RQ18 Peptide Exerts Anti-Melanoma Effects via Apoptosis Induction

Background/Objectives: The rise in cancer cases is a major global public health problem. Treating the disease and maintaining health generate high economic and social costs. In recent years, treatment resistance has become a challenge, reinforcing the need for new anticancer agents. In this context, anticancer peptides (ACPs) stand out for their selective interaction with cancer cell membranes. This study aimed to evaluate the activity of the RQ18 peptide against cancer cells. Methods: The cytotoxicity of RQ18 was determined by the MTT assay in murine melanoma (B16F10-Nex2), human melanoma (Sk-mel-28 and A375), breast cancer (MCF-7), cervical cancer (HeLa), murine macrophage (RAW 264.7), and human fibroblast (FN1). Caspase-3/7 activity was further evaluated in B16F10-Nex2, Sk-mel-28, and A375 melanoma cells to investigate the involvement of apoptotic pathways. In addition, intracellular oxidative stress was assessed using the DCFH-DA probe in these three melanoma cell lines. In B16F10-Nex2 cells, cellular morphological changes were examined by microscopy, while apoptosis-associated events were characterized using the markers MitoTracker Deep Red, and NucBlue, complemented by flow cytometry analyses. In addition, molecular dynamics simulations were employed to investigate its interactions with lipid membranes. Results: The peptide exhibited anticancer activity, with IC50 values of 4.4, 11.58 and 59.99 µM·mL−1, against cells B16F10-Nex2, Sk-mel-28 and A375, respectively. Compared with non-cancerous cells, RQ18 preferentially affected cancer cells, especially B16F10-Nex2. In contrast, the peptide was nontoxic to healthy cells, thus indicating selectivity for cancer cells. Morphological analysis revealed alterations compatible with apoptosis, including cell rounding and chromatin condensation. RQ18 increased caspase-3/7 activity in B16F10-Nex2, Sk-mel-28, and A375 cells and induced intracellular oxidative stress, as indicated by increased DCFH-DA fluorescence. Flow cytometry data confirmed the induction of apoptotic cell death in B16F10-Nex2 cells. Caspase activation, detected by a caspase-3/7 assay in three melanoma cell lines, together with flow cytometry data, supported the involvement of apoptotic cell death. Molecular dynamics simulations suggest that the peptide interacts stably with cancer cell-like membranes and retains an α-helical conformation during membrane association. Conclusions: In summary, the RQ18 peptide demonstrates preferential anticancer activity, particularly against melanoma cells, supporting further investigation of its therapeutic potential.