Dissection of the Structural Features of a Fungicidal Antibody-Derived Peptide

Therapeutic Effect of an Antibody-Derived Peptide in a Galleria mellonella Model of Systemic Candidiasis

The synthetic peptide T11F (TCRVDHRGLTF), with sequence identical to a fragment of the constant region of human IgM, and most of its alanine-substituted derivatives proved to possess a significant candidacidal activity in vitro. In this study, the therapeutic efficacy of T11F, D5A, the derivative most active in vitro, and F11A, characterized by a different conformation, was investigated in Galleria mellonella larvae infected with Candida albicans. A single injection of F11A and D5A derivatives, in contrast with T11F, led to a significant increase in survival of larvae injected with a lethal inoculum of C. albicans cells, in comparison with infected animals treated with saline. Peptide modulation of host immunity upon C. albicans infection was determined by hemocyte analysis and larval histology, highlighting a different immune stimulation by the studied peptides. F11A, particularly, was the most active in eliciting nodule formation, melanization and fat body activation, leading to a better control of yeast infection. Overall, the obtained data suggest a double role for F11A, able to simultaneously target the fungus and the host immune system, resulting in a more efficient pathogen clearance.

In Silico Predicted Antifungal Peptides: In Vitro and In Vivo Anti-Candida Activity

It has been previously demonstrated that synthetic antibody-derived peptides could exert a significant activity in vitro, ex vivo, and/or in vivo against microorganisms and viruses, as well as immunomodulatory effects through the activation of immune cells. Based on the sequence of previously described antibody-derived peptides with recognized antifungal activity, an in silico analysis was conducted to identify novel antifungal candidates. The present study analyzed the candidacidal and structural properties of in silico designed peptides (ISDPs) derived by amino acid substitutions of the parent peptide KKVTMTCSAS. ISDPs proved to be more active in vitro than the parent peptide and all proved to be therapeutic in Galleria mellonella candidal infection, without showing toxic effects on mammalian cells. ISDPs were studied by circular dichroism spectroscopy, demonstrating different structural organization. These results allowed to validate a consensus sequence for the parent peptide KKVTMTCSAS that may be useful in the development of novel antimicrobial molecules.

Anti-Infective Antibody-Derived Peptides Active against Endogenous and Exogenous Fungi

Mycoses still represent relevant opportunistic infections worldwide, although overshadowed in recent years by other severe and more widespread infections. Moreover, deep-seated mycoses are often accompanied by unacceptably high mortality rates. Etiologic agents include endogenous components of the mycobiota, Candida and Malassezia species above all, and exogenous species, both yeasts and filamentous fungi. Old and new fungal pathogens are increasingly characterized by resistance to the existing antifungal agents, making imperative the search for effective and safe new therapeutics. Among the candidate molecules proposed in recent decades, synthetic peptides derived from the complementarity determining and constant regions of diverse antibodies (Abs), as well as the translated products of Ab-encoding genes, have proved of considerable interest. Their anti-infective activities, regardless of the specificity and isotype of the originating Ab, will be briefly presented and discussed in the light of their different mechanisms of action. Intriguing suggestions on the possible function of Abs after their half-life will be presented, following the recent detection, in human serum, of an antimicrobial Ab-derived peptide. Overall, Abs could represent a source of biologically active, highly flexible peptides, devoid of detectable toxicity, which can be easily synthesized and manipulated to be used, alone or in association with already available drugs, for new anti-infective strategies.

Design and Synthesis of A PD-1 Binding Peptide and Evaluation of Its Anti-Tumor Activity

Immune-checkpoint blockades, suchas PD-1 monoclonal antibodies, have shown new promising avenues to treat cancers. Failure responsesof many cancer patients to these agents have led to a massive need for alternative strategies to optimize tumor immunotherapy. Currently, new therapeutic developments involve peptide blocking strategies, as they have high stability and low immunogenicity. Here, we have designed and synthesized a new peptide FITC-YT-16 to target PD-1. We have studied FITC-YT-16 by various experiments, including Molecular Operating Environment MOE modeling, purification testing by HPLC and LC mass, peptide/PD-1 conjugation and affinity by microscale thermophoresis (MST), and T cell immune-fluorescence imaging by fluorescence microscopy and flow cytometry. The peptide was tested for its ability to enhanceT cell activity against tumor cell lines, including TE-13, A549, and MDA-MB-231. Lastly, we assessed T cell cytotoxicity under peptide treatment. YT-16⁻PD-1 interaction showed a high binding affinity as a low energy complex that was confirmed by MOE. Furthermore, the peptide purity and molecular weights were 90.96% and 2344.66, respectively. MST revealed that FITC-YT-16 interacted with PD-1 at a Kd value of 17.8 ± 2.6 nM. T cell imaging and flow cytometry revealed high affinity of FITC-YT-16 to PD-1. Interestingly, FITC-YT-16 efficiently blocked PD-1 signaling pathways and promoted T cell inflammatory responses by elevating IL-2 and INF-γ levels. Moreover, FITC-YT-16 has the ability to activate T cell cytotoxicity. Therefore, FITC-YT-16 significantly enhanced T cell anti-tumor activity by blocking PD-1⁻PD-L1 interactions.