METHOD OF TREATING ISCHEMIA/REPERFUSION INJURY Technical Field

[0001] The invention relates to a method of treating ischemia/reperfusion injury.

Background Art

[0002] Nutlin3a is an Mdm2 inhibitor and is potent to stabilize p53, which is a tumor- suppressor involved in various biological processes such as cell cycle regulation, DNA repair, and apoptosis (see, for example, U.S. Pat. No. 7705007 and Science (2004) 303, 844-848).

[0003] Caylin2 is a Nutlin-3 analog in which trifluoromethyl groups have been

substituted for chlorine on the 2 phenyl rings.

[0004] p53 is a tumor-suppressor that is mutated or deleted in more than half of all human tumors. The physiological roles of p53 are versatile, forming a cell cycle checkpoint and functioning in DNA repair, apoptosis, and energy metabolism (Nature (2009) 458: 1 127-1 130). It has been shown that phosphorylations at multiple sites and subsequent proteasomal degradation are important in the regulation of p53 protein levels (Cell (2009) 137; 609-622). p53 ubiquitination required in its degradation is catalyzed by several ubiquitin ligases such as Mdm2, Pirh2, and Copl (Cell Death Differ. (2010) 17; 86-92). In particular, the mechanism of regulation of p53 by Mdm2 has been well- analyzed. Because the massive stabilization of p53 was able to induce apoptosis in p53 proficient tumor cells (Nature (1991) 352; 345-347), stabilization of p53 via an inhibition of Mdm2 is one of the attractive strategies for cancer therapy. Recently, it has been reported that small molecular compounds such as Nutlin3a and MI-219 act as cell- permeable Mdm2 antagonists (Science (2004) 303; 844-848, Proc. Natl. Acad. Sci. U.S.A.

(2008) 105; 3933— 3938), and their analogs have progressed to preclinical development or early phase clinical trials for anti-cancer therapy (Annu. Rev. Pharmacol. Toxicol.

(2009) 49; 223-241). Because p53 upregulates anti-oxidant and anti-inflammatory genes (Nat. Med. (2005) 1 1 ; 1306-1313, FASEB J (2005) 19; 1030-1032), p53 has a potential to protect from I/R-induced cellular injuries via anti-oxidative and anti-inflammatory responses.

[0005]Parpl is a major enzyme catalyzing poly (ADP-ribosyl) atiori, which is a post- translational protein modification. It is involved in replication, DNA repair, and cell death (Cell Mol. Life Sci. (2005) 62, 769-783, Cancer Sci. (2007) 98, 1528-1535). Parpl is dramatically activated by DNA breaks and then catalyzes poly(ADP-ribosyl)ation on substrate proteins in DNA damage regions, which is required for efficient recruitment of DNA repair factors to the loci (Cell. Biol. (2003) 23, 5919-5927, Nucleic Acids Res. (2007) 35, 7665-7675). On the other hand, over-activation of Parpl decreases cellular NAD+ and ATP levels, resulting in necrotic cell death caused by breakdown of energy metabolism (Proc. Natl. Acad. Sci. U.S.A. (1999) 96, 13978-13982, Mol. Cell. Biol. (1999) 19, 5124-5133). The involvement of Parpl in inflammatory responses has also been reported. Ischemia/reperfusion-induced Parpl over-activation is mediated by production of reactive oxygen species and is involved in NF-kB transactivation (Am. J. Pathol. (2008) 173, 2-13). Furthermore, Parpl has been also characterized as a useful hallmark of apoptosis because full length Parpl is cleaved by the apoptotic proteases, easpase-3 and -7, into p85 and p25 fragments during apoptosis (Cancer Res. (1993) 53, 3976-3985, Nature (1994) 371, 346-347). Therefore, Parpl is an attractive target of cancer chemotherapy and protection from ischemia/reperfusion injury, and severalParpl inhibitors are being evaluated in clinical trials (J. Med. Chem. (2010) 53, 4561-4584).

SUMMARY OF INVENTION

[0006] An object of the present invention is to provide a method of treating

ischemia/reperfusion injury.

