Targeting the oncogenic mutant p53 signaling in colorectal cancer therapy

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Abstract Wide type (Wt) p53 is a tumor suppressor that is mutated or inactivated in more than 50% of colorectal cancers. Mutant P53 represents an oncogenic gain of function phenotype. P53 mutations are known to contribute to disease progression and resistance to chemotherapy and radiotherapy. Therefore, mutant P53 is considered as a major target for drug development. p53 family member p73 is rarely mutated in cancer cells and can elicit a p53-like tumor suppressive function. Thus, small molecules that can activate the p53 family member p73 represent a novel approach for p53 pathway restoration in mt p53 expressing tumors. Our lab has been working on the p53 pathway for the past 20 years. We have been involved with the discovery of endogenous p53 targets and drug discovery for targeting the p53 pathway. Our long term goal is to provide therapy for colorectal cancer patients with safe and efficacious small molecules that restore wild type (wt) p53 function in tumors with p53 mutations. P53 is also considered to be one of the key factors in regulating the cancer stem cell (CSC) population. CSCs are a smaller population of stem/progenitor cells capable of self- renewal that are responsible for long-term sustenance of the tumor, local tumor recurrence and metastatic relapse. CSCs are resistant to conventional chemotherapy since they possess various drug efflux mechanisms such as P-glycoprotein pumps (P-gp) (MDR1). Wt p53 is known to act as a transcriptional repressor of the MDR1 gene. Our hypothesis is that restoration of wt p53 function can not only target bulk tumor cells but also therapy resistant CSCs. p53 pathway restoration in CSCs would be associated with reduced P- gp pump activity and reduced therapy efflux that would support greater efficacy and reduced toxicity from p53 restoration compounds. We have previously established a functional cell-based screen for identifying small molecule compounds targeting mutant p53 protein. Through this screen we identified Prodigiosin, its related compound and CB-7587351 (Chembridge library # 7587351) as potent p53-family transcriptional activators. These compounds can restore wild-type p53 function in colon cancer cells harboring mt p53 in a p73-dependent manner. We will further address p53 pathway restoration in mt p53 expressing colorectal cancer with the following specific aims: Specific Aim1. Evaluate Prodigiosin and its related compound as a lead compound to target mt p53 in therapy of colorectal cancer and its tumor stem cells. Specific Aim2. Evaluate novel compound CB-7587351 as a lead compound to target mt p53 in therapy of colorectal cancer and its tumor stem cells. Specific Aim3. Test in vivo efficacy, pharmacokinetics and safety of p53 pathway restoration in preclinical models of colorectal cancer and its tumor stem cells harboring mt p53. Our proposed studies of p53 pathway restoration will represent a unique regimen that may help overcome resistance and toxicity associated with current chemotherapy. Selective inhibition of mt p53 expressing colon cancer stem cells may help resolve issues associated with therapy resistance and tumor recurrence.