Small Molecule Inhibitor Of AXL Research Articles

S100A10 Is a Critical Mediator of GAS6/AXL-Induced Angiogenesis in Renal Cell Carcinoma.

Angiogenesis is a hallmark of cancer that promotes tumor progression and metastasis. However, antiangiogenic agents have limited efficacy in cancer therapy due to the development of resistance. In clear cell renal cell carcinoma (ccRCC), AXL expression is associated with antiangiogenic resistance and poor survival. Here, we establish a role for GAS6/AXL signaling in promoting the angiogenic potential of ccRCC cells through the regulation of the plasminogen receptor S100A10. Genetic and therapeutic inhibition of AXL signaling in ccRCC tumor xenografts reduced tumor vessel density and growth under the renal capsule. GAS6/AXL signaling activated the expression of S100A10 through SRC to promote plasmin production, endothelial cell invasion, and angiogenesis. Importantly, treatment with the small molecule AXL inhibitor cabozantinib or an ultra-high affinity soluble AXL Fc fusion decoy receptor (sAXL) reduced the growth of a pazopanib-resistant ccRCC patient-derived xenograft. Moreover, the combination of sAXL synergized with pazopanib and axitinib to reduce ccRCC patient-derived xenograft growth and vessel density. These findings highlight a role for AXL/S100A10 signaling in mediating the angiogenic potential of ccRCC cells and support the combination of AXL inhibitors with antiangiogenic agents for advanced ccRCC. SIGNIFICANCE: These findings show that angiogenesis in renal cell carcinoma (RCC) is regulated through AXL/S100A10 signaling and support the combination of AXL inhibitors with antiangiogenic agents for the treatment of RCC.

A Functional Role of GAS6/TAM in Nonalcoholic Steatohepatitis Progression Implicates AXL as Therapeutic Target

Background and AimsGAS6 signaling, through the TAM receptor tyrosine kinases AXL and MERTK, participates in chronic liver pathologies. Here, we addressed GAS6/TAM involvement in Non-Alcoholic SteatoHepatitis (NASH) development.MethodsGAS6/TAM signaling was analyzed in cultured primary hepatocytes, hepatic stellate cells (HSC) and Kupffer cells (KCs). Axl-/-, Mertk-/- and wild-type C57BL/6 mice were fed with Chow, High Fat Choline-Deficient Methionine-Restricted (HFD) or methionine-choline-deficient (MCD) diet. HSC activation, liver inflammation and cytokine/chemokine production were measured by qPCR, mRNA Array analysis, western blotting and ELISA. GAS6, soluble AXL (sAXL) and MERTK (sMERTK) levels were analyzed in control individuals, steatotic and NASH patients.ResultsIn primary mouse cultures, GAS6 or MERTK activation protected primary hepatocytes against lipid toxicity via AKT/STAT-3 signaling, while bemcentinib (small molecule AXL inhibitor BGB324) blocked AXL-induced fibrogenesis in primary HSCs and cytokine production in LPS-treated KCs. Accordingly; bemcentinib diminished liver inflammation and fibrosis in MCD- and HFD-fed mice. Upregulation of AXL and ADAM10/ADAM17 metalloproteinases increased sAXL in HFD-fed mice. Transcriptome profiling revealed major reduction in fibrotic- and inflammatory-related genes in HFD-fed mice after bemcentinib administration. HFD-fed Mertk-/- mice exhibited enhanced NASH, while Axl-/- mice were partially protected. In human serum, sAXL levels augmented even at initial stages, whereas GAS6 and sMERTK increased only in cirrhotic NASH patients. In agreement, sAXL increased in HFD-fed mice before fibrosis establishment, while bemcentinib prevented liver fibrosis/inflammation in early NASH.ConclusionAXL signaling, increased in NASH patients, promotes fibrosis in HSCs and inflammation in KCs, while GAS6 protects cultured hepatocytes against lipotoxicity via MERTK. Bemcentinib, by blocking AXL signaling and increasing GAS6 levels, reduces experimental NASH, revealing AXL as an effective therapeutic target for clinical practice.

Axl Inhibitor R428 Enhances TRAIL-Mediated Apoptosis Through Downregulation of c-FLIP and Survivin Expression in Renal Carcinoma.

R428, a selective small molecule Axl inhibitor, is known to have anti-cancer effects, such as inhibition of invasion and proliferation and induction of cell death in cancer cells. The Axl receptor tyrosine kinase is highly expressed in cancer cells and the level of Axl expression is associated with survival, metastasis, and drug resistance of many cancer cells. However, the effect of Axl inhibition on overcoming anti-cancer drugs resistance is unclear. Therefore, we investigated the capability of Axl inhibition as a therapeutic agent for the induction of TRAIL (tumor necrosis factor-related apoptosis-inducing ligand) sensitivity. In this study, R428 markedly sensitized cancer cells to TRAIL-induced apoptotic cell death, but not in normal human skin fibroblast (HSF) and human umbilical vein cells (EA.hy926). Moreover, knockdown of Axl by siRNA also increased TRAIL-induced apoptosis. R428 decreased c-FLIP proteins levels via induction of miR-708 expression and survivin protein levels at the post-translational level, and we found that knockdown of Axl also decreased both c-FLIP and survivin protein expression. Overexpression of c-FLIP and survivin markedly inhibited R428 plus TRAIL-induced apoptosis. Furthermore, R428 sensitized cancer cells to multiple anti-cancer drugs-mediated cell death. Our results provide that inhibition of Axl could improve sensitivity to TRAIL through downregulation of c-FLIP and survivin expression in renal carcinoma cells. Taken together, Axl may be a tempting target to overcome TRAIL resistance.

