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 K8H2[Ti(H2O)](3)SiW9O34 (Ti3SiW9). The Ti3SiW9 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 Ti3SiW9 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 Ti3SiW9 against Ls-174-T was improved from 0.8 mg mL(-1) to 0.186 and 0.102 mg mL(-1) for Ti3SiW9@MMSN-NH2 and Ti3SiW9@BMSM-NH2, respectively.