Axl Signaling Research Articles

Abstract A011: Discovery and characterization of the first highly potent and selective AXL receptor tyrosine kinase inhibitor AB801

Abstract The AXL receptor (AXL) is a transmembrane protein that is highly expressed in a variety of tumors and correlates with poor prognosis in cancer patients. AXL is expressed in cancer, immune, and stromal cells and has been implicated in the development of resistance to chemotherapy, targeted therapies, and immunotherapies. Activation of AXL by either its ligand, growth arrest specific protein 6 (GAS6), or ligand-independent homo- and hetero-dimerization facilitates AXL phosphorylation and initiates signaling cascades that promote cancer cell proliferation, survival, and an immunosuppressive microenvironment. Historically, most small-molecule inhibitors capable of suppressing AXL signaling are unselective and inhibit several other related kinases. Administration of a truly selective AXL inhibitor would be expected to be free of the off-target toxicity of other kinase inhibitors; this, in turn, might allow the unmasking of the full therapeutic benefit associated with robust AXL inhibition. To this end, we initiated a medicinal chemistry campaign with additional goals of discovering a potent and orally bioavailable inhibitor. Through iterative SAR-guided design we discovered AB801, a reversible AXL inhibitor. Importantly, AB801 exhibits excellent selectivity against MERTK, TYRO3 (closely related tyrosine kinases) and the overall kinome. AB801 exhibits a double-digit picomolar inhibitory constant and retains significant activity in cell-based assays performed in 100% human serum. In vitro, AB801 increases sensitivity to standard of care (SOC) therapeutics such as chemotherapy and results in increased DNA damage, leading to cancer cell death. AB801 treatment also sensitizes tumors to immune checkpoint blockade by increasing immune cell activation. Significant anti-tumor efficacy is observed in combination with SOC therapies in multiple in vivo models. When compared against existing AXL inhibitors such as bemcentinib, AB801 shows large improvements in both potency and selectivity. A placebo-controlled phase 1 study (NCT06004921) to assess the safety and pharmacokinetics of AB801 in healthy volunteers was recently completed; AB801 was well tolerated at all tested doses and exhibited a dose-proportionate increase in exposure. Currently, AB801 is in clinical evaluation in patients with advanced cancer (NCT06120075). Citation Format: Dillon H. Miles, Corinne N. Foley, Shiwei Qu, Dillon H. Miles, Srinivas Paladugu, Ehesan U. Sharif, Joice Thomas, Pradeep Nareddy, Guiling Zhao, Rebecca Grange, Manmohan R. Leleti, Jay P. Powers, Stefan Garrido-Shaqfeh, Ada Chen, Hema Singh, Yue Tong Lee, Xiaoning Zhao, David Green, Hsin-Ting Huang, Lixia Jin, Jhansi Leslie, Logan Chinn, Susan L Paprcka, Ester Fernandez-Salas. Discovery and characterization of the first highly potent and selective AXL receptor tyrosine kinase inhibitor AB801 [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Optimizing Therapeutic Efficacy and Tolerability through Cancer Chemistry; 2024 Dec 9-11; Toronto, Ontario, Canada. Philadelphia (PA): AACR; Mol Cancer Ther 2024;23(12_Suppl):Abstract nr A011.

CSIG-20. LIPOCALIN-2 DRIVES CELL-INTRINSIC FUNCTIONS IN GLIOBLASTOMA

Abstract Glioblastoma (GBM) continues to persist despite aggressive therapies, many of which are cytotoxic, and therapeutic failure is driven, in part, by the tumor cell’s ability to evade multiple forms of cell death, including ferroptosis. Lipocalin-2 (LCN2) functions to sequester iron and is considered an inflammatory marker through its function of limiting iron for bacterial usage; it has also been described to have pro and anti-tumorigenic effects depending on environmental iron status. In previously published studies in brain metastases, LCN2 promotes tumor cell proliferation by sequestering iron for cancer cells growth and survival, but the mechanisms of how LCN2 contributes to GBM progression is unknown. LCN2 expression in patient data revealed that high LCN2 expression is associated with reduced survival in GBM patients. A survey of mouse glioma models demonstrated a range of LCN2 secretion across models with KR158 and CPA being high and medium LCN2 secretors. LCN2 short hairpin knockdown of KR158 and CPA and decreased tumor cell viability and proliferation. Furthermore, when both KR158 and CPA control versus LCN2 knockdown cells were orthotopically implanted into mice, survival was increased. To understand if LCN2 impacted cell death dynamics, we investigated various cell death mechanisms and found that LCN2 knockdown increases tumor susceptibility to ferroptotic death by sensitizing cells to lipid peroxidation as well as reducing key anti-ferroptotic proteins GPX4 and xCT. To elucidate downstream mechanisms, we performed a phosphorylation array and discovered that phosphorylation of AXL, which has recently been linked to ferroptosis, is decreased with LCN2 knockdown. Moreover, AXL phosphorylation was localized to the nucleus, indicating that LCN2 knockdown attenuates AXL processing and downstream signaling. Overall, these findings indicate that LCN2 in GBM promotes tumor cell growth through AXL signaling and evasion of ferroptotic death, ultimately revealing a novel signaling network that can be leveraged for future therapeutic development.