[0007] Aspects of the present invention include the following.

[0008] <1> An agent for treating ischemia/reperfusion injury, comprising a

therapeutically effective amount of a p53 agonist compound comprising a cis- imidazoline structure.

[0009] <2> The agent according to <1>, wherein the p53 agonist compound comprising a cis- imidazoline structure is selected from the group consisting of Nutlin3a, Caylin2 and those pharmaceutically acceptable salts thereof.

[0010] <3> The agent according to <1> or <2>, wherein the ischemia/reperfusion injury is the tissue damage which occurs during at least one selected from the group consisting of ischemic infarction, treatment for ischemic infarction, and ischemic and reperfusion period in organ transplantation.

[001 1] <4> The agent according to any one of <1> to <3>, wherein the

ischemia/reperfusion injury is at least one selected from the group consisting of cerebral infarction, myocardial infarction and pulmonary infarction. [0012] <5> A method of treating ischemia/reperfusion injury, comprising administering to a mammal a therapeutically effective amount of a p53 agonist compound comprising a cis- imidazoline structure.

[0013] <6> The method according to <5>, wherein the p53 agonist compound comprising a cis- imidazoline structure is selected from the group consisting of Nutlin3a, Caylin2 and those pharmaceutically acceptable salts thereof.

[0014] <7> The method according to <5> or <6>, wherein the ischemia/reperfusion injury is the tissue damage which occurs during at least one selected from the group consisting of ischemic infarction, treatment for ischemic infarction, and ischemic and reperfusion period in organ transplantation.

[0015] <8> The method according to any one of <5> to <7>, wherein the

ischemia/reperfusion injury is at least one selected from the group consisting of cerebral infarction, myocardial infarction and pulmonary infarction.

[0016] <9> A method of screening a therapeutic agent for treating an

ischemia/reperfusion injury, comprising:

contacting a test substance with a p53-wild-type tester cell, of which an expression amount of Parpl protein in a case in which the cell is contacted with Nutlin3a or Caylin2 is lower than that before contact with Nutlin3a or Caylin2, and thereafter measuring the expression amount of Parpl protein in the tester cell to obtain a first measurement value;

contacting the tester cell with the test substance and a proteasome inhibitor, and thereafter measuring the expression amount of Parpl protein in the tester cell to obtain a second measurement value; and

selecting the test substance as a candidate substance for use as a therapeutic agent for treating an ischemia/reperfusion injury when the second measurement value is greater than the first measurement value.

[0017] <10> The method of screening a therapeutic agent for treating an

ischemia/reperfusion injury according to <9>, wherein the tester cell is a p53-wild-type mouse fetus-derived fibroblast cell.

BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1A shows that Nutlin3a induces a decrease in Parpl protein levels in mammalian cell lines but that Cpt does not. Mouse fibroblast 3T3-L1 (upper panel) or 3T3-F442A (lower panel) cells were treated with the indicated concentrations of Cpt or Nutlin3a for 24 hours. The cell lysates were analyzed by Western blotting using the indicated antibodies. LE means long exposure.

Figure IB is quantitative data from Fig 1 A.

Figure 1 C shows that 3T3-L1 or 3T3-F442A cells were treated with 25 μΜ of Nutlin3a for the indicated times. Proteins were subjected to Western blotting. In the p53 panel, the arrow and asterisk respectively show the p53 and nonspecific bands.

Figure ID shows that three human cell lines (U20S, A549, and HepG2) were treated with the indicated concentrations of or Cpt or Nutlin3a for 24 h. The cell lysates were analyzed by Western blotting using the indicated antibodies.

All experiments were performed at least three times, and representative data are shown.

[0019] Figure 2 A shows that a decrease in Parpl protein levels induced by Nutlin3a is p53 status dependent. shGFP- and shp53-transiently transfected 3T3-L1.

Figure 2B shows HW, which is a mouse fibroblast cell line from p53 knockout mice, and 3T3-Ll/shp53, which is a p53 stable knockdown cell line.

