Adenoviral mediated mono delivery of BMP2 is superior to the combined delivery of BMP2 and VEGFA in bone regeneration in a critical-sized rat calvarial bone defect

Apart from osteogenesis, neovascularization of the defect area is an important determinant for successful bone healing. Accordingly, several studies have employed the combined delivery of VEGFA and BMP2 for bone regeneration. Nevertheless, the outcomes of these studies are highly variable. The aim of our study was to compare the effectiveness of adenoviral mediated delivery of BMP2 alone and in combination with VEGFA in rat bone marrow stromal cells (rBMSC) seeded on a poly(LLA-co-CL) scaffold in angiogenesis and osteogenesis using a critical-sized rat calvarial defect model. Both mono delivery of BMP2 and the combined delivery of a lower ratio of VEGFA and BMP2 (1:4) led to up-regulation of osteogenic genes (Alpl and Runx2) and increased calcium deposition in vitro, compared with the GFP control. Micro computed tomography (microCT) analysis of the rat calvarial defect at 8 weeks showed that the mono delivery of BMP2 (43.37 ± 3.55% defect closure) was the most effective in healing the bone defect, followed by the combined delivery of BMP2 and VEGFA (27.86 ± 2.89%) and other controls. Histological and molecular analyses supported the microCT findings. Analysis of the angiogenesis, however, showed that both mono delivery of BMP2 and combined delivery of BMP2 and VEGFA had similar angiogenic effect in the calvarial defects. Examination of the key genes related to host response against the adenoviral vectors showed that the current model system was not associated with adverse immune response. Overall, the results show that the mono delivery of BMP2 was superior to the combined delivery of BMP2 and VEGFA in healing the critical-sized rat calvarial bone defect. These findings underscore the importance of appropriate growth factor combination for the successful outcome in bone regeneration.

A novel SRC-2-dependent regulation of epithelial-mesenchymal transition in breast cancer cells

Steroid receptor coactivator 2 (SRC-2) is a nuclear receptor coactivator, important for the regulation of estrogen receptor alpha (ERα)-mediated transcriptional activity in breast cancer cells. However, the transcriptional role of SRC-2 in breast cancer is still ambiguous. Here we aimed to unravel a more precise transcriptional role of SRC-2 and uncover unique target genes in MCF-7 breast cancer cells, as opposed to the known oncogene SRC-3. Gene expression analyses of cells depleted of either SRC-2 or SRC-3 showed that they transcriptionally regulate mostly separate gene sets. However, individual unique gene sets were implicated in some of the same major gene ontology biological processes, such as cellular structure and development. This finding was supported by three-dimensional cell cultures, demonstrating that depletion of SRC-2 and SRC-3 changed the morphology of the cells into epithelial-like hollow acinar structures, indicating that both SRC proteins are involved in maintaining the hybrid E/M phenotype. In clinical ER-positive, HER2-negative breast cancer samples the expression of SRC-2 was negatively correlated with the expression of MCF-7-related luminal, cell cycle and cellular morphogenesis genes. Finally, elucidating SRC-2 unique transcriptional effects, we identified Lyn kinase (an EMT biomarker) to be upregulated exclusively after SRC-2 depletion. In conclusion, we show that both SRC-2 and SRC-3 are essential for the EMT in breast cancer cells, controlling different transcriptional niches.

Identifying Lysophosphatidic Acid Acyltransferase β (LPAAT-β) as the Target of a Nanomolar Angiogenesis Inhibitor from a Phenotypic Screen Using the Polypharmacology Browser PPB2

By screening a focused library of kinase inhibitor analogues in a phenotypic co-culture assay for angiogenesis inhibition, we identified an aminotriazine that acts as a cytostatic nanomolar inhibitor. However, this aminotriazine was found to be completely inactive in a whole-kinome profiling assay. To decipher its mechanism of action, we used the online target prediction tool PPB2 (http://ppb2.gdb.tools), which suggested lysophosphatidic acid acyltransferase β (LPAAT-β) as a possible target for this aminotriazine as well as several analogues identified by structure-activity relationship profiling. LPAAT-β inhibition (IC₅₀ ≈15 nm) was confirmed in a biochemical assay and by its effects on cell proliferation in comparison with a known LPAAT-β inhibitor. These experiments illustrate the value of target-prediction tools to guide target identification for phenotypic screening hits and significantly expand the rather limited pharmacology of LPAAT-β inhibitors.

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

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.

