Group II p21-activated kinases as therapeutic targets in gastrointestinal cancer

Inhibition of NAMPT by PAK4 Inhibitors

The serine/threonine kinase PAK4 plays a crucial role in regulating cell proliferation, survival, migration, and invasion. Overexpression of PAK4 correlates with poor prognosis in some cancers. KPT-9274, a PAK4 inhibitor, significantly reduces the growth of triple-negative breast cancer cells and mammary tumors in mouse models, and it also inhibits the growth of several other types of cancer cells. Interestingly, although it was first identified as a PAK4 inhibitor, KPT-9274 was also found to inhibit the enzyme NAMPT (nicotinamide phosphoribosyltransferase), which is crucial for NAD (nicotinamide adenine dinucleotide) synthesis and vital for cellular energy and growth. These results made us question whether growth inhibition in response to KPT-9274 was due to PAK4 inhibition, NAMPT inhibition, or both. To address this, we tested several other PAK4 inhibitors that also inhibit cell growth, to determine whether they also inhibit NAMPT activity. Our findings confirm that multiple PAK4 inhibitors also inhibit NAMPT activity. This was assessed both in cell-free assays and in a breast cancer cell line. Molecular docking studies were also used to help us better understand the mechanism by which PAK4 inhibitors block PAK4 and NAMPT activity, and we identified specific residues on the PAK4 inhibitors that interact with NAMPT and PAK4. Our results suggest that PAK4 inhibitors may have a more complex mechanism of action than previously understood, necessitating further exploration of how they influence cancer cell growth.

Effects of Sophora alopecuroides in a High-Concentrate Diet on the Liver Immunity and Antioxidant Function of Lambs According to Transcriptome Analysis

The purpose of this study was to determine the effects of Sophora alopecuroides (SA) on liver function, liver inflammatory factor levels, antioxidant indexes and transcriptome in sheep. Twenty-four 3-month-old healthy Dumont hybrid lambs weighing 25.73 ± 2.17 kg were randomly divided into three groups: C1 (the control group), fed a concentrate-to-forage ratio of 50:50; H2 (the high-concentration group), fed a concentrate-to-forage ratio of 70:30; and S3 (the SA group), fed a concentrate-to-forage ratio of 70:30 + 0.1% SA. The results showed that the rumen pH values of the C1 and S3 groups were significant or significantly higher than that of the H2 group (p < 0.05 or p < 0.01). The serum ALT, AST and LDH activities and the LPS and LBP concentrations in the sheep serum and liver in the H2 group were significantly or extremely significantly higher than those in the C1 and S3 groups (p < 0.01), and the IL-10 content and SOD, GPX-PX and T-AOC activities showed the opposite trend (p < 0.05 or p < 0.01). KEGG enrichment analysis showed that the differentially expressed genes were significantly enriched in the ECM-receptor interaction and focal adhesion pathways, which are closely related to immune and antioxidant functions (p-adjust < 0.1). In summary, SA could improve the immune and antioxidant functions of lamb livers under high-concentrate conditions and regulate the mechanism of damage on sheep livers, which is caused by high-concentrate diets and through the expression of related genes in the ECM/FAs pathway.

p21-activated kinase 4 suppresses fatty acid β-oxidation and ketogenesis by phosphorylating NCoR1

PPARα corepressor NCoR1 is a key regulator of fatty acid β-oxidation and ketogenesis. However, its regulatory mechanism is largely unknown. Here, we report that oncoprotein p21-activated kinase 4 (PAK4) is an NCoR1 kinase. Specifically, PAK4 phosphorylates NCoR1 at T1619/T2124, resulting in an increase in its nuclear localization and interaction with PPARα, thereby repressing the transcriptional activity of PPARα. We observe impaired ketogenesis and increases in PAK4 protein and NCoR1 phosphorylation levels in liver tissues of high fat diet-fed mice, NAFLD patients, and hepatocellular carcinoma patients. Forced overexpression of PAK4 in mice represses ketogenesis and thereby increases hepatic fat accumulation, whereas genetic ablation or pharmacological inhibition of PAK4 exhibites an opposite phenotype. Interestingly, PAK4 protein levels are significantly suppressed by fasting, largely through either cAMP/PKA- or Sirt1-mediated ubiquitination and proteasome degradation. In this way, our findings provide evidence for a PAK4-NCoR1/PPARα signaling pathway that regulates fatty acid β-oxidation and ketogenesis.