Figure 2C shows that p53+/+ (n=2) and p53-/- (n=3) MEFs were treated with the indicated concentrations of Nutlin3a for 24 hours. The cell lysates were analyzed by Western blotting using the indicated antibodies. In the p53 panel, the arrow and asterisk respectively show the p53 and nonspecific bands.

All experiments were performed at least twice, and representative data are shown.

[0020] Figure 3 A shows that Nutlin3a downregulates Parpl Protein Levels by

Proteasomal Degradation. A, 3T3-L1, 3T3-F442A, 3T3-Ll/shp53, and HW cells were treated with the indicated concentrations of Nutlin3a for 24 hours. Parpl mRNA was detected by RT-PCR. β-actin was used as a loading control.

Figure 3B shows that 3T3-L1 and 3T3-F442A cells were treated with 25 μΜ of Nutlin3a in the presence or absence of 5 μΜ of the proteasome inhibitor MG132 (MG) for 8 hours, and then the cell lysates were subjected to Western blotting using the indicated antibodies.

All experiments were performed at least three times, and representative data are shown.

[0021] Figure 4A shows that Caylin2 induces decrease in Parpl protein levels in mammalian cell lines but that Nutlin-3b does not. Mouse fibroblast 3T3-L1 (upper panel) or 3T3-F442A (lower panel) were treated with the indicated concentrations of Nutlin3a, Nutlin3b or Caylin2 for 8 hours. The cell lysates were analyzed by Western blotting using the indicated antibodies. In the p53 panel, the arrow and asterisk respectively show the p53 and nonspecific bands.

Figure 4B is quantitative data from Fig 4A.

Figure 4C shows that 3T3-L1 cells were treated with the indicated concentration of Caylin2 for 8 hours. The rate of cell death was analyzed by trypan blue staining.

All experiments were performed at least three times, and representative data are shown.

[0022] Figure 5A shows that a decrease in Parpl protein levels induced by Caylin2 is p53 status dependent. p53+/+ and p53-/- MEFs were treated with the indicated

concentrations of Caylin2 for 8 hours. The cell lysates were analyzed by Western blotting using the indicated antibodies.

Figure 5B is quantitative data from Fig 5A. p53+/+ and p53-/-MEFs of every 2 to 3 clones were analyzed and representative data are shown.

[0023] Figure 6A shows that 3T3-L1 cells were treated with 20 μΜ of Caylin2 for the indicated times. The proteins were subjected to Western blotting.

Figure 6B shows 3T3-L1 cells were treated with 20 μΜ of Caylin2 in the presence or absence of 5 μΜ of the proteasome inhibitor MG132 (MG) for 8 hours, and then the cell lysates were subjected to Western blotting using the indicated antibodies.

DESCRIPTION OF EMBODIMENTS

[0024] The present invention provides an agent for treating ischemia/reperfusion injury, comprising administering to a mammal a therapeutically effective amount of a p53 agonist compound comprising a c is- imidazoline structure.

[0025] The present invention further provides a method of treating ischemia/reperfusion injury, comprising administering to a mammal a therapeutically effective amount of a p53 agonist compound comprising a cis-imidazoline structure.

[0026] The present invention provides a method of screening a therapeutic agent for treating an ischemia/reperfusion injury, comprising:

contacting a test substance with a p53-wild-type tester cell, of which an expression amount of Parpl protein in a case in which the cell is contacted with Nutlin3a or Caylin2 is lower than that before contact with Nutlin3a or Caylin2, and thereafter measuring the expression amount of Parpl protein in the tester cell to obtain a first measurement value; contacting the tester cell with the test substance and a proteasome inhibitor, and thereafter measuring the expression amount of Par l protein in the tester cell to obtain a second measurement value; and

selecting the test substance as a candidate substance for use as a therapeutic agent for treating an ischemia/reperfusion injury when the second measurement value is greater than the first measurement value.

