The Pregnane X Receptor (PXR) contributes to phenotypic plasticity and modulates the sensitivity to targeted therapies in melanoma

Abstract

The challenge in treating advanced metastatic melanoma lies in the development of therapeutic resistance and the risk of recurrence. Understanding the mechanisms underlying tumor adaptation to treatment is therefore crucial, as they can directly influence therapeutic efficacy. Tolerance to targeted therapies may be influenced by drug transport and metabolism within tumors, processes regulated by numerous genes under the transcriptional control of the nuclear receptor PXR (Pregnane X Receptor, NR1I2). We revealed, for the first time, significant and heterogeneous expression of PXR in human melanoma samples. We previously showed that PXR can be activated by BRAF inhibitors (BRAFi), but not by MEK inhibitors (MEKi), which are currently used in combination for the treatment of BRAF-V600E-mutated melanoma. Here, we investigated whether PXR expression influences melanoma cell sensitivity to MAPK pathway inhibitors. Using BRAF-mutated human melanoma cell lines, we showed that stable PXR expression sensitizes cells to combined BRAFi/MEKi treatment. Transcriptomic analysis further revealed that PXR expression is associated with the upregulation of several phenotypic markers, with MITF identified as a major regulator in untreated PXR-overexpressing cells. These findings suggest that PXR promotes a shift toward a melanocytic phenotype, which is associated with increased sensitivity to BRAFi/MEKi treatment. Characterization of the PXR-associated transcriptional signature in melanoma may therefore have translational value for identifying patients more likely to benefit from targeted therapies and support the development of PXR as a predictive biomarker of therapeutic response.