Antiangiogenic Cancer Therapy Research Articles

Gut microbiome influences efficacy of Endostatin combined with PD-1 blockade against colorectal cancer

The combination of anti-angiogenic drugs and immune checkpoint inhibitors (ICIs) in the treatment of tumors is emerging as a way to improve ICIs-resistant tumor therapy. In addition, gut microbes (GMs) are involved in angiogenesis in the tumor microenvironment and are also associated with the antitumor function of immune checkpoint inhibitors. However, it is unclear whether gut microbes have a role in anti-tumor function in the combination of anti-angiogenic drugs and immune checkpoint inhibitors for cancer treatment. Endostatin, an angiogenesis inhibitor, has been widely used as an antiangiogenic therapy for cancer. We showed that combined therapy with an adenovirus encoding human endostatin, named Ad-E, and PD-1 blockade dramatically abrogated MC38 tumor growth. The structure of intestinal microbes in mice was changed after combination treatment. We found that the antitumor function of combination therapy was inhibited after the elimination of intestinal microbes. In mice with depleted microbiota, oral gavage of Bacteroides fragilis salvaged the antitumor effects of combination Ad-E and αPD-1 monoclonal antibody (mAb) to a certain extent. Further, Bacteroides fragilis could improve CD3+T cells, NK cells, and IFNγ+CD8+ T cells in the tumor microenvironment to inhibit tumor growth. Besides, Bacteroides fragilis might restore antitumor function by down-regulating isobutyric acid (IBA). Our results suggested that GMs may be involved in the combination of Ad-E and αPD-1 mAb for cancer treatment, which has oncological implications for tumor growth dynamics and cancer immune surveillance.

Tumor angiogenesis and anti-angiogenic therapy.

Anti-angiogenic drugs (AADs), which mainly target the vascular endothelial growth factor-A signaling pathway, have become a therapeutic option for cancer patients for two decades. During this period, tremendous clinical experience of anti-angiogenic therapy has been acquired, new AADs have been developed, and the clinical indications for AAD treatment of various cancers have been expanded using monotherapy and combination therapy. However, improvements in the therapeutic outcomes of clinically available AADs and the development of more effective next-generation AADs are still urgently required. This review aims to provide historical and perspective views on tumor angiogenesis to allow readers to gain mechanistic insights and learn new therapeutic development. We revisit the history of concept initiation and AAD discovery, and summarize the up-to-date clinical translation of anti-angiogenic cancer therapy in this field.

Celebrating the 1945 JNCI pioneering contribution to antiangiogenic therapy for cancer.

Celebrating the 1945 JNCI pioneering contribution to antiangiogenic therapy for cancer.

Role of Protein Phosphatases in Tumor Angiogenesis: Assessing PP1, PP2A, PP2B and PTPs Activity.

Tumor angiogenesis, the formation of new blood vessels to support tumor growth and metastasis, is a complex process regulated by a multitude of signaling pathways. Dysregulation of signaling pathways involving protein kinases has been extensively studied, but the role of protein phosphatases in angiogenesis within the tumor microenvironment remains less explored. However, among angiogenic pathways, protein phosphatases play critical roles in modulating signaling cascades. This review provides a comprehensive overview of the involvement of protein phosphatases in tumor angiogenesis, highlighting their diverse functions and mechanisms of action. Protein phosphatases are key regulators of cellular signaling pathways by catalyzing the dephosphorylation of proteins, thereby modulating their activity and function. This review aims to assess the activity of the protein tyrosine phosphatases and serine/threonine phosphatases. These phosphatases exert their effects on angiogenic signaling pathways through various mechanisms, including direct dephosphorylation of angiogenic receptors and downstream signaling molecules. Moreover, protein phosphatases also crosstalk with other signaling pathways involved in angiogenesis, further emphasizing their significance in regulating tumor vascularization, including endothelial cell survival, sprouting, and vessel maturation. In conclusion, this review underscores the pivotal role of protein phosphatases in tumor angiogenesis and accentuate their potential as therapeutic targets for anti-angiogenic therapy in cancer.

