Ultrastructural analysis of vasculogenic mimicry in rectal adenocarcinoma after neoadjuvant radiation therapy

Tumor angiogenesis is widely recognized as one of the “hallmarks of cancer”. Consequently, during the last decades the development and testing of commercial angiogenic inhibitors has been a central focus for both basic and clinical cancer research. While antiangiogenic drugs are now incorporated into standard clinical practice, as with all cancer therapies, tumors can eventually become resistant by employing a variety of strategies to receive nutrients and oxygen in the event of therapeutic assault. Herein, we concentrate and review in detail three of the principal mechanisms of antiangiogenic therapy escape: (1) upregulation of compensatory/alternative pathways for angiogenesis; (2) vasculogenic mimicry; and (3) vessel co-option. We suggest that an understanding of how a cancer cell adapts to antiangiogenic therapy may also parallel the mechanisms employed in the bourgeoning tumor and isolated metastatic cells delivering responsible for residual disease. Finally, we speculate on strategies to adapt antiangiogenic therapy for future clinical uses.

Locally Advanced Rectal Cancer: What Does the Local Treatment Response Tell Us About the Global Picture?

Unexpected resistance to anti-angiogenic treatment prompted the investigation of non-angiogenic tumor processes. Vessel co-option (VC) and vasculogenic mimicry (VM) are recognized as primary non-angiogenic mechanisms. In VC, cancer cells utilize pre-existing blood vessels for support, whereas in VM, cancer cells channel and provide blood flow to rapidly growing tumors. Both processes have been implicated in the development of tumor and resistance to anti-angiogenic drugs in many tumor types. The morphology, but rare molecular alterations have been investigated in VC and VM. There is a pressing need to better understand the underlying cellular and molecular mechanisms. Here, we review the emerging circular RNA (circRNA)-mediated regulation of non-angiogenic processes, VC and VM.

New insights into antiangiogenic therapy resistance in cancer: Mechanisms and therapeutic aspects.

4551 Background: Patients with advanced metastatic renal cell carcinoma (RCC) often develop resistance to tyrosine kinase inhibitors (TKIs). Vasculogenic mimicry (VM) refers to the formation of tubular structures by tumor cells mimicking endothelial cells. VM formation is independent of VEGF and endothelial cells, making it inherently resistant to TKIs. Furthermore, hypoxic conditions induced by TKI treatment can promote VM formation, creating a vicious cycle. This study investigates the molecular mechanisms of VM formation and its prognostic significance in RCC. Methods: VM incidence in RCC was assessed using PAS/CD31 staining on tissue microarrays. Single-cell sequencing data were used to identify tumor cells undergoing VM differentiation. Cluster analysis was conducted to characterize these cells, and their prognostic value was validated using TCGA data. Pseudotime trajectory analysis and SCENIC algorithms were used to infer their differentiation pathways and identify transcription factors (TFs) regulating VM formation. Tube formation assays were performed for validation. Results: PAS/CD31 double staining revealed a VM incidence of 15.87% (10/63) among RCC patients. Notably, VM formation was more frequent in recurrent and TKI-resistant patients, suggesting that VM may serve as a mechanism for TKI resistance. Single-cell data from 11 patients with stages T1a-T3 RCC were analyzed, identifying VM-differentiating tumor cells, termed RCC-VM. GSVA revealed that RCC-VM cells were highly enriched in angiogenesis and EMT-related pathways. GO and KEGG analyses also showed enrichment in angiogenesis pathways. Trajectory analysis of tumor cell subpopulations placed RCC-VM at the terminal differentiation state, suggesting it represents a uniquely differentiated tumor cell type. Using SCENIC, we identified FOSL2 as a key TF regulating RCC-VM differentiation. Knockdown of FOSL2 significantly impaired tube formation in 786-O cells in vitro. Additionally, we identified RCC-VM-specific signature genes (VMDEG) and used Lasso-Cox regression to select four key risk factors (PIM1, MT1G, MT-ND4, DDIT3) to construct a survival risk model. Kaplan-Meier survival analysis demonstrated that patients in the high-risk group had significantly shorter survival times compared to the low-risk group (p = 0.0013). The time-dependent ROC curve showed that the model had robust predictive ability, providing potential guidance for personalized treatment of RCC patients. Conclusions: Our study highlights VM as a critical mechanism of TKI resistance in RCC, regulated by the transcription factor FOSL2. VMDEG serves as a valuable prognostic marker for RCC patients. Incorporating VM into staging systems such as pT staging and Fuhrman grading may improve risk stratification and treatment planning for RCC patients.

