Receptor Tyrosine Kinase Mutations Research Articles

MET variants with activating N-lobe mutations identified in hereditary papillary renal cell carcinomas still require ligand stimulation.

In hereditary papillary renal cell carcinoma (HPRCC), the hepatocyte growth factor receptor (MET) receptor tyrosine kinase (RTK) mutations recorded to date are located in the kinase domain and lead to constitutive MET activation. This contrasts with MET mutations identified in non-small-cell lung cancer (NSCLC), which lead to exon 14 skipping and deletion of a regulatory domain: In this latter case, the mutated receptor still requires ligand stimulation. Sequencing of MET in samples from 158 HPRCC and 2808 NSCLC patients revealed 10 uncharacterized mutations. Four of these, all found in HPRCC and leading to amino acid substitutions in the N-lobe of the MET kinase, proved able to induce cell transformation, which was further enhanced by hepatocyte growth factor (HGF) stimulation: His1086Leu, Ile1102Thr, Leu1130Ser, and Cis1125Gly. Similar to the variant resulting in MET exon 14 skipping, the two N-lobe MET variants His1086Leu and Ile1102Thr were found to require stimulation by HGF in order to strongly activate downstream signaling pathways and epithelial cell motility. The Ile1102Thr mutation also displayed transforming potential, promoting tumor growth in a xenograft model. In addition, the N-lobe-mutated MET variants were found to trigger a common HGF-stimulation-dependent transcriptional program, consistent with an observed increase in cell motility and invasion. Altogether, this functional characterization revealed that N-lobe variants still require ligand stimulation, in contrast to other RTK variants. This suggests that HGF expression in the tumor microenvironment is important for tumor growth. The sensitivity of these variants to MET inhibitors opens the way for use of targeted therapies for patients harboring the corresponding mutations.

Missense mutations of the ephrin receptor EPHA1 associated with Alzheimer's disease disrupt receptor signaling functions.

Missense mutations in the EPHA1 receptor tyrosine kinase have been identified in Alzheimer's patients. To gain insight into their potential role in disease pathogenesis, we investigated the effects of four of these mutations. We show that the P460L mutation in the second fibronectin type III (FN2) domain drastically reduces EPHA1 cell surface localization while increasing tyrosine phosphorylation of the cell surface-localized receptor. The R791H mutation in the kinase domain abolishes EPHA1 tyrosine phosphorylation, indicating abrogation of kinase-dependent signaling. Furthermore, both mutations decrease EPHA1 phosphorylation on S906 in the kinase-SAM linker region, suggesting impairment of a noncanonical form of signaling regulated by serine/threonine kinases. The R492Q mutation, also in the FN2 domain, has milder effects than the P460L mutation while the R926C mutation in the SAM domain increases S906 phosphorylation. We also found that EPHA1 undergoes constitutive proteolytic cleavage in the FN2 domain, generating a soluble 55kDaN-terminal fragment containing the ligand-binding domain and a transmembrane 60kDaC-terminal fragment. The 60kDa WT fragment is phosphorylated on both tyrosine residues and S906, suggesting signaling functions. The P460L mutant 60kDa fragment undergoes proteasomal degradation and the R791H mutant fragment lacks tyrosine phosphorylation and has decreased S906 phosphorylation. These findings advance our understanding of EPHA1 signaling mechanisms and support the notion that alterations in EPHA1 signaling due to missense mutations contribute to Alzheimer's disease pathogenesis.

Achondroplasia: aligning mouse model with human clinical studies shows crucial importance of immediate postnatal start of the therapy.