High-throughput barcoding of nanoparticles identifies cationic, degradable lipid-like materials for mRNA delivery to the lungs in female preclinical models

Lipid nanoparticles for delivering mRNA therapeutics hold immense promise for the treatment of a wide range of lung-associated diseases. However, the lack of effective methodologies capable of identifying the pulmonary delivery profile of chemically distinct lipid libraries poses a significant obstacle to the advancement of mRNA therapeutics. Here we report the implementation of a barcoded high-throughput screening system as a means to identify the lung-targeting efficacy of cationic, degradable lipid-like materials. We combinatorially synthesize 180 cationic, degradable lipids which are initially screened in vitro. We then use barcoding technology to quantify how the selected 96 distinct lipid nanoparticles deliver DNA barcodes in vivo. The top-performing nanoparticle formulation delivering Cas9-based genetic editors exhibits therapeutic potential for antiangiogenic cancer therapy within a lung tumor model in female mice. These data demonstrate that employing high-throughput barcoding technology as a screening tool for identifying nanoparticles with lung tropism holds potential for the development of next-generation extrahepatic delivery platforms.

Serum angiopoietin-like protein 2 level in patients who received bevacizumab-containing chemotherapy for metastatic colorectal cancer.

209 Background: Anti-angiogenic agents are important for treating patients with advanced colorectal adenocarcinoma, however, their efficacy is not long-lasting and survival benefits are modest. Reliable biomarkers and novel targets for angiogenesis are still required in this era. Angiopoietin-like protein 2 (AGLP-2) is an emerging biomarker for angiogenesis in cardiovascular disease, but its role in the oncology area is yet to be elucidated. Methods: Serum samples from patients with advanced colorectal carcinoma treated with bevacizumab-containing chemotherapy were retrospectively studied. Blood samples at baseline and at disease progression of the first line systemic therapy were selected. Serum angiopoietin-like protein 2 (AGLP-2) concentrations were measured using ELISA kit, serial changes, and the relationship with progression-free survival and overall survival on the systemic therapy were statistically analyzed. Results: 68 patients were enrolled. Their median age was 66 years old (range, 38-82), and 14 (20.6%) patients had metastatic lesions at 3 or 4 organs. The median serum AGLP-2 levels at baseline and at disease progression (PD) were 41,618 pg/ml (95% confidence interval (CI) 34,560-40,713), and 49,706 pg/ml (95% CI 39,853-49,017), respectively. There was a tendency of difference between AGLP-2 levels at baseline and at PD ( p=0.057). Patients whose baseline serum AGLP-2 levels with 40,000 pg/ml or above showed relatively shorter overall survival (median 31.4 months with 95% CI, 14.4-38.6) compared with patients with serum AGLP-2 level below 40,000 pg/ml at baseline (median 38.6 months with 95% CI, 23.6-127.3), but not statistically significant ( p=0.0946). There was no survival difference observed according to serum AGLP-2 levels at disease progression on the first line bevacizumab-containing chemotherapy. Conclusions: Serum angiopoietin-like protein-2 has potential as a new target for novel anti-angiogenic therapy in metastatic colorectal cancer.

Potential of natural flavonoids to target breast cancer angiogenesis (review).

Angiogenesis is the process by which new blood vessels form and is required for tumour growth and metastasis. It helps in supplying oxygen and nutrients to tumour cells and plays a crucial role in the local progression and distant metastasis of, and development of treatment resistance in, breast cancer. Tumour angiogenesis is currently regarded as a critical therapeutic target; however, anti-angiogenic therapy for breast cancer fails to produce satisfactory results, owing to issues such as inconsistent efficacy and significant adverse reactions. As a result, new anti-angiogenic drugs are urgently needed. Flavonoids, a class of natural compounds found in many foods, are inexpensive, widely available, and exhibit a broad range of biological activities, low toxicity, and favourable safety profiles. Several studies find that various flavonoids inhibit angiogenesis in breast cancer, indicating great therapeutic potential. In this review, we summarize the role of angiogenesis in breast cancer and the potential of natural flavonoids as anti-angiogenic agents for breast cancer treatment. We discuss the value and significance of nanotechnology for improving flavonoid absorption and utilization and anti-angiogenic effects, as well as the challenges of using natural flavonoids as drugs.

Role of Angiogenesis and Its Biomarkers in Development of Targeted Tumor Therapies.

