Synthesis, bioconversion, pharmacokinetic and pharmacodynamic evaluation of N-isopropyl-oxy-carbonyloxymethyl prodrugs of CZh-226, a potent and selective PAK4 inhibitor

Current scenario of fused pyrimidines with in vivo anticancer therapeutic potential

Cancer, characterized by uncontrolled cell growth and metastasis, is responsible for nearly one in six deaths and represents a severe threat to public health worldwide. Chemotherapy can substantially improve the quality of life and survival of patients with cancer, but anticancer chemotherapeutics are associated with a range of adverse effects. Moreover, almost all currently available anticancer chemotherapeutics could develop drug resistance over a period of time of application in cancer patients and ultimately lead to cancer relapse and death in 90% of patients, creating an urgent need to develop new anticancer agents. Fused pyrimidines trait the inextricable part of DNA and RNA and are vital in numerous biological processes. Fused pyrimidines can act on various biological cancer targets and have the potential to address drug resistance. In addition, more than 20 fused pyrimidines have already been approved for clinical treatment of different cancers and occupy a prominent place in the current therapeutic arsenal, revealing that fused pyrimidines are privileged scaffolds for the development of novel anticancer chemotherapeutics. The purpose of this review is to summarize the current scenario of fused pyrimidines with in vivo anticancer therapeutic potential along with their acute toxicity, metabolic profiles as well as pharmacokinetic properties, toxicity and mechanisms of action developed from 2020 to the present to facilitate further rational exploitation of more effective candidates.

Current scenario of pyrazole hybrids with in vivo therapeutic potential against cancers

Chemotherapeutics occupy a pivotal role in the medication of different types of cancers, but the prevalence and mortality rates of cancer remain high. The drug resistance and low specificity of current available chemotherapeutics are the main barriers for the effective cancer chemotherapy, evoking an immediate need for the development of novel anticancer agents. Pyrazole is a highly versatile five-membered heterocycle with two adjacent nitrogen atoms and possesses remarkable therapeutic effects and robust pharmacological potency. The pyrazole derivatives especially pyrazole hybrids have demonstrated potent in vitro and in vivo efficacies against cancers through multiple mechanisms, inclusive of apoptosis induction, autophagy regulation, and cell cycle disruption. Moreover, several pyrazole hybrids such as crizotanib (pyrazole-pyridine hybrid), erdafitinib (pyrazole-quinoxaline hybrid) and ruxolitinib (pyrazole-pyrrolo [2,3-d]pyrimidine hybrid) have already been approved for the cancer therapy, revealing that pyrazole hybrids are useful scaffolds to develop novel anticancer agents. The purpose of this review is to summarize the current scenario of pyrazole hybrids with potential in vivo anticancer efficacy along with mechanisms of action, toxicity, and pharmacokinetics, covering papers published in recent 5 years (2018-present), to facilitate further rational exploitation of more effective candidates.

The Inhibitory Mechanism of 7H-Pyrrolo[2,3-d]pyrimidine Derivatives as Inhibitors of P21-Activated Kinase 4 through Molecular Dynamics Simulation

The overexpression of p21-activated kinase 4 (PAK4) is associated with a variety of cancers. In this paper, the binding modes and inhibitory mechanisms of four 7H-pyrrolo[2,3-d]pyrimidine competitive inhibitors of PAK4 were investigated at the molecular level, mainly using molecular dynamics simulations and binding free energy calculations. The results show that the inhibitors had strong interactions with the hinge region, the β-sheets, and the residues with charged side chains around the 4-substituent. The terminal amino group of the inhibitor 5n was different from the other three, which could cause the enhancement of hydrogen bonds or electrostatic interactions formed with the surrounding residues. Thus, inhibitor 5n had the strongest inhibition capacity. The different halogen atoms on the 2-substituents of the inhibitors 5h, 5g, and 5e caused differences in the positions of the 2-benzene rings and affected the interactions of the hinge region. It also affected to some extent the orientations of the 4-imino groups and consequently their affinities for the surrounding charged residues. The combined results lead to the weakest inhibitory capacity of inhibitor 5e.

