Improved Synthesis of a Novel Biodegradable Tunable Micellar Polymer Based on Partially Hydrogenated Poly(β-malic Acid-co-benzyl Malate)

Advanced Polymeric Nanoparticles for Cancer Immunotherapy: Materials Engineering, Immunotherapeutic Mechanism and Clinical Translation

Cancer immunotherapy, which leverages immune system components to treat malignancies, has emerged as a cornerstone of contemporary therapeutic strategies. Yet, critical concerns about the efficacy and safety of cancer immunotherapies remain formidable. Nanotechnology, especially polymeric nanoparticles (PNPs), offers unparalleled flexibility in manipulation-from the chemical composition and physical properties to the precision control of nanoassemblies. PNPs provide an optimal platform to amplify the potency and minimize systematic toxicity in a broad spectrum of immunotherapeutic modalities. In this comprehensive review, the basics of polymer chemistry, and state-of-the-art designs of PNPs from a physicochemical standpoint for cancer immunotherapy, encompassing therapeutic cancer vaccines, in situ vaccination, adoptive T-cell therapies, tumor-infiltrating immune cell-targeted therapies, therapeutic antibodies, and cytokine therapies are delineated. Each immunotherapy necessitates distinctively tailored design strategies in polymeric nanoplatforms. The extensive applications of PNPs, and investigation of their mechanisms of action for enhanced efficacy are particularly focused on. The safety profiles of PNPs and clinical research progress are discussed. Additionally, forthcoming developments and emergent trends of polymeric nano-immunotherapeutics poised to transform cancer treatment paradigms into clinics are explored.

Enzyme/pH-sensitive nanoparticles based on poly(β-L-malic acid) for drug delivery with enhanced endocytosis

Nanoparticles (NPs) derived from branched copolymers of poly (β-L-malic acid) (PMLA) have been extensively investigated for drug delivery due to their high density of pendant carboxyl groups. This abundant functional group availability enhances their potential as effective drug delivery systems; however, the strong negative charge of PMLA poses a challenge in its uptake by cancer cells due to electrostatic repulsion. In this study, we developed novel enzyme- and pH-sensitive nanoparticles (EP-NPs) based on PMLA, demonstrating tumor-specific behavior and selective activation within tumor tissues. To enhance the cellular internalization of the nanoparticles, we incorporated transactivator of transcription (TAT). In summary, long-chain polyethylene glycol (PEG) was conjugated to PMLA to confer specificity to the TAT peptide. This was achieved using a tetrapeptide linker: alanine-alanine-asparagine-leucine (AANL), which serves as a substrate for legumain. Legumain is a highly conserved cysteine protease primarily found in lysosomes and blood vessels, initially discovered in legumes. It is markedly overexpressed in numerous solid tumors, as well as in endothelial cells and tumor-associated macrophages. The release of doxorubicin in tumor cells was sustained due to the low pH (5.0-5.5) and degradation of PMLA. The PEG modification optimized the particle size and shielded the nanoparticles from plasma proteins and detection by the reticuloendothelial system, thereby prolonging their long circulation time. Once the nanoparticles reached the tumor microenvironment, the AANL was cleaved by legumain, exposing the TAT peptide on the surface, which enhances cellular internalization. Both in vitro and in vivo efficacy studies demonstrated that these EP-NPs significantly inhibited tumor growth while exhibiting negligible systemic toxicity, thereby suggesting that the developed enzyme/pH-sensitive PMLA-based nanoparticle holds great promise as an anti-tumor drug delivery system.

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