Glioblastoma (GBM), the most aggressive form of primary brain tumor in adults, remains a significant clinical challenge due to its high recurrence and poor prognosis. Characterized by rapid growth, invasiveness, and resistance to therapy, GBM relies on a sophisticated vascular network to sustain its progression. Angiogenesis, the process of forming new blood vessels, is central to meeting the metabolic demands of the tumor. To address this issue, there is a growing consensus on the need for multi-pronged therapeutic strategies that not only inhibit angiogenesis but also disrupt alternative neovascular mechanisms. Promising approaches include combining anti-angiogenic drugs with agents targeting pathways like neurogenic locus notch homolog protein (NOTCH), Wnt, and C-X-C motif chemokine receptor 4 (CXCR4)/stromal cellderived factor 1 alpha (SDF-1α) to impede vessel co-option, VM, and GSC trans-differentiation. The search strategy consisted of using material from the PubMed data, focusing on key terms such as: "angiogenesis", "glioblastoma", "glioma", "oncogenesis", "anti-VEGF treatment", "signaling pathways", "hypoxia", "vessels", "resistance", and "neurosurgery. Аs a result of the analysis of existing recent studies, GBM exhibits an adaptive capacity to utilize various neovascular mechanisms, including vessel co-option, vasculogenic mimicry (VM), and the transdifferentiation of glioma stem cells (GSCs) into vascular-like structures, to circumvent traditional antiangiogenic therapies. Initial successes with anti-angiogenic treatments targeting vascular endothelial growth factor (VEGF) showed improvements in progression-free survival. Still, they failed to significantly impact the overall survival due to the tumor's activation of compensatory pathways. Hypoxia, a critical driver of angiogenesis, stabilizes hypoxia-inducible factors (HIF-1α and HIF-2α), which upregulate pro-angiogenic gene expression and facilitate adaptive neovascular responses. These adaptations include vessel co-option, where tumor cells utilize pre-existing vasculature, and VM, where tumor cells form endothelial-like channels independent of typical angiogenesis. Moreover, the role of GSCs in forming new vascular structures through transdifferentiation further complicates treatment, enabling the tumor to maintain its blood supply even when VEGF pathways are blocked. This review highlights the necessity for comprehensive and targeted treatment strategies that encompass the full spectrum of neovascular mechanisms in GBM. Such strategies are crucial for developing more effective therapies that can extend patient survival and improve overall treatment outcomes. To address the challenge of understanding tumor angiogenesis and ways to inhibit it, there is a growing consensus on the need for multifaceted therapeutic strategies that not only suppress angiogenesis but also disrupt alternative neovascular mechanisms. The most successfull approaches include the use of antiangiogenic drugs in combination with agents targeting pathways such as the neurogenic locus of the notch homolog protein (NOTCH), Wnt, and C-X-C receptor chemokine motif 4 (CXCR4)/stromal cell-derived factor 1 alpha (SDF-1α) aiming to inhibit vessel co-option, VM, and GSC transdifferentiation.