Targeting P21-Activated Kinase-1 for Metastatic Prostate Cancer

Metastatic prostate cancer (mPCa) has limited therapeutic options and a high mortality rate. The p21-activated kinase (PAK) family of proteins is important in cell survival, proliferation, and motility in physiology, and pathologies such as infectious, inflammatory, vascular, and neurological diseases as well as cancers. Group-I PAKs (PAK1, PAK2, and PAK3) are involved in the regulation of actin dynamics and thus are integral for cell morphology, adhesion to the extracellular matrix, and cell motility. They also play prominent roles in cell survival and proliferation. These properties make group-I PAKs a potentially important target for cancer therapy. In contrast to normal prostate and prostatic epithelial cells, group-I PAKs are highly expressed in mPCA and PCa tissue. Importantly, the expression of group-I PAKs is proportional to the Gleason score of the patients. While several compounds have been identified that target group-I PAKs and these are active in cells and mice, and while some inhibitors have entered human trials, as of yet, none have been FDA-approved. Probable reasons for this lack of translation include issues related to selectivity, specificity, stability, and efficacy resulting in side effects and/or lack of efficacy. In the current review, we describe the pathophysiology and current treatment guidelines of PCa, present group-I PAKs as a potential druggable target to treat mPCa patients, and discuss the various ATP-competitive and allosteric inhibitors of PAKs. We also discuss the development and testing of a nanotechnology-based therapeutic formulation of group-I PAK inhibitors and its significant potential advantages as a novel, selective, stable, and efficacious mPCa therapeutic over other PCa therapeutics in the pipeline.

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.

Multi-omics data integration reveals correlated regulatory features of triple negative breast cancer

Triple negative breast cancer (TNBC) is an aggressive type of breast cancer with very little treatment options. TNBC is very heterogeneous with large alterations in the genomic, transcriptomic, and proteomic landscapes leading to various subtypes with differing responses to therapeutic treatments. We applied a multi-omics data integration method to evaluate the correlation of important regulatory features in TNBC BRCA1 wild-type MDA-MB-231 and TNBC BRCA1 5382insC mutated HCC1937 cells compared with non-tumorigenic epithelial breast MCF10A cells. The data includes DNA methylation, RNAseq, protein, phosphoproteomics, and histone post-translational modification. Data integration methods identified regulatory features from each omics method that had greater than 80% positive correlation within each TNBC subtype. Key regulatory features at each omics level were identified distinguishing the three cell lines and were involved in important cancer related pathways such as TGFβ signaling, PI3K/AKT/mTOR, and Wnt/beta-catenin signaling. We observed overexpression of PTEN, which antagonizes the PI3K/AKT/mTOR pathway, and MYC, which downregulates the same pathway in the HCC1937 cells relative to the MDA-MB-231 cells. The PI3K/AKT/mTOR and Wnt/beta-catenin pathways are both downregulated in HCC1937 cells relative to MDA-MB-231 cells, which likely explains the divergent sensitivities of these cell lines to inhibitors of downstream signaling pathways. The DNA methylation and RNAseq data is freely available via GEO GSE171958 and the proteomics data is available via the ProteomeXchange PXD025238.

