Jiyuan Yang

Smart Self‐Assembled Hybrid Hydrogel Biomaterials

Hybrid biomaterials are systems created from components of at least two distinct classes of molecules, for example, synthetic macromolecules and proteins or peptide domains. The synergistic combination of two types of structures may produce new materials that possess unprecedented levels of structural organization and novel properties. This Review focuses on biorecognition-driven self-assembly of hybrid macromolecules into functional hydrogel biomaterials. First, basic rules that govern the secondary structure of peptides are discussed, and then approaches to the specific design of hybrid systems with tailor-made properties are evaluated, followed by a discussion on the similarity of design principles of biomaterials and macromolecular therapeutics. Finally, the future of the field is briefly outlined.

Peptide-directed self-assembly of hydrogels

This review focuses on the self-assembly of macromolecules mediated by the biorecognition of peptide/protein domains. Structures forming alpha-helices and beta-sheets have been used to mediate self-assembly into hydrogels of peptides, reactive copolymers and peptide motifs, block copolymers, and graft copolymers. Structural factors governing the self-assembly of these molecules into precisely defined three-dimensional structures (hydrogels) are reviewed. The incorporation of peptide motifs into hybrid systems, composed of synthetic and natural macromolecules, enhances design opportunities for new biomaterials when compared to individual components.

Drug-free macromolecular therapeutics: Induction of apoptosis by coiled-coil-mediated cross-linking of antigens on the cell surface

A new paradigm was designed for apoptosis induction mediated by the biorecognition of coiled-coil motifs at the Raji B cell surface. The heterodimerization of complementary peptides, one bound to Fab’ antibody fragment, the other as grafts to HPMA copolymer, results in crosslinking of CD20 target antigens, and consequently, initiation of apoptosis.

Smart Hydrogels Containing Adenylate Kinase: Translating Substrate Recognition into Macroscopic Motion

Enzyme-based hybrid hydrogels were prepared by covalently incorporating an adenylate kinase mutant, possessing two thiol groups, into HPMA copolymer- or PEG-based hydrogel structures. The nanoscale conformational change of enzyme, triggered by substrate recognition, translated into macroscopic motion of hydrogels.

Synthesis and evaluation of a backbone biodegradable multiblock HPMA copolymer nanocarrier for the systemic delivery of paclitaxel

The performance and safety of current antineoplastic agents, particularly water-insoluble drugs, are still far from satisfactory. For example, the currently widely used Cremophor EL®-based paclitaxel (PTX) formulation exhibits pharmacokinetic concerns and severe side effects. Thus, the concept of a biodegradable polymeric drug-delivery system, which can significantly improve therapeutic efficacy and reduce side effects is advocated. The present work aims to develop a new-generation of long-circulating, biodegradable carriers for effective delivery of PTX. First, a multiblock backbone biodegradable N-(2-hydroxypropyl)methacrylamide(HPMA) copolymer-PTX conjugate (mP-PTX) with molecular weight (Mw) of 335 kDa was synthesized by RAFT (reversible addition-fragmentation chain transfer) copolymerization, followed by chain extension. In vitro studies on human ovarian carcinoma A2780 cells were carried out to investigate the cytotoxicity of free PTX, HPMA copolymer-PTX conjugate with Mw of 48 kDa (P-PTX), and mP-PTX. The experiments demonstrated that mP-PTX has a similar cytotoxic effect against A2780 cells as free PTX and P-PTX. To further compare the behavior of this new biodegradable conjugate (mP-PTX) with free PTX and P-PTX in vivo evaluation was performed using female nu/nu mice bearing orthotopic A2780 ovarian tumors. Pharmacokinetics study showed that high Mw mP-PTX was cleared more slowly from the blood than commercial PTX formulation and low Mw P-PTX. SPECT/CT imaging and biodistribution studies demonstrated biodegradability as well as elimination of mP-PTX from the body. The tumors in the mP-PTX treated group grew more slowly than those treated with saline, free PTX, and P-PTX (single dose at 20 mg PTX/kg equivalent). Moreover, mice treated with mP-PTX had no obvious ascites and body-weight loss. Histological analysis indicated that mP-PTX had no toxicity in liver and spleen, but induced massive cell death in the tumor. In summary, this biodegradable drug delivery system has a great potential to improve performance and safety of current antineoplastic agents.

Backbone Degradable Multiblock N-(2-Hydroxypropyl)methacrylamide Copolymer Conjugates via Reversible Addition Fragmentation Chain Transfer Polymerization and Thiol-ene Coupling Reaction

Telechelic water-soluble HPMA copolymers and HPMA copolymer-doxorubicin (DOX) conjugates have been synthesized by RAFT polymerization mediated by a new bifunctional chain transfer agent (CTA) that contains an enzymatically degradable oligopeptide sequence. Postpolymerization aminolysis followed by chain extension with a bis-maleimide resulted in linear high molecular weight multiblock HPMA copolymer conjugates. These polymers are enzymatically degradable; in addition to releasing the drug (DOX), the degradation of the polymer backbone resulted in products with molecular weights similar to the starting material and below the renal threshold. The new multiblock HPMA copolymers hold potential as new carriers of anticancer drugs.

