Abstract 5412: Expression and inhibition of monocarboxylate transporters in canine osteosarcoma

Abstract

Abstract Background: A distinguishing feature of cancer cells is their ability to undergo aerobic glycolysis, even in the presence of oxygen. This process generates lactic acid, which must be removed from the cell in order to maintain proliferation and survival. Monocarboxylate transporters (MCTs) move lactic acid across the plasma membrane, providing a mechanism for tumor cells to meet their bioenergetic needs during glycolysis in a variety of limiting microenvironments. The objective of this work is to determine the biologic effects of modulating cellular metabolism through inhibition of MCT1 and MCT4 in canine osteosarcoma (OS), a well-established spontaneous large animal model of the human disease. Methods: MCT1 and MCT4 expression was assessed in canine OS cell lines using qRT-PCR and western blotting. Immunohistochemistry and qRT-PCR were performed to determine relative MCT1 and MCT4 expression in primary canine OS tissues. The effects of small molecule inhibitors (NGY066 and NGY008) and shRNA approaches targeting MCT1 and MCT4 on proliferation and survival of canine OS were examined using the CyQUANT Cell Proliferation and Caspase-3/7 assays, respectively. The impact of MCT1/4 inhibition on cellular oxygen consumption was evaluated using the Seahorse Cell Mito Stress Test. Lastly, potential synergistic effects of combining metformin and doxorubicin with MCT1/4 inhibition in canine OS cell lines were investigated using the CyQUANT Assay. Results: We found that while both MCT1 and MCT4 are expressed in canine OS lines and tissues, MCT1 is expressed at higher levels relative to MCT4 in the cell lines. Small molecule inhibitors directed against MCT1 and MCT4 did not significantly inhibit cell proliferation or induce apoptosis even in the presence of limiting cell culture conditions. Maximal respiratory capacity was not increased in canine OS cell lines following inhibition of MCT1 and MCT4 function. However, synergistic anti-proliferative activity was observed when OS cells were treated with doxorubicin or metformin in the presence of MCT1 and MCT4 inhibitors. Conclusions: MCT1 and MCT4 are expressed in canine OS, and therefore represent a good model to evaluate the therapeutic potential of manipulating lactic acid transport. Importantly, drug combinations with synergistic activity may be necessary to realize the full potential of MCT1/4 inhibition. Citation Format: Heather L. Gardner, Joelle M. Fenger, Vincent P. Sandanayaka, Cheryl A. London. Expression and inhibition of monocarboxylate transporters in canine osteosarcoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5412. doi:10.1158/1538-7445.AM2017-5412