In-host modeling of dengue virus and non-structural protein 1 and the effects of ivermectin in patients with acute dengue fever

Abstract

The increased incidence of dengue poses a substantially global public health challenge. There are no approved antiviral drugs to treat dengue infections. Ivermectin, an old anti-parasitic drug, had no effect on dengue viremia, but reduced the dengue non-structural protein 1 (NS1) in a clinical trial. This is potentially important, as NS1 may play a causal role in the pathogenesis of severe dengue. This study established an in-host model to characterize the plasma kinetics of dengue virus and NS1 with host immunity and evaluated the effects of ivermectin, using a population pharmacokinetic-pharmacodynamic (PK-PD) modeling approach, based on two studies in acute dengue fever: a placebo-controlled ivermectin study in 250 adult patients and an ivermectin PK-PD study in 24 pediatric patients. The proposed model described adequately the observed ivermectin pharmacokinetics, viral load, and NS1 data. Bodyweight was a significant covariate on ivermectin pharmacokinetics. We found that ivermectin reduced NS1 with an EC₅₀ of 67.5 μg/mL. In silico simulations suggested that ivermectin should be dosed within 48 h after fever onset, and that a daily dosage of 800 μg/kg could achieve substantial NS1 reduction. The in-host dengue model is useful to assess the drug effect in antiviral drug development for dengue fever.

FIGURE 1

Graphical overview of the dengue viral load, NS1 kinetic and ivermectin PK model. A classical target cell‐limited model was used, which includes target cells (T), infected cells (I), production cells (P) and viral load (V; observations). Adaptive immune serology responses (Dengue‐specific IgM and IgG) were incorporated into the virus elimination pathway, and Dengue NS1‐specific IgG was included in the NS1 elimination pathway. β is the infection rate constant, ktr1 is the transition rate constant for infected cells, δ is the death rate constant of producing cells, p is the virus production rate constant, c is the virus elimination rate constant by innate immunity (IFN, NK cell), and k_A is the elimination (neutralization) rate of virus by dengue‐specific IgG and IgM antibodies (A). The initial number of target cells (T ₀) is fixed to the literature value of 3.5 × 10⁵ cells/mL. The concentration‐time profile of IgM and IgG were fit using sigmoidal maximum effect models $\left(A_{\mathrm{IgM}}\left(t\right)=\frac{E_{\max \_\mathrm{IgM}}·T^{\gamma }}{{\mathit{ET}}_{50\_\mathrm{IgM}}^{\gamma }+T^{\gamma }},A_{\mathrm{IgG}}\left(t\right)=\frac{E_{\max \_\mathrm{IgG}}·T^{\gamma }}{{\mathit{ET}}_{50\_\mathrm{IgG}}^{\gamma }+T^{\gamma }}\right)$, where E _max is the maximum concentration of IgM or IgG, T is time after infection, ET₅₀ is the time to reach 50% maximum levels and γ is the shape parameter. The model‐predicted individual IgM and IgG were normalized to a 0–1 scale by the equation of $A\left(t\right),i=\left(\frac{A_{\mathrm{IgM}}\left(t\right),i}{E_{\max \_\mathrm{IgM},i}}+\frac{A_{\mathrm{IgG}}\left(t\right),i}{E_{\max \_\mathrm{IgG},i}}\right)/2$. NS1 delayed secretion from viral‐producing cells was assumed. k _tr2 is the transition rate constant for the NS1 secretion. k _p is the NS1 production rate, defined by $\frac{E_{\max ,\mathrm{NS}1}·T^{\gamma }}{{\mathit{ET}}_{50,\mathrm{NS}1}^{\gamma }+T^{\gamma }}$, where E _max,NS1 is the maximum production rate of NS1, ET_50,NS1 is the time to reach 50% E _max,NS1, T is the time after infection. k _B is the elimination rate constant of NS1, defined by a spline function, either equal to the initial rate constant (antibodies (Abs) level < a cutoff value) or the initial rate constant + slope· T·Abs (Abs ≥ a cutoff value). Ivermectin PK was described by a two‐ compartment disposition model with six transit absorption compartments. CL is the clearance. V _c is the central volume of distribution. V _P is the peripheral volume of distribution. Q is the inter‐compartment clearance and k_tr3 is the transition rate constant for absorption. The inhibition of NS1 production by ivermectin was driven by an E _max function, where C _IVM is the model‐predicted ivermectin concentration, E _max,IVM is the maximum inhibitory effect, EC_50,IVM is the ivermectin concentration to achieve half of maximum inhibitory effect.

FIGURE 2

Visual predictive checks of the dengue viral kinetic model. (a) Adult patients receiving placebo treatment, (b) Adult patients receiving ivermectin treatment, (c) pediatric patients receiving ivermectin treatment. Based on 1000 stochastic simulations. Upper panel: Open circles represent the observations, solid and dash lines represent the 5th, 50th, and 95th percentiles of the observed data. The shaded areas represent the 95% prediction intervals around the simulated 5th, 50th, and 95th percentiles. Most of observed data fell within the 95% prediction interval. Lower panel: Open circles represent the observed fraction of censored data, and the shaded area represents the 95% prediction interval of the simulated fraction of censored data. LOQ is below the lower limit of quantification.

FIGURE 3

Prediction‐corrected visual predictive checks of the dengue NS1 kinetic model. (a) Adult patients with placebo, (b) Adult patients receiving ivermectin treatment, (c) Pediatric patients receiving ivermectin treatment. Based on 1000 stochastic simulations. Upper panel: Open circles represent the observations, solid and dash lines represent the 5th, 50th, and 95th percentiles of the observed data. The shaded areas represent the 95% prediction intervals around the simulated 5th, 50th, and 95th percentiles. Most of observed data fell within the 95% prediction interval. Lower panel: Open circles represent the observed fraction of censored data, and the shaded area represent the 95% prediction interval of the simulated fraction of censored data. LOQ is below the lower limit of quantification.

FIGURE 4

Simulated median plasma NS1 profiles in different dosing scenarios using the final PK–PD model. The simulation was conducted in a typical adult patient (60 kg bodyweight, serotype 2 or 4 and secondary infection). The simulation scenarios assess the impact of ivermectin treatment timing (a), duration (b, c) and dose (d‐f) on the NS1 profiles. The incubation period of dengue is assumed to be 6 days after the infection. The ivermectin treatment was initiated on 24 (day 7), 48 (day 8) or 72 (day 9) hours after illness onset.