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Multiple myeloma (MM) is the second most common hematological malignancy. For relapsed and refractory MM, a proteasome inhibitor, carfilzomib (CFZ), has become one of the few clinical options. CFZ suffers, nevertheless, metabolic instability and poor bioavailability and may induce severe cardiovascular and renal adverse events. Here, we report that daratumumab (Dar)-decorated polypeptide micelles (Dar-PMs) mediate the targeted delivery of CFZ to CD38-positive MM, effectively boosting its anti-MM efficacy. CFZ-loaded Dar-PMs (Dar-PMs-CFZ) exhibited an average diameter of ca. 80 nm and Dar density-dependent cell endocytosis and anti-MM activity, in which over 6-fold greater inhibitory effect to LP-1 and MM.1S MM cells than nontargeted PMs-CFZ control was achieved at a Dar density of 3.2 (Dar 3.2 -PMs-CFZ). Interestingly, Dar 3.2 -PMs-CFZ markedly enhanced the growth inhibition of orthotopic LP-1 MM in mice and significantly extended the median survival time compared with PMs-CFZ and free CFZ (95 days vs 60 and 54 days, respectively). In line with its high MM targetability and anti-MM efficacy, Dar 3.2 -PMs-CFZ revealed little toxic effects and effectively prevented osteolytic lesions. The antibody-targeted nanodelivery of a proteasome inhibitor appears to be an appealing strategy to treat multiple myeloma.

The incorporation of a phenylboronic acid group has appeared as an attractive strategy to build smart drug delivery systems. Here, we report novel synthesis of phenylboronic acid-functionalized copolypeptides based on an l-boronophenylalanine N -carboxyanhydride (BPA-NCA) monomer and their application for robust co-encapsulation and responsive release of dual anticancer drugs. By employing different poly(ethylene glycol) (PEG) initiators and copolymerizing with varying NCA monomers, linear and star PEG-poly(l-boronophenylalanine) copolymers (PEG-PBPA, star-PEG-PBPA), PEG-poly(l-tyrosine- co -l-boronophenylalanine) [PEG-P(Tyr- co -BPA)], PEG-poly(l-lysine- co -l-boronophenylalanine) [PEG-P(Lys- co -BPA)], and PEG-poly(β-benzyl-l-aspartate- co -l-boronophenylalanine) [PEG-P(BLA- co -BPA)] were obtained with controlled compositions. Interestingly, PEG-PBPA self-assembled into uniform micellar nanoparticles that mediated robust co-encapsulation and hydrogen peroxide (H 2 O 2 ) and acid-responsive release of dual antitumor drugs, curcumin (Cur) and sorafenib tosylate (Sor). These dual drug-loaded nanoparticles (PBN-Cur/Sor) exhibited a greatly enhanced anticancer effect toward U87 MG-luciferase glioblastoma cells. The facile synthesis of phenylboronic acid-functionalized copolypeptides from BPA coupled with their robust drug loading and responsive drug release behaviors make them interesting for construction of smart cancer nanomedicines.

Metastasis is responsible for >90% of the deaths of breast cancer patients in the clinic. Here, we report on cross-linked multifunctional hyaluronic acid nanoparticles carrying docetaxel (DTX-CMHN) for enhanced suppression of highly metastatic 4T1 breast tumors in vivo . DTX-CMHN was formed from a single and all-natural hyaluronic acid- g -polytyrosine-lipoic acid conjugate (HA- g -PTyr-LA; HA, 20 kDa; PTyr, 2.2 kDa), and the size of DTX-CMHN increased from 69 to 78 to 96 nm as the increasing degree of substitution (DS) of PTyr increased from 4 to 11 to 15, respectively. Robust encapsulation of DTX was obtained when DS ≥ 11. DTX-CMHN while steady in a nonreducing environment was destabilized under 10 mM glutathione releasing ∼90% of the DTX within 24 h. It is noteworthy that DTX-CMHN exhibited better antitumor, antimigration, and anti-invasion activity in CD44-overexpressed 4T1-Luc breast cancer cells than free DTX. Interestingly, DTX-CMHN displayed a long elimination half-life of 5.75 h, in contrast to half-lives of 2.11 and 0.75 h for its non-cross-linked counterpart (DTX-MHN) and free DTX, respectively. In vivo therapeutic studies showed significantly better inhibition of primary 4T1-Luc tumor growth and lung metastasis and lower toxicity of DTX-CMHN compared with that of free DTX. These multifunctional nanoformulations based on a single and all-natural hyaluronic acid conjugate emerge as a potential nanoplatform for targeted treatment of CD44-positive metastatic tumors.