Microenvironment-Induced Non-sporadic Expression of the AXL and cKIT Receptors Are Related to Epithelial Plasticity and Drug Resistance

The existence of rare cancer cells that sporadically acquire drug-tolerance through epigenetic mechanisms is proposed as one mechanism that drives cancer therapy failure. Here we provide evidence that specific microenvironments impose non-sporadic expression of proteins related to epithelial plasticity and drug resistance. Microarrays of robotically printed combinatorial microenvironments of known composition were used to make cell-based functional associations between microenvironments, which were design-inspired by normal and tumor-burdened breast tissues, and cell phenotypes. We hypothesized that specific combinations of microenvironment constituents non-sporadically impose the induction of the AXL and cKIT receptor tyrosine kinase proteins, which are known to be involved in epithelial plasticity and drug-tolerance, in an isogenic human mammary epithelial cell (HMEC) malignant progression series. Dimension reduction analysis reveals type I collagen as a dominant feature, inducing expression of both markers in pre-stasis finite lifespan HMECs, and transformed non-malignant and malignant immortal cell lines. Basement membrane-associated matrix proteins, laminin-111 and type IV collagen, suppress AXL and cKIT expression in pre-stasis and non-malignant cells. However, AXL and cKIT are not suppressed by laminin-111 in malignant cells. General linear models identified key factors, osteopontin, IL-8, and type VIα3 collagen, which significantly upregulated AXL and cKIT, as well as a plasticity-related gene expression program that is often observed in stem cells and in epithelial-to-mesenchymal-transition. These factors are co-located with AXL-expressing cells in situ in normal and breast cancer tissues, and associated with resistance to paclitaxel. A greater diversity of microenvironments induced AXL and cKIT expression consistent with plasticity and drug-tolerant phenotypes in tumorigenic cells compared to normal or immortal cells, suggesting a reduced perception of microenvironment specificity in malignant cells. Microenvironment-imposed reprogramming could explain why resistant cells are seemingly persistent and rapidly adaptable to multiple classes of drugs. These results support the notion that specific microenvironments drive drug-tolerant cellular phenotypes and suggest a novel interventional avenue for preventing acquired therapy resistance.

Abstract OT1-01-03: A phase II multi-center study of BGB324 in combination with pembrolizumab in patients with previously treated, locally advanced and unresectable or metastatic triple negative breast cancer (TNBC) or triple negative inflammatory breast cancer (TN-IBC)

Background. The AXL receptor tyrosine kinase is associated with poor overall survival in breast cancer. AXL signaling is an important regulator of tumor plasticity related to epithelial-to-mesenchymal transition (EMT) and stem cell traits that drive metastasis and drug resistance. Upregulation of AXL has been associated with reduced response to anti-PD-1 therapy. Signaling via AXL is also a key suppressor of the anti-tumor innate immune response, and AXL is expressed on several cells associated with the tumor immune microenvironment. Hence AXL signaling contributes uniquely to both tumor cell intrinsic and microenvironmental anti-tumor immune suppression mechanisms. We show that AXL is required for tumor immune evasion in the 4T1/Balb/C mammary adenocarcinoma model and that blocking AXL signaling with BGB324, a selective clinical-stage small molecule AXL kinase inhibitor, enhanced the effect of immune checkpoint blockade. BGB324 + anti-CTLA-4/anti-PD-1 treated tumors displayed enhanced infiltration of cytotoxic T lymphocytes and Natural Killer cells. Importantly, responding animals rejected orthotopic 4T1 tumor cell re-challenge, demonstrating sustained tumor immunity. These data provided a translational rationale for combining AXL targeted therapy with immune checkpoint inhibitors to enhance anti-cancer immune response.

Study Design. BGBC007 (NCT03184558) is an open-label, single arm, multi-center phase II study designed to assess the anti-tumor activity of BGB324 in combination with pembrolizumab in patients with previously treated, locally advanced and unresectable, or metastatic TNBC or TN-IBC. Secondary objectives include safety and pharmacokinetic profile of BGB324 and pembrolizumab in combination. A single arm, extension of Simon's 2-stage design is employed with an interim and final analysis. Up to 56 evaluable patients will be enrolled. Recruitment will be halted once 28 evaluable patients have been entered to determine the Objective Response Rate (ORR, complete response and partial response). If 5 or fewer responses are observed in up to 28 patients, the trial will be terminated in favor of the null for futility. If 11 or more responses are observed, then the trial will be stopped in favor of the alternative for demonstration of activity. If 6 to 10 patients have an observed response then a further 28 patients may be evaluated. This design provides an overall power of 80.6% to test the stated null and alternative hypothesis. BGB324 will be administered orally, once daily, in a fasted state. Days 1, 2 and 3 of BGB324 administration consists of a 'loading' dose of 400 mg followed by a dose of 200 mg daily. A fixed dose of 200 mg pembrolizumab will be given by intravenous infusion over 30 minutes every 3 weeks. BGB324 and pembrolizumab will be given until disease progression, unacceptable dose toxicity, or until 106 weeks (35 cycles). Efficacy endpoints including ORR, Duration of Response, Progression Free Survival are based on tumor imaging evaluation by RECIST 1.1. Tumor specimens will be taken to assess AXL and PD-L1 expression.

Citation Format: Yule M, Wnuk-Lipinska K, Davidsen K, Blø M, Hodneland L, Engelsen A, Kang J, Lie M, Bougnaud S, Aguilera K, Ahmed L, Rybicka A, Milde Nævdal E, Deyna P, Boniecka A, Straume O, Thiery J-P, Chouaib S, Brekken RA, Gausdal G, Lorens JB. A phase II multi-center study of BGB324 in combination with pembrolizumab in patients with previously treated, locally advanced and unresectable or metastatic triple negative breast cancer (TNBC) or triple negative inflammatory breast cancer (TN-IBC) [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr OT1-01-03.