Abstract 2030: Inhibiting the GAS6/AXL axis suppresses tumor progression by blocking the interaction between cancer-associated fibroblasts and cancer cells in gastric carcinoma

Abstract Cancer-associated fibroblasts (CAF) are a major component of tumor stroma and their effect on the progression of gastric carcinoma (GC) has recently been demonstrated. However, agents targeting the interaction between CAF and GC cells have not been applied in a clinical setting. The aim of this study was to investigate the effect of an AXL inhibitor on CAF-induced GC progression. We examined growth arrest specific factor 6 (GAS6) expression and phosphorylation of AXL in various cell lines, including GC cells and non-cancerous cells, by qPCR, western blot, and immunocytochemistry. We investigated the role of CAF-derived GAS6 on the migration and proliferation of GC cells using migration and cell survival assays. The effect of the AXL inhibitor, Bemcentinib, on the CAF-induced aggressive phenotype of GC cells was also investigated. Finally, we performed immunohistochemistry to measure the phosphorylation of AXL in a tissue microarray composed of 175 GC tissues, and evaluated its correlation with the prognosis of GC patients. qPCR and western blot analysis showed that GAS6 expression was higher in CAF relative to other cells. We found that CAF increased the phosphorylation of AXL (P-AXL), differentiation into a mesenchymal-like phenotype, and cell survival in GC cell lines. When the expression of AXL was inhibited in GC cells, the effect of CAF was reduced. In addition, Bemcentinib, a small molecule inhibitor of AXL, suppressed the effects of CAF on GC cell lines. In GC tissues, P-AXL positively correlated with the expression of vimentin (P < 0.001) and high levels of P-AXL were significantly associated with poor overall survival (P = 0.022).These findings suggest that CAF is a major source of GAS6 in the GC microenvironment and actively promotes an aggressive phenotype in GC cells through AXL activation. We conclude that an AXL inhibitor may be a novel agent for GC treatment. Citation Format: Dagyoeng Lee, Jongsu Woo, Cheong A Bae, In-Hye Ham, Hye Jung Oh, Sang-Yong Son, Sang-Uk Han, Tae-Min Kim, Jung Hwan Yoon, Won Sang Park, Hoon Hur. Inhibiting the GAS6/AXL axis suppresses tumor progression by blocking the interaction between cancer-associated fibroblasts and cancer cells in gastric carcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2030.

Abstract 3969: TP-0903, a potent AXL receptor tyrosine kinase inhibitor, enhances the activity of anti-PD-1 therapy in a metastatic preclinical syngeneic model of breast cancer

Abstract The high rate of non-responders to immune checkpoint inhibitors (ICI) represents significant challenges in the field of immune-oncology. Breast cancer has emerged as a cancer type that responds poorly to ICI. Therefore, there is an urgent need to better understand how cancer cells escape immune surveillance and resist immune attacks. Cancer cell clones with mesenchymal features seem to be less susceptible to attacks by immune cells. Hence, epithelial-to-mesenchymal transition (EMT) targeting agents such as TP-0903 are emerging as potential combination candidates to enhance immune checkpoint inhibition. AXL is overexpressed in a variety of cancers, often driving the pathogenesis and progression of disease. AXL overexpression induces cancer growth, invasion, metastasis, drug resistance, and mesenchymal characteristics. Aside from cancer cells, AXL is also expressed on several types of immune cells including macrophages and dendritic cells. Recently, it has been reported that AXL plays an important role as a negative regulator of immune response, contributing to an anti-tumor immune suppression. We have previously identified TP-0903 to be a potent small molecule inhibitor of AXL (IC50=14 nM) capable of reversing EMT. In this study, we evaluated whether TP-0903 could enhance the ICB effect in an ICB-resistant triple negative, metastatic breast cancer mouse model (4T1). In the 4T1 syngeneic model, anti-PD-1 monotherapy failed to inhibit tumor growth indicating that this tumor is resistant to anti-PD-1 treatment. The combination of TP-0903 and anti-PD-1 resulted in statistically significant tumor growth inhibition versus TP-0903 monotherapy (p<0.05). We hypothesized that the combination effect was influenced by potential CD8+ T cell depletion, and further investigated the effects of TP-0903 on immune cells in spleen and tumors. Tumor growth inhibition was found to be associated with a decrease in myeloid-derived suppressor cells (MDSC) in the spleen and an increase in infiltration and activation of dendritic cells (DCs) in the tumor. Gene expression analysis revealed that TP-0903 treatment decreased multiple immunosuppressive cytokines and chemokines including IL-6 and G-CSF in vivo. These results suggest that TP-0903 modulates the immune-suppressive tumor microenvironment (TME) to reinvigorate T cell immunity in anti-PD-1 resistant 4T1 tumors. In conclusion, AXL inhibition with TP-0903 modulates TME and enhances the anti-tumor effects of ICBs in an anti-PD-1 resistant, metastatic breast cancer mouse model. These findings support additional clinical testing of TP-0903 in combination with ICBs, which is currently being investigated in patients with advanced solid tumors in an ongoing clinical study (NCT02729298). Citation Format: Yuka Kumagai, Jun Oishi, Megumi Nakamura, Jason M. Foulks, Clifford J. Whatcott, Steven L. Warner, David J. Bearss, Masashi Goto. TP-0903, a potent AXL receptor tyrosine kinase inhibitor, enhances the activity of anti-PD-1 therapy in a metastatic preclinical syngeneic model of breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3969.

