Targeting PAK4 Inhibits Ras-Mediated Signaling and Multiple Oncogenic Pathways in High-Risk Rhabdomyosarcoma

Interaction between p21-activated kinase 4 and β-catenin as a novel pathway for PTH-dependent osteoblast activation

Parathyroid hormone (PTH) serves dual roles in bone metabolism, exhibiting both anabolic and catabolic effects. The anabolic properties of PTH have been utilized in the treatment of osteoporosis with proven efficacy in preventing fractures. Despite these benefits, PTH can be administered therapeutically for up to 2 years, and its use in patients with underlying malignancies remains a subject of ongoing debate. These considerations underscore the need for a more comprehensive understanding of the underlying mechanisms. p21-activated kinase 4 (PAK4) is involved in bone resorption and cancer-associated osteolysis; however, its role in osteoblast function and PTH action remains unknown. Therefore, in this study, we aimed to clarify the role of PAK4 in osteoblast function and its effects on PTH-induced anabolic activity. PAK4 enhanced MC3T3-E1 osteoblast viability and proliferation and upregulated cyclin D1 expression. PAK4 also augmented osteoblast differentiation, as indicated by increased mineralization found by alkaline phosphatase and Alizarin Red staining. Treatment with PTH (1-34), an active PTH fragment, stimulated PAK4 expression and phosphorylation in a protein kinase A-dependent manner. In addition, bone morphogenetic protein-2 (which is known to promote bone formation) increased phosphorylated PAK4 (p-PAK4) and PAK4 levels. PAK4 regulated the expression of both phosphorylated and total β-catenin, which are critical for osteoblast proliferation and differentiation. Moreover, p-PAK4 directly interacted with β-catenin, and disruption of β-catenin's binding to T-cell factor impaired PAK4- and PTH-induced osteoblast differentiation. Our findings elucidate the effect of PAK4 on enhancing bone formation in osteoblasts and its pivotal role in the anabolic activity of PTH mediated through its interaction with β-catenin. These insights improve the understanding of the mechanisms underlying PTH activity and should inform the development of more effective and safer osteoporosis treatments.

Channeling Nicotinamide Phosphoribosyltransferase (NAMPT) to Address Life and Death

Nicotinamide phosphoribosyltransferase (NAMPT) catalyzes the rate-limiting step in NAD+ biosynthesis via salvage of NAM formed from catabolism of NAD+ by proteins with NADase activity (e.g., PARPs, SIRTs, CD38). Depletion of NAD+ in aging, neurodegeneration, and metabolic disorders is addressed by NAD+ supplementation. Conversely, NAMPT inhibitors have been developed for cancer therapy: many discovered by phenotypic screening for cancer cell death have low nanomolar potency in cellular models. No NAMPT inhibitor is yet FDA-approved. The ability of inhibitors to act as NAMPT substrates may be associated with efficacy and toxicity. Some 3-pyridyl inhibitors become 4-pyridyl activators or "NAD+ boosters". NAMPT positive allosteric modulators (N-PAMs) and boosters may increase enzyme activity by relieving substrate/product inhibition. Binding to a "rear channel" extending from the NAMPT active site is key for inhibitors, boosters, and N-PAMs. A deeper understanding may fulfill the potential of NAMPT ligands to regulate cellular life and death.

Contemporary preclinical mouse models for pediatric rhabdomyosarcoma: from bedside to bench to bedside

Background

Rhabdomyosarcoma (RMS) is the most common pediatric soft-tissue malignancy, characterized by high clinicalopathological and molecular heterogeneity. Preclinical in vivo models are essential for advancing our understanding of RMS oncobiology and developing novel treatment strategies. However, the diversity of scholarly data on preclinical RMS studies may challenge scientists and clinicians. Hence, we performed a systematic literature survey of contemporary RMS mouse models to characterize their phenotypes and assess their translational relevance.

Methods

We identified papers published between 01/07/2018 and 01/07/2023 by searching PubMed and Web of Science databases.