Recent advances on development of p21-activated kinase 4 inhibitors as anti-tumor agents

The p21-activated kinase 4 (PAK4) is a member of the PAKs family. It is overexpressed in multiple tumor tissues. Pharmacological inhibition of PAK4 attenuates proliferation, migration, and invasion of cancer cells. Recent studies revealed that inhibition of PAK4 sensitizes immunotherapy which has been extensively exploited as a new strategy to treat cancer. In the past few years, a large number of PAK4 inhibitors have been reported. Of note, the allosteric inhibitor KPT-9274 has been tested in phase Ⅰ clinic trials. Herein, we provide an update on recent research progress on the PAK4 mediated signaling pathway and highlight the development of the PAK4 small molecular inhibitors in recent 5 years. Meanwhile, challenges, limitations, and future developmental directions will be discussed as well.

Synthesis and biological evaluation of 7H-pyrrolo [2,3-d] pyrimidine derivatives as potential p21-activated kinase 4 (PAK4) inhibitors

PAK4 has been validated as a crucial effector of various signal pathways and play an important role in driving tumor progression. Here, we developed a series of 7H-pyrrolo [2,3-d] pyrimidine derivatives as PAK4 inhibitors. Compounds 5n and 5o showed higher enzymatic inhibitory activities (IC₅₀ = 2.7 and 20.2 nM, respectively) and potent activity (IC₅₀ = 7.8 and 38.3 nM, respectively) against MV4-11 cell line. Further flow cytometry assay revealed that the compound 5n can arrest MV4-11 cells at G₀/G₁ phase and induce cell apoptosis. Molecular mechanism study indicated that compound 5n regulated the phosphorylation of PAK4 in vitro. The docking study supported that compound 5n binds to PAK4 through various hydrogen bonding interactions and hydrophobic interactions. Thus, compound 5n represents a promising lead for the discovery of PAK4 directed therapeutic agents and may be considered for further drug development.

Target-responsive subcellular catabolism analysis for early-stage antibody-drug conjugates screening and assessment

Events including antibody‒antigen affinity, internalization, trafficking and lysosomal proteolysis combinatorially determine the efficiency of antibody-drug conjugate (ADC) catabolism and hence the toxicity. Nevertheless, an approach that conveniently identifies proteins requisite for payload release and the ensuing toxicity for mechanistic studies and quality assessment is lacking. Considering the plethora of ADC candidates under development, we developed a target-responsive subcellular catabolism (TARSC) approach that examines ADC catabolism and probes changes in response to targeted interferences of proteins of interest. We firstly applied TARSC to study the commercial T-DM1 and the biosimilar. We recorded unequivocal catabolic behaviors regardless of the absence and presence of the targeted interferences. Their negligible differences in TARSC profiles agreed with their undifferentiated anti-tumoral efficacy according to further in vitro viability and in vivo tumor growth assays, highlighting TARSC analysis as a useful tool for biosimilarity assessment and functional dissection of proteins requisite for ADC catabolism. Additionally, we employed TARSC to investigate the catabolic behavior of a new trastuzumab-toxin conjugate. Collectively, TARSC can not only characterize ADC catabolism at (sub)cellular level but also comprehensively determine which protein targets affect payload release and therapeutic outcomes. Future use of TARSC is thus anticipated in early-stage screening, quality assessment and mechanistic investigations of ADCs.

p21-activated kinase 4 phosphorylates peroxisome proliferator-activated receptor Υ and suppresses skeletal muscle regeneration

BACKGROUND

Skeletal muscle regeneration is an adaptive response to injury that is crucial to the maintenance of muscle mass and function. A p21-activated kinase 4 (PAK4) serine/threonine kinase is critical to the regulation of cytoskeletal changes, cell proliferation, and growth. However, PAK4's role in myoblast differentiation and regenerative myogenesis remains to be determined.

