Thermoresponsive polysarcosine-based nanoparticles

Polysarcosine modified with limited molar amounts of (N-(2-hydroxypropyl)methacrylamide) yields a block copolymer capable of forming thermoresponsive nanoparticles that are suitable for controlled release applications.

Shell-Sheddable Poly(N-2-hydroxypropyl methacrylamide) Polymeric Micelles for Dual-Sensitive Release of Doxorubicin

Poly(ethylene glycol) (PEG) shell-sheddable micelles are proved to be effective tools for rapid intracellular drug delivery. However, some adverse factors, such as the potential immunogenicity and the accelerated blood clearance, might be accompanied with the traditional PEG sheddable micelles. Here, a poly(N-2-hydroxypropyl methacrylamide) (PHPMA) sheddable block copolymer containing disulfide bonds on the main chain is prepared to form pH- and reduction-dual-responsive micelles. The most optimal synthetic route of the block copolymer is selected from three potential pathways. Doxorubicin is loaded via an acid-labile hydrazone bond to achieve high drug loading content and to prevent premature drug release. As expected, as-prepared shell-sheddable micelles exhibit faster intracellular drug release and more satisfactory in vitro anticancer efficacy than the nonsheddable counterpart did. This design provides a feasible guideline for the efficient synthesis of similar shell-sheddable micelles consisting of PHPMA coatings.

CD44-Targeted Facile Enzymatic Activatable Chitosan Nanoparticles for Efficient Antitumor Therapy and Reversal of Multidrug Resistance

Nanoparticles are attractive platforms for the delivery of various anticancer therapeutics. Nevertheless, their applications are still limited by the relatively low drug loading capacity and the occurrence of multidrug resistance (MDR) against chemotherapeutics. In this study, we report that the integration of d-α-tocopherol succinate (VES) residue with both chitosan and paclitaxel (PTX) led to significant improvement of drug loading capacity and drug loading efficiency through the enhancement of drug/carrier interaction. After the incorporation of hyaluronic acid containing PEG side chains (HA-PEG), higher serum stability and more efficient cellular uptake were obtained. Due to HA coating, VES residues and the enzymatic responsive drug release property, such facile nanoparticles actively targeted cancer cells that overexpress CD44 receptor and efficiently reversed the MDR of treated cells, but caused no significant toxicity to mouse fibroblast (NIH-3T3). More importantly, with HA-PEG coating, longer blood circulation and more effective tumor accumulation were achieved for prodrug nanoparticles. Finally, superior anticancer activity and excellent safety profile was demonstrated by HA-PEG coated enzymatically activatable prodrug nanoparticles compared to commercially available Taxol formulation.

Radiolabelled Polymeric Materials for Imaging and Treatment of Cancer: Quo Vadis?

Owing to their tunable blood circulation time and suitable plasma stability, polymer-based nanomaterials hold a great potential for designing and utilising multifunctional nanocarriers for efficient imaging and effective treatment of cancer. When tagged with appropriate radionuclides, they may allow for specific detection (diagnosis) as well as the destruction of tumours (therapy) or even customization of materials, aiming to both diagnosis and therapy (theranostic approach). This review provides an overview of recent developments of radiolabelled polymeric nanomaterials (natural and synthetic polymers) for molecular imaging of cancer, specifically, applying nuclear techniques such as positron emission tomography (PET) and single-photon emission computed tomography (SPECT). Different approaches to radiolabel polymers are evaluated from the methodical radiochemical point of view. This includes new bifunctional chelating agents (BFCAs) for radiometals as well as novel labelling methods. Special emphasis is given to eligible strategies employed to evade the mononuclear phagocytic system (MPS) in view of efficient targeting. The discussion encompasses promising strategies currently employed as well as emerging possibilities in radionuclide-based cancer therapy. Key issues involved in the clinical translation of radiolabelled polymers and future scopes of this intriguing research field are also discussed.

