(M0930-05-29) Sustained Drug Exposure Drives Efficacy: PK/PD Analysis of Corallopyronin A against Wolbachia Using Physiologically Based Biopharmaceutic Modeling

Purpose: An early understanding of the relationship between pharmacokinetics (PK) and pharmacodynamics (PD) is critical for the rational development of anti-infective therapies. In anti-Wolbachia treatment of filarial diseases, such as onchocerciasis and lymphatic filariasis, conventional PK/PD modeling based on minimum inhibitory concentrations is difficult due to the intracellular localization of the target endosymbionts, Wolbachia. To address this challenge, this study aimed to establish a model-based framework for defining PD efficacy thresholds using in vitro IC₅₀/IC₉₀ data from Wolbachia-infected cell lines. Additionally, an iterative modeling approach was applied to identify exposure-response relationships that best describe the in vivo efficacy of Corallopyronin A (CorA). The latter approach supports the translational evaluation of CorA and enhances the optimization of dosing strategies for anti-Wolbachia therapies.

Methods: A physiologically based biopharmaceutic model (PBBM) for mice was developed using GastroPlus® v9.8.3, incorporating physicochemical properties derived from in vitro and in silico data, along with distribution and elimination kinetics based on i.v. studies. A mechanistic dissolution model for the CorA–povidone suspension was implemented, accounting for particle size distribution and surface pH-dependent solubility. Model validation was performed using PK data from single oral dosing [2] and simulated plasma concentration time profiles were generated for various dosing regimens over a 14-day treatment period. The PK parameters C_max, C_min, AUC and Time above IC₅₀/IC₉₀ were extracted. In vivo efficacy was evaluated in Litomosoides sigmodontis-infected BALB/c mice treated with CorA at doses of 9–36 mg/kg once to three times daily. On day 35 post-infection, adult worms were collected from the pleural cavity. Wolbachia loads in female worms were quantified by qPCR targeting the ftsZ gene of Wolbachia and the L. sigmodontis actin gene. In vitro activity of CorA against Wolbachia was evaluated in Wolbachia-infected Aedes albopictus C6/36 cells. Wolbachia depletion was quantified by qPCR targeting the Wolbachia 16S rDNA and host actin genes. The IC₅₀ and IC₉₀ values were determined using nonlinear regression analysis. To characterize the relationship between in vivo efficacy and PK parameters, a sigmoidal E_max model based on the Hill equation was applied. In addition, an iterative approach was used to determine a model-dependent efficacy threshold based on the best fit to the Hill equation.

Results: PK simulations indicated a slight accumulation of CorA over the 14-day dosing period, particularly with repeated administration (Figure 1). PK parameters used in the subsequent analysis were derived from the corresponding plasma concentration time curves. In vivo, increasing the once-daily dose from 9 to 36 mg/kg improved efficacy, while dividing the daily dose into two or three administrations further enhanced treatment outcomes (Figure 2). In vitro, CorA demonstrated potent activity against Wolbachia with an IC₅₀ of 0.007 ± 0.003 µg/mL and an IC₉₀ of 0.030 ± 0.013 µg/mL (mean ± SEM). No significant correlation was observed between C_max and therapeutic efficacy, indicating that the peak plasma concentrations are not a reliable predictor of treatment response. In contrast, trough-related efficacy was best described by a model dependent threshold of 0.019 µg/mL and the IC₅₀, with strong correlations observed (R² = 0.8881 and 0.8877). Notably, the model dependent threshold lies between the in vitro IC₅₀ and IC₉₀ values. AUC-based analysis yielded consistently strong correlations across all thresholds (R² = 0.8142), highlighting a robust relationship between drug exposure and efficacy. Regarding the pharmacokinetic parameter time above threshold, neither the IC₅₀ nor the IC₉₀ were able to discriminate effectively between the different treatment groups. This limitation was observed exclusively for the model dependent efficacy threshold of 2.25 µg/mL, where the coefficient of determination was R² = 0.9323 (Figure 3).

Conclusion: This study demonstrates the value of a model-informed approach to define PK/PD relationships in the absence of a conventional MIC. Fractionated dosing resulted in superior therapeutic outcomes compared to once-daily administration. In particular, strong correlations were observed for trough-related parameters and AUC across multiple efficacy thresholds. C_max, by contrast, showed no predictive value for treatment response. Time above threshold was not suitable for differentiating treatment groups except when using the model dependent efficacy threshold. These findings highlight the importance of sustained drug exposure over threshold concentrations in optimizing CorA dosing regimens. To validate these results, an independent in vivo infection model using L. sigmodontis in gerbils will be conducted.

References: [1] T. Becker, A.K. Krome, S. Vahdati, A. Schiefer, K. Pfarr, A. Ehrens, T. Aden, M. Grosse, R. Jansen, S. Alt, T. Hesterkamp, M. Stadler, M.P. Hübner, S. Kehraus, G.M. König, A. Hoerauf, K.G. Wagner, In Vitro–In Vivo Relationship in Mini-Scale—Enabling Formulations of Corallopyronin A, (2022) 18.
[2] A.K. Krome, T. Becker, S. Kehraus, A. Schiefer, C. Steinebach, T. Aden, S.J. Frohberger, Á.L. Mármol, D. Kapote, R. Jansen, L. Chaverra-Muñoz, M.P. Hübner, K. Pfarr, T. Hesterkamp, M. Stadler, M. Gütschow, G.M. König, A. Hoerauf, K.G. Wagner, Solubility and Stability Enhanced Oral Formulations for the Anti-Infective Corallopyronin A, (2020) 21.

Acknowledgements: All Animal experiments were performed in accordance with the appropriate local guidelines and approved by the relevant authorities (Landesamt für Natur-, Umwelt- und Verbraucherschutz, Recklinghausen, Germany) under the approval codes 81-02.04.2020.A244, 81-02.05.40.18.057 and AZ 84-02.04.2015.A507. The authors thank Tilman Aden, Martina Fendler, Benjamin Lenz and Helene Neufeld for their significant help and execution of the performed pharmacokinetic and pharmacodynamic studies in rodents. The CorA project has received funding from the German Center for Infection Research (https://www.DZIF.de) grant numbers TTU 09.914 and 09.822, the Federal Ministry of Education and Research (https://www.BMBF.de) grant number 16GW0229 and 16GW0227K, and the Else Krömer Fresenius Stiftung (https://www.ekfs.de) grant number 2022_EKTP26_GMP.