Abstract 2197: The AXL kinase inhibitor, TP-0903, demonstrates efficacy in preclinical models of colorectal cancer independent of KRAS mutation status

Abstract Colorectal cancer (CRC) is the third leading cause of cancer-related mortality in the US (2017). Most patients present with stage II or III disease at diagnosis, with the 5-year survival rate between 53-89%. Survival in patients with stage IV CRC, however, is a discouraging 11%. Metastasis in CRC is linked to a mesenchymal phenotype, which is associated with chemoresistance. AXL, a receptor tyrosine kinase, promotes the mesenchymal phenotype in cancer cells and its expression is associated with drug resistance and poor outcomes. TP-0903, a clinical-stage, investigational small molecule inhibitor of AXL has been shown to reverse the mesenchymal phenotype and restore drug sensitivity in cells that no longer respond to standard agents in preclinical models. TP-0903 is hypothesized to be an active agent in CRC through reversal of the mesenchymal phenotype. In cell viability assays of CRC lines, TP-0903 treatment resulted in IC50 values ranging from 4.5 – 123 nM. Notably, cell growth inhibition by TP-0903 was independent of KRAS mutation status; the KRAS mutant HCT-116 line was the most sensitive CRC cell line tested. Mesenchymal markers, including Snail, were suppressed by 7.6-fold (mRNA) and 4.9-fold (protein) in the HCT-116 line at 500 nM. TP-0903 activity was also assessed in vivo using two KRAS mutant CRC models: HCT-116 and a patient-derived xenograft (PDX) model. In the HCT-116 xenograft model, single agent TP-0903 treatment achieved 69% tumor growth inhibition (%TGI) with an oral dosing schedule at 40 mg/kg. In a KRAS-mutant PDX model, TP-0903 achieved 44% TGI when mice were dosed at 40 mg/kg. Pharmacodynamic analyses were performed on tissues from the HCT-116 and PDX models. The ligand for AXL, GAS6, was significantly upregulated in tissues after TP-0903 treatment in both CRC in vivo models while soluble AXL and GAS6 were significantly downregulated in plasma in the PDX model. Furthermore, Axin2, a Wnt/β-catenin regulated gene, was downregulated by TP-0903 in tumor tissue from the PDX model, suggesting inhibition of the Wnt/βcatenin pathway. These data support a potential role for AXL in the promotion of the mesenchymal phenotype in CRC, and showed that AXL inhibition by TP-0903 suppressed the mesenchymal phenotype and was effective against CRC cells regardless of KRAS mutation status. These observations support further clinical investigation of TP-0903 as a potential therapeutic agent in metastatic CRC. A Phase I trial with this investigational agent is ongoing, including patients with KRAS mutant CRC (clincaltrials.gov, NCT02729298). Citation Format: Ryan Mangelson, Peter Peterson, Jason M. Foulks, Yuta Matsumura, Lars Mouritsen, Clifford J. Whatcott, David J. Bearss, Steven L. Warner. The AXL kinase inhibitor, TP-0903, demonstrates efficacy in preclinical models of colorectal cancer independent of KRAS mutation status [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2197.

Abstract 2006: Targeting AXL kinase with TP-0903 successfully reverses the mesenchymal phenotype and extends survival in preclinical models of advanced ovarian cancer

Abstract Epithelial-to-mesenchymal transition (EMT) is a critical step in the progression of ovarian cancer (OVCA), which drives local invasion, metastasis and drug resistance leading to poor survival. AXL, a receptor tyrosine kinase, functions as a molecular driver of EMT in multiple cancers, including OVCA. The high mortality of this tumor is explained by the fact that the majority (75%) of patients present at an advanced stage, with widely metastatic disease within the peritoneal cavity often associated with ascites. The extent of ascites is a prognostic factor for survival, impacts quality of life, and correlates with the EMT phenotype. Approaches to block or reverse EMT are needed to improve the prognosis of OVCA patients, particularly those with refractory or early relapse (<6 months) disease following debulking surgery and conventional adjuvant treatments. TP-0903 is a potent, small molecule AXL inhibitor that has activity in reversing EMT in multiple models of disease and embryonic development. The objective of this study was to explore the anti-tumor activity in preclinical mesenchymal OVCA-derived models, which may provide rationale to evaluate TP-0903 in treatment-resistant or refractory OVCA patients. TP-0903 showed potent effects on cell viability in multiple OVCA-derived cell lines. The IC50 values in cell viability studies ranged from 33 nM (OVTOKO cells) to 840 nM (OVMANA cells). Kuramochi cells represent the most common ovarian cancer subtype, high-grade serous ovarian cancer and was particularly platinum-resistant (>5 μM), yet sensitive to TP-0903 (210 nM). Baseline phospho-AXL (Y702) was exceptionally high in Kuramochi cells and TP-0903 inhibited this phosphorylation at concentrations as low as 100 nM. TP-0903 reversed EMT in OVCA cells as evident by the down-regulation of mesenchymal markers including Snail and Slug. Consistent with the reversal of the EMT, TP-0903 inhibited the migration of ES-2 OVCA cells in a scratch assay. TP-0903 suppressed ascites development in preclinical models of OVCA and inhibited metastatic intraperitoneal tumor dissemination. Treatment suppressed ascites development (ascites volume, vehicle: 3.34 mL, TP-0903: 0.28 mL; abdominal circumference, vehicle: 7.96 cm (day 15), TP-0903: 6.82 cm (day 15), p<0.05) in an orthotopic ES-2 model and extended overall survival compared to vehicle or cisplatin alone. Phospho-AXL modulation and changes in other mechanism-validating biomarkers were observed in the ES-2 model. Similar preclinical activities, including decreased ascites volume, were observed in A2780cis and OVCAR-3 xenograft models. These results support further clinical evaluation of TP-0903 in either single-agent or combination regimens treating recurrent or refractory OVCA. TP-0903 is investigated in a Phase I trial that includes an expansion cohort of this patient population (NCT02729298). Citation Format: Nozomi Tomimatsu, Ken Fujimura, Yuta Matsumura, Hiroki Umehara, Lars Mouritsen, Steven L. Warner, David J. Bearss. Targeting AXL kinase with TP-0903 successfully reverses the mesenchymal phenotype and extends survival in preclinical models of advanced ovarian cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2006.

