Hydrolytic degradation of benzylated poly(beta-malic acid): influence of sample size, sample shape, and polymer composition

Polymalic acid for translational nanomedicine

With rich carboxyl groups in the side chain, biodegradable polymalic acid (PMLA) is an ideal delivery platform for multifunctional purposes, including imaging diagnosis and targeting therapy. This polymeric material can be obtained via chemical synthesis, or biological production where L-malic acids are polymerized in the presence of PMLA synthetase inside a variety of microorganisms. Fermentative methods have been employed to produce PMLAs from biological sources, and analytical assessments have been established to characterize this natural biopolymer. Further functionalized, PMLA serves as a versatile carrier of pharmaceutically active molecules at nano scale. In this review, we first delineate biosynthesis of PMLA in different microorganisms and compare with its chemical synthesis. We then introduce the biodegradation mechanism PMLA, its upscaled bioproduction together with characterization. After discussing advantages and disadvantages of PMLA as a suitable delivery carrier, and strategies used to functionalize PMLA for disease diagnosis and therapy, we finally summarize the current challenges in the biomedical applications of PMLA and envisage the future role of PMLA in clinical nanomedicine.

The biosynthesis of polymalic acid (PMLA) and its biotechnical high-grade production from microorganisms compared with the chemical synthesis of PMLA

The physicochemical and biological characteristics of PMLA and its derivatives

How PMLA’s general chemical characteristics can be used to generate various macromolecular compounds for pharmaceutical delivery

The concepts of biological and clinical targeting exemplified by PMLA-based drugs and imaging agents and their biodistribution and biodegradability

An evaluation of the mechanisms that generate preclinical antitumor efficacy and the translational potential for clinical imaging

Covalent Binding of Mannosyl Ligand via 6-O Position and Glycolic Arm to Target a PLCA-Type Degradable Drug Carrier toward Macrophages

Mononuclear phagocytes play a central role in the defense against important pathologies. Attempts were made to target drugs toward this cell type by using specific interactions between a mannose ligand and the lectin-type specific receptor present on the macrophage membrane. Basically, the use of a mannosyl radical as a homing device raised several problems: necessity to keep unmodified the part of the molecule which gives rise to lectin recognition, complex protection-deprotection chemistry, and blockage of the aldehyde function to preclude any side reaction. A new method was used to bind α-D-methylmannopy-ranoside, a commercially available precursor, through its primary hydroxyl group to the hydrosoluble bioresorbable drug carrier poly(L-lysine citramide imide). The method consisted of a few steps that did not require special protection of secondary hydroxyl groups. In the resulting conjugate, the pyranose structure of the sugar was retained. In vivo recognition of the conjugate by the lectin of mononuclear phagocytes was preserved.

Synthesis, degradability, and drug releasing properties of methyl esters of fungal poly(beta,L-malic acid)

Methyl esters of microbial poly(beta,L-malic acid) for conversion degrees of 25, 50, 75, and 100% were prepared by treatment of the polyacid with diazomethane. Esterification proceeded with retention of the molecular weight of the parent polyacid and the copolymers displayed a blocky microstructure consisting of short segments of malic and methyl malate sequences. The thermal stability of the copolyesters was lower than those of the parent homopolymers and all of them were fairly crystalline with melting temperatures within the range of 170-175 degrees C. They were degraded rapidly by water, the hydrolysis rate being highly dependent on the methylation degree. Microspheres with mean-average diameters in the range of 1-20 microm were prepared from the 100% methylated product by the emulsion-evaporation solvent method. Encapsulation of erythromycin was efficiently performed in these microparticles and its releasing upon incubation in simulated physiological medium was evaluated for different drug loads. Drug delivery was observed to occur by a releasing mechanism largely determined by the hydrodegradation of the host polymer and independent of the amount of loaded drug.