Abstract 4400: Targeting lactate dehydrogenase-A promotes docetaxel induced cytotoxicity predominantly in castration-resistant prostate cancer cells
Authors: Muramatsu Hiroyuki , Sumitomo Makoto , Morinaga Shingo , Saiki Hiroshi , Kobayashi Ikuo , Kajikawa Keishi , Nishikawa Genya , Kato Yoshiharu , Watanabe Masahito , Kanao Kent , Nakamura Kogenta , Yoshikawa kazuhiro 
Published: July 2017

Abstract
Introduction and objectives: It is well known as Warburg effect that anaerobic glycolytic pathway is activated in various type of advanced cancers including prostate cancer (PC). Lactate dehydrogenase-A (LDH-A) controls the conversion of pyruvate to lactate and plays an important role in glucose metabolism. Since LDH-A pathways have been implicated in chemoresistance in various cancers, we investigated whether inhibition of LDH-A pathway could mediate the sensitivity to docetaxel (DOC) in human PC cells.
Materials and Method: Four PC cell lines (PC3, DU145, LNCaP, LN-CSS ) were used. LN-CSS is one of the LNCaP-derived castration-resistant PC (CRPC) cell lines established in our laboratories. Sodium oxamate (SO) was used as a specific LDH-A inhibitor. The protein expression was detected by western blot analysis using specific antibodies. Cell growth and survival were evaluated by WST-1 assays. Cell cycle progression and apoptotic inducibility were evaluated by flow cytometry using propidium iodide and Annexin V. The cytotoxicity of SO/DOC combination on PC cells was evaluated using the Chou-Talalay combination index (CI) method which offers quantitative definition for additive effect (CI = 1), synergism (CI &lt; 1), and antagonism (CI &gt; 1) in drug combinations.
Result: Western blot analysis showed that LDH-A protein was highly expressed in LN-CSS cells compared with other PC cell lines including the parental LNCaP. WST-1 assays showed that treatment with SO (50 mM) for 72 hours in PC cells resulted in growth inhibition (PC3; ~30%, DU145; ~55%, LNCaP; ~20%,LN-CSS; ~55% ), while SO has little growth inhibitory effects on normal lymphocytes in the concentrations between 1-100 mM. IC50 to DOC in PC cells were showed to be 4 nM, 1 nM, 1nM, and 4.5 nM in PC3, DU145, LNCaP and LN-CSS, respectively, suggesting that both PC3 and LN-CSS were relatively resistant to DOC compared with DU145 and LNCaP. Synergistic cytotoxicity was observed after the combination therapy with DOC and SO in LN-CSS (CI: 0.5) but not in PC3 (CI: 1.9), DU145 (CI: 2.0), or LNCaP (CI: 6.5). Cell cycle analyses revealed that the combination with DOC and SO for 72 hours resulted in the accumulation of cells in G2-M phase followed by sub-G1 accumulation in LN-CSS cells. Annexin V assays showed that 43% apoptosis was induced by the combination therapy in LN-CSS cells, while only 12% by DOC only in LN-CSS cells.
Conclusion: Our results strongly suggest that LDH-A plays an important role in DOC resistance in advanced PC cells and inhibition of LDH-A promotes DOC-sensitivity especially in CRPC cells. Our study may provide valuable information for the future development of targeted therapies in patients with CRPC.
Citation Format: Hiroyuki Muramatsu, Makoto Sumitomo, Shingo Morinaga, Hiroshi Saiki, Ikuo Kobayashi, Keishi Kajikawa, Genya Nishikawa, Yoshiharu Kato, Masahito Watanabe, Kent Kanao, Kogenta Nakamura, kazuhiro Yoshikawa. Targeting lactate dehydrogenase-A promotes docetaxel induced cytotoxicity predominantly in castration-resistant prostate cancer cells [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 4400. doi:10.1158/1538-7445.AM2017-4400