Results

Out of 713 records screened, 118 studies (26.9%) were included in the qualitative synthesis. Cell line-derived xenografts (CDX) were the most commonly utilized (n = 75, 63.6%), followed by patient-derived xenografts (PDX) and syngeneic models, each accounting for 11.9% (n = 14), and genetically engineered mouse models (GEMM) (n = 7, 5.9%). Combinations of different model categories were reported in 5.9% (n = 7) of studies. One study employed a virus-induced RMS model. Overall, 40.0% (n = 30) of the studies utilizing CDX models established alveolar RMS (aRMS), while 38.7% (n = 29) were embryonal phenotypes (eRMS). There were 20.0% (n = 15) of studies that involved a combination of both aRMS and eRMS subtypes. In one study (1.3%), the RMS phenotype was spindle cell/sclerosing. Subcutaneous xenografts (n = 66, 55.9%) were more frequently used compared to orthotopic models (n = 29, 24.6%). Notably, none of the employed cell lines were derived from primary untreated tumors. Only a minority of studies investigated disseminated RMS phenotypes (n = 16, 13.6%). The utilization areas of RMS models included testing drugs (n = 64, 54.2%), studying tumorigenesis (n = 56, 47.5%), tumor modeling (n = 19, 16.1%), imaging (n = 9, 7.6%), radiotherapy (n = 6, 5.1%), long-term effects related to radiotherapy (n = 3, 2.5%), and investigating biomarkers (n = 1, 0.8%). Notably, no preclinical studies focused on surgery.

Conclusions

This up-to-date review highlights the need for mouse models with dissemination phenotypes and cell lines from primary untreated tumors. Furthermore, efforts should be directed towards underexplored areas such as surgery, radiotherapy, and biomarkers.

Targeting NAD+ metabolism: dual roles in cancer treatment

Nicotinamide adenine dinucleotide (NAD+) is indispensable for various oxidation-reduction reactions in mammalian cells, particularly during energy production. Malignant cells increase the expression levels of NAD+ biosynthesis enzymes for rapid proliferation and biomass production. Furthermore, mounting proof has indicated that NAD-degrading enzymes (NADases) play a role in creating the immunosuppressive tumor microenvironment (TME). Interestingly, both inhibiting NAD+ synthesis and targeting NADase have positive implications for cancer treatment. Here we summarize the detrimental outcomes of increased NAD+ production, the functions of NAD+ metabolic enzymes in creating an immunosuppressive TME, and discuss the progress and clinical translational potential of inhibitors for NAD+ synthesis and therapies targeting NADase.

Anticancer Efficacy of KRASG12C Inhibitors Is Potentiated by PAK4 Inhibitor KPT9274 in Preclinical Models of KRASG12C-Mutant Pancreatic and Lung Cancers

KRASG12C inhibitors, such as sotorasib and adagrasib, have revolutionized cancer treatment for patients with KRASG12C-mutant tumors. However, patients receiving these agents as monotherapy often develop drug resistance. To address this issue, we evaluated the combination of the PAK4 inhibitor KPT9274 and KRASG12C inhibitors in preclinical models of pancreatic ductal adenocarcinoma (PDAC) and non-small cell lung cancer (NSCLC). PAK4 is a hub molecule that links several major signaling pathways and is known for its tumorigenic role in mutant Ras-driven cancers. We found that cancer cells resistant to KRASG12C inhibitor were sensitive to KPT9274-induced growth inhibition. Furthermore, KPT9274 synergized with sotorasib and adagrasib to inhibit the growth of KRASG12C-mutant cancer cells and reduce their clonogenic potential. Mechanistically, this combination suppressed cell growth signaling and downregulated cell-cycle markers. In a PDAC cell line-derived xenograft (CDX) model, the combination of a suboptimal dose of KPT9274 with sotorasib significantly reduced the tumor burden (P= 0.002). Similarly, potent antitumor efficacy was observed in an NSCLC CDX model, in which KPT9274, given as maintenance therapy, prevented tumor relapse following the discontinuation of sotorasib treatment (P= 0.0001). Moreover, the combination of KPT9274 and sotorasib enhances survival. In conclusion, this is the first study to demonstrate that KRASG12C inhibitors can synergize with the PAK4 inhibitor KPT9274 and combining KRASG12C inhibitors with KPT9274 can lead to remarkably enhanced antitumor activity and survival benefits, providing a novel combination therapy for patients with cancer who do not respond or develop resistance to KRASG12C inhibitor treatment.

