Abstract 808: Combination therapy with a MEK inhibitor plus T-type calcium channel inhibitor is highly effective in patient-derived pancreatic ductal adenocarcinomas
Authors: Newhook Timothy Eric , Lindberg James M. , Adair Sara J. , Blais Edik , Papin Jason , Gray Lloyd , Parsons J. Thomas , Bauer Todd W. 
Published: May 2015

Introduction: Survival for patients with pancreatic ductal adenocarcinoma (PDAC) remains dismal and novel therapeutic strategies are needed. Mutations in the KRAS oncogene are important drivers of PDAC progression; however, monotherapies targeting the RAS pathway have shown only modest efficacy. The RAS pathway is an activator of calcium (Ca2+) signaling, which has been implicated in PDAC progression. We hypothesized that MEK inhibition combined with the T-type calcium channel inhibitor mibefradil would result in enhanced growth inhibition of PDAC tumors.

Methods and Results: Gene expression profiling of patient-derived PDAC tumors (relative to normal pancreas) and tumors chronically treated with the MEK inhibitor trametinib in vivo revealed an upregulation of Ca2+-signaling related genes including members of the calpain pathway and the calmodulin pathway, both implicated in PDAC progression. To assess the in vivo efficacy of combined T-type calcium channel inhibition and MEK inhibition, mice were engrafted orthotopically with patient-derived KRAS-mutant (Tumor 366) and KRAS-wild type (Tumor 738) PDAC tumors and treated with control, the MEK inhibitor trametinib, the T-type calcium channel inhibitor mibefradil, or combination. Combination therapy with trametinib plus mibefradil was highly effective with greater inhibition of PDAC growth than either therapy alone in the KRAS-mutant Tumor 366, however mibefradil did not augment the level of growth inhibition achieved by trametinib alone in the KRAS-wild type Tumor 738. To evaluate combination trametinib plus mibefradil therapy in patient-derived PDAC tumors following chronic treatment with trametinib, mice were engrafted orthotopically with patient-derived PDAC tumors, allowed to grow to 300-500mm3, and treated with trametinib for 4-6 weeks. Following initial treatment, tumors were harvested, re-implanted, and again exposed to therapy over 4-6 weeks. The cycles of treatment and reimplantation were continued until tumor growth was not significantly reduced by trametinib treatment. Therapy with trametinib plus mibefradil nearly completely inhibited growth in KRAS-mutant PDAC tumors (Tumors 608 and 366) previously resistant to chronic trametinib therapy.

Conclusions: Combination therapy with the MEK inhibitor trametinib plus the T-type calcium channel inhibitor mibefradil results in significant growth inhibition of KRAS-mutant patient-derived PDAC tumors. Moreover, this combination therapy results in near complete growth inhibition of PDAC tumors that have acquired resistance to trametinib. The combination therapy of mibefradil plus trametinib should be further evaluated in clinical trials for patients with PDAC.

Citation Format: Timothy Eric Newhook, James M. Lindberg, Sara J. Adair, Edik Blais, Jason Papin, Lloyd Gray, J. Thomas Parsons, Todd W. Bauer. Combination therapy with a MEK inhibitor plus T-type calcium channel inhibitor is highly effective in patient-derived pancreatic ductal adenocarcinomas. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 808. doi:10.1158/1538-7445.AM2014-808