Rohan Bhavane

Mesoporous silicon particles as a multistage delivery system for imaging and therapeutic applications.

Many nanosized particulate systems are being developed as intravascular carriers to increase the levels of therapeutic agents delivered to targets, with the fewest side effects. The surface of these carriers is often functionalized with biological recognition molecules for specific, targeted delivery. However, there are a series of biological barriers in the body that prevent these carriers from localizing at their targets at sufficiently high therapeutic concentrations. Here we show a multistage delivery system that can carry, release over time and deliver two types of nanoparticles into primary endothelial cells. The multistage delivery system is based on biodegradable and biocompatible mesoporous silicon particles that have well-controlled shapes, sizes and pores. The use of this system is envisioned to open new avenues for avoiding biological barriers and delivering more than one therapeutic agent to the target at a time, in a time-controlled fashion.

Sustained Small Interfering RNA Delivery by Mesoporous Silicon Particles

RNA interference (RNAi) is a powerful approach for silencing genes associated with a variety of pathologic conditions; however, in vivo RNAi delivery has remained a major challenge due to lack of safe, efficient, and sustained systemic delivery. Here, we report on a novel approach to overcome these limitations using a multistage vector composed of mesoporous silicon particles (stage 1 microparticles, S1MP) loaded with neutral nanoliposomes (dioleoyl phosphatidylcholine, DOPC) containing small interfering RNA (siRNA) targeted against the EphA2 oncoprotein, which is overexpressed in most cancers, including ovarian. Our delivery methods resulted in sustained EphA2 gene silencing for at least 3 weeks in two independent orthotopic mouse models of ovarian cancer following a single i.v. administration of S1MP loaded with EphA2-siRNA-DOPC. Furthermore, a single administration of S1MP loaded with-EphA2-siRNA-DOPC substantially reduced tumor burden, angiogenesis, and cell proliferation compared with a noncoding control siRNA alone (SKOV3ip1, 54%; HeyA8, 57%), with no significant changes in serum chemistries or in proinflammatory cytokines. In summary, we have provided the first in vivo therapeutic validation of a novel, multistage siRNA delivery system for sustained gene silencing with broad applicability to pathologies beyond ovarian neoplasms.

The effect of shape on the margination dynamics of non-neutrally buoyant particles in two-dimensional shear flows

The margination dynamics of microparticles with different shapes has been analyzed within a laminar flow mimicking the hydrodynamic conditions in the microcirculation. Silica spherical particles, quasi-hemispherical and discoidal silicon particles have been perfused in a parallel plate flow chamber. The effect of the shape and density on their margination propensity has been investigated at different physiologically relevant shear rates S. Simple scaling laws have been derived showing that the number n of marginating particles scales as S(-0.63) for the spheres; S(-0.85) for discoidal and S(-1) for quasi-hemispherical particles, regardless of their density and size. Within the range considered for the shear rate, discoidal particles marginate in a larger number compared to quasi-hemispherical and spherical particles. These results may be of interest in drug delivery and bio-imaging applications, where particles are expected to drift towards and interact with the walls of the blood vessels.

The association of silicon microparticles with endothelial cells in drug delivery to the vasculature

Endothelial targeting is an approach evolving for drug delivery to the vasculature of pathological lesions. Nano-porous silicon-based multi-functional particles are of particular interest, since they can be manufactured in essentially any size and shape, employing methods of photolithography, to optimize their ability to localize on target endothelia. In this study we tested the impact of surface charge, serum opsonization, and inflammation on the ability of vascular endothelial cells to associate with nano-porous silicon microparticles. Vascular endothelial cells were capable of rapidly internalizing both positive and negative silicon microparticles by an actin-dependent mechanism involving both phagocytosis and macropinocytosis. However, following serum opsonization, internalization was selective for APTES (originally positive) modified microparticles, despite the finding that all opsonized microparticles had a net negative charge. Conversely, macrophages displayed a preference for internalization of serum opsonized oxidized (originally negative) microparticles, supporting the choice of positive microparticles for endothelial targeting. The internalization of opsonized microparticles by endothelial cells was further enhanced by the presence of inflammatory cytokines. These findings suggest that it may be possible to bioengineer silicon microparticles to favor opsonization with proteins that enhance uptake by endothelial cells, without a concurrent enhanced uptake by macrophages.

Tailoring the degradation kinetics of mesoporous silicon structures through PEGylation

Injectable and implantable porosified silicon (pSi) carriers and devices for prolonged and controlled delivery of biotherapeutics offer great promise for treatment of various chronic ailments and acute conditions. Polyethylene glycols (PEGs) are important surface modifiers currently used in clinic mostly to avoid uptake of particulates by reticulo-endothelial system (RES). In this work we show for the first time that covalent attachment of PEGs to the pSi surface can be used as a means to tune degradation kinetics of silicon structures. Seven PEGs with varying molecular weights (245, 333, 509, 686, 1214, 3400, and 5000 Da) were employed and the degradation of PEGylated pSi hemispherical microparticles in simulated physiological conditions was monitored by means of ICP-AES, SEM, and fluorimetry. Biocompatibility of the systems with human macrophages in vitro was also evaluated. The results clearly indicate that controlled PEGylation of silicon microparticles can offer a sensitive tool to finely tune their degradation kinetics and that the systems do not induce release of proinflammatory cytokines IL-6 and IL-8 in THP1 human macrophages.

