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Mutations in TP53 occur commonly in the majority of human tumors and confer aggressive tumor phenotypes, including metastasis and therapy resistance. CB002 and structural-analogs restore p53 signaling in tumors with mutant-p53 but we find that unlike other xanthines such as caffeine, pentoxifylline, and theophylline, they do not deregulate the G2 checkpoint. Novel CB002-analogs induce pro-apoptotic Noxa protein in an ATF3/4-dependent manner, whereas caffeine, pentoxifylline, and theophylline do not. By contrast to caffeine, CB002-analogs target an S-phase checkpoint associated with increased p-RPA/RPA2, p-ATR, decreased Cyclin A, p-histone H3 expression, and downregulation of essential proteins in DNA-synthesis and DNA-repair. CB002-analog #4 enhances cell death, and decreases Ki-67 in patient-derived tumor-organoids without toxicity to normal human cells. Preliminary in vivo studies demonstrate anti-tumor efficacy in mice. Thus, a novel class of anti-cancer drugs shows the activation of p53 pathway signaling in tumors with mutated p53, and targets an S-phase checkpoint.

Kim and colleagues reported a p53/p21 complex regulates cancer cell invasion and apoptosis by targeting the Bcl-2 family ([1][1]). Interaction of overexpressed p53 and p21 proteins in p53-null H1299 cells correlated with decreased cell invasion. No coimmunoprecipitation experiments documenting

P53 tumor suppressor gene mutations occur in the majority of human cancers and contribute to tumor development, progression and therapy resistance. Direct functional restoration of p53 as a transcription factor has been difficult to achieve in the clinic. We performed a functional screen using a bioluminescence-based transcriptional read-out to identify small molecules that restore the p53 pathway in mutant p53-bearing cancer cells. We identified CB002, as a candidate that restores p53 function in mutant p53-expressing colorectal cancer cells and without toxicity to normal human fibroblasts. Cells exposed to CB002 show increased expression of endogenous p53 target genes NOXA, DR5, and p21 and cell death which occurs by 16 hours, as measured by cleaved caspases or PARP. Stable knockdown of NOXA completely abrogates PARP cleavage and reduces sub-G1 content, implicating NOXA as the key mediator of cell death induction by CB002. Moreover, CB002 decreases the stability of mutant p53 in RXF393 cancer cells and an exogenously expressed R175H p53 mutant in HCT116 p53-null cells. R175H p53 expression was rescued by addition of proteasome inhibitor MG132 to CB002, suggesting a role for ubiquitin-mediated degradation of the mutant protein. In summary, CB002, a p53 pathway-restoring compound that targets mutant p53 for degradation and induces tumor cell death through NOXA, may be further developed as a cancer therapeutic.

Much effort is currently focused on the p53 pathway. p53 is a key tumor suppressor, which is mutated or lost in many human cancers. Restoration of the p53 pathway holds the potential to induce selective cell death in tumor cells without harming normal cells that have intact p53 pathways. Most tumor cells express mutated p53 or suppress p53 by overexpression of MDM2. In this study, a compound referred to as CB002 with one closely related compound from the Chembridge library were evaluated for tumor cytotoxicity without affecting normal cells by restoration of the p53 pathway. A decrease of mutant p53 protein expression, restoration of inactivated p53, or some activation of p73 are candidate mechanisms this agent could cause tumor cell apoptosis and growth arrest. We further show that CB002 activates p53 pathway signaling in part via p73 in p53 mutant cancer cell lines. However, it is important to note that we have not established a role for p73 in the anti-tumor effect of CB002 or R1. CB002 causes tumor cell death with synergistic effects with traditional chemotherapeutics CPT-11 and 5-FU.