CD73 promotes non–small cell lung cancer metastasis by regulating Axl signaling independent of GAS6

As catabolic enzyme, CD73 dephosphorylates adenosine monophosphate (AMP) and can also regulate tumor cell proliferation and metastasis. To date, very few studies have explored the role of CD73 in mediating non-small cell lung cancer (NSCLC) metastasis, and the underlying transducing signal has not been elucidated. In the present study, we demonstrated that the CD73/Axl axis could regulate Smad3-induced epithelial-to-mesenchymal transition (EMT) to promote NSCLC metastasis. Mechanically, CD73 can be secreted via the Golgi apparatus transport pathway. Then secreted CD73 may activate AXl by directly bind with site R55 located in Axl extracellular domain independently of GAS6. In addition, we proved that CD73 can stabilize Axl expression via inhibiting CBLB expression. We also identified the distinct function of CD73 activity in adenocarcinoma and squamous cell carcinoma. Our findings indicated a role of CD73 in mediating NSCLC metastasis and propose it as a therapeutic target for NSCLC.

NPS-1034 Exerts Therapeutic Efficacy in Renal Cell Carcinoma Through Multiple Targets of MET, AXL, and TNFRSF1A Signaling in a Metastatic Model.

Renal cell carcinoma (RCC) has diverse pathological subtypes, most of which have a poor prognosis. Patients with advanced RCC require systemic therapies for disease control. Although targeted therapies and immune checkpoint inhibitors have shown therapeutic efficacy, patients eventually succumb to disease progression. Therefore, additional therapies targeting different pathways are needed to provide more therapeutic options for sequential treatment. Our study explored the biological mechanisms and therapeutic outcomes for NPS-1034, a dual MET/AXL inhibitor, in RCC, both in vivo and in vitro. Our results showed that NPS-1034 can significantly inhibit tumor proliferation and induce cancer cell apoptosis. Besides MET and AXL, known targets of NPS-1034, we identified TNFRSF1A as another target gene inhibited by NPS-1034 via antibody arrays. This was further supported by next-generation sequencing, showing that the TNF signaling pathway is one of the most significant NPS-1034-regulated pathways. Furthermore, one of the identified target genes, GADD45A, responsible for NPS-1034 anticancer properties, was significantly associated with patient survival in RCC. GADD45A expression was significantly upregulated via NPS-1034 and downregulated via TNFRSF1A overexpression. Finally, its therapeutic efficacy was demonstrated in vivo, showing that NPS-1034 significantly alleviated the tumor burden and inhibited cell proliferation in a lung metastatic animal model. In conclusion, we explored the therapeutic mechanism of NPS-1034 and found that it targets not only MET and AXL but also TNFRSF1A. In a lung metastatic animal model, we confirmed that NPS-1034 is a potential candidate for systemic therapy in RCC.

New potential ligand-receptor axis involved in tissue repair as therapeutic targets in progressive multiple sclerosis.

Progressive multiple sclerosis (PMS) represents the worsening phase of the disease by accumulative neurodegeneration and disability, mainly refractory to current treatments. The therapeutic options remain challenging based partially on the lack of understanding of the pathogenic mechanisms but also because the early dogma was centered on neuroinflammation, overshadowing the critical role of the tissue repair process. The tissue repair target should necessarily start early in disease development and PMS should combine anti-inflammatory and neuroprotective therapeutic strategies. Increasing preclinical evidence, together with the new era of omics applied on frozen human brain tissue, shed light on some ligand receptors axis, such as GAS6/TYRO3 and PROS1/AXL required to dampen inflammation, promote tissue repair and engage remyelination, at the early stages of multiple sclerosis (MS) as a critical step in preventing or stopping neurodegeneration. Here, we will discuss those receptor/ligand pairs that could be targetable for therapeutic intervention in progressive MS disease. Significance Statement The aim for PMS should be to combine anti-inflammatory and neuroprotective therapeutic strategies based on early intervention. The TYRO3, AXL, and MERTK (TAM) signaling axis, particularly GAS6/TYRO3 and PROS1/AXL, which are involved in tempering inflammation, promoting tissue repair, and engaging remyelination, could significantly benefit patients at the early PMS.

