AXL Activation Research Articles

Pharmacological profiling identifies divergent chemosensitivities of differentiating and maturing iPSC-derived human cortical neuron populations.

Neuronal differentiation and maturation are extended developmental processes. To determine whether neurons at different developmental stages have divergent chemosensitivities, we screened differentiating and maturing neuronal populations using a small compound library comprising FDA-approved and investigational drugs. Using a neurotoxicity assay format, both respective neuronal population-based screening campaigns performed robustly (Z-factors = 0.7-0.8), although the hit rate for the differentiating neurons (2.8%) was slightly higher than for maturing neurons (1.9%). While the majority of hits were toxic to both neuronal populations, these hits predominantly represented promiscuous drugs. Other drugs were selectively neurotoxic, with receptor tyrosine kinase inhibitors disproportionally represented after confirmation. Ponatinib and amuvatinib were neuroinhibitory for differentiating and maturing neurons, respectively. Chemoinformatic analyses confirmed differences in potential drug targets that may be differentially expressed during neuronal development. Subsequent studies demonstrated neuronal expression of AXL, an amuvatinib target, in both neuronal populations. However, functional AXL activity was confirmed only in the maturing neuronal population as determined by AXL phosphorylation in response to GAS6, the cognate ligand of AXL, and concurrent STAT3Y705 phosphorylation. Differentiating neurons were unresponsive to the effects of GAS6 suggesting that the AXL-STAT3 signaling axis was nonfunctional. Amuvatinib treatment of maturing neuronal cultures significantly reduced pAXL levels. These studies indicate that neuronal developmental states may exhibit unique chemosensitivities and that drugs may have different neuro-inhibitory effects depending upon the developmental stage of the neuronal population.

Inhibition of a new AXL isoform, AXL3, induces apoptosis of mantle cell lymphoma cells

AbstractMantle cell lymphoma (MCL) is an aggressive B-cell non-Hodgkin lymphoma having a poor overall survival that is in need for the development of new therapeutics. In this study, we report the identification and expression of a new isoform splice variant of the tyrosine kinase receptor AXL in MCL cells. This new AXL isoform, called AXL3, lacks the ligand-binding domain of the commonly described AXL splice variants and is constitutively activated in MCL cells. Interestingly, functional characterization of AXL3, using CRISPR inhibition, revealed that only the knock down of this isoform leads to apoptosis of MCL cells. Importantly, pharmacological inhibition of AXL activity resulted in a significant decrease in the activation of well-known proproliferative and survival pathways activated in MCL cells (ie, β-catenin, Ak strain transforming, and NF-κB). Therapeutically, preclinical studies using a xenograft mouse model of MCL indicated that bemcentinib is more effective than ibrutinib in reducing the tumor burden and to increase the overall survival. Our study highlights the importance of a previously unidentified AXL splice variant in cancer and the potential of bemcentinib as a targeted therapy for MCL.

In Vitro and Reactive Metabolites Investigation of Metabolic Profiling of Tyrosine Kinase Inhibitors Dubermatinib in HLMs by LC–MS/MS

Dubermatinib (DMB, TP-0903), a benzenesulfonamide, is an inhibitor of the tyrosine kinase AXL, which is a member of the TAM family and can prevent GAS6-mediated activation of AXL in cancer cells. Patients with previously treated chronic lymphocytic leukemia are being studied in phase I/II clinical trials to determine its antineoplastic potential (CLL). In the current work, the Xenosite web predictor tool was employed to predict the vulnerable sites of metabolism and the reactivity pathways (cyanide and GSH) of DMB. Subsequently, we present the analysis and identification of in vitro and reactive intermediates of DMB using liquid chromatography ion trap mass spectrometry (LC–ITMS). Human liver microsomes (HLMs) were exposed to dimethylbenzene in a laboratory setting, and the resulting metabolites were collected through protein precipitation. Intense reactivity toward nucleophilic macromolecules was seen in the metabolites of the piperazine and pyrimidine rings in DMB, iminium, and 2,5-quinone-imine, respectively. To assess the toxicities of the possibly reactive metabolites, DMB was incubated with HLMs in the presence of 1.0 mM KCN and 1.0 mM glutathione. The DMB metabolites found by LC–MS/MS were seven in vitro phase I metabolites, three cyano adducts, and two GSH conjugates. Phase I in vitro metabolic reactions included N-demethylation, hydroxylation, and dechlorination. DMB and its metabolites have not been investigated for their metabolism in vitro.

AX-0085, a novel AXL kinase inhibitor, and effects on osimertinib-resistance in non–small-cell lung cancer.

e15121 Background: Osimertinib is a third-generation epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor (TKI) having high efficacy in treating patients with advanced non-small cell lung cancer (NSCLC) with EGFR activating mutations and EGFR T70M mutations. Although, osimertinib is a frontline anticancer agent for treating NSCLC, many patients inevitably develop osimertinib-resistance tumor recurrence. The activation of AXL was reported to be a major factor driving osimertinib-resistance in NSCLC. Thus, AXL is a promising therapeutic target for the treatment of osimertinib-resistant NSCLC, and we developed a new small-molecule AXL inhibitor, AX-0085. Methods: We established osimertinib-resistant cell lines from EGFR-mutated NSCLC cell lines, HCC827 and H1975, after high dose exposure and stepwise exposure to osimertinib in culture. We investigated the cell viability of AX-0085 and other kinase inhibitors, and the anti-tumor activity of AX-0085 on the proliferation, migration, apoptosis, and epithelial-mesenchymal transition (EMT) in osimertinib-resistant cells. Results: Compared to the parental cells, IC50 of resistant cell to osimertinib was significantly increased and osimertinib-resistant cells showed remarkably increased expression of AXL/pAXL and p-SRC as compared to the parental HCC827 cell. AX-0085 was completely blocked the AXL and SRC activation but EGFR inhibitors (gefitinib and osimertinib) did not inhibit the activation of AXL and SRC in the osimertinib-resistant cell line. AX-0085 (IC50: 4.4nM for AXL kinase in cell-based kinase assay) was one of the most potent AXL inhibitors and showed the strongest cytotoxicity against osimertinib-resistant cells compared to other kinase inhibitors. AX-0085 effectively down-regulated mRNA level of AXL and AXL regulating transcription factors in NSCLC cell lines such as HCC827 and H1975. AX-0085 treatment effectively inhibited the activation of AXL in acquired osimertinib-resistant cells and decreased the mRNA level of AXL and AXL regulating transcription factors. AX-0085 significantly inhibited the cell proliferation, apoptosis, migration, and EMT in acquired osimertinib-resistant cells. Conclusions: Our results showed that AX-0085 selectively inhibits the activation of AXL to overcome acquired resistance to osimertinib, suggesting an effective AXL-based therapy for patients with osimertinib-resistant tumors. Currently, AX-0085 is undergoing non-clinical trials.

