pH-responsive controlled release of antitumour-active polyoxometalate from mesoporous silica materials.

Two efficient pH-responsive oral delivery systems have been fabricated through a dative bonding between the amino-functionalized mesoporous silica materials, including MCM-41-type mesoporous silica nanospheres (MMSNs) and bimodal mesoporous silica microspheres (BMSMs), and an antitumour-active polyoxometalate K(8)H(2)Ti(H(2)O)SiW(9)O(34) (Ti(3)SiW(9)). The Ti(3)SiW(9) loaded in the pores of MMSNs and BMSMs are up to 23.72 wt% and 28.69 wt% at pH 6.5, respectively. Both delivery systems reveal an increase of Ti(3)SiW(9) release under mildly alkaline conditions, while zero premature release is observed under acidic and neutral conditions, making them ideal for use as a new class of colon-specific oral delivery systems. Importantly, these systems provide very promising possibilities for many medical applications that require an increase or decrease in the rate of drug release, depending on disease evolution. Upon incorporation into mesoporous silica materials, the antitumour activity of Ti(3)SiW(9) against Ls-174-T was improved from 0.8 mg mL(-1) to 0.186 and 0.102 mg mL(-1) for Ti(3)SiW(9)@MMSN-NH(2) and Ti(3)SiW(9)@BMSM-NH(2), respectively.