrams, where each dot represents an individual ear (Figure 4). The diagrams not only show the biological variation in response to injury and zebularine treatment but clearly expose the contrast between the control and zebularine treated groups.

In order to evaluate dose dependent regenerative response, the effects of zebularine doses of 200, 500, and 1000 mg/kg body weight were examined (Figure 5). The effect of intraperitoneal zebularine delivery on the ear pinnae hole closure was compared with that of subcutaneous one. Subcutaneous injections gave statistically significant response but proved less effective than intraperitoneal delivery

(Figure 6).

Example 2.

Determining the effect of systemic zebularine treatment on the expression of pluripotency and developmental genes

In order to determine the effect of zebularine on the expression of pluripotency, developmental and cell cycle genes, the transcript levels for a panel of selected genes including Cdkn2a, Msxl, Nanog, Sox2, Bdnf Soxl, Nog, and Mytll were examined in the injury/repair area, in zebularine treated and control mice at the day 7, 14, 21 and 42 following injury in addition to unwounded ear pinnae designated as day 0. For the purpose, the ear punched mice were sacrificed at selected time points, the ears were collected on RNAlater reagent (Qiagen), stored at -80 °C until the rings surrounding the holes were excised using a 3 mm biopsy punch, following RNA extraction from thus obtained tissues using RNeasy kit (Qiagen). The levels of selected transcripts were determined for 6 mice (8 ears) for each time point using real-time PCR quantitation and Tbp and Actb as the reference genes. The PCR primers are listed in Table 1. Significantly enhanced expression of the selected transcripts in the mouse treated with zebularine was observed on the day 7 after injury. The most remarkable changes were found for the pluripotency genes, Nanog and Sox2 (Figure 7).

Example 3.

Determining the effect of systemic zebularine treatment on the global DNA methylation levels in the injury and regeneration area

DNA methylation in promoter regions is one of key epigenetic mechanisms responsible for gene repression. In order to determine the zebularine demethylating effect on DNA in the regenerating tissues, the content of 5-methylcytosine was compared in the tissues collected from the rings surrounding the ear pinnae holes in the zebularine treated and control animals. For the purpose, the ear punched zebularine treated and control mice were sacrificed at the days 7, 14, 21, and 42 after injury. The ears were collected, and the rings surrounding the holes were excised with a 3 mm biopsy punch, following genomic DNA extraction from thus obtained tissues using DNeasy kit (Qiagen). The levels of 5-methylcytosine were estimated using 5-mC DNA ELISA Kit (ZYMO, D5325) in 100 ng aliquots of genomic DNA. The results demonstrate a significant decrease in DNA methylation on the day 7 following injury in zebularine treated animals (Figure 8), thus indicating that DNA demethylation accompanies the regenerative response in the injury area.

Example 4.

Synergistic action of zebularine and retinoic acid (RA) to stimulate regenerative responses

While retinoic acid (RA) stimulates expression of multiple genes involved in development, zebularine, as a demethylating agent is supposed to re-activate genes repressed by DNA methylation in the course of development. Therefore, the combination of these two agents was supposed to potentiate the regenerative response in the ear pinnae injury model. The effect of combined delivery of zebularine and RA on ear pinnae hole closure was compared with those of RA or zebularine delivered alone. Trough-and-through holes of 2 mm diameter were made in the ear pinnae of the B ALB/c mice using scissor style ear punch. The mice were randomly divided into four groups consisting of six 2- month-old female individuals each. The mice of the first group were intraperitoneally injected with zebularine 1000 mg/kg body weight, dissolved in saline (50 mg/ml) and RA 16 mg/kg body weight suspended in 3% dimethyl sulfoxide in rapeseed oil (2 mg/ml). The injections of zebularine were made, on the day of injury directly after punching, and 1, 2, 3, 4, 7, 10 days after injury, while those of RA on the day of injury directly after punching, and 2, 4, 7, 9 and 11 days after injury. The second group was administered with RA 16 mg/kg body weight alone, the third one with 16 mg/kg body weight of 4-keto retinoic acid (4-keto RA), which is a cellular metabolite generated through cytochrome oxidation of RA, and the fourth control group received vehiculum only according to the safhe schedule. The mouse ears were photographed every 7 days, for 42 days, and ear hole closure was tracked by determining the area using computer-assisted image analysis. Partial ear hole closure was noted in the control groups administered with RA and 4-keto RA and a very limited ear hole closure was observed in the mice receiving vehiculum alone. The combined treatment with zebularine and RA resulted in accelerated and complete closure as shown in the representative photographs (Figure 9). The timeline of ear pinnae hole-closure for the animals treated with the combination of RA and zebularine contrasted with those receiving either zebularine, RA or vehiculum alone are presented in Figure 10.

Example 5.

The effect of 5-azacytidine on ear hole closure

Similarly as zebularine, 5-azacytidine is a nucleoside inhibitor of DNA methyltransferases. The effect of 5-azacytidine on ear hole closure was examined using the same delivery schedule as for zebularine, but a much lower dose (0,25 mg/kg body weight) was applied. 5-azacytidine, unlike zebularine is not subjected to rapid metabolic conversion to uridine, so it is more active but also more toxic than zebularine. The mouse ears were photographed every 7 days, for 42 days, and ear hole closure was tracked by determining the area using computer-assisted image analysis. The comparison of results obtained for 6 mice that received i.p. injected 5-azacytidine with those recorded for zebularine and saline treated animals showed that 5-azacytidine did not stimulate ear hole closure, and, on the contrary, it inhibited the limited physiological closure observed in saline controls (Figure 11). The example indicates that any freely selected DNA methyltransferase inhibitor cannot replace zebularine as a pro-regenerative agent.

Example 6

The effect of topically delivered zebularine on skin wound healing

The effect of topically delivered zebularine on wound healing was determined using the dorsal skin excision model. Six 2-month-old female mice of the BALB/c strain were used for the experiment. Prior to the injury the mice were anaesthetized. The dorsal skin was shaved and disinfected. Two symmetrical full-thickness excisional wounds were made in the dorsum using a biopsy punch of 6 mm diameter. Ten microliter of zebularine suspension (200 mg per 1 ml of saline) was dropped directly onto the wound immediately after wounding and once daily for the next four days. Promptly after zebularine application, the wounds were covered with a transparent dressing, and next, the dressing was fastened with adhesive plaster wrapped around the mouse. An analogical experiment was performed for six mice of control group that were not treated with zebularine. The animal study protocol was approved by the Local Ethics Committee for Animal Experimentation at the University of Science and Technology in Bydgoszcz, Poland (Permit No. 49/2016).

The wounds were photographed on the day of injury (dO) and on the day 2, 4, 7, 9, 1 1, 14, and 18 after wounding. The wound closure progress was tracked by determining wound area using computer- assisted image analysis. Zebularine treatment significantly accelerated wound healing. As demonstrated in Figure 12, the time of wound closure was decreased by approximately 7 days in the zebularine treated mice. Complete wound closure was observed on the day 11 for zebularine treated mice and on the day 18 for the control ones (Figure 13).

Table 1

Nucleotide sequences of PCR primers used for quantitating transcript levels.

REFERENCES

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