[0027] Using Nutlin3a, we have analyzed p53 functions that are independent of DNA damage response and incidentally found thatParpl proteins disappear in Nutlin3a -treated cells. In this study, we show the basic characterization of Nutlin3a -mediated Parpl protein degradation and discuss the use of Nutlin3a as a Parpl inhibitor for therapy and protection from ischemia/reperfusion injury.

[0028] Here we demonstrate that Nutlin3a treatment in mammalian cells reduces the protein levels of poly(ADP-ribose) polymerasel (Parpl). Parpl functions in DNA repair, replication, and transcription and has been regarded as a target molecule for anti-cancer therapy and protection from ischemia/reperfusion injury. In this study, first we found that Nutlin3a, but not DNA damaging agents such as camptothecin (Cpt) and cisplatin, induced a decrease in the Parpl protein levels. This decrease was not associated with cell death and not observed in p53 deficient cells. Next, because Nutlin3a treatment did not alter Parpl mRNA levels, we expected that a protein degradation pathway might contribute to this phenomenon. Finally, we found that a proteasome inhibitor, MG132, inhibited the Nutlin3a -induced decrease in the levels of Parpl protein. These results show that Nutlin3a induces the proteasomal degradation ofParpl in a p53-dependent manner. Our findings will lead to the novel use of Nutlin3a as a Parpl inhibitor for therapy and protection from ischemia/reperfusion injury.

[0029] The present invention is described in detail below. Although the below

descriptions of the constituent elements sometimes refer to representative embodiments of the invention, the invention is by no means limited to the embodiments.

The term "ischemia/reperfusion injury" as used in the invention refers to disorders caused by an increase in the activity of Parpl protein. Specific examples of the disorders include ischemic infarction such as cerebral infarction, myocardial infarction and pulmonary infarction, reperfusion disorders accompanying treatment of such infarctions, and tissue damage caused by vessel ligation and reperfusion during organ transplantation.

The term "a p53 agonist compound" as used in the invention refers to compounds that have a potent to induce p53 protein accumulation in vitro or in vivo. Specific examples of the p53 agonist compound comprising a cis- imidazoline structure include Nutlin3a, Caylin2, Caylinl and pharmaceutically acceptable salts thereof.

In the invention, a p53 agonist compound comprising a cis-imidazoline structure is preferably selected from the group consisting of Nutlin3a, Caylin2, and

pharmaceutically acceptable salts thereof.

In the invention, examples of the tester cell include a p53-wild-type cell of which the expression amount of Parpl in a case in which the cell is contacted with Nutlin3a is lower than that before contact with Nutlin3a, and specific examples thereof include a p53-wild-type mouse fetus-derived fibroblast cell, mouse preadipocyte strains 3T3-L1 and 3T3-F442A and human lung carcinoma strain A549.

In the invention, examples of the proteasome inhibitor include MG132

(manufactured by Wako Pure Chemical Industries Ltd.), MG1 12, Lactacystin,

Epoxomicin, PS-341 (Bortezomib), TMC-95A, Tyropeptin A, Salinosporamide A, Belactosin A, and Agosterol C.

In the invention, the term "contact" or "contacting" may refer to, for example, dissolving Nutlin3a, Caylin2 and/or another physiologically-active agent in a medium in which the tester cell is cultured, and culturing the tester cell for a certain period of time.

EXAMPLES

[0030] Examples of the invention are described below. However, the invention is not limited by the examples. In the descriptions below, "%" is based on mass unless indicated otherwise.

[0031 ] EXPERIMENTAL PROCEDURES

[0032] Cell Culture and Drugs

[0033] Mouse fibroblast cell line 3T3-L1, human lung cancer cell line A549, and human hepatoma cell line HepG2 were purchased from the RIKEN Bioresource Center (Japan). Mouse fibroblast cell line 3T3-F442A and human osteosarcoma cell line U20S were purchased from the European Collection of Animal Cell Cultures (U.K.). p53 deficient mouse-derived fibroblast cell line HW (J. Med. Chem. (2010) 53, 4561-4584) was kindly provided by Dr. Masayuki Saito (Tenshi University, Japan). The cells were maintained in Dulbecco's modified Eagle's medium (low glucose) (WAKO, Japan) with 10% (3T3-L1 , 3T3-F442A, HW, U20S, and HepG2) or 5% (A549) fetal calf serum and 1 %

penicillin/streptomycin (SIGMA). Cpt and MG132 were purchased from WAKO (Japan). Nutlin3a, Nutlin3b, and Caylin2 were supplied by Cayman (USA). p53 knockdown by shRNA