A phase 1 study of concurrent cabozantinib and cetuximab in recurrent or metastatic head and neck squamous cell cancer.

6025 Background: Epidermal growth factor receptor (EGFR) targeting with cetuximab (CTX) is a standard therapy for head and neck squamous cell carcinoma (HNSCC). Resistance to CTX can be mediated by activation of the receptor tyrosine kinase AXL. Cabozantinib (cabo) is a tyrosine kinase inhibitor (TKI) of AXL/c-MET/VEGFR which demonstrated antitumor activity in HNSCC preclinical models. We conducted a phase I trial to assess the safety and efficacy of the cabo-CTX combination in recurrent or metastatic (R/M) HNSCC. Methods: Eligibility criteria included RECIST v1.1 measurable disease and incurable R/M HNSCC. Prior treatment with CTX was allowed. Patients received an initial CTX loading dose of 400 mg/m2 followed by 250 mg/m2 weekly. CTX maintenance dose was later amended to 500 mg/m2 biweekly. Cabo was given concurrently on days 1-28 of each 28-day cycle. Primary endpoint was maximally tolerated dose (MTD) of cabo, as identified using a 3+3 dose-escalation design. Tumor responses were assessed every 2 cycles. Secondary endpoints included overall response rate (ORR), progression-free survival (PFS) and overall survival (OS). Results: Of 22 patients enrolled between 2018 and 2022, 2 did not start therapy. Among treated patients, median age was 59 (range 33-71) and 90% (n = 18) of patients were male. Primary tumor sites included the oropharynx (n = 13), oral cavity (n = 3), larynx (n = 2), hypopharynx (n = 1) and unknown primary (n = 1). p16 antigenic testing for HPV status was positive in 11 oropharyngeal cancers (85%). Most patients were previously treated with immune checkpoint inhibitors (n = 19), chemotherapy (n = 19), CTX (n = 16), or other TKI (n = 2). 12 patients received biweekly CTX dosing at 500 mg/m2. Initial cabo dose was 40 mg for the first 11 patients, and 60 mg afterwards (MTD). No dose-limiting toxicity (DLT) was recorded. Common adverse events (AEs) included fatigue (80%), acneiform rash (75%), increased aspartate aminotransferase (AST) (70%), anemia (70%) and hypothyroidism (70%). Grade ≥3 AEs occurred in 65% (n = 13), including increased AST (45%), increased alkaline phosphatase (15%), increased bilirubin (10%) and erythrodysesthesia (10%). AEs led to dose reductions in 20% (n = 4) and treatment discontinuation in 15% (n = 3). In the preliminary efficacy analysis, 4 patients had partial responses (PRs) with an ORR of 20%, including 2 PRs in patients with prior CTX resistance. Disease control rate (DCR) was 75% in the overall population and 75% in those with previous CTX treatment. Median PFS was 3.4 mo and median OS was 8.1 mo. PFS differed according to HPV status, with median PFS 7.1 mo versus 3.1 mo in HPV-positive and -negative patients respectively (p = 0.03). Conclusions: The cabo and CTX combination showed an acceptable toxicity profile with liver toxicity as a common AE. The regimen showed preliminary efficacy data in patients with R/M HNSCC, including those with prior CTX resistance. Clinical trial information: NCT03667482 .

Antitumor activity of AX-0085, a novel AXL kinase inhibitor: Analysis of apoptotic cell death in triple-negative breast cancer cells.

e15120 Background: Triple-negative breast cancer (TNBC) is insensitive to targeted therapies due to the negative expression of human epidermal growth factor receptor-2, estrogen receptor and progesterone receptor. TNBC cells express higher levels of AXL more often than other breast cancer subtypes. The receptor tyrosine kinase AXL plays a role in survival, invasion, migration, epithelial-mesenchymal transition (EMT), metastasis, resistance, and immune suppression in cancer cells including in TNBC. Thus, AXL is a promising therapeutic target for the treatment of TNBC, and we developed a new small-molecule AXL inhibitor, AX-0085. Methods: The interaction mechanism between AX-0085 and AXL was studied by molecular dynamic simulations, cell-based kinase assay, and western blotting in TNBC cells. We investigated the anti-tumor activity of AX-0085 on the AXL-dependent pro-tumorigenic properties such as cell proliferation, invasion, migration, EMT, and immune suppression (PD-L1 expression) in TNBC cell lines and investigated in vivo efficacy of AX-0085 with the 4T1 xenograft model. Results: In the molecular dynamic simulations, estimated binding energy of AX-0085 and cabozantinib to AXL was -10.1Kcal/mol and -8.1Kcal/mol, respectively. AX-0085 was made a hydrogen bond with catalytically important residue Lys567 and blocked the activation of AXL by inhibiting the salt bridge with Lys567-Glu585. AX-0085 (IC50: 4.4nM for AXL kinase in cell-based kinase assay) was one of the most potent AXL inhibitors. AX-0085 showed a high antitumor activity against all TNBC subtypes and was a more potent anti-proliferative activity than other kinase inhibitors in MDA-MB-231 cell line. AX-0085 effectively blocked the activation of AXL in TNBC and further inhibited AXL-dependent pro-tumorigenic events such as cell proliferation, invasion, migration, EMT, and PD-L1 expression in TNBC cell. AX-0085 induced cell cycle arrest at G1 phase and suppressed the expression of CDK2 and Cyclin E in TNBC. AX-0085 promoted apoptotic cell death by up-regulating cleaved caspase-9 and down-regulating Bcl-2 in TNBC. Pharmacological investigation showed that the AX-0085 treated tumors displayed a dose-dependent reduction in volume and weight of the tumors in the 4T1 mouse xenograft. Conclusions: Our results demonstrated that AX-0085 selectively blocks AXL activation which confers an effective therapeutic value in the treatment of TNBC. Currently, AX-0085 is undergoing non-clinical trials.

