Multimodal imaging probes and delivery systems for cancer nanomedicine

Nanoparticles have emerged as one of the most promising tools for addressing central challenges in cancer diagnostics and therapy. This thesis presents the design, surface functionalization, biocompatibility, intracellular interactions and applicability of nanoparticles as potential tools for cancer diagnosis and RNAi therapeutics. The thesis is divided into two parts; 1) cancer cell imaging and 2) siRNA delivery.
In part 1, studies were performed with inherently fluorescent carbon-based nanoparticles (nanodiamonds, NDs, and nanographene oxide, nGO) in order to evaluate their suitability for cancer cell imaging (in vivo and in vitro). A novel application of NDs in super resolution correlative light and electron microscopy is presented here, whereby NDs are used as a dual-purpose fluorescent and electron dense probes for correlative multi-modal microscopy. Further, the intracellular interactions of NDs are studied to understand the biocompatibility of nondegradable NDs and the reasons underlying the biocompatibility.
Moreover, this thesis elucidates the role of organic surface modifications for enhancing the optical properties of nanographene oxide (nGO) for in vivo imaging. When nGO was surface functionalized with the organic polymer PEG-PEI (polyethyleneimine – a polyethylene glycol co-polymer), and attached to the cancer cell affinity ligand FA (folic acid), its dispersibility, cellular internalization and quantum efficiency were improved compared to the non-modified nGO. The surface functionalized nGOs were further applied as optical markers for the non-invasive in vivo imaging of cancer cells in a model organism. The nGOs were found to be well suited for detecting cancer cells over the studied 1-week period.
In part 2, systems for the efficient delivery of therapeutic cargo to cancer cells were studied using a nanodiamond (ND) - silica (MSN) composite (ND@MSN) and mesoporous silica nanoparticles (MSN) with redox responsive linkers. ND@MSN, a novel composite material was synthesized by taking advantage of the properties of both the ND (photoluminescence) and the MSN (drug-delivery). The validation of ND@MSN for drug delivery was performed by surface functionalizing the composite particles with the co-polymer PEG-PEI and by loading the ND@MSN with a hydrophobic luminescent dye, which acted as a model drug. The intracellular delivery of a hydrophobic drugs is generally challenging, but the ND@MSN surface functionalized with co-polymers (Cop) demonstrated excellent efficiency for the intracellular delivery of the hydrophobic model drug. Other noteworthy features related to the use of ND@MSN-Cop were that no premature extracellular release of the dye was observed, that the endosomal escape and intracellular release of the cargo were achieved and that the subsequent tracking of the NDs in the cell was possible.
For the delivery of siRNAs into cancer cells, the MSN nanocarriers were synthesized, in attempt to overcome challenges associated with the in vivo delivery of siRNA. Hyperbranched PEI and redox-responsive intracellular triggerable bonds were thus incorporated into the developed MSN nanocarriers. The design of the MSN nanocarriers took into consideration important aspects of in vivo delivery, such as the high loading of siRNA, intracellular cleavable linkers, high cellular uptake, and a large pore size to host the siRNA molecules and to protect them from degradation. In the experimental set-up, the MSN nanocarriers demonstrated the sustained intracellular release of the siRNA (120h), while offering protection from enzymatic degradation. The gene knockdown efficiency was further evaluated using a transfection control siRNA. The MSN nanocarriers performed remarkably well and showed excellent transfection efficiency.