While the heightened tumor accumulation of systemically administered nanomedicines relative to conventional chemotherapeutic agents has been well established, corresponding improvements in therapeutic efficacy have often been incommensurate. This observation may be attributed to the limited exposure of cancer cells to therapy due to the heterogeneous intratumoral distribution and poor interstitial penetration of nanoparticle-based drug delivery systems. In the present work, the spatio-temporal distribution of block copolymer micelles (BCMs) of different sizes was evaluated in multicellular tumor spheroids (MCTS) and tumor xenografts originating from human cervical (HeLa) and colon (HT29) cancer cells using image-based, computational techniques. Micelle penetration was found to depend on nanoparticle size, time as well as tumor and spheroid cell line. Moreover, spheroids demonstrated the capacity to predict relative trends in nanoparticle interstitial transport in tumor xenografts. Overall, techniques are presented for the assessment of nanoparticle distribution in spheroids and xenografts and used to evaluate the influence of micelle size and cell-line specific tissue properties on micelle interstitial penetration.
While 3-D tissue models have received increasing attention over the past several decades in the development of traditional anti-cancer therapies, their potential application for the evaluation of advanced drug delivery systems such as nanomedicines has been largely overlooked. In particular, new insight into drug resistance associated with the 3-D tumor microenvironment has called into question the validity of 2-D models for prediction of in vivo anti-tumor activity. In this work, a series of complementary assays was established for evaluating the in vitro efficacy of docetaxel (DTX) -loaded block copolymer micelles (BCM+DTX) and Taxotere® in 3-D multicellular tumor spheroid (MCTS) cultures. Spheroids were found to be significantly more resistant to treatment than monolayer cultures in a cell line dependent manner. Limitations in treatment efficacy were attributed to mechanisms of resistance associated with properties of the spheroid microenvironment. DTX-loaded micelles demonstrated greater therapeutic effect in both monolayer and spheroid cultures in comparison to Taxotere®. Overall, this work demonstrates the use of spheroids as a viable platform for the evaluation of nanomedicines in conditions which more closely reflect the in vivo tumor microenvironment relative to traditional monolayer cultures. By adaptation of traditional cell-based assays, spheroids have the potential to serve as intermediaries between traditional in vitro and in vivo models for high-throughput assessment of therapeutic candidates.
The current study investigates the potential of estrone-3-sulphate (E3S) as a ligand for targeting Organic Anion Transporting Polypeptides (OATP), a family of membrane associated uptake transporters, for detection and diagnosis of hormone dependent breast cancers. E3S, an OATP substrate, is a predominant source of tumour estradiol in post-menopausal patients. To assess the potential of E3S as a ligand, distribution of exogenous E3S was determined at the whole body, tumour and cellular levels in murine models of hormone-dependent (MCF-7) and independent (MDA-MB-231) breast cancers. The highest levels of tumour uptake were observed at 6 h post injection (p.i) with significant difference (p?=?0.04) between the level in MCF-7 (13.9±3.1%ID/g) and MDA-MB-231 (10.4±1.1%ID/g) (%ID/g: percentage of the total injected dose per gram tissue). The highest tumour-to-blood ratios (MCF-7?7.4±1.2; MDA-MB-231?9.1±2.1) were observed at 48 p.i., and highest tumour-to-muscle ratios (MCF-7?10.7±1.5; MDA-MB-231?3.8±0.7) were observed at 6 h p.i. Analogous to total tumour uptake, ex vivo tumour cell uptake at 2 h p.i. was 6 fold higher in MCF-7 in comparison to MDA-MB-231 tumour cells. Blocking studies, conducted by pre-administration of 100-fold excess E3S, resulted in significantly lower (MCF-7: p?=?0.01; MDA-MB-231: p?=?0.02) tumour uptake in both xenograft models, suggesting the involvement of an active carrier-mediated process. The expression of OATP1A2 was detected in tumour sections from both xenografts, with significantly higher expression (p?=?0.002) in the MCF-7 xenografts. Overall, the higher tumour uptake and tumour-to-muscle ratio, alongside the higher expression of OATP1A2, in the MCF-7 xenograft model suggests the potential of E3S to serve as a novel ligand for targeting hormone dependent breast cancers.