Over the last decade my lab has developed a number of models involving treatment of mice with either early stage microscopic metastatic disease for adjuvant therapy or late stage overt metastatic disease for metastatic therapy studies1-3. More recently, models of neoadjuvant therapy have been developed as well with the lab of Dr. John Ebos4. The rationale for utilizing the first two models is that they may be superior in predicting future activity in patients enrolled in randomized phase III adjuvant or metastatic therapy clinical trials, in comparison to conventional treatment models involving mice with unresected established primary tumors, and evaluating the effect on the primary tumor growth only1. As an example, we reported that sunitinib (or pazopanib) or DC101, the VEGFR-2 antibody were all devoid of anti-tumor activity when treating mice with advanced metastatic breast cancer after primary tumor resection, whereas in contrast, all showed efficacy when treating orthotopic primary tumors in control experiments5. Combining chemotherapy with sunitinib also did not improve outcomes in the metastatic setting. In contrast, combining chemotherapy with DC101 caused a small but statistically significant benefit in survival. These results retrospectively correlated with outcomes of four metastatic breast cancer phase III trials evaluating sunitinib alone or in combination with chemotherapy in the metastatic setting (all were negative) or multiple phase III trials evaluating the VEGF antibody, bevacizumab, with chemotherapy, which showed variable benefits in improving PFS in metastatic breast cancer5. With respect to adjuvant therapy modelling, we reported in 2009 that adjuvant sunitinib therapy of mice with microscopic metastases after resection of orthotopic primary human breast cancer xenografts resulted in a worsened survival outcome, with accelerated progression of metastatic disease2. On the basis of the results we raised a cautionary “flag” about the rationale of antiangiogenic drugs in the clinic for adjuvant setting6. As is now well known, there have been multiple adjuvant trials evaluating bevacizumab plus chemotherapy in postsurgical early stage colorectal or breast cancer, as well as sorafenib in hepatocellular carcinoma, and all of these trials have failed to meet their primary endpoint of a benefit in disease free survival7. This has provoked considerable discussion and debate about the basis for such failures in contrast to the same drugs/therapies showing efficacy in the more advanced metastatic settings of the same malignancies. One basis for the modest positive effects noted of such therapies in the metastatic setting, and for the failure in the adjuvant setting, concerns the impact that “vessel co-option”, especially in distant metastases, may have on therapeutic outcomes. Evidence is growing that a variety of tumors and especially overt metastases in certain sites such as the lungs, liver, and brain are minimally or non-angiogenic and instead “hijack” the existing vasculature in such organ sites8. The same may be the case for microscopic metastases. Consequently, there will be growing interest in evaluating whether vessel co-option can be therapeutically targeted (and also what the implications may be for drug-induced vascular normalization). In this regard there are a number of strategies being evaluated such as the impact of metronomic chemotherapy and targeting other pro-angiogenic factors/pathways beyond VEGF such as ang2/tie29, which may be effective as an adjuvant therapy strategy9.

Background: In the UK, triple-negative breast cancer (TNBC) comprises 10-15% of breast cancer diagnoses annually. TNBC represents a clinical challenge due to a lack of expression of three treatable drug targets, namely oestrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor 2 (HER-2). The mainstay of treatment involves the use of neoadjuvant chemotherapy (NACT) followed by surgical excision where up to 50% of patients will achieve a pathological complete response (pCR). The addition of neo-adjuvant immunotherapy may increase the pCR rate to 60%. The presence of lymphatics and blood vessels within/around malignant tumours plays a role in cancer progression as does the formation of new blood vessels (angiogenesis). The vascular endothelial growth factor (VEGF) family and their receptors (VEGFRs) play an important role in angiogenesis as well as promoting the growth and survival of cancer cells. VEGFR is frequently overexpressed in TNBC and promotes changes in vascular endothelial cells, the basement membrane and the surrounding extracellular matrix. Co-expression of epidermal growth factor receptor (EGFR) and VEGFR enhances tumour growth and angiogenesis in an autocrine and paracrine manner. An alternate mechanism for tumour microcirculation in tumours is vasculogenic mimicry (VM). This is distinct from classical tumour angiogenesis. The presence of VM is associated with poor overall survival in breast cancer patients and anti-angiogenic treatment of TNBC may even promote tumour growth, proliferation and metastasis by stimulating VM. Conventional imaging techniques such as B-mode ultrasound and MRI are commonly used to monitor disease response in the breast but have limited accuracy in predicting pCR or residual disease. High-resolution contrast-enhanced ultrasound (HRCEUS) may offer a more accurate test to monitor TNBC response to NACT. This method utilises intravenously injected microbubbles, which consist of a gas core with an outer shell of lipid/albumin to image tumour microvasculature as well as gross tumour morphology. Trial Design: Single-centre study to evaluate HRCEUS to image the microvasculature of TNBC tumours in patients undergoing (NACT) and correlate imaging results with established markers of angiogenesis, proliferation and vasculogenic mimicry. Eligibility Criteria: Female, 18 to 60 years, histologically confirmed invasive TNBC with planned NACT, able to consent and in the Investigator’s opinion, adhering to the trial recommendations and governance. Aims: To investigate if imaging changes in the tumour microvasculature indicate a response to NACT and are reflected in the expression of proliferative markers. To determine whether changes in the tumour microvasculature and disease response are driven by angiogenesis +/- VM. To investigate whether overall disease response and changes in the microvasculature are influenced by the basal type phenotype or germline mutations in BRCA 1/2. Investigate patient satisfaction with the contrast ultrasound test. Statistical Methods: Quantify HRCEUS imaging characteristics of microvasculature at 3 treatment points. Compare this with the results of conventional imaging and the histopathological results of surgical excision at the end of NACT. Quantify immunohistochemical markers of angiogenesis, proliferation and VM at three treatment points and compare this with HRCEUS. Determine phenotype of all cases using immunohistochemistry to identify the basal Perform subtype analysis to assess if the basal phenotype is associated with imaging and immunohistochemical changes in the microvasculature during NACT. Test patients for germline BRCA1/2 gene mutations. Perform subtype analysis to assess if germline BRCA1/2 mutations are associated with imaging and immunohistochemical changes in the microvasculature during NACT. Present accrual (2 patients) and target accrual (5 patients) Contact details: j.rait@nhs.net Citation Format: Jaideep Rait, Michelle Garrett, Catherine Harper-Wynne, Sonia Saw, Mengxing Tang, Priya Palanisamy, Matthieu TOULEMONDE, Karina Cox. Imaging of tumour microvasculature using high-resolution contrast enhanced ultrasound together with markers of proliferation/angiogenesis/vascular mimicry to characterise response to NACT in TNBC [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO1-18-11.