Marsdenia tenacissima extract induces endoplasmic reticulum stress-associated immunogenic cell death in non-small cell lung cancer cells through targeting AXL

Ethnopharmacological relevanceMarsdenia Tenacissima (Roxb.) Wight et Arn. is a traditional Chinese medicine. Its standardized extract (MTE), with the trade name Xiao-Ai-Ping injection, is widely used for cancer treatment. The pharmacological effects of MTE-inducing cancer cell death have been primarily explored. However, whether MTE triggers tumor endoplasmic reticulum stress (ERS)-associated immunogenic cell death (ICD) is unknown. Aim of the studyTo determine the potential role of endoplasmic reticulum stress in the anti-cancer effects of MTE, and uncover the possible mechanisms of endoplasmic reticulum stress-associated immunogenic cell death induced by MTE. Material and methodsThe anti-tumor effects of MTE on non-small cell lung cancer (NSCLC) were examined through CCK-8 and wound healing assay. Network pharmacology analysis and RNA-sequencing (RNA seq) were performed to confirm the biological changes of NSCLCs after MTE treatment. Western blot, qRT-PCR, reactive oxygen species (ROS) assay, and mitochondrial membrane potential (MMP) assay were used to explore the occurrence of endoplasmic reticulum stress. Immunogenic cell death-related markers were tested by ELISA and ATP release assay. Salubrinal was used to inhibit the endoplasmic reticulum stress response. SiRNA and bemcentinib (R428) were used to impede the function of AXL. AXL phosphorylation was regained by recombinant human Gas6 protein (rhGas6). The effects of MTE on endoplasmic reticulum stress and immunogenic cell death response were also proved in vivo. The AXL inhibiting compound in MTE was explored by molecular docking and confirmed by Western blot. ResultsMTE inhibited cell viability and migration of PC-9 and H1975 cells. Enrichment analysis identified that differential genes after MTE treatment were significantly enriched in endoplasmic reticulum stress-related biological processes. MTE decreased mitochondrial membrane potential (MMP) and increased ROS production. Meanwhile, endoplasmic reticulum stress-related proteins (ATF6, GRP-78, ATF4, XBP1s, and CHOP) and immunogenic cell death-related markers (ATP, HMGB1) were upregulated, and the AXL phosphorylation level was suppressed after MTE treatment. However, when salubrinal (an endoplasmic reticulum stress inhibitor) and MTE were co-treated cells, the inhibitory effects of MTE on PC-9 and H1975 cells were impaired. Importantly, inhibition of AXL expression or activity also promotes the expression of endoplasmic reticulum stress and immunogenic cell death-related markers. Mechanistically, MTE induced endoplasmic reticulum stress and immunogenic cell death by suppressing AXL activity, and these effects were attenuated when AXL activity recovered. Moreover, MTE significantly increased the expression of endoplasmic reticulum stress-related markers in LLC tumor-bearing mouse tumor tissues and plasma levels of ATP and HMGB1. Molecular docking illustrated that kaempferol has the strongest binding energy with AXL and suppresses AXL phosphorylation. ConclusionMTE induces endoplasmic reticulum stress-associated immunogenic cell death in NSCLC cells. The anti-tumor effects of MTE are dependent upon endoplasmic reticulum stress. MTE triggers endoplasmic reticulum stress-associated immunogenic cell death by inhibiting AXL activity. Kaempferol is an active component that inhibits AXL activity in MTE. The present research revealed the role of AXL in regulating endoplasmic reticulum stress and enriched the anti-tumor mechanisms of MTE. Moreover, kaempferol may be considered a novel AXL inhibitor.

Analysis of Tumor Heterogeneity Through AXL Activation in Primary Resistance to EGFR Tyrosine Kinase Inhibitors

IntroductionEGFR tyrosine kinase inhibitors are standard therapeutic agents for patients with advanced NSCLC harboring EGFR mutations. Nevertheless, some patients exhibit primary resistance to EGFR tyrosine kinase inhibitors in the first-line treatment setting. AXL, a member of the TYRO3, AXL, and MERTK family of receptor tyrosine kinases, is involved in primary resistance to EGFR tyrosine kinase inhibitors in EGFR-mutated NSCLC. MethodsWe investigated spatial tumor heterogeneity using autopsy specimens and a patient-derived cell line from a patient with EGFR-mutated NSCLC having primary resistance to erlotinib plus ramucirumab. ResultsQuantitative polymerase chain reaction analysis revealed that AXL mRNA expression differed at each metastatic site. In addition, AXL expression levels were likely to be negatively correlated with the effectiveness of erlotinib plus ramucirumab therapy. Analysis of a patient-derived cell line established from the left pleural effusion before initiation of treatment revealed that the combination of EGFR tyrosine kinase inhibitors and an AXL inhibitor remarkably inhibited cell viability and increased cell apoptosis in comparison with EGFR tyrosine kinase inhibitor monotherapy or combination therapy of these inhibitors with ramucirumab. ConclusionsOur observations suggest that AXL expression may play a critical role in the progression of spatial tumor heterogeneity and primary resistance to EGFR tyrosine kinase inhibitors in patients with EGFR-mutated NSCLC.

