Mechanisms and Novel Therapeutic Approaches for KRAS-Mediated Resistance to Anti-EGFR Therapy in Colorectal Cancer Cells

Colorectal cancer (CRC) is the third-leading cause of cancer-related deaths in the United States. The treatment of metastatic disease remains a significant clinical challenge, with nearly 90% of patients dying within five years after diagnosis. The successful treatment of CRC is heavily dependent upon the genetic makeup of the tumors. Mutations in the KRAS oncogene, which occur in 35-40% of CRCs, generally exhibit lack of response to anti-epidermal growth factor receptor (EGFR) antibody targeted therapy, a front-line treatment option that improves the efficacy of standard chemotherapy regimens. Unfortunately, despite intensive efforts, direct therapeutic targeting of mutant KRAS has been largely unsuccessful. As a result, it is necessary to further elucidate the underlying mechanisms of sensitivity and resistance to anti-EGFR therapy in CRC cells in order to uncover novel therapeutic strategies. In this study, we found that clinically-utilized anti-EGFR antibodies kill CRC cells by upregulating the pro-apoptotic B cell CLL/lymphoma-2 (Bcl-2) family protein p53-upregulated modulator of apoptosis (PUMA) through the p53 homologue p73. In CRC cells with acquired resistance to anti-EGFR antibodies due to KRAS mutations or genetic amplification, PUMA expression was strongly suppressed when compared to parental cells after antibody treatment. To overcome resistance to anti-EGFR therapy, we first conducted a compound screen which revealed that Aurora kinase inhibition can preferentially kill isogenic CRC cells with KRAS mutations. Aurora kinase inhibition was found to enhance the induction of apoptosis in combination with anti-EGFR antibody treatment in resistant CRC cells with KRAS amplification in cell culture. We also found that the combination treatment completely suppressed tumor growth and promoted apoptosis in resistant cell tumors in nude mice. Collectively, our data indicate that PUMA and other Bcl-2 family proteins play a critical role in mediating the sensitivity and resistance to anti-EGFR antibodies. Furthermore, our results indicate that targeting apoptotic pathways can be utilized to overcome KRAS-mediated resistance to targeted therapies