Abstract 4101: Off-target lapatinib activity up-regulates TRAIL death receptors in colon cancer cells
Authors: Dolloff Nathan G. , Mayes Patrick , Hart Lori , Dicker David , Humphreys Robin , El-Deiry Wafik 
Published: July 2012

Abstract
Lapatinib is a dual HER2/EGFR inhibitor that is FDA-approved for the treatment of HER2+ metastatic breast cancer when combined with capecitabine. Colon cancer cells express high levels of EGFR and to a lesser extent, HER2, and therefore, we set out to identify effective therapeutic combinations involving lapatinib in colon cancer. We screened for therapeutic partners of lapatinib using SW620 cells, a cell line that expresses mutant p53 and is resistant to various chemotherapies and apoptosis-inducing agents. We found that high concentrations of lapatinib (10 microM) failed to induce cell death as a single agent or in combination with chemotherapy. However, lapatinib significantly enhanced the pro-apoptotic effects of TRAIL, a finding that we confirmed in a panel of colon cancer cell lines. Lapatinib also sensitized colon cancer cells to the agonistic TRAIL receptor antibodies mapatumumab and lexatumumab. We then tested this novel combination in vivo, and found that tumors from mice treated with lapatinib/TRAIL combinations exhibited increased staining for cleaved caspase-8, a biomarker of death receptor activity, compared to lapatinib or TRAIL treatment alone. Furthermore, the combination therapy suppressed tumor growth, whereas single agent treatments had little effect. Mechanistically, we found that lapatinib up-regulates both pro-apoptotic TRAIL death receptors, DR4 and DR5. Lapatinib increased DR5 mRNA, but had no effects on DR5 protein stability, suggesting that lapatinib up-regulates death receptors through a pre-translational or translational mechanism. Interestingly, other EGFR and HER2 inhibitors, individually or in combination, failed to increase death receptor expression or TRAIL sensitivity, leading us to hypothesize that this activity of lapatinib was due to an off-target effect. In support of this idea, lapatinib induced death receptor up-regulation in SW620 cells, which lack EGFR expression and have undetectable levels of HER2 signaling. In addition, lower lapatinib concentrations, which completely inhibited EGFR and HER2, were failed to induce death receptor expression and increase TRAIL sensitivity, further demonstrating the off-target nature of this effect. High concentrations of lapatinib increased phosphorylation of c-Jun, extracellular signal related kinase (ERK) and c-Jun N-terminal kinase (JNK). RNAi-mediated knockdown experiments proved that c-Jun and JNK, but not ERK, were required for lapatinib-induced DR5 up-regulation. We conclude that high concentrations of lapatinib, through an EGFR/HER2-indpendent mechanism, up-regulate TRAIL death receptors and increase TRAIL sensitivity by a mechanism involving the JNK/c-Jun signaling pathway. From a clinical perspective, therapeutic benefit may be gained from this off-target activity by using high doses of lapatinib and introducing TRAIL receptor-activating agents into the treatment regimen.
Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 4101. doi:10.1158/1538-7445.AM2011-4101