Gas6/Axl Axis Activation Dampens the Inflammatory Response in Osteoarthritic Fibroblast-like Synoviocytes and Synovial Explants.

Osteoarthritis (OA) is the most prevalent joint disease, and it is characterized by cartilage degeneration, synovitis, and bone sclerosis, resulting in swelling, stiffness, and joint pain. TAM receptors (Tyro3, Axl, and Mer) play an important role in regulating immune responses, clearing apoptotic cells, and promoting tissue repair. Here, we investigated the anti-inflammatory effects of a TAM receptor ligand, i.e., growth arrest-specific gene 6 (Gas6), in synovial fibroblasts from OA patients. TAM receptor expression was determined in synovial tissue. Soluble Axl (sAxl), a decoy receptor for the ligand Gas6, showed concentrations 4.6 times higher than Gas6 in synovial fluid of OA patients. In OA fibroblast-like synoviocytes (OAFLS) exposed to inflammatory stimuli, the levels of sAxl in the supernatants were increased, while the expression of Gas6 was downregulated. In OAFLS under TLR4 stimulation by LPS (Escherichia coli lipopolysaccharide), the addition of exogenous Gas6 by Gas6-conditioned medium (Gas6-CM) reduced pro-inflammatory markers including IL-6, TNF-α, IL-1β, CCL2, and CXCL8. Moreover, Gas6-CM downregulated IL-6, CCL2, and IL-1β in LPS-stimulated OA synovial explants. Pharmacological inhibition of TAM receptors by a pan inhibitor (RU301) or by a selective Axl inhibitor (RU428) similarly abrogated Gas6-CM anti-inflammatory effects. Mechanistically, Gas6 effects were dependent on Axl activation, determined by Axl, STAT1, and STAT3 phosphorylation, and by the downstream induction of the suppressors of the cytokine signaling family (SOCS1 and SOCS3). Taken together, our results showed that Gas6 treatment dampens inflammatory markers of OAFLS and synovial explants derived from OA patients associated with SOCS1/3 production.

PRAME Is a Novel Target of Tumor-Intrinsic Gas6/Axl Activation and Promotes Cancer Cell Invasion in Hepatocellular Carcinoma.

(1) Background: Activation of the receptor tyrosine kinase Axl by Gas6 fosters oncogenic effects in hepatocellular carcinoma (HCC), associating with increased mortality of patients. The impact of Gas6/Axl signaling on the induction of individual target genes in HCC and its consequences is an open issue. (2) Methods: RNA-seq analysis of Gas6-stimulated Axl-proficient or Axl-deficient HCC cells was used to identify Gas6/Axl targets. Gain- and loss-of-function studies as well as proteomics were employed to characterize the role of PRAME (preferentially expressed antigen in melanoma). Expression of Axl/PRAME was assessed in publicly available HCC patient datasets and in 133 HCC cases. (3) Results: Exploitation of well-characterized HCC models expressing Axl or devoid of Axl allowed the identification of target genes including PRAME. Intervention with Axl signaling or MAPK/ERK1/2 resulted in reduced PRAME expression. PRAME levels were associated with a mesenchymal-like phenotype augmenting 2D cell migration and 3D cell invasion. Interactions with pro-oncogenic proteins such as CCAR1 suggested further tumor-promoting functions of PRAME in HCC. Moreover, PRAME showed elevated expression in Axl-stratified HCC patients, which correlates with vascular invasion and lowered patient survival. (4) Conclusions: PRAME is a bona fide target of Gas6/Axl/ERK signaling linked to EMT and cancer cell invasion in HCC.

Abstract 410: Tumor heterogeneity via AXL activation on primary resistance to EGFR tyrosine kinase inhibitors in EGFR mutated lung cancer

Abstract Epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (TKIs) are the standard treatments for patients with advanced non-small cell lung cancer (NSCLC) harboring EGFR mutations. However, some patients show primary resistance to EGFR-TKIs at the first-line treatment setting. AXL, a member of the TAM family of receptor tyrosine kinase, was reported to be involved in primary resistance to EGFR-TKIs for EGFR mutated NSCLC patients. In the present study, we investigated spatial tumor heterogeneity using autopsy specimens from EGFR mutated NSCLC patients, showing primary resistance to erlotinib plus ramucirumab. qPCR analysis showed that the AXL mRNA expression levels differed in each metastatic site. In addition, the AXL expression levels were likely to negatively correlate with the efficacy of erlotinib plus ramucirumab therapy. The analysis of patient-derived cell lines, established from left pleural effusion before initiation of the treatment, showed that the combination of EGFR-TKIs and an AXL inhibitor remarkably inhibited cell viability compared with EGFR-TKI monotherapy or combination with ramucirumab. Our observations suggested that tumor AXL expression might play a critical role in progression of spatial tumor heterogeneity and primary resistance to EGFR-TKIs for EGFR mutated NSCLC patients. Citation Format: Tadaaki Yamada, Ryota Nakamura, Hiroyuki Fujii, Takeshi Yaoi, Kyoko Itoh, Shinsaku Tokuda, Koichi Takayama. Tumor heterogeneity via AXL activation on primary resistance to EGFR tyrosine kinase inhibitors in EGFR mutated lung cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 410.