Therapy resistance in solid tumors is of growing concern due to the failure of multiple therapeutic approaches. Targeting tumor cells alone with chemotherapy, tumor vasculature with antiangiogenic therapies (AAT) and tumor-infiltrating myeloid cells with CSF1R inhibitor have all lead to the development of refractory tumors with greater relapse rates. There is an urgent need to understand molecular mechanisms of therapy resistance in cancer. There could be tumor cell extrinsic and intrinsic mechanisms in the tumor microenvironment. We focused our study to investigate tumor cell intrinsic pathways using glioblastoma (GBM) as a model tumor and AAT (antiVEGF-VEGFR) as a model therapy. The benefits of AAT are transient with increased relapse owing to adaptive responses by the GBM. Our preclinical study and in vitro data, for the very first time, identified that AAT induces transdifferentiation of tumor cells into endothelial-like cells, capable of forming functional blood vessels in the growing tumors, termed as vasculogenic mimicry (VM). We observed that anti-VEGFR2 (Vatalanib) induced VM vessels are positive for periodic acid-Schiff (PAS) matrix but devoid of any endothelium on the inner side and lined by tumor cells on the outer-side. The PAS+ matrix is positive for basal laminae (laminin) indicating vascular structures. Vatalanib treated GBM displayed various stages of VM such as initiation (mosaic), sustenance, and full-blown VM. In addition to this, vatalanib treated tumors show significantly increased Laminin positive loops characteristic of VM in tumor center as well as at the periphery. A positive correlation was observed between the VM-like structures and the tumor size. We also performed in vitro tube formation assays with AAT treated GBM cells alone and HUVEC cells (co-culture) to confirm the role of GBM cells in the formation of mosaic vessels in normoxic conditions. Interestingly, tumor cells are incorporated into the tubes formed by HUVEC cells. We found a higher number of complete tube like structures with AAT treated tumor cells as compared to control. Cytokine array with the condition media from tumor cells treated with AAT showed a significant upregulation in the levels of IL8. We observed a significant increase in the CXCR1+ and CXCR2+ endothelial-like GBM cells following treatment with AAT. Ongoing investigations are focused on study of IL8-CXCR1/2 pathway in VM regulation using loss or gain of function approaches. The study will identify critical mediators of VM in GBM. In clinics, discovering novel targets causing VM associated therapy resistance is essential for identifying subset of patients that could be treated with alternate regimens. Citation Format: Kartik Angara, Mohammad Rashid, Thaiz Borin, Bhagelu Achyut, Meenu Jain, ASM Iskander, Roxan Ara, Ali Arbab. Vascular mimicry mediated mechanisms drive therapy resistance in glioblastoma [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 787. doi:10.1158/1538-7445.AM2017-787