In vivo evaluation of safety of nanoporous silicon carriers following single and multiple dose intravenous administrations in mice

Porous silicon (pSi) is being extensively studied as an emerging material for use in biomedical applications, including drug delivery, based on the biodegradability and versatile chemical and biophysical properties. We have recently introduced multistage nanoporous silicon microparticles (S1MP) designed as a cargo for nanocarrier drug delivery to enable the loaded therapeutics and diagnostics to sequentially overcome the biological barriers in order to reach their target. In this first report on biocompatibility of intravenously administered pSi structures, we examined the tolerability of negatively (-32.5±3.1mV) and positively (8.7±2.5mV) charged S1MP in acute single dose (10(7), 10(8), 5×10(8) S1MP/animal) and subchronic multiple dose (10(8) S1MP/animal/week for 4 weeks) administration schedules. Our data demonstrate that S1MP did not change plasma levels of renal (BUN and creatinine) and hepatic (LDH) biomarkers as well as 23 plasma cytokines. LDH plasma levels of 145.2±23.6, 115.4±29.1 vs. 127.0±10.4; and 155.8±38.4, 135.5±52.3 vs. 178.4±74.6 were detected in mice treated with 10(8) negatively charged S1MP, 10(8) positively charged S1MP vs. saline control in single and multiple dose schedules, respectively. The S1MPs did not alter LDH levels in liver and spleen, nor lead to infiltration of leukocytes into the liver, spleen, kidney, lung, brain, heart, and thyroid. Collectively, these data provide evidence of a safe intravenous administration of S1MPs as a drug delivery carrier.

Dual-Energy Computed Tomography Imaging of Atherosclerotic Plaques in a Mouse Model Using a Liposomal-Iodine Nanoparticle Contrast Agent

Background— The accumulation of macrophages in inflamed atherosclerotic plaques has long been recognized. In an attempt to develop an imaging agent for detection of vulnerable plaques, we evaluated the feasibility of a liposomal-iodine nanoparticle contrast agent for computed tomography imaging of macrophage-rich atherosclerotic plaques in a mouse model. Methods and Results— Liposomal-iodine formulations varying in particle size and polyethylene glycol coating were fabricated and shown to stably encapsulate the iodine compound. In vitro uptake studies using optical and computed tomography imaging in the RAW 264.7 macrophage cell line identified the formulation that promoted maximal uptake. Dual-energy computed tomography imaging using this formulation in apolipoprotein E–deficient (ApoE−/−) mice (n=8) and control C57BL/6 mice (n=6) followed by spectral decomposition of the dual-energy images enabled imaging of the liposomes localized in the plaque. Imaging cytometry confirmed the presence of liposomes in the plaque and their colocalization with a small fraction (≈2%) of the macrophages in the plaque. Conclusions— The results demonstrate the feasibility of imaging macrophage-rich atherosclerotic plaques using a liposomal-iodine nanoparticle contrast agent and dual-energy computed tomography.

A multistage nanodelivery system for therapeutic applications and medical imaging: in vivo biodistribution and efficacy study in a murine orthotopic breast cancer model.

Abstract #2160 The ability to deliver therapeutic compounds specifically to diseased sites is crucial for effectively treating human illnesses. Nanotechnology is emerging as a tool for resolving challenges in the delivery of poorly administrable drugs by transforming them into nanometer-sized particles (nanotherapeutics). The progress thus far gave rise to a large number of nanotherapeutics, but the accomplishment of the original objective, which is to increase drug concentration at target sites, has not been fully realized. A series of biological barriers pose as insurmountable obstacles which limit or completely abolish the ability to selectively deliver a therapeutic agent. We hypothesized that a multi-stage system for systemic delivery (MSDS) could be designed to interact with and successfully overcome sequential biological barriers. We developed a MSDS using biodegradable, biocompatible silicon particles optimally sized and shaped to travel into the blood flow, avoid RES, marginate and adhere to tumor vasculature. The first stage carriers (FSCs) contain nanopores of specific size that can load, carry, release over time, and deliver multiple types of second stage nanoparticles (SSNs). The nanoparticles can be optimized to reach, through vessels fenestrations, the tumor environment and finally release their therapeutic payload into target cells.
 The ease in chemically modifying the silicon surface permits the attachment of fluorescent and radiolabeled imaging molecules to the FSCs. Fluorescent and magnetic SSNs can be loaded into the pores of the FSCs. Once assembled, the resulting MSDS can be imaged using different in vivo imaging modalities from its administration to its final localization into the body. We further modified our FSCs with PEG molecules to increase their circulation time and with antibodies directed against the VEGFR2 membrane protein to increase the localization of the MSDS in tumor associated vessels. We monitored the biodistribution of all MSDSs and characterized their biocompatibility in the different tissues. Finally, we loaded the pores of the FSCs with a lipidic nanoformulation of the potent anti cancer drug doxorubicin (dox-liposomes and dox-micelles) and followed the efficacy of this treatment. Taken together, these studies provide first time evidence that silicon nanoporous particles can be used as effective carriers for the simultaneous delivery of different nanotherapeutics in vivo. Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 2160.