Investigation into the Biological Impact of Block Size on Cathepsin S-Degradable HPMA Copolymers

Protease-triggered bioresponsive drug delivery for the targeted theranostics of malignancy

Proteases have a fundamental role in maintaining physiological homeostasis, but their dysregulation results in severe activity imbalance and pathological conditions, including cancer onset, progression, invasion, and metastasis. This striking importance plus superior biological recognition and catalytic performance of proteases, combining with the excellent physicochemical characteristics of nanomaterials, results in enzyme-activated nano-drug delivery systems (nanoDDS) that perform theranostic functions in highly specific response to the tumor phenotype stimulus. In the tutorial review, the key advances of protease-responsive nanoDDS in the specific diagnosis and targeted treatment for malignancies are emphatically classified according to the effector biomolecule types, on the premise of summarizing the structure and function of each protease. Subsequently, the incomplete matching and recognition between enzyme and substrate, structural design complexity, volume production, and toxicological issues related to the nanocomposites are highlighted to clarify the direction of efforts in nanotheranostics. This will facilitate the promotion of nanotechnology in the management of malignant tumors.

In Vitro Evaluation and Biodistribution Studies of HPMA Copolymers Targeting the Gastrin Releasing Peptide Receptor in Prostate Cancer

PURPOSE

The development of diagnostic and therapeutic agents utilizing small peptides (e.g., bombesin (BBN)) to target the overexpression of the gastrin-releasing peptide receptor (GRPR) in cancers has been widely investigated. Herein, we examine the capabilities of BBN-modified HPMA copolymers to target the GRPR.

METHODS

Four positive, four negative, and two zwitterionic BBN HPMA copolymer conjugates of varying peptide content and charge were synthesized. In vitro and in vivo studies were conducted in a GRPR-overexpressing prostate cancer cell line (PC-3) and a normal CF-1 mouse model, respectively.

RESULTS

Cellular uptake of the conjugates were found to be charge and BBN density dependent. The positively-charged conjugates illustrated a direct relationship between the extent of cellular internalization, ranging from 0.7 to 20%, and BBN-incorporation density. The negative and zwitterionic conjugates showed low PC-3 uptake values. Blocking studies confirmed the GRPR-targeting effect of the positively-charged constructs. In vivo studies of the positively-charged copolymers resulted in rapid blood clearance by the mononuclear phagocyte system (MPS)-associated tissues (e.g., liver and spleen).

CONCLUSION

Positively-charged BBN-HPMA copolymer conjugates demonstrated good GRPR-targeting and internalization in vitro. However, the impact of peptide density and charge on in vivo MPS recognition are parameters that must be optimized in future agent development.

Polymer nanomedicines

Polymer nanomedicines (macromolecular therapeutics, polymer-drug conjugates, drug-free macromolecular therapeutics) are a group of biologically active compounds that are characterized by their large molecular weight. This review focuses on bioconjugates of water-soluble macromolecules with low molecular weight drugs and selected proteins. After analyzing the design principles, different structures of polymer carriers are discussed followed by the examination of the efficacy of the conjugates in animal models and challenges for their translation into the clinic. Two innovative directions in macromolecular therapeutics that depend on receptor crosslinking are highlighted: a) Combination chemotherapy of backbone degradable polymer-drug conjugates with immune checkpoint blockade by multivalent polymer peptide antagonists; and b) Drug-free macromolecular therapeutics, a new paradigm in drug delivery.

Cathepsin-sensitive nanoscale drug delivery systems for cancer therapy and other diseases

Cathepsins are an important category of enzymes that have attracted great attention for the delivery of drugs to improve the therapeutic outcome of a broad range of nanoscale drug delivery systems. These proteases can be utilized for instance through actuation of polymer-drug conjugates (e.g., triggering the drug release) to bypass limitations of many drug candidates. A substantial amount of work has been witnessed in the design and the evaluation of Cathepsin-sensitive drug delivery systems, especially based on the tetra-peptide sequence (Gly-Phe-Leu-Gly, GFLG) which has been extensively used as a spacer that can be cleaved in the presence of Cathepsin B. This Review Article will give an in-depth overview of the design and the biological evaluation of Cathepsin-sensitive drug delivery systems and their application in different pathologies including cancer before discussing Cathepsin B-cleavable prodrugs under clinical trials.

pH- and enzyme-triggered drug release as an important process in the design of anti-tumor drug delivery systems

It is necessary to design a reasonable drug delivery system(DDS) for targeted release to overcome the potential toxicity and poor selectivity of anti-tumor drug. How a drug is released from a DDS is a critical issue that determines whether the DDS is designed successfully. We all know that the microenvironment of tumors is quite different from normal tissues, such as its acidic environment, different expression levels of some enzymes, etc. These features are widely used in the design of DDSs and play an important role in the drug release process in vivo. Numerous DDSs have been designed and synthesized. This article attention to how drugs are released from DDSs. We summarizes and classify the characteristic enzymes and chemical bonds used in the drug release process by browsing a large number of papers, and describes how they are applied in DDSs with specific examples. By understanding these acid-sensitive chemical bonds and over-expressed enzymes in tumors, different DDSs can be designed for different drug structures to solve specific problems of anti-tumor drugs.

Biorecognition: A key to drug-free macromolecular therapeutics

This review highlights a new paradigm in macromolecular nanomedicine - drug-free macromolecular therapeutics (DFMT). The effectiveness of the new system is based on biorecognition events without the participation of low molecular weight drugs. Apoptosis of cells can be initiated by the biorecognition of complementary peptide/oligonucleotide motifs at the cell surface resulting in the crosslinking of slowly internalizing receptors. B-cell CD20 receptors and Non-Hodgkin lymphoma (NHL) were chosen as the first target. Exposing cells to a conjugate of one motif with a targeting ligand decorates the cells with this motif. Further exposure of decorated cells to a macromolecule (synthetic polymer or human serum albumin) containing multiple copies of the complementary motif as grafts results in receptor crosslinking and apoptosis induction in vitro and in vivo. The review focuses on recent developments and explores the mechanism of action of DFMT. The altered molecular signaling pathways demonstrated the great potential of DFMT to overcome rituximab resistance resulting from either down-regulation of CD20 or endocytosis and trogocytosis of rituximab/CD20 complexes. The suitability of this approach for the treatment of blood borne cancers is confirmed. In addition, the widespread applicability of DFMT as a new concept in macromolecular therapeutics for numerous diseases is exposed.