Association of Warfarin Use With Lower Overall Cancer Incidence Among Patients Older Than 50 Years

IMPORTANCE

In cancer models, warfarin inhibits AXL receptor tyrosine kinase-dependent tumorigenesis and enhances antitumor immune responses at doses not reaching anticoagulation levels. This study investigates the association between warfarin use and cancer incidence in a large, unselected population-based cohort.

OBJECTIVE

To examine the association between warfarin use and cancer incidence.

DESIGN, SETTING, AND PARTICIPANTS

This population-based cohort study with subgroup analysis used the Norwegian National Registry coupled with the Norwegian Prescription Database and the Cancer Registry of Norway. The cohort comprised all persons (N = 1 256 725) born between January 1, 1924, and December 31, 1954, who were residing in Norway from January 1, 2006, through December 31, 2012. The cohort was divided into 2 groups-warfarin users and nonusers; persons taking warfarin for atrial fibrillation or atrial flutter were the subgroup. Data were collected from January 1, 2004, to December 31, 2012. Data analysis was conducted from October 15, 2016, to January 31, 2017.

EXPOSURES

Warfarin use was defined as taking at least 6 months of a prescription and at least 2 years from first prescription to any cancer diagnosis. If warfarin treatment started after January 1, 2006, each person contributed person-time in the nonuser group until the warfarin user criteria were fulfilled.

MAIN OUTCOMES AND MEASURES

Cancer diagnosis of any type during the 7-year observation period (January 1, 2006, through December 31, 2012).

RESULTS

Of the 1 256 725 persons in the cohort, 607 350 (48.3%) were male, 649 375 (51.7%) were female, 132 687 (10.6%) had cancer, 92 942 (7.4%) were classified as warfarin users, and 1 163 783 (92.6%) were classified as nonusers. Warfarin users were older, with a mean (SD) age of 70.2 (8.2) years, and were predominantly men (57 370 [61.7%]) as compared with nonusers, who had a mean (SD) age of 63.9 (8.6) years and were mostly women (613 803 [52.7%]). Among warfarin users and compared with nonusers, there was a significantly lower age- and sex-adjusted incidence rate ratio (IRR) in all cancer sites (IRR, 0.84; 95% CI, 0.82-0.86) and in prevalent organ-specific sites (lung, 0.80 [95% CI, 0.75-0.86]; prostate, 0.69 [95% CI, 0.65-0.72]; and breast, 0.90 [95% CI, 0.82-1.00]). There was no observed significant effect in colon cancer (IRR, 0.99; 95% CI, 0.93-1.06). In a subgroup analysis of patients with atrial fibrillation or atrial flutter, the IRR was lower in all cancer sites (IRR, 0.62; 95% CI, 0.59-0.65) and in prevalent sites (lung, 0.39 [95% CI, 0.33-0.46]; prostate, 0.60 [95% CI, 0.55-0.66]; breast, 0.72 [95% CI, 0.59-0.87]; and colon, 0.71 [95% CI, 0.63-0.81]).

CONCLUSIONS AND RELEVANCE

Warfarin use may have broad anticancer potential in a large, population-based cohort of persons older than 50 years. This finding could have important implications for the selection of medications for patients needing anticoagulation.

Small-Molecule Inhibition of Axl Targets Tumor Immune Suppression and Enhances Chemotherapy in Pancreatic Cancer

Activation of the receptor tyrosine kinase Axl is associated with poor outcomes in pancreatic cancer (PDAC), where it coordinately mediates immune evasion and drug resistance. Here, we demonstrate that the selective Axl kinase inhibitor BGB324 targets the tumor-immune interface to blunt the aggressive traits of PDAC cells in vitro and enhance gemcitibine efficacy in vivo Axl signaling stimulates the TBK1-NFκB pathway and innate immune suppression in the tumor microenvironment. In tumor cells, BGB324 treatment drove epithelial differentiation, expression of nucleoside transporters affecting gemcitabine response, and an immune stimulatory microenvironment. Our results establish a preclinical mechanistic rationale for the clinical development of Axl inhibitors to improve the treatment of PDAC patients.Significance: These results establish a preclinical mechanistic rationale for the clinical development of AXL inhibitors to improve the treatment of PDAC patients. Cancer Res; 78(1); 246-55. ©2017 AACR.

