Identification of a core EMT signature that separates basal-like breast cancers into partial- and post-EMT subtypes

Epithelial-mesenchymal transition (EMT) is a cellular plasticity program critical for embryonic development and tissue regeneration, and aberrant EMT is associated with disease including cancer. The high degree of plasticity in the mammary epithelium is reflected in extensive heterogeneity among breast cancers. Here, we have analyzed RNA-sequencing data from three different mammary epithelial cell line-derived EMT models and identified a robust mammary EMT gene expression signature that separates breast cancers into distinct subgroups. Most strikingly, the basal-like breast cancers form two subgroups displaying partial-EMT and post-EMT gene expression patterns. We present evidence that key EMT-associated transcription factors play distinct roles at different stages of EMT in mammary epithelial cells.

AXL targeting by a specific small molecule or monoclonal antibody inhibits renal cell carcinoma progression in an orthotopic mice model

AXL tyrosine kinase activation enhances cancer cell survival, migration, invasiveness, and promotes drug resistance. AXL overexpression is typically detected in a high percentage of renal cell carcinomas (RCCs) and is strongly associated with poor prognosis. Therefore, AXL inhibition represents an attractive treatment option in these cancers. In this preclinical study, we investigated the antitumor role of a highly selective small molecule AXL inhibitor bemcentinib (BGB324, BerGenBio), and a newly developed humanized anti-AXL monoclonal function blocking antibody tilvestamab, (BGB149, BerGenBio), in vitro and an orthotopic RCC mice model. The 786-0-Luc human RCC cells showed high AXL expression. Both bemcentinib and tilvestamab significantly inhibited AXL activation induced by Gas6 stimulation in vitro. Furthermore, tilvestamab inhibited the downstream AKT phosphorylation in these cells. The 786-0-Luc human RCC cells generated tumors with high Ki67 and vimentin expression upon orthotopic implantation in athymic BALB/c nude mice. Most importantly, both bemcentinib and tilvestamab inhibited the progression of tumors induced by the orthotopically implanted 786-0 RCC cells. Remarkably, their in vivo antitumor effectiveness was not significantly enhanced by concomitant administration of a multi-target tyrosine kinase inhibitor. Bemcentinib and tilvestamab qualify as compounds of potentially high clinical interest in AXL overexpressing RCC.

602 AXL targeting with bemcentinb restores PD-1 blockade sensitivity of STK11/LKB1 mutant NSCLC through innate immune cell mediated expansion of TCF1+ CD8 T cells

Background

Mutations in tumor suppressor STK11/LKB1 are associated with negative predictive and prognostic impact in NSCLC patients receiving immune checkpoint inhibitors (CPI) in several published cohorts, although there have been some conflicting reports on the association of such mutations with patient outcomes in this setting [1–9]. STK11/LKB1 tumors are characterized by a suppressive tumor micro-environment devoid of cytotoxic T cells, and we hypothesized that targeting the receptor tyrosine kinase AXL, a known driver of an innate immune suppressive microenvironment, would restore sensitivity to PD-1 in syngeneic pre-clinical models as well as in patients harboring STK11/LKB1 mutated NSCLC.

Methods

Stk11/Lkb1 (L) mutation was introduced by CRISPR technology into murine lung adenocarcinomas driven by mutant Kras and Trp53 loss (KP). Sensitivity towards anti-PD-1 was evaluated in the absence and presence of the small molecule AXL inhibitor bemcentinib in the KPL model and in a human NSCLC xenograft model carrying a STK11/LKB1 mutation. The immune tumor landscape was mapped following introduction of the Stk11/Lkb1 mutation and therapeutic intervention with anti-PD-1/pembrolizumab and bemcentinib. FFPE fine-needle aspirate biopsies of target lesions were acquired from patients at screening immediately prior to enrollment in BGBC008, a PhII single-arm, 2-stage study with bemcentinib (200mg/d) and pembrolizumab (200 mg/q3wk) for previously-treated stage IV lung adenocarcinoma patients who were CPI naïve or CPI refractory. Patients were assessed for response according to RECIST1.1 criteria at scheduled scan intervals.

