Chemoresponsive smart mesoporous silica systems - An emerging paradigm for cancer therapy

Nanotechnology-based interventions have gained popularity in the past decade for cancer therapy owing to their ability to overcome several shortcomings encountered in conventional therapy. Among the various nanoparticles that have been explored as drug carriers, mesoporous silica possesses certain desirable properties such as regulated pore size, high surface area, chemical and thermal stability, amenability for surface modification and biocompatibility. These systems have been widely investigated for site-specific delivery of single and multiple therapeutic agents as well as for imaging and theranostic applications. In recent times, the concept of targeted and sustained delivery of the therapeutic agent has transformed into a more attractive and effective approach of triggered drug release thereby ushering in an era of 'on-demand' drug delivery. Mesoporous silica due to its tunable surface functionalities has emerged in the forefront of triggered release systems. Though different types of external stimuli have been extensively investigated to bring about triggered drug release from mesoporous silica, chemo-responsive systems offer more therapeutic effectiveness with minimal collateral damage commonly associated with external stimuli. Chemo-responsiveness is generally achieved by introducing an appropriate gate-keeper molecule at the pore surface that regulates the diffusion of the drug molecules. This review analyzes different strategies that have been attempted to achieve 'on-demand' drug release in mesoporous silica carriers in response to various types of chemical stimuli. Emerging trends in the field of chemo-responsive mesoporous silica are also presented in this review.