Abstract 3010: Broad reduction in cancer incidence in patients treated with warfarin: a prospective cohort study

BACKGROUND

Evidence shows that the vitamin K-antagonist warfarin, a popular anti-coagulant in clinical use for decades, has anti-tumor activity. This is recently attributed to disruption of post-translational modification of Gas6, the common ligand of the Axl receptor tyrosine kinase family. Gas6-Axl signaling is associated with malignancy and is required for tumoriogenesis and progression in several preclinical cancer models. Warfarin is shown to inhibit Axl signaling-dependent malignant traits and enhance anti-tumor immune responses at doses that do not achieve anticoagulation. The objective of this study is to investigate the association between warfarin use and cancer incidence in a large unselected Norwegian cohort. Our results reveal a remarkable reduction in cancer incidence associated with warfarin use across a wide range of tumor types.

METHODS

A cohort selected from the Norwegian population registry included all persons born between 1924-1954, living in Norway 2006-2012 (n=1 256 725). We cross-referenced this cohort using the unique Norwegian National ID Number to: 1) the Cancer Registry of Norway and retrieved information on all cancer cases 2006-2012; 2) information on filled warfarin prescriptions (ATC: B01AA03) from the Norwegian Prescriptions Database (2004-2012). Warfarin-use was defined > 6 months and minimum 2 years between first warfarin prescription and cancer diagnosis. We also performed a subgroup analysis on persons prescribed warfarin for atrial fibrillation/flutter (n=33 313) compared to non-users. Mantel-Haenzel method was used to calculate the incidence rate ratio (IRR), adjusting for sex and age.

RESULTS

In this cohort, 92 942 persons were classified as warfarin users, and we observed 132 687 cancer cases in the 7-year study period. We observed a significantly lower sex and age-adjusted risk for cancer development across all malignancy types in the warfarin user group compared to the non-user group (IRR: 0.842, 95% CI, 0.824-0.861). The association was similar among many cancers including major types (prostate IRR: 0.687,95% CI 0.653-0.722; lung IRR: 0.801, 95% CI 0.749-0.856; breast IRR: 0.903, 95% CI 0.817-0.998). Given the expected confounding effect of thrombotic disease on cancer incidence, we conducted a subgroup analysis among patients prescribed warfarin for atrial fibrillation/flutter (AF-group), a subgroup with reduced comorbidity. Warfarin users in the AF-group showed a stronger overall cancer risk reduction (IRR: 0.619, 95%CI 0.592-0.646), including all major cancer types, particular lung cancer. (Prostate, IRR: 0.604, 95%CI 0.552-0.662; Lung IRR: 0.391, 95%CI 0.332-0.460; Breast IRR: 0.720, 95%CI 0.594-0.871)

CONCLUSION

We show that warfarin use is associated with a broad cancer protective effect in a large unselected patient cohort. Subgroup analysis of arrhythmia patients to reduce confounders reinforced the notion that warfarin exerts important anti-tumor effects.

Citation Format: Gry S. Haaland, Ragnhild S. Falk, Oddbjørn Straume, James B. Lorens. Broad reduction in cancer incidence in patients treated with warfarin: a prospective cohort study [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 3010. doi:10.1158/1538-7445.AM2017-3010

Clear Cell Renal Cell Carcinoma is linked to Epithelial-to-Mesenchymal Transition and to Fibrosis

Clear cell renal cell carcinoma (ccRCC) represents the most common type of kidney cancer with high mortality in its advanced stages. Our study aim was to explore the correlation between tumor epithelial-to-mesenchymal transition (EMT) and patient survival. Renal biopsies of tumorous and adjacent nontumorous tissue were taken with a 16 g needle from our patients (n = 26) undergoing partial or radical nephrectomy due to ccRCC RNA sequencing libraries were generated using Illumina TruSeq® Access library preparation protocol and TruSeq Small RNA library preparation kit. Next generation sequencing (NGS) was performed on Illumina HiSeq2500. Comparative analysis of matched sample pairs was done using the Bioconductor Limma/voom R-package. Liquid chromatography-tandem mass spectrometry and immunohistochemistry were applied to measure and visualize protein abundance. We detected an increased generic EMT transcript score in ccRCC Gene expression analysis showed augmented abundance of AXL and MMP14, as well as down-regulated expression of KL (klotho). Moreover, microRNA analyses demonstrated a positive expression correlation of miR-34a and its targets MMP14 and AXL Survival analysis based on a subset of genes from our list EMT-related genes in a publicly available dataset showed that the EMT genes correlated with ccRCC patient survival. Several of these genes also play a known role in fibrosis. Accordingly, recently published classifiers of solid organ fibrosis correctly identified EMT-affected tumor samples and were correlated with patient survival. EMT in ccRCC linked to fibrosis is associated with worse survival and may represent a target for novel therapeutic interventions.

