Polyphosphazene-based nanocarriers for the release of agrochemicals and potential anticancer drugs

The synthesis and characterisation of novel polyphosphazene nanocarriers, based on hydrophilic polyalkylene oxide Jeffamine M1000 and hydrophobic steroids with a glycinate linker for pH-controlled release of diosgenin and two brassinosteroids (DI31 and S7) with agrochemical and potential anticancer activity, is hereby described. Polyphosphazenes carrying approximately 17 wt% of DI31 or S7 self-assembled in water to form 120-150 nm nanoaggregates, which showed an excellent plant growth effect on radish cotyledons due to sustained delivery of approximately 30% of the agrochemicals after 4 days. Cytotoxic evaluation showed that all polymers carrying steroids and Jeffamine M1000 resulted in strong to moderate toxicity to MCF-7 cancer cells and were non-toxic to primary human lung fibroblast cells at 0.1 to 0.025 mg mL-1. Thus, DI31 and S7 bearing polymers applied at 10-4 to 10-6 mg mL-1 for delivery of recommended DI31 or S7 quantities to crops should be harmless to humans. Particularly, DI31 and S7 bearing polymers with strong cytotoxicity on MCF-7 and non-toxicity on primary human lung fibroblasts, good cell uptake after 6 hours, proper hydrodynamic sizes between 100 and 200 nm, and slow sustained release of cytotoxic drugs (DI31, S7) in acidic conditions might potentiate their accumulation in cancer tissues with good antitumour effects and minor side effects. These results demonstrated that preparation of brassinosteroid bearing polymers is a promising strategy for the preparation of better agrochemicals with reduced pollutant impact on sustainable agriculture and potential anticancer formulations based on analogues of brassinosteroids.