[0034] We designed a mouse p53 shRNA expression vector based on target sequences for effective p53 knockdown, as previously reported (J. Biol. Chem. (2003) 278, 1 1731- 1 1734). Two oligonucleotides, 5'- gatccccGTACGTGTGTAGTAGCTTCttcaagagaGGAGCTATTACACATGTACtttttg gaaa -3' (SEQ ID NO: 1) and 5'- agcttttccaaaaaGTACATGTGTAATAGCTCCtctcttgaaGAAGCTACTACACACGTA Cggg -3' (SEQ ID NO:2) (upper case letters, target sequences against p53; lower case letters, Bglll, Hindlll or loop structure sequences) were chemically synthesized (Operon

Biotechnology, USA). The annealed oligos were directly ligated into a Bglll and Hindlll- digested pSUPER-puro shRNA expression vector gifted from Dr. Shigeo Ohno

(Yokohama City University, Japan) (Cell Sci. (2006) 1 19, 2107-21 18). The produced vector, termed pSUPER-puro-shmp53, was transfected with Lipofectamine LTX

(Invitrogen, USA) into 3T3-L1 cells, according to the manufacturer's protocol. For stable p53 knockdown cell lines, the transfected cells were selected with puromycin and resistant clones were isolated by trypsinization using cloning cylinders.

[0035] Preparation of Primary Mouse Embryonic Fibroblasts (MEFs)

[0036] p53 heterozygous mice (Accession Number, CDB 0001K) (Oncogene (1993) 8, 3313-3322) were purchased from RIKEN BRC (Saitama, Japan). p53 heterozygous males and females were crossed, and MEFs were prepared from the pregnant females. Each 13- to 15-day-old embryo was dissected from the uterus and washed with PBS. After removal of the head, tail, limbs, and blood-enriched organs, the trimmed embryo was washed with PBS and minced. After trypsinization at 37°C for 10 min followed by inactivation of trypsin by addition of FCS, MEFs were separated by filtration through a cell-strainer. p53 status was confirmed by PCR using previously described primers (forward primer for p53 genomic sequence, 5 ' - A ATTG AC A AGTT ATGC ATC C A AC AGT AC A- 3 ' (SEQ ID NO:3); reverse primer for p53 genomic sequence, 5'-

ACTCCTCAACATCCTGGGGCAGCAACAGAT-3' (SEQ ID NO:4), forward primer for neo sequence, 5 '-GAACCTGCGTGC AATCC ATCTTGTTCAATG-3 ' (SEQ ID NO:5)) (Oncogene (1993) 8, 3313-3322), and the established MEFs were maintained in DMEM high glucose with 10% FCS, 2-mercaptoethanol (2-ME), and antibiotics.

[0037] Western Blotting [0038] Cells were lyzed by the addition of lysis buffer (50 mM Tris-HCl pH6.8, 2% SDS, 5% glycerol), boiled for 5 min, and sonicated. Protein concentrations of the soluble fraction were determined by BCA protein assay (PIERCE, USA) according to the manufacturer's protocol, and standardized by the addition of lysis buffer. Following this, the proteins were added to 2-ME and bromophenol blue so as to obtain final

