Mechanistic viral dynamic modelling of in vitro cytomegalovirus infection based on viral DNA and viral titre

24 Aims: Ganciclovir and its prodrug valganciclovir are the standard treatments for cytomegalovirus (CMV) infection. Despite their efficacy, these antiviral agents have a very narrow therapeutic window due to high myelotoxicity. Although the in vivo viral dynamics of CMV have been studied, previous published models have relied solely on viral DNA profiles, which indicates the amount of both infectious and non-infectious virus instead of infectious virus only. In this study, both viral DNA and viral titre (i.e., infectious virus) were characterized, and their relationship was elucidated through the development of a mechanistic viral dynamic model of in vitro CMV infection. Methods: The viral dynamic model development was carried out using NONMEM (v.7.5). First, natural cell growth rate of the susceptible cell counts (S) and death rate (δ) of infected cells (I) were derived from the cell counts data of the uninfected and infected group. Next, a target cell-limited (TCL) model [1] was applied to characterize the viral dynamics by fitting both the viral DNA and viral titre data. Key viral kinetic parameters estimated included viral infection rate (β), cell growth rate (λ), production rate of viral DNA (π) and viral clearance (γ). Different functions were tested to describe the relationship between total (V) and infectious virus (Vi). Results: The fitting results showed that the natural cell growth curve can be best described by an exponential saturated function of which the natural growth rate was 0.77 day−1. When the cells were infected, the proliferation of susceptible cells drastically reduced by 87%, decreasing from 0.77 to 0.1 day−1 with a death rate of infected cells of 0.996 day−1. A TCL model well captured the viral load profile with β = 1.27*10−8 copy−1/day, λ = 0.1 day−1, π = 7.48*104 copy/cell/day. The relationship between V and Vi can be best characterized using a power law model: Vi = f(V) = B*VHill, where B = 0.032 and Hill = 0.848, indicating each new DNA copy came with approximately 0.03 infectious virion. Conclusions: This is the first known viral kinetic model of in vitro CMV infection that characterizes the dynamics of CMV as well as the relationship between viral DNA and viral titre, providing an ideal basis to study the in vitro PK-PD of CMV and ganciclovir in a dynamic in vitro infection model with the potential to translate to a clinical setting afterwards. References [1] Duke, Elizabeth R, Boshier, FAT, Boeckh, M, Schiffer, JT, Cardozo-Ojeda, EF “ Mathematical modeling of within-host, untreated, cytomegalovirus infection dynamics after allogeneic transplantation.” Viruses vol. 13, 11 2292. 16 Nov. 2021, doi:10.3390/v13112292 [2] Iyaniwura, Sarafa A, Ribeiro, RM, Zitzmann, C, Phan, T, Ke, R, Perelson, AS “ The kinetics of SARS-CoV-2 infection based on a human challenge study.” Proc Natl Acad Sci U S A vol. 121,46 (2024): e2406303121. 10.1073/pnas.2406303121