Novel Macrocyclic Peptidomimetics Targeting the Polo-Box Domain of Polo-Like Kinase 1

Macrocycles and macrocyclization in anticancer drug discovery: Important pieces of the puzzle

Increasing disease-related proteins have been identified as novel therapeutic targets. Macrocycles are emerging as potential solutions, bridging the gap between conventional small molecules and biomacromolecules in drug discovery. Inspired by successful macrocyclic drugs of natural origins, macrocycles are attracting more attention for enhanced binding affinity and target selectivity. Due to the conformation constraint and structure preorganization, macrocycles can reach bioactive conformations more easily than parent acyclic compounds. Also, rational macrocyclization combined with sequent structural modification will help improve oral bioavailability and combat drug resistance. This review introduces various strategies to enhance membrane permeability in macrocyclization and subsequent modification, such as N-methylation, intramolecular hydrogen bonding modulation, isomerization, and reversible bicyclization. Several case studies highlight macrocyclic inhibitors targeting kinases, HDAC, and protein-protein interactions. Finally, some macrocyclic agents targeting tumor microenvironments are illustrated.

Novel dual targeting cubosomes modified with angiopep-2 for co-delivery GNA and PLHSpT to brain glioma

3Glioblastoma multiforme is the most aggressive malignant brain tumor. However, the treatment of glioblastoma multiforme faces great challenges owing to difficult penetration of the blood-brain barrier. Therefore, more effective treatment strategies are desired quite urgently. In our study, a dual-targeting drug delivery system for co-loading with hydrophobic Gambogenic acid and hydrophilic PLHSpT was developed by cubosomes with angiopep-2 decorating. The Ang-cubs-(GNA + PLHSpT) was prepared by high-temperature emulsification-low-temperature solidification demonstrating excellent physical properties.Transmission electron microscopy revealed that Ang-cubs-(GNA + PLHSpT) was nearly spherical with a "core-shell" double-layer structure. Differential scanning calorimetry suggested that a new phase was formed. Small-angle X-ray scattering also verified that Ang-cubs-(GNA + PLHSpT) retains the Pn3m cubic. Moreover, laser confocal indicated that Ang-cubs-(GNA + PLHSpT) was capable of crossing BBB via binding to lipoprotein receptor-related protein-1, likely suggesting the potential tumor-specific targeting characteristic. Compared to free drug and cubs-(GNA + PLHSpT), Ang-cubs-(GNA + PLHSpT) was easily taken up by C6 cell and exhibited better anti-glioma effects in vitro. Importantly, GNA and PLHSpT co-loaded Ang-cubs could suppress tumor growth and significantly prolong survival in vivo. In conclusion, Ang-cubs-(GNA + PLHSpT) acts as a new dual-targeting drug delivery system for the treatment of GBM.

Inhibitors of the PLK1 polo-box domain: drug design strategies and therapeutic opportunities in cancer

INTRODUCTION

Polo Like Kinase 1 (PLK1) is a key regulator of mitosis and its overexpression is frequently observed in a wide variety of human cancers, while often being associated with poor survival rates. Therefore, it is considered a potential and attractive target for cancer therapeutic development. The Polo like kinase family is characterized by the presence of a unique C terminal polobox domain (PBD) involved in regulating kinase activity and subcellular localization. Among the two functionally essential, druggable sites with distinct properties that PLK1 offers, targeting the PBD presents an alternative approach for therapeutic development.

AREAS COVERED

Significant progress has been made in progressing from the peptidic PBD inhibitors first identified, to peptidomimetic and recently drug-like small molecules. In this review, the rationale for targeting the PBD over the ATP binding site is discussed, along with recent progress, challenges, and outlook.

EXPERT OPINION

The PBD has emerged as a viable alternative target for the inhibition of PLK1, and progress has been made in using compounds to elucidate mechanistic aspects of activity regulation and in determining roles of the PBD. Studies have resulted in proof of concept of in vivo efficacy suggesting promise for PBD binders in clinical development.

Present and Future Perspective on PLK1 Inhibition in Cancer Treatment

Polo-like kinase 1 (PLK1) is the principle member of the well conserved serine/threonine kinase family. PLK1 has a key role in the progression of mitosis and recent evidence suggest its important involvement in regulating the G2/M checkpoint, in DNA damage and replication stress response, and in cell death pathways. PLK1 expression is tightly spatially and temporally regulated to ensure its nuclear activation at the late S-phase, until the peak of expression at the G2/M-phase. Recently, new roles of PLK1 have been reported in literature on its implication in the regulation of inflammation and immunological responses. All these biological processes are altered in tumors and, considering that PLK1 is often found overexpressed in several tumor types, its targeting has emerged as a promising anti-cancer therapeutic strategy. In this review, we will summarize the evidence suggesting the role of PLK1 in response to DNA damage, including DNA repair, cell cycle progression, epithelial to mesenchymal transition, cell death pathways and cancer-related immunity. An update of PLK1 inhibitors currently investigated in preclinical and clinical studies, in monotherapy and in combination with existing chemotherapeutic drugs and targeted therapies will be discussed.