Retraction Note: LncRNA HOTAIR regulates HIF-1α/AXL signaling through inhibition of miR-217 in renal cell carcinoma

Retraction Note: LncRNA HOTAIR regulates HIF-1α/AXL signaling through inhibition of miR-217 in renal cell carcinoma

Aberrant activation of AXL may drive progression of squamous cell carcinoma in CLL patients: a mechanistic study with clinical implications.

Occurrence of squamous cell carcinoma (SCC) even in early-stage, untreated chronic lymphocytic leukemia (CLL) patients can be a significant morbidity issue with occasional transformation into metastatic skin lesions. CLL cells and extracellular vesicles (EVs) from CLL patients' blood/plasma were purified and used. Expression/activation of AXL and its functions in normal keratinocytes (HEKa) were assessed in vitro co-culture system and in SCC tissues. We detected aberrant activation of AXL, AKT and ERK-1/2 in SCC cell lines compared to HEKa. We also detected increased expression of AXL in primary SCC tissues obtained from CLL patients. Increased activation of AXL, AKT, ERK-1/2 and Src was discernible in HEKa upon co-culturing with CLL cells. Further analysis suggests that Gas6, a ligand of AXL, regulates AXL activation in co-cultured HEKa. Interestingly, exposure of HEKa cells to CLL plasma-derived EVs induced expression of AXL, P-AKT, and EMT-associated markers leading to migration of the cells. Finally, pharmacologic inhibition of AXL induced cell death in SCC lines in a dose dependent manner. Our findings that CLL cells likely are involved in driving SCC progression, at least in part, via activation of the AXL signaling axis, indicating that AXL inhibition may be beneficial for our CLL patients with SCC.

Clinical and molecular characterization of AXL in colorectal cancer: CALGB (Alliance)/SWOG 80405 and real-world data.

3145 Background: Dysregulation of AXL signaling is linked with chemotherapy and targeted therapy resistance. However, it remains unclear which patients may benefit from therapies targeting AXL, given its role in both tumor cell intrinsic resistance and immune microenvironmental reprogramming. Here, we present a clinical and molecular characterization of AXL in colorectal cancer (CRC). Methods: 24,257 CRC samples tested at Caris Life Sciences (Phoenix, AZ) with WTS (Illumina NovaSeq), NextGen DNA sequencing (NextSeq, 592 genes and NovaSEQ, WES), and PD-L1 expression (22C3 clone; TPS ≥ 1%) were analyzed. RNA deconvolution analysis with QuantiSEQ estimated cell infiltration in the tumor microenvironment (TME). In this cohort, AXL expression was categorized as high (H) or low (L) using median cutoff: overall survival (OS) was evaluated from treatment initiation using insurance claims data. Data from the phase III CALGB/SWOG 80405 trial on 433 metastatic CRC (mCRC) patients treated with bevacizumab (Bev, n = 226) or cetuximab (Cet, n = 207) in combination with first-line chemotherapy were also evaluated. RNA isolated from FFPE tumor samples were sequenced with HiSeq 2500 (Illumina). OS and progression-free survival (PFS) were compared using categorical gene expression tertiles (high (T3), medium (T2), and low (T1)) adjusting for age, demographics, ECOG, and tumor/treatment characteristics. Results: BRAF and RNF43 mutations were more prevalent in AXL-H, but APC, NRAS, KRAS, and PIK3CA correlated with AXL-L (all q< .001). AXL-H had increased B cells, M1/M2 macrophages, T-regs, and NK cells in the TME while increased neutrophils and dendritic cells were associated with AXL-L (all q< .001). AXL-H had increased PD-L1 positivity (5.1 vs 2.6%) and pathway activation of epithelial-mesenchymal transition (EMT), inflammatory/IFN-G response, and TNF-a signaling (all q< .005). AXL-H demonstrated worse OS in FOLFOX/FOLFIRI treated CRC (H: 35.7 vs L: 38.7 months [mo], P = .003; HR 1.08, 95% CI [1.03-1.14]). The effect persisted within KRAS wildtype (wt) CRC (45.4 vs 40.1 mo, P = .005; HR 1.12 [1.04-1.22]) but not KRASmutant (mt). In 80405, higher AXLexpression was associated with worse PFS and OS ( Plinear = 2E-04 and 2.2E-05, respectively). AXL-T3 showed significantly shorter PFS (T3: 9.2 vs T2: 11.7 vs T1: 12.9 mo, T3 vs T1 (reference) adjusted HR 1.53 [1.19-1.97]) and OS (24.2 vs 34.0 vs 34.7 mo, adjusted HR 1.73 [1.33-2.25]). No significant interaction between AXL expression and treatment was observed for PFS and OS (likelihood ratio test). Conclusions: Our results indicate increased AXL expression is associated with immune cell infiltration, EMT, and inflammatory signaling. AXL-H confers worse OS/PFS on first-line chemotherapy, with a more pronounced effect in KRASwt CRC. This data supports evaluation of AXL as a prognostic marker and potential therapeutic target in CRC. Trial Identifier: NCT00265850.