Abstract 2638: Galectin-3 activates the receptor tyrosine kinase Tyro3 and stimulates ERK signaling, cell survival and migration in human head and neck cancer cells

Abstract The beta-galactoside-binding protein galectin-3 (Gal-3) has been shown to influence the tumorigenic behaviour of cancer cells, and elevated serum levels of Gal-3 have been linked to tumor metastasis in several different cancers. Previously, Gal-3 was shown to be a ligand MerTK, a member of the TAM (Tyro3, Axl, MerTK) subfamily of receptor tyrosine kinases (RTKs) - these RTKs are implicated in tumorigenesis and/or enabling tumor chemoresistance in many different cancers. However, it is not known whether Gal-3 is also a ligand for the other two TAM RTKs, nor what signaling pathways it activates to regulate cancer cell functions. This study is aimed at determining the ligand properties of Gal-3 against Tyro3 and Axl RTKs in human cancer cells and the oncogenic signal pathways linked to them. The cultured human head and neck squamous cell carcinoma (HNSCC) cell line SCC-25 was determined by western blot and qPCR to express both Axl and Tyro3, but not MerTK. Recombinant Gal-3 and the TAM ligands Gas6 and ProS1 were added to serum-starved cells over a time-period of minutes and cells lysed to determine activation/phosphorylation of RTKs and intracellular signal mediators by western blotting. Longer incubations were performed to measure cell viability (MTS assay) and cell migration rate (scratch assay). All experiments were carried out a minimum three times. The known TAM ligands Gas6 and ProS1 stimulated TAM RTKs differentially in SCC-25 cells: Gas6 activated Axl strongly within minutes, with ProS1 having a weak effect. In contrast, ProS1 was the strongest ligand for Tyro3, activating it by fourfold, followed by Gal-3 at threefold and Gas6 at twofold. All three exogenous proteins also rapidly stimulated ERK1/2 phosphorylation by two-fold, whereas only Gas6 and Gal-3 stimulated Akt phosphorylation. All three proteins significantly maintained cell survival during acute induction of apoptosis by staurosporine. However, only Gas6 conferred a survival effect over long-term serum starvation-induced cell death. In addition, Gal-3 significantly stimulated cell migration during Axl blockade with the small molecule Axl inhibitor BGB324, further suggesting a role for Tyro3 in this effect. These results have shown that Gal-3 is a ligand for Tyro3 RTK, and that Gal-3 promotes cell survival and migration in HNSCC cells, coupled with activation of both the related signal pathways ERK and Akt. The data therefore reveal a new mechanism of Tyro3 activation; however, it remains to be determined whether Gal-3 interacts with the glycosyl chain on the RTK or else via other interfaces. Finally, cancer therapeutic strategies targeting Gal-3 action and/or cell surface glycosylation may be viable approaches in further research. Citation Format: Sassan Hafizi, Nour Al Kafri. Galectin-3 activates the receptor tyrosine kinase Tyro3 and stimulates ERK signaling, cell survival and migration in human head and neck cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2638.

Abstract 276: Targeting AXL sensitizes non-small cell lung cancer to ATR inhibitors by enhancing replication stress

Abstract Therapeutic resistance limits effective treatment of non-small cell lung cancer (NSCLC) and a better understanding of mechanisms contributing to resistance and strategies to overcome these are urgently needed. AXL, a TAM family receptor tyrosine kinase, has emerged as a key determinant of intrinsic and acquired resistance to chemotherapy, radiation and targeted therapies in NSCLC and other cancers, through its roles in mediating epithelial-mesenchymal transition (EMT) and immune escape. We previously showed that AXL may also play a role in DNA damage repair and that AXL overexpression mediated primary as well as acquired resistance to inhibitors of WEE1, a replication stress response kinase, in small cell lung cancer. In the present study, we further investigated the role of AXL in replication stress response. We found that, in NSCLC cell lines, AXL inhibition with the selective small-molecule AXL inhibitor BGB324 caused replication stress checkpoint activation, as indicated by increased RPA32 hyper-phosphorylation and ATR-mediated CHK1 phosphorylation. We further screened ATR inhibitors, VX-970 and AZD6738, in a panel of 20 NSCLC cell lines and correlated drug sensitivity with baseline expression of over 200 phosphorylated and total proteins, measured by reverse phase protein array. Notably, AXL was one of the biomarkers of resistance to the ATR inhibitor VX-970 (rho=0.52, p<0.05). Therefore, we hypothesized that AXL plays a unique role in regulating replication stress and targeting AXL will sensitize NSCLC cells to ATR inhibitors. Combination of BGB324 and ATR inhibitors (VX-970 and AZD6738) significantly decreased cell proliferation in a panel of human and GEMM-derived NSCLC cell lines as compared to single agents alone. In NSCLC cells with primary resistance to ATR inhibition, co-targeting AXL and ATR significantly increased RPA32 hyper-phosphorylation, concomitantly with increased DNA double strand breaks and inactivated G2/M checkpoint, resulting in mitotic catastrophe. AXL knockdown in a GEMM-derived Kras/Trp53 mutant NSCLC model also showed similar results. Notably, NSCLC cell lines with low levels of SLFN11 (a DNA/RNA helicase that induces replication arrest following DNA damage independently of ATR) were more sensitive to AXL/ATR co-targeting. In conclusion, these findings suggest that AXL may play a novel and unexpected role in regulating replication stress. Furthermore, our results show that targeting AXL sensitizes NSCLC cell lines with primary resistance to ATR inhibitors and that AXL/ATR inhibitor combinations could be useful in treating platinum- and PARP inhibitor-resistant SLFN11-low tumors. Citation Format: Kavya Ramkumar, Pan Tong, You-Hong Fan, David Peng, John V. Heymach, Don L. Gibbons, Jing Wang, Lauren A. Byers. Targeting AXL sensitizes non-small cell lung cancer to ATR inhibitors by enhancing replication stress [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 276.