Rac1, A Potential Target for Tumor Therapy

RAS-related C3 botulinum toxin substrate 1 (Rac.1) is one of the important members of Rho GTPases. It is well known that Rac1 is a cytoskeleton regulation protein that regulates cell adhesion, morphology, and movement. Rac1 is highly expressed in different types of tumors, which is related to poor prognosis. Studies have shown that Rac1 not only participates in the tumor cell cycle, apoptosis, proliferation, invasion, migration and angiogenesis, but also participates in the regulation of tumor stem cell, thus promoting the occurrence of tumors. Rac1 also plays a key role in anti-tumor therapy and participates in immune escape mediated by the tumor microenvironment. In addition, the good prospects of Rac1 inhibitors in cancer prevention and treatment are exciting. Therefore, Rac1 is considered as a potential target for the prevention and treatment of cancer. The necessity and importance of Rac1 are obvious, but it still needs further study.

Sterically stabilized liposomes targeting P21 (RAC1) activated kinase-1 and secreted phospholipase A2 suppress prostate cancer growth and metastasis

Metastatic prostate cancer (PCa) has a very high mortality rate in men, in Western countries and lacks reliable treatment. The advanced-stage PCa cells overexpress P21 (RAC1) activated kinase-1 (PAK1) and secreted phospholipase A2 (sPLA2) suggesting the potential utility of pharmacologically targeting these molecules to treat metastatic PCa. The small molecule, inhibitor targeting PAK1 activation-3 (IPA3) is a highly specific allosteric inhibitor of PAK1; however, it is metabolically unstable once in the plasma thus, limiting its utility as a chemotherapeutic agent. In the present study, the efficacy and specificity of IPA3 were combined with the stability and the sPLA2-targeted delivery method of two sterically stabilized liposomes [sterically stabilized long-circulating liposomes (SSL)-IPA3 and sPLA2 responsive liposomes (SPRL)-IPA3, respectively] to inhibit PCa growth and metastasis. It was found that twice-a-week administration of either SSL-IPA3 or SPRL-IPA3 for 3 weeks effectively suppressed the growth of PC-3 cell tumor xenografts implanted in athymic nude mice. Both drug formulations also inhibited the metastasis of intravenously administered murine RM1 PCa cells to the lungs of C57BL/6 mice. Whereas the twice-a-week administration of SSL-IPA3 significantly inhibited the spontaneous PCa metastasis to the lungs in Transgenic Adenocarcinoma of the Mouse Prostate mice, the administration of free IPA3 had no significant therapeutic benefit. The results present two novel IPA3 encapsulated liposomes to treat metastatic PCa.

Phosphorylation Sites in Protein Kinases and Phosphatases Regulated by Formyl Peptide Receptor 2 Signaling

FPR1, FPR2, and FPR3 are members of Formyl Peptides Receptors (FPRs) family belonging to the GPCR superfamily. FPR2 is a low affinity receptor for formyl peptides and it is considered the most promiscuous member of this family. Intracellular signaling cascades triggered by FPRs include the activation of different protein kinases and phosphatase, as well as tyrosine kinase receptors transactivation. Protein kinases and phosphatases act coordinately and any impairment of their activation or regulation represents one of the most common causes of several human diseases. Several phospho-sites has been identified in protein kinases and phosphatases, whose role may be to expand the repertoire of molecular mechanisms of regulation or may be necessary for fine-tuning of switch properties. We previously performed a phospho-proteomic analysis in FPR2-stimulated cells that revealed, among other things, not yet identified phospho-sites on six protein kinases and one protein phosphatase. Herein, we discuss on the selective phosphorylation of Serine/Threonine-protein kinase N2, Serine/Threonine-protein kinase PRP4 homolog, Serine/Threonine-protein kinase MARK2, Serine/Threonine-protein kinase PAK4, Serine/Threonine-protein kinase 10, Dual specificity mitogen-activated protein kinase kinase 2, and Protein phosphatase 1 regulatory subunit 14A, triggered by FPR2 stimulation. We also describe the putative FPR2-dependent signaling cascades upstream to these specific phospho-sites.