Results

Introduction of a STK11/LKB1 mutation into murine lung adenocarcinomas driven by mutant Kras and Trp53 loss resulted in a PD-1 refractory syngeneic KPL tumor. Mechanistically this occurred because KPL mutant NSCLCs lacked TCF1-expressing CD8 T cells, a phenotype that was recapitulated in human STK11/LKB1 mutant NSCLCs. Systemic inhibition of AXL with bemcentinib resulted in increased type I interferon secretion from dendritic cells resulting in expansion of tumor-associated TCF1+PD-1+CD8 T cells and restored therapeutic response to PD-1. This effect was observed in a syngeneic immunocompetent mouse model and in humanized mice bearing STK11/LKB1 mutant NSCLC human tumor xenografts.In an ongoing clinical trial (NCT03184571), 3 evaluable NSCLC patients with identified STK11/LKB1 mutations demonstrated objective clinical response/clinical benefit to the combination of AXL inhibitor bemcentinib and pembrolizumab

Conclusions

In these models, AXL is a critical targetable driver of immune suppression in STK11/LKB1 mutant NSCLC contributing to CPI resistance. Our results show that inhibition of AXL rescues this deficit and represents a new clinical strategy in combination with anti-PD-1 therapy in NSCLC patients carrying a STK11/LKB1 mutation

Acknowledgements

The authors would like to thank all patients and their caretakers for participating in this trial.

Trial Registration

Patients treated with bemcentinib and pembrolizumab combination therapy were enrolled in the BGBC008 clinical trial (BerGenBio ASA and Merck & Co., Inc., Kenilworth NJ, USA, NCT03184571)

References

Gu M, Xu T, Chang P. KRAS/LKB1 and KRAS/TP53 co-mutations create divergent immune signatures in lung adenocarcinomas. Ther Adv Med Oncol. 2021;13:17588359211006950.

Cho BC, Lopes G, Kowalski DM. Relationship between STK11 and KEAP1 mutational status and efficacy in KEYNOTE-042: pembrolizumab monotherapy as first-line therapy for PD-L1 positive advanced NSCLC. Cancer Res. 2020;80(16 Supplement):CT084.

Aredo JV, Padda SK, Kunder CA. Impact of KRAS mutation subtype and concurrent pathogenic mutations on non-small cell lung cancer outcomes. Lung Cancer. 2019;133:144–150.

Kwack WG, Shin SY, Lee SH. Primary Resistance to Immune Checkpoint Blockade in an STK11/TP53/KRAS-Mutant Lung Adenocarcinoma with High PD-L1 Expression. Oncol Targets Ther. 2020;13:8901–8905.

Shire NJ, Klein AB, Golozar A. STK11 (LKB1) mutations in metastatic NSCLC: Prognostic value in the real world. PLoS One. 2020;15(9):e0238358. 6. Skoulidis F, Goldberg ME, Greenawalt DM. STK11/LKB1 Mutations and PD-1 Inhibitor Resistance in KRAS-Mutant Lung Adenocarcinoma. Cancer Discov. 2018;8(7):822–835. 7. Wang H, Guo J, Shang X. Less immune cell infiltration and worse prognosis after immunotherapy for patients with lung adenocarcinoma who harbored STK11 mutation. Int. Immunopharmacol. 2020;84:106574. 8. Kitajima S, Ivanova E, Gou S. Suppression of STING Associated with LKB1 Loss in KRAS-Driven Lung Cancer. Cancer Discov. 2019;9(1):34–45. 9. Mograbi B, Heeke S, Hofman P. The Importance of STK11/LKB1 Assessment in Non-Small Cell Lung Carcinomas. Diagnostics (Basel). 2021;11(2):196.

Ethics Approval

This study was approved by the following ethical committees: Use of human cord blood: UT Southwestern (UTSW) Parkland Hospital, STU 112010-047Animal studies: UTSW Medical Center, Institutional Animal Care and Use Committee, APN 2015-100921Clinical study: London Bridge Research Ethics Committee (UK): 17/LO/0418; REC-South East (Norway): 2017/473; Drug Research Ethics Committee of the University Hospital Clinic of Barcelona (Spain): BGBC008/MK-3475_PN-531; Medical College of Wisconsin Institutional Review Board #4 (USA): PRO00029453

Phosphatidylserine Receptor Enhancement of SARS-CoV-2 Entry: AXL as a Therapeutic Target for COVID-19