Achondroplasia is the most common form of human dwarfism caused by mutations in the FGFR3 receptor tyrosine kinase. Current therapy begins at 2 years of age and improves longitudinal growth but does not address the cranial malformations including midface hypoplasia and foramen magnum stenosis, which lead to significant otolaryngeal and neurologic compromise. A recent clinical trial found partial restoration of cranial defects with therapy starting at 3months of age, but results are still inconclusive. The benefits of achondroplasia therapy are therefore controversial, increasing skepticism among the medical community and patients. We used a mouse model of achondroplasia to test treatment protocols aligned with human studies. Early postnatal treatment (from day 1) was compared with late postnatal treatment (from day 4, equivalent to ~5months in humans). Animals were treated with the FGFR3 inhibitor infigratinib and the effect on skeleton was thoroughly examined. We show that premature fusion of the skull base synchondroses occurs immediately after birth and leads to defective cranial development and foramen magnum stenosis in the mouse model to achondroplasia. This phenotype appears significantly restored by early infigratinib administration when compared with late treatment, which provides weak to no rescue. In contrast, the long bone growth is similarly improved by both early and late protocols. We provide clear evidence that immediate postnatal therapy is critical for normalization of skeletal growth in both the cranial base and long bones and the prevention of sequelae associated with achondroplasia. We also describe the limitations of early postnatal therapy, providing a paradigm-shifting argument for the development of prenatal therapy for achondroplasia.

Evaluation of the efficacy of PD‑1/PD‑L1 inhibitor plus bevacizumab and chemotherapy for the treatment of patients with driver gene‑negative advanced‑stage lung adenocarcinoma: A retrospective cohort study.

Driver gene-negative advanced-stage lung adenocarcinoma is associated with a poor prognosis and insufficient treatment options. The present study aimed to evaluate the efficacy and safety profile of a programmed cell death protein 1/programmed death-ligand 1 inhibitor plus bevacizumab and chemotherapy (PBC) regimen for the treatment of patients with driver gene-negative advanced-stage lung adenocarcinoma under real-world clinical conditions. Data from 65 patients with advanced-stage lung adenocarcinoma without sensitizing epidermal growth factor receptor, ALK receptor tyrosine kinase or ROS proto-oncogene 1 receptor tyrosine kinase mutations who received a PBC regimen or only a BC regimen were reviewed in the present retrospective cohort study. The results revealed that the objective response rate was higher (70.4 vs. 47.4%; P=0.065) in the PBC group compared with that in the BC group, while not reaching statistical significance. Progression-free survival (PFS) time was longer in the PBC group than in the BC group [median PFS: 10.8 months (95% confidence interval (CI), 7.2-14.4) vs. 7.6 months (95% CI, 5.0-10.2); P=0.016], while overall survival (OS) exhibited a non-significant trend to be longer in the PBC group compared with that in the BC group [median OS: 20.6 months (95% CI, 16.8-24.4) vs. 15.9 months (95% CI, 11.8-20.0); P=0.115]. Following adjustment by multivariate Cox analysis, the PBC (vs. BC) regimen was found to be independently associated with an improved PFS time (P=0.045). The common adverse events in the PBC group were neutropenia, alopecia, leukopenia, nausea and vomiting, fatigue, anemia and peripheral neuropathy. Moreover, the incidence of each adverse event did not differ significantly between the PBC and BC groups. In conclusion, the present study demonstrated that the PBC regimen serves as a superior treatment option for patients with driver gene-negative advanced-stage lung adenocarcinoma; however, further verification of its efficacy is still required.

Could Somatic Gene Rescue Explain Frequency of Compound Heterozygous and Concurrent Receptor Tyrosine Kinase Mutations in Hematological Diseases?

Could Somatic Gene Rescue Explain Frequency of Compound Heterozygous and Concurrent Receptor Tyrosine Kinase Mutations in Hematological Diseases?

Distinct phenotypic consequences of cholangiocarcinoma-associated FGFR2 alterations depend on biliary epithelial maturity.