Group II p21-activated kinase, PAK4, is needed for activation of focal adhesion kinases, MAPK, GSK3, and β-catenin in rat pancreatic acinar cells

PAK4 is the only member of the Group II p21-activated kinases (PAKs) present in rat pancreatic acinar cells and is activated by gastrointestinal hormones/neurotransmitters stimulating PLC/cAMP and by various pancreatic growth factors. However, little is known of the role of PAK4 activation in cellular signaling cascades in pancreatic acinar cells. In the present study, we examined the role of PAK4's participation in five different cholecystokinin-8 (CCK-8)-stimulated signaling pathways (PI3K/Akt, MAPK, focal adhesion kinase, GSK3, and β-catenin), which mediate many of its physiological acinar-cell effects, as well as effects in pathophysiological conditions. To define PAK4's role, the effect of two different PAK4 inhibitors, PF-3758309 and LCH-7749944, was examined under experimental conditions that only inhibited PAK4 activation and not activation of the other pancreatic PAK, Group I PAK2. The inhibitors' effects on activation of these five signaling cascades by both physiological and pathophysiological concentrations of CCK, as well as by 12-O-tetradecanoylphobol-13-acetate (TPA), a PKC-activator, were examined. CCK/TPA activation of focal adhesion kinases(PYK2/p125^FAK) and the accompanying adapter proteins (paxillin/p130^CAS), Mek1/2, and p44/42, but not c-Raf or other MAPKs (JNK/p38), were mediated by PAK4. Activation of PI3K/Akt/p70s6K was independent of PAK4, whereas GSK3 and β-catenin stimulation was PAK4-dependent. These results, coupled with recent studies showing PAK4 is important in pancreatic fluid/electrolyte/enzyme secretion and acinar cell growth, show that PAK4 plays an important role in different cellular signaling cascades, which have been shown to mediate numerous physiological and pathophysiological processes in pancreatic acinar cells.NEW & NOTEWORTHY In pancreatic acinar cells, cholecystokinin (CCK) or 12-O-tetradecanoylphobol-13-acetate (TPA) activation of focal adhesion kinases (p125^FAK,PYK2) and its accompanying adapter proteins, p130CAS/paxillin; Mek1/2, p44/42, GSK3, and β-catenin are mediated by PAK4. PI3K/Akt/p70s6K, c-Raf, JNK, or p38 pathways are independent of PAK4 activation.

Mitochondrial PAK6 inhibits prostate cancer cell apoptosis via the PAK6-SIRT4-ANT2 complex

Rationale: P21-activated kinase 6 (PAK6) is a member of the class II PAKs family, which is a conserved family of serine/threonine kinases. Although the effects of PAK6 on many malignancies, especially in prostate cancer, have been studied for a long time, the role of PAK6 in mitochondria remains unknown. Methods: The expression of PAK6, SIRT4 and ANT2 in prostate cancer and adjacent non-tumor tissues was detected by immunohistochemistry. Immunofuorescence and immunoelectron microscopy were used to determine the subcellular localization of PAK6. Immunoprecipitation, immunofuorescence and ubiquitination assays were performed to determine how PAK6 regulates SIRT4, how SIRT4 regulates ANT2, and how PAK6 regulates ANT2. Flow cytometry detection and xenograft models were used to evaluate the impact of ANT2 mutant expression on the prostate cancer cell cycle and apoptosis regulation. Results: The present study revealed that the PAK6-SIRT4-ANT2 complex is involved in mitochondrial apoptosis in prostate cancer cells. It was found that PAK6 is mainly located in the mitochondrial inner membrane, in which PAK6 promotes SIRT4 ubiquitin-mediated proteolysis. Furthermore, SIRT4 deprives the ANT2 acetylation at K105 to promote its ubiquitination degradation. Hence, PAK6 adjusts the acetylation level of ANT2 through the PAK6-SIRT4-ANT2 pathway, in order to regulate the stability of ANT2. Meanwhile, PAK6 directly phosphorylates ANT2 atT107 to inhibit the apoptosis of prostate cancer cells. Therefore, the phosphorylation and deacetylation modifications of ANT2 are mutually regulated, leading to tumor growth in vivo. Consistently, these clinical prostate cancer tissue evaluations reveal that PAK6 is positively correlated with ANT2 expression, but negatively correlated with SIRT4. Conclusion: These present findings suggest the pivotal role of the PAK6-SIRT4-ANT2 complex in the apoptosis of prostate cancer. This complex could be a potential biomarker for the treatment and prognosis of prostate cancer.

