A Polymer Prodrug Strategy to Switch from Intravenous to Subcutaneous Cancer Therapy for Irritant/Vesicant Drugs.

Chemotherapy is almost exclusively administered via the intravenous (IV) route, which has serious limitations (e.g., patient discomfort, long hospital stays, need for trained staff, high cost, catheter failures, infections). Therefore, the development of effective and less costly chemotherapy that is more comfortable for the patient would revolutionize cancer therapy. While subcutaneous (SC) administration has the potential to meet these criteria, it is extremely restrictive as it cannot be applied to most anticancer drugs, such as irritant or vesicant ones, for local toxicity reasons. Herein, we report a facile, general, and scalable approach for the SC administration of anticancer drugs through the design of well-defined hydrophilic polymer prodrugs. This was applied to the anticancer drug paclitaxel (Ptx) as a worst-case scenario due to its high hydrophobicity and vesicant properties (two factors promoting necrosis at the injection site). After a preliminary screening of well-established polymers used in nanomedicine, polyacrylamide (PAAm) was chosen as a hydrophilic polymer owing to its greater physicochemical, pharmacokinetic, and tumor accumulation properties. A small library of Ptx-based polymer prodrugs was designed by adjusting the nature of the linker (ester, diglycolate, and carbonate) and then evaluated in terms of rheological/viscosity properties in aqueous solutions, drug release kinetics in PBS and in murine plasma, cytotoxicity on two different cancer cell lines, acute local and systemic toxicity, pharmacokinetics and biodistribution, and finally their anticancer efficacy. We demonstrated that Ptx-PAAm polymer prodrugs could be safely injected subcutaneously without inducing local toxicity while outperforming Taxol, the commercial formulation of Ptx, thus opening the door to the safe transposition from IV to SC chemotherapy.

The crucial role of macromolecular engineering, drug encapsulation and dilution on the thermoresponsiveness of UCST diblock copolymer nanoparticles used for hyperthermia.

Poly(acrylamide-co-acrylonitrile) (P(AAm-co-AN)), an upper critical solution temperature (UCST)-type copolymer in water, was synthesized by reversible addition fragmentation chain transfer (RAFT) copolymerization and used as a macro-RAFT agent for the polymerization of oligo(ethylene glycol) methyl ether methacrylate (OEGMA) to yield amphiphilic diblock P(AAm-co-AN)-b-POEGMA copolymer. A series of copolymers with different AN content was obtained allowing to finely tune the UCST behavior (cloud point (Tt-UCST) from 35 to 78 °C). Addition of the POEGMA block did not modify the Tt-UCST regardless its Mn but provided a lower critical solution temperature behavior at high temperature. Nanoparticles were then formulated by the nanoprecipitation technique revealing that copolymers with higher Tt-UCST yield smaller, better-defined nanoparticles. Eventually, doxorubicin (Dox) was encapsulated into nanoparticles made from the copolymer having a Tt-UCST close to mild hyperthermia (~43 °C). Surprisingly, Dox encapsulation increased Tt-UCST and gave smaller nanoparticles as opposed to their unloaded counterparts. The dilution of the suspension also led to a decrease of Tt-UCST. No obvious hyperthermia effect was observed on the cytotoxicity of Dox-loaded nanoparticles. Our study highlighted the influence of macromolecular engineering, drug encapsulation and nanoparticle dilution on UCST behavior, important features often overlooked despite their crucial impact in the development of thermosensitive nanoscale drug delivery systems.

Thermoresponsive polymer nanocarriers for biomedical applications.

Polymer nanocarriers allow drug encapsulation leading to fragile molecule protection from early degradation/metabolization, increased solubility of poorly soluble drugs and improved plasmatic half-life. However, efficiently controlling the drug release from nanocarriers is still challenging. Thermoresponsive polymers exhibiting either a lower critical solution temperature (LCST) or an upper critical solution temperature (UCST) in aqueous medium may be the key to build spatially and temporally controlled drug delivery systems. In this review, we provide an overview of LCST and UCST polymers used as building blocks for thermoresponsive nanocarriers for biomedical applications. Recent nanocarriers based on thermoresponsive polymer exhibiting unprecedented features useful for biomedical applications are also discussed. While LCST nanocarriers have been studied for over two decades, UCST nanocarriers have recently emerged and already show great potential for effective thermoresponsive drug release.

