The biphosphinic paladacycle complex induces melanoma cell death through lysosomal–mitochondrial axis modulation and impaired autophagy

• BPC11 induces LMP with release of CatB from lysosome to cytosol.
• Bax is translocated to mitochondria, resulting in ↓ ΔΨm and cleaved caspase-3;.
• BPC11 increases LC3II and p62 protein levels, suggesting autophagy impairment.
• Inhibition of autophagy seems to enhance the anti-melanoma effects of BPC11;
• Finally BPC11 induces both (Tm5 and 4C11-) cell death in a similar way.

Recently, palladium complexes have been extensively studied as cyclization of these complexes by cyclometallation reactions increased their stability making them promising antitumor compounds. In this study, we have investigated apoptosis induced by the Biphosphinic Paladacycle Complex (BPC11) and possible cross talk between apoptosis and autophagy in cell line models of metastatic (Tm5) and non-metastatic (4C11-) melanoma. The BPC11-induced cell death in melanoma involved the lysosomal–mitochondrial axis, which is characterized by LMP, CatB activation and increased Bax protein levels following its translocation to mitochondria. Mitochondrial hyperpolarization, followed by membrane potential dissipation and cleavage of caspase-3, also resulted in cell death after 24 h of incubation. We also found that BPC11-mediated LC3II formation and increased p62 protein levels, suggesting blocked autophagy, probably due to LMP. Interestingly, the treatment of Tm5 and 4C11− cells with 3-methyladenine (3-MA), an inhibitor of the initial stage of autophagy, potentiated the effects of BPC11. We conclude that BPC11 is an anti-melanoma agent and that autophagy may be acting as a mechanism of melanoma cells resistance. Also, these data highlight the importance of studies involving autophagy and apoptosis during pre-clinical studies of new drugs with anticancer properties.

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