Systemic analysis of the expression and prognostic significance of PAKs in breast cancer

PAKs (p21-activated kinases) are reported to play crucial roles in a variety of cellular processes and participate in the progression of human cancers. However, the expression and prognostic values of PAKs remain poorly explored in breast cancers. In our study, we examined the mRNA and protein expression levels of PAKs and the prognostic value. We also analyzed the interaction network, genetic alteration, and functional enrichment of PAKs. The results showed that the mRNA levels of PAK1, PAK2, PAK4 and PAK6 were significantly up-regulated in breast cancer compared with normal tissues, while the reverse trend for PAK3 and PAK5 was found, furthermore, the proteins expression of PAK1, PAK2 and PAK4 in breast cancer tissues were higher than that in normal breast tissues. Survival analysis revealed breast cancer patients with low mRNA expression of PAK3 and PAK5 showed worse RFS, conversely, elevated PAK4 levels predicted worse RFS. In addition, the breast cancer patients with PAKs genetic alterations correlated with worse OS. These results indicated that PAKs might be promising potential biomarkers for breast cancer.

Phosphorylation-dependent activity-based conformational changes in P21-activated kinase family members and screening of novel ATP competitive inhibitors

P21-activated kinases (PAKs) are serine/threonine protein kinases that are subdivided into two groups on the basis of their domain architecture: group-I (PAK1–3) and group-II (PAK4–6). PAKs are considered as attractive drug targets that play vital role in cell proliferation, survival, motility, angiogenesis and cytoskeletal dynamics. In current study, molecular dynamics simulation-based comparative residual contributions and differential transitions were monitored in both active and inactive states of human PAK homologs for therapeutic intervention. Due to their involvement in cancer, infectious diseases, and neurological disorders, it is inevitable to develop novel therapeutic strategies that specifically target PAKs on the basis of their activity pattern. In order to isolate novel inhibitors that are able to bind at the active sites of PAK1 and PAK4, high throughput structure-based virtual screening was performed. Multiple lead compounds were proposed on the basis of their binding potential and targeting region either phosphorylated (active) or unphosphorylated PAK isoform (inactive). Thus, ATP-competitive inhibitors may prove ideal therapeutic choice against PAK family members. The detailed conformational readjustements occurring in the PAKs upon phosphorylation-dephosphorylation events may serve as starting point for devising novel drug molecules that are able to target on activity basis. Overall, the observations of current study may add valuable contribution in the inventory of novel inhibitors that may serve as attractive lead compounds for targeting PAK family members on the basis of activity-based conformational changes.

PB-10, a thiazolo[4,5-d] pyrimidine derivative, targets p21-activated kinase 4 in human colorectal cancer cells

Targeting p21-activated kinase 4 (PAK4) is a potential therapeutic strategy against human colorectal cancer (CRC). In this study, we synthesized a series of novel thiazolo[4,5-d]pyrimidine derivatives (PB-1-12) and identified PB-10 (PAK4 IC₅₀ = 15.12 μM) as a potential and potent PAK4 inhibitor. Our results showed that PB-10 significantly suppressed the proliferation and colony formation of human CRC cells. PB-10 also arrested HCT-116 CRC cells at sub G0/G1 phase while promoting the expression of proapoptotic proteins. In addition, PB-10 inhibited migration, invasion, and adhesion as well as the PAK4 downstream signaling pathway in HCT-116 cells. Molecular docking analysis showed possible binding modes between PB-10 and PAK4. Our study provides a novel compound that may block the PAK4 signaling in CRC cells.