P53 is a transcription factor that becomes stimulated upon genotoxic and cellular stress signals ultimately leading to the transcriptional activation of genes involved in processes such as DNA repair, cell cycle arrest, and apoptosis etc. TP53 is the most commonly mutated tumor suppressor and this is associated with cancer initiation, cancer progression and therapy resistance. P53-targeted therapy has proven to be challenging because direct functional restoration of p53 as a transcription factor has been difficult to achieve. We haven taken a different approach by investigating small molecules that functionally restore the p53-signaling pathway instead of direct p53 targeting. To date there is no approved drug that restores the p53 pathway in cancer cells with mutant p53. Therefore, we performed a high-throughput screen to identify such molecules. We identified a family of small molecules, CB002 and its structural analogs, as candidates for restoration of the p53 pathway in p53-null and mutant p53-expressing cancer cells. CB002 was specific in causing apoptosis in colorectal cancer cells and not in normal human fibroblasts cells as indicated by a Sub-G1 assay. Utilizing the xCELLigence RTCA DP system and CIM-Plate we show that CB002 treatment decreases the ability of colorectal cancer cells to migrate. The ability of CB002 to restore the p53 pathway was validated by studying the activation of p53 target genes p21, DR5, and NOXA in various cancer cell lines and expression of well-established apoptotic markers. Stable knockdown of NOXA completely abrogated the expression of cleaved PARP and reduced Sub-G1 cells, implicating the relevance of NOXA as a key mediator of cell death induction by CB002. We are currently exploring the mechanism by which NOXA induces apoptosis, as preliminary results suggest that degradation of Mcl-1 is not required for CB002 mediated cell death. In addition, we are evaluating the ability of CB002 structural analogs in decreasing the stability of mutant p53 using a larger panel of p53 mutants, as CB002 appears to target R175H p53 mutants. Our data supports the continued investigation of CB002 as a p53 pathway-restoring compound that may be further developed as a cancer therapeutic for p53-null tumors as well as tumors with p53 mutations. Citation Format: Liz J. Hernandez Borrero, Shengliang Zhang, David T. Dicker, Wafik S. El-Deiry. CB002, a novel p53 pathway-restoring compound that induces apoptosis through the pro-apototic protein NOXA [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5178. doi:10.1158/1538-7445.AM2017-5178

Tumor suppressor p53 is a master regulator of genotoxic and cellular stress signals, controlling cell fate by transcriptionally activating genes involved in DNA repair, cell cycle arrest, and apoptosis. p53 is mutated in over half of human cancers and this is associated with tumor development and chemotherapy resistance. TP53 gene mutations can result in the abolishment of p53 contact with DNA and disruption of p53 structural conformation. These mutations not only prevent p53 to exert its normal tumor suppressive functions but can result in gain-of-function activity, acquiring oncogenic characteristics. Therefore, altering the stability of mutant p53 protein is an attractive therapeutic strategy in cancer cells. We investigated small molecules that modulate mutant p53 stability and restore the p53-signaling pathway. We identified a small molecule, CB002, as a candidate for restoration of the p53 pathway in mutant p53-bearing cancer cells. Three colorectal cancer cell lines: SW480, DLD-1, HCT116-R175H and the RXF393 renal cancer cell line, were treated with different concentrations of CB002 at various time points. Cell lines exposed to CB002 showed an increase in apoptotic and cell death markers, such as NOXA/DR5 induction, cleaved caspases and PARP, as early as 16 hrs. CB002 decreased mutant p53 stability in structural conformation-mutant bearing cells (HCT116 R175H and RXF393). Our data suggests that CB002 stimulates an increase of p53 target genes and promotes expression of pro-apoptotic proteins. R175H p53 mutant protein expression was largely rescued by the co-treatment with MG132, a proteasomal inhibitor, implicating a role for the ubiquitin proteasome system. Furthermore, we observed significant autophagy induction upon CB002 treatment, as indicated by LC3 conversion and p62 levels. Autophagy inhibition decreased levels of cell death markers and increased the stability of the R175H-mutant p53, suggesting that autophagy might be required for CB002-induced cell death and mutant p53 turnover. Therefore, we hypothesize that CB002 is capable of degrading mutant p53 and restoring the p53 pathway through p53 family members in colorectal cancer cells. Currently we are investigating p53 degradation mechanism by CB002, the role of p53 family members in the restoration of the pathway and autophagy on mutant p53 stability. Hence, our results provide an insight on effective p53 pathway activation through the use of small molecules. Citation Format: Liz J. Hernandez Borrero, Shengliang Zhang, David Dicker, Wafik El-Deiry. Anti-tumor effect and destabilization of R175H-mutant p53 by CB002, a p53-pathway restoring small molecule that stimulates autophagy. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 327.