concentrations of 5% and 0.025%, respectively, and boiled for 5 min. Equal amounts of proteins (5 to 20 μg) were subjected to SDS-PAGE and transferred to nitrocellulose membranes. The membranes were blocked with 2.5% skim milk and 0.25% BSA in TBS (50 mM Tris, pH 7.4, 150 mM NaCl) containing 0.1% Tween 20 (TTBS) for 1 h at room temperature, and then probed with appropriate primary antibodies overnight at 4°C or for 2 h at room temperature. As primary antibodies, anti-Parpl (clone C-2-10, WAKO, Japan), anti-p53 (clone Ab-1 , Calbiochem, USA), anti- jS actin (clone AC- 15, SIGMA, USA), or anti-caspase-3 (clone 1F3, MBL, Japan) antibodies were used. After washes with TTBS, the membranes were incubated with the appropriate secondary antibody, horseradish peroxidase-conjugated F(ab')2 fragment of goat anti-mouse IgG or anti- rabbit IgG (Jackson Immunoresearch, USA), for 1 h at room temperature. After washing the membrane with TTBS, the membranes were incubated with ImmunoStar LD reagent (WAKO, Japan). The specific proteins were visualized with LAS3000 (FUJI FILM, Japan), and the data were analyzed using MultiGauge software (FUJI FILM, Japan).

[0039] RNA Purification and RT-PCR

[0040] Cells were lyzed by RNAiso PLUS (TaKaRa, Japan), and then total RNA was purified using a FastPure RNA kit (TaKaRa, Japan) according to manufacturer's protocol. One mg RNA was subjected to reverse transcription with PrimeScript Reverse

Transcriptase (TaKaRa, Japan) and random hexamer (TaKaRa, Japan). The PCR reaction was performed using Platinum Taq DNA Polymerase High Fidelity (Invitrogen, USA) and Parpl (forward, 5'-TGCTCATCTTCAACCAGCAG-3' (SEQ ID NO:6); reverse, 5'- TCCTTTGGAGTTACCC ATTCC-3 ' (SEQ ID NO:7)) or j8 -actin primers (forward, 5'- TCTTTGCAGCTCCTTCGTTG-3 ' (SEQ ID NO: 8); reverse, 5'- GGCCTCGTC ACCC AC ATAG-3 ' (SEQ ID NO:9)) as follows: initiation step, at 94°C for 1 min; amplification step, 30 (Parpl) or 25 ( β -actin) cycles of at 94°C for 1 min, at 52°C (Parpl) or 61°C ( β -actin) for 15 sec, at 68°C for 15 sec; termination step, 68°C 15 sec. PCR products were subjected to 1.8% agarose gel electrophoresis, stained with ethidium bromide, and visualized with LAS3000. The data was analyzed using MultiGauge software (FUJI FILM, Japan).

[0041] RESULTS

[0042] Nutlin3a Induces a Decrease in Parpl Protein Levels in Mammalian Cell Lines.

[0043]When analyzing proteins of the Nutlin3a-treated mouse fibroblast cell line 3T3-L1 , we observed a significant reduction in the levels of full length of Parpl protein without cleavage into p85 and p25 apoptotic fragments. Interestingly, under this condition, a trypan blue exclusion assay showed that the cells were viable (data not shown), suggesting that the reduction of Parpl protein was independent of cell death. To examine whether p53 stabilization induces the decrease in Parpl protein, 3T3-L1 and 3T3^F442A mouse fibroblast cells were treated with a DNA damaging agent, Cpt, or Nutlin3a. As shown in Fig. 1 A and IB, in both cell lines, Cpt treatment did not alter the Parpl protein levels, and Nutlin3a markedly decreased it, although both drugs induced p53 stabilization. Furthermore, another DNA damaging agent, cisplatin, treatment and overexpression of p53 protein did not affect Parpl protein levels (data not shown). Consistent with our previous observations, no caspase-3 activation, which is a hallmark of apoptosis, was detected in these conditions. The time course analysis showed that Parpl protein diminished by a treatment with 25 fM Nutlin3a for 8 h (Fig. 1C). To confirm whether the Nutlin3a-inducedParpl decrease is observed in human cells, we analyzed various

Nutlin3a -treated human cell lines, A549, U20S, and HepG2. As shown in Fig. ID, we detected the Nutlin3 a- induced Parpl decrease in only A549 cells. These results suggest that in certain mammalian cells Nutlin3a induces the reduction of Parpl protein in a cell death- independent manner.

