Peptides as Diagnostic, Therapeutic, and Theranostic Tools: Progress and Future Challenges.

Peptides are emerging as a promising candidate for therapeutic as well as diagnostic applications within the domain of clinical and scientific research. They are recognized for being highly selective, sensitive and efficacious with minimal or no toxicity. Small size, non-immunogenicity, ease of synthesis and huge scope of modification are some of the well-established properties of peptides, which make them an excellent alternative to not only small drug molecules but also to protein-based biopharmaceuticals such as antibodies and enzymes. The attractive pharmacological profile and intrinsic properties of peptides also make them an interesting diagnostic tool for imaging at the molecular and cellular levels. Molecular imaging coupled with targeted therapy using peptides as theranostics is a two-edged sword. Besides, traditional peptide formats, multifunctional newer peptide designs with improved pharmacokinetics and targetability are also being explored presently. In this review, we come up with a comprehensive summary of the latest progress on peptides and their potential applications in therapeutics and diagnosis for infectious and non-infectious diseases. The last part of the review discusses suitable carrier systems for the delivery of peptides along with highlighting the future challenges.