The p53 tumor suppressor is frequently inactivated by mutations in cancer. Most p53 point mutations are located in the DNA binding domain that prevent folding or disrupt the DNA binding surface. Rescuing the structural defect and transcriptional activity of mutant p53 in tumor cells should induce cell death or cell cycle arrest that bring significant therapeutic benefits. However, this hypothesis remains unproven because currently there are no specific drugs capable of efficiently reactivating mutant p53. To bypass this limitation and rigorously test the clinical potential of mutant p53 functional rescue, we established a procedure to induce sustained hypothermia in mice by pharmacological blockade of brain- regulated thermogenesis. This mouse model enabled us to use hypothermia to reactivate temperature- sensitive (ts) p53 mutants in tumors to evaluate therapeutic efficacy. Preliminary experiments demonstrated the ability of ts p53 activation in combination with chemotherapy to induce regression of lymphoma xenografts. Importantly, durable remission was observed in a subset of tumors. This promising finding provides proof-of-concept for mutant p53 functional rescue as a potential cancer treatment. Furthermore, since ~14% of p53 point mutants in cancer are temperature-sensitive, our results raised the possibility of using therapeutic hypothermia to treat tumors expressing ts mutant p53. To explore the translational potential and molecular mechanism of this novel approach, we propose the following specific aims: (1) Investigate tumor response to ts p53 activation and optimize therapeutic efficacy. (2) Investigate the potential of ts mutant p53 in solid tumors and PDX models. (3) Investigate the effect of endogenous ts p53 activation using a genetically engineered mouse model. (4) Identify all p53 ts mutants with tumor suppressor activity in vivo by saturation screen. These experiments will provide proof-of-concept for specific targeting of tumors expressing ts mutant p53, with the potential to impact a large number of cancer patients.

Project Narrative This proposal investigates the therapeutic potential of using hypothermia to restore activity of temperature-sensitive p53 mutants in mouse tumor models. The p53 tumor suppressor is frequently inactivated by mutations in cancer. Currently no approved drugs are available for restoring the activity of mutant p53. Although p53 missense mutants are inactive at 37°C, ~14% are temperature-sensitive (ts) that regain activity at 32°C. The p53 ts mutants represent a unique class that may be activated by mild hypothermia, which is currently standard of care for post- cardiac arrest patients. We have established conditions for inducing controlled hypothermia in mice. Preliminary experiments demonstrated the ability of hypothermia to induce regression and stable remission of tumors expressing ts mutant p53. We will use this system to further investigate conditions that can improve the efficacy of ts p53 targeting and achieving long-term remission. We will also test the effect the hypothermia against clinically-relevant patient-derived xenograft models (PDX) expressing ts mutant p53, and against spontaneous tumors developed in a mutant mouse with germline ts p53 mutation.