Ultrasound-induced mild hyperthermia improves the anticancer efficacy of both Taxol® and paclitaxel-loaded nanocapsules.

We study the influence of ultrasound on paclitaxel-loaded nanocapsules in vitro and in vivo. These nanocapsules possess a shell of poly(dl-lactide-co-glycolide)-poly(ethylene glycol) (PLGA-PEG) and a liquid core of perfluorooctyl bromide (PFOB). In vitro experiments show that mechanical effects such as cavitation are negligible for nanocapsules due to their small size and thick and rigid shell. As the mechanical effects were unable to increase paclitaxel delivery, we focused on the thermal effects of ultrasound in the in vivo studies. A focused ultrasound sequence was therefore optimized in vivo under magnetic resonance imaging guidance to obtain localized mild hyperthermia with high acoustic pressure. Ultrasound-induced mild hyperthermia (41-43°C) was then tested in vivo in a subcutaneous CT-26 colon cancer murine model. As hyperthermia is applied, an inhibition of tumor growth for both paclitaxel-loaded nanocapsules and the commercial formulation of paclitaxel, namely Taxol® have been observed (p<0.05). Ultrasound-induced mild hyperthermia at high acoustic pressure appears as an interesting strategy to enhance cytotoxic efficacy locally.

Paclitaxel-loaded PEGylated nanocapsules of perfluorooctyl bromide as theranostic agents.

We optimize the encapsulation of paclitaxel (PTX) into nanocapsules made of a shell of poly(lactide-co-glycolide)-polyethylene glycol and a core of perfluorooctyl bromide (PFOB) to serve as theranostic agents. Two main challenges were met: keeping the imaging moiety (PFOB) encapsulated while loading the polymer shell with a hydrophobic drug very prone to crystallization. Encapsulation is performed by a modified emulsion-evaporation method leading to 120nm diameter nanocapsules with a drug loading compatible with tumor treatment. The optimized formulation tested in vitro on CT-26 colon cancer cells yields a similar IC50 as the generic Taxol® formulation. In vivo, 19F-MRI shows that PTX encapsulation does not modify the ability of nanocapsules to accumulate passively in CT-26 tumors in mice by the enhanced permeation and retention (EPR) effect. This accumulation leads to a promising and statistically significant twofold reduction in tumor growth as compared with negative control and generic Taxol® group. Altogether these results advocate for an interesting potential of these paclitaxel-loaded theranostic agents.

Ultrasound-triggered drug delivery for cancer treatment using drug delivery systems: From theoretical considerations to practical applications.

Ultrasound-triggered drug delivery is now becoming a mature technology with first patients enrolling in clinical trials. Having a clear overview of the field is complicated as it mixes ultrasound physics and biological effects, particle formulation, and pharmacokinetics and biodistribution. The scope of this review is to move from basics to the latest developments of combined techniques using ultrasound for triggering drug release. Generalities on ultrasound are first given to better understand the parameters on which the clinician can operate to modulate the amount of delivered energy. Ultrasound effects on biological tissues such as thermal effects, mechanical effects and radiation forces are also presented. The second part of this review deals with the combination of ultrasound and drug delivery systems to enhance the efficacy of current cancer treatment. The in vivo behavior of drug delivery systems and how ultrasounds can be combined to improve treatment efficacy are detailed. The example of ThermoDox®, a new formulation of thermosensitive liposomes undergoing a phase III clinical trial, is particularly discussed on the basis of the available clinical data. Through the present article, researchers will be able to better grasp the different levels of complexity when designing an efficient formulation to be combined with ultrasound.