Phosphatidylserine (PS) receptors enhance infection of a wide range of enveloped RNA viruses through virion-associated PS binding that is termed apoptotic mimicry. Here we show that this broadly shared uptake mechanism is utilized by SARS-CoV-2. Under ACE2lo conditions, expression of members of the TIM and TAM families of PS receptors synergized with ACE2 to enhance SARS-CoV-2 infection; however, PS receptors alone did not mediate infection. PS receptors enhanced SARS-CoV-2 binding to the surface of cells. While PS receptors did not interact directly with purified SARS-CoV-2 spike, addition of PS liposomes reduced entry of VSV-SARS-CoV-2 spike pseudovirions, providing evidence that PS/PS receptor interactions are mediating the effect. AXL being abundant on airway cell lines, we evaluated small molecule inhibitors of AXL signaling such as bemcentinib for their ability to inhibit SARS-CoV-2 infection. Bemcentinib robustly inhibited virus infection of some lung cell lines that expressed AXL. This inhibition correlated well with inhibitors that block cathepsin activity, consistent with AXL-mediated uptake of SARS-CoV-2 into the endosomal compartment. RNAseq studies in Vero E6 and A549-hACE2 cells demonstrated that bemcentinib reduced SARS-CoV-2 transcripts dramatically. The ability of bemcentinib to decrease coronavirus infection in vivo was assessed using the betacoronavirus mouse hepatitis virus (MHV). Liver titers and virus load of MHV were significantly inhibited by bemcentinib at day 5 of infection. In total, our findings provide evidence that PS receptors facilitate infection of the pandemic coronavirus SARS-CoV-2 and that inhibition of signaling of the PS receptor AXL has therapeutic potential against SARS-CoV-2.

Role of the receptor tyrosine kinase AXL in regulating antitumor response and relationship with hypoxic stress

Tumor hypoxia has long been considered as a driving force of tumor progression and to play a key role in remodeling the tumor stroma and favoring the emergence of tolerance. The receptor tyrosine kinase AXL is associated with drug resistance in several solid tumors and AXL-targeting agents are currently in clinical trials. We investigated the relationship between tumor hypoxia, AXL expression and the emergence of tumor resistant variants. Our data indicate that hypoxia promotes EMT, AXL expression and resistance to CTLs and NK in NSCLC. We have next investigated the molecular basis of AXL-induced resistance to cell-mediated cytotoxicity and demonstrated that AXL targeting resulted in an increase in target susceptibility to CTLs and NK mediated cell lysis by a mechanism involving ICAM and the NKG2D ligand (ULBP1).

We next investigated the effect of pseudo hypoxia (hypoxic stress in presence of oxygen) in clear cell renal cell carcinoma (ccRCC). In fact, in this type of cancer, Von Hippel-Lindau (VHL) mutations induce a hypoxic microenvironment under normoxic conditions. We showed that pseudo-hypoxia induced by VHL dysfunctions, promotes ccRCC resistance to immune cell-mediated cytotoxicity by a mechanism involving HIF-2α.

We then sked wheter the pseudo-hypoxia associated with VHL mutation in RCC could impact AXL expression. We obtained in vtro evidence indicating that both HIF2α and EMT associated transcription factors (ZEB1, ZEB2) play a role in AXL expression regulation. Using a cohort of 324 metastatic RCC patients treated with anti-PD1, we could demonstrate that AXL expression may interfere with the clinical outcome. The relationship between VHL dysfunction, AXL expression and patient response to anti-PD1 will be discussed.

Abstract 1200: AXL targeting enhances lymphocyte-mediated cytotoxicity of lung cancer cells

As immunotherapies are now used to treat a large proportion of NSCLC patients, defining mechanisms of immune resistance is critical. Immune resistance may arise from both genetic instability and tumor heterogeneity driven by microenvironmental stresses such as hypoxia that promotes carcinoma cell plasticity as well as extrinsic or intrinsic mechanisms of immune resistance. AXL, a member of the TAM receptor tyrosine kinase family is widely expressed human cancers and increasingly recognized for its role in cell plasticity and drug resistance. In this study, we used a model of hypoxia-induced tumor plasticity to generate multiple lung cancer clones with mesenchymal and epithelial features to address mechanisms of immune resistance. We demonstrate that AXL expression is dramatically increased in mesenchymal lung cancer clones. Moreover, expression of AXL in the cells was correlated with an increased cancer cell intrinsic resistance to both NK and CTL-mediated killing, Notably, small molecule AXL targeting potently sensitized mesenchymal lung cancer cells to cytotoxic lymphocyte-mediated killing. Mechanistically, we showed that attenuation of AXL-dependent immune resistance to immune cells involved a novel molecular network comprising NF-κB activation, increased ICAM1 expression, and upregulation of ULBP1 expression coupled with MAPK inhibition. Congruently, higher ICAM1 and ULBP1 tumor expression, correlated with improved patient survival in two NSCLC cohorts. These results reveal a novel AXL-mediated immune escape regulatory pathway, suggest AXL as a novel candidate biomarker for tumor resistance to NK and CTL immunity, and support AXL targeting to optimize immune response in NSCLC.

