Biphenylsulfonacetic Acid Inhibitors of the Human Papillomavirus Type 6 E1 Helicase Inhibit ATP Hydrolysis by an Allosteric Mechanism Involving Tyrosine 486

Abstract

Human papillomaviruses (HPVs) are the causative agents of benign and malignant lesions of the epithelium. Despite their high prevalence, there is currently no antiviral drug for the treatment of HPV-induced lesions. The ATPase and helicase activities of the highly conserved E1 protein of HPV are essential for viral DNA replication and pathogenesis and hence are considered valid antiviral targets. We recently described novel biphenylsulfonacetic acid inhibitors of the ATPase activity of E1 from HPV type 6 (HPV6). Based on kinetics and mutagenesis studies, we now report that these compounds act by an allosteric mechanism. They are hyperbolic competitive inhibitors of the ATPase activity of HPV6 E1 and also inhibit its helicase activity. Compounds in this series can also inhibit the ATPase activity of the closely related enzyme from HPV11; however, the most potent inhibitors of HPV6 E1 are significantly less active against the type 11 protein. We identified a single critical residue in HPV6 E1, Tyr-486, substituted by a cysteine in HPV11, which is primarily responsible for this difference in inhibitor potency. Interestingly, HPV18 E1, which also has a tyrosine at this position, could be inhibited by biphenylsulfonacetic acid derivatives, thereby raising the possibility that this class of inhibitors could be optimized as antiviral agents against multiple HPV types. These studies implicate Tyr-486 as a key residue for inhibitor binding and define an allosteric pocket on HPV E1 that can be exploited for future drug discovery efforts.Papillomaviruses infect the squamous and mucosal epithelia of many different mammals, including humans, often resulting in the development of benign and sometimes malignant lesions (reviewed in references 16, 31, and 42). There are over 100 types of human papillomavirus (HPV), each exhibiting a particular tropism for specific tissue types (8). For example, HPV1 causes plantar warts, HPV6 and -11 cause anogenital warts (condyloma acuminata), and infection with HPV16 and -18, among others, can lead to cervical cancer (2, 42). Among the HPV types that infect the anogenital region, those that are associated with cancer are collectively referred to as "highrisk" types, whereas those that cause only benign warts are known as "low-risk" types (42). Despite the medical burden associated with treating and screening for HPV infections, an HPV-specific antiviral drug is still lacking, and there are only a few reports of HPV-specific inhibitors which could serve as potential leads for drug discovery. To our knowledge, the E1 ATPase inhibitors described in this report and our previously published series of E2 inhibitors (37, 39) are the only potent and selective small molecules targeting HPV DNA replication proteins ever to be reported.All papillomaviruses have a small circular double-stranded DNA genome which encodes for only eight well-characterized proteins (for a recent review, see reference 21). The most highly conserved protein, and the only one with enzymatic activity, is the E1 helicase (review...

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