One of the most explored cancer targets has been the tumor suppressor p53. p53 is mutated in more than half of all human tumors and therefore provides an attractive way to selectively target cancer cells that harbor the mutant protein. Mutant p53 protein can acquire a gain-of-function activity, losing its normal tumor suppressor properties and gaining oncogenic characteristics. Various approaches have been taken to restore the p53 pathway in mutant p53 expressing cells including the modulation of mutant p53 conformation to wild-type, and through the upregulation of p53 family members i.e. p73. Unlike p53, p73 is not commonly mutated in cancer cells and thus confers restoration of the p53 pathway through pharmacological stimulation. We characterized a small molecule that restores the p53 pathway through p73. A high-throughput cell-based screen identified small molecule CB002 as a potential candidate for the restoration of the p53 pathway in mutant p53 containing human colorectal cancer cells. Two colorectal cancer cell lines: SW480, DLD-1, and the RXF393 renal cancer cell line, were treated with different concentrations of CB002 for various time points. SW480 cells treated with CB002 for 8 hrs showed a decrease in p53 followed by an increase in DR5 expression at 16 hrs. DLD-1 cells treated with CB002 showed a decrease in p53 expression at 8 hrs. Although no change was observed in proteins involved in cell cycle arrest or cell death that were tested, colony formation was suppressed as compared to control. RXF393 cells treated with CB002 for 48 hrs showed decreased expression of p53 levels and increased levels of p21. These data suggest that CB002 is able to decrease mutant p53 protein expression, increase p53 target genes and promote expression of proteins involved in apoptosis, such as p21 and DR5, respectively. It appears that the CB002 mechanism is different depending on the cell line tested. We hypothesize that CB002 is capable of degrading mutant p53 and restoring the p53 pathway through p73 in colorectal cancer cells. Current undergoing experiments are focused on unraveling the p73 dependence through p73 knockdown and the mechanism of action involved in each cell line. The following project will aid in the understanding of the role of p73 in pharmacological restoration of the p53 pathway in cancer therapy. Citation Format: Liz J. Hernandez Borrero, Shengliang Zhao, David T. Dicker, Wafik El-Deiry. Small molecule identification for the restoration of p53 pathway through p73 and by degradation of mutant p53. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2643. doi:10.1158/1538-7445.AM2015-2643