Angiogenesis plays a significant role in the human body, from wound healing to tumor progression. "Angiogenic switch" indicates a time-restricted event where the imbalance between pro- and antiangiogenic factors results in the transition from prevascular hyperplasia to outgrowing vascularized tumor, which eventually leads to the malignant cancer progression. In the last decade, molecular players, i.e., angiogenic biomarkers and underlying molecular pathways involved in tumorigenesis, have been intensely investigated. Disrupting the initiation and halting the progression of angiogenesis by targeting these biomarkers and molecular pathways has been considered as a potential treatment approach for tumor angiogenesis. This review discusses the currently known biomarkers and available antiangiogenic therapies in cancer, i.e., monoclonal antibodies, aptamers, small molecular inhibitors, miRNAs, siRNAs, angiostatin, endostatin, and melatonin analogues, either approved by the U.S. Food and Drug Administration or currently under clinical and preclinical investigations.

Advances in Predictive Biomarkers for Anti-Angiogenic Therapy in Non-Small Cell Lung Cancer.

This study aimed to explore advances in biomarkers related to anti-angiogenic therapy in patients with non-small cell lung cancer (NSCLC), thereby enhancing treatment selection, advancing personalized and precision medicine to improve treatment outcomes and patient survival rates. This article reviews key discoveries in predictive biomarkers for anti-angiogenic therapy in NSCLC in recent years, such as (1) liquid biopsy predictive biomarkers: studies have identified activated circulating endothelial cells (aCECs) via liquid biopsy as potential predictive biomarkers for the efficacy of anti-angiogenic therapy; (2) imaging biomarkers: advanced imaging technologies, such as dynamic contrast-enhanced integrated magnetic resonance positron emission tomography (MR-PET), are used to assess tumor angiogenesis in patients with NSCLC and evaluate the clinical efficacy of anti-angiogenic drugs; (3) genetic predictive biomarkers: research has explored polymorphisms of Vascular Endothelial Growth Factor Receptor-1 (VEGFR-1) and vascular endothelial growth factor-A (VEGF-A), as well as how plasma levels of VEGF-A can predict the outcomes and prognosis of patients with non-squamous NSCLC undergoing chemotherapy combined with bevacizumab. Despite progress in identifying biomarkers related to anti-angiogenic therapy, several challenges remain, including limitations in clinical trials, heterogeneity in NSCLC, and technical hurdles. Future research will require extensive clinical validation and in-depth mechanistic studies to fully exploit the potential of these biomarkers for personalized treatment.

Biomechanical stimulation promotes blood vessel growth despite VEGFR-2 inhibition

BackgroundAngiogenesis, or the growth of new vasculature from existing blood vessels, is widely considered a primary hallmark of cancer progression. When a tumor is small, diffusion is sufficient to receive essential nutrients; however, as the tumor grows, a vascular supply is needed to deliver oxygen and nutrients into the increasing mass. Several anti-angiogenic cancer therapies target VEGF and the receptor VEGFR-2, which are major promoters of blood vessel development. Unfortunately, many of these cancer treatments fail to completely stop angiogenesis in the tumor microenvironment (TME). Since these therapies focus on the biochemical activation of VEGFR-2 via VEGF ligand binding, we propose that mechanical cues, particularly those found in the TME, may be a source of VEGFR-2 activation that promotes growth of blood vessel networks even in the presence of VEGF and VEGFR-2 inhibitors.ResultsIn this paper, we analyzed phosphorylation patterns of VEGFR-2, particularly at Y1054/Y1059 and Y1214, stimulated via either VEGF or biomechanical stimulation in the form of tensile strains. Our results show prolonged and enhanced activation at both Y1054/Y1059 and Y1214 residues when endothelial cells were stimulated with strain, VEGF, or a combination of both. We also analyzed Src expression, which is downstream of VEGFR-2 and can be activated through strain or the presence of VEGF. Finally, we used fibrin gels and microfluidic devices as 3D microtissue models to simulate the TME. We determined that regions of mechanical strain promoted increased vessel growth, even with VEGFR-2 inhibition through SU5416.ConclusionsOverall, understanding both the effects that biomechanical and biochemical stimuli have on VEGFR-2 activation and angiogenesis is an important factor in developing effective anti-angiogenic therapies. This paper shows that VEGFR-2 can be mechanically activated through strain, which likely contributes to increased angiogenesis in the TME. These proof-of-concept studies show that small molecular inhibitors of VEGFR-2 do not fully prevent angiogenesis in 3D TME models when mechanical strains are introduced.