[0044] Nutlin3a-Induced Decrease inParpl Protein Is Mediated by p53.

[0045] Since Nutlin3a stabilizes p53 via inhibition of Mdm2, we examined whether p53 contributes to the Nutlin3a- induced Parpl reduction. shRN A- mediated transient knockdown of p53 in 3T3-L1 cells attenuated the decrease in Parpl by Nutlin3a treatment (Fig. 2A). Since p53 knockdown efficiency is not sufficient, we next analyzed this using two p53 deficient cell lines. 3T3-Ll/shp53 cells were established by stable transfection with the pSUPER-puro-shmp53 plasmid vector followed by clone isolation, and its p53 protein expression levels were very much lower than in the transient knockdown. HW cells are a fibroblast cell line derived from p53 deficient mice. In these cell lines, the Nutlin3a-induced decrease in Parpl was diminished significantly (Fig. 2B). Furthermore, we confirmed p53 dependency in the Nutlin3a- induced Parpl reduction by using mouse embryonic fibroblasts derived from p53+/+ or -/- mice, and obtained similar results (Fig. 2C). These results show that Nutlin3a reduces the Parpl protein levels in a p53-dependent manner.

[0046] Nutlin3a down-regulates Parpl protein via proteasome.

[0047] To examine whether the decrease in Parpl protein by Nutlin3a treatment is caused by down-regulation of its mRNA, p53 proficient (3T3-L1 and 3T3-F442A) and deficient (3T3-Ll/shp53 and HW) cell lines were treated with Nutlin3a, and then the Parpl mRNA of each was analyzed by RT-PCR. Parpl mRNA did not change in either p53 proficient or deficient cell lines, even at doses of Nutlin3a where levels of Parpl protein were completely diminished (Fig. 3A). Therefore, we speculated that Nutlin3 a- induced Parpl reduction might involve proteasomal degradation. Thus, the effects of proteasome inhibition on Nutlin3a-inducedParpl reduction were examined. Treatment with the proteasome inhibitor MG132 alone did not affect basal Parpl protein levels, but it clearly inhibited the Nutlin3a- induced reduction in Parpl (Fig. 3B). Taken together, these results indicate that the Nutlin3a treatment induced proteasome-mediated degradation of Parpl protein.

[0048] Nutlin3b and Caylin2 were studied using the same method as in the case of Nutlin3a. The results are shown from Fig. 4A to Fig. 6B.

[0049] As shown in Figs. 4A and 4B, in both cell lines, Nutlin3a and Caylin2, but not Nutlin3b, markedly decreased the Parpl protein levels and induced p53 protein stabilization. These results suggest that in certain mammalian cells Caylin2 also induces the reduction of Parpl protein in a cell death-independent manner. Interestingly, 100 fM Caylin2 treatment induced Parpl cleavage, a hallmark of apoptosis, although 20 fM Caylin2 treatment induced Parpl protein decrease without any trace of its apoptotic cleavage. This result also supports that the decrease in Parpl protein level is not caused by cell death.

[0050] Furthermore, we confirmed p53 dependency in the Caylin2- induced Parpl reduction by using mouse embryonic fibroblasts derived from p53+/+ or -/- mice, and obtained similar results to those of Nutlin3a treatment (Figs. 5A and 5B). These results show that Caylin2 reduces the Parpl protein levels in a p53-dependent manner.