Serum GAS6, sAXL, IL-10, NO, and BCL-2 levels are decreased in patients with Behçet's disease.

Behçet's disease (BD) is an autoimmune chronic systemic inflammatory disease characterized by a versatile clinical spectrum. Growth arrest specific protein 6 (GAS6)/soluble AXL (sAXL) signaling pathway draws attention in the resolution of inflammation, and its deficiency is associated with chronic inflammatory, autoimmune diseases, as well as clearance of apoptotic cells by phagocytes - efferocytosis. In this study, it was aimed to investigate whether GAS6/sAXL, interleukin (IL)-10, nitric oxide (NO), and BCL-2 levels were associated with inflammation and efferocytosis contributes to the pathogenesis of BD. A total of 37 Behçet patients with ocular involvement and 30 healthy control subjects were included in this study. GAS6, sAXL, IL-10, NO, and BCL-2 levels were quantified using enzyme-linked immunosorbent assay (ELISA) method. Serum GAS6, sAXL, IL-10, NO, and BCL-2 levels were significantly lower in patients with BD compared to the controls (P < 0.005, P < 0.001, P < 0.001, P < 0.001, and P < 0.001, respectively). In correlation analysis, research parameters decreased in patients with BD was significantly correlated with each other: GAS6-IL-10 (r = 0.585, P < 0.001), GAS6-BCL-2 (r = 0.541, P < 0.001), sAXL-BCL-2 (r = 0.696, P < 0.001), IL-10-NO (r = 0.717, P < 0.001), IL-10-BCL-2 (r = 0.759, P < 0.001), and NO-BCL-2 (r = 0.541, P < 0.001). In conclusion, decreased serum BCL-2 level may be an indicator of increased apoptosis in these patients and decreased levels of GAS6/sAXL, IL-10, and NO may indicate insufficient clearance of apoptotic bodies released as a result of increased apoptosis in BD patients.

Tumor-Extrinsic Axl Expression Shapes an Inflammatory Microenvironment Independent of Tumor Cell Promoting Axl Signaling in Hepatocellular Carcinoma.

The activation of the receptor tyrosine kinase Axl by Gas6 is a major driver of tumorigenesis. Despite recent insights, tumor cell-intrinsic and -extrinsic Axl functions are poorly understood in hepatocellular carcinoma (HCC). Thus, we analyzed the cell-specific aspects of Axl in liver cancer cells and in the tumor microenvironment. We show that tumor-intrinsic Axl expression decreased the survival of mice and elevated the number of pulmonary metastases in a model of resection-based tumor recurrence. Axl expression increased the invasion of hepatospheres by the activation of Akt signaling and a partial epithelial-to-mesenchymal transition (EMT). However, the liver tumor burden of Axl+/+ mice induced by diethylnitrosamine plus carbon tetrachloride was reduced compared to systemic Axl-/- mice. Tumors of Axl+/+ mice were highly infiltrated with cytotoxic cells, suggesting a key immune-modulatory role of Axl. Interestingly, hepatocyte-specific Axl deficiency did not alter T cell infiltration, indicating that these changes are independent of tumor cell-intrinsic Axl. In this context, we observed an upregulation of multiple chemokines in Axl+/+ compared to Axl-/- tumors, correlating with HCC patient data. In line with this, Axl is associated with a cytotoxic immune signature in HCC patients. Together these data show that tumor-intrinsic Axl expression fosters progression, while tumor-extrinsic Axl expression shapes an inflammatory microenvironment.

