Beyond Binary: Mapping the Evolution of Melanoma Across a Discrete Gradient of Acquired Chemoresistance

Models of cancers with acquired MultiDrug Resistance (MDR) commonly employ a binary state that compares MDR to treatment naïve cohorts. While convenient, this paradigm also oversimplifies the dynamic process of acquiring MDR as cellular processes (and corresponding therapies targeting them) could perform differently at each intermediate stage of resistance. However, comparisons of discrete levels of chemoresistance, particularly with regards to carbohydrate transport or transiently expressed genes, remain limited. Here we characterize a B16 melanoma cell panel comprising a gradient of doxorubicin resistance (1 nM to 1 µM). Across the MDR gradient, we observed minimal changes in class I glucose transporter (GLUT) expression and reduced carbohydrate influx, despite increases in P-glycoprotein (P-gp) efflux. This suggests enhanced P-gp efflux is not compensated by GLUT-mediated influx, but rather, attenuated carbohydrate metabolism. Indeed, RNA-seq revealed decreases in glycolytic enzymes alongside additional interferon-stimulated genes (including Isg15 and Bst2 ) with transient differential expression only at intermediate levels of MDR. Overall, this study provides proof-of-principle that selection of a particular level of MDR is non-trivial, particularly for studies involving the transiently expressed genes or carbohydrate processing, and might explain why there remains significant debate over which in-vitro level of MDR is optimally prognostic of in-vivo performance.