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INTRODUCTION Mutant p53 cancer cells are poorly responsive to chemotherapy. A small molecule drug, PRIMA-1, can bind to wildtype and mutant p53 to induce structural conformation that enhances p53 DNA binding. In a quest for new effective combination chemotherapies, we hypothesized that sequential treatment of GBM cells with doxorubicin then PRIMA-1 could stabilize and refold p53 to enhance chemotherapy-induced cellular apoptosis. We evaluated this combination in GBM cells engineered to express different p53 mutants and exhibiting different phenotypes. METHODS We constructed split reporter biosensors incorporating different structural mutants of p53 (p53Y220C, p53G245S, and p53R282W) all within p53-null Ln308 GBM cells, to evaluate PRIMA-1-mediated refolding of p53 using bioluminescence imaging. We used these cells, and other GBM cells endogenously dissimilar for p53 phenotypes (U87MG with wt-p53, and Ln229 with mutant p53 [mt-p53P98L/p14ARFdel/p16del]), to investigate the anticancer activity of doxorubicin plus PRIMA-1 by using immunoblot analysis of p53 downstream pathway proteins. We also evaluated treatment by imaging mice implanted with GBMs of different p53 phenotypes. RESULTS PRIMA-1 induced reporter complementation at &gt; 80 mM in all GBM cells regardless of p53 status. Doxorubicin stabilized p53 and increased its levels significantly more than in control cells. Significant changes in apoptotic index occurred in GBM cells treated with doxorubicin (1mM) followed by PRIMA-1 (40 mM), compared to cells treated with each drug independently, or with PRIMA-1 followed by doxorubicin. There was upregulation of p53, p21, and Bax, but downregulation of Bcl2 after combination therapy. PRIMA-1 and doxorubicin acted synergistically in GBM cells, but not significantly compared to using doxorubicin followed by PRIMA-1. CONCLUSION Our molecular imaging biosensor is useful to detect drug-induced restoration of p53 wildtype conformation. Doxorubicin stabilizes and increases p53 levels in GBM cells for subsequent enhanced PRIMA-1-mediated p53 refolding and increased levels of cellular apoptosis—an effective anti-GBM combination treatment.

neuro-oncology

EXTH-30. PRECEDING p53 STABILIZATION USING DOXORUBICIN AUGMENTS PRIMA-1-MEDIATED p53 REFOLDING AND INCREASED CELLULAR APOPTOSIS: EVALUATION OF A SEQUENTIAL COMBINATION THERAPY AGAINST GLIOBLASTOMA