[0051] Treatment with the proteasome inhibitor MG132 alone did not affect basal Parpl protein levels, but it clearly inhibited the Caylin2-induced reduction in Parpl (Figs. 6A and 6B). These results indicate that the Caylin2 treatment induced proteasome-mediated degradation of Parpl protein. [0052] We demonstrated that the Mdm2 inhibitor, Nutlin3a and Caylin2, induce the reduction of Parpl protein by a p53-dependent mechanism. Interestingly, DNA damaging agents (camptothecin and cisplatin), a proteasome inhibitor (MG132), and overexpression of p53 protein did not evoke a significant reduction in Parpl protein, although these all induced p53 accumulation similar to Nutlin3a and Caylin2. These results suggest that in the process of Nutlin3a or Caylin2-inducedParpl reduction, Mdm2 inhibition is more important than p53 accumulation. Therefore, we examined whether the other

commercially available Mdm2 inhibitors induced a reduction in Parpl protein irr 3T3-Ll and A549 cells (data not shown). However, we could not identify Mdm2 inhibitors that induce a reduction in Parpl protein in both cells. To conclude this issue, additional experiments with Mdm2 knockdown studies would be required.

[0053] We also showed that MG132 blocks the decrease in Parpl protein. It was reported that Parpl can be ubiquitinated in vivo, although it is unclear whether the ubiquitination is involved in proteasomal degradation ofParpl (J. Cell. Biochem. (2008) 104, 318-328). Taken together with our findings, it is likely that the ubiquitin-proteasome pathway directly regulates the degradation of Parpl protein.

[0054] In comparison to the many Parpl inhibitors evaluated in ongoing clinical trials (J. Med. Chem. (2010) 53, 4561 -4584), the regulatory mechanism of Parpl protein that we discovered provides some advantages. The first advantage is the novel mechanism of action as an inhibitor of the Parpl signaling pathway. Because most of the Parpl - inhibiting compounds previously identified block the catalyzing activity of the protein, the specificity of these drugs in the other Parp family proteins that possess the highly conserved catalytic domain is a big issue (J. Med. Chem. (2010) 53, 4561-4584). On the other hand, Nutlin3a and Caylin2 inhibit Parpl signaling via induction of Parpl protein degradation. Therefore, we expect that the inhibition specificity for Parpl protein in the Parp family could be high. In any case, it is important to analyze the effects of Nutlin3a and Caylin2 treatment on the protein levels of the other Parp family proteins. The second advantage is its cell type selectivity. A subset of cell lines that were used in this study was responsive to Nutlin3a, with decreases observed in Parpl protein (Fig. 1A and Fig. ID). It has been reported that Nutlin3a induces cleavage of Parpl into two apoptotic fragments in the human colon cancer cell line, HCT1 16, and the human myeloid leukemia cell line, ML- 1 (Mol. Cancer Res. (2007) 5, 1 133-1 145, Cell Cycle (2009) 8, 171 1-1719). In fact, we confirmed that there was no significant reduction in Parpl protein other than apoptotic cleavage in HCT1 16 cells treated with various doses of Nutlin3a (data not shown). Taken together, we believe that Nutlin3a or Caylin2-induced Parpl degradation has cell type selectivity. Furthermore, as its clinical application, considering co-treatment with DNA damaging agents, Nutlin3a and Caylin2 may reduce side effects caused by DNA damaging agents. It is well known that alkylating agents cause Parpl over-activation, resulting in massive inflammation due to undesirable necrotic cell death caused by NAD+ and ATP depletion (Proc. Natl. Acad. Sci. U.S.A. (1999) 96, 13978-13982, Mo.l Cell. Biol. (1999) 19, 5124-5133), and that Parpl is required for NF- κ B transactivation involved in inflammatory responses (Am. J. Pathol. (2008) 173, 2-13). Therefore, co-treatment with Nutlin3a or Caylin2 may also attenuate necrotic cell death and inflammation induced by Parpl over- activation.

[0055] Thus, elucidation of the regulatory mechanism according to which a p53 agonist compound comprising a cis-imidazoline structure induces elimination of Parpl protein is important for the optimization of compounds inducing this phenomenon, resulting in establishment of selective chemotherapeutic strategies against cancer and

ischemia/reperfusion injury.

[0056] The present application claims the benefits of priority to U.S. application Ser. No. 61/437,692, filed January 31, 2011. The contents of that application are incorporated herein by reference in their entirety. All publications, patent applications, and technical standards mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication, patent application, or technical standard was specifically and individually indicated to be incorporated by reference.