Citation Format: Sallem Chouaib, Stephane Terry, Stephanie Buart, Agnete Engelsen, Gro Gausdal, James Lorens, Jean Paul Thiery, Fathia Mami-Chouaib. AXL targeting enhances lymphocyte-mediated cytotoxicity of lung 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 1200.

A randomized clinical trial of chemotherapy with gemcitabine/cisplatin/nabpaclitaxel with or without the AXL inhibitor bemcentinib (BGB324) for patients with advanced pancreatic cancer

TPS473

Background: The Axl pathway coordinately mediates immune evasion and drug resistance in pancreatic cancer. Systemic Axl inhibition can enhance the efficacy of cancer therapy by blocking tumor cell proliferation, survival and drug resistance associated with epithelial-mesenchymal transition (EMT), and targeting innate immune suppression in the tumor microenvironment. Bemcentinib (BGB324) is a first in class, selective oral inhibitor of Axl. Our group has shown that bemcentinib therapy, in combination with gemcitabine, improved survival in multiple preclinical models of pancreatic cancer. Methods: This is a multicenter, randomized, phase 1b/2 clinical trial of nab-paclitaxel/gemcitabine/cisplatin with or without bemcentinib. Patients with metastatic pancreatic cancer, good performance status and preserved liver, kidney and hematologic function are eligible. The treatment schedule is as follows: Bemcentinib 100 or 200 mg daily, nab-paclitaxel 125 mg/m2, gemcitabine 1000 mg/m2 and cisplatin 25 mg/m2 intravenously on D1, 8 every 21 days. 3 -12 patients will be recruited in part 1 following a modified 3+3 dose finding scheme. Part 2 of the study is a 1:1 randomized phase 2 design enrolling 62 patients. The primary objective is to determine complete response rate. Secondary end points are overall response rate, PFS and adverse events. A parallel biomarker study will accompany the trial analyzing blood and tissue samples to determine the effect of chemotherapy and bemcentinib on 1) Axl pathway activity in tumor tissue, 2) changes in immune landscape including upregulation of immune cytokines, and immune cell infiltration into the tumor, 3) apoptosis and decreased proliferation of tumor and 4) to identify predictive biomarkers of response. Clinical trial information: NCT03649321.

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.

Abstract CT056: A Phase Ib/II randomised open label study of BGB324 in combination with pembrolizumab or dabrafenib/trametinib compared to pembrolizumab or dabrafenib/trametinib alone, in patients with advanced non-resectable (Stage IIIc) or metastatic (Stage IV) melanoma

Background. MAPK inhibitors and immune checkpoint inhibitors are major breakthroughs in metastatic melanoma showing high response rates and durable responses. To further improve patient outcome, and to overcome treatment resistance, combination strategies have been suggested. We have initiated a phase Ib/II randomized clinical trial with the selective AXL inhibitor BGB324 (IC50=14 nM R428 Bergen Bio AS) with or without immune check point inhibition (pembrolizumab) or MAPK inhibitors (dabrafenib+trametinib) (NCT02872259). Upregulation of the AXL kinase has been associated with reduced response to anti-PD-1 therapy. The drug resistant low MITF/ high AXL melanoma signature has been associated with an immune suppressive micro-environment. AXL is a key negative feedback regulator of the innate immune response and attenuates macrophage, dendritic and natural killer (NK) cell activity. Hence, AXL signaling contributes to both tumor intrinsic and microenvironmental immune suppression mechanisms. Further we have recently shown that BGB324 sensitizes the highly metastatic K1736 murine melanoma tumors to anti-PD-1 treatment. This provides a rationale for targeting AXL to enhance the anti-cancer immune response. AXL dependent cell plasticity signaling pathways confer resistance to inhibitors of BRAF/MEK. Melanomas display either a high E-cadherin/high MITF-M expression on the one hand, or high N-cadherin/high AXL expression on the other. The low MITF/high AXL phenotype is linked to drug-resistance in mutant BRAF and NRAS melanoma cell lines. Interestingly, AXL-mediated resistance to BRAF and MEK targeting agents could be predicted by levels of soluble AXL receptor in patient blood samples and prevented by coadministration of BGB324,

