RESUMEN
Anaplastic lymphoma kinase positive anaplastic large cell lymphomas (ALK+ ALCL) are an aggressive pediatric disease. The therapeutic options comprise chemotherapy, which is efficient in approximately 70% of patients, and targeted therapies, such as crizotinib (an ALK tyrosine kinase inhibitor (TKI)), used in refractory/relapsed cases. Research efforts have also converged toward the development of combined therapies to improve treatment. In this context, we studied whether autophagy could be modulated to improve crizotinib therapy. Autophagy is a vesicular recycling pathway, known to be associated with either cell survival or cell death depending on the cancer and therapy. We previously demonstrated that crizotinib induced cytoprotective autophagy in ALK+ lymphoma cells and that its further intensification was associated with cell death. In line with these results, we show here that combined ALK and Rapidly Accelerated Fibrosarcoma 1 (RAF1) inhibition, using pharmacological (vemurafenib) or molecular (small interfering RNA targeting RAF1 (siRAF1) or microRNA-7-5p (miR-7-5p) mimics) strategies, also triggered autophagy and potentiated the toxicity of TKI. Mechanistically, we found that this combined therapy resulted in the decrease of the inhibitory phosphorylation on Unc-51-like kinase-1 (ULK1) (a key protein in autophagy initiation), which may account for the enforced autophagy and cytokilling effect. Altogether, our results support the development of ALK and RAF1 combined inhibition as a new therapeutic approach in ALK+ ALCL.
RESUMEN
Anaplastic lymphoma kinase (ALK)-positive anaplastic large cell lymphomas are tumors that carry translocations involving the ALK gene at the 2p23 locus, leading to the expression of ALK tyrosine kinase fusion oncoproteins. Amongst hematologic malignancies, these lymphomas are particular in that they express very low levels of B-cell lymphoma 2 (BCL2), a recognized inhibitor of apoptosis and autophagy, two processes that share complex interconnections. We have previously shown that treatment of ALK-positive anaplastic large cell lymphoma cells with the ALK tyrosine kinase inhibitor crizotinib induces autophagy as a pro-survival response. Here, we observed that crizotinib-mediated inactivation of ALK caused an increase in BCL2 levels that restrained the cytotoxic effects of the drug. BCL2 downregulation in combination with crizotinib treatment potentiated loss of cell viability through both an increase in autophagic flux and cell death, including apoptosis. More importantly, our data revealed that the blockade of autophagic flux completely reversed impaired cell viability, which demonstrates that excessive autophagy is associated with cell death. We propose that the downregulation of BCL2 protein, which plays a central role in the autophagic and apoptotic machinery, combined with crizotinib treatment may represent a promising therapeutic alternative to current ALK-positive anaplastic large cell lymphoma treatments.