Abstract P2-04-08: BGB324, a selective small molecule inhibitor of the receptor tyrosine kinase AXL, enhances immune checkpoint inhibitor efficacy in mammary adenocarcinoma

The AXL receptor tyrosine kinase is associated with poor overall survival in breast cancer. Axl signaling is an important regulator of tumor plasticity related to epithelial-to-mesenchymal transition (EMT) and stem cell traits that drive metastasis and drug resistance. Signaling via AXL is also a key suppressor of the anti-tumor innate immune response. AXL is expressed on several cells associated with the tumor immune microenvironment including natural killer cells, dendritic cells and tumor-associated macrophages. AXL is required for tumor immune evasion in mammary adenocarcinoma models and EMT-mediated resistance to cytotoxic T cell and natural killer (NK)-cell mediated cell killing. Hence AXL signaling contributes uniquely to both tumor cell intrinsic and microenvironmental anti-tumor immune suppression mechanisms in breast cancer. We evaluated whether blocking AXL signaling with BGB324, a selective clinical-stage small molecule Axl kinase inhibitor, enhances the effect of immune checkpoint blockade in the aggressive mammary adenocarcinoma (4T1) syngeneic (Balb/C) mouse modelthat display limited immunogenicity.

Immune therapy with anti-CTLA-4/anti-PD-1 increased AXL and EMT-marker expression in 4T1 tumors, and correlated with lack of response to immune therapy. Combination treatment with BGB324 (50 mg/kg bid) significantly enhanced responsiveness to anti-CTLA-4/anti-PD-1 treatment (10 mg/kg of each, 4 doses) in Balb/C mice bearing established 4T1 tumors. 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 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 were concomitantly abrogated in the animals responding to the combination treatment. In addition, BGB324 + anti-CTLA-4/anti-PD-1 treated tumors displayed enhanced infiltration of cytotoxic T lymphocytes (CTLs). Enhanced presence of CTLs was also detected in spleens from animals responding to treatment. BGB324 + anti-CTLA-4/anti-PD-1 treatment increased the number of NK cells, macrophages and polymorphonuclear neutrophils, but decreased the number of mMDSC. Importantly, responding animals rejected orthotopic 4T1 tumor cell re-challenge, demonstrating sustained tumor immunity.

Together with recent results in other tumor types that support a prominent role for AXL in resistance to immune therapy and encouraging results from ongoing clinical trials with BGB324, support combining BGB324 with immune checkpoint inhibitors to improve treatment of breast cancer.

Citation Format: Lorens JB, Lipinska KW, Davidsen K, Blø M, Hodneland L, Engelsen A, Kang J, Lie MK, Bougnaud S, Aguilera K, Ahmed L, Rybicka A, Nævdal EM, Deyna P, Boniecka A, Straume O, Chouaib S, Brekken RA, Gausdal G. BGB324, a selective small molecule inhibitor of the receptor tyrosine kinase AXL, enhances immune checkpoint inhibitor efficacy in mammary adenocarcinoma [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P2-04-08.

Acquisition of tumor cell phenotypic diversity along the EMT spectrum under hypoxic pressure: Consequences on susceptibility to cell-mediated cytotoxicity

Tumor escape to immunosurveillance and resistance to immune attacks present a major hurdle in cancer therapy, especially in the current era of new cancer immunotherapies. We report here that hypoxia, a hallmark of most solid tumors, orchestrates carcinoma cell heterogeneity through the induction of phenotypic diversity and the acquisition of distinct epithelial-mesenchymal transition (EMT) states. Using lung adenocarcinoma cells derived from a non-metastatic patient, we demonstrated that hypoxic stress induced phenotypic diversity along the EMT spectrum, with induction of EMT transcription factors (EMT-TFs) SNAI1, SNAI2, TWIST1, and ZEB2 in a hypoxia-inducible factor-1α (HIF1A)-dependent or -independent manner. Analysis of hypoxia-exposed tumor subclones, with pronounced epithelial or mesenchymal phenotypes, revealed that mesenchymal subclones exhibited an increased propensity to resist cytotoxic T lymphocytes (CTL), and natural killer (NK) cell-mediated lysis by a mechanism involving defective immune synapse signaling. Additionally, targeting EMT-TFs, or inhibition of TGF-β signaling, attenuated mesenchymal subclone susceptibility to immune attack. Together, these findings uncover hypoxia-induced EMT and heterogeneity as a novel driving escape mechanism to lymphocyte-mediated cytotoxicity, with the potential to provide new therapeutic opportunities for cancer patients.

Microsphere cytometry to interrogate microenvironment-dependent cell signaling

A novel microsphere-based flow cytometry approach to study adherent cell signaling responses in different microenvironmental contexts at the single cell level.

Adaptive mechanisms of resistance to anti-neoplastic agents

Intrinsic and acquired resistance to conventional and targeted therapeutics is a fundamental reason for treatment failure in many cancer patients. Targeted approaches to overcome chemoresistance as well as resistance to targeted approaches require in depth understanding of the underlying molecular mechanisms. The anti-cancer activity of a drug can be limited by a broad variety of molecular events at different levels of drug action in a cell-autonomous and non-cell-autonomous manner. This review summarizes recent insights into the adaptive mechanisms used by tumours to resist therapy including cellular phenotypic plasticity, dynamic alterations of the tumour microenvironment, activation of redundant signal transduction pathways, modulation of drug target expression levels, and exploitation of pro-survival responses.

