BEYOND KRAS: Other markers and potential treatment strategies for KRAS mutant and wild-type patients

Polymorphisms in Genes Involved in EGFR Turnover Are Predictive for Cetuximab Efficacy in Colorectal Cancer

Transmembrane receptors, such as the EGFR, are regulated by their turnover, which is dependent on the ubiquitin-proteasome system. We tested in two independent study cohorts whether SNPs in genes involved in EGFR turnover predict clinical outcome in cetuximab-treated metastatic colorectal cancer (mCRC) patients. The following SNPs involved in EGFR degradation were analyzed in a screening cohort of 108 patients treated with cetuximab in the chemorefractory setting: c-CBL (rs7105971; rs4938637; rs4938638; rs251837), EPS15 (rs17567; rs7308; rs1065754), NAE1 (rs363169; rs363170; rs363172), SH3KBP1 (rs7051590; rs5955820; rs1017874; rs11795873), SGIP1 (rs604737; rs6570808; rs7526812), UBE2M (rs895364; rs895374), and UBE2L3 (rs5754216). SNPs showing an association with response or survival were analyzed in BRAF and RAS wild-type samples from the FIRE-3 study. One hundred and fifty-three FOLFIRI plus cetuximab-treated patients served as validation set, and 168 patients of the FOLFIRI plus bevacizumab arm served as controls. EGFR FISH was done in 138 samples to test whether significant SNPs were associated with EGFR expression. UBE2M rs895374 was significantly associated with progression-free survival (log-rank P = 0.005; HR, 0.60) within cetuximab-treated patients. No association with bevacizumab-treated patients (n = 168) could be established (P = 0.56; HR, 0.90). rs895374 genotype did not affect EGFR FISH measurements. EGFR recycling is an interesting mechanism of secondary resistance to cetuximab in mCRC. This is the first report suggesting that germline polymorphisms in the degradation process predict efficacy of cetuximab in patients with mCRC. Genes involved in EGFR turnover may be new targets in the treatment of mCRC.

Hsp90 inhibitors and drug resistance in cancer: the potential benefits of combination therapies of Hsp90 inhibitors and other anti-cancer drugs

Hsp90 is a chaperone protein that interacts with client proteins that are known to be in the cell cycle, signaling and chromatin-remodeling pathways. Hsp90 inhibitors act additively or synergistically with many other drugs in the treatment of both solid tumors and leukemias in murine tumor models and humans. Hsp90 inhibitors potentiate the actions of anti-cancer drugs that target Hsp90 client proteins, including trastuzumab (Herceptin™) which targets Her2/Erb2B, as Hsp90 inhibition elicits the drug effects in cancer cell lines that are otherwise resistant to the drug. A phase II study of the Hsp90 inhibitor 17-AAG and trastuzumab showed that this combination therapy has anticancer activity in patients with HER2-positive metastatic breast cancer progressing on trastuzumab. In this review, we discuss the results of Hsp90 inhibitors in combination with trastuzumab and other cancer drugs. We also discuss recent results from yeast focused on the genetics of drug resistance when Hsp90 is inhibited and the implications that this might have in understanding the effects of genetic variation in treating cancer in humans.