Let-7a microRNA modulates caspase-3-dependent apoptosis in melanoma cells treated with dabrafenib and trametinib combination.

BACKGROUND

Malignant melanoma is an aggressive tumor with high resistance to therapy. The emergence of RAS-driven secondary cancers and BRAF-inhibitor resistance has led to the development of combination therapies targeting both BRAF and MEK.

AIMS: This study explored the mechanisms underlying the synergistic effects of dabrafenib (DAB) and trametinib (TM) in drug-resistant A375 and RPMI 7951 melanoma cells.

METHODS

Cytotoxicity was assessed via MTT assay and combination effects were evaluated via combination index analysis. Apoptosis was analyzed by DNA fragmentation ELISA, while ectopic let-7a miRNA expression and inhibition were performed using lipofection. Gene expression levels were quantified by qRT-PCR, and protein expression was assessed via Western blot.

RESULTS

The combination of 0.7 μM DAB and 5.0 μM TM exhibited synergistic cytotoxicity by inhibiting the pERK1/2 signaling pathway and inducing MITF expression. This resulted in mitochondria-mediated apoptosis, characterized by a decrease in anti-apoptotic Bcl-2 and an increase in pro-apoptotic Bax, caspase-9, and caspase-3 levels. Additionally, Let-7a was identified as a crucial regulator of apoptosis sensitivity by targeting caspase-3, the key executor of apoptosis.

CONCLUSIONS

These findings provide new insights into overcoming melanoma drug resistance through combined BRAF/MEK inhibition.