Abstract 5182: A rapid in vivo screen for pancreatic ductal adenocarcinoma therapeutics using the tumor marker Rgs16::GFP

Pancreatic Ductal Adenocarcinoma (PDA) is the most lethal major cancer in the USA due to lack of early diagnostics and effective treatments. Activating Kras mutations (such as KrasG12D) occur early in tumor progression and are present in about 90% of PDA. Pancreatic Intraepithelial Neoplasms (PanIN) are the most common initial neoplastic lesions and those with activating Kras alleles typically progress to carcinoma in situ and metastasize.

Receptor Tyrosine Kinases (RTK) and G-protein Coupled Receptors (GPCR) can indirectly activate Kras and are therefore potential drug targets. We previously showed that a feedback inhibitor of GPCRs, Regulator of G-protein Signaling 16 (Rgs16), is expressed in pancreatic progenitors during embryonic development. Rgs16 expression continues postnatally in ducts and beta cells during isletogenesis but is absent in normal glycemic adults. On the other hand, Rgs16 expression returns to ducts and islet beta cells after chronic hyperglycemia in mouse models of Type 1 and Type 2 Diabetes mellitus. Our hypothesis is that Rgs16::GFP is induced in these pancreatic cells in response to GPCR agonists released during chronic stress. In an effort to conduct drug screens in primary duct cell culture, we investigated Rgs16::GFP expression in pancreatic neoplasia by crossing it into a mouse model of aggressive PDA, called KIC (KrasG12D; Cdkn2aL/L; Ptf1a::Cre).

In Rgs16::GFP-KIC mice, Rgs16 was expressed at the initiation of PDA in early PanINs, as early as two weeks after birth (P15), and throughout tumor progression. Rgs16::GFP expression increased with tumor mass through one month of age (P29). We used this tumor specific characteristic of Rgs16 expression to set-up a two-week in vivo quantitative assay to test chemotherapeutic drug effectiveness. In a proof-of-principle study, the standard PDA therapeutics gemcitabine and nab-Paclitaxel reduced Rgs16::GFP expression and tumor burden compared to untreated mice at P29. Targeting Axl, an RTK highly expressed in PDA, with two different inhibitors of Axl signaling, BGB324 or warfarin, in combination with gemcitabine and nab-Paclitaxel further reduced PDA initiation and progression compared to standard chemotherapy alone. Survival studies with Rgs16::GFP-KIC mice showed that treatment with gemcitabine and warfarin extended median life span about two weeks while nearly doubling the maximum life span compared to untreated group.

In summary, Rgs16::GFP-KIC mice provide an in vivo model to rapidly identify more effective PDA chemotherapeutics and treatment protocols.

Citation Format: Ozhan Ocal, Victor Pashkov, Rahul K. Kollipara, James B. Lorens, Galvin H. Swift, Rolf A. Brekken, Thomas M. Wilkie. A rapid in vivo screen for pancreatic ductal adenocarcinoma therapeutics using the tumor marker Rgs16::GFP. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 5182.

Abstract B014: BGB324, a selective small molecule inhibitor of the receptor tyrosine kinase AXL, enhances immune checkpoint inhibitor efficacy

Signaling via the AXL receptor tyrosine kinase is a key suppressor of anti-tumor innate immune response. AXL is expressed on several cells associated with the suppressive tumor immune microenvironment including natural killer cells, dendritic cells and tumor-associated macrophages. AXL is also an important regulator of tumor plasticity related to epithelial-to-mesenchymal transition (EMT) that contributes to anti-tumor immune evasion. Hence AXL signaling contributes uniquely to tumor intrinsic and microenvironmental immune suppression in tumors. We therefore evaluated whether blocking AXL signaling with BGB324, a selective clinical-stage small molecule Axl kinase inhibitor, enhances the effect of immune checkpoint blockade in syngeneic cancer mouse models that display limited immunogenicity.

We measured the effect of BGB324 in combination with anti-CTLA-4 and anti-PD-1 in the mammary adenocarcinoma 4T1/Balb/C syngeneic mouse model. BGB324 (50 mg/kg bid) significantly enhanced responsiveness to anti-CTLA-4/anti-PD-1 treatment (10 mg/kg of each, 4 doses) in Balb/C mice bearing 4T1 tumors. The combination of BGB324 + anti-CTLA-4/anti-PD-1 resulted in complete tumor clearance in 46.1 % of mice versus complete tumor clearance in 11.7 % of the mice treated with anti-CTLA-4/anti-PD-1 (p = 0.0087). BGB324 + anti-CTLA-4/anti-PD-1 treated tumors displayed enhanced CD8+ T cell tumor infiltration. Combination of BGB324 with immune checkpoint inhibitors is being evaluated in additional models, and detailed interrogation of AXL-dependent immune effector cell activity in tumors is in progress.

In conclusion, AXL inhibition represents a unique opportunity to target anti-tumor immune suppressive mechanisms and supports clinical translation of BGB324 in combination with cancer immunotherapy in human cancer.

