Abstract 2844: The role of oxidative phosphorylation (OXPHOS) in melanoma brain metastasis (MBM) formation and growth
Authors: Fischer Grant M. , Guerrieri Renato A. , Hu Qianghua , Carapeto Fernando C. , Joon Aron Y. , Gopal Vashisht Y. , Knighton Barbara , Deng Wanleng , Haydu Lauren E. , Gershenwald Jeffrey E. , Lazar Alexander J. , Tetzlaff Michael T. , Davies Michael A. 
Published: July 2021

Abstract
Introduction: MBMs are a deadly complication of melanoma. We previously showed that OXPHOS is increased in MBMs, but the roles of OXPHOS in MBM formation and growth are unknown.
Methods: To determine if OXPHOS predicts formation of MBMs, RNA-sequencing (RNAseq) was performed on primary melanomas from patients (pts) diagnosed with MBM (P_MBM; n=19) and from pts diagnosed with metastases (mets) solely to non-CNS sites within 3-18 months of initial diagnosis (P_ECM; n=16), as well as pts who did not develop any mets within 5 years (P_NoMet; n=19). To functionally test the role of OXPHOS in brain and lung met formation and maintenance, brain-tropic YUMM5.2-Br3 cells were treated in vitro with the direct OXPHOS inhibitor IACS-010759 (100 nM) or vehicle control for 12 hours, and then injected into the left ventricle (intracardiac; ICa) in C57BL/6 mice. Mice were randomized to in vivo treatment with vehicle or IACS-010759 (7.5 mg/kg daily) for 14 days. Mice were euthanized and ex vivo bioluminescence imaging (BLI) was performed to evaluate the extent of brain and lung mets. We also evaluated A375P and G361 human melanoma cell lines stably transfected with shRNAs targeting the OXPHOS mediator PGC1α (shPGC1α) or scrambled control (shScr). Cells were injected ICa, intracranially (ICr) or subcutaneously (SQ) in CD-1 nude mice. Lung and brain tissues were harvested for histological analysis of mets once mice became moribund. SQ tumors were measured twice weekly to assess tumor growth. Mice with ICr injection were monitored for survival and euthanized once moribund.
Results: Pathway analysis of the primary tumors from pts demonstrated elevated KEGG OXPHOS gene set expression in P_MBM and P_ECM groups compared to P_NoMet (FDR q-val= 0.048 and &lt;0.001, respectively), suggesting a role for OXPHOS in metastasis. However, there was no significant enrichment of OXPHOS genes in P_MBM vs. P_ECM (FDR q-val=0.516), indicating a lack of specific association with MBM risk. Treatment with IACS-010759 (in vitro and/or in vivo) in the YUMM5.2-Br3 model did not impact the incidence of lung or brain mets. However, in vivo treatment with IACS-010759 significantly decreased MBM (but not lung) tumor burden. PGC1α knockdown (shPGC1α) reduced OXPHOS in A375P and G361 compared to shScr, but less than IACS-010759 treatment. shPGC1α did not impact lung or brain met formation or burden following ICa injection of A375P and G361 cells. shPGC1α also did not inhibit tumor incidence with SQ or ICr injection, and there was no significant difference in SQ tumor growth. However, shPGC1α significantly prolonged survival of mice injected ICr with A375P (p=0.0003) and G361 (p=0.0097).
Conclusions: OXPHOS was associated with increased risk of mets in pts, but not specifically MBMs. In mice, OXPHOS inhibition did not prevent MBM formation, but reduced the growth of established MBMs. Thus, OXPHOS is critical to MBM maintenance.
Citation Format: Grant M. Fischer, Renato A. Guerrieri, Qianghua Hu, Fernando C. Carapeto, Aron Y. Joon, Vashisht Y. Gopal, Barbara Knighton, Wanleng Deng, Lauren E. Haydu, Jeffrey E. Gershenwald, Alexander J. Lazar, Michael T. Tetzlaff, Michael A. Davies. The role of oxidative phosphorylation (OXPHOS) in melanoma brain metastasis (MBM) formation and growth [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2844.