Abstract
We present evidence that the cisplatin-resistant human ovarian cancer lines, A2780S/CP1 (S/CP1), A2780S/CP3 (S/CP3) and A2780S/CP5 (S/CP5), derived by subjecting the sensitive A2780S ovarian cancer line to multiple rounds of cisplatin treatments followed by recovery and are resistant to 1, 3 and 5 μM cisplatin, respectively, have increased colony-forming ability and altered morphology that is consistent with enhanced motility, migration and invasiveness in vitro. The malignant phenotype progresses with increasing resistance and is associated with hyperactive epidermal growth factor receptor (EGFR)/extracellular signal-regulated kinase (Erk)1/2 and janus kinases (Jaks), aberrant signal transducer and activator of transcription (Stat) 3 activation promoted by EGFR and Jaks, and epithelial-mesenchymal transition (EMT) in vitro. Survivin and FLIP anti-apoptotic factors, vascular endothelial growth factor (VEGF) and matrix metalloproteinase activities are also elevated in the resistant cells. Accordingly, the ectopic expression of constitutively-active Stat3C in the sensitive A2780S cells diminished cisplatin sensitivity. The inhibition of EGFR or Stat3 activity repressed Survivin, VEGF and Vimentin expression and the colony-forming potential, viability, motility and migration of the resistant cells, and sensitized them to cisplatin. Analysis of human ovarian cancer patients' tumor tissues shows aberrantly-active EGFR and Stat3 that in certain cases correlate with Vimentin over-expression. Intra-peritoneal mouse xenograft studies revealed, compared with the sensitive A2780S line that had low tumor incidence restricted to the ovary, a high tumor incidence for the resistant S/CP3 and S/CP5 lines that formed tumor nodules at several locations on the small intestine and colon, and which responded poorly to cisplatin, but were sensitive to concurrent treatment with cisplatin and EGFR or Stat3 inhibitor. Hyperactive EGFR signaling through Stat3 and the Jak-Stat3 activity together promote ovarian cancer progression to cisplatin resistance and therefore represent targets for preventing the development of cisplatin resistance and the recurrent disease during cisplatin therapy in ovarian cancer.