Role of the hypoxic tumor microenvironment in the resistance to anti-angiogenic therapies

Oxygen Sensor-Guided Fine Needle Biopsy Studies of Human Cancer Xenografts in Mice

An oxygen sensor-mounted fine-needle biopsy tool was used for in vivo measurement of oxygen levels in tumor xenografts. The system provides a means of measuring the oxygen content in harvested tumor tissue from specific locations. Oxygen in human tumor xenografts in a murine model was observed for over 1 min. Tissues were mapped in relation to oxygen tension (pO2) readings and sampled for conventional cytological examination. Careful modeling of the pO2 readings over 60 seconds yielded a diffusion coefficient for oxygen at the sensor tip, providing additional diagnostic information about the tissue before sampling. Oxygen level measurement may provide a useful adjunct to the use of biomarkers in tumor diagnosis.

Impact of Nintedanib and Anti-Angiogenic Agents on Uveal Melanoma Cell Behavior

Purpose

The purpose of this study was to investigate the direct impact of the combined angiokinase inhibitor nintedanib as well as the anti-angiogenic agents ranibizumab, bevacizumab, and aflibercept on the primary uveal melanoma (UM) cell line Mel270 and liver metastasis UM cell line OMM2.5.

Methods

The metabolic activity, viability, and oxidative stress levels were analyzed by the Thiazolyl Blue Tetrazolium Bromide (MTT), LIVE/DEAD, and reactive oxygen species (ROS) assays. Expression of intracellular VEGF-A165 and VEGF receptor-2 was detected by immunofluorescent staining. The secretion of VEGF-A165 into the cell culture supernatants was evaluated by VEGF-A165 ELISA.

Results

Nintedanib, at a concentration of 1 µg/mL, resulted in a median reduction of metabolic activity (for Mel270 of approximately 38% and for OMM2.5 of 46% compared to the untreated control) without exerting toxicity in either cell line, whereas the other 3 substances did not result in any changes (which also means that none of the 4 substances led to an increased cell death). Moreover, nintedanib (1 µg/mL) induced oxidative stress in the Mel270 by approximately 1.2 to 1.5-fold compared to the untreated control, but not the OMM2.5 cells.

Conclusions

Nintedanib could suppress the growth of UM cells in a concentration-dependent manner. The metastatic UM cell line OMM2.5 was not sensitive to the pro-oxidant activity of nintedanib. This study was the first to investigate nintedanib in the context of UM. We propose further investigation of this substance to elucidate its effects on this tumor entity with the hope of identifying advantageous therapeutic options for future adjuvant tumor therapies.

The Role of Hypoxia in Brain Tumor Immune Responses

Oxygen is a vital component of living cells. Low levels of oxygen in body tissues, known as hypoxia, can affect multiple cellular functions across a variety of cell types and are a hallmark of brain tumors. In the tumor microenvironment, abnormal vasculature and enhanced oxygen consumption by tumor cells induce broad hypoxia that affects not only tumor cell characteristics but also the antitumor immune system. Although some immune reactions require hypoxia, hypoxia generally negatively affects immunity. Hypoxia induces tumor cell invasion, cellular adaptations to hypoxia, and tumor cell radioresistance. In addition, hypoxia limits the efficacy of immunotherapy and hinders antitumor responses. Therefore, understanding the role of hypoxia in the brain tumor, which usually does not respond to immunotherapy alone is important for the development of effective anti-tumor therapies. In this review, we discuss recent evidence supporting the role of hypoxia in the context of brain tumors.

Design Strategies of Tumor-Targeted Delivery Systems Based on 2D Nanomaterials

Conventional chemotherapy and radiotherapy are nonselective and nonspecific for cell killing, causing serious side effects and threatening the lives of patients. It is of great significance to develop more accurate tumor-targeting therapeutic strategies. Nanotechnology is in a leading position to provide new treatment options for cancer, and it has great potential for selective targeted therapy and controlled drug release. 2D nanomaterials (2D NMs) have broad application prospects in the field of tumor-targeted delivery systems due to their special structure-based functions and excellent optical, electrical, and thermal properties. This review emphasizes the design strategies of tumor-targeted delivery systems based on 2D NMs from three aspects: passive targeting, active targeting, and tumor-microenvironment targeting, in order to promote the rational application of 2D NMs in clinical practice.

Enhancing Doxorubicin Delivery in Solid Tumor by Superhydrophobic Amorphous Calcium Carbonate-Doxorubicin Silica Nanoparticles with Focused Ultrasound

The current approach of delivering chemotherapy via pH-sensitive amorphous calcium carbonate-doxorubicin silica nanoparticles (ADS NPs) faces the challenge of insufficient drug dose due to drug instability within the bloodstream and poor tumor penetration. To overcome these long-standing obstacles, we proposed a superhydrophobic coating on the surface of the ADS NPs that could be easily modified via fluorination (ADSF NPs). The surface of fluorinated ADS NPs was further modified with a phospholipid layer to reduce aggregation and improve biocompatibility (ADSFL NPs). The contact angle and mean size of ADSFL NPs were 30.2 ± 4.4° and 353.1 ± 54.2 nm, respectively. The superhydrophobic layer generated interfacial nanobubbles on the outer shell of the NPs that reduced water-induced leakage of doxorubicin (DOX) sevenfold compared with the uncoated group and induced a cavitation effect upon ultrasound (US) sonication. Moreover, release of DOX from the ADSFL NPs could be triggered by US, and this release was further improved 1.6-fold in acidic aqueous conditions, indicating that the ADSFL NPs retained pH responsiveness. Enhanced sonography contrast and histological examination demonstrated that US could trigger cavitation activities from ADSFL NPs in vivo to induce vessel disruption and enhance the fluorescence intensity of DOX within the tumor region threefold under US imaging guidance compared with the ADSFL NPs-only group.

