Micelle-Forming Block Copolymers Tailored for Inhibition of P-gp-Mediated Multidrug Resistance: Structure to Activity Relationship

Overcoming P-glycoprotein-mediated multidrug resistance in cancer cells through micelle-forming PHPMA-b-PPO diblock copolymers for doxorubicin delivery

Multidrug resistance (MDR) represents one of the major concerns in cancer therapy as it may cause reduced efficacy of chemotherapeutic drugs due to the overexpression of ABC transporters, particularly P-glycoprotein (P-gp). This study explores the potential of novel amphiphilic diblock (DB) copolymers composed of poly[N-(2-hydroxypropyl)methacrylamide]-based copolymers (PHPMA) and poly(propylene oxide) (PPO) to overcome MDR mechanisms. The DB copolymers and their doxorubicin (Dox) conjugates significantly increased Dox accumulation in P-gp positive cells, markedly sensitizing them to Dox cytotoxic activity. The underlying mechanisms included depletion of intracellular ATP with subsequent inhibition of P-gp mediated drug efflux, an altered mitochondrial membrane potential, and increased ROS production. Moreover, the DB-Dox conjugates inhibited tumor growth in vivo more effectively compared to the corresponding PHPMA-based drug delivery system. Copolymers with additionally loaded PPO in the micelle core demonstrated superior efficacy in terms of P-gp inhibition, ATP depletion, and chemosensitizing effect in vitro, as well as antitumor activity in vivo. DB copolymers effectively depleted ATP levels both in vitro and in vivo using patient-derived xenograft (PDX) models, underscoring their capacity to enhance the effectiveness of standard chemotherapy and translational potential.

Simultaneous Delivery of Doxorubicin and Protease Inhibitor Derivative to Solid Tumors via Star-Shaped Polymer Nanomedicines Overcomes P-gp- and STAT3-Mediated Chemoresistance

The derivative of protease inhibitor ritonavir (5-methyl-4-oxohexanoic acid ritonavir ester; RD) was recently recognized as a potent P-gp inhibitor and cancerostatic drug inhibiting the proteasome and STAT3 signaling. Therefore, we designed high-molecular-weight HPMA copolymer conjugates with a PAMAM dendrimer core bearing both doxorubicin (Dox) and RD (Star-RD + Dox) to increase the circulation half-life to maximize simultaneous delivery of Dox and RD into the tumor. Star-RD inhibited P-gp activity, potently sensitizing both low- and high-P-gp-expressing cancer cells to the cytostatic and proapoptotic activity of Dox in vitro. Star-RD + Dox possessed higher cytostatic and proapoptotic activities compared to Star-Dox and the equivalent mixture of Star-Dox and Star-RD in vitro. Star-RD + Dox efficiently inhibited STAT3 signaling and induced caspase-3 activation and DNA fragmentation in cancer cells in vivo. Importantly, Star-RD + Dox was found to have superior antitumor activity in terms of tumor growth inhibition and increased survival of mice bearing P-gp-expressing tumors.

Polymer-Based Drug-Free Therapeutics for Anticancer, Anti-Inflammatory, and Antibacterial Treatment

This paper summarizes the area of biomedicinal polymers, which serve as nanomedicines even though they do not contain any anticancer or antiinflammatory drugs. These polymer nanomedicines with unique design are in the literature highlighted as a novel class of therapeutics called "drug-free macromolecular therapeutics." Their therapeutic efficacy is based on the tailored multiple presentations of biologically active vectors, i.e., peptides, oligopeptides, or oligosaccharides. Thus, they enable, for example, to directly induce the apoptosis of malignant cells by the crosslinking of surface slowly internalizing receptors, or to deplete the efficacy of tumor-associated proteins. The precise biorecognition of natural binding motifs by multiple vectors on the polymer construct remains the crucial part in the designing of these drug-free nanomedicines. Here, the rationales, designs, synthetic approaches, and therapeutic potential of drug-free macromolecular therapeutics consisting of various active vectors are described in detail. Recent developments and achievements for namely B-cell lymphoma treatment, Gal-3-positive tumors, inflammative liver injury, and bacterial treatment are reviewed and highlighted. Finally, a possible future prospect within this highly exciting new field of nanomedicine research is presented.

PEGylated N-(2 hydroxypropyl) methacrylamide polymeric micelles as nanocarriers for the delivery of doxorubicin in breast cancer