Design, synthesis and anticancer activity evaluation of 4-(3-1H-indazolyl)amino quinazoline derivatives as PAK4 inhibitors

A novel series of 4-(3-1H-indazolyl)amino quinazoline derivatives were developed as PAK4 inhibitors based on a scaffold hopping strategy. Compounds 27e, 27g, 27i and 27j were found to exhibit potent inhibitory activity against PAK4 (IC50 = 10, 13, 11 and 9 nM, respectively). Subsequent cellular assay demonstrated that compound 27e possessed the strongest antiproliferative activity against A549 cells with an IC50 value of 0.61 μM, a little bit better than PF-3758309. Further anticancer mechanistic investigation revealed that compound 27e significantly induced apoptosis of A549 cells in a concentration-dependent manner and blocked the cell cycle at phase G0/G1. A docking model between compound 27e and PAK4 was proposed to elucidate its possible binding modes. As a promising PAK4 inhibitor, compound 27e may serve as a candidate for the development of novel PAK4-targeted anticancer drug.

PAK1 overexpression promotes myxofibrosarcoma angiogenesis through STAT5B-mediated CSF2 transactivation: clinical and therapeutic relevance of amplification and nuclear entry

Myxofibrosarcoma is genetically complex without established nonsurgical therapies. In public datasets, PAK1 was recurrently gained with mRNA upregulation. Using myxofibrosarcoma cells, we explored the oncogenic underpinning of PAK1 with genetic manipulation and a pan-PAK inhibitor (PF3758309). Myxofibrosarcoma specimens were analyzed for the levels of PAK1, phospho-PAKT423, CSF2 and microvascular density (MVD) and those of PAK1 gene and mRNA. PAK1-expressing xenografts were assessed for the effects of PF3758309 and CSF2 silencing. Besides pro-proliferative and pro-migrator/pro-invasive attributes, PAK1 strongly enhanced angiogenesis in vitro, which, not phenocopied by PAK2-4, was identified as CSF2-mediated using antibody arrays. PAK1 underwent phosphorylation at tyrosines153,201,285 and threonine423 to facilitate nuclear entry, whereby nuclear PAK1 bound STAT5B to co-transactivate the CSF2 promoter, increasing CSF2 secretion needed for angiogenesis. Angiogenesis driven by PAK1-upregulated CSF2 was negated by CSF2 silencing, anti-CSF2, and PF3758309. Clinically, overexpressed whole-cell phospho-PAKT423, related to PAK1 amplification, was associated with increased grades, stages, and PAK1 mRNA, higher MVD, and CSF2 overexpression. Overexpressed whole-cell phospho-PAKT423 and CSF2 independently portended shorter metastasis-free survival and disease-specific survival, respectively. In vivo, both CSF2 silencing and PF3758309 suppressed PAK1-driven tumor proliferation and angiogenesis. Conclusively, the nuclear entry of overexpressed/activated PAK1 endows myxofibrosarcomas with pro-angiogenic function, highlighting the vulnerable PAK1/STAT5B/CSF2 regulatory axis.

Recent advances of targeting nicotinamide phosphoribosyltransferase (NAMPT) for cancer drug discovery

Nicotinamide phosphoribosyltransferase (NAMPT) is the rate-limiting enzyme for the biosynthesis of NAD⁺ in the salvage pathway. NAMPT is overexpressed in various cancers, associating with a poor prognosis and tumor progression. Beyond cancer metabolism, recent evidence unravels additional roles of NAMPT in cancer biology, including DNA repair machinery, crosstalk with oncogenic signaling pathways, cancer cell stemness, and immune responses. NAMPT is a promising therapeutic target for cancer. However, first-generation NAMPT inhibitors exhibited limited efficacy and dose-limiting toxicities in clinical trials. Multiple strategies are being exploited to improve their efficacy and minimize toxic-side effects. This review discusses the biomarkers predictive of response to NAMPT inhibitors, and summarizes the most significant advances in the evolution of structurally distinct NAMPT inhibitors, the manipulation of targeted delivery technologies via antibody-drug conjugates (ADCs), PhotoActivated ChemoTherapy (PACT) and the intratumoral delivery system, as well as the development and pharmacological outcomes of NAMPT degraders. Finally, a discussion of future perspectives and challenges in this area is also included.

Metabolic Interventions in Tumor Immunity: Focus on Dual Pathway Inhibitors

The metabolism of tumors and immune cells in the tumor microenvironment (TME) can affect the fate of cancer and immune responses. Metabolic reprogramming can occur following the activation of metabolic-related signaling pathways, such as phosphoinositide 3-kinases (PI3Ks) and the mammalian target of rapamycin (mTOR). Moreover, various tumor-derived immunosuppressive metabolites following metabolic reprogramming also affect antitumor immune responses. Evidence shows that intervention in the metabolic pathways of tumors or immune cells can be an attractive and novel treatment option for cancer. For instance, administrating inhibitors of various signaling pathways, such as phosphoinositide 3-kinases (PI3Ks), can improve T cell-mediated antitumor immune responses. However, dual pathway inhibitors can significantly suppress tumor growth more than they inhibit each pathway separately. This review discusses the latest metabolic interventions by dual pathway inhibitors as well as the advantages and disadvantages of this therapeutic approach.

