There is a need for the improvement of conventional cancer treatment strategies by incorporation of targeted and non-invasive procedures aimed to reduce side-effects, drug resistance, and recurrent metastases. The anti-cancer drug, 5-fluorouracil (5-FU), is linked to a variety of induced-systemic toxicities due to its lack of specificity and potent administration regimens, necessitating the development of delivery vehicles that can enhance its therapeutic potential, while minimizing associated side-effects. Polymeric mesoporous silica nanoparticles (MSNs) have gained popularity as delivery vehicles due to their high loading capacities, biocompatibility, and good pharmacokinetics. MSNs produced in this study were functionalized with the biocompatible polymers, chitosan, and poly(ethylene)glycol to produce monodisperse NPs of 36–65 nm, with a large surface area of 710.36 m2/g, large pore volume, diameter spanning 9.8 nm, and a favorable zeta potential allowing for stability and enhanced uptake of 5-FU. Significant drug loading (0.15–0.18 mg5FU/mgmsn), controlled release profiles (15–65%) over 72 hours, and cell specific cytotoxicity in cancer cells (Caco-2, MCF-7, and HeLa) with reduced cell viability (≥50%) over the non-cancer (HEK293) cells were established. Overall, these 5FU-MSN formulations have been shown to be safe and effective delivery systems in vitro, with potential for in vivo applications.

With increasing incidence and mortality rates, cancer remains one of the most devastating global non-communicable diseases. Restricted dosages and decreased bioavailability, often results in lower therapeutic outcomes, triggering the development of resistance to conventionally used drug/gene therapeutics. The development of novel therapeutic strategies using multimodal nanotechnology to enhance specificity, increase bioavailability and biostability of therapeutics with favorable outcomes is critical. Gated vectors that respond to endogenous or exogenous stimuli, and promote targeted tumor delivery without prematurely cargo loss are ideal. Mesoporous silica nanoparticles (MSNs) are effective delivery systems for a variety of therapeutic agents in cancer therapy. MSNs possess a rigid framework and large surface area that can incorporate supramolecular constructs and varying metal species that allow for stimuli-responsive controlled release functions. Its high interior loading capacity can incorporate combination drug/gene therapeutic agents, conferring increased bioavailability and biostability of the therapeutic cargo. Significant advances in the engineering of MSNs structural and physiochemical characteristics have since seen the development of nanodevices with promising in vivo potential. In this review, current trends of multimodal MSNs being developed and their use in stimuli-responsive passive and active targeting in cancer therapy will be discussed, focusing on light, redox, pH, and temperature stimuli.

The fruition, commercialisation and clinical application combining nano-engineering, nanomedicine and material science for utilisation in drug delivery is becoming a reality. The successful integration of nanomaterial in nanotherapeutics requires their critical development to ensure physiological and biological compatibility. Mesoporous silica nanoparticles (MSNs) are attractive nanocarriers due to their biodegradable, biocompatible, and relative malleable porous frameworks that can be functionalized for enhanced targeting and delivery in a variety of disease models. The optimal formulation of an MSN with polyethylene glycol (2% and 5%) and chitosan was undertaken, to produce sterically stabilized, hydrophilic MSNs, capable of efficient loading and delivery of the hydrophobic anti-neoplastic drug, doxorubicin (DOX). The pH-sensitive release kinetics of DOX, together with the anticancer, apoptosis and cell-cycle activities of DOX-loaded MSNs in selected cancer cell lines were evaluated. MSNs of 36-60 nm in size, with a pore diameter of 9.8 nm, and a cumulative surface area of 710.36 m 2 /g were produced. The 2% pegylated MSN formulation (PCMSN) had the highest DOX loading capacity (0.98 mg dox /mg msn ), and a sustained release profile over 72 h. Pegylated-drug nanoconjugates were effective at a concentration range between 20-50 µg/mL, inducing apoptosis in cancer cells, and affirming their potential as effective drug delivery vehicles.Molecules 2020, 25, 742 2 of 22 MSNs possess a large active surface area which can be selectively polymerised or functionalised for stimuli-responsive purposes [11], tunable pore size and large pore volumes for the loading and controlled release of the cargo, and have shown favourable tolerance levels both in vitro and in vivo [12][13][14].MSNs are being extensively researched as theranostic devices for diseases, especially for cancer therapy [15]. Conventional cancer treatment options such as surgery, radiotherapy and chemotherapy [16], have not been fully effective, resulting in snowballing recurrence rates and depression in the quality of life [17,18]. Unpleasant side-effects are often linked to the anti-neoplastic drugs used, which act by inhibiting cellular mechanisms of DNA replication that are up-regulated in cancer cells. These cytostatic or cytotoxic compounds usually have low bioavailability and are thus administered at high dosages or for prolonged dosing intervals, leading to systemic side effects at non-specific sites [19,20].Doxorubicin (DOX) remains one of the most efficient anthracycline drugs available and is used in the treatment of diverse cancers, including breast, cervical, bone, gastric and leukaemia [21][22][23]. Despite its popularity, its low solubility [24][25][26], coupled with increased dosing frequencies [27][28][29] has resulted in many associated side effects, including cardiotoxicity [30][31][32], myelosuppression [33,34], induced vomiting with nausea [35,36], and alopecia [18,37]. Critical evaluation of these detrimental side-effects that become more...