Serotonin signalling in cancer: Emerging mechanisms and therapeutic opportunities.

BACKGROUND: Serotonin (5-hydroxytryptamine) is a multifunctional bioamine serving as a neurotransmitter, peripheral hormone and mitogen in the vertebrate system. It has pleiotropic activities in central nervous system and gastrointestinal function via an orchestrated action of serotonergic elements, particularly serotonin receptor-mediated signalling cascades. The mitogenic properties of serotonin have garnered recognition for years and have been exploited for repurposing serotonergic-targeted drugs in cancer therapy. However, emerging conflicting findings necessitate a more comprehensive elucidation of serotonin's role in cancer pathogenesis. MAIN BODY AND CONCLUSION: Here, we provide an overview of the biosynthesis, metabolism and action modes of serotonin. We summarise our current knowledge regarding the effects of the peripheral serotonergic system on tumourigenesis, with a specific emphasis on its immunomodulatory activities in human cancers. We also discuss the dual roles of serotonin in tumour pathogenesis and elucidate the potential of serotonergic drugs, some of which display favourable safety profiles and impressive efficacy in clinical trials, as a promising avenue in cancer treatment. KEY POINTS: Primary synthesis and metabolic routes of peripheral 5-hydroxytryptamine in the gastrointestinal tract. Advanced research has established a strong association between the serotonergic components and carcinogenic mechanisms. The interplay between serotonergic signalling and the immune system within the tumour microenvironment orchestrates antitumour immune responses. Serotonergic-targeted drugs offer valuable clinical options for cancer therapy.

CPE correlates with poor prognosis in gastric cancer by promoting tumourigenesis.

Aims: To investigate the potential functions and mechanisms of tumourigenesis in carboxypeptidase E (CPE) and its prognostic value in gastric cancer, and to develop a predictive model for prognosis based on CPE. Results: Transcriptome level variation and the prognostic value of CPE in different types of cancers were investigated using bioinformatics analyses. The association between CPE and clinicopathological characteristics was specifically explored in gastric cancer. Elevated CPE expression was associated with poor survival and recurrence prognosis and was found in cases with a later clinical stage of gastric cancer. The CPE was considered an independent prognostic factor, as assessed using Cox regression analysis. The prognostic value of CPE was further verified through immunohistochemistry and haematoxylin staining. Enrichment analysis provided a preliminary confirmation of the potential functions and mechanisms of CPE. Immune cell infiltration analysis revealed a significant correlation between CPE and macrophage infiltration. Eventually, a prognosis prediction nomogram model based on CPE was developed. Conclusion: CPE was identified as an independent biomarker associated with poor prognosis in gastric cancer. This suggests that CPE overexpression promoted epithelial-mesenchymal transition via the activation of the Erk/Wnt pathways, leading to proliferation, invasion, and metastasis. Targeted therapeutic strategies for gastric cancer may benefit from these findings.

Ribogenesis boosts controlled by HEATR1-MYC interplay promote transition into brain tumour growth.

Cell commitment to tumourigenesis and the onset of uncontrolled growth are critical determinants in cancer development but the early events directing tumour initiating cell (TIC) fate remain unclear. We reveal a single-cell transcriptome profile of brain TICs transitioning into tumour growth using the brain tumour (brat) neural stem cell-based Drosophila model. Prominent changes in metabolic and proteostasis-associated processes including ribogenesis are identified. Increased ribogenesis is a known cell adaptation in established tumours. Here we propose that brain TICs boost ribogenesis prior to tumour growth. In brat-deficient TICs, we show that this dramatic change is mediated by upregulated HEAT-Repeat Containing 1 (HEATR1) to promote ribosomal RNA generation, TIC enlargement and onset of overgrowth. High HEATR1 expression correlates with poor glioma patient survival and patient-derived glioblastoma stem cells rely on HEATR1 for enhanced ribogenesis and tumourigenic potential. Finally, we show that HEATR1 binds the master growth regulator MYC, promotes its nucleolar localisation and appears required for MYC-driven ribogenesis, suggesting a mechanism co-opted in ribogenesis reprogramming during early brain TIC development.

MicroRNA Expression Profiling-Potential Molecular Discrimination of Papillary Thyroid Carcinoma Subtypes.

