(T1230-03-17) Development of Long-Acting Decoquinate Nanocrystal-Based Formulations as a Chemical Vaccine for Malaria

Purpose: Malaria still represents a major global public health problem, with 608,000 deaths per year [1]. Despite availability of several drugs employed to treat the disease, preventing transmission remains a challenge, especially for travelers and healthcare professionals who need to work in endemics areas [2]. While advances in vaccination are being observed, current vaccines are not universally available, only protecting young children in endemics zones [3]. Decoquinate (DQ) is a synthetic coccidiostat that exhibits potent antimalarial activity against various stages of Plasmodium parasite. However, DQ’s highly hydrophobic properties lead to low bioavailability [4]. Nanocrystal (NC)-based formulations, and in particular long-acting nanosuspensions, present an alternative solution to overcome this limitation allowing for the formation of intramuscular depots from which drugs are released for weeks or months [5]. In this study, we report the development and characterization of long-acting DQ nanosuspensions for malaria prophylaxis (Figure 1A).

Methods: DQ-NC were formulated via media milling methodology in a small laboratory scale [6], employing various stabilizers at different concentrations, reaching to two main candidates containing Poloxamer^® (P188) 0.5 and 1% w/v (DQ-NC_0.5 and DQ-NC₁). The nanoformulations were characterized for mean particle size, polydispersity index (PDI), zeta potential (ZP) using a Nanobrook Omni particle sizer. Differential scanning calorimetry (DSC) was used to assess sample crystallinity and particle morphology was compared with coarse DQ using scanning electron microscopy (SEM). Moreover, the drug content and in vitro release profiles were obtained quantifying the drug using an in-house validated HPLC-UV method.

Results: DQ-NC were successfully obtained using media milling. P188 was the most suitable stabilizer in the milling process (Figure 1 B), leading mean particle sizes of 214 ± 1.87 nm and 228.16 ± 0.91 nm, and PDI values between 0.15 and 0.17 for DQ-NC_0.5 and DQ-NC₁, respectively (Figure 1 D). The ZP value for DQ-NC_0.5 was -12.91± 0.64 mV, and 15.30 ± 2.41 mV for DQ-NC₁ (Figure 1E). All crystalline peaks of DQ were observed in DSC traces, with a lower intensity in NCs formulations due to thermally-induced amorphization and lower particle size (Figure 2A). DQ was measured in the formulations at proportions of 40% and 57% for DQ-NC_0.5 and DQ-NC₁, respectively. The SEM images revealed the formation of flat crystals, contrasting with DQ’s presentation as a drug aggregates (Figure 2B). In the in vitro study, it was observed that both formulations were visually well dispersed, and this reflected in the release rate. DQ-NCs were released at a higher rate compared to the pure drug within the 192-hour period, 19% (DQ-NC_0.5) and 25% (DQ-NC₁), while the pure drug released only 13% within the same timeframe (Figure 2C), indicating potential for long-acting drug release.

Conclusion: After preliminary studies, DQ-NCs demonstrated advantageous physicochemical and morphological characteristics that suggest they may be developed as a malaria prophylaxis treatment. However, further studies are required for conclusive characterization and evaluation in malaria experimental models.

References: 1- World malaria report 2023. Geneva: World Health Organization (2023). 2- Freedman, C. et al (2016). The New England Journal of Medicine, 2016, 375. 3- Bakshi, R. et al (2018). Nature Communications, 2018, 9. 4- Zeng, S. (2022). Malaria Journal, 2022, 21. 5– McGuckin, M. et al (2022). Journal of Controlled Release, 2022, 345. 6- Abbate, M. et al (2023). International Journal of Pharmaceutics, 2023, 640.

Acknowledgements: Caroline Sousa is a fellow of the Institutional Program for Internationalization (Print) - CAPES - PrInt (Brazil)


Figure 1. (A) Purpose of Decoquinate nanocrystals formulation for malaria prophylaxis. (B, C) DQ screening with different stabilizers measuring size (nm) and polydispersity index (PDI); the initial concentration for screening the stabilizers was 2%. (D, E) DQ nanoformulations assessed in different concentrations of P188.


Figure 2. (A) DSC of the two best formulations. (B) SEM of nanocrystals after freeze dryer comparing with the pure drug. (C) Percentual of drug release from dialysis membrane studies over 192 hours. PM: physical mixture.