Inhibition of autophagosomal degradation in melanoma cells promotes the release of mediators that increase global resistance to vemurafenib.

FALCON C; ZURITA A; CUELLO ORLANDI SF; SANGIACOMO M; RUIZ ML; IBAÑEZ I; MONS J; PEREZ C; ALVAREZ SE

Congreso; SAIC 2022; 2022

Vemurafenib (Vem) is used in the treatment of melanomas that have the BRAFV600E mutation but resistance to this drug is rapidly induced. Autophagy has been implicated in resistance to Vem.Objective: to study the influence of autophagosomal degradation inhibition on resistance to Vem in human melanoma cells.Results: Lu1205 cells cultured in hypoxia (Hx) have higher resistance to Vem than in normoxia (Nx). We show by western blot that Hx produces accumulation of LC3 and p62, indicating decreased autophagic flux. Although autophagy inhibition with NH4Cl or Chloroquine (Cq) in Nx and Hx increased sensitivity to Vem (MTT viability and apoptosis), only conditioned media (CM) from cultures in Hx transferred Vem resistance to sensitive cells and this ability was not significantly modified by autophagy inhibitors. Surprisingly, CM from Lu1205 cultured in Nx with NH4Cl or Cq increased the resistance to Vem of sensitive cells, similarly to CM-Hx. In addition, we developed a novel cell line derived from Lu1205 cells expressing the M2 protein of the influenza virus A/PR8 strain, which inhibits the autophagosome-lysosome fusion. These cells (Lu1205-M2iv) showed increased resistance to Vem both in Nx and Hx and augmented migratory capacity with respect to the parental line. In addition, CM obtained from Lu1205-M2iv cells enhanced chemoattraction of PMA-differentiated THP-1 cells and transferred resistance to sensitive cells. Finally, Lu1205 cells with acquired resistance to Vem (Lu1205R) showed strongly decreased autophagic flux and increased expression of mRNA of RAB27a and RAB27b involved in excretory pathways. These cells subtly decreased their viability when cultured with Vem in the presence of the autophagy inhibitors and showed an increased ability to induce Vem resistance in sensitive cells.Conclusion: Therapy with inhibitors of autophagosomal degradation in melanoma cells increases initial sensitivity to Vem but could promote the general tumor resistance to treatment.