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Drugging the undruggable-targeting P53: A comparative analysis of APR-246 and coti-2 in human tumor primary culture explants.

e15092 Background: The TP53 tumor suppressor is the most commonly mutated gene in human cancer. P53 protein comprised of 393 amino acids functions as a tetramer with the loss of function mutations concentrated in “hotspots” that often affect DNA binding domains. APR-246 and COTI-2 are novel small molecules that are under clinical investigation for the treatment of P53 mutated cancers. APR, a quinuclidine binds to P53 cysteine residues altering the functional conformation while COTI is a thio-semicarbazone, found active in P53 mutant tumors using a novel computational platform. As the mechanisms of action may differ we undertook a comparative analysis of these compounds in 3D human tumor explants derived from surgical specimens. Methods: Ex Vivo Analyses of Programmed Cell Death (EVA/PCD) (D’Amora, P et al Gyn. Oncol. 2021) was applied to 236 human tumor primary culture explants isolated from surgical specimens. After disaggregation, micro-spheroids, isolated by precise density centrifugation were exposed to APR, COTI and other agents for 72-96 hours. Drug-induced cell death was measured by delayed-loss-of-membrane integrity and ATP content (luciferase). Dose response curves were interpolated to LC50 values. Synergy analysis used the method of Chou & Talalay. Correlation coefficients used Pearson moment. Results: APR and COTI reveal the highest activity in hematologic neoplasms. Solid tumor activity patterns diverged with COTI active in gynecologic malignancies and NSCLC and moderately active in breast and colorectal while APR is active in colorectal but less active in breast and NSCLC. Pearson moments for COTI vs APR revealed an R value = 0.146 (NS). COTI activity correlated with Nitrogen Mustard and Alpelisib (PIK3CA) while APR activity correlated with Doxorubicin and Everolimus. COTI combinations focused upon ovarian cancers identified synergy in 25% and antagonism in 18%. Conclusions: P53’s function as the “guardian of the genome” is consistent with our findings that many cytotoxic and targeted agents that induce cell death reveal correlations with APR and COTI. While APR affects the structural conformation of P53, COTI may function downstream via oxidative, metabolic or other stress responses. The correlation coefficient for APR vs COTI at 0.146 (NS) suggests distinct mechanisms of action. This is supported by different disease-specific-profiles and correlations with other drugs. COTI synergy in ovarian cancers, the target of current clinical trials at 25% is below expectations. With differing disease specificities, selecting between these and related agents to optimize clinical outcomes may require a more granular examination of cellular mechanisms of response and resistance. Primary culture analyses offer insights into drug mechanisms of action, combinatorial potential and have the capacity to improve patient selection.