Development of a Peptide-Drug Conjugate for Topically Treating the Viral Skin Disease Molluscum Contagiosum

ABSTRACT Molluscum contagiosum (MC) is a highly contagious skin disease caused by the poxvirus, MCV. It remains an Unmet Medical Need due to lack of an approved antiviral drug. MC appears as lesions on the body and face that can spread and last months-years before resolving. Lesions occur most frequently in children (5%) and immune compromised individuals (5-18%). The infection is confined to the epidermal skin layers; it is not systemic. Transmission spreads directly from person-person contact, autoinoculation, or indirect contact with fomites. A principal concern is infection of the eyelids by rubbing skin lesions from distal sites. Infection of the eyelids is especially distressful and can lead to inflammation of the conjunctiva causing "pink eye" and follicular conjunctivitis. Current treatments can be painful, cause scarring, and psychological distress. None of the current treatments that include a range of physical, chemical, and medicinal interventions are uniformly accepted or FDA approved. No MC approved drug has been developed because the virus cannot be grown in tissue culture for testing. We have now made 4 major breakthroughs: First, we identified a protein target (mD4) of MCV that is specific for viral replication. Second, we constructed a surrogate virus (mD4-VV), providing the first cell-based system for screening compounds against the viral target protein (mD4) in infected cells. Third, we synthesized a small molecule (7269) that binds a precise region of the mD4 target protein to cause unfolding and loss of function. However, although 7269 blocks infection of the surrogate virus, we were unable to improve its potency or eliminate its slight toxicity despite an intense medicinal chemistry campaign. Fourth, we overcame this impasse by conjugating a peptide to produce TriValine-7269 that increases antiviral potency 6.3-fold greater than that of unconjugated 7269 with no measurable toxicity. Since the increased potency of TriValine-7269 is not related to an increase in target binding, it is likely due to cell uptake or stability. The Challenge for future clinical drug development is that TriValine-7269 has no related conjugated peptide analogs of equal or greater potency to mitigate risk. To address this requirement, we have synthesized 68 new analogs related to TriValine-7269 (C-Pep1) from which emerged C-Pep2 & C-Pep3 exhibiting even greater antiviral potency. Our GOAL is to optimize the 3 C-Peps to generate a pre-clinical Lead with the other two as Backups to topically treat MC lesions on all areas of the skin including the eyelids. Our AIMS are to: (I) Use medicinal chemistry to generate 100 new analogs of the C-Peps; (II) Screen the chemically modified C-Peps for: validation of mD4-target engagement, antiviral potency, cytotoxicity, binding the mD4 target; (III) Use 3D Organotypic skin cultures and Liposomes for developing and delivering advanced C-Peps to treat all lesions, including eyelids; (IV) Assay in vitro ADME and multiple Off-Target Activities; (V) Initiate pre-clinical development for non-GMP API scale-up and pre- formulation manufacturing and stability.