Recent research has revealed the importance of miRNAs in the diagnosis and clinical evolution of papillary thyroid cancer (PTC). We aim to identify a specific miRNA profile that could differentiate between specific subtypes of PTC. METHODS: In this cross-sectional study, total RNA was extracted from paraffin-embedded tissues of 43 patients, 17 with an infiltrative follicular variant of PTC (iFVPTC) and 26 with a conventional variant of PTC (cPTC). Nine miRNAs were evaluated using qRT-PCR technology and specific miRNA assays. RESULTS: We found specific patterns for cPTC and iFVPTC, such as miRNA altered in both types of tumours (miR-146b-5p, miR-181a-5p, miR-221-3p, miR-21-5p and miR-222-3p) and two miRNAs significantly expressed only in cPTC (miR-20b-5p, miR-21-5p). The iFVPTC group presented strong and moderate correlations between miRNA expression and clinical data. miR-221-3p, miR-195-5p, miR-181-5p, miR-146b-5p and miR-222 were correlated with age, tumour size (TS) or lymph node metastases (N), while only miR-20b-5p, miR-195-5p and miR-181-5p were correlated with TS, N and age in the cPTC group. CONCLUSIONS: The present study allowed the identification of a signature of two miRNAs to confirm miRNA differences between the two histological subtypes of TC. Our results provide advances in the molecular diagnosis of TC and could help to improve the diagnostic performance of already existing molecular classifiers.

Loss of two-pore channel 2 function in melanoma-derived tumours reduces tumour growth in vivo but greatly increases tumour-related toxicity in the organism.

BACKGROUND: Melanoma, a severe form of skin cancer, poses significant health risks due to its aggressive nature and potential for metastasis. The role of two-pore channel 2 (TPC2) in the development and progression of melanoma remains poorly understood. This study aims to investigate the impact of TPC2 knockout (KO) on melanoma-derived tumors, focusing on tumour growth and related toxicity in the organism. METHODS: The study utilized CHL-1 and B16 melanoma cell lines with TPC2 KO to assess the changes in proliferation dynamics. Methods included real-time monitoring of cell proliferation using the xCELLigence system, in vivo tumour growth assays in mice, histopathological analyses, inflammation marker assessment, and quantitative PCR (qPCR) for gene expression analysis RESULTS: TPC2 KO was found to significantly alter the proliferation dynamics of CHL-1 and B16 melanoma cells. The in vivo studies demonstrated reduced tumor growth in TPC2 KO cell-derived tumors. However, a notable increase in tumor-related toxicity in affected organs, such as the liver and spleen, was observed, indicating a complex role of TPC2 in melanoma pathology. CONCLUSIONS: The loss of TPC2 function in melanoma cells leads to reduced tumour growth but exacerbates tumour-related toxicity in the organism. These findings highlight the dual role of TPC2 in melanoma progression and its potential as a therapeutic target. Further research is needed to fully understand the mechanisms underlying these effects and to explore TPC2 as a treatment target in melanoma.

Dysregulated Signalling Pathways Driving Anticancer Drug Resistance.

One of the leading causes of death worldwide, in both men and women, is cancer. Despite the significant development in therapeutic strategies, the inevitable emergence of drug resistance limits the success and impedes the curative outcome. Intrinsic and acquired resistance are common mechanisms responsible for cancer relapse. Several factors crucially regulate tumourigenesis and resistance, including physical barriers, tumour microenvironment (TME), heterogeneity, genetic and epigenetic alterations, the immune system, tumour burden, growth kinetics and undruggable targets. Moreover, transforming growth factor-beta (TGF-ß), Notch, epidermal growth factor receptor (EGFR), integrin-extracellular matrix (ECM), nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB), phosphoinositol-3-kinase/protein kinase B/mammalian target of rapamycin (PI3K/Akt/mTOR), wingless-related integration site (Wnt/ß-catenin), Janus kinase/signal transducers and activators of transcription (JAK/STAT) and RAS/RAF/mitogen-activated protein kinase (MAPK) signalling pathways are some of the key players that have a pivotal role in drug resistance mechanisms. To guide future cancer treatments and improve results, a deeper comprehension of drug resistance pathways is necessary. This review covers both intrinsic and acquired resistance and gives a comprehensive overview of recent research on mechanisms that enable cancer cells to bypass barriers put up by treatments, and, like "satellite navigation", find alternative routes by which to carry on their "journey" to cancer progression.

NF-κB: a mediator that promotes or inhibits angiogenesis in human diseases?