Abstract 1337: Characterization of anti-AXL CAR-NK cell therapy for the treatment of melanoma

Abstract AXL is a receptor tyrosine kinase (RTK) that is commonly expressed in metastatic melanoma and several other forms of cancer. Activation of AXL signaling is linked to tumor cell growth, invasion, metastatic transformation, drug resistance, and immune response regulation. However, treatment of metastatic melanoma continues to present clinical challenges due to its capacity to rapidly develop drug resistance, which manifests under the influence of AXL signaling. As such, AXL may be a viable antigen target for immunotherapies. Despite their successes in hematological malignancies, chimeric antigen receptor (CAR)-T cell therapies remain limited by their susceptibility to causing off-target toxicity. In contrast, natural killer (NK) cells are not associated with such risks, which makes them clinically appealing as an alternative to T cells. However, studies on the application of CAR-NK cells to treat solid tumors remain acutely scarce. To explore the clinical viability of CAR-NK cells for the treatment of metastatic melanoma, AXL-specific CAR-NK cells were generated by transfecting NK cells obtained from NK cell lines. Preliminary data from a cytotoxicity assay indicated that the cytotoxicity of CAR-NK92-MI cells against AXL-positive melanoma cell lines was significantly stronger (up to a 10-fold difference) than the corresponding parental cells. Further in vitro characterization of this CAR-NK cell line and other CAR-NK cell lines, as well as in vivo evaluation of their efficacy in a mouse xenograft model of melanoma metastasis, is underway. Citation Format: Winston Hibler, Glenn Merlino, Yan Lin Yu. Characterization of anti-AXL CAR-NK cell therapy for the treatment of melanoma [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 1337.

Abstract 1941: AXL activation promotes adaptive resistance to KRAS-G12C inhibitors in KRAS-G12C-mutated non-small cell lung cancer

Abstract Background: KRAS is the most frequent targetable oncogene in non-small cell lung cancer (NSCLC). Recently, novel KRAS inhibitor have been clinically developed for treatment of KRAS G12C-mutated NSCLC patients. However, it is difficult to achieve complete remission of tumor. Therefore, the optimal combined therapeutic intervention with KRAS G12C inhibitors has a potentially crucial role in the clinical outcomes of patients. In this study, we focused on the mechanisms underlying adaptive resistance to KRAS G12C inhibitors and therapeutic strategies required to overcome them. Methods: We used KRAS G12C-mutated NSCLC cell lines to evaluate the adaptive response to KRAS G12C inhibitors in vitro and in vivo. We also investigated the correlation between AXL expression in pre-treated tumors and clinical outcomes with sotorasib for KRAS G12C-mutated NSCLC patients. Results: We revealed that AXL signaling leads to the adaptive resistance to KRAS G12C inhibitors in KRAS-G12C mutated NSCLC, activation of which is induced by GAS6 production via transcriptional coactivator YAP. AXL inhibition reduced the viability of AXL-overexpressing KRAS G12C-mutated lung cancer cells by enhancing KRAS G12C inhibition-induced apoptosis. In xenograft models of AXL-overexpressing KRAS G12C-mutated lung cancer treated with KRAS G12C inhibitors, initial combination therapy with AXL inhibitor markedly delayed tumor regrowth compared with KRAS G12C inhibitor alone or the combination after acquired resistance to KRAS G12C inhibitor. AXL was highly expressed in clinical specimens of KRAS G12C-mutated lung cancers and its high expression was associated with a low treatment response to sotorasib. Conclusions: These results indicated pivotal roles for AXL activation and its inhibition in the intrinsic resistance to KRAS G12C inhibitor. Citation Format: Kenji Morimoto, Tadaaki Yamada, Soichi Hirai, Yuki Katayama, Kei Kunimasa, Takaaki Sasaki, Makoto Nishida, Satoshi Watanabe, Shinsuke Shiotsu, Hisanori Uehara, Koichi Takayama. AXL activation promotes adaptive resistance to KRAS-G12C inhibitors in KRAS-G12C-mutated non-small cell lung 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 1941.

