Date Published: February 9, 2017
Publisher: Public Library of Science
Author(s): Mart Toots, Mart Ustav, Andres Männik, Karl Mumm, Kaido Tämm, Tarmo Tamm, Ene Ustav, Mart Ustav, Paul Francis Lambert.
Human papillomaviruses (HPVs) are oncogenic viruses that cause numerous different cancers as well as benign lesions in the epithelia. To date, there is no effective cure for an ongoing HPV infection. Here, we describe the generation process of a platform for the development of anti-HPV drugs. This system consists of engineered full-length HPV genomes that express reporter genes for evaluation of the viral copy number in all three HPV replication stages. We demonstrate the usefulness of this system by conducting high-throughput screens to identify novel high-risk HPV-specific inhibitors. At least five of the inhibitors block the function of Tdp1 and PARP1, which have been identified as essential cellular proteins for HPV replication and promising candidates for the development of antivirals against HPV and possibly against HPV-related cancers.
Human papillomaviruses (HPVs) are small, double-stranded DNA viruses that infect the epithelium of the skin and mucosa. To date, at least 202 HPVs have been characterized, but studies suggest that the true number is considerably higher[1,2]. HPVs induce benign lesions in the mucosal and cutaneous epithelia, and most of the infections are cleared by the immune system within a year after infection. However, a small fraction of infections become persistent and may lead to the transformation of cells and the development of invasive cancers. The vast majority of HPV-associated cancer cases are related to oncogenic mucosal high-risk HPVs from genus alpha (types 16, 18, 31, 33, 35, 39, 45, 51, 52, 56, 58, 59, and 68); types 16, 18, 31, 33 and 45 are estimated to cause more than 99% of cervical cancers [3–5]. Cervical cancer was the seventh most common cancer and the fourth most common among women in the year 2012. There are an estimated 528,000 new cases per year, with 80% in developing countries, leading to 266,000 deaths. In the United States alone, 6 million new HPV cases are diagnosed every year. In addition to alpha PVs, infection with cutaneous beta PVs is also prevalent in the population. These viruses have not been as thoroughly studied as alpha PVs, but an increasing number of studies suggest their association with skin cancer[8,9]. In addition to serious health problems, HPV-related infections and cancers are a serious economic burden: in the United States, a total of 3.4 billion is spent annually on the diagnosis and treatment of HPV-related cancers, which does not even account for the cost for treating various warts and other benign papillomas. These numbers suggest that there is a clear need for better prevention and treatment solutions regarding HPV-related diseases.
U2OS cells, an osteosarcoma cell line, are suitable for studying the replication properties of various types of HPVs from different phylogenetic genera[36,37]. Studies performed in our lab show that the transcriptomes of both alpha and beta papillomaviruses are very similar to that described in keratinocytes. Therefore, U2OS cells seem to be an adequate model for studying replication, gene expression and other aspects of the HPV life cycle[67,68].