Hydroxychloroquine: A Physiologically-Based Pharmacokinetic Model in the Context of Cancer-Related Autophagy Modulation

Abstract

Hydroxychloroquine (HCQ) is a lysosomotropic autophagy inhibitor being used in over 50 clinical trials either alone or in combination with chemotherapy. Pharmacokinetic (PK) and pharmacodynamic (PD) studies with HCQ have shown that drug exposure in the blood does not correlate with autophagy inhibition in either peripheral blood mononuclear cells or tumor tissue. To better explain this PK/PD disconnect, a PBPK was developed for HCQ describing the tissue-specific absorption, distribution, metabolism, and excretion as well as lysosome-specific sequestration. Using physiologic and biochemical parameters derived from literature or obtained experimentally, the model was first developed and validated in mice, and then adapted to simulate human HCQ exposure in whole blood and urine through allometric scaling and species-specific parameter modification. The human model accurately simulated average steady-state concentrations (Css) of those observed in five different HCQ combination clinical trials across seven different doses, which was then expanded by comparison of the Css distribution in a virtual human population at this range of doses. Value of this model lies in its ability to simulate HCQ PK in patients while accounting for PK modification by combination treatment modalities, drug concentrations at the active site in the lysosome under varying pH conditions, and exposure in tissues where toxicity is observed.

Fig. 1.

HCQ molecular structure with key physicochemical properties.

Fig. 2.

Schematic of model describing key organs involved in HCQ ADME after oral dosing. Absorption occurs in the gut, metabolism in the liver, and excretion in the kidneys. Skin and eyes exhibit unusual PK properties due to extensive binding to melanin. Heart is included due to cardiomyopathy as an observed side effect in some cases. The rest of the organs are split into slowly perfused (muscle, fat, bone) and rapidly perfused (internal viscera).

Fig. 3.

Intracellular mechanism of HCQ PK with pH dependence. HCQ crosses membranes readily, but accumulates in acidic compartments due to being nonpermeable in the +2 state.

Fig. 4.

Mouse PK data compared with PBPK simulation. Mice were treated with a single i.p. dose of HCQ at 20, 40, and 80 mg/kg (left, middle, and right columns), and data were collected at 3, 6, 12, 24, 48, and 72 hours from whole blood (A), liver (B), kidney (C), and gut (D). Circles represent tissues from treated mice (three replicates per time point, n = 54), and lines represent simulation output.

Fig. 5.

Human whole-blood and urine concentrations of HCQ (points) were compared with PBPK simulation (lines) (Tett et al., 1988, 1989). Whole-blood concentrations of patient 4 from the studies were simulated after a single 200 mg oral dose (A). Urinary excretion of HCQ was simulated in patient 5 from the studies following 200 mg oral and i.v. doses (B). Whole-blood concentrations of patient 4 from the studies were simulated after a single 200 mg i.v. infusion (C) and of patient 1 after 200 and 400 mg i.v. infusions (D).

Fig. 6.

Whole-blood concentrations of HCQ at steady state—comparison between five different human cancer clinical trials and PBPK model output at varying doses. The combination trials represented include (A) temsirolimus (Rangwala et al., 2014a), (B) vorinostat (Mahalingam et al., 2014), (C) temozolomide in glioblastoma patients (Rosenfeld et al., 2014), (D) bortezomib (Vogl et al., 2014), and (E) temozolomide in advanced solid tumor and melanoma patients (Rangwala et al., 2014b). Clinical trial data represent Css between the second and third quartile of patients, except for the vorinostat trial (B), which represents the mean ± S.D. Css from the PBPK model were taken as the average concentration occurring at 20 days of once-daily oral dosing. Black lines represent the regression lines for clinical trial data; dotted black lines represent the 95% confidence interval; and gray lines represent the regression line for PBPK simulated data. The only trial that had a regression slope statistically different from the PBPK simulation was the temozolomide glioblastoma trial (C).

Fig. 7.

Distribution of whole-blood Css (at 20 days) for patients in different dosing cohorts—a comparison of simulated data versus actual patient data from four clinical trials. Plots in gray represent the PBPK model simulation of HCQ in a virtual population of 500 patients (half male and half female) randomly generated using demographic data from the bortezomib trial. Plots in white represent the whole-blood HCQ concentration distribution for patients in one of the four clinical trials, including (A) bortezomib (Vogl et al., 2014), (B) temozolomide in glioblastoma patients (Rosenfeld et al., 2014), (C) temozolomide in patients with solid tumors or melanoma (Rangwala et al., 2014b), and (D) temsirolimus (Rangwala et al., 2014a). Virtual population was generated for 250 males and 250 females using the PopGen web software and pulling patient data from the P3M patient database.