Rasmus Henninger 1, Wietse M. Schouten 2, Jean-Yves Gillon 3, Charles E. Mowbray 3, Jadel Müller Kratz 4, Katrien Van Bocxlaer 5, Thomas P.C. Dorlo 1
1 Department of Pharmacy, Uppsala University (Uppsala, Sweden), 2 Department of Pharmacy & Pharmacology, Antoni van Leeuwenhoek/The Netherlands Cancer Institute (Amsterdam, The Netherlands), 3 Drugs for Neglected Diseases Initiative (Geneva, Switzerland), 4 Drugs for Neglected Diseases Initiative (Rio de Janeiro, Brazil), 5 Skin Research Centre, Hull York Medical School, University of York (York, United Kingdom)
Introduction: Preclinical efficacy models that recapitulate Leishmania parasite infection and treatment response can play a key role in developing much-needed novel therapies for cutaneous leishmaniasis (CL). For this dermal parasitic infection, orally administered drugs must distribute from the systemic circulation into infected dermis to reach intracellular parasites in infected immune cells [1]. Therefore, understanding drug exposure at the site of disease is critical. Bioluminescent Leishmania infection models enable longitudinal readouts of skin parasite burden, allowing target-site exposure to be linked to treatment response. DNDI-6174, a cytochrome bc₁ inhibitor with high selectivity for the parasite target, is a promising oral candidate for which target-site PK/PD can support translation [2].
Objectives: To quantify the plasma-to-tissue exposure relationship for DNDI-6174 at target organs of Leishmania infection; to link skin exposure to parasite burden dynamics in a murine L. major infection model, including characterization of natural disease progression; and to perform target-attainment simulations to support prediction of efficacious human doses.
Methods: PK/PD data were gathered from a dose-response study where fifty female BALB/c mice (17–20 g) were infected with bioluminescent L. major Friedlin REH promastigotes in the rump. Ten days post infection, mice were assigned to untreated vehicle control (n = 5), paromomycin (n = 5), or DNDI-6174 HBr (3.125–50 mg/kg p.o. qd for 10 days; n = 8/dose). Plasma concentrations (days 1 and 10) and end-of-treatment tissue concentrations (infected/non-infected skin, liver, spleen) were quantified by UPLC–MS/MS, and longitudinal parasite burden was measured by in vivo bioluminescent imaging along with daily lesion size measurements. PK/PD analyses and simulations were conducted in NONMEM 7.5.1, PsN 5.3.0, and R 4.5.1. Estimated PK parameters were allometrically scaled to derive typical human PK parameter values after correction for differences in plasma protein binding. Predicted human PK parameters were combined with tissue distribution characteristics and PD components from the murine PK/PD model, and infected skin concentrations over time were used to simulate clinical efficacy of DNDI-6174 toward a target of 99% reduction in parasite burden.
Results: Plasma concentrations were best described by a one-compartment model with first-order absorption, Michaelis–Menten elimination (Vmax/F = 36.4 µg/hr; Km = 2500 µg/L), and a reduced relative bioavailability at the highest dose only (Frel,50 mg/kg = 0.674). Non-linearities in the tissue distribution required a capacity-limited distribution model. Penetration coefficients were 3.89 (infected skin), 2.46 (non-infected skin), 14.6 (liver), and 1.72 (spleen), with corresponding Bmax values of 622, 543, 1690, and 865 µg/L, respectively. Infected skin was associated with a higher skin-to-plasma ratio than non-infected skin, corresponding to a 1.58-fold higher total exposure in infected tissue. Based on vehicle-control data, the net parasite growth rate constant knet was estimated at 0.0264 hr⁻¹ (doubling time ≈ 25 hr), with a maximum parasite burden (Pmax) of 3.53 log₁₀ photons/s, after background normalization. Drug-induced parasite elimination was adequately described using a direct linear model in the lower dose groups (3.125–12.5 mg/kg), while the observed effect at higher doses (25–50 mg/kg) was slightly underpredicted. Clinical dosing of 2.0 mg/kg (140 mg in a 70-kg adult) qd for 10 days was predicted to be sufficient to achieve a 99% reduction in parasite burden in >90% of simulated PK/PD profiles, comparable to predicted efficacious dosing for visceral leishmaniasis [2].
Conclusions: In this study, a translational PK/PD model was developed to characterize the effect of DNDI-6174 over time against CL caused by L. major in an in vivo mouse infection model. The established exposure-response relationship was integrated with allometrically scaled human PK, and simulations suggested that a clinical dosing regimen of 2.0 mg/kg qd for 10 days would be sufficient to achieve a high probability of therapeutic success.
References:
[1] K. V. Bocxlaer and S. L. Croft, “Pharmacokinetics and pharmacodynamics in the treatment of cutaneous leishmaniasis – challenges and opportunities,” RSC Med. Chem., vol. 12, no. 4, pp. 472–482, Apr. 2021, doi: 10.1039/D0MD00343C.
[2] S. Braillard et al., “DNDI-6174 is a preclinical candidate for visceral leishmaniasis that targets the cytochrome bc1,” Sci Transl Med, vol. 15, no. 726, p. eadh9902, Dec. 2023, doi: 10.1126/scitranslmed.adh9902.
Reference: PAGE 34 (2026) Abstr 12179 [www.page-meeting.org/?abstract=12179]
Poster: Drug/Disease Modelling - Infection