Poly(2-hydroxyethyl methacrylate) (pHEMA) hydrogels loaded with core cross-linked PEG-b-PCL micelles with different morphologies (spherical and rod-like) were prepared and evaluated for use as drug-eluting soft contact lenses. The relationship between the composition of micelle-loaded pHEMA hydrogels and properties such as transparency and swelling were determined. The incorporation of core cross-linked micelles into pHEMA hydrogels led to the formation of different internal nanostructures which were dependent on the amount and morphology of the micelles added. 7-Hydroxy-9H-(1,3-dichloro-9,9-dimethylacridin-2-one) (DDAO), a hydrophobic fluorescent dye, was loaded into the micelles prior to their incorporation within the hydrogel matrix. The in vitro release of DDAO demonstrated the potential of the micelles/pHEMA hydrogels to provide controlled drug delivery for at least 14 days. This study demonstrates the feasibility of both chemical and physical incorporation of block co-polymer micelles within pHEMA hydrogels as a means to achieve sustained release of drugs for potential application in ophthalmic therapies.
While silicone elastomers generally have excellent biomaterials properties, their hydrophobicity can elicit undesired local biological responses through adsorption and denaturation of proteins. Surface-bound poly(ethylene glycol) (PEG) can ameliorate the situation by preventing contact between the external biology and the silicone elastomer. It is further possible to manipulate the biocompatibility of the surface by linking peptides, proteins or other biological entities to the PEG. Previous synthetic approaches to PEG-protected surfaces are compromised by issues of reproducibility. We describe two rapid and efficient approaches to silicone surface modification by PEG-linked adhesion peptides that overcome this problem: SiH groups are introduced throughout a silicone elastomer during elastomer synthesis or only at the surface after cure; then, in either case, protein-repellent PEG brushes at the surface are introduced by hydrosilylation to give surfaces that can be stored for extensive periods of time without degradation. Activation of the free alcohol with an NSC group followed by immediate conjugation to relevant biological molecules occurs in high yields, as shown for RGDS and GYRGDS. High surface grafting density of the peptides was demonstrated using radiolabeling techniques. Biological activity was demonstrated by a 5-fold increase in cell adhesion on the peptide-modified surfaces when compared to unmodified PDMS control surfaces.
Docetaxel (DTX), a chemotherapeutic agent, was coupled to the hydrophobic block of poly(ethylene glycol)-b-poly(epsilon-caprolactone) (PEG-b-PCL) copolymers synthesized by metal free ring-opening polymerization. Synthesis of the copolymers and the copolymer-drug conjugate (PEG-b-PCL-DTX) were confirmed by (1)H NMR and GPC analyses. The PEG-b-PCL-DTX conjugates had a approximately 1:3 drug/copolymer ratio (w/w) and a low critical micelle concentration in aqueous solution (14 mg/L). Encapsulation of DTX in PEG-b-PCL-DTX micelles resulted in an 1840-fold increase in the aqueous solubility of the drug. Release of physically encapsulated DTX from PEG-b-PCL-DTX micelles was slower than drug release from PEG-b-PCL micelles due to the improved compatibility between DTX and the micelle core. Core-conjugated DTX was released over the course of one week indicating that PEG-b-PCL-DTX micelles have the capacity for sustained drug release in the absence of physically encapsulated drug. Importantly, conjugation of DTX to the core-forming block had a profound effect on the morphology of the copolymer aggregates.
The use of block copolymer micelles (BCMs) for the targeted delivery of chemotherapeutics has proven to be a promising approach for improving the therapeutic efficacy of pharmaceutical cancer therapy. Acceleration of the translation of BCM-based drug formulations from the fundamental stages of pre-clinical development to clinical use requires a greater understanding of the transport mechanisms that influence the fate of these nano-carrier systems at the whole body, tissue, and cellular levels. New information emerging regarding the intratumoral distribution, and tumor penetration of BCMs and other nanosystems in vivo, by non-invasive image-based assessment, has the potential to revolutionize our understanding and current approach to drug delivery in this field. This review aims to highlight these and other important advancements as well as to bring attention to the many critical questions that remain to be addressed regarding the fate of BCM-based drug formulations in vivo.
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