Anticancer efficacy of KRASG12C inhibitors is potentiated by PAK4 inhibitor KPT9274 in preclinical models of KRASG12C mutant pancreatic and lung cancers

KRASG12C inhibitors have revolutionized the treatment landscape for cancer patients harboring the G12C mutant isoform of KRAS. With the recent FDA approval of sotorasib and adagrasib, patients now have access to more promising treatment options. However, patients who receive these agents as a monotherapy usually develop drug resistance. Thus, there is a need to develop logical combination strategies that can delay or prevent the onset of resistance and simultaneously enhance the antitumor effectiveness of the treatment regimen. In this study, we aimed at pharmacologically targeting PAK4 by KPT9274 in combination with KRASG12C inhibitors in KRASG12C mutant pancreatic ductal adenocarcinoma (PDAC) and nonâ€"small cell lung cancer (NSCLC) preclinical models. PAK4 is a hub molecule that links several major signaling pathways and is known for its tumorigenic role in mutant Ras-driven cancers. We assessed the cytotoxicity of PAK4 and KRASG12C inhibitors combination in KRASG12C mutant 2D and 3D cellular models. KPT9274 synergized with both sotorasib and adagrasib in inhibiting the growth of KRASG12C mutant cancer cells. The combination was able to reduce the clonogenic potential of KRASG12C mutant PDAC cells. We also evaluated the antitumor activity of the combination in a KRASG12C mutant PDAC cell line-derived xenograft (CDX) model. Oral administration of a sub-optimal dose of KPT9274 in combination with sotorasib (at one-fourth of MTD) demonstrated significant inhibition of the tumor burden ( p = 0.002). Similarly, potent antitumor efficacy was observed in an NSCLC CDX model where KPT9274, acting as an adjuvant, prevented tumor relapse following the discontinuation of sotorasib treatment ( p = 0.0001). KPT9274 and sotorasib combination also resulted in enhanced survival. This is the first study showing that KRASG12C inhibitors can synergize with PAK4 inhibitor KPT9274 both in vitro and in vivo resulting in remarkably enhanced antitumor activity and survival outcomes.

Significance

KRASG12C inhibitors demonstrate limited durable response in patients with KRASG12C mutations. In this study, combining PAK4 inhibitor KPT9274 with KRASG12C inhibitors has resulted in potent antitumor effects in preclinical cancer models of PDAC and NSCLC. Our results bring forward a novel combination therapy for cancer patients that do not respond or develop resistance to KRASG12C inhibitor treatment.

LncRNA PVT-1 promotes osteosarcoma cancer stem-like properties through direct interaction with TRIM28 and TSC2 ubiquitination

Osteosarcoma, the most common pediatric bone tumor, is an aggressive heterogeneous malignancy defined by complex chromosomal aberrations. Overall survival rates remain at ~70%, but patients with chemoresistant or metastatic disease have extremely poor outcomes of <30%. A subgroup of tumors harbor amplification of chromosome 8q24.2 and increased expression of the oncogenic long noncoding RNA (lncRNA) Plasmacytoma Variant Translocation-1 (PVT-1), which is associated with an extremely poor clinical prognosis. This study demonstrates that PVT-1 is critical for osteosarcoma tumor-initiation potential. Chromatin Hybridization by RNA Purification analysis identified Tripartite-Motif Containing Family 28 (TRIM28) as a novel PVT-1 binding partner. Mechanistically, co-immunoprecipitation studies showed the PVT-1/TRIM28 complex binds and increases SUMOylation of phosphatidylinositol 3-kinase catalytic subunit type 3 (Vps34), which leads to enhanced ubiquitination and degradation of tumor suppressor complex 2 (TSC2), thus contributing to increased self-renewal and stem cell phenotypes. Furthermore, we identified that osteosarcoma cells with increased PVT-1 have enhanced sensitivity to the SUMOylation inhibitor, TAK-981. Altogether, this study elucidated a role for PVT-1 in the enhancement of cancer stem-like behaviors, including migration and invasion, in osteosarcoma, and identified the novel PVT-1/TRIM28 axis signaling cascade as a potential therapeutic target for osteosarcoma treatment.

