PAK4-NAMPT Dual Inhibition as a Novel Strategy for Therapy Resistant Pancreatic Neuroendocrine Tumors. Cancers (Basel). 2019;11. [PMID: 31795447 PMCID: PMC6966587 DOI: 10.3390/cancers11121902]

Current understanding of pathogenetic mechanisms in neuroendocrine neoplasms

INTRODUCTION

Despite the fact that important advances in research on neuroendocrine neoplasms (NENs) have been made, consistent data about their pathogenetic mechanism are still lacking. Furthermore, different primary sites may recognize different pathogenetic mechanisms.

AREAS COVERED

This review analyzes the possible biological and molecular mechanisms that may lead to NEN onset and progression in different organs. Through extensive research of the literature, risk factors including hypercholesterolemia, inflammatory bowel disease, chronic atrophic gastritis are evaluated as potential pathogenetic mechanisms. Consistent evidence is available regarding sporadic gastric NENs and MEN1 related duodenopancreatic NENs precursor lesions, and genetic-epigenetic mutations may play a pivotal role in tumor development and bone metastases onset. In lung neuroendocrine tumors (NETs), diffuse proliferation of neuroendocrine cells on the bronchial wall (DIPNECH) has been proposed as a premalignant lesion, while in lung neuroendocrine carcinoma nicotine and smoke could be responsible for carcinogenic processes. Also, rare primary NENs such as thymic (T-NENs) and Merkel cell carcinoma (MCC) have been analyzed, finding different possible pathogenetic mechanisms.

EXPERT OPINION

New technologies in genomics and epigenomics are bringing new light to the pathogenetic landscape of NENs, but further studies are needed to improve both prevention and treatment in these heterogeneous neoplasms.

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.

Combined blockade of mTOR and p21-activated kinases pathways prevents tumour growth in KRAS-mutated colorectal cancer

BACKGROUND

The identification of novel therapeutic strategies for metastatic colorectal cancer (mCRC) patients harbouring KRAS mutations represents an unmet clinical need. In this study, we aimed to clarify the role of p21-activated kinases (Paks) as therapeutic target for KRAS-mutated CRC.

METHODS

Paks expression and activation levels were evaluated in a cohort of KRAS-WT or -mutated CRC patients by immunohistochemistry. The effects of Paks inhibition on tumour cell proliferation and signal transduction were assayed by RNAi and by the use of three pan-Paks inhibitors (PF-3758309, FRAX1036, GNE-2861), evaluating CRC cells, spheroids and tumour xenografts' growth.

RESULTS

Paks activation positively correlated with KRAS mutational status in both patients and cell lines. Moreover, genetic modulation or pharmacological inhibition of Paks led to a robust impairment of KRAS-mut CRC cell proliferation. However, Paks prolonged blockade induced a rapid tumour adaptation through the hyper-activation of the mTOR/p70S6K pathway. The addition of everolimus (mTOR inhibitor) prevented the growth of KRAS-mut CRC tumours in vitro and in vivo, reverting the adaptive tumour resistance to Paks targeting.

CONCLUSIONS

In conclusion, our results suggest the simultaneous blockade of mTOR and Pak pathways as a promising alternative therapeutic strategy for patients affected by KRAS-mut colorectal cancer.

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.

Hyperactivation of p21-Activated Kinases in Human Cancer and Therapeutic Sensitivity

Over the last three decades, p21-activated kinases (PAKs) have emerged as prominent intracellular nodular signaling molecules in cancer cells with a spectrum of cancer-promoting functions ranging from cell survival to anchorage-independent growth to cellular invasiveness. As PAK family members are widely overexpressed and/or hyperactivated in a variety of human tumors, over the years PAKs have also emerged as therapeutic targets, resulting in the development of clinically relevant PAK inhibitors. Over the last two decades, this has been a promising area of active investigation for several academic and pharmaceutical groups. Similar to other kinases, blocking the activity of one PAK family member leads to compensatory activity on the part of other family members. Because PAKs are also activated by stress-causing anticancer drugs, PAKs are components in the rewiring of survival pathways in the action of several therapeutic agents; in turn, they contribute to the development of therapeutic resistance. This, in turn, creates an opportunity to co-target the PAKs to achieve a superior anticancer cellular effect. Here we discuss the role of PAKs and their effector pathways in the modulation of cellular susceptibility to cancer therapeutic agents and therapeutic resistance.