The nuclear factor of κ-light chain of enhancer-activated B cells (NF-κB) signaling pathway, which is conserved in invertebrates, plays a significant role in human diseases such as inflammation-related diseases and carcinogenesis. Angiogenesis refers to the growth of new capillary vessels derived from already existing capillaries and postcapillary venules. Maintaining normal angiogenesis and effective vascular function is a prerequisite for the stability of organ tissue function, and abnormal angiogenesis often leads to a variety of diseases. It has been suggested that NK-κB signalling molecules under pathological conditions play an important role in vascular differentiation, proliferation, apoptosis and tumourigenesis by regulating the transcription of multiple target genes. Many NF-κB inhibitors are being tested in clinical trials for cancer treatment and their effect on angiogenesis is summarised. In this review, we will summarise the role of NF-κB signalling in various neovascular diseases, especially in tumours, and explore whether NF-κB can be used as an attack target or activation medium to inhibit tumour angiogenesis.

Activation of ß-Adrenoceptors Promotes Lipid Droplet Accumulation in MCF-7 Breast Cancer Cells via cAMP/PKA/EPAC Pathways.

Physiologically, ß-adrenoceptors are major regulators of lipid metabolism, which may be reflected in alterations in lipid droplet dynamics. ß-adrenoceptors have also been shown to participate in breast cancer carcinogenesis. Since lipid droplets may be seen as a hallmark of cancer, the present study aimed to investigate the role of ß-adrenoceptors in the regulation of lipid droplet dynamics in MCF-7 breast cancer cells. Cells were treated for up to 72 h with adrenaline (an endogenous adrenoceptor agonist), isoprenaline (a non-selective ß-adrenoceptor agonist) and salbutamol (a selective ß2-selective agonist), and their effects on lipid droplets were evaluated using Nile Red staining. Adrenaline or isoprenaline, but not salbutamol, caused a lipid-accumulating phenotype in the MCF-7 cells. These effects were significantly reduced by selective ß1- and ß3-antagonists (10 nM atenolol and 100 nM L-748,337, respectively), indicating a dependence on both ß1- and ß3-adrenoceptors. These effects were dependent on the cAMP signalling pathway, involving both protein kinase A (PKA) and cAMP-dependent guanine-nucleotide-exchange (EPAC) proteins: treatment with cAMP-elevating agents (forskolin or 8-Br-cAMP) induced lipid droplet accumulation, whereas either 1 µM H-89 or 1 µM ESI-09 (PKA or EPAC inhibitors, respectively) abrogated this effect. Taken together, the present results demonstrate the existence of a ß-adrenoceptor-mediated regulation of lipid droplet dynamics in breast cancer cells, likely involving ß1- and ß3-adrenoceptors, revealing a new mechanism by which adrenergic stimulation may influence cancer cell metabolism.

Podoplanin promotes the carcinogenicity of gastric cancer by activating ezrin and mediating the crosstalk between tumour cells and cancer-associated fibroblasts.

NEW FINDINGS: What is the central question of this study? To reveal the role and biological mechanism of PDPN in the progression of gastric cancer. What is the main finding and its importance? This study focused on a prognostic predictor, PDPN, which acted as a promoter in the progression of gastric cancer through the activation of Ezrin expression and CAFs. This finding may expand a new route for the gene-targeted therapy in gastric cancer. ABSTRACT: Gastric cancer (GC) is a frequent malignant disease and the main cause of cancer-related death in the world. Podoplanin (PDPN) has been proved to be involved in the progression of various cancers. However, the role and biological mechanism of PDPN in GC are still vague. In our study, we detected the expression of PDPN in GC tissues and cell lines using RT-qPCR, western blot and datasets. The overall survival of GC patients was analysed with a Kaplan-Meier plot. The effects of PDPN overexpression and silencing on GC cell progression were assessed by Cell Counting Kit-8, flow cytometry and a wound healing assay. Besides, the modulation of PDPN on ezrin activation was investigated. We further explored the role of PDPN in the crosstalk between GC cells and cancer associated fibroblasts (CAFs). Results showed that PDPN was upregulated in GC tissues and cell lines. High expression of PDPN was correlated with poor prognosis of GC patients. PDPN positively regulated the viability, migration and invasion, but inhibited apoptosis, of GC cells by mediating the activation of ezrin. Meanwhile, the change in PDPN in GC cells activated CAFs and promoted the production of cytokines secreted by CAFs, which induced the progression of GC cells. These findings may provide a novel target for GC therapy.

The role of miRNAs and lncRNAs in neurofibromatosis type 1.