Abstract 518: AB801 is a highly potent and selective AXL kinase inhibitor that demonstrates significant anti-tumor activity

Abstract Background: AXL receptor tyrosine kinase (AXL) is overexpressed in a variety of tumors and correlates with poor prognosis in cancer patients. AXL is expressed in cancer, stromal, and select immune cells, and has been implicated in the development of resistance to chemotherapy, targeted therapies & immunotherapies. Activation of AXL can be mediated by its ligand, growth arrest specific protein 6 (GAS6), or via ligand-independent homo/hetero-dimerization, both of which facilitate AXL phosphorylation, initiation of signaling cascades that promote cancer cell proliferation, survival, and an immunosuppressive microenvironment. Here we present the discovery and characterization of a novel, highly potent and selective AXL inhibitor, AB801. Materials and Methods: The potency and selectivity of AB801 against AXL and other kinases were determined using a panel of HTRF KinEASE-TK assays and via a competition binding assay utilizing DNA-tagged kinases. The effects of AB801 were further assessed by a cell-based phospho-AXL ELISA. The pharmacokinetic (PK) profile of the molecule was evaluated in preclinical species. AB801 was characterized in routine in vitro safety assays, including hERG inhibition. Downstream signaling of AXL was evaluated by phospho-array, Western blot, and qPCR. Pharmacodynamics (PD) and anti-tumor efficacy in combination with standard of care (SOC) therapies were assessed in murine cancer models. Results: The novel AXL inhibitor AB801 is potent, reversible, and selective. AB801 exhibits cellular activity at low nanomolar concentrations and retains significant activity in 100% human serum. Excellent selectivity was observed against MERTK (860x), TYRO3 (1,400x), and the overall kinome. Importantly, AB801 does not show significant CYP450 or hERG inhibition. Favorable preclinical PK is consistent with projected once-a-day oral administration in humans. AB801 increases sensitivity to SOC therapeutics such as chemotherapy, and results in increased DNA damage. Moreover, AB801 treatment sensitizes tumors to checkpoint blockade by increasing immune cell activation. Significant anti-tumor efficacy is observed in combination SOC therapies in multiple in vivo models. Conclusions: AXL inhibition is a promising therapeutic mechanism for impairing the growth of tumors resistant to SOC therapeutics. AB801 exhibits improved potency, selectivity, and safety profiles compared to other AXL inhibitors currently advancing into clinical development. Citation Format: Susan Lee Paprcka, Armon Goshayeshi, Suan Liu, Ruben Flores, Lauren Rocha, Jhansi L. Leslie, Dillon H. Miles, Corinne N. Foley, Shiwei Qu, Manjunath Lamani, Srinivas Paladugu, Hsin-Ting Huang, Nidhi Tribewal, Ada Chen, Joseph Kulusich, Stefan Garrido-Shaqfeh, Patricia Fabila, Salema Jafri, Anuja Devarajan, Ester Fernandez-Salas. AB801 is a highly potent and selective AXL kinase inhibitor that demonstrates significant anti-tumor activity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 518.

Abstract 395: Resistance to tyrosine kinase inhibitor confers an immunosuppressive microenvironment and cross-resistance to immunotherapy through AXL/PDPK1 axis in liver cancer

Abstract Systemic therapy is the current standard of care for unresectable advanced hepatocellular carcinoma (HCC), the most malignant form of liver cancer. Clinical practice guideline for HCC includes the management of the second-line immunotherapies after patients become unresponsive to first-line targeted therapies using tyrosine kinase inhibitors (TKI), which is expected to generate optimal therapeutic effect due to the distinct mechanism of action between TKIs and immunotherapies. However, evidence from clinical trials suggests that the response to immunotherapy following TKI treatment is often compromised in TKI-resistant HCC as compared with treatment-naïve HCC, indicating a potential cross-resistance to immunotherapy, which impedes the optimal therapeutic effect of the second-line immunotherapies. In the present study, we first explored the therapeutic effect of anti-PD-1 immunotherapy in TKI-resistant HCC and successfully validated the putative cross-resistance to immunotherapy after TKI treatment. We further observed that TKI-resistant HCC exhibits an immune-evasive microenvironment, characterized by decreased CD8+ T cell and dendritic cell infiltration. This is potentially caused by the intratumoral activation of receptor tyrosine kinase AXL and its downstream target PDPK1 which protect TKI-resistant HCC cells from mitochondrial oxidative stress and the cytosolic leakage of mitochondrial DNA, which subsequently suppresses cGAS-STING together with its downstream interferon pathways and immunogenic cell death. Genetic manipulation of AXL and PDPK1 in TKI-resistant HCC cells abrogated the protective effect and thus activated the immunogenic responses. Blockade of AXL with a selective inhibitor BGB324 re-sensitized TKI-resistant HCC to anti-PD-1 treatment. The current findings suggest that targeting AXL/PDPK1 signaling axis might overcome cross-resistance to second-line immunotherapy for HCC patients who progress on TKI treatment. Citation Format: Yunong Xie, Bosheng Huang, Huajian Yu, Jia-Jian Loh, Rainbow Wing-Hei Leung, Terence Lee, Stephanie Ma, Man Tong. Resistance to tyrosine kinase inhibitor confers an immunosuppressive microenvironment and cross-resistance to immunotherapy through AXL/PDPK1 axis in liver cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 395.