Review of various NAMPT inhibitors for the treatment of cancer

Nicotinamide phosphoribosyltransferase (NAMPT) is a rate-limiting enzyme in the NAD salvage pathway of mammalian cells and is overexpressed in numerous types of cancers. These include breast cancer, ovarian cancer, prostate cancer, gastric cancer, colorectal cancer, glioma, and b-cell lymphoma. NAMPT is also known to impact the NAD and NADPH pool. Research has demonstrated that NAMPT can be inhibited. NAMPT inhibitors are diverse anticancer medicines with significant anti-tumor efficacy in ex vivo tumor models. A few notable NAMPT specific inhibitors which have been produced include FK866, CHS828, and OT-82. Despite encouraging preclinical evidence of the potential utility of NAMPT inhibitors in cancer models, early clinical trials have yielded only modest results, necessitating the adaptation of additional tactics to boost efficacy. This paper examines a number of cancer treatment methods which target NAMPT, including the usage of individual inhibitors, pharmacological combinations, dual inhibitors, and ADCs, all of which have demonstrated promising experimental or clinical results. We intend to contribute further ideas regarding the usage and development of NAMPT inhibitors in clinical therapy to advance the field of research on this intriguing target.

Identification of new FK866 analogues with potent anticancer activity against pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC) is one of the most lethal diseases for which chemotherapy has not been very successful yet. FK866 ((E)-N-(4-(1-benzoylpiperidin-4-yl)butyl)-3-(pyridin-3-yl)acrylamide) is a well-known NAMPT (nicotinamide phosphoribosyltransferase) inhibitor with anti-cancer activities, but it failed in phase II clinical trials. We found that FK866 shows anti-proliferative activity in three PDAC cell lines, as well as in Jurkat T-cell leukemia cells. More than 50 FK866 analogues were synthesized that introduce substituents on the phenyl ring of the piperidine benzamide group of FK866 and exchange its buta-1,4-diyl tether for 1-oxyprop-3-yl, (E)-but-2-en-1,4-diyl and 2- and 3-carbon tethers. The pyridin-3-yl moiety of FK866 was exchanged for chlorinated and fluorinated analogues and for pyrazin-2-yl and pyridazin-4-yl groups. Several compounds showed low nanomolar or sub-nanomolar cell growth inhibitory activity. Our best cell anti-proliferative compounds were the 2,4,6-trimethoxybenzamide analogue of FK866 ((E)-N-(4-(1-(2,4,6-trimethoxybenzoyl)piperidin-4-yl)butyl)-3-(pyridin-3-yl)acrylamide) (9), the 2,6-dimethoxybenzamide (8) and 2-methoxybenzamide (4), which exhibited an IC50 of 0.16 nM, 0.004 nM and 0.08 nM toward PDAC cells, respectively.

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.

The trilogy of P21 activated kinase, autophagy and immune evasion in pancreatic ductal adenocarcinoma

Pancreatic Ductal Adenocarcinoma (PDA) is one of the most lethal types of cancer with a dismal prognosis. KRAS mutation is a commonly identified oncogene in PDA tumorigenesis and P21-activated kinases (PAKs) are its downstream mediator. While PAK1 is more well-studied, PAK4 also attracted increasing interest. In PDA, PAK inhibition not only reduces cancer cell viability but also sensitises it to chemotherapy. While PDA remains resistant to existing immunotherapies, PAK inhibition has been shown to increase cancer immunogenicity of melanoma, glioblastoma and PDA. Furthermore, autophagy plays an important role in PDA immune evasion, and accumulating evidence has pointed to a connection between PAK and cancer cell autophagy. In this literature review, we aim to summarize currently available studies that have assessed the potential connection between PAK, autophagy and immune evasion in PDA biology to guide future research.

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.

Progress in the therapeutic inhibition of Cdc42 signalling

Cdc42 is a member of the Rho family of small GTPases and a key regulator of the actin cytoskeleton, controlling cell motility, polarity and cell cycle progression. It signals downstream of the master regulator Ras and is essential for cell transformation by this potent oncogene. Overexpression of Cdc42 is observed in several cancers, where it is linked to poor prognosis. As a regulator of both cell architecture and motility, deregulation of Cdc42 is also linked to tumour metastasis. Like Ras, Cdc42 and other components of the signalling pathways it controls represent important potential targets for cancer therapeutics. In this review, we consider the progress that has been made targeting Cdc42, its regulators and effectors, including new modalities and new approaches to inhibition. Strategies under consideration include inhibition of lipid modification, modulation of Cdc42-GEF, Cdc42-GDI and Cdc42-effector interactions, and direct inhibition of downstream effectors.

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.