NGR-bearing human adenovirus type 5 infects cells in flotillin- or caveolin-mediated manner depending on the NGR insertion site

Human adenoviruses represent attractive candidates for the design of cancer gene therapy vectors. Modification of adenovirus tropism by incorporating a targeting ligand into the adenovirus capsid proteins allows retargeting of adenovirus towards the cells of interest. Human adenovirus type 5 (HAdV-C5) bearing NGR containing peptide (CNGRCVSGCAGRC) inserted into the fiber (AdFNGR) or the hexon (AdHNGR) protein demonstrated an increased transduction of endothelial cells showing expression of aminopeptidase N, also known as CD13, and αvβ3 integrin both present on tumor vasculature, indicating that NGR-bearing adenoviruses could be used as tools for anti-angiogenic cancer therapy. Here we investigated how AdFNGR and AdHNGR infect cells lacking HAdV-C5 primary receptor, coxsackie and adenovirus receptor, and we showed that both AFNGR and AdHNGR enter cells by dynamin- and lipid raft-mediated endocytosis, while clathrin is not required for endocytosis of these viruses. We present evidence that productive infection of both AdFNGR and AdHNGR involves lipid rafts, with usage of flotillin-mediated cell entry for AdFNGR and limited role of caveolin in AdHNGR transduction efficiency. Lipid rafts play important role in angiogenesis and process of metastasis. Therefore, the ability of AdFNGR and AdHNGR to use lipid raft-dependent endocytosis, involving respectively flotillin- or caveolin-mediated pathway, could give them an advantage in targeting tumor cells lacking HAdV-C5 primary receptor.

Molecularly Imprinted Nanomedicine for Anti-angiogenic Cancer Therapy via Blocking Vascular Endothelial Growth Factor Signaling.

The VEGF-VEGFR2 (VEGF = vascular endothelial growth factor) signaling has been a promising target in cancer therapy. However, because conventional anti-angiogenic therapeutics suffer from drawbacks, particularly severe side effects, novel anti-angiogenic strategies are much needed. Herein, we report the rational engineering of VEGF-targeted molecularly imprinted polymer nanoparticles (nanoMIP) for anti-angiogenic cancer therapy. The anti-VEGF nanomedicine was prepared via a state-of-the-art molecular imprinting approach using the N-terminal epitope of VEGF as the template. The nanoMIP could target the two major pro-angiogenic isoforms (VEGF165 and VEGF121) with high affinity and thereby effectively block the VEGF-VEGFR2 signaling, yielding a potent anti-angiogenic effect of "killing two birds with one stone". In vivo experiments demonstrated that the anti-VEGF nanoMIP effectively suppressed tumor growth via anti-angiogenesis in a xenograft model of human colon carcinoma without apparent side effects. Thus, this study not only proposes an unprecedented anti-angiogenic strategy for cancer therapy but also provides a new paradigm for the rational development of MIPs-based "drug-free" nanomedicines.

ENO2-derived phosphoenolpyruvate functions as an endogenous inhibitor of HDAC1 and confers resistance to antiangiogenic therapy.

Metabolic reprogramming is associated with resistance to antiangiogenic therapy in cancer. However, its molecular mechanisms have not been clearly elucidated. Here, we identify the glycolytic enzyme enolase 2 (ENO2) as a driver of resistance to antiangiogenic therapy in colorectal cancer (CRC) mouse models and human participants. ENO2 overexpression induces neuroendocrine differentiation, promotes malignant behaviour in CRC and desensitizes CRC to antiangiogenic drugs. Mechanistically, the ENO2-derived metabolite phosphoenolpyruvate (PEP) selectively inhibits histone deacetylase 1 (HDAC1) activity, which increases the acetylation of β-catenin and activates the β-catenin pathway in CRC. Inhibition of ENO2 with enolase inhibitors AP-III-a4 or POMHEX synergizes the efficacy of antiangiogenic drugs in vitro and in mice bearing drug-resistant CRC xenograft tumours. Together, our findings reveal that ENO2 constitutes a useful predictive biomarker and therapeutic target for resistance to antiangiogenic therapy in CRC, and uncover a previously undefined and metabolism-independent role of PEP in regulating resistance to antiangiogenic therapy by functioning as an endogenous HDAC1 inhibitor.

Vascular Endothelial Growth Factor-D (VEGF-D): An Angiogenesis Bypass in Malignant Tumors.

