Development of Upconversion and Mesoporous Silica based Nanoparticle Systems for Therapeutic, Bioimaging and Bio-sensing Applications

Abstract

The advent of nanomedicine has been one of the most significant developments impacting the applied fields of physics, chemistry and life sciences, that took place in past few decades. Still being in early stage at present, nanomedicine is expected to have a revolutionary effect on health care in future. Research in nanomedicine covers wider areas, such as therapeutics (drug delivery, multifunctional therapeutics, vaccine development), diagnosis (point-of-care nanoplatforms, bioanalytics, bioimaging) and biomaterials (biological, non-biological, hybrid or biomimetic materials, etc.). Although nanomedicine offers some key advantages over the conventional medicine, there are certain challenges yet to be addressed to enhance the efficacy of nanomedicine. Current formulations of nanomedicine still lacks target specificity and therefore confining the therapeutic effect in the affected area is a major problem. A probable solution is to turn on and control the therapeutic action of nanomedicine within a particular target zone by the action of an external stimulus acting as a remote trigger, locally. In this context, herein, we have developed upconversion nanoparticles (UCNPs) and mesoporous silica (MS) based nanoparticles systems to demonstrate an enhancement of therapeutic efficacy using near infra-red (NIR) laser (980 nm), acting as an external stimulus to turn on and regulate the therapeutic effect in a non-invasive manner in vitro. In this dissertation, we have attempted to validate the enhanced therapeutic efficacy of our developed nanoformulations for distally located tumours such as colorectal cancer (CRC). Using the similar formulations, we have also integrated three different therapeutic modalities within a single nanoplatform that can be applied to treat cancers, which show resistance to a particular therapeutic modality due to mutative adaptations, often known as ‘multi-drug resistance’ (MDR). Also, these nanoplatforms have been explored for bioanalytical applications. The first chapter of this dissertation talks about general introduction of nanomedicine and justifies the purpose of the research described here with a brief background information about UCNP and mesoporous silica nanoparticles (MSN).
The second chapter reported here involved tuning of the upconversion emission behaviour to generate a sharp and diverse emission profile that can effectively excite multiple photoactive agents, simulteneously. In this project the intense emission from UCNP was utilized to get an enhanced therapeutic output in the form of a non-invasive photodynamic therapy (PDT). The excitation of multiple photosensitizers by the upconversion core through FRET served the basis of enhanced reactive oxygen species (ROS) generation, which induced cancer cell death. This work successfully demonstrated that the system in report would be most suitable than the conventionally reported photodynamic platforms, where multiple triggers for enhanced therapeutic effects were desired. Also, the intense visible emission profile enabled the bioimaging of those particles incorporated within animal cells using a cost-efficient customised set-up in absennce of any sophisticated detector, such as photomultiplier tube (PMT). The enhanced PDT effects by photoactivation of two chemically different photosensitizers (PSs), triggered by the NIR upconversion emmisions from white emitting UCNP along with the facile upconversion imaging from the cells formed the main novel embodiments of this work.(ChemNanoMat, 2018, 4, 583-595).
In the work presented as the third chapter, mesoporous silica nanoparticles capped with guar gum (GG) polymer was exploited for colon specific delivery of anticancer drug by utilizing a natural bioprocess of enzymatic degradation acting as the trigger for the delivery mechanism. This work, for the first time, demonstrated the use of a rigid framework of mesoporous silica nanoparticles along with guar gum polymer to achieve zero premature release behaviour at various pH conditions, encountered in the GI tract. This work provided an interesting insight to design an oral formulation towards colorectal cancer therapy with smart and controlled release behaviour. The results successfully established that the formulation was capable of arresting the cells in S-phase, thus, leading to the accumulation of the cells in the particular phase, typically found as the result of impaired DNA replication mechanism, ultimately causing the death of the cancerous cells. The present study presented first report on mesoporous silica (MSN) based colon targeted delivery for possible oral application. (Colloids Surf. B: Biointerfaces., 2017, 150, 352-361)
Furthermore, in the next work presented as the fourth chapter, application of upconversion based therapeutic platform was manipulated to achieve dual modality for therapeutic effects, with an integrated approach of colon-targeted drug delivery and photodynamic therapy. Herein, the UCNPs were engineered to get a higher intensity emission output, using the core-shell based UCNP composition (CSU). Next, a photosensitizer (Rose Bengal) was chemically conjugated to the CSU followed by encapsulation using mesoporous silica (MS) layer. Chemotherapeutic drug 5FU was loaded inside MS layer through GG capping. The work in discussion was a first time demonstration of the novel nanoplatform fabrication strategy to enhance the therapeutic output by combining the enzyme triggered colon targeted delivery of therapeutic molecules with photodynamic therapy triggered by NIR laser. The nanoplatform was also employed for bioimaging using the customised setup designed in the previous work discussed above. For the first time, a bimodal therpeutic nanoplatform integrating enzyme triggered delivery of anticancer drug along with NIR triggered PDT with intended administration through oral route was reported; thus, forming the main novelty of this work. (Manuscript accepted in Nanotechnology, IOPScience, 2019).
In the fifth chapter, an attempt was made to develop a multifunctional theranostic nanoplatform with triple therapeutic modalities (i.e., photodynamic therapy, chemotherapy and photothermal therapy) integrated in a single nanoplatform that can be triggered by single NIR wavelength. Herein, through a rational design, a novel multifunctional nanoplatform was developed to demonstrate synergistically enhanced therapeutic output even at low NIR power and administration dosage. The engineered upconversion nanocrystals showed a strong PL emission in a diverse wavelength range that allowed the successful incorporation of hyperthermic agent with photodynamic and on-demand chemotherapy. The as-fabricated system is the first time demonstration of an efficient integration of several therapeutic modalities via well-defined and precisely controlled mechanism wiithin a single nanoplatform activated by a single NIR wavelength as a trigger. This strategy would provide an alternative route to specifically treat those types of carcinomas that show resistance towards a certain therapeutic routes. The efficacy of the system was assessed in vitro on cancerous cell lines. Apart from the multiple synergistic therapeutic effect, the core-shell UCNPs demonstrated an excellent upconversion luminiscence (UCL) imaging characteristics, thus realizing the goal of developing an efficient multimodal therapy with image-guided approach. The main novel embodiment of this work reported an NIR responsive theranostic nanoplatform with precisely controlled triple therapeutic modalities, i.e. PDT, chemotherapy and PTT, integrated in a single nanoplatform. The multimodality was achieved by a single NIR trigger by synchronous activation of incorporated multiple photoactive agents. (Manuscript submitted in Journal of Physical Chemistry B, ACS, 2019).
For bio-sensing application, a simple, sensitive, fluorescence-based assay for dopamine (DA) detection was developed in the sixth chapter using highly photoluminescent NIR activated blue-emitting core-shell upconversion (BCSU) nanoparticles. A MS layer was used as a shell to facilitate the adsorption of the analyte. The detection mechanism has been proved to be mediated by FRET based phenomenon. The detection limit for DA was calculated to be as low as 0.63 nM. The applicability of the nanoplatform for pH sensing was demonstrated fluorometrically. This work is the first demonstration of NIR-upconversion based DA and pH sensing using core-active shell UCNP and MS-based functionality in a nanoprobe. (Manuscript accepted in ChemistrySelect, Wiley, 2019)
In the last chapter, a general conclusion alongwith the future scope of the research has been presented.