Epithelial cancers disrupt tissue architecture and are often driven by mutations in genes that normally play important roles in epithelial morphogenesis. The intrahepatic biliary system is an epithelial tubular network that forms within the developing liver via the de novo initiation and expansion of apical lumens. Intrahepatic biliary tumors are often driven by different types of mutations in the FGFR2 receptor tyrosine kinase which plays important roles in epithelial morphogenesis in other developmental settings. Using a physiologic and quantitative 3D model we have found that FGFR signaling is important for biliary morphogenesis and that oncogenic FGFR2 mutants disrupt biliary architecture. Importantly, we found that both the trafficking and signaling of normal FGFR2 and the phenotypic consequences of FGFR2 mutants are influenced by the epithelial state of the cell. Unexpectedly, we found that different tumor-driving FGFR2 mutants disrupt biliary morphogenesis in completely different and clinically relevant ways, informing our understanding of morphogenesis and tumorigenesis and highlighting the importance of convergent studies of both.

Discovery of NFκB2-Coordinated Dual Regulation of Mitochondrial and Nuclear Genomes Leads to an Effective Therapy for Acute Myeloid Leukemia.

Acute myeloid leukemia (AML) has a poor survival rate for both pediatric and adult patients due to its frequent relapse. To elucidate the bioenergetic principle underlying AML relapse, we investigated the transcriptional regulation of mitochondrial-nuclear dual genomes responsible for metabolic plasticity in treatment-resistant blasts. Both the gain and loss of function results demonstrated that NFκB2, a noncanonical transcription factor (TF) of the NFκB (nuclear factor kappa-light-chain-enhancer of activated B cells) family, can control the expression of TFAM (mitochondrial transcription factor A), which is known to be essential for metabolic biogenesis. Furthermore, genetic tracking and promoter assays revealed that NFκB2 is in the mitochondria and can bind the specific "TTGGGGGGTG" region of the regulatory D-loop domain to activate the light-strand promoter (LSP) and heavy-strand promoter 1 (HSP1), promoters of the mitochondrial genome. Based on our discovery of NFκB2's novel function of regulating mitochondrial-nuclear dual genomes, we explored a novel triplet therapy including inhibitors of NFκB2, tyrosine kinase, and mitochondrial ATP synthase that effectively eliminated primary AML blasts with mutations of the FMS-related receptor tyrosine kinase 3 (FLT3) and displayed minimum toxicity to control cells ex vivo. As such, effective treatments for AML must include strong inhibitory actions on the dual genomes mediating metabolic plasticity to improve leukemia prognosis.

Functional Investigation of IGF1R Mutations in Multiple Myeloma.

High expression of the receptor tyrosine kinase (RTK) insulin-like growth factor-1 receptor (IGF1R) and RTK mutations are associated with high-risk/worse prognosis in multiple myeloma (MM). Combining the pIGF1R/pINSR inhibitor linsitinib with the proteasome inhibitor (PI) bortezomib seemed promising in a clinical trial, but IGF1R expression was not associated with therapy response. Because the oncogenic impact of IGF1R mutations is so far unknown, we investigated the functional impact of IGF1R mutations on survival signaling, viability/proliferation and survival response to therapy. We transfected four human myeloma cell lines (HMCLs) with IGF1RWT, IGF1RD1146N and IGF1RN1129S (Sleeping Beauty), generated CRISPR-Cas9 IGF1R knockouts in the HMCLs U-266 (IGF1RWT) and L-363 (IGF1RD1146N) and tested the anti-MM activity of linsitinib alone and in combination with the second-generation PI carfilzomib in seven HMCLs. IGF1R knockout entailed reduced proliferation. Upon IGF1R overexpression, survival signaling was moderately increased in all HCMLs and slightly affected by IGF1RN1129S in one HMCL, whereby the viability remained unaffected. Expression of IGF1RD1146N reduced pIGF1R-Y1135, especially under serum reduction, but did not impact downstream signaling. Linsitinib and carfilzomib showed enhanced anti-myeloma activity in six out of seven HMCL irrespective of the IGF1R mutation status. In conclusion, IGF1R mutations can impact IGF1R activation and/or downstream signaling, and a combination of linsitinib with carfilzomib might be a suitable therapeutic approach for MM patients potentially responsive to IGF1R blockade.