Vascular endothelial growth factors (VEGFs) are the key regulators of vasculogenesis in normal and oncological development. VEGF-A is the most studied angiogenic factor secreted by malignant tumor cells under hypoxic and inflammatory stress, which made VEGF-A a rational target for anticancer therapy. However, inhibition of VEGF-A by monoclonal antibody drugs led to the upregulation of VEGF-D. VEGF-D was primarily described as a lymphangiogenic factor; however, VEGF-D's blood angiogenic potential comparable to VEGF-A has already been demonstrated in glioblastoma and colorectal carcinoma. These findings suggested a role for VEGF-D in facilitating malignant tumor growth by bypassing the anti-VEGF-A antiangiogenic therapy. Owing to its high mitogenic ability, higher affinity for VEGFR-2, and higher expression in cancer, VEGF-D might even be a stronger angiogenic driver and, hence, a better therapeutic target than VEGF-A. In this review, we summarized the angiogenic role of VEGF-D in blood vasculogenesis and its targetability as an antiangiogenic therapy in cancer.

Single-cell RNA sequencing reveals small extracellular vesicles derived from malignant cells that contribute to angiogenesis in human breast cancers

BackgroundBreast cancer is the most common cancer affecting women across the world. Tumor endothelial cells (TECs) and malignant cells are the major constituents of the tumor microenvironment (TME), but their origin and role in shaping disease initiation, progression, and treatment responses remain unclear due to significant heterogeneity.MethodsTissue samples were collected from eight patients presenting with breast cancer. Single-cell RNA sequencing (scRNA-seq) analysis was employed to investigate the presence of distinct cell subsets in the tumor microenvironment. InferCNV was used to identify cancer cells. Pseudotime trajectory analysis revealed the dynamic process of breast cancer angiogenesis. We validated the function of small extracellular vesicles (sEVs)-derived protein phosphatase 1 regulatory inhibitor subunit 1B (PPP1R1B) in vitro experiments.ResultsWe performed single-cell transcriptomics analysis of the factors associated with breast cancer angiogenesis and identified twelve subclusters of endothelial cells involved in the tumor microenvironment. We also identified the role of TECs in tumor angiogenesis and confirmed their participation in different stages of angiogenesis, including communication with other cell types via sEVs. Overall, the research uncovered the TECs heterogeneity and the expression levels of genes at different stages of tumor angiogenesis.ConclusionsThis study showed sEVs derived from breast cancer malignant cells promote blood vessel formation by activating endothelial cells through the transfer of PPP1R1B. This provides a new direction for the development of anti-angiogenic therapies for human breast cancer.

Jujuboside B suppresses angiogenesis and tumor growth via blocking VEGFR2 signaling pathway

Jujuboside B (JuB), one of the main active triterpenoid saponins from the traditional Chinese medicine Ziziphus jujuba, possesses a wide range of pharmacological activities. However, it is unknown whether JuB can inhibit tumor angiogenesis, a crucial step in solid tumor growth. In this study, we found that JuB significantly inhibited the proliferation, migration, and tube formation of human umbilical vein endothelial cells in a dose-dependent manner. JuB also suppressed angiogenesis in chick embryo chorioallantoic membranes and Matrigel plugs. Moreover, through angiogenesis inhibition, JuB delayed the growth of human HCT-15 colorectal cancer xenograft in mice. Western blot assay demonstrated that JuB inhibited the phosphorylation of VEGFR2 and its key downstream protein kinases, such as Akt, FAK, Src, and PLCγ1. In conclusion, the antiangiogenic potency and molecular mechanism of JuB are revealed for the first time, indicating that this triterpene saponin may be further explored as a potential drug candidate or lead compound for antiangiogenic cancer therapy.

Efficacy and safety of combined immunotherapy and antiangiogenic therapy for advanced non-small cell lung cancer: a real-world observation study

