The effect of the organosulfur garlic compound bisPMB for HPV16 and HPV18 Pseudovirus Infection In Vitro

Abstract

Human papillomavirus (HPV) is the most frequent sexually transmitted infection known to be responsible for most cervical cancer occurrences worldwide, especially in less-resourced nations. HPV are small, double-stranded, non-enveloped DNA viruses mainly transmitted through skin-to-skin contact. Up to now, there is still no successful treatment for a progressing HPV infection, although there are highly efficient prophylactic vaccines. However, these vaccines confer only type-specific immunity, they are very costly, and their efficacy is limited in patients already infected by the virus. There is clearly a necessity to elucidate further cost-effective modalities and alternative means for the prevention of HPV infection and/or treatment. In the context of an Honours project in our laboratory in 2018, bisPMB, a synthetic analogue of the garlic compound ajoene was discovered for the first time to significantly reduce HPV16 pseudovirus (HPV16-PsVs) infection of the cervical cancer cell line HeLa. This thesis aimed to further characterize the effects of bisPMB on the most oncogenic HPV types, HPV16 and HPV18 for infection of cancerous and non-cancerous cell lines, with the long-term aim to aid in the conception of new approaches for blocking HPV infection. SDS-PAGE, virus-encapsidated reporter gene (Gaussia luciferase) activity, PsVs infection-neutralization, and cell viability assays were used to assess the effect of bisPMB on HPV- PsVs infection. In this research, bisPMB inhibited cell proliferation at an IC50 concentration of 5.20 ± 2.15 μM in HeLa cells and 4.83 ± 0.50 μM in the normal keratinocyte cell line NIKS. Inhibition assays were then performed at sub-toxic concentrations to evaluate whether bisPMB could inhibit HPV infection. BisPMB was confirmed to decrease HPV16-PsVs (at 5 and 10 μM) and HPV18-PsVs (at 10 μM) infections in HeLa cells, with decreased cell viability at higher concentrations. We also observed that bisPMB decreased HPV16-PsVs infection (at 2.5, 5, and 10 μM) but increased HPV18-PsVs infection (at 5 and 10 μM) in NIKS cells. However, as inhibition of HPV-PsVs infection was at an already toxic concentration (10 μM) to the cells, bisPMB is unlikely to be used as prophylactic treatment. Our results suggest that bisPMB might block HPV infection type-specifically, both in cancerous and non-cancerous cell lines, with HPV16 being more susceptible to bisPMB treatment than HPV18. Further investigations using other HPV strains and both cancerous and non-cancerous cell line models need to be carried out to support these observations.