Regulation and metabolic functions of mTORC1 and mTORC2

Cells metabolize nutrients for biosynthetic and bioenergetic needs to fuel growth and proliferation. The uptake of nutrients from the environment and their intracellular metabolism is a highly controlled process that involves cross talk between growth signaling and metabolic pathways. Despite constant fluctuations in nutrient availability and environmental signals, normal cells restore metabolic homeostasis to maintain cellular functions and prevent disease. A central signaling molecule that integrates growth with metabolism is the mechanistic target of rapamycin (mTOR). mTOR is a protein kinase that responds to levels of nutrients and growth signals. mTOR forms two protein complexes, mTORC1, which is sensitive to rapamycin, and mTORC2, which is not directly inhibited by this drug. Rapamycin has facilitated the discovery of the various functions of mTORC1 in metabolism. Genetic models that disrupt either mTORC1 or mTORC2 have expanded our knowledge of their cellular, tissue, as well as systemic functions in metabolism. Nevertheless, our knowledge of the regulation and functions of mTORC2, particularly in metabolism, has lagged behind. Since mTOR is an important target for cancer, aging, and other metabolism-related pathologies, understanding the distinct and overlapping regulation and functions of the two mTOR complexes is vital for the development of more effective therapeutic strategies. This review discusses the key discoveries and recent findings on the regulation and metabolic functions of the mTOR complexes. We highlight findings from cancer models but also discuss other examples of the mTOR-mediated metabolic reprogramming occurring in stem and immune cells, type 2 diabetes/obesity, neurodegenerative disorders, and aging.

Physical activity differentially regulates VEGF, PlGF, and their receptors in the human placenta

Physical activity (PA) has beneficial effects on the function of many organs by modulating their vascular development. Regular PA during pregnancy is associated with favorable short‐ and long‐term outcomes for both mother and fetus. During pregnancy, appropriate vascularization of the placenta is crucial for adequate maternal–fetal nutrient and gas exchange. How PA modulates angiogenic factors, VEGF, and its receptors in the human placenta, is as of yet, unknown. We objectively measured the PA of women at 24–28 and 34–38 weeks of gestation. Participants were considered “active” if they had met or exceeded 150 min of moderate‐intensity PA per week during their 2nd trimester. Term placenta tissues were collected from active (n = 23) or inactive (n = 22) women immediately after delivery. We examined the expression of the angiogenic factors VEGF, PlGF, VEGFR‐1, and VEGFR‐2 in the placenta. Western blot analysis showed VEGF and its receptor, VEGFR‐1 was significantly (p < 0.05) higher both at the protein and mRNA levels in placenta from physically active compared to inactive women. No difference in VEGFR‐2 was observed. Furthermore, immunohistochemistry showed differential staining patterns of VEGF and its receptors in placental endothelial, stromal, and trophoblast cells and in the syncytial brush border. In comparison, PlGF expression did not differ either at the protein or mRNA level in the placenta from physically active or inactive women. The expression and localization pattern of VEGF and its receptors suggest that PA during pregnancy may support a pro‐angiogenic milieu to the placental vascular network.

NAD+ metabolism, stemness, the immune response, and cancer

NAD⁺ was discovered during yeast fermentation, and since its discovery, its important roles in redox metabolism, aging, and longevity, the immune system and DNA repair have been highlighted. A deregulation of the NAD⁺ levels has been associated with metabolic diseases and aging-related diseases, including neurodegeneration, defective immune responses, and cancer. NAD⁺ acts as a cofactor through its interplay with NADH, playing an essential role in many enzymatic reactions of energy metabolism, such as glycolysis, oxidative phosphorylation, fatty acid oxidation, and the TCA cycle. NAD⁺ also plays a role in deacetylation by sirtuins and ADP ribosylation during DNA damage/repair by PARP proteins. Finally, different NAD hydrolase proteins also consume NAD⁺ while converting it into ADP-ribose or its cyclic counterpart. Some of these proteins, such as CD38, seem to be extensively involved in the immune response. Since NAD cannot be taken directly from food, NAD metabolism is essential, and NAMPT is the key enzyme recovering NAD from nicotinamide and generating most of the NAD cellular pools. Because of the complex network of pathways in which NAD⁺ is essential, the important role of NAD⁺ and its key generating enzyme, NAMPT, in cancer is understandable. In the present work, we review the role of NAD⁺ and NAMPT in the ways that they may influence cancer metabolism, the immune system, stemness, aging, and cancer. Finally, we review some ongoing research on therapeutic approaches.

Typical and Atypical Carcinoid Tumors of the Mediastinum: A Biomarker Analysis of 27 Cases With Clinical Correlation

Thymic typical and atypical carcinoids are rare and appear to be more aggressive than similar tumors in other sites. We retrospectively analyzed a group of biomarkers that hold therapeutic and prognostic utility, in 27 of these tumors. All cases were immunohistochemically stained with PAX5, MET, CRMP5, paxillin, p21, p27, EZH2, PDL-1, and Ki-67, and then H-scored. Clinicopathologic and survival data were statistically analyzed against staining (χ² test). Five- and 10-year-survival rates were 53% and 18%, respectively. Mitotic counts ≥4 per 2 mm² and tumor size ≥5 cm, associated with death of disease (DoD; P = .010 and .016). Ki-67 expression ≥1% associated with DoD (P = .003) and death within 5 years (P = .031). Biomarkers stained tumor cases as follows: PDL-1 = 0%, PAX-5 = 0%, MET = 7.4%, paxillin = 41%, CRMP5 = 78%, p21 = 63%, p27 = 63%, EZH2 = 37%, and MASH1 = 59%. Overall ± staining did not associate with survival or grade. Cases with low CRMP5 H-scores (<80) associated with DoD (P = .002), while CRMP5 H-scores >80 associated with 10-year survival (P = .022). Cases with high MASH1 H-score (>100) associated with DoD (P = .021). Accurate grading and staging remain paramount in predicting clinical outcome. Biomarkers may have significance in subsets of patients and the use of these studies likely should be focused on a more personalize type of approach.