Therapeutic Potential of Axl Blockade in BCR-ABL Negative Myeloproliferative Neoplasms (MPN)

Axl, a member of the TAM family of receptor tyrosine kinases, mediates survival and therapy resistance of different cancer cells. The Axl ligand growth-arrest specific gene 6 (Gas6) was discovered to promote proliferation of leukemia cells in acute and chronic myeloid leukemia and Axl was identified as a potential therapeutic target in these diseases. Based on these data we investigated the role of Axl in BCR-ABL negative myeloproliferative neoplasms (MPN) and the therapeutic potential of Axl blockade in this group of diseases.We studied the effects of Axl blockade using the small molecule Axl inhibitor BGB324 and performing a lentivirus shRNA mediated knockdown of Axl in human SET-2 and murine BaF3-Jak2V617F MPN cell lines. Pharmacologic Axl blockade resulted in a significant dose dependent decrease in viability of MPN cell lines as measured by WST-1 cell viability assay. Annexin+ staining revealed an increased rate of apoptotic cells upon BGB324 treatment for SET-2 (increase by 15% at 1µM, p<0.001) and BaF3-Jak2V617F cells (increase by 54% at 2µM, p<0.05). Moreover, Western Blot analysis showed higher levels of cleaved caspase 3 in BGB324 treated SET-2 cells and decreased levels of anti-apoptotic bcl-2 in BGB324 treated BaF3-Jak2V617F cells. Additionally, BrdU incorporation assays showed a dose dependent decrease in proliferating cells upon treatment with BGB324 in MPN cell lines (p<0.05). Genetic knockdown of Axl in SET-2 cells decreased cell viability by 75% (p<0.01), increased apoptosis levels as measured by Annexin+ staining by 61% (p<0.05) and decreased proliferation as measured by BrdU incorporation by 35% (p<0.001) compared to control-transduced cells. Furthermore, Western Blot analysis revealed that genetic knockdown of Axl resulted in decreased phosphorylation of Stat3 and Stat5 compared to control-transduced cells. Combined Axl and Jak2 blockade, using BGB324 and the Jak2-inhibitor ruxolitinib, showed additive effects on reducing cell viability in SET-2 and BaF3-Jak2V617F cells (p<0.01 and p<0.001, respectively). Western Blot analysis identified inhibition of Stat5 by BGB324 single treatment in SET-2 cells whereas additive effects of combined Axl and Jak2 blockade resulted from additional inhibition of Stat3. In BaF3-Jak2V617F cells, BGB324 single treatment resulted in downstream inhibition of Akt signaling whereas additive effects of combined Axl and Jak2 blockade were exerted via additional inhibition of Stat5, Stat3 and Erk.The finding that BGB324 inhibits growth of MPN cells was further corroborated in vivo. A xenograft tumor model with SET-2 cells was set up in vivo. SET-2 tumor bearing mice treated with BGB324 50mg/kg showed a slower tumor growth (n=8, p<0.01), with a 60% reduction of tumor weight compared to vehicle treated mice (n=8/8, p<0.01). As a second in vivo model, a systemic model of Jak2V617F driven disease was used. After intravenous injection of BaF3-Jak2V617F cells, mice were treated with 50mg/kg BGB324 or vehicle starting the day after inoculation. BGB324 treated mice had a longer overall survival compared to vehicle treated mice (n=10/11, p*<0.05).Furthermore, to evaluate the potential of BGB324 in primary MPN cells, peripheral blood mononuclear cells (PBMC) were isolated from MPN patients and healthy donors. Western Blot analysis showed higher levels of Axl expression by PBMC from MPN patients compared to PBMC from healthy donors. Moreover, colony-forming assays with PBMC were performed in the presence of different concentrations of BGB324. Here, a higher reduction in the number of colony forming units (BFU-E and CFU-GEMM) was observed in samples from MPN patients compared to healthy donors upon treatment with 1µM (77% vs. 5%, respectively; p<0.001) or 2µM (100% vs. 60%, respectively; p<0.01) of BGB324 (n=5/5).In conclusion, these data indicate therapeutic potential of Axl blockade in BCR-ABL negative MPN as monotherapy and in combination with Jak2-inhibition, supporting the need for clinical investigation. Disclosuresvon Amsberg:Novartis: Honoraria, Speakers Bureau; Ipson: Honoraria, Speakers Bureau; Bristol-Myers Squibb: Honoraria, Speakers Bureau; Sanofi: Honoraria, Speakers Bureau; Astellas: Honoraria, Speakers Bureau; MSD: Honoraria, Speakers Bureau. Loges:BerGenBio: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding.