Abstract 3245: AXL as a therapeutic target in STK11 mutant NSCLC

Abstract STK11 (LKB1) is a tumor suppressor, and loss-of-function mutations contribute to tumorigenesis. Mutations in the STK11 gene (STK11m) are present in ~ 20% of NSCLCs and are associated with poor response to chemotherapy and immune checkpoint inhibition (ICI) resulting in inferior survival outcomes. STK11m tumors are characterized by high oxidative stress/ROS, EMT, enhanced replication stress tolerance, resistance to DNA damage and a highly immunosuppressive tumor microenvironment with limited activation and expansion of anti-tumor CD8 T-cells. AXL, a member of the TAM family of receptor tyrosine kinases, is activated in response to cellular stress such as ROS and hypoxia. AXL expression and activation is associated with EMT and drug resistance, tumor tolerance towards oxidative stress and apoptosis, as well as an immunosuppressed tumor microenvironment. We have previously shown that selective AXL inhibition by bemcentinib potentiated ICI in STK11m NSCLC preclinical models and led to objective clinical response in individuals with STK11m NSCLC receiving bemcentinib and pembrolizumab (NCT03184571). Data from this clinical study, an independent real-world cohort of patients studied at the Haukeland Hospital in Bergen, Norway (REC 45562) and published results1, suggest AXL is expressed in ~ 80% of NSCLCs harboring a STK11m, indicating AXL expression is a characteristic of STK11m NSCLC and confirming that AXL is an attractive target in STK11m NSCLC. Inhibition of AXL in dendritic cells has been shown to increase ICI responses in preclinical models of STK11m NSCLC1. The relative contribution of targeting AXL in STK11m tumor cells vs the tumor microenvironment, and the impact on tumor cells after tumor cell targeting needs further exploration. Transcriptional analysis of STK11m and STK11wt sequences from public datasets, NCT03184571 patients and NSCLC cell lines identified transcriptional signatures consistent with the known roles of STK11 in DNA damage response and immunosuppression. Treatment of STK11m NSCLC cell lines with the AXL inhibitor bemcentinib led to a reduction in the STK11-associated DDR signature and increase in inflammatory signatures demonstrating the impact of AXL targeting on tumor cells. Due to the high unmet medical need in individuals harboring a STK11 mutation, the encouraging efficacy in the NCT03184571 clinical trial and the high incidence of AXL protein expression in STK11m tumors, a global, open-label Phase 1b/2a trial to determine the safety, tolerability and anti-tumor activity of bemcentinib with SOC (pembrolizumab, pemetrexed and carboplatin) in 1L advanced/metastatic non-squamous NSCLC patients with STK11 mutations and no actionable mutations is currently enrolling. The Phase 1b part of the study will evaluate the safety and tolerability of bemcentinib regardless of STK11 status, whereas the Phase 2a part will assess the efficacy in NSCLC patients with STK11 mutations. 1 Li et al., 2022; Cell Rep Med., PMID: 35492873 Citation Format: Magnus Blø, Austin Rayford, Noëlly Madeleine, Fabian Gärtner, Dana Bohan, Natalie Ruggio, Huiyu Li, Luc Girard, Rolf Brekken, John Minna, Marianne Ånerud, Wendy Maury, Claudia Gorcea-Carson, Gro Gausdal, David R. Micklem, Nigel McCracken. AXL as a therapeutic target in STK11 mutant NSCLC [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3245.

Targeting AXL Using the AVB-500 Soluble Receptor and through Genetic Knockdown Inhibits Bile Duct Cancer Growth and Metastasis

Bile duct cancer, or cholangiocarcinoma, is a rare disease with limited treatment options that include surgery and cytotoxic chemotherapy. The high recurrence rate and poor prognosis of this type of cancer highlights the need to identify new and more effective therapeutic targets. In this study, we found that AXL, a receptor tyrosine kinase, is highly expressed in biliary cancer patients and significantly correlated with poor patient outcomes, including metastasis and low survival rates. We also demonstrated that targeting AXL inhibits tumor progression. In vitro studies with bile duct cancer cells (SNU1196 and HUCCT1) showed that genetic knockdown of AXL significantly reduced both tumor cell growth and invasion. In addition, in vivo studies using subcutaneous and orthotopic intrahepatic models demonstrated that genetic inhibition of AXL resulted in tumor-growth delay. To further examine the possible clinical translation of AXL inhibition in the clinic, we tested the efficacy of AVB-500, a soluble AXL receptor, in reducing AXL activation and tumor growth. AVB-500 was effective at inhibiting AXL activation and decreasing the growth and invasion of SNU1196 and HUCCT1 tumors which possess high AXL expression. Most importantly, AVB-500 was highly effective at decreasing tumor dissemination of bile duct tumor cells in the peritoneal cavity. This study strongly supports the idea of using the AXL receptor as a new therapeutic target to treat the growth and progression of biliary cancer.

Axl regulated survival/proliferation network and its therapeutic intervention in mouse models of glomerulonephritis

BackgroundLupus nephritis (LN) is the most common and serious complication of systemic lupus erythematosus (SLE). LN pathogenesis is not fully understood. Axl receptor tyrosine kinase is upregulated and contributes to the pathogenic progress in LN. We have reported that Axl disruption attenuates nephritis development in mice.MethodsIn this study, we analyzed the gene expression profiles with RNA-seq using renal cortical samples from nephritic mice. Axl-KO mice were bred onto a B6.lpr spontaneous lupus background, and renal disease development was followed and compared to the Axl-sufficient B6.lpr mice. Finally, anti-glomerular basement membrane (anti-GBM) Ab-induced nephritic mice were treated with Axl small molecule inhibitor, R428, at different stages of nephritis development. Blood urine nitrogen levels and renal pathologies were evaluated.ResultsTranscriptome analysis revealed that renal Axl activation contributed to cell proliferation, survival, and motility through regulation of the Akt, c-Jun, and actin pathways. Spontaneous lupus-prone B6.lpr mice with Axl deficiency showed significantly reduced kidney damages and decreased T cell infiltration compared to the renal damage and T cell infiltration in Axl-sufficient B6.lpr mice. The improved kidney function was independent of autoAb production. Moreover, R428 significantly reduced anti-GBM glomerulonephritis at different stages of GN development compared to the untreated nephritic control mice. R428 administration reduced inflammatory cytokine (IL-6) production, T cell infiltration, and nephritis disease activity.ConclusionsResults from this study emphasize the important role of Axl signaling in LN and highlight Axl as an attractive target in LN.