Methods. This is a Phase Ib/II, multicentre, open label, parallel group study in patients with metastatic melanoma. Part 1 is a dose selection phase in up to 12 patients to evaluate the safety of BGB324 when administered in combination with dabrafenib+trametinib and to determine the BGB324 dose to be administered in the combination in Part 2 and Part 3. Part 2 is an open label, multiple arm, randomised treatment phase evaluating efficacy and safety of pembrolizumab and dabrafenib+trametinib in combination with BGB324 as first line treatment in 80 patients with advanced melanoma compared to pembrolizumab or dabrafenib/trametinib alone. Patients will be stratified according to BRAF status and tumor load to receive pembrolizumab or dabrafenib+trametinib with or without BGB324, randomised in a 2:1 ratio. Part 3 is an open label, multiple arm, non-randomised treatment phase evaluating efficacy and safety of pembrolizumab and dabrafenib/trametinib in combination with BGB324 or alone, as second line treatment in patients continuing from Part 1 or Part 2. Co-primary endpoints are safety and response rates according to RECIST 1.1. Enrollment began in January 2017.

Citation Format: Oddbjorn Straume, Cornelia Schuster, James Lorens, Bjørn Tore Gjertsen. A Phase Ib/II randomised open label study of BGB324 in combination with pembrolizumab or dabrafenib/trametinib compared to pembrolizumab or dabrafenib/trametinib alone, in patients with advanced non-resectable (Stage IIIc) or metastatic (Stage IV) melanoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr CT056. doi:10.1158/1538-7445.AM2017-CT056

Abstract B027: BGB324, a selective small molecule inhibitor of AXL receptor tyrosine kinase, enhances immune checkpoint inhibitor efficacy

The AXL receptor tyrosine kinase is expressed by several tumor types and is associated with poor overall survival in patients. AXL signaling is an important regulator of tumor cell plasticity related to epithelial-to-mesenchymal transition (EMT) and stem cell traits that drive metastasis, drug resistance and immune evasion. AXL is also expressed on several cells associated with the inflammatory tumor immune microenvironment including natural killer (NK) cells, dendritic cells and tumor-associated macrophages. Signaling via AXL is a key suppressor of the anti-tumor innate immune response. Hence, AXL signaling contributes uniquely to tumor cell intrinsic and microenvironmental anti-tumor immune suppression mechanisms in cancer. We evaluated whether blocking AXL signaling with BGB324, a selective clinical-stage small molecule AXL kinase inhibitor, enhanced the effect of immune checkpoint blockade in aggressive adenocarcinomas that display limited immunogenicity.

Immune therapy with anti-PD-1/anti-PD-L1 or anti-CTLA-4/anti-PD-1 increased AXL and EMT-marker expression in the murine lung cancer (Lewis lung, LL2) and mammary adenocarcinoma (4T1) syngeneic models, and correlated with a lack of response to immune checkpoint therapy. Combination treatment with BGB324 (50 mg/kg bid) significantly enhanced responsiveness to anti-PD-1/anti-PD-L1 or anti-CTLA-4/anti-PD-1 treatment (10 mg/kg of each, 6 doses for LL2; 4 doses for 4T1) in mice bearing established LL2 or 4T1 tumors respectively. BGB324 in combination with anti-PD-1/anti-PD-L1 or anti-CTLA-4/anti-PD-1 enhanced tumor infiltration of cytotoxic T lymphocytes (CTLs). Increased CTLs were also detected in spleens from animals responding to treatment. BGB324 + anti-CTLA-4/anti-PD-1 combination treatment increased the number of NK cells, macrophages and polymorphonuclear neutrophils, but decreased the number of tumor-associated myeloid-derived suppressor cells (MDSC).

In the 4T1 model, the combination of BGB324 + anti-CTLA-4/anti-PD-1 resulted in durable primary tumor clearance in 23% of treated mice versus 5.6% obtained with anti-CTLA-4/anti-PD-1 alone (p = 0.0157). In a separate study, BGB324 + anti-CTLA-4 therapy treated resulted in 22% long-term primary tumor clearance while no response was observed with anti-CTLA4 treatment alone. The extensive metastasis to the lung, liver and spleen characteristic of this model was concomitantly abrogated in the animals responding to the combination treatment. Importantly, responding animals rejected orthotopic 4T1 tumor cell re-challenge, demonstrating sustained tumor immunity

These findings along with the favorable safety profile and clinical activity of BGB324 in ongoing monotherapy clinical trials, support a rationale for clinical testing of BGB324 in combination with immune checkpoint inhibitors in cancer patients.