MERTK Mediates Intrinsic and Adaptive Resistance to AXL-targeting Agents.

The TAM (TYRO3, AXL, MERTK) family receptor tyrosine kinases (RTK) play an important role in promoting growth, survival, and metastatic spread of several tumor types. AXL and MERTK are overexpressed in head and neck squamous cell carcinoma (HNSCC), triple-negative breast cancer (TNBC), and non-small cell lung cancer (NSCLC), malignancies that are highly metastatic and lethal. AXL is the most well-characterized TAM receptor and mediates resistance to both conventional and targeted cancer therapies. AXL is highly expressed in aggressive tumor types, and patients with cancer are currently being enrolled in clinical trials testing AXL inhibitors. In this study, we analyzed the effects of AXL inhibition using a small-molecule AXL inhibitor, a monoclonal antibody (mAb), and siRNA in HNSCC, TNBC, and NSCLC preclinical models. Anti-AXL-targeting strategies had limited efficacy across these different models that, our data suggest, could be attributed to upregulation of MERTK. MERTK expression was increased in cell lines and patient-derived xenografts treated with AXL inhibitors and inhibition of MERTK sensitized HNSCC, TNBC, and NSCLC preclinical models to AXL inhibition. Dual targeting of AXL and MERTK led to a more potent blockade of downstream signaling, synergistic inhibition of tumor cell expansion in culture, and reduced tumor growth in vivo Furthermore, ectopic overexpression of MERTK in AXL inhibitor-sensitive models resulted in resistance to AXL-targeting strategies. These observations suggest that therapeutic strategies cotargeting both AXL and MERTK could be highly beneficial in a variety of tumor types where both receptors are expressed, leading to improved survival for patients with lethal malignancies. Mol Cancer Ther; 17(11); 2297-308. ©2018 AACR.

1266P - Update on the randomised phase Ib/II study of the selective small molecule AXL inhibitor bemcentinib (BGB324) in combination with either dabrafenib/trametinib or pembrolizumab in patients with metastatic melanoma

Abstract Background Upregulation of the receptor tyrosine kinase Axl has been linked with both a reduced response to immune checkpoint blockade as well as the development of therapy resistance to BRAF directed therapies in melanoma. Bemcentinib is a first-in-class orally bioavailable selective inhibitor of Axl which is currently being explored in several phase II clinical trials. BGBIL006 (NCT02872259) is an open label phase Ib/II trial designed to explore whether combinations with bemcentinib improves ORR and duration of response compared to standard of care therapies in patient (pts) with metastatic melanoma (MM). Trial design Patients are randomized 2:1 to receive D/T or pembro +/- bemcentinib, respectively, based on mutation status and tumour load. BRAF positive pts are allowed to switch D/T with pembrolizumab and vice versa upon progression. Tumour responses are assessed per investigator using RECIST v1.1. Plasma protein biomarker levels are measured using the DiscoveryMap v3.3 panel (Myriad RBM) in pts pre-dose and at C2D1. In June 2019, a formal interim analysis of clinical safety and efficacy data will be performed when at least 20 randomised patients have completed up to 12 cycles of treatment. Currently, 50 pts (92 planned) have been enrolled in the trial. Tolerability of the bemcentinib RP2D (200 mg daily) in combination with either D/T or pembro, and AE profiles for either therapeutic approach alone will be reported. Protein biomarkers candidates predictive of pt benefit following treatment and pre/post treatment changes of soluble proteins will be presented. Preliminary efficacy outcome data and safety data from the first formal preplanned interim analysis will be presented together with the recommendations from the Data Monitoring Committee. Clinical trial identification NCT02872259. Legal entity responsible for the study The authors. Funding Research Council Norway. Disclosure O. Straume: Travel / Accommodation / Expenses: BerGenBio. J.B. Lorens: Shareholder / Stockholder / Stock options: BerGenBio ASA. G. Gausdal: Full / Part-time employment: BerGenBio ASA. All other authors have declared no conflicts of interest.

Abstract 3774: BGB324, a selective small-molecule inhibitor of receptor tyrosine kinase AXL, targets tumor immune suppression and enhances immune checkpoint inhibitor efficacy