Neurofibromatosis Type 1 (NF1) is a frequent cancer predisposition syndrome. The common hallmark of patients with this multisystemic genetic disorder is the formation of peripheral nerve sheath tumors, which can be seen as either dermal, plexiform, and malignant forms. MicroRNA (miRNA) is an essential gene regulation factor and consists of 22-25 nucleotides. MiRNAs are identified to act as both tumor suppressors and oncogenes (oncomirs) in a wide variety of human cancers. They play multiple roles in molecular pathways responsible for tumor homing, progression, and invasion. Long noncoding RNA (lncRNA) also has a key role in cancer transcriptomics. Altered lncRNA expression levels have been found in various malignancies. This review aims to summarize the role of two noncoding RNA groups, miRNAs and lncRNAs, in NF1 establishment, development, and progression. We also highlight their potential for future clinical interventions and devising new diagnostic tools.

An update on the role of complement in hepatocellular carcinoma.

As a main producer of complement, the environment in the liver is greatly affected by the complement system. Although the complement system is considered to have the ability of nonself discrimination, remarkable studies have revealed the tight association between improper complement activation in tumour initiation and progression. As complement activation predominantly occurs within the liver, the protumourigenic role of the complement system may contribute to the development of hepatocellular carcinoma (HCC). Improvement in the understanding of the molecular targets involved in complement-mediated tumour development, metastasis, and tumour-promoting inflammation in HCC would certainly aid in the development of better treatments. This minireview is focused on recent findings of the protumourigenic role of the complement system in HCC.

ISG15 is associated with cervical cancer development.

Cervical cancer (CC) is a complex disease. Numerous factors contribute to the tumourigenesis and progression of CC neoplasms. The present study analysed transcriptomic differences and simulated tumour progression to explore the pathogenesis of CC. RNA sequencing was performed to analyse the transcriptomic differences among normal tissue (NC), paracarcinoma tissue (TP), and primary tumour tissue (TT). Pseudo-time analysis was performed to simulate tumour progression. Reverse transcription-quantitative PCR (RT-qPCR) and immunohistochemistry (IHC) were used to analyse the expression levels of ISG15 ubiquitin-like modifier (ISG15). Cell proliferation wound healing and Transwell assays were used to examine the effect of ISG15 inhibition and overexpression on HeLa cells. The RT-qPCR and IHC results indicated that ISG15 expression was significantly upregulated in TT. An increasing trend of ISG15 expression from NC to TP to TT was observed, which suggested that elevated ISG15 expression was closely associated with malignant evolution in CC tissues. HeLa cell experiments revealed that ISG15-small interfering RNA inhibited cell proliferation and invasion. The present study demonstrated that ISG15 was upregulated in CC and positively associated with the development of CC. ISG15 may act as an oncogene in the tumourigenesis of CC.

Unfolded protein response at the cross roads of tumourigenesis, oxygen sensing and drug resistance in clear cell renal cell carcinoma.

Clear cell renal cell carcinoma (ccRCC) is the most common form of kidney cancer. Despite therapeutic advances, long term survival in patients diagnosed with advanced disease is low. Efforts to understand the mechanisms promoting disease progression will likely produce novel therapeutic targets. The unfolded protein response (UPR) is activated when unfolded protein accumulates in the endoplasmic reticulum (ER) upon cellular stress. Constitutive UPR activation is a characteristic of many malignancies. We discuss the accumulating evidence that describes a role for the UPR in ccRCC. Studies focused on UPR signalling may provide compelling avenues for therapeutic intervention in the future.

FDX1 expression predicts favourable prognosis in clear cell renal cell carcinoma identified by bioinformatics and tissue microarray analysis.

Ferredoxin 1 (FDX1), an iron-sulphur protein, is responsible for electron transfer in a range of metabolic redox reactions. Clear cell renal cell carcinoma (ccRCC) is an aggressive cancer characterised by metabolic reprogramming, and FDX1 is a critical regulator of cuproptosis. However, the expression profile and prognostic value of FDX1 associated with clinicopathological features in ccRCC remain largely unelucidated. In this study, we integrated a series of public bioinformatic analysis to explore the mRNA and protein profiles of FDX1 across human cancers and cell lines and validated its expression and prognostic value, especially in ccRCC. In this study, FDX1 mRNA and protein expression were aberrantly downregulated and associated with ccRCC grade, stage, and nodal metastasis, whereas in adjacent non-tumour kidney tissue, it was abundantly expressed and cytoplasmically localised in renal tubular epithelial cells. Multivariate analysis indicated that low FDX1 expression contributed to unfavourable overall and disease-free survival. The functional enrichment of FDX1 co-expressed genes in ccRCC involved mainly mitochondrial dysfunction in various metabolic processes and biological oxidation, besides iron-sulphur cluster biogenesis. Furthermore, FDX1 modulates immunological infiltration to affect prognosis. Thus, FDX1 downregulation is mechanistically because of ccRCC tumourigenesis and is a promising prognostic biomarker to stratify patients with ccRCC.