Nanomedicines are deemed as the most promising treatment modality for malignant cancers. Particularly, cancer nanomedicines based on synthetic polypeptides have gained interest because they possess excellent safety, unique hierarchical structure, and tailorable functionalities to suit for delivery of diverse drugs including synthetic drugs, peptides, proteins, and nucleic acids. A few polypeptide-based nanoformulations (e.g., NK105, NC6004, NK911, CT2103) are under phases I-III clinical investigation for treating patients with advanced solid tumors. In recent years, progress has been made in the development of robust and high drug loading, tumor-targeting, membrane-disrupting, and stimuli-sensitive nanomedicines from de novo functional polypeptides, which afford not only better safety and reduced adverse effects, but also further improved anticancer efficacy over clinical formulations. Moreover, virus-mimicking vehicles have been devised from polypeptides for efficient nonviral delivery of highly potent peptides, proteins, and nucleic acids, greatly advancing biotherapy for cancers. In this Perspective, we highlight the state-of-the-art design and fabrication of cancer nanomedicines based on synthetic polypeptides and, at the end, give our viewpoints on their future development for targeted cancer therapy and potential challenges for clinical translation.

Polypeptide micelles, though having been proved to be an appealing nanoplatform for cancer chemotherapy, are met with issues like inefficient drug encapsulation, gradual drug release, and low tumor cell selectivity and uptake. Here, we report on cRGD-decorated, small-sized, robust, and reduction-responsive polytyrosine micelles (cRGD-rPTM) based on poly(ethylene glycol)- b-poly(l-tyrosine)-lipoic acid (PEG- b-PTyr-LA) conjugate for high loading and targeted delivery of doxorubicin (Dox). Notably, cRGD-rPTM exhibited efficient loading of Dox, giving cRGD-rPTM-Dox with a drug loading content (DLC) of 18.5 wt % and a small size of 45 nm at a theoretical DLC of 20 wt %. cRGD-rPTM-Dox displayed reduction-triggered drug release, high selectivity and superior antiproliferative activity toward α v β 3 integrin positive MDA-MB-231 breast cancer cells (IC 50 = 1.5 μg/mL) to both nontargeted rPTM-Dox and clinical liposomal formulation (LP-Dox). cRGD-rPTM-Dox demonstrated a prolonged circulation time compared with the noncrosslinked cRGD-PTM-Dox control and significantly better accumulation in MDA-MB-231 breast tumor xenografts than nontargeted rPTM-Dox. Moreover, cRGD-rPTM-Dox at 6 mg Dox equiv/kg could remarkably suppress growth of MDA-MB-231 human breast tumor without inducing obvious side effects, outperforming both rPTM-Dox and LP-Dox. These reduction-responsive multifunctional polytyrosine micelles appear to be a viable and versatile nanoplatform for targeted chemotherapy.