MiR-199a-3p-regulated alveolar macrophage-derived secretory autophagosomes exacerbate lipopolysaccharide-induced acute respiratory distress syndrome

Purpose

Acute respiratory distress syndrome (ARDS) is a prevalent illness in intensive care units. Extracellular vesicles and particles released from activated alveolar macrophages (AMs) assist in ARDS lung injury and the inflammatory process through mechanisms that are unclear. This study investigated the role of AM-derived secretory autophagosomes (SAPs) in lung injury and microRNA (MiR)-199a-3p-regulated inflammation associated with ARDS in vitro and in a murine model.

Methods

The ARDS model in mouse was established by intratracheal LPS lipopolysaccharide (LPS) injection. The agomirs or antagomirs of MiR-199a-3p were injected into the caudal vein to figure out whether MiR-199a-3p could influence ARDS inflammation and lung injury, whereas the mimics or inhibitors of MiR-199a-3p, siRNA of Rab8a, or PAK4 inhibitor were transfected or applied to RAW264.7 cells to evaluate the mechanism of SAP release. Culture supernatants of RAW264.7 cells treated with LPS or bronchoalveolar lavage fluid from mice were collected for the isolation of SAPs.

Results

We found that MiR-199a-3p was over-expressed in the lungs of ARDS mice. The MiR-199a-3p antagomir alleviated, whereas the MiR-199a-3p agomir exacerbated LPS-induced inflammation in mice by promoting AM-derived SAP secretion. In addition, MiR-199a-3p over-expression exacerbated LPS-induced ARDS via activating Rab8a, and Rab8a silencing significantly suppressed the promoting influence of the MiR-199a-3p mimic on SAP secretion. Furthermore, MiR-199a-3p mimic activated Rab8a by directly inhibiting PAK4 expression.

Conclusion

The novel finding of this study is that MiR-199a-3p participated in the regulation of SAP secretion and the inflammatory process via targeting of PAK4/Rab8a, and is a potential therapeutic candidate for ARDS treatment.

Rho family GTPase signaling through type II p21-activated kinases

Signaling from the Rho family small GTPases controls a wide range of signaling outcomes. Key among the downstream effectors for many of the Rho GTPases are the p21-activated kinases, or PAK group. The PAK family comprises two types, the type I PAKs (PAK1, 2 and 3) and the type II PAKs (PAK4, 5 and 6), which have distinct structures and mechanisms of regulation. In this review, we discuss signal transduction from Rho GTPases with a focus on the type II PAKs. We discuss the role of PAKs in signal transduction pathways and selectivity of Rho GTPases for PAK family members. We consider the less well studied of the Rho GTPases and their PAK-related signaling. We then discuss the molecular basis for kinase domain recognition of substrates and for regulation of signaling. We conclude with a discussion of the role of PAKs in cross talk between Rho family small GTPases and the roles of PAKs in disease.

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 of selective PAK4 inhibitors for lung metastasis of lung cancer and melanoma cells

The p21 activated kinase 4 (PAK4) is serine/threonine protein kinase that is critical for cancer progression. Guided by X-ray crystallography and structure-based optimization, we report a novel subseries of C-3-substituted 6-ethynyl-1H-indole derivatives that display high potential and specificity towards group II PAKs. Among these inhibitors, compound 55 exhibited excellent inhibitory activity and kinase selectivity, displayed superior anti-migratory and anti-invasive properties against the lung cancer cell line A549 and the melanoma cell line B16. Compound 55 exhibited potent in vivo antitumor metastatic efficacy, with over 80% and 90% inhibition of lung metastasis in A549 or B16-BL6 lung metastasis models, respectively. Further mechanistic studies demonstrated that compound 55 mitigated TGF-β1-induced epithelial-mesenchymal transition (EMT).

Clinical development of metabolic inhibitors for oncology

Metabolic inhibitors have been used in oncology for decades, dating back to antimetabolites developed in the 1940s. In the past 25 years, there has been increased recognition of metabolic derangements in tumor cells leading to a resurgence of interest in targeting metabolism. More recently there has been recognition that drugs targeting tumor metabolism also affect the often acidic, hypoxic, immunosuppressive tumor microenvironment (TME) and non-tumor cell populations within it, including immune cells. Here we review small-molecule metabolic inhibitors currently in clinical development for oncology applications. For each agent, we evaluate the preclinical studies demonstrating antitumor and TME effects and review ongoing clinical trials. The goal of this Review is to provide an overview of the landscape of metabolic inhibitors in clinical development for oncology.

