198. Lactate shuttle: a key component in osteosarcoma

Abstract

<h3>BACKGROUND CONTEXT</h3> Osteosarcoma (OS) is the most common primary malignant bone tumor in children and adolescents and prognosis remains poor, particularly when in the spine. However, the unique metabolism of OS may allow for novel, targeted therapies. Increased glucose uptake and upregulated glycolysis in aerobic conditions are hallmarks of cancer (the"Warburg effect"). Lactate, once considered a mere byproduct of this increased glycolysis, has now proven to be a critical metabolite in most tumors, including OS. Recent work has highlighted a role for lactate transport in osteosarcoma, although whether OS cells produce or consume lactate is currently debated. Here we present data exploring the role of lactate transport in osteosarcoma by examining up and down regulation of the major lactate transporters, the monocarboxylate transporters (MCTs). <h3>PURPOSE</h3> Due to the poor prognosis of spinal osteosarcoma, identifying novel targets for cancer therapy is crucial. Here, we studied the importance of lactate as a metabolite for OS progression. Drugs specific to non-invasive biomarkers of metabolism such as lactate transporters in OS cells could help design future clinical trials. <h3>METHODS</h3> Gene expression profiles of various OS cell lines (SaOs, MNNG, HOS) in varying metabolic conditions (varying lactate and glucose concentrations) were analyzed. qPCR and immunoblotting were used to analyze expression patterns of overall MCT1 and MCT4, and surface expression of MCTs were determined using immunofluorescence microscopy. For each trial, cell proliferation was analyzed via CyQuant direct cell proliferation kit (Fischer Sci). Experiments were performed in triplicate. Conditions included combinations of low, normal, and high glucose (1, 6, and 20 mM respectively) with low, and high lactate (0.1, 1, and 5 mM respectively). All data are presented as the means ± SD where appropriate. We performed statistical analysis using Student'st-test; p less than 0.05 was considered statistically significant. <h3>RESULTS</h3> MCT1 and MCT4 were expressed in OS cell lines. MCT4 expression was upregulated in high glucose (20mM) conditions, but reduced drastically in the absence of glucose. On the other hand, MCT1 expression was not perturbed even in the absence of glucose. Conversely, MCT1, which is a bidirectional transporter of lactate, is expressed irrespective of presence of glucose. Finally, use of commercial MCT inhibitors namely AZD396, BAY8002, BAY87-2243 and Syrosingopine resulted in decreased cell survival, with simultaneous inhibition of MCT1 and MCT4 leading to the most profound effects. <h3>CONCLUSIONS</h3> The main lactate exporter, MCT4, was upregulated in high glucose conditions, indicating an increase in glycolysis to lactate with increased lactate export. Further, cells were not viable when cultured with lactate alone, unlike numerous other nontumorous tissues that uptake and use lactate as a fuel. OS cells appear to preferentially produce and export lactate, particularly if glucose is abundant, regardless of the local oxygen tension (the "Warburg effect"). Together these data suggest that lactate exportation via MCT4s is critical to osteosarcomagenesis and may serve as a unique target for spinal osteosarcomas. <h3>FDA DEVICE/DRUG STATUS</h3> AZD 3695 (Investigational/Not Approved), Syrosingopine (Not approved for this indication), BAY-8002 (Not approved for this indication)