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

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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 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. 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. The reason why no approved drug against MCV has been developed is because the virus cannot be grown in tissue culture for testing. We have now made four major breakthroughs: First, we have identified a protein target (mD4) of MCV that is essential for replication. The mD4 protein functions as a processivity factor (PF) that tethers the viral Polymerase (Pol) to the template to enable continuous synthesis of DNA. Second, we have constructed a mD4- surrogate virus (mD4-VV), providing the first cell-based system for screening compounds against an essential MCV target protein (mD4) in infected cells. Third, we have synthesized a small molecule (7269) that that binds a precise region of the mD4 target protein, causing it to unfold and no longer function. While 7269 can block infection by 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 binds the mD4 with a potency that is 6.3-fold greater than that of unconjugated 7269 and has no measurable toxicity. Since TriValine-7269 does not alter direct binding to the mD4 target, its increased potency is due to cellular penetration and/or stability. The challenge that impedes further drug development is that TriValine-7269 has no related analog of equal or greater potency to mitigate risk in the next stages of drug development. The GOAL is to identify analogs of TriValine-7269 of equal or greater potency as essential backups. AIM 1 will utilize medicinal chemistry to synthesize analogs of TriValine-7269. The focus will be to vary both the Peptide and Linker portions of TriValine-7269. The 7269 portion will not be modified since it has already been optimized. We will produce 30-40 analogs. AIM 2 will evaluate new analogs for antiviral potency against the surrogate virus; cytotoxicity; blocking in vitro processive DNA synthesis; binding to the mD4 target. AIM 3 will evaluate structurally distinct analogs for in vitro ADME activities that are relevant for topical application including metabolic stability, solubility and cell permeability. Conjugates with criteria that exceed or match TriValine-7269 will provide the minimum number of analogs for future drug development.