Design, synthesis and evaluation of antimalarial potential of polyphosphazene linked combination therapy of primaquine and dihydroartemisinin

Various polymer drug conjugates (13-16) such as primaquine and dihydroartemisinin conjugated 2-propoxy substituted polyphosphazenes (13), primaquine and dihydroartemisinin conjugated 4-acetamidophenoxy substituted polyphosphazenes (14), primaquine and dihydroartemisinin conjugated 4-formyl substituted polyphosphazenes (15) and primaquine and dihydroartemisinin conjugated 4-aminoethylbenzoate substituted polyphosphazenes (16) were synthesized using substituted polyphosphazenes as polymer and primaquine and dihydroartemisinin as combination antimalarial pharmacophores and formulated to nanoparticles to achieve novel controlled combined drug delivery approach for radical cure of malaria. The polymeric backbone was suitably substituted to impart different physicochemical properties. The polymer-drug conjugates were characterized by IR, (1)H NMR, (31)P NMR and their molecular weights were determined by Gel Permeation Chromatography. The thermal properties of the conjugates (13-16) were studied by DSC and TGA. The conjugates (13-16) were then formulated to nanoparticles formulations to increase their uptake by hepatocytes and to achieve targeted drug delivery. The nanoparticle formulations were characterized by Zeta Sizer and their morphology were studied by TEM (Transmission Electron Microscopy) imaging. The nanoparticles formulations exhibited biphasic in vitro drug release profile, the initial burst release followed by a sustained release owing to the non-fickian diffusion during first step release and fickian diffusion during second step release. In vivo antimalarial efficacy was tested using Plasmodium berghei (NK65 resistant strain) infected swiss albino mice at different doses. The combination therapy exhibited promising antimalarial efficacy at lower doses in comparison to the standard drug combination. Further, this combination therapy provided protection over 35days without any recrudescence, thus proving to be effective against resistant malaria. The study provides an alternative combination regimen found to be effective in the treatment of resistant malaria.