Well-defined, reversible disulfide cross-linked micelles for on-demand paclitaxel delivery

Abstract

To minimize premature release of drugs from their carriers during circulation in the blood stream, we have recently developed reversible disulfide cross-linked micelles (DCMs) that can be triggered to release drug at the tumor site or in cancer cells. We designed and synthesized thiolated linear-dendritic polymers (telodendrimers) by introducing cysteines to the dendritic oligo-lysine backbone of our previously reported telodendrimers comprised of linear polyethylene glycol (PEG) and a dendritic cluster of cholic acids. Reversibly cross-linked micelles were then prepared by the oxidization of thiol groups to disulfide bond in the core of micelles after the self-assembly of thiolated telodendrimers. The DCMs were spherical with a uniform size of 28 nm, and were able to load paclitaxel (PTX) in the core with superior loading capacity up to 35.5% (w/w, drug/micelle). Cross-linking of the micelles within the core reduced their apparent critical micelle concentration and greatly enhanced their stability in non-reductive physiological conditions as well as severe micelle-disrupting conditions. The release of PTX from the DCMs was significantly slower than that from non-cross-linked micelles (NCMs), but can be gradually facilitated by increasing the concentration of reducing agent (glutathione) to an intracellular reductive level. The DCMs demonstrated a longer in vivo blood circulation time, less hemolytic activities, and superior toxicity profiles in nude mice, when compared to NCMs. DCMs were found to be able to preferentially accumulate at the tumor site in nude mice bearing SKOV-3 ovarian cancer xenograft. We also demonstrated that the disulfide cross-linked micellar formulation of PTX (PTX-DCMs) was more efficacious than both free drug and the non-cross-linked formulation of PTX at equivalent doses of PTX in the ovarian cancer xenograft mouse model. The anti-tumor effect of PTX-DCMs can be further enhanced by triggering the release of PTX on-demand by the administration of the FDA approved reducing agent, N-acetylcysteine, after PTX-DCMs have reached the tumor site.

Biodistribution and pharmacokinetics of a telodendrimer micellar paclitaxel nanoformulation in a mouse xenograft model of ovarian cancer

“…We recently reported on the development of disulfide or boronate-catechol cross-linked nanomicelles 23,24 that are much more stable than the non-crosslinked micelles reported here. The main advantage of crosslinked micelles is that premature drug release in the circulation can be minimized.…”

“…One explanation for this is that the current nanomicelle formulation is not stable in blood and that the nanomicelles disassemble partially and the loaded drug begins to release from the nanomicelles immediately after in vivo administration and diffusion into normal organs, resulting in a rapid decrease of 14 C-PTX in the circulation. 23,24 In contrast, the 125 I-telodendrimers, even if coming from dissociated nanomicelles, still remain in the blood circulation for a longer time, contributing to a much higher radioactive signal in the blood during the 24 hours post injection.…”

Discovery of specific targeting ligands as the biomarkers for colorectal cancer

“…Recently, Lam et al developed several novel nanocarriers for the delivery of paclitaxel (PTX) and other hydrophobic anticancer drugs [33,34]. Using a reversible polyethylene glycol (PEG)-based disulfide cross-linked micelle derivatized with cholic acid (PEG 5k -Cys 4-CA 8 telodendrimers), hydrophobic drugs were encapsulated in the micelle core, and triggered for release at the tumor site and inside the cancer cells with high reductive potential [23].…”

Nanoparticles Mediated Drug Delivery

“…It is mostly composed of polyamidoamines [15,16]. For example telodendrimers made of polyethylene glycol and dendritic cholic acid subunits [17,18].…”