Circulating small extracellular vesicles promote proliferation and migration of vascular smooth muscle cells via AXL and MerTK activation.

The proliferation and migration of vascular smooth muscle cells (VSMCs) after vascular injury lead to neointimal hyperplasia, thus aggravating vascular diseases. However, the molecular mechanisms underlying neointima formation are not fully elucidated. Extracellular vesicles (EVs) are mediators of various intercellular communications. The potential of EVs as regulators in cardiovascular diseases has raised significant interest. In the current study we investigated the role of circulating small extracellular vesicles (csEVs), the most abundant EVs (1010 EVs/mL serum) in VSMC functions. csEVs were prepared from bovine, porcine or rat serum. We showed that incubation with csEVs (0.5 × 1010-2 × 1010) dose-dependently enhanced the proliferation and migration of VSMCs via the membrane phosphatidylserine (PS). In rats with ligation of right carotid artery, we demonstrated that application of csEVs in the ligated vessels aggravated neointima formation via interaction of membrane PS with injury. Furthermore, incubation with csEVs markedly enhanced the phosphorylation of AXL and MerTK in VSMCs. Pretreatment with BSM777607 (pan-TAM inhibitor), bemcentinib (AXL inhibitor) or UNC2250 (MerTK inhibitor) blocked csEV-induced proliferation and migration of VSMCs. We revealed that csEV-activated AXL and MerTK shared the downstream signaling pathways of Akt, extracellular signal-regulated kinase (ERK) and focal adhesion kinase (FAK) that mediated the effects of csEVs. We also found that csEVs increased the expression of AXL through activation of transcription factor YAP, which might constitute an AXL-positive feedback loop to amplify the signals. Finally, we demonstrated that dual inhibition of AXL/MerTK by ONO-7475 (0.1 µM) effectively hindered csEV-mediated proliferation and migration of VSMCs in ex vivo mouse aorta injury model. Based on these results, we propose an essential role for csEVs in proliferation and migration of VSMCs and highlight the feasibility of dual AXL/MerTK inhibitors in the treatment of vascular diseases.

Decreased CSTB, RAGE, and Axl Receptor Are Associated with Zika Infection in the Human Placenta.

Zika virus (ZIKV) compromises placental integrity, infecting the fetus. However, the mechanisms associated with ZIKV penetration into the placenta leading to fetal infection are unknown. Cystatin B (CSTB), the receptor for advanced glycation end products (RAGE), and tyrosine-protein kinase receptor UFO (AXL) have been implicated in ZIKV infection and inflammation. This work investigates CSTB, RAGE, and AXL receptor expression and activation pathways in ZIKV-infected placental tissues at term. The hypothesis is that there is overexpression of CSTB and increased inflammation affecting RAGE and AXL receptor expression in ZIKV-infected placentas. Pathological analyses of 22 placentas were performed to determine changes caused by ZIKV infection. Quantitative proteomics, immunofluorescence, and western blot were performed to analyze proteins and pathways affected by ZIKV infection in frozen placentas. The pathological analysis confirmed decreased size of capillaries, hyperplasia of Hofbauer cells, disruption in the trophoblast layer, cell agglutination, and ZIKV localization to the trophoblast layer. In addition, there was a significant decrease in CSTB, RAGE, and AXL expression and upregulation of caspase 1, tubulin beta, and heat shock protein 27. Modulation of these proteins and activation of inflammasome and pyroptosis pathways suggest targets for modulation of ZIKV infection in the placenta.

Escape from Type II JAK2 Inhibition in MPN Depends on AXL/MAPK Activation and Is Targetable

