mTOR and MEK1/2 inhibition differentially modulate tumor growth and the immune microenvironment in syngeneic models of oral cavity cancer
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Harrison Cash1, Sujay Shah1, Ellen Moore1, Andria Caruso2, Ravindra Uppaluri3, Carter Van Waes1, Clint Allen1,4
1Tumor Biology Section, Head and Neck Surgery Branch, National Institutes of Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, MD, USA
2Department of Otolaryngology-Head and Neck Surgery, Walter Reed National Military Medical Center, Bethesda, MD, USA
3Department of Otolaryngology-Head and Neck Surgery, Washington University in St. Louis School of Medicine, St. Louis, MO, USA
4Department of Otolaryngology-Head and Neck Surgery, Johns Hopkins School of Medicine, Baltimore, MD, USA
Clint Allen, e-mail: firstname.lastname@example.org
Keywords: head and neck/oral cancers, signal transduction pathways, inflammation and tumor development, animal models of cancer, immunomodulation
Received: July 11, 2015 Accepted: October 09, 2015 Published: October 22, 2015
We investigated the effects of mTOR and MEK1/2 inhibition on tumor growth and the tumor microenvironment in immunogenic and poorly immunogenic models of murine oral cancer. In vitro, rapamycin and PD901 inhibited signaling through expected downstream targets, but only PD901 reduced viability and altered function of MOC cells. Following transplantation of MOC cells into immune-competent mice, effects on both cancer and infiltrating immune cells were characterized following rapamycin and/or PD901 treatment for 21 days. In vivo, both rapamycin and PD901 inhibition reduced primary growth of established MOC tumors on treatment. Following withdrawal of PD901, rapid rebound of tumor growth limited survival, whereas durable tumor control was observed following rapamycin treatment in immunogenic MOC1 tumors despite more robust inhibition of oncogenic signaling by PD901. Characterization of the immune microenvironment revealed diminished infiltration and activation of antigen-specific CD8+ T-cells and other immune cells following PD901 but not rapamycin in immunogenic tumors. Subsequent in vitro T-cell assays validated robust inhibition of T-cell expansion and activation following MEK inhibition compared to mTOR inhibition. CD8 cell depletion abrogated rapamycin-induced primary tumor growth inhibition in MOC1 mice. These data have critical implications in the design of combination targeted and immune therapies in oral cancer.
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