In the present study, polymeric micelles constituted of N-(2-hydroxypropyl)methacrylamide (HPMA) and methoxypoly(ethylene glycol) (mPEG)-based copolymer, mPEG-b-HPMA was studied for the delivery of an anticancer drug, doxorubicin (DOX) by physically loading the drug into its core. A series of mPEG-b-HPMA copolymers of different molecular weights (MWs, ∼4000-25,000 Da) by using various initiator: monomer feed ratios (1:25/75/125/175) were synthesized by radical polymerization technique. The DOX-loaded micelles were prepared at different drug to polymer ratios by thin film hydration method. Block copolymers were structurally characterized by gel permeation chromatography (GPC), ¹H-NMR spectroscopy, fourier transform infrared spectroscopy (FTIR), and critical micelles concentration studies. The DLS and SEM studies indicated that the micelles were spherical with diameters ∼20-100 nm. The DOX-loaded mPEG-b-HPMA micelles, P6-M1, prepared by the polymer synthesized using initiator: monomer feed ratios of 1:175 and at polymer to drug ratios of 10:1 exhibited low particle sizes (∼46.8 nm), highest drug loading and encapsulation efficiencies (5.6 %, and 63.3 %, respectively) compared to the other tested formulations. Confocal microscopy study indicated that the P6-M1 was taken up by breast cancer cell lines, 4T1, MCF-7, and MDA-MB-231in a time-dependent manner. P6-M1 displayed lower half maximal inhibitory concentration (IC₅₀) compared to free drug in all tested treatment durations compared to free DOX. P6-M1 was safe in hemolysis studies with sustained DOX residence in circulation compared to free DOX. The results indicated that mPEG-b-HPMA could be utilized to load DOX effectively, and the optimized nano-micelles, P6-M1 could serve as a promising nanomedicine to treat breast cancer.

Clinically-Relevant ABC Transporter for Anti-Cancer Drug Resistance

Multiple drug resistance (MDR), referring to the resistance of cancer cells to a broad spectrum of structurally and mechanistically unrelated drugs across membranes, severely impairs the response to chemotherapy and leads to chemotherapy failure. Overexpression of ATP binding cassette (ABC) transporters is a major contributing factor resulting in MDR, which can recognize and mediate the efflux of diverse drugs from cancer cells, thereby decreasing intracellular drug concentration. Therefore, modulators of ABC transporter could be used in combination with standard chemotherapeutic anticancer drugs to augment the therapeutic efficacy. This review summarizes the recent advances of important cancer-related ABC transporters, focusing on their physiological functions, structures, and the development of new compounds as ABC transporter inhibitors.

HPMA-Based Copolymers Carrying STAT3 Inhibitor Cucurbitacin-D as Stimulus-Sensitive Nanomedicines for Oncotherapy

The study describes the synthesis, physicochemical properties, and biological evaluation of polymer therapeutics based on N-(2-hydroxypropyl)methacrylamide (HPMA) copolymers intended for a tumor-targeted immuno-oncotherapy. Water-soluble linear and cholesterol-containing HPMA precursors were synthesized using controlled reversible addition–fragmentation chain transfer polymerization to reach molecular weight M_n about 2 × 10⁴ g·mol⁻¹ and low dispersity. These linear or self-assembled micellar conjugates, containing immunomodulatory agent cucurbitacin-D (CuD) or the anticancer drug doxorubicin (Dox) covalently bound by the hydrolytically degradable hydrazone bond, showed a hydrodynamic size of 10–30 nm in aqueous solutions. The CuD-containing conjugates were stable in conditions mimicking blood. Importantly, a massive release of active CuD in buffer mimicking the acidic tumor environment was observed. In vitro, both the linear (LP-CuD) and the micellar (MP-CuD) conjugates carrying CuD showed cytostatic/cytotoxic activity against several cancer cell lines. In a murine metastatic and difficult-to-treat 4T1 mammary carcinoma, only LP-CuD showed an anticancer effect. Indeed, the co-treatment with Dox-containing micellar polymer conjugate and LP-CuD showed potentiation of the anticancer effect. The results indicate that the binding of CuD, characterized by prominent hydrophobic nature and low bioavailability, to the polymer carrier allows a safe and effective delivery. Therefore, the conjugate could serve as a potential component of immuno-oncotherapy schemes within the next preclinical evaluation.

Mussel-Inspired Polydopamine: The Bridge for Targeting Drug Delivery System and Synergistic Cancer Treatment

Polydopamine (PDA), a mussel-inspired molecule, has been recognized as attractive in cancer therapy due to a number of inherent advantages, such as good biocompatibility, outstanding drug-loading capacity, degradability, superior photothermal conversion efficiency, and low tissue toxicity. Furthermore, due to its strong adhesive property, PDA is able to functionalize various nanomaterials, facilitating the construction of a PDA-based multifunctional platform for targeted or synergistic therapy. Herein, recent PDA research, including targeted drug delivery, single-mode therapy, and diverse synergistic therapies against cancer, are summarized and discussed. For synergistic therapy, advanced developments are highlighted, such as photothermal/radiotherapy, chemo-/photothermal/gene therapy, photothermal/immune therapy, and photothermal/photodynamic/immune therapy. Finally, the challenges and promise of PDA for biomedical applications in the future are discussed.

Graft copolymers with tunable amphiphilicity tailored for efficient dual drug delivery via encapsulation and pH-sensitive drug conjugation

Amphiphilic poly(ε-caprolactone)-graft-(poly-N-(2-hydroxypropyl) methacrylamide) copolymers with tunable solution properties form stable micelles with high drug payload via simultaneous encapsulation and pH-sensitive covalent conjugation.