Integrating Computational and Experimental Approaches for the Discovery of Multifunctional Peptides from the Marine Gastropod Pisania pusio with Antimicrobial and Anticancer Properties

Marine invertebrates are a prime source of biologically active peptides due to their role in humoral immunity. These peptides typically exhibit broad-spectrum functions, including antibacterial, antifungal, anticancer, and immunomodulatory activities. In this report, we describe the identification and biological characterization of five novel bioactive peptides from the marine mollusk <i>Pisania pusio</i>. An extract of <i>P. pusio</i> was analyzed using nanoLC-ESI-MS-MS, and five peptides (PP1-5) were selected via bioinformatic screening as potential antimicrobial and anticancer peptides and subsequently validated experimentally. Among these, PP1, PP2, and PP4 were identified as cryptides derived from the proteolytic cleavage of actin, while PP3 and PP5 are novel peptides with no known protein precursors. All peptides exhibited moderate activity against <i>Pseudomonas aeruginosa</i>, <i>Escherichia coli</i>, <i>Staphylococcus aureus</i>, and <i>Klebsiella pneumoniae</i> with minimum inhibitory concentrations (MICs) predominantly at 100 µM. In contrast, only PP1 and PP5 were active against cancer cells, with PP1 being the most effective against A375 melanoma cells (IC₅₀ = 17.08 µM). This experimental validation confirmed the utility of the integrated in silico/peptidomic pipeline for lead identification. None of these peptides showed significant hemolytic activity or toxicity on fetal lung fibroblasts over 800 μM, demonstrating promising in vitro selectivity. These results highlight the multifunctional nature of <i>P. pusio</i>-derived peptides and their potential as lead compounds for further optimization and development into therapeutic agents against microbial infections and cancer, subject to more comprehensive safety evaluations in relevant models.