Citation Format: Gro Gausdal, Kjersti Davidsen, Katarzyna Wnuk-Lipinska, Kathleen Wiertel, Monica Hellesøy, Magnus Blø, Lavina Ahmed, Linn Hodneland, Sergej Kiprijanov, Rolf A Brekken, James B Lorens. BGB324, a selective small molecule inhibitor of the receptor tyrosine kinase AXL, enhances immune checkpoint inhibitor efficacy. [abstract]. In: Proceedings of the CRI-CIMT-EATI-AACR Inaugural International Cancer Immunotherapy Conference: Translating Science into Survival; September 16-19, 2015; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(1 Suppl):Abstract nr B014.

A rapid in vivo screen for pancreatic ductal adenocarcinoma therapeutics

Pancreatic ductal adenocarcinoma (PDA) is the fourth leading cause of cancer-related deaths in the United States, and is projected to be second by 2025. It has the worst survival rate among all major cancers. Two pressing needs for extending life expectancy of affected individuals are the development of new approaches to identify improved therapeutics, addressed herein, and the identification of early markers. PDA advances through a complex series of intercellular and physiological interactions that drive cancer progression in response to organ stress, organ failure, malnutrition, and infiltrating immune and stromal cells. Candidate drugs identified in organ culture or cell-based screens must be validated in preclinical models such as KIC (p48(Cre);LSL-Kras(G12D);Cdkn2a(f/f)) mice, a genetically engineered model of PDA in which large aggressive tumors develop by 4 weeks of age. We report a rapid, systematic and robust in vivo screen for effective drug combinations to treat Kras-dependent PDA. Kras mutations occur early in tumor progression in over 90% of human PDA cases. Protein kinase and G-protein coupled receptor (GPCR) signaling activates Kras. Regulators of G-protein signaling (RGS) proteins are coincidence detectors that can be induced by multiple inputs to feedback-regulate GPCR signaling. We crossed Rgs16::GFP bacterial artificial chromosome (BAC) transgenic mice with KIC mice and show that the Rgs16::GFP transgene is a Kras(G12D)-dependent marker of all stages of PDA, and increases proportionally to tumor burden in KIC mice. RNA sequencing (RNA-Seq) analysis of cultured primary PDA cells reveals characteristics of embryonic progenitors of pancreatic ducts and endocrine cells, and extraordinarily high expression of the receptor tyrosine kinase Axl, an emerging cancer drug target. In proof-of-principle drug screens, we find that weanling KIC mice with PDA treated for 2 weeks with gemcitabine (with or without Abraxane) plus inhibitors of Axl signaling (warfarin and BGB324) have fewer tumor initiation sites and reduced tumor size compared with the standard-of-care treatment. Rgs16::GFP is therefore an in vivo reporter of PDA progression and sensitivity to new chemotherapeutic drug regimens such as Axl-targeted agents. This screening strategy can potentially be applied to identify improved therapeutics for other cancers.

Warfarin Blocks Gas6-Mediated Axl Activation Required for Pancreatic Cancer Epithelial Plasticity and Metastasis

Repurposing "old" drugs can facilitate rapid clinical translation but necessitates novel mechanistic insight. Warfarin, a vitamin K "antagonist" used clinically for the prevention of thrombosis for more than 50 years, has been shown to have anticancer effects. We hypothesized that the molecular mechanism underlying its antitumor activity is unrelated to its effect on coagulation, but is due to inhibition of the Axl receptor tyrosine kinase on tumor cells. Activation of Axl by its ligand Gas6, a vitamin K-dependent protein, is inhibited at doses of warfarin that do not affect coagulation. Here, we show that inhibiting Gas6-dependent Axl activation with low-dose warfarin, or with other tumor-specific Axl-targeting agents, blocks the progression and spread of pancreatic cancer. Warfarin also inhibited Axl-dependent tumor cell migration, invasiveness, and proliferation while increasing apoptosis and sensitivity to chemotherapy. We conclude that Gas6-induced Axl signaling is a critical driver of pancreatic cancer progression and its inhibition with low-dose warfarin or other Axl-targeting agents may improve outcome in patients with Axl-expressing tumors.

Abstract B78: Warfarin blocks Gas6-mediated Axl activation required for pancreatic tumor plasticity and metastasis

Warfarin, a vitamin K antagonist anti-coagulant in clinical use for over 50 years, is reported to exert anti-cancer effects. We hypothesized that the molecular mechanism underlying the observed anti-tumor effects of warfarin is unrelated to generalized anti-coagulation, but rather due to inhibition of the Axl receptor tyrosine kinase. Activation of Axl by its ligand Gas6, a vitamin K-dependent protein, is inhibited at doses of warfarin that do not affect coagulation. Here we document that inhibiting Gas6-mediated Axl activation with low dose warfarin blocks pancreatic cancer progression and spread. Warfarin and other Axl-targeting agents inhibit tumor progression and block spontaneous metastasis in multiple murine models of pancreatic cancer. Warfarin inhibited Axl-dependent tumor cell migration, invasiveness and proliferation while increasing apoptosis and sensitivity to chemotherapy. We demonstrate that Axl signaling is necessary for pancreatic tumor cell epithelial plasticity which is potently reversed by warfarin or selective Axl inhibition in vitro and in vivo. We anticipate Axl is a critical driver of pancreatic cancer progression and its inhibition with low dose warfarin or Axl-selective targeting agents may significantly improve outcome in patients.