Mercaptan acids modified amphiphilic copolymers for efficient loading and release of doxorubicin

In this paper, four different kinds of mercaptan acids modified amphiphilic copolymers mPEG-b-PATMC-g-SRCOOH (R=CH₂, CH₂CH₂, (CH₂)₁₀ and CH(COOH)CH₂) were successfully synthesized by thiol-ene "click" reaction between pendent carbon-carbon double bonds of PEG-b-PATMC and thiol groups of thioglycolic acid, 3-mercaptopropionic acid, 11-mercaptoundecanoic acid or 2-mercaptosuccinic acid. DLS and TEM measurements showed that all the mPEG-b-PATMC-g-SRCOOH copolymers could self-assemble to form micelles which dispersed in spherical shape with nano-size before and after DOX loading. The positively-charged DOX could effectively load into copolymer micelles via synergistic hydrophobic and electrostatic interactions. All DOX-loaded mPEG-b-PATMC-g-SRCOOH micelles displayed sustained drug release behavior without an initial burst which could be further adjusted by the conditions of ionic strength and pH. Especially in the case of mPEG-b-PATMC-g-S(CH₂)₁₀COOH (P3) micelles, the suitable hydrophobility and charge density were not only beneficial to improve the DOX-loading efficiency, they were also good for obtaining smaller particle size, higher micelle stability and more timely drug delivery. Confocal laser scanning microscopy (CLSM) and MTT assays further demonstrated efficient cellular uptake of DOX delivered by mPEG-b-PATMC-g-SRCOOH micelles and potent cytotoxic activity against cancer cells.

Indium-based and iodine-based labeling of HPMA copolymer-epirubicin conjugates: Impact of structure on the in vivo fate

Recently, we developed 2nd generation backbone degradable N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer-drug conjugates which contain enzymatically cleavable sequences (GFLG) in both polymeric backbone and side-chains. This design allows using polymeric carriers with molecular weights above renal threshold without impairing their biocompatibility, thereby leading to significant improvement in therapeutic efficacy. For example, 2nd generation HPMA copolymer-epirubicin (EPI) conjugates (2P-EPI) demonstrated complete tumor regression in the treatment of mice bearing ovarian carcinoma. To obtain a better understanding of the in vivo fate of this system, we developed a dual-labeling strategy to simultaneously investigate the pharmacokinetics and biodistribution of the polymer carrier and drug EPI. First, we synthesized two different types of dual-radiolabeled conjugates, including 1) (111)In-2P-EPI-(125)I (polymeric carrier 2P was radiolabeled with (111)In and drug EPI with (125)I), and 2) (125)I-2P-EPI-(111)In (polymeric carrier 2P was radiolabeled with (125)I and drug EPI with (111)In). Then, we compared the pharmacokinetics and biodistribution of these two dual-labeled conjugates in female nude mice bearing A2780 human ovarian carcinoma. There was no significant difference in the blood circulation between polymeric carrier and payload; the carriers ((111)In-2P and (125)I-2P) showed similar retention of radioactivity in both tumor and major organs except kidney. However, compared to (111)In-labeled payload EPI, (125)I-labeled EPI showed lower radioactivity in normal organs and tumor at 48h and 144h after intravenous administration of conjugates. This may be due to different drug release rates resulting from steric hindrance to the formation of enzyme-substrate complex as indicated by cleavage experiments with lysosomal enzymes (Tritosomes). A slower release rate of EPI(DTPA)(111)In than EPI(Tyr)(125)I was observed. It may be also due to in vivo catabolism and subsequent iodine loss as literature reported. Nevertheless, tumor-to-tissue uptake ratios of both radionuclides were comparable, indicating that drug-labeling strategy does not affect the tumor targeting ability of HPMA copolymer conjugates.

Poly(d,l-lactic acid)-block-poly(N-(2-hydroxypropyl)methacrylamide) nanoparticles for overcoming accelerated blood clearance and achieving efficient anti-tumor therapy

The substitution of PEG with PHPMA maintained the long circulation of PDLLA-b-PEG and alleviated the accelerated blood clearance (ABC).

Acid degradable poly(vinylcaprolactam)-based nanogels with ketal linkages for drug delivery

We developed acid degradable P(VCL-ketal-HPMA) nanogels for drug delivery via precipitation polymerization using ketal-bonded DMAEP as a cross-linker and hydrophilic HPMA as a comonomer.