Role of Structural Modifications in Peptidomimetic Compounds as Potential Antimicrobial Agents against <i>Staphylococcus aureus</i> and <i>Streptococcus pyogenes</i>: Balancing Bioavailability, Safety, and Antimicrobial Activity

The emergence of drug-resistant Gram-positive pathogens, particularly<i>Staphylococcus aureus</i>and<i>Streptococcus pyogenes</i>, has driven the need for novel antimicrobial agents. This study explores 21 newly synthesized peptidomimetic analogues of cystatin C <i>N</i>-terminal fragment, designed to enhance bioactivity, solubility, and safety. These compounds were evaluated for antimicrobial potency, cytotoxicity, pro-proliferative effects, and pharmacokinetic properties. Key findings indicate that analogues A-192 and A-164 exhibited the strongest antimicrobial effects against <i>S. aureus</i> and <i>S. pyogenes</i>. Most compounds were inactive against Gram-negative bacteria. Cytotoxicity profiling identified several derivatives with low to moderate toxicity and favorable pro-proliferative effects at specific concentrations. Stability tests confirmed the robustness in aqueous and plasma environments. Computational absorption, distribution, metabolism, excretion, and toxicity (ADMET) modeling revealed low gastrointestinal absorption, but favorable parameters for topical applications. Exploratory analyses (principal component analysis (PCA) and two-way hierarchical cluster analysis (2D-HCA)) linked structural featuressuch as branching, molecular weight, and solubility, with biological activity. These results support the potential of structurally optimized peptidomimetics as targeted, topical therapeutics for Gram-positive infections and provide a rationale for further preclinical development.