Fig. 6.
Therapeutic opportunity to limit BRAFi resistance. a Heatmap depicting the effects of different AhR ligands on OCA2 and CYP1A1 mRNA in 501Mel cells and pigmentation (48 h). Three groups: exo- and endo-gene ligands (TCDD, B(a)P and FICZ, L-Kynurenine, respectively), BRAFi and AhR antagonists (Resveratrol and CH-223191). b Binding model of the antagonist Resveratrol (RSV) to the PAS B of AHR. RSV is predicted to bind to the α-pocket. Free binding energy is reported in Supplementary Table 1. c RSV prevents CYP1A1 mRNA induction (48 h) by TCDD. 501Mel cells were pre-treated with 5 μM RSV 2 h before 10 nM TCDD. d Gene expression profile of 501Mel cells exposed to vehicle, TCDD (10 nM), RSV (5 μM), or RSV (5 μM) + TCDD (10 nM) (n = 2) for 48 h. Heatmap focused on differentially expressed genes as a function of treatment. e–g 501Mel cells were treated with Vem (1 μM) alone or in combination with RSV (5 μM) for 48 h for pigmentation analyses (e), OCA2 mRNA expression levels (f), and phospho-ERK and ERK total detection by Western blotting (g). h 501Mel cells were pretreated for 2 h with RSV (5 μM) before Vem addition (1 μM). 501Mel cell density was evaluated by methylene blue staining followed by quantification at 620 nm (n = 2). i–k Two pairs of BRAFi-sensitive (S) and -resistant (R) melanoma cells (501Mel and SKMel28) were pre-treated or not for 1 week with RSV (1 μM, every 2 days) before treatment with Vem in order to establish Vem IC50 3 days after BRAFi treatment. Values, calculated with GraphPad PRISM (i), represent IC50 of Vem for control cells (without RSV pre-treatment) or after 1 week of RSV (j). % of BRAFi-persister cell values correspond to the percentage of residual cells following 3 days of Vem (5 μM) treatment in comparison to melanoma cells without RSV treatment (k). l PDX tumor volumes 14 days after daily treatment with Dabrafenib (30 mg/kg) (n = 8) or in combination with RSV (40 mg/kg) (n = 7). m Number of days to reach max tumor volume (endpoint: >800 mm3). Values correspond to the mean ± sem. Two-tailed unpaired t test for the different treatments was performed: **p < 0.01