AXL signal mediates adaptive resistance to KRAS G12C inhibitors in KRAS G12C-mutant tumor cells

Recently, novel Kirsten rat sarcoma viral oncogene homolog (KRAS) inhibitors have been clinically developed to treat KRAS G12C-mutated non-small cell lung cancer (NSCLC) patients. However, achieving complete tumor remission is challenging. Therefore, the optimal combined therapeutic intervention with KRAS G12C inhibitors has a potentially crucial role in the clinical outcomes of patients. We investigated the underlying molecular mechanisms of adaptive resistance to KRAS G12C inhibitors in KRAS G12C-mutated NSCLC cells to devise a strategy preventing drug-tolerant cell emergence. We demonstrate that AXL signaling led to the adaptive resistance to KRAS G12C inhibitors in KRAS G12C-mutated NSCLC, activation of which is induced by GAS6 production via YAP. AXL inhibition reduced the viability of AXL-overexpressing KRAS G12C-mutated lung cancer cells by enhancing KRAS G12C inhibition-induced apoptosis. In xenograft models of AXL-overexpressing KRAS G12C-mutated lung cancer treated with KRAS G12C inhibitors, initial combination therapy with AXL inhibitor markedly delayed tumor regrowth compared with KRAS G12C inhibitor alone or with the combination after acquired resistance to KRAS G12C inhibitor. These results indicated pivotal roles for the YAP-GAS6-AXL axis and its inhibition in the intrinsic resistance to KRAS G12C inhibitor.

Predicting prognosis and immune status in sarcomas by identifying necroptosis-related lncRNAs.

Sarcomas are a type of highly heterogeneous malignant tumors originating from mesenchymal tissues. Necroptosis is intricately connected to the oncogenesis and progression of tumors. The main goal of this research is to assess the prognostic value of necroptosis-related lncRNAs (NRlncRNAs) in sarcomas and to develop a risk model based on NRlncRNAs to evaluate prognostic and immune status of the sarcomas. We screened NRlncRNAs using the gene co-expression network, developed a prognostic risk model of sarcomas, and then verified the model. Following that, various bioinformatics analysis algorithms were employed to analyze the distinct characteristics of patients of the risk model. Furthermore, the function and regulatory mechanism of NRlncRNA SNHG6 in sarcomas were investigated through osteosarcoma cell experiments, such as qRT-PCR, Western blot, CCK-8, clone formation, and transwell assay. We successfully developed a NRlncRNAs-related prognostic risk model and screened 5 prognosis-related NRlncRNAs, with SNGH6 being the most significant for prognosis of patients. According to results, the significant differences exist in prognosis, clinical characteristics, and tumor immune status among patients of the risk model. The experiments of osteosarcoma cells demonstrated that NRlncRNA SNHG6 knockdown significantly attenuated the cells' proliferation, migration, and invasion. qRT-PCR and WB results showed that SNHG6 regulated AXL and AKT signaling. We have developed an innovative investigation on NRlncRNAs, which can serve as a reference for diagnosis, therapy, and prognosis of sarcomas. Additionally, we demonstrated that NRlncRNA SNHG6 regulated AXL and AKT signaling in osteosarcoma cells and the proliferation, migration, and invasion of tumor cells.

RNASE4 promotes malignant progression and chemoresistance in hypoxic glioblastoma via activation of AXL/AKT and NF-κB/cIAPs signaling pathways.

Glioblastoma (GBM) is the most malignant brain tumor frequently characterized by a hypoxic microenvironment. In this investigation, we unveiled unprecedented role of Ribonuclease 4 (RNASE4) in GBM pathogenesis through integrative methodologies. Leveraging The Cancer Genome Atlas (TCGA) dataset and clinical specimens from normal brain tissues, low- and high-grade gliomas, alongside rigorous in vitro and in vivo functional analyses, we identified a consistent upregulation of RNASE4 correlating with advanced GBM pathological stages and poor clinical survival outcomes. Functional assays corroborated the pivotal influences of RNASE4 on key tumorigenic processes such as cell proliferation, migration, invasion, stemness properties and temozolomide (TMZ) resistance. Further, Gene Set Enrichment Analysis (GSEA) illuminated the involvement of RNASE4 in modulating epithelial-mesenchymal transition (EMT) via activation of AXL, AKT and NF-κB signaling pathways. Furthermore, recombinant human RNASE4 (hRNASE4)-mediated NF-κB activation through IκBα phosphorylation and degradation could result in the upregulation of inhibitors of apoptosis proteins (IAPs), such as cIAP1, cIAP2, and SURVIVIN. Notably, treating RNASE4-induced TMZ-resistant cells with the SURVIVIN inhibitor YM-155 significantly restored cellular sensitivity to TMZ therapy. Herein, this study positions RNASE4 as a potent prognostic biomarker and therapeutic target, offering new insights into molecular pathogenesis of GBM and new avenues for future therapeutic interventions.