Vasculogenic mimicry (VM) is a newly proposed pattern of tumour angiogenesis that has been identified in some malignancies and is associated with poor prognosis. The purpose of this study was to investigate whether sebaceous carcinomas of the eyelid exhibit VM and to determine whether these fluid-conducting patterns are associated with clinicopathologic features, the number of microvessels and the levels of endothelial growth factor (VEGF) and matrix metalloprotease-2 (MMP-2) in tumours. Forty paraffin-embedded samples of sebaceous carcinoma of the eyelid were collected, along with complete clinical and pathologic data for all the cases. Tissue sections were stained for CD34, periodic acid and Schiff (PAS), VEGF and MMP-2. VM was identified by the presence of PAS-positive and CD34-negative loops lined by tumour cells. The VM status of tumour samples was compared with the clinical and pathological data using statistical tests. The levels of VEGF, MMP-2 and the number of microvessels were compared between patients with and without VM. VM was detected in 14 of 40 (35%) tumour samples. The existence of VM in tumours was associated with tumour size (p=0.007) and recurrence (p=0.021). The number of microvessels was lower in tumours with VM (13.03+/-4.02 versus 22.99+/-7.72; p<0.0001). The staining index of MMP-2 was higher in tumours with VM (27.43, range: 0-5.3) compared to tumours without VM (16.77, range: 0-2.7; p=0.004). However, there was no difference in the expression of VEGF between groups with and without VM (p=0.244). Vasculogenic mimicry is present in sebaceous carcinoma of the eyelid making it an unfavourable prognosis sign. MMP-2 is associated with VM formation in sebaceous carcinoma of the eyelid.

Simple SummaryTumors rely on blood vessels to grow and metastasize. Malignant tumors can employ different strategies to create a functional vascular network. Tumor cells can use normal processes of vessel formation but can also employ cancer-specific mechanisms, by co-opting normal vessels present in tissues or by turning themselves into vascular cells. These different types of tumor vessels have specific molecular and functional characteristics that profoundly affect tumor behavior and response to therapies, including drugs targeting the tumor vasculature (antiangiogenic therapies). In this review, we discuss how vessels formed by different mechanisms affect the intrinsic sensitivity of tumors to therapy and, on the other hand, how therapies can affect tumor vessel formation, leading to resistance to drugs, cancer recurrence, and treatment failure. Potential strategies to avoid vessel-mediated resistance to antineoplastic therapies will be discussed.Blood vessels in tumors are formed through a variety of different mechanisms, each generating vessels with peculiar structural, molecular, and functional properties. This heterogeneity has a major impact on tumor response or resistance to antineoplastic therapies and is now emerging as a promising target for strategies to prevent drug resistance and improve the distribution and efficacy of antineoplastic treatments. This review presents evidence of how different mechanisms of tumor vessel formation (vasculogenesis, glomeruloid proliferation, intussusceptive angiogenesis, vasculogenic mimicry, and vessel co-option) affect tumor responses to antiangiogenic and antineoplastic therapies, but also how therapies can promote alternative mechanisms of vessel formation, contributing to tumor recurrence, malignant progression, and acquired drug resistance. We discuss the possibility of tailoring treatment strategies to overcome vasculature-mediated drug resistance or to improve drug distribution and efficacy.

The cellular and molecular mechanisms of tumor angiogenesis and its prospects for anti-angiogenic cancer therapy are major issues in almost all current concepts of both cancer biology and targeted cancer therapy. Currently, (1) sprouting angiogenesis, (2) vascular co-option, (3) vascular intussusception, (4) vasculogenic mimicry, (5) bone marrow-derived vasculogenesis, (6) cancer stem-like cell-derived vasculogenesis and (7) myeloid cell-driven angiogenesis are all considered to contribute to tumor angiogenesis. Many of these processes have been described in developmental angiogenesis; however, the relative contribution and relevance of these in human brain cancer remain unclear. Preclinical tumor models support a role for sprouting angiogenesis, vascular co-option and myeloid cell-derived angiogenesis in glioma vascularization, whereas a role for the other four mechanisms remains controversial and rather enigmatic. The anti-angiogenesis drug Avastin (Bevacizumab), which targets VEGF, has become one of the most popular cancer drugs in the world. Anti-angiogenic therapy may lead to vascular normalization and as such facilitate conventional cytotoxic chemotherapy. However, preclinical and clinical studies suggest that anti-VEGF therapy using bevacizumab may also lead to a pro-migratory phenotype in therapy resistant glioblastomas and thus actively promote tumor invasion and recurrent tumor growth. This review focusses on (1) mechanisms of tumor angiogenesis in human malignant glioma that are of particular relevance for targeted therapy and (2) controversial issues in tumor angiogenesis such as cancer stem-like cell-derived vasculogenesis and bone-marrow-derived vasculogenesis.