Loss-of-function mutations of the TIE1 receptor tyrosine kinase cause late-onset primary lymphedema.

Primary lymphedema (PL), characterized by tissue swelling, fat accumulation, and fibrosis, results from defects in lymphatic vessels or valves caused by mutations in genes involved in development, maturation, and function of the lymphatic vascular system. Pathogenic variants in various genes have been identified in about 30% of PL cases. By screening of a cohort of 755 individuals with PL, we identified two TIE1 (tyrosine kinase with immunoglobulin- and epidermal growth factor-like domains 1) missense variants and one truncating variant, all predicted to be pathogenic by bioinformatic algorithms. The TIE1 receptor, in complex with TIE2, binds angiopoietins to regulate the formation and remodeling of blood and lymphatic vessels. The premature stop codon mutant encoded an inactive truncated extracellular TIE1 fragment with decreased mRNA stability, and the amino acid substitutions led to decreased TIE1 signaling activity. By reproducing the two missense variants in mouse Tie1 via CRISPR/Cas9, we showed that both cause edema and are lethal in homozygous mice. Thus, our results indicate that TIE1 loss-of-function variants can cause lymphatic dysfunction in patients. Together with our earlier demonstration that ANGPT2 loss-of-function mutations can also cause PL, our results emphasize the important role of the ANGPT2/TIE1 pathway in lymphatic function.

Brefeldin A and M-COPA block the export of RTKs from the endoplasmic reticulum via simultaneous inactivation of ARF1, ARF4, and ARF5

Normal receptor tyrosine kinases (RTKs) need to reach the plasma membrane (PM) for ligand-induced activation, whereas its cancer-causing mutants can be activated before reaching the PM in organelles, such as the Golgi/trans-Golgi network (TGN). Inhibitors of protein export from the endoplasmic reticulum (ER), such as brefeldin A (BFA) and 2-methylcoprophilinamide (M-COPA), can suppress the activation of mutant RTKs in cancer cells, suggesting that RTK mutants cannot initiate signaling in the ER. BFA and M-COPA block the function of ADP-ribosylation factors (ARFs) that play a crucial role in ER–Golgi protein trafficking. However, among ARF family proteins, the specific ARFs inhibited by BFA or M-COPA, that is, the ARFs involved in RTKs transport from the ER, remain unclear. In this study, we showed that M-COPA blocked the export of not only KIT but also PDGFRA/EGFR/MET RTKs from the ER. ER-retained RTKs could not fully transduce anti-apoptotic signals, thereby leading to cancer cell apoptosis. Moreover, single knockdown of ARF1, ARF3, ARF4, ARF5, or ARF6 could not block ER export of RTKs, indicating that BFA/M-COPA treatment cannot be mimicked by knockdown of only one ARF member. Interestingly, simultaneous transfection of ARF1, ARF4, and ARF5 siRNAs mirrored the effect of BFA/M-COPA treatment. Consistent with these results, in vitro pulldown assays showed that BFA/M-COPA blocked the function of ARF1, ARF4, and ARF5. Taken together, these results suggest that BFA/M-COPA targets at least ARF1, ARF4, and ARF5; in other words, RTKs require the simultaneous activation of ARF1, ARF4, and ARF5 for their ER export.

RAF and MEK Inhibitors in Non-Small Cell Lung Cancer.

Lung cancer, despite recent advancements in survival rates, represents a significant global health burden. Non-small cell lung cancer (NSCLC), the most prevalent type, is driven largely by activating mutations in Kirsten rat sarcoma viral oncogene homologue (KRAS) and receptor tyrosine kinases (RTKs), and less in v-RAF murine sarcoma viral oncogene homolog B (BRAF) and mitogen-activated protein-kinase kinase (MEK), all key components of the RTK-RAS-mitogen-activated protein kinase (MAPK) pathway. Learning from melanoma, the identification of BRAFV600E substitution in NSCLC provided the rationale for the investigation of RAF and MEK inhibition as a therapeutic strategy. The regulatory approval of two RAF-MEK inhibitor combinations, dabrafenib-trametinib, in 2017, and encorafenib-binimetinib, in 2023, signifies a breakthrough for the management of BRAFV600E-mutant NSCLC patients. However, the almost universal emergence of acquired resistance limits their clinical benefit. New RAF and MEK inhibitors, with distinct biochemical characteristics, are in preclinical and clinical development. In this review, we aim to provide valuable insights into the current state of RAF and MEK inhibition in the management of NSCLC, fostering a deeper understanding of the potential impact on patient outcomes.

