Abstract #2952: Paradoxical molecular changes in cisplatin-resistant ovarian tumor cells: up-regulation of drug-sensitizing and down-regulation of resistance-inducing genes
Authors: Zai-Feng Huang, Guangan He, Abdul Khokhar, Zahid Siddik
Journal: Cancer Research (2009)

A major limitation of cisplatin in the treatment of human ovarian cancers is the onset of resistance, which is multifactorial, with several mechanisms co-existing in tumor cells. Nevertheless, specific analogs of cisplatin may circumvent this resistance, but how this is accomplished is not well understood. The inherent gene expression profile of resistant cells is a potential source for identifying genes not only contributing to resistance but also involved in circumvention of resistance by analogs, such as DACH-acetato-Pt(IV) (DAP). Therefore, we examined gene expression profiles in sensitive A2780 and its isogenic cisplatin-resistant 2780CP ovarian tumor models. Eppendorf DualChip human cancer microarrays indicated that expression of 55 genes in the resistant model was significantly altered (>1.5-fold), with 19 downregulated and 36 upregulated. As expected, several genes reported to be involved in resistance (e.g., MMP\#8217;s, EGF, IL6R and SOD1) were upregulated and genes involved in drug sensitivity (e.g., CAV1, EGR1, IRF1 and SPARC) were downregulated in resistant cells. Paradoxically, genes associated with resistance (e.g., ADAM9, CRADD, E2F5 and AXL) were also downregulated and those involved in drug sensitivity (e.g., CASP2 and TRADD) upregulated. Therefore, resistance in 2780CP cells likely represents a net effect of anti- and pro-apoptotic molecular changes. Conversely, circumvention of resistance in these cells by DAP must involve a net shift toward pro-apoptotic events, but which, if any, of the 55 genes are involved in this shift was next investigated by microarray analysis after cisplatin or DAP treatment, but initially in A2780 cells so that effects of the two drugs could be compared without interference from resistance mechanisms. This analysis in sensitive cells did not show drug-induced changes in expression of 10 selected genes that were most upregulated in resistant cells. Of the ten selected genes most downregulated in resistance, CAV1, p21, HGF and CLK1 were induced by cisplatin, but only p21 and HGF were induced by DAP. Which of these two candidate genes plays a role in circumvention of resistance by DAP was examined in drug-treated 2780CP cells. The low basal expression of HGF was unaffected by either drug, but a differential induction of p21 was observed. Western analysis confirmed that p21 was not induced by cisplatin but was elevated by DAP in resistant cells. Moreover, siRNA knockdown investigation in A2780 cells indicated that p21 is a determinant of tumor cell sensitivity for both cisplatin and DAP. These systematic studies demonstrate that resistant cells harbor expected and counterintuitive changes in expression of both pro-apoptotic and anti-apoptotic genes, but restoration by induction of a critical pro-apoptotic gene may be sufficient to circumvent resistance. (NCI grants CA127263 and CA16672).  Citation Information: In: Proc Am Assoc Cancer Res; 2009 Apr 18-22; Denver, CO. Philadelphia (PA): AACR; 2009. Abstract nr 2952.