Estrogen induces cell proliferation by promoting ABCG2-mediated efflux in endometrial cancer cells

Recently, it has reported that overeating of lipid-food has led to increase the amount of estrogen in vivo and the incidence of endometrial carcinomas. It is well-known that ATP-binding cassette transporter sub-family G2 (ABCG2) is highly expressed in cancer stem cells (CSCs). CSCs possess the ability for differentiation, tumorigenesis, stem cell self-renewal, and the efflux of anti-cancer drug and these abilities affect malignancy of cancer cells. However, little is known about the relationship between the expression of ABCG2 and malignancy of cancer cells. The present study aimed at understanding the regulatory mechanism underlying 17-β-estradiol (E2)-induced cell proliferation under the control of ABCG2. E2 increased cell viability with a peak at 1 μM and facilitated ABCG2 mRNA expression followed by the increase of ABCG2 expression level at plasma membrane. E2-induced cell proliferation was inhibited by reserpine, an inhibitor of ABCG2, and the ABCG2 siRNA treatment. Thus, these results imply that ABCG2 plays an important role in the promotion of E2-induced cell proliferation in Ishikawa cells.

P21-activated kinase 4 in pancreatic acinar cells is activated by numerous gastrointestinal hormones/neurotransmitters and growth factors by novel signaling, and its activation stimulates secretory/growth cascades

p21-activated kinases (PAKs) are highly conserved serine/threonine protein kinases, which are divided into two groups: group-I (PAKs1-3) and group-II (PAKs4-6). In various tissues, Group-II PAKs play important roles in cytoskeletal dynamics and cell growth as well as neoplastic development/progression. However, little is known about Group-II PAK's role in a number of physiological events, including their ability to be activated by gastrointestinal (GI) hormones/neurotransmitters/growth factors (GFs). We used rat pancreatic acini to explore the ability of GI hormones/neurotransmitters/GFs to activate Group-II-PAKs and the signaling cascades involved. Only PAK4 was detected in pancreatic acini. PAK4 was activated by endothelin, secretagogues-stimulating phospholipase C (bombesin, CCK-8, and carbachol), by pancreatic GFs (insulin, insulin-like growth factor 1, hepatocyte growth factor, epidermal growth factor, basic fibroblast growth factor, and platelet-derived growth factor), and by postreceptor stimulants (12-O-tetradecanoylphobol-13-acetate and A23187 ). CCK-8 activation of PAK4 required both high- and low-affinity CCK1-receptor state activation. It was reduced by PKC-, Src-, p44/42-, or p38-inhibition but not with phosphatidylinositol 3-kinase-inhibitors and only minimally by thapsigargin. A protein kinase D (PKD)-inhibitor completely inhibited CCK-8-stimulated PKD-activation; however, stimulated PAK4 phosphorylation was only inhibited by 60%, demonstrating that it is both PKD-dependent and PKD-independent. PF-3758309 and LCH-7749944, inhibitors of PAK4, decreased CCK-8-stimulated PAK4 activation but not PAK2 activation. Each inhibited ERK1/2 activation and amylase release induced by CCK-8 or bombesin. These results show that PAK4 has an important role in modulating signal cascades activated by a number of GI hormones/neurotransmitters/GFs that have been shown to mediate both physiological/pathological responses in acinar cells. Therefore, in addition to the extensive studies on PAK4 in pancreatic cancer, PAK4 should also be considered an important signaling molecule for pancreatic acinar physiological responses and, in the future, should be investigated for a possible role in pancreatic acinar pathophysiological responses, such as in pancreatitis. NEW & NOTEWORTHY This study demonstrates that the only Group-II p21-activated kinase (PAK) in rat pancreatic acinar cells is PAK4, and thus differs from islets/pancreatic cancer. Both gastrointestinal hormones/neurotransmitters stimulating PLC and pancreatic growth factors activate PAK4. With cholecystokinin (CCK), activation is PKC-dependent/-independent, requires both CCK1-R affinity states, Src, p42/44, and p38 activation. PAK4 activation is required for CCK-mediated p42/44 activation/amylase release. These results show PAK4 plays an important role in mediating CCK physiological signal cascades and suggest it may be a target in pancreatic acinar diseases besides cancer.