Abstract The AXL receptor tyrosine kinase is associated with poor overall survival in a wide spectrum of cancers. AXL signaling is important for tumor cell plasticity related to epithelial-to-mesenchymal transition (EMT), immune escape and intrinsic resistance to cytotoxic lymphocytes. AXL is expressed on several cells associated with the tumor immune microenvironment, including natural killer (NK) cells, dendritic cells and a subset of tumor-associated myeloid cells. AXL signaling enhances secretion of immune-suppressive cytokines from innate immune cells that limit antitumor immunity. Hence AXL resides uniquely at the nexus between tumor and microenvironmental antitumor immune suppression mechanisms. BGB324, a selective clinical-stage small-molecule Axl kinase inhibitor, is currently being evaluated in combination with pembrolizumab in three phase II clinical trials in patients with TNBC (NCT03184558), NSCLC (NCT03184571) and melanoma (NCT02872259). We show that BGB324 targets immune suppression mechanisms in the tumor microenvironment that improve immunotherapy in different murine tumor models. BGB324 treatment reduces myeloid-derived suppressor cells and tumor-associated macrophages, and lowers CCL11, IL-7, IL-1β, and IL-6 in murine pancreatic cancer models. This altered immune landscape is associated with increased tumor infiltration of NK and CD8+ T cells and enhanced therapy responses. Further, BGB324 targets tumor intrinsic immune resistance and enhances human CD8+ T cell and NK-cell mediated NSCLC tumor cell lysis. We are currently using high-dimensional mass cytometry analysis (CyTOF) to map adaptive Axl-dependent immune suppression during immune checkpoint blockade. Collectively these results highlight a prominent function for AXL in resistance to immune therapy and support continued clinical translation of combining BGB324 with immune checkpoint inhibitors to improve cancer treatment. Citation Format: Kjersti Davidsen, Katarzyna Wnuk-Lipinska, Wenting Du, Magnus Blø, Agnete Engelsen, Stephane Terry, Stacey D´mello, Maria Lie, Jing Kang, Linn Hodneland, Sebastien Bougnaud, Kristina Aguilera, Oddbjørn Straume, Salem Chouaib, Rolf A. Brekken, Gro Gausdal, James B. Lorens. BGB324, a selective small-molecule inhibitor of receptor tyrosine kinase AXL, targets tumor immune suppression and enhances immune checkpoint inhibitor efficacy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3774.

Activation of the Receptor Tyrosine Kinase AXL Regulates the Immune Microenvironment in Glioblastoma.

Glioblastoma (GBM) is a lethal disease with no effective therapies available. We previously observed upregulation of the TAM (Tyro-3, Axl, and Mer) receptor tyrosine kinase family member AXL in mesenchymal GBM and showed that knockdown of AXL induced apoptosis of mesenchymal, but not proneural, glioma sphere cultures (GSC). In this study, we report that BGB324, a novel small molecule inhibitor of AXL, prolongs the survival of immunocompromised mice bearing GSC-derived mesenchymal GBM-like tumors. We show that protein S (PROS1), a known ligand of other TAM receptors, was secreted by tumor-associated macrophages/microglia and subsequently physically associated with and activated AXL in mesenchymal GSC. PROS1-driven phosphorylation of AXL (pAXL) induced NFκB activation in mesenchymal GSC, which was inhibited by BGB324 treatment. We also found that treatment of GSC-derived mouse GBM tumors with nivolumab, a blocking antibody against the immune checkpoint protein PD-1, increased intratumoral macrophages/microglia and activation of AXL. Combinatorial therapy with nivolumab plus BGB324 effectively prolonged the survival of mice bearing GBM tumors. Clinically, expression of AXL or PROS1 was associated with poor prognosis for patients with GBM. Our results suggest that the PROS1-AXL pathway regulates intrinsic mesenchymal signaling and the extrinsic immune microenvironment, contributing to the growth of aggressive GBM tumors.Significance: These findings suggest that development of combination treatments of AXL and immune checkpoint inhibitors may provide benefit to patients with GBM. Cancer Res; 78(11); 3002-13. ©2018 AACR.

A randomized phase Ib/II study of the selective small molecule axl inhibitor bemcentinib (BGB324) in combination with either dabrafenib/trametinib or pembrolizumab in patients with metastatic melanoma.

9548Background: Upregulation of the receptor tyrosine kinase Axl has been linked with both a reduced response to PD-1 blockade and the development of therapy resistance to BRAF directed therapies i...

Second-Line Treatment Landscape for Renal Cell Carcinoma: A Comprehensive Review.

This review article provides the reader with a comprehensive overview of current treatment options for patients with advanced clear-cell renal cell carcinoma (RCC) whose disease has progressed after their first therapy. As many patients with RCC experience disease progression with initial treatments, effective second-line therapies are critical. Nivolumab, cabozantinib, and lenvatinib plus everolimus have recently been approved as second-line treatments. The new agents discussed in this review increase the therapeutic options available and provide physicians with opportunities to individualize treatments for their patients, with a view to improving disease control and survival outcomes.

Combination of bemcentinib (BGB324): A first-in-class selective oral AXL inhibitor, with pembrolizumab in patients with triple negative breast cancer and adenocarcinoma of the lung.

TPS43 Background: Activation of the receptor tyrosine kinase AXL has a profound suppressive effect on the innate immune system. AXL is overexpressed on multiple cell types in the tumour immune microenvironment including dendritic cells, NK cells and tumour-associated macrophages. AXL signalling in immune cells supports tumour immune escape by downregulating dendritic cell activity, modulating efferocytosis as well as favouring an immunosuppressive chemokine profile and M-MDSC expansion. AXL is prevalent in tumours resistant to anti-PD-1 therapy (Hugo, 2016). Axl expression in tumour cells confers resistance to effector T cell cytotoxicity. Bemcentinib (BGB324) is a first-in-class, highly selective and orally bioavailable small molecule AXL inhibitor in phase II clinical development. In pre-clinical models of pancreas, breast and lung cancer, inhibition of AXL signalling with bemcentinib reversed multiple tumour immune suppressive mechanisms as evidenced by increased infiltration of cytotoxic T lymphocytes, NK and NKT cells and decreased infiltration of M-MDSCs (Wnuk-Lipinska, 2017). Bemcentinib enhanced the effect of immune checkpoint blockade via PD-1 or CTLA-4 in lung and mammary adenocarcinoma mouse models and achieved sustained tumour immunity. Methods: BGBC007 (NCT03184558) and BGBC008 (NCT03184571) are open-label, phase II studies designed to assess the anti-tumour activity of bemcentinib in combination with pembrolizumab in patients with previously treated TNBC and adenocarcinoma of the lung respectively. All patients will be treated with bemcentinib in combination with pembrolizumab continuously for up to two years. The primary endpoint is objective response rate, secondary endpoints include duration of response, progression free survival according to RECIST 1.1, pharmacokinetics, safety and tolerability. Pretreatment tumour specimens are scheduled to assess AXL expression/signalling and PD-L1 expression; the levels of circulating immune-related cytokines and soluble AXL receptor will also be measured in longitudinal patient plasma samples. Both studies are open to recruitment. Clinical trial information: NCT03184558.