Abstract 5949: The clinical dual KRASG12C inhibitor FMC-376 has demonstrated potential as both a monotherapy and in combination for the treatment of patients with KRASG12C mutation positive NSCLC

Abstract KRAS, a membrane-associated guanosine triphosphatase (GTPase), is the most frequently mutated oncogene in cancer with activating mutations occurring in approximately 25% of NSCLC. Of these, KRASG12C occurs in approximately 14% of adenocarcinomas and in 0.5 to 4% of squamous NSCLCs. This mutation impairs GTPase activity and GTP-hydrolysis leading to an increase in the active, GTP-bound (ON), state. KRAS was long considered undruggable until the recent discovery of inhibitors that bind the GDP-bound, inactive (OFF) state of KRASG12C. The most clinically advanced of these first-generation molecules have demonstrated clinical response rates of 37-43% and 6 to 7-month progression-free survival in patients with KRASG12C positive NSCLC. While significant, a majority of cancers do not respond, and acquired resistance is common. FMC-376 is a next-generation dual inhibitor of both the ON and OFF states of KRASG12Cwith the potential to deliver improved outcomes as both a monotherapy and in combination, for patients with KRASG12C positive NSCLC. FMC-376 was discovered through the FrontierTM platform, which integrates chemoproteomics, machine-learning, and covalent fragment-based drug discovery. The potential for FMC-376 in the treatment of patients with KRASG12C mutant NSCLC has been assessed in a broad panel of NSCLC PDX models representing settings of sotorasib/adagrasib resistance, in a model of NSCLC CNS-metastasis and in combination with an immune checkpoint inhibitor. The dual ON + OFF state mechanism of action of FMC-376 is highly active across a panel of NSCLC CDX and PDX models, including those that carry co-mutations that are associated with both primary and acquired resistance to the OFF-state inhibitors adagrasib and sotorasib in NSCLC. These drivers of resistance include activating mutations of receptor tyrosine kinases (e.g. EGFR, MET, etc.), co-mutations including KEAP1 and adaptive resistance due to release of negative feedback control. Evaluation of FMC-376 in models where EGFR signaling is induced by EGF demonstrated rapid and durable target engagement in contrast to both sotorasib and adagrasib which show decreased effectiveness after EGF stimulation. As a result, FMC-376 is highly effective in NSCLC PDX models that have EGFR and MET upregulation. In addition, 27-42% of patients with KRASG12C positive NSCLC present with CNS metastasis. FMC-376 is highly active in an intracranial NSCLC model of CNS-metastasis, resulting in tumor regression. Furthermore, FMC-376 has demonstrated activity in combination with an anti-PD-1 mAb in a KRASG12C mutant mouse syngeneic tumor model. Together, these data demonstrate the potential of FMC-376, a next-generation clinical stage dual inhibitor of ON and OFF state KRASG12C, for the treatment of patients with KRASG12C mutant NSCLC as well as other KRASG12C positive tumors. Citation Format: Yan Wang, Allison Roberts, Philamer Calses, Richard M. Neve, Jocelyn Staunton, Kevin R. Webster. The clinical dual KRASG12C inhibitor FMC-376 has demonstrated potential as both a monotherapy and in combination for the treatment of patients with KRASG12C mutation positive NSCLC [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 5949.