Citation Format: Katarzyna Wnuk-Lipinska, Kjersti Davidsen, Magnus Blø, Linn Hodneland, Agnete Engelsen, Jing Kang, Maria Lie, Sebastien Bougnaud, Kristina Aguilera, Lavina Ahmed, Agata Rybicka, Elina Milde, Paulina Deyna, Anna Boniecka, Oddbjørn Straume, Salem Chouaib, Rolf Brekken, Gro Gausdal, James Lorens. BGB324, a selective small molecule inhibitor of AXL receptor tyrosine kinase, enhances immune checkpoint inhibitor efficacy [abstract]. In: Proceedings of the Second CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; 2016 Sept 25-28; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(11 Suppl):Abstract nr B027.

Abstract A095: The microenvironmental basis of AXL regulation

AXL tyrosine kinase expression is a strong negative prognostic factor for survival of human breast cancer, and its expression is significant in metastases. Breast cancer metastasis is promoted by epithelial-mesenchymal transition (EMT), where epithelial cells lose their cell-to-cell contacts and polarity, resulting in transformation to a fibroblastic migratory phenotype. During EMT process, AXL is highly expressed, and knockdown of AXL completely prevents the invasion of breast cancer cells via EMT-based mechanisms. EMT is promoted by specific transcription factors like slug or oncogenes like Ras, but interestingly, without extracellular signaling feedback, cells will lose the EMT state and invasion capability.

In this study we characterize extracellular stimuli that stabilize AXL expression and the EMT-phenotype in human mammary epithelial cells. In Vitro studies were implemented with HMEC-derived cell lines, which have traceable origins and were derived through defined immortalization steps. Mammary epithelial cells were induced into an EMT phenotype by Slug-overexpression and exposure to different microenvironments. AXL and other EMT markers were monitored in each cell passage. Results have shown that with Slug-expressing cells lose the EMT phenotype after a few cell passages. When Slug induced HMECs were cultured on Micro Environment microArrays (MEArray), specific microenvironments were revealed that increased and stabilized AXL expression. Our results show that microenvironmental signals are essential to induce and maintain the EMT phenotype.

Citation Format: Tiina Jokela, Martha Stampfer, James Lorens, Mark LaBarge. The microenvironmental basis of AXL regulation. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Breast Cancer Research: Genetics, Biology, and Clinical Applications; Oct 3-6, 2013; San Diego, CA. Philadelphia (PA): AACR; Mol Cancer Res 2013;11(10 Suppl):Abstract nr A095.

Effects of enoxaparin and dalteparin on proliferation and migration of patient-derived vascular smooth muscle cells

BACKGROUND

Proliferation and migration are the two main processes of intimal hyperplasia: the primary cause of intermediate and late vascular graft failure. Low-molecular-weight heparins (LMWHs) inhibit these processes on vascular smooth muscle cells (VSMCs) in animal models, but have failed to improve patency of vascular grafts in clinical trials. Despite these findings, they are still used therapeutically to reduce intimal hyperplasia following vascular interventions. This study was designed to investigate the effects of LMWHs compared to unfractioned heparin in patient-derived VSMCs.

MATERIAL AND METHODS

Arterial patient-derived VSMCs were used to study the effects of enoxaparin and dalteparin on proliferation, migration and mitogen-activated protein kinase extracellular signal-regulated kinase (MAPK-ERK) signal transduction. The VSMCs were treated with the LMWHs in a range of concentrations and evaluated using image based cell enumeration, real time migration monitoring and flow cytometry. Series treated with unfractioned heparin were included as positive controls and untreated series as negative controls.

RESULTS

Neither enoxaparin nor dalteparin influenced proliferation and MAPK-ERK phosphorylation. Migration was reduced slightly by both LMWHs. Unfractioned heparin exhibited dose-dependent effects different from those of the LMWHs in all analyses.