ONC201/TIC10 is a potent small molecule anti-tumor agent in several types of solid tumors and lymphomas. ONC201/TIC10 is on track to enter clinical trials for patients with advanced cancer in 2014, with IND issued by the FDA in March, 2014. Early trials will evaluate the safety and efficacy of ONC201/TIC10 as a monoagent in hematological malignancies. In the current study, we evaluated the anti-cancer effects of the small molecule in Acute Lymphoblastic Leukemia (ALL). Analysis of cell viability by the CellTiter-Glo method revealed that ONC201/TIC10 treatment reduces the viability of three ALL cell lines (Reh, Jurkat, MOLT-4) in a dose- (2.5/5/10 μM) and time-dependent manner (24/48/72 h). We have previously reported that ONC201/TIC10-mediated reduction in cell viability and apoptosis in various types of solid tumors occurs at 60/72 h. Interestingly, ONC201/TIC10 reduces the viability of ALL cell lines within 24/48 h at the indicated doses. An inactive TIC10 isomer compound synthesized by Medkoo Biosciences with a structure related to the active ONC201/TIC10 compound does not reduce the viability of ALL cells. Sub-G1 analysis indicated that ONC201/TIC10 induces apoptosis in ALL cells and a pan-caspase inhibitor reduces ONC201/TIC10-mediated apoptosis. Western blot analysis was used to further investigate the mechanism of ONC201/TIC10-mediated apoptosis. ONC201/TIC10-mediated apoptosis involves PARP cleavage and caspase-9 activation. Anti-apoptotic Bcl-2 family members Bcl-2 and Bcl-xl are downregulated while the pro-apoptotic Bcl-2 family member Bim is upregulated in response to ONC201/TIC10 treatment. ONC201/TIC10 also downregulates the inhibitor of apoptosis (IAP) family proteins cIAP1 and cIAP2. We have previously shown that the anti-tumor effect of ONC201/TIC10 involves inhibition Akt and ERK phosphorylation resulting in Foxo3a activation and TRAIL-gene transcription. We observed inhibition of Akt phosphorylation upon ONC201/TIC10 treatment of ALL cells. Thus, ONC201/TIC10 holds promise as a novel agent for the treatment of ALL based on its robust activity in preclinical models of the disease. Our ongoing studies are evaluating the impact of this novel therapy on ALL cells with different translocations, and are introducing combination therapy with ONC201/TIC10 for ALL. Figure 1 Figure 1. Disclosures Allen: Oncoceutics: Employment, Equity Ownership, Patents & Royalties. El-Deiry:Oncoceutics, Inc.: Equity Ownership, Patents & Royalties.

Quinacrine is a bioactive acridine derivative which has been used for treatment of malaria, giardiasis, systemic lupus erythematosus, and rheumatoid arthritis. In searching for p53 pathway activating agents for cancer therapy, we found that quinacrine stabilizes p53 and induces p53-dependent and p53-independent tumor cell death. Quinacrine also induces expression of TRAIL Death Receptor 5 (DR5) and reduces expression of anti-apoptotic Mcl-1 in tumor cells. These activities predict synergies with TRAIL (tumor necrosis factor-related apoptosis inducing ligand) and chemotherapeutic agents in inducing extrinsic and intrinsic pathway mediated apoptosis. In addition, quinacrine suppresses NFkB activity in tumor cells. Clinical trials have been ongoing for treatment of solid tumors including colon cancer, renal cancer, prostate cancer, and non-small cell lung cancer with quinacrine in combination with chemotherapy or tyrosine-kinase inhibitors, however, the therapeutic potential of quinacrine in blood cancer cells has not been established. We tested quinacrine on hematopoietic malignant cells, which included cell lines of myeloid leukemia, lymphoblastic leukemia, B-cell lymphoma, T-cell lymphoma, and multiple myeloma. We found that quinacrine induces massive cell death in the cell lines tested, at concentrations from as less as 1 microM to 5 microM, 2-10 times lower than required to induce solid tumor cell death. Quinacrine synergizes with TRAIL in inducing cell death of TRAIL-sensitive cells and reverses resistance in TRAIL-resistant cells. Quinacrine also synergizes with chemotherapeutic agents, such as antimetabolites, alkylating agents, and tyrosine kinase inhibitors, in inducing apoptosis of hematopoietic cancer cell lines. Our work supports translational efforts to advance the use of quinacrine from bench to clinic and provides rationale for combination chemotherapeutic regimes for treatment of hematopoietic malignancies. Disclosures No relevant conflicts of interest to declare.

