Specific Cell Targeting Therapy Bypasses Drug Resistance Mechanisms in African Trypanosomiasis

African trypanosomiasis is a deadly neglected disease caused by the extracellular parasite Trypanosoma brucei. Current therapies are characterized by high drug toxicity and increasing drug resistance mainly associated with loss-of-function mutations in the transporters involved in drug import. The introduction of new antiparasitic drugs into therapeutic use is a slow and expensive process. In contrast, specific targeting of existing drugs could represent a more rapid and cost-effective approach for neglected disease treatment, impacting through reduced systemic toxicity and circumventing resistance acquired through impaired compound uptake. We have generated nanoparticles of chitosan loaded with the trypanocidal drug pentamidine and coated by a single domain nanobody that specifically targets the surface of African trypanosomes. Once loaded into this nanocarrier, pentamidine enters trypanosomes through endocytosis instead of via classical cell surface transporters. The curative dose of pentamidine-loaded nanobody-chitosan nanoparticles was 100-fold lower than pentamidine alone in a murine model of acute African trypanosomiasis. Crucially, this new formulation displayed undiminished in vitro and in vivo activity against a trypanosome cell line resistant to pentamidine as a result of mutations in the surface transporter aquaglyceroporin 2. We conclude that this new drug delivery system increases drug efficacy and has the ability to overcome resistance to some anti-protozoal drugs.
Author Summary Drug resistance is complicating the treatment of parasitic diseases including African trypanosomiasis, a fatal disease if left untreated. Development of a vaccine is unlikely due to parasite antigenic variation. Current chemotherapy relies primarily on four drugs. Three of these drugs access the cell’s interior through surface transporters and resistance mechanisms are largely associated with loss-of-function mutations in the involved surface drug transporters. We reasoned that using an alternative drug entrance would circumvent parasite resistance due to mutation in a surface transporter. We have developed a drug nanocarrier that consists of polymeric nanoparticles coated with a single domain antibody that targets the trypanosome surface. This new formulation reduces the minimal curative dose and, most importantly, circumvents drug resistance in a resistant cell line as a result of mutations in the surface transporter that mediate drug uptake. This study presents a proof-of-concept of a novel technology for reversing transporter-related drug resistance with applications to other infectious diseases.