Apoptosis recognition receptors regulate skin tissue repair in mice.

Apoptosis and clearance of apoptotic cells via efferocytosis are evolutionarily conserved processes that drive tissue repair. However, the mechanisms by which recognition and clearance of apoptotic cells regulate repair are not fully understood. Here, we use single-cell RNA sequencing to provide a map of the cellular dynamics during early inflammation in mouse skin wounds. We find that apoptotic pathways and efferocytosis receptors are elevated in fibroblasts and immune cells, including resident Lyve1+ macrophages, during inflammation. Interestingly, human diabetic foot wounds upregulate mRNAs for efferocytosis pathway genes and display altered efferocytosis signaling via the receptor Axl and its ligand Gas6. During early inflammation in mouse wounds, we detect upregulation of Axl in dendritic cells and fibroblasts via TLR3-independent mechanisms. Inhibition studies in vivo in mice reveal that Axl signaling is required for wound repair but is dispensable for efferocytosis. By contrast, inhibition of another efferocytosis receptor, Timd4, in mouse wounds decreases efferocytosis and abrogates wound repair. These data highlight the distinct mechanisms by which apoptotic cell detection coordinates tissue repair and provides potential therapeutic targets for chronic wounds in diabetic patients.

Gas6-Axl Signaling Induces SRF/MRTF-A Gene Transcription via MICAL2.

MICAL2 is an actin-regulatory protein that functions through redox modification of actin. Nuclear localized MICAL2 triggers the disassembly of nuclear actin, which subsequently leads to nuclear retention of the actin-binding transcriptional coregulator myocardin-related transcription factor-A (MRTF-A), which leads to the activation of serum response factor (SRF)/MRTF-A-dependent gene transcription. In this study, we show that the secreted signaling protein GAS6 (growth-arrest specific 6) and its cognate receptor Axl, a transmembrane tyrosine kinase, also induce the activation of SRF/MRTF-A and their downstream target genes. We find that serum-induced SRF/MRTF-A-dependent gene expression can be blocked, in part, by the inhibition of Axl signaling. Furthermore, we find that Gas6/Axl-induced SRF/MRTF-A-dependent transcription is dependent on MICAL2. Gas6/Axl promotes cell invasion, which is blocked by MICAL2 knockdown, suggesting that MICAL2 promotes cytoskeletal effects of the Gas6/Axl pathway. We find that Gas/6/Axl signaling promotes the nuclear localization of MICAL2, which may contribute to the ability of Gas6/SRF to augment SRF/MRTF-A-dependent gene transcription. The physiological significance of the Gas6/Axl-MICAL2 signaling pathway described here is supported by the marked gene expression correlation across a broad array of different cancers between MICAL2 and Axl and Gas6, as well as the coexpression of these genes and the known SRF/MRTF-A target transcripts. Overall, these data reveal a new link between Gas6/Axl and SRF/MRTF-A-dependent gene transcription and link MICAL2 as a novel effector of the Gas6/Axl signaling pathway.

Structure-based drug discovery of novel fused-pyrazolone carboxamide derivatives as potent and selective AXL inhibitors

As a novel and promising antitumor target, AXL plays an important role in tumor growth, metastasis, immunosuppression and drug resistance of various malignancies, which has attracted extensive research interest in recent years. In this study, by employing the structure-based drug design and bioisosterism strategies, we designed and synthesized in total 54 novel AXL inhibitors featuring a fused-pyrazolone carboxamide scaffold, of which up to 20 compounds exhibited excellent AXL kinase and BaF3/TEL-AXL cell viability inhibitions. Notably, compound 59 showed a desirable AXL kinase inhibitory activity (IC50: 3.5 nmol/L) as well as good kinase selectivity, and it effectively blocked the cellular AXL signaling. In turn, compound 59 could potently inhibit BaF3/TEL-AXL cell viability (IC50: 1.5 nmol/L) and significantly suppress GAS6/AXL-mediated cancer cell invasion, migration and wound healing at the nanomolar level. More importantly, compound 59 oral administration showed good pharmacokinetic profile and in vivo antitumor efficiency, in which we observed significant AXL phosphorylation suppression, and its antitumor efficacy at 20 mg/kg (qd) was comparable to that of BGB324 at 50 mg/kg (bid), the most advanced AXL inhibitor. Taken together, this work provided a valuable lead compound as a potential AXL inhibitor for the further antitumor drug development.