CONCLUSIONS

This study demonstrated a difference in proliferative and migratory effects between the two LMWHs and unfractioned heparin in patient-derived VSMCs. The effects corresponded to the MAPK-ERK activation, suggesting different mechanisms of action. These results can explain why clinical trials using LMWHs to prevent intimal hyperplasia have failed to observe a reduced incidence of restenosis and do not support prolonged therapeutic use to prevent intimal hyperplasia.

Abstract 4888: Axl receptor signaling in required for stem cell traits and metastasis in breast cancer

Epithelial-to-mesenchymal transition (EMT) endows carcinoma cells with migratory, survival and stem cell-like attributes that facilitate therapeutic resistance and metastasis. Expression of the Axl receptor tyrosine kinase in aggressive breast cancer correlates with EMT, poor survival and is prevalent in patient metastases. Induction of EMT in immortalized mammary epithelial cells by EMT-transcription factors, TGFbeta or hypoxia upregulates Axl and establishes an autocrine-signaling loop with its ligand, Gas6. Axl receptor signaling is required to maintain EMT-related invasive, drug resistance and cancer stem cell (CSC) traits of malignant breast cancer cells. Targeting Axl signaling with RNAi or pharmacological agents blocks the EMT/CSC gene program and inhibits malignant functions including invasiveness, drug resistance, mammosphere formation, in vivo tumor initiation, and spontaneous metastasis in orthotopic breast cancer models. These results suggest that Axl expression is requisite for the maintenance of EMT and stem cell-like traits during malignant progression. The EMT program is characteristic of normal adult mammary epithelial stem/progenitor cells. Congruently, we show that the Axl receptor expressed on mammary epithelial stem/progenitor cells, and Axl signaling is necessary for mammary epithelial multipotent progenitor activity. Thus Axl receptor signaling represents a novel regulatory pathway linking normal mammary stem/progenitor cells and breast cancer stem cells. Hence, clinical Axl inhibitors represent a novel therapeutic avenue to target EMT/CSC traits of aggressive breast cancer.

Citation Format: Crina Tiron, Fanny Pelissier, Katarzyna Wnuk-Lipinska, Ingunn Stefansson, Reeta Virtakoivu, Masaru Miyano, Tone Sandal, David Micklem, James Garbe, Martha Stampfer, Johanna Ivaska, Lars Akslen, Mark LaBarge, James Lorens. Axl receptor signaling in required for stem cell traits and metastasis in breast cancer. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4888. doi:10.1158/1538-7445.AM2013-4888

Abstract C76: Axl signaling is required for stem cell traits and metastasis in breast cancer

Epithelial-to-mesenchymal transition (EMT) endows carcinoma cells with migratory, survival and stem cell-like attributes that facilitate therapeutic resistance and metastasis. Expression of the Axl receptor tyrosine kinase in breast cancer correlates with EMT, poor survival and is prevalent in patient metastases. Axl upregulation in mammary epithelial cells by EMT-transcription factors, TGFbeta or hypoxia, establishes an autocrine-signaling loop with its ligand, Gas6. Inhibition of Axl signaling blocks EMT/ cancer stem cell traits including invasiveness, drug resistance, mammosphere formation, in vivo tumor initiation, and prevents spontaneous metastasis in orthotopic breast cancer models. Congruently, we show that Axl is expressed on mammary epithelial stem/progenitor cells and regulates multipotent progenitor activity. Thus Axl signal transduction represents a novel regulatory pathway linking normal mammary stem/progenitor cells and breast cancer stem cell activity. Clinical Axl-inhibitors represent a novel therapeutic opportunity to treat aggressive breast cancer.

Citation Format: Crina Tiron, Fanny Pelissier, Katarzyna Wnuk-Lipinska, Ingunn Stefansson, Reeta Virtakoivu, Masaru Miyano, Tone Sandal, David Micklem, James Garbe, Martha Stampfer, Johanna Ivaska, Lars Akslen, Mark LaBarge, James Lorens. Axl signaling is required for stem cell traits and metastasis in breast cancer. [abstract]. In: Proceedings of the AACR Special Conference on Tumor Invasion and Metastasis; Jan 20-23, 2013; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2013;73(3 Suppl):Abstract nr C76.

