Cell cycle control and apoptosis of p53-isogenic cell lines treated with Hsp90 inhibitors

Abstract

3202 Most patients enrolled in clinical trials have advanced disease associated with loss or mutation of p53. The goal of new molecularly-targeted therapies is to increase the therapeutic index of drug resistant tumors, many of which have non-functional p53. However, there is limited knowledge on the role of p53 in response to these agents. Upon DNA damage, cells that express wild-type p53 undergo G1 and/or G2 arrest whereas mutant or null p53 cells are presumed to arrest transiently in G2. If the G2 checkpoint is abrogated, cells will undergo apoptosis. We tested the Hsp90 inhibitors, geldanamycin and its analogues, 17-DMAG and 17-AAG, and a checkpoint inhibitor, Gö6976, as potential abrogators of the G2 checkpoint in cells treated with traditional chemotherapeutic agents, such as Doxorubicin. Isogenic pairs of lymphoblastoid, breast, lung, and colon cancer cell lines were generated through retroviral transduction of siRNA for p53 or scramble (SC) encoding vectors. Survival, p53-dependent responses, cell cycle and apoptosis were used to determine if combining DNA damage and molecularly-targeted therapy leads to mitotic catastrophe and an increase in cell death. Sequential addition of DNA damaging agents with molecular therapies was synergistic in inducing cell death in cells that arrested in G2. Such sequential use of drugs may provide a rational approach to combination therapy in cancers with functional inactivation of p53, as a means to circumvent drug-resistance to traditional chemotherapeutic agents. No significant financial relationships to disclose.