Citation Format: Amanda Kirane, Kathleen W. Ludwig, Gry Haaland, Tone Sandal, Renata Ranaweera, Jason E. Toombs, Laura A. Sullivan, Miao Wang, Noah Sorrelle, Sean P. Dineen, Michael T. Dellinger, James B. Lorens, Rolf A. Brekken. Warfarin blocks Gas6-mediated Axl activation required for pancreatic tumor plasticity and metastasis. [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer: Innovations in Research and Treatment; May 18-21, 2014; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2015;75(13 Suppl):Abstract nr B78.

Cellular context-mediated Akt dynamics regulates MAP kinase signaling thresholds during angiogenesis

This study examines the temporal regulation of Akt in endothelial cells during formation of capillary-like networks induced by cell–cell contact with vascular smooth muscle cells (vSMCs) and vSMC-associated VEGF. Heterotypic cell–cell interaction between mural and endothelial cells alters Akt kinase protein dynamics, which regulates angiogenesis.

The formation of new blood vessels by sprouting angiogenesis is tightly regulated by contextual cues that affect angiogeneic growth factor signaling. Both constitutive activation and loss of Akt kinase activity in endothelial cells impair angiogenesis, suggesting that Akt dynamics mediates contextual microenvironmental regulation. We explored the temporal regulation of Akt in endothelial cells during formation of capillary-like networks induced by cell–cell contact with vascular smooth muscle cells (vSMCs) and vSMC-associated VEGF. Expression of constitutively active Akt1 strongly inhibited network formation, whereas hemiphosphorylated Akt1 epi-alleles with reduced kinase activity had an intermediate inhibitory effect. Conversely, inhibition of Akt signaling did not affect endothelial cell migration or morphogenesis in vSMC cocultures that generate capillary-like structures. We found that endothelial Akt activity is transiently blocked by proteasomal degradation in the presence of SMCs during the initial phase of capillary-like structure formation. Suppressed Akt activity corresponded to the increased endothelial MAP kinase signaling that was required for angiogenic endothelial morphogenesis. These results reveal a regulatory principle by which cellular context regulates Akt protein dynamics, which determines MAP kinase signaling thresholds necessary drive a morphogenetic program during angiogenesis.

Vimentin-ERK Signaling Uncouples Slug Gene Regulatory Function

Epithelial-mesenchymal transition (EMT) in cells is a developmental process adopted during tumorigenesis that promotes metastatic capacity. In this study, we advance understanding of EMT control in cancer cells with the description of a novel vimentin-ERK axis that regulates the transcriptional activity of Slug (SNAI2). Vimentin, ERK, and Slug exhibited overlapping subcellular localization in clinical specimens of triple-negative breast carcinoma. RNAi-mediated ablation of these gene products inhibited cancer cell migration and cell invasion through a laminin-rich matrix. Biochemical analyses demonstrated direct interaction of vimentin and ERK, which promoted ERK activation and enhanced vimentin transcription. Consistent with its role as an intermediate filament, vimentin acted as a scaffold to recruit Slug to ERK and promote Slug phosphorylation at serine-87. Site-directed mutagenesis established a requirement for ERK-mediated Slug phosphorylation in EMT initiation. Together, these findings identified a pivotal step in controlling the ability of Slug to organize hallmarks of EMT.

Akt1 activity regulates vessel maturation in a tissue engineering model of angiogenesis

Akt kinase is a central signal transduction node that integrates extracellular cues that regulate cell migratory, proliferative, and morphological functions during angiogenesis. However, how Akt activity is modulated and contributes to subsequent vessel maturation is unclear. In this study we investigated the role of Akt1 in vessel maturation using human dermal microvascular endothelial cells (HDMVECs) expressing constitutively active and hemiphosphorylated Akt1 epi-alleles with graded kinase activity. HDMVECs expressing Akt1 epi-alleles were analyzed in vivo in a tissue engineering setting using a model of angiogenesis comprising cell-seeded poly-L-lactic acid scaffolds implanted subcutaneously into NOD/SCID murine hosts. The resultant intraimplant microvasculature was quantified for vascular parameters, including vessel diameter, perfusion, vascular density, and pericyte coverage. We found that constitutive Akt1 kinase activity in implanted HDMVECs correlated with loss of neovasculature function. Further, we found that the presence of coimplanted vascular smooth muscle cells (vSMCs) in the implants failed to promote blood vessel growth and maturation in a graded, Akt1 kinase activity-dependent manner. These results indicate that constitutive Akt1 activity disrupts the normal blood vessel growth and maturation. Therefore, we suggest that a downregulation of Akt1 activity is necessary for vSMC-induced maturation of newly formed blood vessels to occur.