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 2D cultures of 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 mesenchymal-to-epithelial transition (MET). By the second week, MAPK–ERK signalling was restored, with activation of the FOS–TEAD/Hippo axis involved in the “female pregnancy” functional module coinciding with replication stress, G2M checkpoint delay, and mitotic slippage. By days 12–15, ~3-4% of cells exhibited hyperploidy with 4–8 subnuclei, some arranged as rosettes and encased by a Zona pellucida-positive structure resembling oocytes, zygotes, or blastula, occasionally releasing sub-cells or stalling in a diapause. These parasexual processes eventually ceased, and escaping cells resumed mitotic proliferation with their original mito-meiotic profile and epithelial to mesenchymal transition (EMT). When the experiment was repeated in non-adherent 3D spheroids, multinucleated giant polyploid cells, resistant to VEM, increased threefold at the leading edge. Their modified cytoskeleton features suggested metastatic propensity. Transcriptome and phylogenetic analyses of differentially expressed genes in the 2D VEM cultures revealed a paradoxical ontogeny reverse: from developmental “differentiation” induced by senescence, back to the “blastula”- like state, including meiosis and oocyte maturation. This reverse appears to be caused by replication stress, FOS-HIPPO activating the “female pregnancy”-like invasive program of Euteleostomi.This new evidence of paradoxical circular causation of senescence-induced differentiation, PGCC blastulation and recurrent proliferation helps explain the inevitability of melanoma relapse post-treatment with Vemurafenib.