Consequences of the loss of p53, RB1, and PTEN: Relationship to gefitinib resistance in endometrial cancer

Objective. These studies demonstrate how loss of function mutations or downregulation of key tumor suppressors missing from type I and type II endometrial cancer cells contributes to carcinogenesis and to resistance to the EGFR inhibitor gefitinib (ZD1839). Methods. Cell models devoid of tumor suppressors PTEN and RB1 or PTEN were studied. PTEN, RB1 and p53 expression was reinstated, and the effects on cell cycle, apoptosis, and cell cycle regulators were evaluated. Results. In Ishikawa H cells that model type I endometrial cancer in the loss of PTEN and RB1, re-expressing PTEN and RB1 increased the apoptotic and G I phases and decreased the S and G2-M phases, which further sensitize the cells to gefitimb. Expressing p53 in Hec50co that model type II tumors by loss of this minor suppressor arrested cells at the G1-S checkpoint, and apoptosis was also induced. Yet this did not improve sensitivity to gefitimb. Modulation of the cell cycle regulators responsible for these changes is explored, and a potential new therapeutic target, MDM2, is identified. Conclusion. The downregulation of p53 expression in type If Hec50co cells is linked to gefitimb resistance. In addition, the overexpression of MDM2, the principal factor that inhibits p53 function also occurs in these resistant cells. MDM2 phosphorylation is only partially blocked by gefitimb, and high MDM2 expression may relate to drug resistance. (c) 2007 Elsevier Inc. All rights reserved.