PurposeThis study was performed to investigate the efficacy and safety of combined immunotherapy and antiangiogenic therapy for advanced non-small cell lung cancer (NSCLC) in the real world.MethodsData on clinicopathological features, efficacy and adverse events (AEs) were collected retrospectively in advanced NSCLC patients who received immunotherapy combined with antiangiogenic therapy.ResultsA total of 85 advanced NSCLC patients were enrolled. The patients had a median progression-free survival (PFS) of 7.9 months and a median overall survival (OS) of 18.60 months. The objective response rate and disease control rate were 32.9% and 83.5%, respectively. Subgroup analysis revealed that NSCLC patients with stage IV (p = 0.042), brain metastasis (p = 0.016) and bone metastasis (p = 0.016) had shorter PFS. NSCLC patients with brain metastasis (p = 0.025), liver metastasis (p = 0.012), bone metastasis (p = 0.014) and EGFR mutations (p = 0.033) had shorter OS. Multivariate analysis revealed that brain metastasis (HR = 1.798, 95% CI: 1.038, 3.112, p = 0.036) and bone metastasis (HR = 1.824, 95% CI: 1.077, 3.090, p = 0.025) were independent predictive factors of PFS, and bone metastasis (HR = 2.00, 95% CI: 1.124, 3.558, p = 0.018) was an independent predictive factor of OS. In addition, patients receiving immunotherapy combined with antiangiogenic therapy in second-line therapy had longer OS than those receiving immunotherapy in third- or later-line therapy (p = 0.039). Patients with EGFR mutations who received combination therapy had worse OS than those with KRAS mutations (p = 0.026). Furthermore, PD-L1 expression was associated with treatment responses in advanced NSCLC (χ2 = 22.123, p = 0.000). AEs of different grades occurred in 92.9% (79/85) of NSCLC patients, most of which were mild grade 1/2 AEs. No grade 5 fatal AEs occurred.ConclusionImmunotherapy combined with antiangiogenic therapy was an option for advanced NSCLC patients with good safety and tolerability. Brain metastases and bone metastases were potentially independent negative predictors of PFS. Bone metastases were a potential independent negative predictor of OS. PD-L1 expression was a potential predictor of response for immunotherapy combined with antiangiogenic therapy.

Anti-angiogenic therapy in ovarian cancer: Current understandings and prospects of precision medicine.

Ovarian cancer (OC) remains the most fatal disease of gynecologic malignant tumors. Angiogenesis refers to the development of new vessels from pre-existing ones, which is responsible for supplying nutrients and removing metabolic waste. Although not yet completely understood, tumor vascularization is orchestrated by multiple secreted factors and signaling pathways. The most central proangiogenic signal, vascular endothelial growth factor (VEGF)/VEGFR signaling, is also the primary target of initial clinical anti-angiogenic effort. However, the efficiency of therapy has so far been modest due to the low response rate and rapidly emerging acquiring resistance. This review focused on the current understanding of the in-depth mechanisms of tumor angiogenesis, together with the newest reports of clinical trial outcomes and resistance mechanism of anti-angiogenic agents in OC. We also emphatically summarized and analyzed previously reported biomarkers and predictive models to describe the prospect of precision therapy of anti-angiogenic drugs in OC.

Abstract P2-20-08: Expression of ACVRL1 in a subset of recruited tumor-associated macrophages drives resistance to PD-1 therapy in human breast cancer

Abstract The activin-like kinase receptor 1 (ALK1, encoded by ACVRL1) is a member of the transforming growth factor β (TGF-β) superfamily. Expression of ALK1 has been historically associated with endothelial cells, thus serving as a potential target for antiangiogenic therapy in cancer. Despite promising preclinical results with a ligand trap (RAP-041/dalantercept), clinical trials did not show additional benefit of dalantercept when combined or contrasted with the standard of care. This outcome raises the question about patient selection and optimal combination partner in the clinical setting. Moreover, from the biological perspective, how ALK1 signaling shapes the features of a tumor is still largely uncharted. Based on our previous observations, we confirmed that the genetic network correlated with ACVRL1 expression is associated with immune processes in human breast cancer. Next, we validated that inhibition of ALK1 altered the immune landscape in experimental primary breast cancer (MMTV-PyMT model), providing a rationale for a combined regimen with immunotherapy. After developing and validating a murine model of adjuvant therapy with RAP-041 (syngeneic E0771 and 4T1 cell lines), we discovered that ALK1 blockade potentiated immune checkpoint inhibitors. Based on bulk RNA-sequencing and a multicolor FACS approach, addition of RAP-041 to immunotherapy significantly reduced the number of intratumoral macrophages compared with either treatment alone. Notably, these changes were coupled with systemic alterations in peripheral blood cell composition, with the combined administration suppressing circulating monocytes. Interestingly, ALK1 signaling appears to be a pivotal contributor to this phenotype, as fewer circulating monocytes were also detected in the RAP-041 cohort. Based on our in vitro characterization, we revealed that ALK1 expression is not limited to endothelial cells, as different myeloid populations readily expressed Acvrl1, suggesting a direct functional role of ALK1. Stimulation of ALK1 did not alter macrophage polarization, even though different levels of mediators downstream of ALK1 characterized the M1/M2 states. Furthermore, apoptosis and necrosis did not seem to be affected upon activation of ALK1, while the effect on the cell cycle awaits confirmation. In vitro genetic modulation of ALK1 activity is ongoing, with co-culture systems, transendothelial adhesion and migration being currently assessed. Inspection of several human sc-RNA-sequencing datasets confirmed the existence of ACVRL1-positive monocytes in human PBMCs from healthy individuals as well as in human solid cancers, including breast cancer. Focusing on the immune compartment, ACVRL1 expression characterized recruited tumor-associated macrophages (TAMs) and their cycling counterpart. In light of this feature, longitudinal follow-up of patients exposed to chemotherapy and/or anti-PD-1/PD-L1 revealed that expression of ACVRL1 decreased following exposure to chemotherapy. Notably, high ACVRL1 expression and an increased proportion of ACVRL1-positive TAMs were found at progression with anti-PD-1 treatment. In agreement with our preclinical data, ACVRL1-positive cells were depleted from circulation upon recurrence, indicating a migration from blood to tumors. Finally, survival analysis determined that ACVRL1hi signature in macrophages correlated with a significantly lower survival in a 5-year follow-up in breast cancer. In conclusion, our work sheds light on the value of ALK1 as a promising dual antiangiogenic and immunomodulatory target for precision medicine in cancer. Citation Format: Mehrnaz Safaee Talkhoncheh, Jonas Sjölund, Paulina Bolivar Balbas, Ewa Kurzejamska, Sara Larsson, Eugenia Cordero, Clara R. Oudenaarden, Jessica Pantaleo, Göran Jonsson, Charlotte Rolny, Matteo Bocci, Kristian Pietras. Expression of ACVRL1 in a subset of recruited tumor-associated macrophages drives resistance to PD-1 therapy in human breast cancer. [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P2-20-08.