The resistance mechanisms to EGFR-TKIs in Non-Small Cell Lung Cancer (NSCLC) are not well elucidated. Here we evaluate EGFR degradation as a mechanism of tumor evasion in EGFR-TKI resistant NSCLC cells (H1975) compared to EGFR-TKI sensitive cells (HCC827). After erlotinib treatment, EGFR protein half-life was quantified by cycloheximide chase. EGFR expression on cell membrane was measured by flow cytometry and transcription levels were measured by Real-Time PCR. EGFR half-life was shorter in H1975 compared to HCC827 cells after cycloheximide inhibition of protein synthesis. EGFR phosphorylation levels were not affected by erlotinib in H1975 while in HCC827 they were significantly reduced (p &amp;lt; 0.001). EGFR expression on cell membrane decreased similarly in both H1975 and HCC827 cell lines. Also the transcription levels of EGFR remained unaffected by erlotinib treatment in both cell lines. However, there was more apoptosis in HCC827 compared to H1975 with 64% vs. 22%. Our results suggest that H1975 cells present more EGFR degradation however, they show less cell death by apoptosis and this could represent a resistance mechanism to EGFR-TKIs. Citation Format: Hernandez-Pedro Y. Norma, Soca-Chafre Giovanny, Orozco-Morales Mario, Barrios-Bernal Pedro, Arrieta Oscar. Evaluation of EGFR degradation as a mechanism of tumor evasion in EGFR-TKI resistant non-small cell lung cancer (NSCLC) cells compared to EGFR-TKI sensitive cells [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 LB-186.

PURPOSEVessel co-option and vascular mimicry are important resistant factors with ant-angiogenic treatment for glioblastoma, but those precise evaluation is not clear. We had three types of glioblastoma surgically removed specimens treated with / without bevacizumab (Bev). Using these samples, pathogenesis of co-option and mimicry was morphometrically clarified.MATERIALS / METHODSThree types of glioblastoma specimens were analyzed; 1) Bev naive (N group, n 14), 2) Bev effective that was treated preoperative neoadjuvant Bev (E group, n 5), 3) Bev refractory that recurred with continuous Bev treatment for paired E group (R group, n 5). Vascular density was defined as a number of type IV collagen covered lumen. Vascular mimicry was measured as a ratio of CD34 negative / type IV collagen positive lumen. Vessel co-option was graded to 3 degrees (-), (+), (++) at tumor margin.RESULTS(1)Vascular density was significantly lower with E group (p<0.01) and R gr up (p<0.02) compared to N group. (2)Mimicry was significantly higher with R group compared to N and E group (p<0.01). Between paired samples, refractory case was constantly higher than effective sample. (3) Co-option was increases with R group compared to N group.DISCUSSION/CONCLUSIONThe effect of Bev for glioblastoma was investigated on three points (vascular density, vascular mimicry and vessel co-option) and two pathogeneses were clarified. In Bev refractory case, density was decreased, but mimicry and co-option were increased compared to Bev naive case. In Bev effective case, density was decreased, but mimicry and co-option were unchanged. Anti-angiogenic treatment for initial and Bev refractory glioblastoma should consider targeting co-option and mimicry in addition to Bev.

Anti-angiogenic therapies (AATs) have been widely used for cancer treatment. But the beneficial effects of AATs are short, because AAT-induced tumor revascularization facilitates the tumor relapse. In this mini-review, we described different forms of tumor neovascularization and revascularization including sprouting angiogenesis, vessel co-option, intussusceptive angiogenesis, and vasculogenic mimicry, all of which are closely mediated by vascular endothelial growth factor (VEGF), angiopoietins, matrix metalloproteinases, and exosomes. We also summarized the current findings for the resistance mechanisms of AATs including enhancement in pro-angiogenic cytokines, heterogeneity in tumor-associated endothelial cells (ECs), crosstalk between tumor cells and ECs, masking of extracellular vesicles, matrix stiffness and contributions from fibroblasts, macrophages and adipocytes in the tumor microenvironment. We highlighted the revascularization following AATs, particularly the role of exosome stimulating factors such as hypoxia and miRNA, and that of exosomal cargos such as cytokines, miRNAs, lncRNAs, and circRNAs from the tumor ECs in angiogenesis and revascularization. Finally, we proposed that renormalization of tumor ECs would be a more efficient cancer therapy than the current AATs.