Abstract
Pifithrinโฮฑ (PFTฮฑ) is a small molecule inhibitor of p53. By reversibly blocking apoptosis in response to DNA damage, PFTฮฑ protects normal cells from lethal doses of ฮณโradiation (Komarov et al., Science, 1999;285:1733โ7). We examined the effect of PFTฮฑ on the chemosensitivity of a human cancer in which cell cycle arrest, not apoptosis, is the principle cellular consequence of p53 activation. This was of interest because E6 silencing of p53 sensitizes U87MG astrocytic glioma cells to BCNU and temozolomide (TMZ), cytotoxic drugs that are modestly helpful in the treatment of aggressive astrocytic gliomas. We observed that exposure of U87MG cells to PFTฮฑ before cytotoxic chemotherapy attenuated p53โmediated induction of p21WAF1 protein levels, sensitizing U87MG cells to BCNU and TMZ. Sensitization of U87MG cells was associated with G1 arrest, delayed entry into Sโphase and decreased repair of DNA damage by BCNU. Our findings suggest that in addition to protecting normal cells from the toxic effects of radiation and chemotherapy, small molecule inhibitors of p53, like PFTฮฑ, might play a role in clinical oncology by sensitizing certain resistant cancers to cytotoxic chemotherapies. ยฉ 2005 WileyโLiss, Inc.