Expression of oncogenic HRAS in human Rh28 and RMS-YM rhabdomyosarcoma cells leads to oncogene-induced senescence

Rhabdomyosarcoma (RMS) is the most common pediatric soft tissue sarcoma. The two predominant histologic variants of RMS, embryonal and alveolar rhabdomyosarcoma (eRMS and aRMS, respectively), carry very different prognoses. While eRMS is associated with an intermediate prognosis, the 5-year survival rate of aRMS is less than 30%. The RMS subtypes are also different at the molecular level-eRMS frequently has multiple genetic alterations, including mutations in RAS and TP53, whereas aRMS often has chromosomal translocations resulting in PAX3-FOXO1 or PAX7-FOXO1 fusions, but otherwise has a "quiet" genome. Interestingly, mutations in RAS are rarely found in aRMS. In this study, we explored the role of oncogenic RAS in aRMS. We found that while ectopic oncogenic HRAS expression was tolerated in the human RAS-driven eRMS cell line RD, it was detrimental to cell growth and proliferation in the human aRMS cell line Rh28. Growth inhibition was mediated by oncogene-induced senescence and associated with increased RB pathway activity and expression of the cyclin-dependent kinase inhibitors p16 and p21. Unexpectedly, the human eRMS cell line RMS-YM, a RAS wild-type eRMS cell line, also exhibited growth inhibition in response to oncogenic HRAS in a manner similar to aRMS Rh28 cells. This work suggests that oncogenic RAS is expressed in a context-dependent manner in RMS and may provide insight into the differential origins and therapeutic opportunities for RMS subtypes.

Why is PAK4 overexpressed in cancer?

Understanding why proteins are overexpressed in cancer is of great interest, as it holds the potential for improved cancer diagnosis and treatment. A noteworthy candidate, p21-activated kinase 4 (PAK4), is frequently overexpressed in cancer and a key player in multiple hallmarks of cancer. Here we review findings backing PAK4 overexpression in cancer and motivate PAK4 as a suitable target for the development of cancer therapy.

Advances in NAD-Lowering Agents for Cancer Treatment

Nicotinamide adenine dinucleotide (NAD) is an essential redox cofactor, but it also acts as a substrate for NAD-consuming enzymes, regulating cellular events such as DNA repair and gene expression. Since such processes are fundamental to support cancer cell survival and proliferation, sustained NAD production is a hallmark of many types of neoplasms. Depleting intratumor NAD levels, mainly through interference with the NAD-biosynthetic machinery, has emerged as a promising anti-cancer strategy. NAD can be generated from tryptophan or nicotinic acid. In addition, the "salvage pathway" of NAD production, which uses nicotinamide, a byproduct of NAD degradation, as a substrate, is also widely active in mammalian cells and appears to be highly exploited by a subset of human cancers. In fact, research has mainly focused on inhibiting the key enzyme of the latter NAD production route, nicotinamide phosphoribosyltransferase (NAMPT), leading to the identification of numerous inhibitors, including FK866 and CHS-828. Unfortunately, the clinical activity of these agents proved limited, suggesting that the approaches for targeting NAD production in tumors need to be refined. In this contribution, we highlight the recent advancements in this field, including an overview of the NAD-lowering compounds that have been reported so far and the related in vitro and in vivo studies. We also describe the key NAD-producing pathways and their regulation in cancer cells. Finally, we summarize the approaches that have been explored to optimize the therapeutic response to NAMPT inhibitors in cancer.

PAK1 and PAK4 as therapeutic targets for Ewing sarcoma: a commentary

Ewing sarcoma (ES) is an aggressive pediatric bone tumor that is prone to metastasis. Due to low five-year survival rates and limited therapeutic options for metastatic disease, there is a dire clinical need for improved ES treatments. Targeting p21-activated kinases (PAKs) may be key. PAK1 and PAK4 are associated with aggressive ES and poor patient outcomes, although their molecular mechanisms remain largely uncharacterized in this disease. This commentary aims to highlight the recent advancements made to the understanding of PAK1 and PAK4 in ES in the paper "p21-activated kinases as viable therapeutic targets for the treatment of high-risk Ewing sarcoma" by Qasim et al.