AXL receptor tyrosine kinase inhibition improves the anti-tumor effects of CD8+ T cells by inducing CD103+ dendritic cell-mediated T cell priming

AXL is a member of TAM receptor family and has been highlighted as a potential target for cancer treatment. Accumulating evidence has uncovered the critical role of the AXL signaling pathway in tumor growth, metastasis, and resistance against anti-cancer drugs, as well as its association with cancer immune escape. However, the function of AXL as a manipulator of the immune system in the tumor microenvironment (TME) remains unclear. Therefore, in this study, we investigated the impact of AXL on immune cells in the TME of a syngeneic tumor model using AXL knockout (AXL−/−) mice. Compared to AXL wild-type (AXL+/+) mice, tumor growth was significantly suppressed in AXL−/− mice, and an induced population of tumor-infiltrated CD8+ T cells and CD103+ dendritic cells (DCs) was observed. The change of CD8+ T cells and CD103+ DCs was also confirmed in tumor-draining lymph nodes (TdLN). In addition, the clonal expansion of OVA-specific CD8+ T cells was dominant in AXL−/− mice. Finally, anti-PD-1 treatment evidenced synergistic anti-cancer effects in AXL−/− mice. Overall, our data indicate that AXL signaling may inhibit the clonal expansion of tumor-specific CD8+ T cells through the regulation of the migration of CD8+ T cells and DCs in TME. Thus, AXL may be a powerful molecular target to improve anti-cancer effects through single or combined therapy with immune checkpoint inhibitors (ICI).

LCK and resistance to cytotoxic chemotherapy via activating an AXL-PEAK1 signaling axis in cholangiocarcinoma.

27 Background: Cholangiocarcinoma (CCA) is a devastating cancer with few effective treatment options. We have previously discovered LCK can activate AXL, a TAM receptor tyrosine kinase (RTK), by phosphorylation of AXL-Y866 ( J Hepatol 2022). AXL is known to confer therapeutic resistance to solid cancers. However, the role of AXL in CCA, and the impact of AXL-Y866 activation by LCK still remains to be elucidated. Here, we investigated the significance of AXL expression, signaling, and activation by LCK on Y866. Methods: We first evaluated the expression levels of AXL in CCA and its association with patient outcome using The Cancer Genome Atlas (TCGA) dataset. Next, to evaluate whether AXL inactivation sensitizes CCA cells to gemcitabine and cisplatin (GC), AXL downregulation was achieved via siRNA approach and the selective AXL inhibitor bemcentinib (Bem) using human CCA cell lines, HuCCT1 and RBE, and murine SB-1. We examined 50% inhibitory concentration (IC50) value on GC with or without AXL knockdown (KD) using cell viability assay. Then we assessed the efficacy of the combination of GC and Bem utilizing Calcusyn software and apoptosis by Annexin V assay. I n vivo efficacy was assessed using both a patient derived CCA xenograft and SB-1 a syngeneic model of CCA treated with vehicle, GC, Bem, or the combination. Next, we defined the interactome of wildtype AXL- Y866 compared to AXL-Y866F using biotin proximity labelling methods (BioID), validation of downstream target proteins using Western blot (WB), and a functional study with AXL-/- cells reconstituted with either AXL WT, or AXL Y866F. Results: In TCGA cohorts, AXL transcripts are more abundant than in normal adjacent liver, and higher levels are correlated with worse clinical outcome. In in vitro study, IC50 values of GC decreased after AXL KD. Synergistic effects were observed in the combination. The combination caused increased apoptosis compared to other treatments. In the in vivo studies, the combination suppressed tumor growth and the Ki67 levels, and the phosphorylation levels of PEAK1 decreased in the combination group compared to other groups. In BioID experiments, among the 222 proteins which were detected in both AXL WT and AXL Y866F interactomes, PEAK1 kinase, which localizes to actin cytoskeleton and focal adhesions, was most altered when Y866 was inactivated by the Y866F mutation. In gene ontology analysis, cell-cell adhesion and focal adhesion related proteins were enriched. In WB, we validated that the phosphorylation of PEAK1 decreased after AXL or LCK knockout (KO) and after Bem treatment in above in vivo study. In cell viability assay, reconstitution of AXL KO cells with WT AXL increased the IC50 to GC while reconstitution with AXL-Y866F did not. Conclusions: AXL inhibition sensitizes CCA cells to cytotoxic chemotherapy in preclinical model. LCK-AXL Y866-PEAK1 signaling axis is a potential target for the treatment of CCA.