Discovery of 2-(4-Substituted-piperidin/piperazine-1-yl)-N-(5-cyclopropyl-1H-pyrazol-3-yl)-quinazoline-2,4-diamines as PAK4 Inhibitors with Potent A549 Cell Proliferation, Migration, and Invasion Inhibition Activity

A series of novel 2,4-diaminoquinazoline derivatives were designed, synthesized, and evaluated as p21-activated kinase 4 (PAK4) inhibitors. All compounds showed significant inhibitory activity against PAK4 (half-maximal inhibitory concentration IC₅₀ < 1 μM). Among them, compounds 8d and 9c demonstrated the most potent inhibitory activity against PAK4 (IC₅₀ = 0.060 μM and 0.068 μM, respectively). Furthermore, we observed that compounds 8d and 9c displayed potent antiproliferative activity against the A549 cell line and inhibited cell cycle distribution, migration, and invasion of this cell line. In addition, molecular docking analysis was performed to predict the possible binding mode of compound 8d. This series of compounds has the potential for further development as PAK4 inhibitors for anticancer activity.

Decrypting the PAK4 transcriptome profile in mammary tumor forming cells using Next Generation Sequencing

The p-21 Activated Kinase 4 (PAK4) protein kinase is implicated in many cancers, including breast cancer. Overexpression of PAK4 is sufficient to cause mouse mammary epithelial cells (iMMECs) to become tumorigenic. To gain insight into the long-term gene expression changes that occur downstream to PAK4, we performed Next Generation Sequencing of RNA collected from PAK4 overexpressing iMMECs and wild-type iMMECs. We identified a list of genes whose expression levels were altered in response to PAK4 overexpression in iMMECs. Some of these genes, including FoxC2 and ParvB, are consistent with a role for PAK4 in cancer. In addition, PAK4 regulates many genes that are frequently associated with the inflammatory response, raising the possibility that there is a connection between PAK4, inflammation, and the tumor microenvironment. This study delineates the PAK4 transcriptome profile in transformed mammary cells and can provide translational utility in other types of cancers as well.

LC-0882 targets PAK4 and inhibits PAK4-related signaling pathways to suppress the proliferation and invasion of gastric cancer cells

Gastric cancer is the most common malignant tumor and globally the third leading cause of cancer-related deaths. Therefore, there exists an urgent need to identify new effective gastric cancer treatments. Given the important roles in tumorigenesis and progression, p21-activated kinase 4 (PAK4) has been regarded as an attractive high-value druggable target. In this study, we examined the effects and molecular mechanisms of action of the small molecular compound LC-0882 on gastric cancer cells in vitro. LC-0882 was found to significantly inhibit the proliferation of human gastric cancer cells by repressing phospho-PAK4/cyclin D1 and CDK4/6 expression. In addition, LC-0882 was found to attenuate cell invasion by blocking the PAK4/LIMK1/cofilin signaling pathway. Finally, analysis of immunofluorescence revealed that LC-0882 exposure decreased filopodia formation and induced cell elongation in BGC823 and SGC7901 gastric cancer cells. These findings suggest that targeting PAK4 with the novel compound LC-0882 may provide a new chemotherapeutic approach in gastric cancer treatment.

P21 activated kinase 4 binds translation elongation factor eEF1A1 to promote gastric cancer cell migration and invasion

P21 activated kinase 4 (PAK4), as an effector of Cdc42, playing important roles in regulating the processes of cytoskeleton organization. PAK4 has been considered to be an oncogenic protein, which has strong relationship with gastric cancer metastasis. However, the mechanism of PAK4 in regulating gastric cancer metastasis is still not fully understood. In this study, using yeast two-hybrid system, we identified that the eukaryotic elongation factor 1 α1 (eEF1A1) is a new binding partner of PAK4. The interaction between PAK4 and eEF1A1 was confirmed by GST pull-down and co-immunoprecipitation. PAK4 co-localized with eEF1A1 in the cytoplasm of gastric cancer cells. Overexpression of PAK4 enhanced the expression level of eEF1A1 and vice versa. PAK4 and eEF1A1 could cooperate to promote gastric cancer cell migration and invasion. Furthermore, the expression of PAK4 and eEF1A1 in clinical gastric cancer samples were examined by western blotting and immunohistochemistry. Statistical analysis indicated that there was positive correlation between the expression of PAK4 and eEF1A1. This study demonstrated for the first time that PAK4 interacted with eEF1A1 to promote migration and invasion of gastric cancer cells, thereby providing new insights into the function of PAK4 and eEF1A1 in the progression of gastric cancer.

