Delivery strategies in treatments of leukemia

Leukemia is a hematological malignancy associated with the uncontrolled proliferation of mutant progenitors, suppressing the production of normal blood cells. Current treatments, including chemotherapy, radiotherapy, and immunotherapy, still lead to unsatisfactory results with a 5 year survival rate of only 30-50%. The poor prognosis is related to both disease relapse and treatment-associated toxicity. Delivery strategies can improve the in vivo pharmacokinetics of drugs, navigating the therapeutics to target cells or the tumor microenvironment and reversing drug resistance, which maximizes tumor elimination and alleviates systematic adverse effects. This review discusses available FDA-approved anti-leukemia drugs and therapies with a focus on the advances in the development of anti-leukemia drug delivery systems. Additionally, challenges in clinical translation of the delivery strategies and future research opportunities in leukemia treatment are also included.

Possibility for double optimization of siRNA intracellular delivery efficiency and antibacterial activity: Structure screening of pH-sensitive triblock amphiphilic polycation micelles

Optimal combination of hydrophobic-hydrophilic balance, proton buffering and electrostatic interaction is the key issue for designing polycations as efficient gene vectors and antibacterial agents. Herein, we screened a series of pH-sensitive quaternary ammonium-based amphiphilic triblock copolymers, mPEG_2k-P(DPA_a/DMA_b)-PQA_c (TDDE-x), which had different pKa values and proton buffering capacities. Significantly, we found that both the highest siRNA intracellular delivery efficiency and the strongest antibacterial capacity occurred on TDDE-3 micelles with the segment structure of mPEG_2k-P(DPA₅₀/DMA₅₆)-PQA₅₅. The TDDE-3/siRNA complex achieved 67% silencing efficiency on H9C2 cells (N/P = 5, 50 nM siRNA), higher than the advanced commercial transfection reagents RNAiMAX (58%) and Lipo2000 (30%). Moreover, TDDE-3 micelles showed quite low MICs of 32 μg/mL and 8 μg/mL against E. coli and S. aureus, respectively. Further studies on the structure-function relationship indicated that TDDE-3 micelles could mediate robust endosome escape and siRNA cytosolic release, and strong bacterial cell membrane-destabilizing function. Undoubtedly, this work reveals the possibility for double optimization of siRNA intracellular delivery efficiency and antibacterial activity of amphiphilic polycations by reasonable structure design, which is significant for low-cost development and clinical translation of efficient multifunctional polycations.

Well-Defined Cationic N-[3-(Dimethylamino)propyl]methacrylamide Hydrochloride-Based (Co)polymers for siRNA Delivery

Cationic glycopolymers have shown to be excellent candidates for the fabrication of gene delivery devices due to their ability to electrostatically interact with negatively charged nucleic acids and the carbohydrate residues ensure enhanced stability and low toxicity of the polyplexes. The ability to engineer the polymers for optimized compositions, molecular weights, and architectures is critical in the design of effective gene delivery vehicles. Therefore, in this study, the aqueous reversible addition-fragmentation chain transfer polymerization (RAFT) was used to synthesize well-defined cationic glycopolymers with various cationic segments. For the preparation of cationic parts, N-[3-(dimethylamino)propyl]methacrylamide hydrochloride (DMAPMA·HCl), water-soluble methacrylamide monomer containing tertiary amine, was polymerized to produce DMAPMA·HCl homopolymer, which was then used as macroCTA in the block copolymerization with two other methacrylamide monomers containing different pendant groups, namely, 2-aminoethyl methacrylamide hydrochloride (AEMA) (with primary amine) and N-(3-aminopropyl) morpholine methacrylamide (MPMA) (with morpholine ring). In addition, statistical copolymers of DMAPMA.HCl with either AEMA or MPMA were also synthesized. All resulting cationic polymers were utilized as macroCTA for the RAFT copolymerization with 2-lactobionamidoethyl methacrylamide (LAEMA), which consists of the pendent galactose residues to achieve DMAPMA·HCl-based glycopolymers. From the in vitro cytotoxicity study, the cationic glycopolymers showed better cell viabilities than the corresponding cationic homopolymers. Furthermore, complexation of the cationic polymers with siRNA, cellular uptake of the resulting polyplexes, and gene knockdown efficiencies were evaluated. All cationic polymers/glycopolymers demonstrated good complexation ability with siRNA at low weight ratios. Among these cationic polymer-siRNA polyplexes, the polyplexes prepared from the two glycopolymers, P(DMAPMA₆₅-b-LAEMA₁₅) and P[(DMAPMA₆₅-b-MPMA₆₃)-b-LAEMA₁₆], showed outstanding results in the cellular uptake, high EGFR knockdown, and low post-transfection toxicity, suggesting the great potential in siRNA delivery of these novel glycopolymers.