The positive regulatory loop of TCF4N/p65 promotes glioblastoma tumourigenesis and chemosensitivity.

BACKGROUND: NF-κB signaling is widely linked to the pathogenesis and treatment resistance in cancers. Increasing attention has been paid to its anti-oncogenic roles, due to its key functions in cellular senescence and the senescence-associated secretory phenotype (SASP). Therefore, thoroughly understanding the function and regulation of NF-κB in cancers is necessary prior to the application of NF-κB inhibitors. METHODS: We established glioblastoma (GBM) cell lines expressing ectopic TCF4N, an isoform of the ß-catenin interacting transcription factor TCF7L2, and evaluated its functions in GBM tumorigenesis and chemotherapy in vitro and in vivo. In p65 knock-out or phosphorylation mimic (S536D) cell lines, the dual role and correlation of TCF4N and NF-κB signaling in promoting tumorigenesis and chemosensitivity was investigated by in vitro and in vivo functional experiments. RNA-seq and computational analysis, immunoprecipitation and ubiquitination assay, minigene splicing assay and luciferase reporter assay were performed to identify the underlying mechanism of positive feedback regulation loop between TCF4N and the p65 subunit of NF-κB. A eukaryotic cell-penetrating peptide targeting TCF4N, 4N, was used to confirm the therapeutic significance. RESULTS: Our results indicated that p65 subunit phosphorylation at Ser 536 (S536) and nuclear accumulation was a promising prognostic marker for GBM, and endowed the dual functions of NF-κB in promoting tumorigenesis and chemosensitivity. p65 S536 phosphorylation and nuclear stability in GBM was regulated by TCF4N. TCF4N bound p65, induced p65 phosphorylation and nuclear translocation, inhibited its ubiquitination/degradation, and subsequently promoted NF-κB activity. p65 S536 phosphorylation was essential for TCF4N-led senescence-independent SASP, GBM tumorigenesis, tumor stem-like cell differentiation and chemosensitivity. Activation of p65 was closely connected to alterative splicing of TCF4N, a likely positive feedback regulation loop between TCF4N and p65 in GBM. 4N increased chemosensitivity, highlighting a novel anti-cancer strategy. CONCLUSION: Our study defined key roles of TCF4N as a novel regulator of NF-κB through mutual regulation with p65 and provided a new avenue for GBM inhibition.

The Role of SLC7A11 in Cancer: Friend or Foe?

SLC7A11 controls the uptake of extracellular cystine in exchange for glutamate at a ratio of 1:1, and it is overexpressed in a variety of tumours. Accumulating evidence has shown that the expression of SLC7A11 is fine-tuned at multiple levels, and plays diverse functional and pharmacological roles in tumours, such as cellular redox homeostasis, cell growth and death, and cell metabolism. Many reports have suggested that the inhibition of SLC7A11 expression and activity is favourable for tumour therapy; thus, SLC7A11 is regarded as a potential therapeutic target. However, emerging evidence also suggests that on some occasions, the inhibition of SLC7A11 is beneficial to the survival of cancer cells, and confers the development of drug resistance. In this review, we first briefly introduce the biological properties of SLC7A11, including its structure and physiological functions, and further summarise its regulatory network and potential regulators. Then, focusing on its role in cancer, we describe the relationships of SLC7A11 with tumourigenesis, survival, proliferation, metastasis, and therapeutic resistance in more detail. Finally, since SLC7A11 has been linked to cancer through multiple approaches, we propose that its contribution and regulatory mechanism require further elucidation. Thus, more personalised therapeutic strategies should be adapted when targeting SLC7A11.

Long-Term Exposure to Decabromodiphenyl Ether Promotes the Proliferation and Tumourigenesis of Papillary Thyroid Carcinoma by Inhibiting TRß.