A novel orally bioavailable compound KPT-9274 inhibits PAK4, and blocks triple negative breast cancer tumor growth

Breast cancer is a heterogeneous disease consisting of several subtypes. Among these subtypes, triple negative breast cancer is particularly difficult to treat. This is due to a lack of understanding of the mechanisms behind the disease, and consequently a lack of druggable targets. PAK4 plays critical roles in cell survival, proliferation, and morphology. PAK4 protein levels are high in breast cancer cells and breast tumors, and the gene is often amplified in basal like breast cancers, which are frequently triple negative. PAK4 is also overexpressed in other types of cancer, making it a promising drug target. However, its inhibition is complicated by the fact that PAK4 has both kinase-dependent and -independent functions. Here we investigate a new clinical compound KPT-9274, which has been shown to inhibit PAK4 and NAMPT. We find that KPT-9274 (and its analog, KPT-8752) can reduce the steady state level of PAK4 protein in triple negative breast cancer cells. These compounds also block the growth of the breast cancer cells in vitro, and stimulate apoptosis. Most importantly, oral administration of KPT-9274 reduces tumorigenesis in mouse models of human triple negative breast cancer. Our results indicate that KPT-9274 is a novel therapeutic option for triple negative breast cancer therapy.

Structure, biochemistry, and biology of PAK kinases

PAKs, p21-activated kinases, play central roles and act as converging junctions for discrete signals elicited on the cell surface and for a number of intracellular signaling cascades. PAKs phosphorylate a vast number of substrates and act by remodeling cytoskeleton, employing scaffolding, and relocating to distinct subcellular compartments. PAKs affect wide range of processes that are crucial to the cell from regulation of cell motility, survival, redox, metabolism, cell cycle, proliferation, transformation, stress, inflammation, to gene expression. Understandably, their dysregulation disrupts cellular homeostasis and severely impacts key cell functions, and many of those are implicated in a number of human diseases including cancers, neurological disorders, and cardiac disorders. Here we provide an overview of the members of the PAK family and their current status. We give special emphasis to PAK1 and PAK4, the prototypes of groups I and II, for their profound roles in cancer, the nervous system, and the heart. We also highlight other family members. We provide our perspective on the current advancements, their growing importance as strategic therapeutic targets, and our vision on the future of PAKs.

GL-1196 Suppresses the Proliferation and Invasion of Gastric Cancer Cells via Targeting PAK4 and Inhibiting PAK4-Mediated Signaling Pathways

Gastric cancer, which is the most common malignant gastrointestinal tumor, has jumped to the third leading cause of cancer-related mortality worldwide. It is of great importance to identify novel and potent drugs for gastric cancer treatment. P21-activated kinase 4 (PAK4) has emerged as an attractive target for the development of anticancer drugs in consideration of its vital functions in tumorigenesis and progression. In this paper, we reported that GL-1196, as a small molecular compound, effectively suppressed the proliferation of human gastric cancer cells through downregulation of PAK4/c-Src/EGFR/cyclinD1 pathway and CDK4/6 expression. Moreover, GL-1196 prominently inhibited the invasion of human gastric cancer cells in parallel with blockage of the PAK4/LIMK1/cofilin pathway. Interestingly, GL-1196 also inhibited the formation of filopodia and induced cell elongation in SGC7901 and BGC823 cells. Taken together, these results provided novel insights into the potential therapeutic strategy for gastric cancer.