Myeloproliferative neoplasms (MPN) are characterized by dysregulated JAK2 signaling. Clinical type I JAK2 inhibitors as ruxolitinib are hampered by limited disease-modifying effects and occurrence of resistance. Based on pre-clinical data, novel type II JAK2 inhibitors as CHZ868 effectively stabilize inactive JAK2, reduce MPN clones and overcome resistance to ruxolitinib. We study whether MPN cells could escape from type ll JAK2 inhibition, and characterize therapeutic approaches. To assess potential escape from type II JAK inhibition, JAK2V617F MPN cells incl. SET2, UKE-1 and Ba/F3 EPOR Jak2V617F were exposed long-term to CHZ868. Outgrowing cells showed significantly increased IC50 to CHZ868 and reduced susceptibility for apoptosis induction. No second-site mutations in JAK2 were detected. Phosphoproteomic analysis identified >2500 differentially phosphorylated sites with most prominent activation of the MAPK pathway in JAK inhibitor resistant cells. Type II JAK inhibition persistently suppressed JAK2 - STAT3/5 signaling, while MAPK target activation incl. MEK and ERK was prominent also by phospho-immunoblot suggesting MAPK pathway signaling as a driver of escape from type II JAK inhibition. To characterize the molecular basis, we profiled differential gene expression and chromatin accessibility by RNA-sequencing and ATAC-sequencing in MPN cells escaping JAK inhibition. Paired analysis of RNA-seq/ATAC-seq revealed enrichment of H3K27me3 and PRC2 signatures with overall more compacted chromatin. Expression of AXL tyrosine kinase known to signal through the MAPK pathway, was significantly increased along with enriched RAS signaling target gene patterns by GSEA. Motif analysis suggested differential transcriptional programs with loss of ETS and increased accessibility of GATA transcription factor family binding sites. Enhanced AXL expression was confirmed by immunoblotting and depletion of AXL by AXL-specific shRNA knock-down resensitized resistant cells to CHZ868 with decreased IC50. Since these findings pointed towards a role of AXL activation for escape of MPN cells from type II JAK inhibition, we targeted AXL activation using respective inhibitors. AXL inhibitor bemcentinib and AXL/FLT3 inhibitor gilteritinib reduced proliferation of resistant cells with up to 5.6-fold and 3.4-fold decreased IC50, respectively. Given that type II JAK inhibition with CHZ868 maintained suppression of JAK2-STAT3/5 activation in resistant cells, we combined JAK2 and AXL inhibition. Notably, dual JAK2 / AXL inhibition with CHZ868 / bemcentinib or CHZ868 / gilteritinib showed most pronounced inhibitory effects with IC50 similar to values seen in JAK inhibitor sensitive cells and effective induction of apoptosis. Resistant MPN cells engrafted subcutaneously into immunocompromised NSG mice and resulted in robust tumor growth despite JAK2 inhibitor treatment. However, AXL inhibition with bemcentinib reduced progression of type II JAK inhibitor resistant tumors. Combined JAK2 and AXL inhibition showed most pronounced suppression of subcutaneous tumor growth with minimal progression. Given that inhibitors of MAPK signaling targeting e.g. MEK-ERK activation, are in clinical use for other malignancies with favorable tolerability profiles, we then characterized combined JAK2 / MAPK inhibition to overcome AXL-MAPK driven escape of MPN cells from type II JAK inhibitors. Combination of CHZ868 and MEK inhibitor trametinib significantly reduced subcutaneous tumor growth in NSG mice similarly to JAK2 / AXL inhibition. Expression of MAPK pathway effectors as DUSP6 was substantially reduced. Furthermore, intravenous engraftment of JAK inhibitor resistant cells into NSG mice led to substantial bone marrow (BM) infiltration shown by luciferase imaging and hCD45 immunohistochemistry despite treatment with CHZ868. Combined JAK2 / MAPK inhibition with CHZ868 and trametinib significantly reduced BM infiltration by luciferase imaging and histology supporting that escape from type II JAK inhibition is dependent on AXL-MAPK activation. In summary, we report on a novel mechanism of AXL-MAPK driven escape from type II JAK2 inhibition which is targetable in vitro and in vivo. Our findings highlight that rationally designed combination therapy approaches can restore sensitivity to JAK inhibitor therapy in MPN, which may have potential implications for other malignant settings. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

GAS6 Promotes Robust Expansion of Human Hematopoietic Stem and Progenitor Cells with High Serial Engraftment Activity

Hematopoietic stem cell transplantation is a curative therapy for over 30 hematopoietic illnesses. The inability to sufficiently expand functional HSCs in cultures has partly hampered their therapeutic potential and limited molecular understanding of HSCs. Stem cell agonists (SCA) such as UM171 and StemReginin1 (SR1) have been shown to promote HSC expansion. Recently, we discovered that Ascorbic acid-2-phosphate (AA2P) can act as a novel SCA. Furthermore, using mathematical modeling we formulated a series of stem cell agonist cocktails (SCACs) composed of varying concentrations of 4 SCAs. SCACs promote robust expansion of HSPCs and limited dilution transplant assay revealed that the lead cocktail X2A promoted 15- and 4-fold expansions of scid repopulating cells, when compared to non-cultured cells or cells expanded with the combination of UM171 and SR1 (Manesia et al., 2019). The objective of the present study was to characterize the molecular programs supporting the strong expansion of HSCs in X2A cultures. RNA-Seq data from SCACs expanded CD34+CD45RA- cells revealed the upregulation of several receptor tyrosine kinases (RTKs) including AXL, but also its ligand GAS6 preferentially with X2A. AXL was recently shown to be essential for the self-renewal of leukemia initiating cells. Single cell RNA-seq analyses of CD34+ cells was done to characterize the graft composition of SCACs expanded HSPCs. These analyses revealed that AXL expression is enriched within CD34+CD45RA-CD90+CD49f+ HSC-enriched clusters. Image-flowcytometry analyses confirmed that HSC-enriched cell populations respond to GAS6-activation, resulting in the activation of ERK1/2 downstream of AXL activation. Epigenetic analysis revealed that GAS6/AXL upregulation is regulated by AA2P through DNA-demethylation in a TET dependent manner. Using genetic knockdown, chemical inhibition and GAS6 neutralizing antibody approaches we confirmed that GAS6 activation of AXL drives human HSPC expansion within X2A. In addition, supplementation of SCAC or single SCA-based cultures with GAS6 significantly enhanced the expansion of HSPC subsets with little induction of differentiation (e.g., 640- Vs. 1975-fold for CD34+CD45RA- HSPC in X2A and X2A+GAS6 cultures, respectively (n=3, p<0.05)). Transplant assays with day-14 expanded HSPC (progeny of 850 CD34+ starting cells/mouse) revealed that GAS6 supplementation in X2A cultures increased ensuing engraftment by 10-fold in both primary and secondary NSG mice (n=2, p<0.0001). For instance, the % of human CD45+ BM cells in secondary mice were of 2.3±0.1% and 25.7±1.3% in X2A and X2A+GAS6 groups. Remarkably, the net numbers of human colony-forming unit and CD34+ BM cells were increased by 7- and 15-fold (p<0.0001) in primary, and by 20- and 26-fold (p<0.0001) in secondary transplants by GAS6, respectively. In contrast, GAS6 neutralization in cultures impaired ensuing serial engraftment by 8- and 30-fold respectively Vs. X2A control (p<0.01). Lastly, SCAC and GAS6 were also shown to improve the expansion of adult G-CSF mobilized peripheral blood stem cells. In conclusion, we demonstrate that AA2P-mediated HSPC expansion is driven through DNA demethylation leading to enhanced expression of AXL and its ligand GAS6. We also show for the first time that GAS6 is a potent growth factor that promote robust expansion of human HSPCs including serial engrafting HSCs resulting in unexpectedly high engraftment.