Abstract 2001: Autocrine HGF maturation as a targetable regulatory step in cetuximab resistance in colorectal cancer

Abstract Although amplifications and mutations in receptor tyrosine kinases (RTKs) act as bona fide oncogenes, in most cancers, RTKs maintain moderate expression and remain wild-type. Consequently, cognate ligands control many facets of tumorigenesis, including resistance to anti-RTK therapies. Herein, we show that the ligands for the RTKs MET and RON, HGF and HGFL, respectively, are synthesized as inactive precursors that are activated by cellular proteases. Our newly generated HGF/HGFL protease inhibitors could overcome both de novo and acquired cetuximab resistance in colorectal cancer (CRC). Conversely, HGF overexpression was necessary and sufficient to induce cetuximab resistance and loss of polarity. Moreover, HGF-induced cetuximab resistance could be overcome by the downstream MET inhibitor, crizotinib, and upstream protease inhibitors. Additionally, HAI-1, an endogenous inhibitor of HGF proteases, (i) was downregulated in CRC, (ii) exhibited increased genomic methylation that correlated with poor prognosis, (iii) HAI-1 expression correlated with cetuximab response in a panel of cancer cell lines, and (iv) exogenous addition of recombinant HAI-1 overcame cetuximab resistance in CC-HGF cells. Thus, we describe a targetable, autocrine HAI-1/Protease/HGF/MET axis in cetuximab resistance in CRC. Citation Format: Vivian Truong Jones, Ramona Graves-Deal, Zheng Cao, Galina Bogatcheva, Marisol A. Ramirez, Sarah J. Harmych, James N. Higginbotham, Claudia C. Wahoski, Neeraj Joshi, Joseph T. Roland, Gregory D. Ayers, Qi Liu, Robert J. Coffey, James W. Janetka, Bhuminder Singh. Autocrine HGF maturation as a targetable regulatory step in cetuximab resistance in colorectal cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 2001.

EGFR signaling and pharmacology in oncology revealed with innovative BRET-based biosensors

Mutations of receptor tyrosine kinases (RTKs) are associated with the development of many cancers by modifying receptor signaling and contributing to drug resistance in clinical settings. We present enhanced bystander bioluminescence resonance energy transfer-based biosensors providing new insights into RTK biology and pharmacology critical for the development of more effective RTK-targeting drugs. Distinct SH2-specific effector biosensors allow for real-time and spatiotemporal monitoring of signal transduction pathways engaged upon RTK activation. Using EGFR as a model, we demonstrate the capacity of these biosensors to differentiate unique signaling signatures, with EGF and Epiregulin ligands displaying differences in efficacy, potency, and responses within different cellular compartments. We further demonstrate that EGFR single point mutations found in Glioblastoma or non-small cell lung cancer, impact the constitutive activity of EGFR and response to tyrosine kinase inhibitor. The BRET-based biosensors are compatible with microscopy, and more importantly characterize the next generation of therapeutics directed against RTKs.

Inhibition of autocrine HGF maturation overcomes cetuximab resistance in colorectal cancer

Although amplifications and mutations in receptor tyrosine kinases (RTKs) act as bona fide oncogenes, in most cancers, RTKs maintain moderate expression and remain wild-type. Consequently, cognate ligands control many facets of tumorigenesis, including resistance to anti-RTK therapies. Herein, we show that the ligands for the RTKs MET and RON, HGF and HGFL, respectively, are synthesized as inactive precursors that are activated by cellular proteases. Our newly generated HGF/HGFL protease inhibitors could overcome both de novo and acquired cetuximab resistance in colorectal cancer (CRC). Conversely, HGF overexpression was necessary and sufficient to induce cetuximab resistance and loss of polarity. Moreover, HGF-induced cetuximab resistance could be overcome by the downstream MET inhibitor, crizotinib, and upstream protease inhibitors. Additionally, HAI-1, an endogenous inhibitor of HGF proteases, (i) was downregulated in CRC, (ii) exhibited increased genomic methylation that correlated with poor prognosis, (iii) HAI-1 expression correlated with cetuximab response in a panel of cancer cell lines, and (iv) exogenous addition of recombinant HAI-1 overcame cetuximab resistance in CC-HGF cells. Thus, we describe a targetable, autocrine HAI-1/Protease/HGF/MET axis in cetuximab resistance in CRC.