Low tolerability and tumor selectivity restricts many potent anticancer drugs including mertansine from wide clinical use. Here, glutathione-activatable hyaluronic acid-SS-mertansine prodrug (HA-SS-DM1) was designed and developed to achieve enhanced tolerability and targeted therapy of CD44+ human breast tumor xenografts. DM1 was readily conjugated to HA using 2-(2-pyridyldithio)-ethylamine as a linker. Notably, HA-SS-DM1 with a high DM1 content of 20 wt % had a mean size of ∼170 nm at concentrations above 0.2 mg/mL while transformed into unimers upon dilution to 0.04 mg/mL. HA-SS-DM1 exhibited a superior targetability to MCF-7 cancer cells with an exceptionally low IC 50 of 0.13 μg DM1/mL. The pharmacokinetic studies displayed that Cy5-labeled HA-SS-DM1 had an elimination half-life of 2.12 h. Notably, HA-SS-DM1 displayed better tolerability with a maximum-tolerated dose 4-fold higher than free DM1. Cy5-labeled HA-SS-DM1 quickly accumulated in the MCF-7 tumor, the fluorescence intensity of which was maximized at 24 h post injection and kept strong in 48 h. The tumor Cy5 level reached 8.17%ID/g at 24 h. The therapeutic results demonstrated that HA-SS-DM1 effectively inhibited tumor growth at 800 μg DM1 equiv/kg while causing reduced side effects as compared to free DM1. Glutathione-cleavable HA-SS-DM1 prodrug with superior drug content, excellent targetability, enhanced tolerability, and easy large-scale synthesis appears to be a highly promising alternative to clinically used Trastuzumab emtansine (T-DM1) for targeted breast tumor therapy.

pH-Responsive chimaeric polypeptide-based polymersomes (refer to as pepsomes) were designed and developed from asymmetric poly(ethylene glycol)-b-poly(l-leucine)-b-poly(l-glutamic acid) (PEG-PLeu-PGA, PEG is longer than PGA) triblock copolymers for efficient encapsulation and triggered intracellular delivery of doxorubicin hydrochloride (DOX·HCl). PEG-PLeu-PGA was conveniently prepared by sequential ring-opening polymerization of l-leucine N-carboxyanhydride and γ-benzyl-l-glutamate N-carboxyanhydride using PEG-NH2 as an initiator followed by deprotection. Pepsomes formed from PEG-PLeu-PGA had unimodal distribution and small sizes of 64-71 nm depending on PLeu block lengths. Interestingly, these chimaeric pepsomes while stable at pH 7.4 were quickly disrupted at pH 5.0, likely due to alternation of ionization state of the carboxylic groups in PGA that shifts PGA blocks from hydrophilic and random coil structure into hydrophobic and α-helical structure. DOX·HCl could be actively loaded into the watery core of pepsomes with a high loading efficiency. Remarkably, the in vitro release studies revealed that release of DOX·HCl was highly dependent on pH, in which about 24.0% and 75.7% of drug was released at pH 7.4 and 5.0, respectively, at 37 °C in 24 h. MTT assays demonstrated that DOX·HCl-loaded pepsomes exhibited high antitumor activity, similar to free DOX·HCl in RAW 264.7 cells. Moreover, they were also potent toward drug-resistant MCF-7 cancer cells (MCF-7/ADR). Confocal microscopy studies showed that DOX·HCl-loaded pepsomes delivered and released drug into the cell nuclei of MCF-7/ADR cells in 4 h, while little DOX·HCl fluorescence was observed in MCF-7/ADR cells treated with free drug under otherwise the same conditions. These chimaeric pepsomes with facile synthesis, efficient drug loading, and pH-triggered drug release behavior are an attractive alternative to liposomes for targeted cancer chemotherapy.

