Morphine Reduces Tumor Growth in Glioma Mouse Xenograft through Modulation of IDH1 Activity and Metabolic Reprogramming

Abstract

Background Isocitrate dehydrogenase 1 (IDH1) is a key extra-mitochondrial enzyme, responsible for converting isocitrate to α-ketoglutarate. In low grade gliomas, IDH1 is often mutated (Arg132His), altering the enzymatic product to the oncometabolite 2-hydroxyglutarate (2HG) and inducing drastic metabolic reprogramming1. 2HG also inhibits DNA demethylases thus causing DNA hypermethylation. Contrary to expectation, IDH1 mutation slows tumor growth and increases susceptibility to antineoplastic agents, improving patient outcome2. We previously found that morphine, a commonly used opiate for pain management in cancer patients, is a mixed partial inhibitor of wild type IDH1. We sought to determine if morphine's effect on IDH1 activity replicates the beneficial changes caused by IDH1 mutation. Methods U87 cells (IDH1 wild type) were treated with clinically relevant concentrations of morphine (0.1-10µM) or equipotent hydromorphone for 7 days. Hydromorphone has no effect on IDH1 activity and served as a negative opiate control. DNA methylation was quantified by ELISA assay. Targeted metabolomics was performed using LC/MS. Mitochondrial function was determined using a Seahorse assay. The in vivo effect of morphine was tested using a mouse xenograft model (intraperitoneal U87 injection), with daily subcutaneous injections of morphine (5mg/kg or 10mg/kg) or hydromorphone (2mg/kg). Tumors at 30 days were measured by weight and histopathology. Cooperative capacity of morphine and the antineoplastic drug temozolomide (TMZ) was determined by measuring in vitro cell viability. Results We observed a dose-dependent increase in both DNA methylation (91%, p<0.05) and 2HG oncometabolite levels (75%, p<0.01) relative to vehicle in morphine samples. Levels of 22 metabolites were uniquely affected by morphine (fig. 1). Pathway enrichment analysis highlighted changes to glutamate metabolism, glycolysis, and the pentose phosphate pathway, all previously implicated in the beneficial IDH1 mutant glioma phenotype. Consistent with metabolic reprogramming, morphine reduced basal and ATP-coupled respiration (15%, p<0.01). Tumors from morphine treated mice were significantly smaller than vehicle (3.7-fold, p<0.01). Histological staining of these tumors revealed increased apoptosis (172%, p<0.01) and reduced proliferation (26%, p<0.01) (fig. 2). Morphine potentiated the effect of TMZ, co-treatment exhibited more cell death after 36 hours (18%, p<0.05) than either drug alone. Conclusion Our research has shown that morphine treatment, through its interaction with IDH1, is able to increase 2HG and DNA methylation. The opiate altered pathways significant in glioma metabolism and energy production. Moreover, it significantly reduced glioma tumor growth and enhanced the chemotherapeutic effect of TMZ, much like the known impact of the IDH1 mutation. We conclude that the interaction between morphine and IDH1 mimics the beneficial IDH1 mutation phenotype. Our research highlights the need for personalized medicine pathways, illustrating that that even the choice of opiate for pain management can potentially alter the course of oncologic disease. Sources 1. Dang, L. et al. Nature (2009) 2. Paldor, I. et al. J. Clin. Neurosci. (2016)