Coordinated dysregulation of cancer progression by the HER family and p21-activated kinases

Most epithelial cancer types are polygenic in nature and are driven by coordinated dysregulation of multiple regulatory pathways, genes, and protein modifications. The process of coordinated regulation of cancer promoting pathways in response to extrinsic and intrinsic signals facilitates the dysregulation of several pathways with complementary functions, contributing to the hallmarks of cancer. Dysregulation and hyperactivation of cell surface human epidermal growth factor receptors (HERs) and cytoskeleton remodeling by p21-activated kinases (PAKs) are two prominent interconnected aspects of oncogenesis. We briefly discuss the discoveries and significant advances in the area of coordinated regulation of HERs and PAKs in the development and progression of breast and other epithelial cancers. We also discuss how initial studies involving heregulin signaling via HER3-HER2 axis and HER2-overexpressing breast cancer cells not only discovered a mechanistic role of PAK1 in breast cancer pathobiology but also acted as a bridge in generating a broader cancer research interest in other PAK family members and cancer types and catalyzed establishing the role of PAKs in human cancer, at-large. In addition, growth factor stimulation of the PAK pathway also helped to recognize new facets of PAKs, connecting the PAK pathway to oncogenesis, nuclear signaling, gene expression, mitotic progression, DNA damage response, among other phenotypic responses, and shaped the field of PAK cancer research. Finally, we recount some of the current limitations of HER- and PAK-directed therapeutics in counteracting acquired therapeutic resistance and discuss how cancer's as a polygenic disease may be best targeted with a polygenic approach.

Pancreatic neuroendocrine tumors: Therapeutic challenges and research limitations

Pancreatic neuroendocrine tumors (PNETs) are known to be the second most common epithelial malignancy of the pancreas. PNETs can be listed among the slowest growing as well as the fastest growing human cancers. The prevalence of PNETs is deceptively low; however, its incidence has significantly increased over the past decades. According to the American Cancer Society’s estimate, about 4032 (> 7% of all pancreatic malignancies) individuals will be diagnosed with PNETs in 2020. PNETs often cause severe morbidity due to excessive secretion of hormones (such as serotonin) and/or overall tumor mass. Patients can live for many years (except for those patients with poorly differentiated G3 neuroendocrine tumors); thus, the prevalence of the tumors that is the number of patients actually dealing with the disease at any given time is fairly high because the survival is much longer than pancreatic ductal adenocarcinoma. Due to significant heterogeneity, the management of PNETs is very complex and remains an unmet clinical challenge. In terms of research studies, modest improvements have been made over the past decades in the identification of potential oncogenic drivers in order to enhance the quality of life and increase survival for this growing population of patients. Unfortunately, the majority of systematic therapies approved for the management of advanced stage PNETs lack objective response or at most result in modest benefits in survival. In this review, we aim to discuss the broad challenges associated with the management and the study of PNETs.

Beyond Energy Metabolism: Exploiting the Additional Roles of NAMPT for Cancer Therapy

Tumor cells have increased requirements for NAD⁺. Thus, many cancers exhibit an increased reliance on NAD⁺ production pathways. This dependence may be exploited therapeutically through pharmacological targeting of NAMPT, the rate-limiting enzyme in the NAD⁺ salvage pathway. Despite promising preclinical data using NAMPT inhibitors in cancer models, early NAMPT inhibitors showed limited efficacy in several early phase clinical trials, necessitating the identification of strategies, such as drug combinations, to enhance their efficacy. While the effect of NAMPT inhibitors on impairment of energy metabolism in cancer cells has been well-described, more recent insights have uncovered a number of additional targetable cellular processes that are impacted by inhibition of NAMPT. These include sirtuin function, DNA repair machinery, redox homeostasis, molecular signaling, cellular stemness, and immune processes. This review highlights the recent findings describing the effects of NAMPT inhibitors on the non-metabolic functions of malignant cells, with a focus on how this information can be leveraged clinically. Combining NAMPT inhibitors with other therapies that target NAD⁺-dependent processes or selecting tumors with specific vulnerabilities that can be co-targeted with NAMPT inhibitors may represent opportunities to exploit the multiple functions of this enzyme for greater therapeutic benefit.