Block Copolymer Based Magnetic Nanoclusters for Cancer-Theranostics: Synthesis, Characterization and In Vitro Evaluation

“There is plenty of room at the bottom”. In this visionary lecture in 1959 Prof. Richard Feynman spoke of the interesting ramifications of working with matter at the atomic scale. Since then, scientists have worked relentlessly towards realizing his vision. The influence of nanobiotechnology on material science and polymer chemistry has given rise to a new field called ‘theranostics’, combining drug delivery and diagnostics within the same nanostructures, thereby enabling simultaneous diagnosis, targeted drug delivery and continued therapy monitoring. Iron oxide nanoparticles (MNPs) are one such class of MRI contrast agents that can be converted into theranostic nanomedicines for cancer therapy. However, development of a stable theranostic contrast system comprising of MNPs is complex and requires a careful balance between the therapeutic diagnostic components. We explored the potential of biodegradable hydrophilic block ionomers such as anionic poly (glutamic acid-b-ethylene glycol) and cationic poly (l-lysine-b-ethylene glycol) in formulating stable magnetic nanoclusters (MNCs). These MNCs were extensively characterized for their composition, colloidal stability and factors influencing their MRI capability. Extensive in vitro studies revealed that the anionic cisplatin-loaded MNCs showed minimal non-specific uptake, a highly preferred feature for targeted cancer therapy. Luteinizing hormone releasing hormone receptor (LHRHr) targeting significantly enhanced the uptake of these formulations in LHRHr-positive ovarian cancer cells. LHRHr targeting also helped improve the theranostic efficacy in cisplatin resistant ovarian cancer cells. One the other hand, cationic MNCs were used to demonstrate the potential of MNCs to function as stimuli-responsive theranostic systems capable of releasing the payload in the acidic milieu breast and ovarian cancer cells. These cationic MNCs also exhibited significantly enhanced T2-weighted MRI contrasts at much lower concentrations than the anionic counterparts. Finally, we successfully evaluated the feasibility of kinetically controlled flash nanoprecipitation technique using multi-inlet vortex mixer (MIVM) to formulate well-defined MNCs from non-ionic amphiphilic Pluronic tri-block copolymers. In comparison to self-assembly techniques, flash nanoprecipitation resulted in significant reduction in polydispersity. It was observed that the hydrophobic block-length of the copolymer dictates the extent of encapsulation hydrophobic therapeutic agents along with the MNPs. exhibited the potential to function as both T1 and T2 contrast agents. In summary, looking at the bigger picture, the work presented here emphasizes on the importance of product development in establishing a critical balance between the therapeutic and imaging functionalities when designing an efficient targeted theranostic nanosystems

Remote Actuation of Magnetic Nanoparticles For Cancer Cell Selective Treatment Through Cytoskeletal Disruption

Motion of micron and sub-micron size magnetic particles in alternating magnetic fields can activate mechanosensitive cellular functions or physically destruct cancer cells. However, such effects are usually observed with relatively large magnetic particles (>250 nm) that would be difficult if at all possible to deliver to remote sites in the body to treat disease. Here we show a completely new mechanism of selective toxicity of superparamagnetic nanoparticles (SMNP) of 7 to 8 nm in diameter to cancer cells. These particles are coated by block copolymers, which facilitates their entry into the cells and clustering in the lysosomes, where they are then magneto-mechanically actuated by remotely applied alternating current (AC) magnetic fields of very low frequency (50 Hz). Such fields and treatments are safe for surrounding tissues but produce cytoskeletal disruption and subsequent death of cancer cells while leaving healthy cells intact

Formulation design facilitates magnetic nanoparticle delivery to diseased cells and tissues

Magnetic nanoparticles (MNPs) accumulate at disease sites with the aid of magnetic fields; biodegradable MNPs can be designed to facilitate drug delivery, influence disease diagnostics, facilitate tissue regeneration and permit protein purification. Because of their limited toxicity, MNPs are widely used in theranostics, simultaneously facilitating diagnostics and therapeutics. To realize therapeutic end points, iron oxide nanoparticle cores (5–30 nm) are encapsulated in a biocompatible polymer shell with drug cargos. Although limited, the toxic potential of MNPs parallels magnetite composition, along with shape, size and surface chemistry. Clearance is hastened by the reticuloendothelial system. To surmount translational barriers, the crystal structure, particle surface and magnetic properties of MNPs need to be optimized. With this in mind, we provide a comprehensive evaluation of advancements in MNP synthesis, functionalization and design, with an eye towards bench-to-bedside translation

Luteinizing Hormone Releasing Hormone-Targeted Cisplatin-Loaded Magnetite Nanoclusters for Simultaneous MR Imaging and Chemotherapy of Ovarian Cancer

Given the superior soft tissue contrasts obtained by MRI and the long residence times of magnetic nanoparticles (MNPs) in soft tissues, MNP-based theranostic systems are being developed for simultaneous imaging and treatment. However, development of such theranostic nanoformulations presents significant challenges of balancing the therapeutic and diagnostic functionalities in order to achieve optimum effect from both. Here we developed a simple theranostic nanoformulation based on magnetic nanoclusters (MNCs) stabilized by a bisphosphonate-modified poly­(glutamic acid)-<i>b</i>-(ethylene glycol) block copolymer and complexed with cisplatin. The MNCs were decorated with luteinizing hormone releasing hormone (LHRH) to target LHRH receptors (LHRHr) overexpressed in ovarian cancer cells. The targeted MNCs significantly improved the uptake of the drug in cancer cells and decreased its IC₅₀ compared to the nontargeted formulations. Also, the enhanced LHRHr-mediated uptake of the targeted MNCs resulted in enhancement in the T₂-weighted negative contrast in cellular phantom gels. Taken together, the LHRH-conjugated MNCs show good potential as ovarian cancer theranostics