METHODS

We used a mouse model of myotoxin (notexin)-induced muscle regeneration. In vitro myogenesis was performed in the C2C12 myoblast cell line, primary myoblasts, and primary satellite cells. In vivo overexpression of PAK4 or kinase-inactive mutant PAK4^S474A was conducted in skeletal muscle to examine PAK4's kinase-dependent effect on muscle regeneration. The regeneration process was evaluated by determining the number and size of multinucleated myofibres and expression patterns of myogenin and eMyHC. To explore whether PAK4 inhibition improves muscle regeneration, mice were injected intramuscularly with siRNA that targeted PAK4 or orally administered with a chemical inhibitor of PAK4.

RESULTS

p21-activated kinase 4 was highly expressed during the myoblast stage, but expression gradually and substantially decreased as myoblasts differentiated into myotubes. PAK4 overexpression, but not kinase-inactive mutant PAK4^S474A overexpression, significantly impeded myoblast fusion and MyHC-positive myotube formation in C2C12 cells, primary myoblasts, and satellite cells (P < 0.01). Conversely, PAK4 silencing led to an 8.7% and a 20.3% increase in the number of multinucleated larger myotubes in C2C12 cells and primary myoblasts. Further, in vivo overexpression of PAK4 by adenovirus injection to mice prior to and after myotoxin-induced injury led to a 52.6% decrease in the number of eMyHC-positive myofibres on Day 5 in tibialis anterior muscles as compared with those injected with control adenoviruses (P < 0.01), while Ad-PAK4^S474A showed comparable muscle regeneration parameters. PAK4-induced repression of muscle regeneration coincided with an increase in phosphatase and tensin homologue (PTEN) expression and a decrease in phosphoinositide 3-kinase-Akt signalling. In contrast, PAK4 silencing reduced PTEN expression in mice. Consistent with these findings, prodrug of PAK4 inhibitor CZh-226 (30 mg/kg) orally administered to mice repressed PTEN expression and accelerated myotube formation. Subsequent mechanistic studies revealed that PAK4 directly phosphorylates PPARγ at S273 to increase its transcription activity, thereby up-regulating PTEN expression. Importantly, an analysis of the Genotype-Tissue Expression database showed a positive correlation between PAK4 and PTEN in human skeletal muscle tissues (P < 0.01).

CONCLUSIONS

p1-activated kinase 4 is a new member of PPARγ kinase, and PAK4 inhibition may have a therapeutic role as an accelerant of muscle regeneration.

Drug discovery targeting p21-activated kinase 4 (PAK4): a patent review

Introduction: The Ser/Thr protein kinase PAK4 is a downstream regulator of Cdc42, mediating cytoskeleton remodeling, and cell motility, and inhibiting apoptosis and transcriptional regulation. Nowadays, efforts in PAK4 inhibitor development are focusing on improving inhibitory selectivity, cellular potency, and in vivo pharmacokinetic properties, and identifying the feasibility of immunotherapy combination in oncology therapy.Areas covered: This review summarized the development of PAK4 inhibitors that reported on patents in the past two decades. According to their binding features, these inhibitors were classified into type I, type I 1/2, and PAMs. Their designing ideas and SAR were elucidated in this review. Moreover, synergistic therapy of PAK4 inhibitors with PD-1/PD-L1 or CAR-T were also summarized .Expert opinion: In the past years, preclinical and clinical studies of PAK4 inhibitors ended in failure due to poor selectivity, cellular activity, or pharmacokinetic issues. There are researchers questioning the reliability of PAK4 as a drug target, particularly PAK4-related therapy is concerned with the distinguishment of the non-kinase functions and catalytic functions triggered by PAK4 phosphorylation. Meanwhile, synergistic effects of PAK4 inhibitors with PD-1/PD-L1 and CAR-T immunotherapy shed light for the development of PAK4 inhibitors.