Abstract 2783: Monitoring of a novel LDH inhibitor and mitochondrial inhibitor efficacy in vivo in a glycolytic pancreatic cancer model using hyperpolarized13C MRI
Authors: Oshima Nobu , Ishida Ryo , Kishimoto Shun , Brender Jeffrey R. , Okada Tomoaki , Obama Kazuataka , Sakai Yoshiharu , Krishna Murali C. , Neckers Leonard M. 
Published: September 2020

Abstract
Increased “glycolysis”, conversion of pyruvate(Pyr) to lactate by Lactate(Lac) Dehydrogenase (LDH), is a feature of many neoplasms. Therefore, LDH inhibition is considered a promising approach toward developing a new therapeutic strategy against glycolityic cancers. In tumor, however, it's still unclear that glycolysis and oxidative phosphorylation(OXPHOS) are functionally integrated in vivo and both are essential to maintain metabolic plasticity and tumor growth. To elucidate these points, a feasible noninvasive-imaging approach that can dynamically evaluate LDH activity in vivo would be highly beneficial. A new imaging thechonology, Hyperpolarized 13C-pyruvate(Pyr) magnetic resonance spectroscopic imaging (HP-MRSI), can permit real-time monitoring of pyruvate flux in vivo through dynamic observation of conversion of 13C-Pyr into its metabolite(s). This study aimed to apply HP-MRSI in support of a therapeutic strategy to explore efficacy of a newly developed and highly potent in vivo-active LDH inhibitor (NCI-006) and the mitochondrial inhibitor (Metformin) in a glycolytic tumor model using MiaPaCa-2(MP2) xenografts in mice. First, HP-MRSI was performed before and after a single NCI-006 IV injection to assess the inhibitor impact on intratumoral metabolic flux in vivo. HP-MRSI confirmed that NCI-006 suppressed intratumor LDH activity. In addition, HP-MRSI could visualize lactate production in the tumor was suppressed 30 minutes after IV administration of NCI-006, as was the 13C-lac to 13C-pyr (13C-L/P) ratio decreased by 83.3 ± 4.4 % compared to vehicle controls. Importantly, the close correlation of these data with the resuts of the ex vivo LDH activity assay, suggests that HP-MRSI can reliably monitor in vivo on target effects of NCI-006. Next, we investigated the impact of metformin on the 13C-L/P ratio in MP2 xenografts using HP-MRSI. HP-MRSI revealed a significant increase in tumor 13C-L/P ratio by 3 h after PO dosing (69.9±6.6% increase) and L/P ratio remained elevated at 5 h in MP2 xenografts. These results are consistent with inhibition of mitochondrial pyruvate oxidation by metformin.Further, to examine the anticipated combinatorial impact on in vivo metabolic flux, HP-MRSI was carried out using MP2 xenografts treated with NCI-006 (50 mg/kg, IV) and/or metformin (50 mg/kg, PO). This treatment resulted in a significantly decreased 13C-L/P ratio. In contrast to LDH inhibitor treatment alone, the 13C Bicarbonate/Pyr ratio did not changesignificantly while the 13C Alanin/Pyr ratio significantly increased. The enhanced transaminase-mediated conversion of Pyr to alanine with combination therapy is consistent with re-wiring of flux away from both Lac (through LDH) and bicarbonate (through the mitochondrion).Finally, we explored whether this combinatorial activity was reflected in greater growth inhibition of MP2 xenografts. We did find that combination treatment caused greater growth reduction in both tumor models compared to either treatment alone.In conclusion, intratumoral inhibition of glycolysis by NCI-006 and of OXPHOS by metformin in vivo was readily visualized by HP-MRSI, confirming the utility of this noninvasive method. This methodology can be of great value in developing new therapeutic strategies using glycolysis and OXPHOS inhibitors to treat cancers.
Citation Format: Nobu Oshima, Ryo Ishida, Shun Kishimoto, Jeffrey R. Brender, Tomoaki Okada, Kazuataka Obama, Yoshiharu Sakai, Murali C. Krishna, Leonard M. Neckers. Monitoring of a novel LDH inhibitor and mitochondrial inhibitor efficacy in vivo in a glycolytic pancreatic cancer model using hyperpolarized13C MRI [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 2783.