Background: Because Plasmodium falciparum displays increase tolerance against the recommended artemisinin combination therapies (ACT), new classes of anti-malarial drugs are urgently required. Previously synthesized artemisinin-aminoquinoline hybrids were evaluated to ascertain whether the potent low nanomolar in vitro anti-plasmodial activity would carry over in vivo against Plasmodium vinckei. A snapshot pharmacokinetic analysis was carried out on one of the hybrids to obtain an indication of the pharmacokinetic properties of this class of anti-malarial drugs.
Methods: In vitro activity of hybrids 2 and 3 were determined against the 3D7 strain of P. falciparum. Plasmodium vinckei-infected mice were treated with hybrids 1 - 3 for four days at a dosage of 0.8 mg/kg, 2.5 mg/kg, 7.5 mg/kg or 15 mg/kg intraperitoneally (ip), or orally (per os) with 2.7 mg/kg, 8.3 mg/kg, 25 mg/kg or 50 mg/kg. Artesunate was used as reference drug. A snapshot oral and IV pharmacokinetic study was performed on hybrid 2.
Results: Hybrids 1 - 3 displayed potent in vivo anti-malarial activity with ED50 of 1.1, 1.4 and <0.8 mg/kg by the ip route and 12, 16 and 13 mg/kg per os, respectively. Long-term monitoring of parasitaemia showed a complete cure of mice (without recrudescence) at 15 mg/kg via ip route and at 50 mg/kg by oral route for hybrid 1 and 2, whereas artesunate was only able to provide a complete cure at 30 mg/kg ip and 80 mg/kg per os.
Conclusions: These compounds provide a new class of desperately needed anti-malarial drug. Despite a short half-life and moderate oral bioavailability, this class of compounds was able to cure malaria in mice at very low dosages. The optimum linker length for anti-malarial activity was found to be a diaminoalkyl chain consisting of two carbon atoms either methylated or unmethylated.