Purpose: Pancreatic neuroendocrine tumors (PNETs), although rare, often metastasize, such that surgery, the only potentially curative therapy, is not possible. There is no effective systemic therapy for patients with advanced PNETs. Therefore, new strategies are needed. Toward that end, we investigated the potential benefit of dual therapeutic targeting of the epidermal growth factor receptor (EGFR) and mammalian target of rapamycin (mTOR) kinases, using a preclinical mouse model of PNET.
Materials and methods: Rapamycin and erlotinib, inhibitors of mTOR and EGFR, respectively, were used to treat RIP-Tag2 transgenic mice bearing advanced multifocal PNET. Tumor growth and survival were monitored, and tumors were surveyed for potential biomarkers of response to the therapeutics.
Results: Rapamycin monotherapy was notably efficacious, prolonging survival concomitant with tumor stasis (stable disease). However, the tumors developed resistance, as evidenced by eventual relapse to progressive tumor growth. Erlotinib monotherapy slowed tumor growth and elicited a marginal survival benefit. In combination, there was an unprecedented survival benefit in the face of this aggressive multifocal cancer and, in contrast to either monotherapy, the development of adaptive resistance was not apparent. Additionally, the antiapoptotic protein survivin was implicated as a biomarker of sensitivity and beneficial responses to the dual targeted therapy.
Conclusion: Preclinical trials in a mouse model of endogenous PNET suggest that combined targeting of the mTOR and EGFR signaling pathways could have potential clinical benefit in treating PNET. These results have encouraged development of an ongoing phase II clinical trial aimed to evaluate the efficacy of this treatment regimen in human neuroendocrine tumors.