Polybrominated diphenyl ethers (PBDEs) have been reported to possess endocrine-disrupting and tumour-promoting activity. However, the effects of long-term exposure to decabromodiphenyl ether (BDE209) on thyroid tumourigenesis of papillary thyroid carcinoma (PTC) and the underlying mechanisms remain poorly defined. In this study, functional assays in vitro and mouse models in vivo were used to evaluate the toxic effects of long-term exposure to environmental concentrations of BDE209 on the pathogenesis and progression of PTC. MTS, EdU and colony-forming assays confirmed the chronic toxicity of BDE209 on the proliferation of human normal follicular epithelial cell line (Nthy-ori 3-1) and PTC-derived cell lines (TPC-1 and BCPAP). Wound and Transwell assays showed that BDE209 exacerbated the aggressiveness of PTC cells. BDE209 significantly promoted cell proliferation during the S and G2/M phases of the cell cycle. Mechanistically, BDE209 altered the thyroid system by acting as a competitive inhibitor of thyroid receptor beta (TRß) expression and function, which was further proven by public databases and RNA-seq bioinformation analysis. Taken together, these results demonstrated that BDE209 has chronic toxicity and potential tumourigenic effects on the thyroid by inhibiting TRß.

The epigenetic-metabolic interplay in gliomagenesis.

Although tumourigenesis occurs due to genetic mutations, the role of epigenetic dysregulations in cancer is also well established. Epigenetic dysregulations in cancer may occur as a result of mutations in genes encoding histone/DNA-modifying enzymes and chromatin remodellers or mutations in histone protein itself. It is also true that misregulated gene expression without genetic mutations in these factors could also support tumour initiation and progression. Interestingly, metabolic rewiring has emerged as a hallmark of cancer due to gene mutations in specific metabolic enzymes or dietary/environmental factors. Recent studies report an intricate cross-talk between epigenetic and metabolic reprogramming in cancer. This review discusses the role of epigenetic and metabolic dysregulations and their cross-talk in tumourigenesis with a special focus on gliomagenesis. We also discuss the role of recently developed human embryonic stem cells/induced pluripotent stem cells-derived organoid models of gliomas and how these models are proving instrumental in uncovering human-specific cellular and molecular complexities of gliomagenesis.

The immune environment of the mammary gland fluctuates during post-lactational regression and correlates with tumour growth rate.

Post-lactational mammary gland regression encompasses extensive programmed cell death and removal of milk-producing epithelial cells, breakdown of extracellular matrix components and redifferentiation of stromal adipocytes. This highly regulated involution process is associated with a transient increased risk of breast cancer in women. Using a syngeneic tumour model, we show that tumour growth is significantly altered depending on the stage of involution at which tumour cells are implanted. Tumour cells injected at day 3 involution grew faster than those in nulliparous mice, whereas tumours initiated at day 6 involution grew significantly slower. These differences in tumour progression correlate with distinct changes in innate immune cells, in particular among F4/80-expressing macrophages and among TCRδ+ unconventional T cells. Breast cancer post-pregnancy risk is exacerbated in older first-time mothers and, in our model, initial tumour growth is moderately faster in aged mice compared with young mice. Our results have implications for breast cancer risk and the use of anti-inflammatory therapeutics for postpartum breast cancers.

Targeting the KRAS α4-α5 allosteric interface inhibits pancreatic cancer tumorigenesis.

RAS is the most frequently mutated oncogene in human cancer with nearly ~20% of cancer patients possessing mutations in one of three RAS genes (K, N or HRAS). However, KRAS is mutated in nearly 90% of pancreatic ductal carcinomas (PDAC). Although pharmacological inhibition of RAS has been challenging, KRAS(G12C)-specific inhibitors have recently entered the clinic. While KRAS(G12C) is frequently expressed in lung cancers, it is rare in PDAC. Thus, more broadly efficacious RAS inhibitors are needed for treating KRAS mutant-driven cancers such as PDAC. A RAS-specific tool biologic, NS1 Monobody, inhibits HRAS- and KRAS-mediated signalling and oncogenic transformation both in vitro and in vivo by targeting the α4-α5 allosteric site of RAS and blocking RAS self-association. Here, we evaluated the efficacy of targeting the α4-α5 interface of KRAS as an approach to inhibit PDAC development using an immunocompetent orthotopic mouse model. Chemically regulated NS1 expression inhibited ERK and AKT activation in KRAS(G12D) mutant KPC PDAC cells and reduced the formation and progression of pancreatic tumours. NS1-expressing tumours were characterized by increased infiltration of CD4 + T helper cells. These results suggest that targeting the #x3B1;4-#x3B1;5 allosteric site of KRAS may represent a viable therapeutic approach for inhibiting KRAS-mutant pancreatic tumours.