Abstract P6-12-05: The role of endothelial-specific AXL and its associated signaling pathways in the tumor microenvironment

Abstract Most breast cancer deaths result from the development of metastases. The complex tumor microenvironment provides signals that can instruct both breast cancer cells to invade and tumor blood vessels to be leaky, hence supporting metastasis. We identified the receptor tyrosine kinase (RTK) AXL to be essential for metastasis. Genetic ablation of Axl in mouse models of HER2+ breast cancer, either globally or specifically in mammary epithelial cells, blunts metastasis but not primary tumor growth. We found that Axl expressed in tumor cells contributes to the remodeling of the tumor microenvironment, including immune cell recruitment and abnormal blood vessels. Hence, AXL in epithelial cells promotes cell invasion and shapes a pro-metastatic microenvironment that would be poorly responding to treatments such as immunotherapy. While AXL is known to be expressed on endothelial cells, its endothelial function has yet to be clearly defined. This project aims to address the hypothesis that AXL expressed on endothelial cells promotes processes that lead to abnormal blood vessel formation to promote metastasis. To address this hypothesis, we first studied the specific intracellular interactions between two RTKs, AXL and the known pro-angiogenic receptor VEGFR. Our preliminary analyses indicates that GAS6 can not only induce the phosphorylation of the permeability marker eNOS on its own but can also potentiate the VEGF’s response. The index of linearity of the endothelial tight junctions upon GAS6 stimulation show increased permeability of the endothelial cells. To further characterize the signaling pathways controlled by these receptors, we plan to perform a phosphoproteomics screen. We will focus on studying the AXL+VEGFR phosphoproteome and define the signaling pathways that impact vascular permeability. The most interesting candidate(s) will be studied in the context of mouse tumor models. In parallel, we are generating a conditional deletion of Axl in endothelial cells by crossing Axlfx/fx mice with Pdgfb:iCreER animals. With this, we will study the specific endothelial effects of Axl in vivo, specifically with vessel permeability and retinal angiogenesis assays. Multiple anti-angiogenic therapies for cancer failed in the clinic highlighting the need for new strategies to target endothelial cells in cancer. This project will provide essential information on the role of endothelial specific AXL, in the context of the HER2 breast cancer, and of its downstream effectors. With more specific targets, anti-angiogenic therapies could decrease their off-target effects and increase their efficacy in the clinic. This project has the potential to uncover therapeutic targets that could reduce the metastatic burden in breast cancer patients, and therefore better the prognostic for the HER2 cancer subtype. Citation Format: Andréane Lalonde, Jean-François Côté. The role of endothelial-specific AXL and its associated signaling pathways in the tumor microenvironment [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P6-12-05.