Resistance of BRAFV600E-mutant melanoma to Vemurafenib: a senescence-induced swing from differentiation to blastulation followed by proliferation.

Resistance to Vemurafenib (VEM), a targeted BRAFV600E inhibitor, was examined in the metastatic paratetraploid (XX, abnormal Y chromosome) melanoma cell line, SkMel28. During the first week of treatment, pERK suppression coincided with transcriptomic and phenotypic changes related to senescence, autophagy/mitophagy, neuro-melanogenesis, and cell co-alignment. By the second week, MAPK-ERK signalling was restored, coinciding with surmounting the G1/S checkpoint, G2M checkpoint delay, mitotic slippage (MS), and downregulation of senescence and melanogenesis. The dynamics of melanogenesis and MS were highly correlated. By days 12-15, ∼8% of cells with melanin remnants exhibited hyperploidy and multinucleation, some arranged as rosettes, encased by a Zona pellucida-positive structure reminiscent of oocytes, zygotes, or blastulae, occasionally yielding cellularised sub-cells or stalling in diapause. These parasexual processes eventually ceased; cells resumed proliferative clonogenic growth and their initial mito-meiotic, mesenchymal profile. Transcriptomic analysis confirmed the reversal of their cell fate direction: from senescence-induced neuro-melanogenesis to its suppression and activation of female meiosis-like and mitosis states. The transition point of this cell-fate reversal coincided with S-phase resumption, highlighted by replication delay and activation of the FOS-TEAD/Hippo axis of the "female pregnancy" (stress-response, embryonal placentation, vascularisation, stemness, anti-apoptosis) gene ontology module. We conclude that resistance to VEM in SkMel28 cells encompasses the transition between three possible cell fates: (1) senescence/differentiation, (2) reprogramming/blastulation, and (3) recovery of the proliferative mito-meiotic profile. The coexpression of senescence, reprogramming and gametogenetic genes in a dataset of late-stage melanoma patient samples supports these results.