Polymyxins remain the last line treatment for multidrug-resistant (MDR) infections. As polymyxins resistance emerges, there is an urgent need to develop effective antimicrobial agents capable of mitigating MDR. Here, we report biodegradable guanidinium-functionalized polycarbonates with a distinctive mechanism that does not induce drug resistance. Unlike conventional antibiotics, repeated use of the polymers does not lead to drug resistance. Transcriptomic analysis of bacteria further supports development of resistance to antibiotics but not to the macromolecules after 30 treatments. Importantly, high in vivo treatment efficacy of the macromolecules is achieved in MDR A. baumannii-, E. coli-, K. pneumoniae-, methicillin-resistant S. aureus-, cecal ligation and puncture-induced polymicrobial peritonitis, and P. aeruginosa lung infection mouse models while remaining non-toxic (e.g., therapeutic index—ED50/LD50: 1473 for A. baumannii infection). These biodegradable synthetic macromolecules have been demonstrated to have broad spectrum in vivo antimicrobial activity, and have excellent potential as systemic antimicrobials against MDR infections.

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A series of vitamin E-containing biodegradable antimicrobial cationic polycarbonates is designed and synthesized via controlled organocatalytic ring-opening polymerization. The incorporation of vitamin E significantly enhances antimicrobial activity. These polymers demonstrate broad-spectrum antimicrobial activity against various microbes, e.g., S. aureus (Gram-positive), E-coli (Gram-negative) and C. albicans (fungi). More importantly, the co-delivery of such polymers with selected antibiotics (e.g., doxycycline) shows high synergism towards difficult-to-kill bacteria P. aeruginosa. These findings suggest that these vitamin E-functionalized polycarbonates are potentially useful antimicrobial agents against challenging bacterial/fungal infections.

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In this study, ‘ABA’‐type triblock copolymers of vitamin E‐functionalized polycarbonate and poly(ethylene glycol), i.e., VitEm‐PEG‐VitEm, with extremely short hydrophobic block VitEm, are synthesized and employed to form physically cross‐linked injectable hydrogels for local and sustained delivery of Herceptin. The hydrogels are formed at low concentrations (4–8 wt%). By varying polymer composition and concentration, the rheological behavior, porosity, and drug release properties of hydrogels are readily tunable. The in vitro antitumor specificity and efficacy of Herceptin in hydrogel and solution are investigated by MTT assay against normal and human breast cancer cell lines with different HER2 expression levels. The results demonstrate that the Herceptin‐loaded hydrogel is specific towards HER2‐overexpressing cancer cells and cytotoxic action is comparable to that of the Herceptin solution. The biocompatibility and biodegradability of hydrogel are evaluated in mice with subcutaneous injection by histological examination. It is observed that the hydrogel does not evoke a chronic inflammatory response and degrades within 6 weeks post administration. Biodistribution and anti‐tumor efficacy studies performed in BT474 tumor‐bearing mice show that single subcutaneous injection of Herceptin‐loaded hydrogel at a site close to the tumor enhances the retention of the antibody within the tumor. This leads to superior anti‐tumor efficacy as compared to intravenous (i.v.) and subcutaneous (s.c.) delivery of Herceptin in solution. The tumor size shrank by 77% at Day 28. When the hydrogel is injected at a distal location away from the tumor site, anti‐tumor efficacy is similar to that of weekly i.v. injections of Herceptin solution over 4 weeks, with the number of injections reduced from 4 to 1. These findings suggest that this hydrogel has great potential for use in subcutaneous and sustained delivery of antibodies to increase therapeutic efficacy and/or improve patient compliance.

In order to mitigate antibiotic resistance, a new strategy to increase antibiotic potency and reverse drug resistance is needed. Herein, the translocation mechanism of an antimicrobial guanidinium‐functionalized polycarbonate is leveraged in combination with traditional antibiotics to afford a potent treatment for drug‐resistant bacteria. Particularly, this polymer–antibiotic combination approach reverses rifampicin resistance phenotype in Acinetobacter baumannii demonstrating a 2.5 × 105‐fold reduction in minimum inhibitory concentration (MIC) and a 4096‐fold reduction in minimum bactericidal concentration (MBC). This approach also enables the repurposing of auranofin as an antibiotic against multidrug‐resistant (MDR) Gram‐negative bacteria with a 512‐fold MIC and 128‐fold MBC reduction, respectively. Finally, the in vivo efficacy of polymer–rifampicin combination is demonstrated in a MDR bacteremia mouse model. This combination approach lays foundational ground rules for a new class of antibiotic adjuvants capable of reversing drug resistance phenotype and repurposing drugs against MDR Gram‐negative bacteria.

In this study, bortezomib (BTZ, a cytotoxic water-insoluble anticancer drug) was encapsulated in micellar nanoparticles having a catechol-functionalized polycarbonate core through a pH-sensitive covalent bond between phenylboronic acid (PBA) in BTZ and catechol, and these drug-loaded micelles were incorporated into hydrogels to form micelle/hydrogel composites. A series of injectable, biodegradable hydrogels with readily tunable mechanical properties were formed and optimized for sustained delivery of the BTZ-loaded micelles through ionic coacervation between PBA-functionalized polycarbonate/poly(ethylene glycol) (PEG) "ABA" triblock copolymer and a cationic one having guanidinium- or thiouronium-functionalized polycarbonate as "A" block. An in vitro release study showed the pH dependence in BTZ release. At pH 7.4, the BTZ release from the micelle/hydrogel composite remained low at 7%, whereas in an acidic environment, ∼85% of BTZ was released gradually over 9 days. In vivo studies performed in a multiple myeloma MM.1S xenograft mouse model showed that the tumor progression of mice treated with BTZ-loaded micelle solution was similar to that of the control group, whereas those treated with the BTZ-loaded micelle/hydrogel composite resulted in significant delay in the tumor progression. The results demonstrate that this hydrogel has great potential for use in subcutaneous and sustained delivery of drug-loaded micelles with superior therapeutic efficacy.