Design expert assisted nanoformulation design for co-delivery of topotecan and thymoquinone: Optimization, in vitro characterization and stability assessment

Abstract

Poor and suboptimal therapeutic outcomes with single anticancer drugs have led to a keen interest in combination chemotherapy. Co-delivery of potent anticancer agents with high efficacy and least off-target site effects is highly desirable but often requires focussed formulatory approaches. The unique physiochemical properties of the chosen drugs further add to the challenge. The current work is an attempt to co-deliver topotecan (hydrophilic moiety) and thymoquinone (lipophilic moiety) from a nanomatrix eliciting a suitable release profile. Topotecan- thymoquinone loaded PLGA nanomatrix (TP-TY NPs) were formulated by a modified double emulsion solvent evaporation method where topotecan is solubilized in the inner aqueous phase while thymoquinone is incorporated into the organic phase of the double emulsion. Independent and dependent variables were optimized using central composite design (CCD) to obtain TP-TY NPs which were then characterized in terms of zeta potential, surface morphology, residual PVA content, injectability, syringeability, and reconstitution time. The nature of entrapped drugs was confirmed by DSC and XRD analyses and drug release pattern was studied. CCD indicated quadratic as the best fit model. The optimized formulation had particle size of 240.7±8.3nm and percent entrapment and loading of 62.6±2.6 and 6.52±0.25 respectively for thymoquinone and 42.3±1.2% and 3.6±0.26 for topotecan respectively. The particles had a spherical shape, residual PVA content of 6.22% and negative zeta potential of −1.16mV indicating the stability of the nanoparticles. DSC and XRD confirmed the transformation of drug from its crystalline to amorphous form when entrapped in the PLGA nanomatrix. The lyophilized particles reconstituted within 30s and suspension thus obtained conformed to the standard tests of syringeability and injectability. TP-TY NPs revealed a sustained release pattern of both the drugs with a minimal burst release and a total percentage release >90% in 96h. Finally, the short term accelerated stability analysis showed no significant changes with a minimal variation in the release pattern. Conclusively, the CCD supported successful formulation of nanomatrix aimed at co-delivery of topotecan and thymoquinone.