Insulin Receptor/Insulin-like Growth Factor1Receptor Pathway Confers Resistance Of Lapatinib In HER-2Positive Gastric Cancer Cell Lines

Background:HER-2amplification is found in approximately20%of gastric cancers and is associated with poor prognosis. Trastuzumab was approved in advanced gastric cancer patients, confirming the effectiveness of targeting HER-2in gastric cancer. Lapatinib, a dual HER-2and epidermal growth factor receptor tyrosine kinase inhibitor, has shown promising results in early clinical trials in treating HER-2positive cancer patients, and two phase Ⅲ trial are underway. However, there are evidence that activation of alternative receptor tyrosine kinases can confer resistance to HER-2targeted therapy. Here, we investigated whether activated insulin receptor (IR) and insulin-like growth factor1receptor (IGF1R) can confer resistance to lapatinib inhibition in HER-2positive gastric cancer cells.Methods:N87and SNU216, expressing high levels of HER-2, showed high sensitivity to lapatinib.OSI906is an inhibitor of IR/IGF1R. IR knockdown by IR siRNA was used to confirm that IR knockdown could cause enhanced killing of lapatinib. Clonal assay was adopted to assess whether insulin could confer resistance to lapatinib. Synergy test of laptinib and OSI906was done to evaluate synergism of these two drugs. Western blot was carried out to clarify the mechanism of insulin induced resistance to lapatinib.Results:Synergy was observed when down-regulating IR expression with siRNA in both cell lines. Synergy was also observed when co-treated with lapatinib and OSI906in both cell lines. Clonal assay showed that insulin could rescue the inhibition of lapatinib in both cell lines. Western blot analysis indicated insulin activated p-IR/IGFIR and p-AKT, leading to the rescue of lapatinib-induced growth inhibition, and the rescue effect of insulin could be abrogated by inhibiting IR/IGF1R with OSI906. Conclusions:IR/IGF1R-conferred resistance to lapatinib is a novel mechanism of resistance to HER-2-targeted agents, which is achieved by re-activating AKT inhibited by lapatinib. Inhibiting IR/IGF1R when treating with HER-2targeted agents may abrogate drug resistance caused by activation of IR/IGF1R.