Sequential combination therapy of ovarian cancer with degradable N-(2-hydroxypropyl)methacrylamide copolymer paclitaxel and gemcitabine conjugates

Significance In previous clinical testing, first-generation N-(2-hydroxypropyl)-methacrylamide (HPMA) copolymer-drug conjugates circumvented drug resistance and showed reduced side effects, although only minor improvement was seen in therapeutic efficacy. For effective clincial translation, second-generation high-molecular weight backbone-degradable HPMA copolymer carriers designed by our group sought to provide prolonged blood circulation and enhanced tumor accumulation to enable sufficient exposure of tumors to effective drug concentrations, and guarantee their biocompatibility by making polymer backbone degradable. The second-generation conjugates showed favorable pharmacokinetic profiles and controlled drug release, resulting in a dramatic improvement of therapeutic efficacy, as compared with first-generation conjugates and free drugs. For future industrial-scale manufacture, a new reversible addition-fragmentation chain transfer agent was developed that enables synthesis of conjugates in one step. For rapid and effective clinical translation, polymer-based anticancer therapeutics need long circulating conjugates that produce a sustained concentration gradient between the vasculature and solid tumor. To this end, we designed second-generation backbone-degradable diblock N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer carriers and evaluated sequential combination therapy of HPMA copolymer-paclitaxel and HPMA copolymer-gemcitabine conjugates against A2780 human ovarian carcinoma xenografts. First, extensive in vitro assessment of administration sequence impact on cell cycle, viability, apoptosis, migration, and invasion revealed that treatment with paclitaxel conjugate followed by gemcitabine conjugate was the most effective scheduling strategy. Second, in an in vivo comparison with first-generation (nondegradable, molecular weight below the renal threshold) conjugates and free drugs, the second-generation degradable high-molecular weight conjugates showed distinct advantages, such as favorable pharmacokinetics (three- to five-times half-life compared with the first generation), dramatically enhanced inhibition of tumor growth (complete tumor regression) by paclitaxel and gemcitabine conjugate combination, and absence of adverse effects. In addition, multimodality imaging studies of dual-labeled model conjugates confirmed the efficacy of second-generation conjugates by visualizing more than five-times enhanced tumor accumulation, rapid conjugate internalization, and effective intracellular release of payload. Taken together, the results indicate that the second-generation degradable HPMA copolymer carrier can provide an ideal platform for the delivery of a range of antitumor compounds, which makes it one of the most attractive candidates for potential clinical application.

Water-soluble HPMA copolymer - Prostaglandin E1 conjugates containing a cathepsin K sensitive spacer

A novel bone targeting, N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer based, prostaglandin E1 (PGE1) delivery system was designed, synthesized and characterized. PGE1 was bound to the polymer backbone via a spacer, composed of a cathepsin K sensitive tetrapeptide (Gly-Gly-Pro-Nle) and a self-eliminating 4-aminobenzyl alcohol structure. The HPMA copolymer conjugates were prepared by photo–initiated free radical copolymerization of HPMA, PGE1-containing macromonomer, and optionally a comonomer containing a reactive p-nitrophenyl ester group. The latter group was used as attachment points for the d-aspartic acid octapeptide targeting moieties. Incubation of the PGE1-containing macromonomer and HPMA copolymer-PGE1 conjugates with cathepsin K resulted in release of unmodified PGE1. The rate of release depended on the composition of the conjugate. The higher the PGE1 content in the conjugate, the slower the PGE1 release. This appeared to be the result of association of hydrophobic side-chains in aqueous media, which rendered the formation of the enzyme substrate complex more difficult. The data seems to indicate that HPMA copolymer-PGE1 conjugates have a potential in the treatment of osteoporosis and other bone diseases.

HPMA copolymer-based combination therapy toxic to both prostate cancer stem/progenitor cells and differentiated cells induces durable anti-tumor effects

Current treatments for prostate cancer are still not satisfactory, often resulting in tumor regrowth and metastasis. One of the main reasons for the ineffective anti-prostate cancer treatments is the failure to deplete cancer stem-like cells (CSCs) - a subset of cancer cells with enhanced tumorigenic capacity. Thus, combination of agents against both CSCs and bulk tumor cells may offer better therapeutic benefits. Several molecules with anti-cancer stem/progenitor cell activities have been under preclinical evaluations. However, their low solubility and nonspecific toxicity limit their clinical translation. Herein, we designed a combination macromolecular therapy containing two drug conjugates: HPMA copolymer-cyclopamine conjugate (P-CYP) preferentially toxic to cancer stem/progenitor cells, and HPMA copolymer-docetaxel conjugate (P-DTX) effective in debulking the tumor mass. Both conjugates were synthesized using RAFT (reversible addition-fragmentation chain transfer) polymerization resulting in narrow molecular weight distribution. The killing effects of the two conjugates against bulk tumor cells and CSCs were evaluated in vitro and in vivo. In PC-3 or RC-92a/hTERT prostate cancer cells, P-CYP preferentially kills and impairs the function of CD133+ prostate cancer stem/progenitor cells; P-DTX was able to kill bulk tumor cells instead of CSCs. In a PC-3 xenograft mice model, combination of P-DTX and P-CYP showed the most effective and persistent tumor growth inhibitory effect. In addition, residual tumors contained less CD133+ cancer cells following combination or P-CYP treatments, indicating selective killing of cancer cells with stem/progenitor cell properties.

Synthesis of Long-Circulating, Backbone Degradable HPMA Copolymer–Doxorubicin Conjugates and Evaluation of Molecular-Weight-Dependent Antitumor Efficacy

Backbone degradable, linear, multiblock N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer-doxorubicin (DOX) conjugates are synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization followed by chain extension via thiol-ene click reaction. The examination of molecular-weight-dependent antitumor activity toward human ovarian A2780/AD carcinoma in nude mice reveals enhanced activity of multiblock, second-generation, higher molecular weight conjugates when compared with traditional HPMA copolymer-DOX conjugates. The examination of body weight changes during treatment indicates the absence of non-specific adverse effects.