A novel and versatile family of enzymatically and reductively degradable α-amino acid-based poly(ester amide)s (SS-PEAs) were developed from solution polycondensation of disulfide-containing di-p-toluenesulfonic acid salts of bis-l-phenylalanine diesters (SS-Phe-2TsOH) with di-p-nitrophenyl adipate (NA) in N,N-dimethylformamide (DMF). SS-PEAs with Mn ranging from 16.6 to 23.6 kg/mol were obtained, depending on NA/SS-Phe-2TsOH molar ratios. The chemical structures of SS-PEAs were confirmed by (1)H NMR and FTIR spectra. Thermal analyses showed that the obtained SS-PEAs were amorphous with a glass transition temperature (Tg) in the range of 35.2-39.5 °C. The in vitro degradation studies of SS-PEA films revealed that SS-PEAs underwent surface erosion in the presence of 0.1 mg/mL α-chymotrypsin and bulk degradation under a reductive environment containing 10 mM dithiothreitol (DTT). The preliminary cell culture studies displayed that SS-PEA films could well support adhesion and proliferation of L929 fibroblast cells, indicating that SS-PEAs have excellent cell compatibility. The nanoparticles prepared from SS-PEA with PVA as a surfactant had an average size of 167 nm in phosphate buffer (PB, 10 mM, pH 7.4). SS-PEA nanoparticles while stable under physiological environment undergo rapid disintegration under an enzymatic or reductive condition. The in vitro drug release studies showed that DOX release was accelerated in the presence of 0.1 mg/mL α-chymotrypsin or 10 mM DTT. Confocal microscopy observation displayed that SS-PEA nanoparticles effectively transported DOX into both drug-sensitive and -resistant MCF-7 cells. MTT assays revealed that DOX-loaded SS-PEA nanoparticles had a high antitumor activity approaching that of free DOX in drug-sensitive MCF-7 cells, while more than 10 times higher than free DOX in drug-resistant MCF-7/ADR cells. These enzymatically and reductively degradable α-amino acid-based poly(ester amide)s have provided an appealing platform for biomedical technology in particular controlled drug delivery applications.

Reduction-sensitive shell-sheddable glyco-nanoparticles were designed and developed based on poly(ε-caprolactone)-graft-SS-lactobionic acid (PCL-g-SS-LBA) copolymer for efficient hepatoma-targeting delivery of doxorubicin (DOX). PCL-g-SS-LBA was prepared by ring-opening copolymerization of ε-caprolactone and pyridyl disulfide carbonate followed by postpolymerization modification with thiolated lactobionic acid (LBA-SH) via thiol-disulfide exchange reaction. The dynamic light scattering (DLS) and transmission electron microscopy (TEM) showed that PCL-g-SS-LBA was self-assembled into monodisperse nanoparticles (SS-GNs) with a mean diameter of about 80 nm. SS-GNs while remaining stable under physiological conditions (37 °C, pH 7.4) were prone to rapid shell-shedding and aggregation in the presence of 10 mM dithiothreitol (DTT). DOX was loaded into SS-GNs with a decent loading content of 12.0 wt %. Notably, in vitro release studies revealed that about 80.3% DOX was released from DOX-loaded SS-GNs in 24 h under a reductive condition while low drug release (<21%) was observed for DOX-loaded PCL-g-LBA nanoparticles (reduction-insensitive control) under otherwise the same condition and for DOX-loaded SS-GNs under a nonreductive condition. The flow cytometry and confocal microscopy observations indicated that SS-GNs were efficiently taken up by asialoglycoprotein receptor (ASGP-R)-overexpressing HepG2 cells likely via a receptor-mediated endocytosis mechanism and DOX was released into the nuclei of cells following 4 h incubation. MTT assays showed that DOX-loaded SS-GNs exhibited a high antitumor activity toward HepG2 cells, which was comparable to free DOX and about 18-fold higher than their reduction-insensitive counterparts, while blank SS-GNs were nontoxic up to a tested concentration of 1.0 mg/mL. These shell-sheddable glyco-nanoparticles are promising for hepatoma-targeting chemotherapy.