PI3K/Akt and Ras/MAPK pathways are attractive therapeutic targets in almost all tumor types, including AML and MM. Apo2L/TRAIL has been deemed a promising therapeutic given its selectivity towards cancer cells although its clinical development has been hampered by various limitations including short half-life and general shortcoming of protein-based therapeutics. ONC201/TIC10 (Oncoceutics, Inc.) is a first-in-class small molecule inducer of TRAIL expression. ONC201/TIC10 has previously been shown to up-regulate TRAIL and its death inducing receptor DR5 in HCT116 colon cancer cells, in part through the inhibition of Foxo3a phosphorylation mediated by dual inhibition of Akt and ERK (Allen JE et al, Sci Transl Med., 2013). Currently, ONC201/TIC10 is set to enter clinical trials for patients with advanced malignancies after the IND was approved by the FDA in March, 2014. We thus investigated the therapeutic potential of ONC201/TIC10 in AML and MM given a major unmet need when conventional therapy fails. We explored the possibility that ONC201/TIC10 induces apoptosis in MM and AML in part through dual inhibition of the PI3K/Akt and Ras/MAPK pathways. We tested a panel of four human MM cell lines (KMS18, MM.1S, MM.1S 33X and RPMI-8226) and three human AML cell lines (Kasumi-1, HL60, HL60/VCR). The Cell-titer Glo assay demonstrated a time and dose-dependent decrease in viability in the entire panel of MM and AML cells. EC50 values ranged from 1-2.5 µM for the MM and 2-5µM for the AML cell lines, respectively. Bortezomib-resistant cells MM.1S 33X and vincristine- resistant cells HL60/VCR were also significantly sensitive to ONC201/ TIC10 as a single agent with EC50s on par with the corresponding parental cell lines. Given the previously reported pro-apoptotic effects of ONC201/TIC10 against solid tumor cells, we assessed apoptosis by performing Sub-G1 analyses and assessing caspase-3 cleavage as two widely used methods to analyze apoptotic cell death. We observed an average of 10-fold induction of ONC201/TIC10–mediated apoptosis in MM cells at 5 mM at 48 hrs post-treatment. Rescue of ONC201/TIC10-mediated apoptosis was demonstrated using the pan-caspase inhibitor (Z-VAD-FMK). In addition, western blot analysis in MM cells indicated a dose-dependent decrease in the anti-apoptotic protein XIAP which is a key mediator of apoptosis inhibition and is reported to be highly up-regulated in MM cells. Dose and time dependent induction of apoptosis was noted in western blot analysis of caspase-3 cleavage in AML cell lines treated with 2.5 µM or 5 µM of ONC201/TIC10 for 48 hrs prior to analysis. Western Blot analysis further demonstrated inhibition of Akt and Foxo3a phosphorylation in Kasumi-1 cells, in line with the previously proposed mechanism of ONC201/TIC10 against solid tumor cells. To further investigate the therapeutic potential of ONC201/TIC10 in the context of AML, fresh AML cells were treated with ONC201/TIC10. The primary cells were also found to be sensitive to ONC201/TIC10 (60% decrease in cell viability 72 hrs post 5mM ONC201/TIC10 treatment). Similarly, caspase 3/7 activity was significantly increased as assessed by the Caspase Glo 3/7 assay (~5 fold induction in activity 72 hrs post 5mM ONC201/TIC10 treatment). To explore further the therapeutic potential of ONC201/TIC10, we performed combinatorial experiments with bortezomib and vincristine using the MM.1S 33X MM cells and the HL60/VCR AML cell lines. ONC201/ TIC10 showed an additive effect with both these compounds against the MM and AML lines. Our work demonstrates activity of ONC201/TIC10 against AML and MM cell lines including fresh AML tumor cells. The efficacy data with resistant cells is in par with the applicability of TIC10 in patients with refractory/relapsed hematological malignancies. The long-term goal of this project is to provide a rationale for a phase 1b trial of ONC201/TIC10 for refractory/relapsed MM and AML in combination with existing therapies. Figure 1: Efficacy of ONC201/TIC10 in AML and MM cells Figure 1:. Efficacy of ONC201/TIC10 in AML and MM cells Disclosures Allen: Oncoceutics, Inc.: Employment, Equity Ownership, Patents & Royalties. El-Deiry:Oncoceutics, Inc.: Equity Ownership, Patents & Royalties.