NTRK2 expression in gastrointestinal stromal tumors with a special emphasis on the clinicopathological and prognostic impacts

Gastrointestinal stromal tumors (GISTs) are typically characterized by activating mutations of the KIT proto-oncogene receptor tyrosine kinase (KIT) or platelet-derived growth factor receptor alpha (PDGFRA). Recently, the neurotrophic tyrosine receptor kinase (NTRK) fusion was reported in a small subset of wild-type GIST. We examined trk IHC and NTRK gene expressions in GIST. Pan-trk immunohistochemistry (IHC) was positive in 25 (all 16 duodenal and 9 out of 16 small intestinal GISTs) of 139 cases, and all pan-trk positive cases showed diffuse and strong expression of c-kit. Interestingly, all of these cases showed only trkB but not trkA/trkC expression. Cap analysis of gene expression (CAGE) analysis identified increased number of genes whose promoters were activated in pan-trk/trkB positive GISTs. Imbalanced expression of NTRK2, which suggests the presence of NTRK2 fusion, was not observed in any of trkB positive GISTs, despite higher mRNA expression. TrkB expression was found in duodenal GISTs and more than half of small intestinal GISTs, and this subset of cases showed poor prognosis. However, there was not clear difference in clinical outcomes according to the trkB expression status in small intestinal GISTs. These findings may provide a possible hypothesis for trkB overexpression contributing to the tumorigenesis and aggressive clinical outcome in GISTs of duodenal origin.

Pan-Canadian consensus recommendations for GIST management in high- and low-throughput centres across Canada.

Gastrointestinal stromal tumours (GISTs) are mesenchymal tumours that originate from the interstitial cells of Cajal. GISTs are mainly driven by gain-of-function mutations in receptor tyrosine kinase or platelet-derived growth factor receptor alpha. Surgical resection is the only curative treatment for localized tumours and all currently approved medical GIST treatments are based on orally available tyrosine kinase inhibitors. Recent discoveries in the molecular and clinical features of GISTs have greatly impacted GIST management. Due to the provincially rather than nationally administered Canadian healthcare system, there have been inconsistencies in the treatment of GISTs across the country. Therefore, guidance on the latest knowledge, clinical management and treatment of GIST is needed to standardize the approach to GIST management nationwide. To establish pan-Canadian guidance, provide up-to-date data and harmonize the clinical practice of GIST management in high- and low-throughput centres across Canada; a panel of 20 physicians with extensive clinical experience in GIST management reviewed relevant literature. This included radiologists, pathologists, interventional radiologists, surgeons and medical oncologists across Canada. The structured literature focused on seven key domains: molecular profiling, radiological techniques/reporting, targeted localized therapy, intricacies of systemic treatments, emerging tests, multidisciplinary care and patient advocacy. This literature review, along with clinical expertise and opinion, was used to develop this concise and clinically relevant consensus paper to harmonize the knowledge and clinical practice on GIST management across Canada. The content presented here will help guide healthcare providers, especially in Canada, in terms of approaching and managing GIST.

Abstract C010: A comprehensive predictive biomarker analysis for MEK Inhibitors in Patient-derived Xenograft (PDX) models