The immunomodulatory activity of bemcentinib (BGB324): A first-in-class selective oral AXL inhibitor in patients with relapsed/refractory acute myeloid leukemia or myelodysplastic syndrome.

70 Background: The tyrosine kinase AXL acts as suppressive immune checkpoint of the innate immune system. AXL signalling leads to immunosuppression and tumour immune escape by downregulating dendritic cell activity, modulating efferocytosis as well as favouring an immunosuppressive chemokine profile and M-MDSC expansion. Therefore it represents an interesting novel immune oncology target. Bemcentinib (BGB324) is a first-in-class, highly selective and orally bioavailable small molecule AXL inhibitor in phase II clinical development. In pre-clinical models, inhibition of AXL signalling with bemcentinib reversed multiple established immune suppressive mechanisms leading to increased infiltration of CTLs, NK and NKT cells and decreased infiltration of M-MDSCs (Wnuk-Lipinska, 2017). We explored safety, PK, efficacy and the effects of treatment with bemcentinib on the T- and B cell repertoire in patients with relapsed AML or MDS. Methods: BGBC003 (NCT02488408) is an open-label, dose finding study of bemcentinib in patients with R/R AML or MDS. Three dose levels have been explored and a loading dose of 400 mg on days one to three followed by 200 mg daily thereafter has been established as safe and recommended phase 2 dose. The TCRß repertoire was quantified by NGS of DNA isolated from PBMNCs using an Illumina MiSeq sequencer. TCRß genes and the IGH repertoire were analysed with BIOMED2-TCRß-A and –B and BIOMED2-FR1/-FR3 primer pools, respectively. Using genomic DNA as template, the amplicons were tagged with Illumina adapters and indices in two consecutive PCR reactions. Demultiplexing and FastQ formated data output was generated by the MiSeq reporter. Analysis of TCRß and IGH data was performed on a Microsoft Cloud using our in-house analysis pipeline Pippa. Results: Early evidence of antileukemic activity was seen. Diversification of the TCR and IGH repertoire could be detected in peripheral blood at day 21 of therapy compared to pre-treatment in three and two out of five matched samples, respectively. Conclusions: Bemcentinib shows preliminary evidence of immune modulation in AML. Clinical trial information: NCT02488408.

EXTH-38. AXL INHIBITION BY R428 ATTENUATES TEMOZOLOMIDE INDUCED pAXL EXPRESSION IN PATIENT DERIVED METASTATIC BRAIN CANCER CELLS

As patients with cancer are living longer, the incidence of brain metastasis is rising. Current treatment options for metastatic brain tumors are very limited. Axl, a receptor tyrosine kinase, has been reported as a key mediator for epithelial-mesenchymal transition (EMT), a process necessary for metastasis to occur. Increases of Axl expression have also been linked to highly aggressive and treatment resistance glioblastoma. A small molecule inhibitor of AXL (R428 – also known as BGB324) is currently in early phase clinical trials for non-small cell lung cancer and acute myeloid leukemia. Temozolomide (TMZ) is the standard chemotherapy of choice for primary brain tumors. We generated a patient derived cell line from a breast cancer metastasis to brain. The brain metastasis was (Her2, ER, PR negative). After confirming the cell line expressed Axl through Western blot and flow cytometry, we tested whether R428 alone or in combination with TMZ had any effect on Axl and pAxl expression. We also determined the impact of R428 and TMZ on cell proliferation. Interestingly, our data indicates a robust, inverse correlation between Axl and pAxl expression in response to TMZ treatment. As expected, R428 alone effectively inhibited the expression of pAxl and significantly attenuated TMZ mediated increases of pAxl expression in our patient-derived cell line. Additionally, our data suggests that increases in pAxl by TMZ may stimulate mechanisms that facilitate TMZ resistance. We will discuss the mechanisms and combination therapeutic effect on tumor growth during the meeting.

P3.04-012 Phase 1 Study of the AXL Inhibitor DS-1205c in Combination with Osimertinib in Subjects with Metastatic or Unresectable EGFR-Mutant NSCLC

In patients with metastatic EGFR-mutant (EGFRm) non-small cell lung cancer (NSCLC), resistance to EGFR tyrosine kinase inhibition arises from the T790M EGFR mutation in over half of cases; up-regulation of “bypass track” activity in non-EGFR signaling pathways is observed in other cases. Up-regulation of expression of the AXL tyrosine kinase has been observed in EGFRm NSCLC patients experiencing disease progression on erlotinib, and xenograft studies have explored the role of AXL inhibition in combination with EGFR TKI treatment in overcoming such resistance. DS-1205c is a novel, orally administered, specific small molecule inhibitor of AXL.