Hepatoma-targeting reduction-sensitive chimaeric biodegradable polymersomes were designed and developed based on galactose-poly(ethylene glycol)-poly(ε-caprolactone) (Gal-PEG-PCL), PEG-PCL-poly(2-(diethylamino)ethyl methacrylate) (PEG-PCL-PDEA, asymmetric), and PEG-SS-PCL for facile loading and triggered intracellular delivery of proteins. The chimaeric polymersomes formed from PEG-PCL-PDEA and PEG-SS-PCL had a monodisperse distribution with average sizes ranging from 95.5 to 199.2 nm depending on PEG-SS-PCL contents. Notably, these polymersomes displayed decent loading of bovine serum albumin (BSA), ovalbumin (OVA), and cytochrome C (CC) proteins likely due to presence of electrostatic and hydrogen bonding interactions between proteins and PDEA block located in the interior of polymersomes. The in vitro release studies showed that protein release was largely accelerated under a reductive condition containing 10 mM dithiothreitol (DTT). For example, ca. 77.2 and 22.1% of FITC-BSA were released from CP(SS50) (chimaeric polymersomes containing 50 wt % PEG-SS-PCL) at 37 °C in 12 h in the presence and absence of 10 mM DTT, respectively. Confocal microscopy showed that FITC-CC-loaded Gal-decorated CP(SS40) could efficiently deliver and release FITC-CC into HepG2 cells following 24 h treatment, in contrast to little or negligible fluorescence detected in HepG2 cells treated with FITC-CC-loaded nontargeting polymersomes or free CC. MTT assays revealed that CC-loaded Gal-decorated CP(SS40) exhibited apparent targetability and pronounced antitumor activity to HepG2 cells, in which cell viabilities decreased from 81.9, 60.6, 49.5, 42.2 to 31.5% with increasing Gal-PEG-PCL contents from 0, 10, 20, 30 to 40 wt %. Most remarkably, granzyme B-loaded Gal-decorated chimaeric polymersomes effectively caused apoptosis of HepG2 cells with a markedly low half-maximal inhibitory concentration (IC(50)) of 2.7 nM. These reduction-responsive chimaeric biodegradable polymersomes offer a multifunctional platform for efficient intracellular protein delivery.

Reduction-sensitive reversibly core-cross-linked micelles were developed based on poly(ethylene glycol)-b-poly(N-2-hydroxypropyl methacrylamide)-lipoic acid (PEG-b-PHPMA-LA) conjugates and investigated for triggered doxorubicin (DOX) release. Water-soluble PEG-b-PHPMA block copolymers were obtained with M(n,PEG) of 5.0 kg/mol and M(n,HPMA) varying from 1.7 and 4.1 to 7.0 kg/mol by reversible addition-fragmentation chain transfer (RAFT) polymerization. The esterification of the hydroxyl groups in the PEG-b-PHPMA copolymers with lipoic acid (LA) gave amphiphilic PEG-b-PHPMA-LA conjugates with degrees of substitution (DS) of 71-86%, which formed monodispersed micelles with average sizes ranging from 85.3 to 142.5 nm, depending on PHPMA molecular weights, in phosphate buffer (PB, 10 mM, pH 7.4). These micelles were readily cross-linked with a catalytic amount of dithiothreitol (DTT). Notably, PEG-b-PHPMA(7.0k)-LA micelles displayed superior DOX loading content (21.3 wt %) and loading efficiency (90%). The in vitro release studies showed that only about 23.0% of DOX was released in 12 h from cross-linked micelles at 37 °C at a low micelle concentration of 40 μg/mL, whereas about 87.0% of DOX was released in the presence of 10 mM DTT under otherwise the same conditions. MTT assays showed that DOX-loaded core-cross-linked PEG-b-PHPMA-LA micelles exhibited high antitumor activity in HeLa and HepG2 cells with low IC(50) (half inhibitory concentration) of 6.7 and 12.8 μg DOX equiv/mL, respectively, following 48 h incubation, while blank micelles were practically nontoxic up to a tested concentration of 1.0 mg/mL. Confocal laser scanning microscope (CLSM) studies showed that DOX-loaded core-cross-linked micelles released DOX into the cell nuclei of HeLa cells in 12 h. These reduction-sensitive disassemblable core-cross-linked micelles with excellent biocompatibility, superior drug loading, high extracellular stability, and triggered intracellular drug release are promising for tumor-targeted anticancer drug delivery.