Abstract Introduction: The RAS-RAF-MEK-ERK pathway has been extensively studied for its prominent role in cancer development. Activating mutations in receptor tyrosine kinases, RAS, or RAF, are commonly observed in cancer. Pathway activation caused by these mutations is mediated through MEK kinases, making MEK inhibition an attractive therapeutic strategy. Although several in vitro studies have been carried out to identify predictive biomarkers for sensitivity to MEK inhibition, the results have not been validated in vivo. Methods: Cryopreserved or fresh PDX tumor tissues (~2–3 mm in diameter) were transplanted into NOD/SCID or BALB/c nude mice subcutaneously. Trametinib was administered orally daily at 0.3mg - 1mg/kg of body weight, starting when tumor size reached 100-300 mm3. Sequencing reads were aligned to both human and mouse reference genomes. Based on which alignment yielded fewer mismatches, they were subsequently sorted into human or mouse groups, representing cancer and stromal transcriptomes, respectively. Ambiguous readings were discarded. Transcript abundance was quantified using the Kallisto software tool. Nucleotide variants in human genes were detected using the GATK best practice workflow. Results: We systematically analyzed tumor growth data collected from 62 PDX models in 9 cancer types (colorectal, head and neck, esophageal, kidney, melanoma, lung, gastric, ovarian, and pancreatic) treated with Trametinib, an allosteric MEK1/2 inhibitor. The responses to Trametinib were classified into 3 categories based on the amount of tumor growth inhibition (TGI) achieved. About 20% of these models were sensitive to Trametinib treatment (TGI > 70% compared to vehicle), 35% were resistant (TGI ≤ 30% compared to vehicle), and the remaining showed a partial response (30% < TGI ≤ 70% compared to vehicle). Cross-group comparisons of PDX transcriptomic and mutation profiles allowed identification of novel biomarkers as well as validation of biomarkers previously reported in in vitro studies. Conclusions: The different sensitivity to MEK inhibition observed in PDX models mirrors the patient heterogeneity observed in clinic. Thus, our results highlight the need to identify the appropriate genetic background using predictive biomarkers when applying targeted therapies. Citation Format: Yanghui Sheng, Wubin Qian, Jingjing Wang, Sheng Guo. A comprehensive predictive biomarker analysis for MEK Inhibitors in Patient-derived Xenograft (PDX) models [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2023 Oct 11-15; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2023;22(12 Suppl):Abstract nr C010.

Transient TKI-resistant CD44+pBAD+ blasts undergo intrinsic homeostatic adaptation to promote the survival of acute myeloid leukemia in vitro.

Acute myeloid leukemia (AML) patients have frequent mutations in FMS-like receptor tyrosine kinase 3 (FLT3-mut AML), who respond poorly to salvage chemotherapies and targeted therapies such as tyrosine kinase inhibitors (TKIs). Disease relapse is a common reason of treatment failures in FLT3-mut AML patients, but its intracellular refractory mechanism remains to be discovered. In this study, we designed serial in vitro time-course studies to investigate the biomarkers of TKI-resistant blasts and their survival mechanism. First, we found that a group of transient TKI-resistant blasts were CD44+Phosphorylated-BAD (pBAD)+ and that they could initiate the regrowth of blast clusters in vitro. Notably, TKI-treatments upregulated the compensation pathways to promote PIM2/3-mediated phosphorylation of BAD to initiate the blast survival. Next, we discovered a novel process of intracellular adaptive responses in these transient TKI-resistant blasts, including upregulated JAK/STAT signaling pathways for PIM2/3 expressions and activated SOCS1/SOCS3/PIAS2 inhibitory pathways to down-regulate redundant signal transduction and kinase phosphorylation to regain intracellular homeostasis. Finally, we found that the combination of TKIs with TYK2/STAT4 pathways-driven inhibitors could effectively treat FLT3-mut AML in vitro. In summary, our findings reveal that TKI-treatment can activate a JAK/STAT-PIM2/3 axis-mediated signaling pathways to promote the survival of CD44+pBAD+blasts in vitro. Disrupting these TKIs-activated redundant pathways and blast homeostasis could be a novel therapeutic strategy to treat FLT3-mut AML and prevent disease relapse in vivo.

Novel Mechanisms of Venetoclax Resistance in Acute Myeloid Leukemia Based on Genomic Rearrangements

Novel Mechanisms of Venetoclax Resistance in Acute Myeloid Leukemia Based on Genomic Rearrangements