Folate-decorated PEGylated triblock copolymer as a pH/reduction dual-responsive nanovehicle for targeted intracellular co-delivery of doxorubicin and Bcl-2 siRNA

Co-delivery of chemotherapeutic drug and small interfering RNA (siRNA) within a single nanovehicle has emerged as a promising combination therapy approach to treating cancers because of their synergistic effect. Nanocarrier delivery systems with low cytotoxicity and high efficiency are needed for such a purpose. In this study, a novel folate-conjugated PEGylated cationic triblock copolymer, poly(acrylhydrazine)-block-poly(3-dimethylaminopropyl methacrylamide)-block-poly(acrylhydrazine) (PAH-b-PDMAPMA-b-PAH), was synthesized and evaluated as a stimuli-sensitive vehicle for the targeted co-delivery of doxorubicin (DOX) and Bcl-2 siRNA into breast cancer MCF-7 cells. The synthetic process of the PEGylated triblock copolymer involved sequential reversible addition-fragmentation chain transfer polymerization, PEGylation and removal of tert-butoxy carbamate protecting groups. Folate-conjugated and/or -unconjugated poly(ethylene glycol) segments were grafted onto PAH-b-PDMAPMA-b-PAH via a reduction-sensitive disulfide linkage. The synthetic polymers were characterized by ¹H NMR and gel permeation chromatography. The PEGylated triblock copolymer could chemically conjugate DOX onto PAH blocks via pH-responsive hydrazone bonds and simultaneously complex negatively charged Bcl-2 siRNA with cationic PDMAPMA blocks through electrostatic interactions at N/P ratios≥32:1 to form multifunctional nanomicelleplexes. The nanomicelleplexes exhibited spherical shape, possessed a positively charged surface with a zeta potential of +22.5mV and had a desirable and uniform particle size of 187nm. In vitro release studies revealed that the nanomicelleplexes could release DOX and Bcl-2 siRNA in a reduction and pH dual-sensitive manner and the payload release was significantly enhanced in a reductive acidic environment mimicking the endosomes/lysosomes of cancer cells compared to under physiology conditions. Furthermore, the release of both DOX and siRNA was found to follow Higuchi kinetic model. Confocal laser scanning microscopy, flow cytometry and MTT analyses confirmed that, compared with folate-undecorated nanomicelleplexes, folate-decorated nanomicelleplexes could more effectively co-deliver DOX and Bcl-2 siRNA into MCF-7 cells and showed a stronger cell-killing effect. The pristine PEGylated triblock copolymer exhibited good cytocompatibility. Moreover, co-delivery of DOX and Bcl-2 siRNA achieved a significant synergistic antitumor efficacy. These findings suggested that the folate-decorated PEGylated cationic triblock copolymer might be a promising vehicle for targeted intracellular co-delivery of DOX and siRNA in MCF-7 cells, representing a potential clinical combination therapy for breast cancer treatment.

Study of the RAFT homopolymerization and copolymerization of N-[3-(dimethylamino)propyl]methacrylamide hydrochloride and evaluation of the cytotoxicity of the resulting homo- and copolymers

Well-defined p(DMAPMA·HCl) homopolymers with good chain extension ability were obtained by the RAFT in acidic conditions and precipitation in acetone.

Reduction-responsive modification-induced higher efficiency for attenuation of tumor metastasis of low molecular weight heparin functionalized liposomes

Higher efficiency of attenuation of tumor metastasis was achievedviareduction-responsive modification of low molecular weight heparin on doxorubicin liposomes.

Stimuli-induced multiple dissociation and micellization transitions of random copolymers

Upon UV irradiation, random copolymer P(NBMA-co-MEO₂MA-co-OEGMA) was converted into P(MAA-co-MEO₂MA-co-OEGMA) with disruption of the initial micelles. Further increasing the temperature or decreasing the pH induced the reformation of micelles.