Abstract B105: Axl is an essential epithelial-to-mesenchymal transition-induced regulator of breast cancer metastasis and patient survival

Metastasis underlies the majority of cancer-related deaths. Hence, furthering our understanding of the molecular mechanisms that enable tumor cell dissemination is a vital health issue. Epithelial-to-mesenchymal transitions (EMT) endow carcinoma cells with enhanced migratory and survival attributes that facilitate malignant progression. Characterization of EMT effectors is likely to yield new insights into metastasis and novel avenues for treatment. We show that the presence of the receptor tyrosine kinase Axl in mammography-detected primary breast cancers independently predicts strongly reduced overall patient survival, and matched patient metastatic lesions show enhanced Axl expression. We demonstrate that Axl is strongly induced by epithelial-to-mesenchymal transition in pre-malignant mammary epithelial cells that establishes an autocrine signaling loop with its ligand, Gas6. Using epi-allelic RNA interference analysis in metastatic breast cancer cells we delineated a distinct threshold of Axl expression for mesenchymal-like in vitro cell invasiveness, and to form tumors in foreign and tissue engineered microenvironments in vivo. Importantly, Axl knockdown completely prevented the spread of highly metastatic breast carcinoma cells from the mammary gland to lymph nodes and several major organs, and increased overall survival, in two different optical imaging-based experimental breast cancer models. Thus, Axl represents a novel downstream effector of tumor cell EMT that is required for breast cancer metastasis. The detection and targeted treatment of Axl-expressing tumors represents an important new therapeutic strategy for breast cancer.

Citation Information: Mol Cancer Ther 2009;8(12 Suppl):B105.

Rapid production of retroviruses for efficient gene delivery to mammalian cells using 293T cell-based systems

This unit details the applications of one of the more common retroviral packaging systems, based on the highly transfectable 293T cell. The packaging system employs the use of the Phoenix cell lines. Calcium phosphate-mediated transfection is described for efficient introduction of retroviral vector plasmid DNA into the cells to generate high yields of virion-containing supernatant. An alternate protocol describes a method for transfecting retroviruses that contain a vesicular stomatitis virus G (VSV G) protein. Such virions are said to be "pseudotyped" with VSV G glycoprotein. Support protocols provide a simple method for concentrating VSV-G-pseudotyped retroviruses, as well as methods for culturing, cryopreserving, thawing, and drug selecting the Phoenix packaging cell lines. Finally, several methods for transfecting adherent or suspension cells with retroviruses are described.

Intracellular protein scaffold-mediated display of random peptide libraries for phenotypic screens in mammalian cells

BACKGROUND

Mammalian cell screens of peptide libraries for changes in cellular phenotype may identify novel functional peptides and their cognate binding partners, and allow identification of signal transduction network members or proteins important in disease processes.

RESULTS

Green fluorescent protein (GFP) peptide libraries with different structural biases were tested by retroviral expression in A549 carcinoma cells, HUVEC and other cell types. Three different loop replacement libraries, containing 12 or 18 random residues, were compatible with enhanced GFP (EGFP) folding, as was a C-terminally fused random 20-mer library. Library concentrations in A549 cells ranged from ca. 1 to 54 microM. Replacement of loop 3 with known nuclear localization sequence (NLS) peptides, but not with inactive mutants, directed EGFP to the nucleus. Microscopy-based screens of three different libraries for non-uniform localization revealed novel NLS peptides, novel variants of a peroxisomal localization motif, a variety of partial NLS peptides, peptides localized to the nucleolus, and nuclear-excluded peptides.

CONCLUSIONS

Peptides can be presented by EGFP in conformations that can functionally interact with cellular constituents in mammalian cells. A phenotypic screen resulting in the discovery of novel localization peptides that were not cell type-specific suggests that this methodology may be applied to other screens in cells derived from diseased organisms, and illustrates the use of intracellular combinatorial peptide chemistry in mammalian cells.

Toso, a cell surface, specific regulator of Fas-induced apoptosis in T cells

Fas is a surface receptor that can transmit signals for apoptosis. Using retroviral cDNA library-based functional cloning we identified a gene, toso, that blocks Fas-mediated apoptosis. Toso expression was confined to lymphoid cells and was enhanced after cell-specific activation processes in T cells. Toso appeared limited to inhibition of apoptosis mediated by members of the TNF receptor family and was capable of inhibiting T cell self-killing induced by TCR activation processes that up-regulate Fas ligand. We mapped the effect of Toso to inhibition of caspase-8 processing, the most upstream caspase activity in Fas-mediated signaling, potentially through activation of cFLIP. Toso therefore serves as a novel regulator of Fas-mediated apoptosis and may act as a regulator of cell fate in T cells and other hematopoietic lineages.