Overcoming Hypoxia-Induced Drug Resistance via Promotion of Drug Uptake and Reoxygenation by Acousto–Mechanical Oxygen Delivery

Hypoxia-induced drug resistance (HDR) is a critical issue in cancer therapy. The presence of hypoxic tumor cells impedes drug uptake and reduces the cytotoxicity of chemotherapeutic drugs, leading to HDR and increasing the probability of tumor recurrence and metastasis. Microbubbles, which are used as an ultrasound contrast agent and drug/gas carrier, can locally deliver drugs/gas and produce an acousto–mechanical effect to enhance cell permeability under ultrasound sonication. The present study applied oxygen-loaded microbubbles (OMBs) to evaluate the mechanisms of overcoming HDR via promotion of drug uptake and reoxygenation. A hypoxic mouse prostate tumor cell model was established by hypoxic incubation for 4 h. After OMB treatment, the permeability of HDR cells was enhanced by 23 ± 5% and doxorubicin uptake was increased by 11 ± 7%. The 61 ± 14% reoxygenation of HDR cells increased the cytotoxicity of doxorubicin from 18 ± 4% to 58 ± 6%. In combination treatment with OMB and doxorubicin, the relative contributions of uptake promotion and reoxygenation towards overcoming HDR were 11 ± 7% and 28 ± 10%, respectively. Our study demonstrated that reoxygenation of hypoxic conditions is a critical mechanism in the inhibition of HDR and enhancing the outcome of OMB treatment.

The Anti-VEGF(R) Drug Discovery Legacy: Improving Attrition Rates by Breaking the Vicious Cycle of Angiogenesis in Cancer

Resistance to anti-vascular endothelial growth factor (VEGF) molecules causes lack of response and disease recurrence. Acquired resistance develops as a result of genetic/epigenetic changes conferring to the cancer cells a drug resistant phenotype. In addition to tumor cells, tumor endothelial cells also undergo epigenetic modifications involved in resistance to anti-angiogenic therapies. The association of multiple anti-angiogenic molecules or a combination of anti-angiogenic drugs with other treatment regimens have been indicated as alternative therapeutic strategies to overcome resistance to anti-angiogenic therapies. Alternative mechanisms of tumor vasculature, including intussusceptive microvascular growth (IMG), vasculogenic mimicry, and vascular co-option, are involved in resistance to anti-angiogenic therapies. The crosstalk between angiogenesis and immune cells explains the efficacy of combining anti-angiogenic drugs with immune check-point inhibitors. Collectively, in order to increase clinical benefits and overcome resistance to anti-angiogenesis therapies, pan-omics profiling is key.

Tumor Microenvironment Sensitive Nanocarriers for Bioimaging and Therapeutics

The tumor microenvironment (TME), which is composed of cancer cells, stromal cells, immune cells, and extracellular matrices, plays an important role in tumor growth and progression. Thus, targeting the TME using a well-designed nano-drug delivery system is emerging as a promising strategy for the treatment of solid tumors. Compared to normal tissues, the TME presents several distinguishable physiological features such as mildly acidic pH, hypoxia, high level of reactive oxygen species, and overexpression of specific enzymes, that are exploited as stimuli to induce specific changes in the nanocarrier structures, and thereby facilitates target-specific delivery of imaging or chemotherapeutic agents for the early diagnosis or effective treatment, respectively. Recently, smart nanocarriers that respond to more than one stimulus in the TME have also been designed to elicit a more desirable spatiotemporally controlled drug release. This review highlights the recent progress in TME-sensitive nanocarriers designed for more efficient tumor therapy and imaging. In particular, the design strategies, challenges, and critical considerations involved in the fabrication of TME-sensitive nanocarriers, along with their in vitro and in vivo evaluations are discussed.

Sunitinib Treatment-elicited Distinct Tumor Microenvironment Dramatically Compensated the Reduction of Myeloid-derived Suppressor Cells

BACKGROUND/AIM

The clinical response rate of prostate cancer to tyrosine kinase inhibitor (TKI) monotherapy is low. The mechanisms of resistance to TKI are unclear. This study aimed to examine if the tumor microenvironment (TME) is involved in the resistance.

MATERIALS AND METHODS

The anti-vascular effect of Sutent was examined by immunofluorescent staining in TRAMP-C1 tumor. The percentage of CD11b⁺ population were analyzed by flow cytometry. The level of cytokines and chemokines were measured by multiplex immunoassay.

RESULTS

The Sutent monotherapy caused 1.5 days of tumor growth delay, chronic hypoxia, and more mature vasculature. Sutent monotherapy increased the percentage of polymorphonuclear myeloid-derived suppressor cells (MDSCs) in peripheral blood. The evolved TME triggered the re-distribution of myeloid cells in chronically hypoxic areas. The multiplex immunoassay indicated higher levels of several cytokines and chemokines both in tumors and the blood.

CONCLUSION

Sunitinib treatment induced a distinct tumor microenvironment that impaired the efficient reduction of MDSCs by TKI.

Relieving immunosuppression during long-term anti-angiogenesis therapy using photodynamic therapy and oxygen delivery

Angiogenesis is an irreplaceable therapeutic cancer target, where anti-angiogenesis are drugs that are limited by their hydrophobicity and low therapeutic effects. What is more, the long-term shutdown of tumor blood vessel density also aggravates hypoxia and causes immunosuppression in the tumor microenvironment (TME). In order to solve these shortcomings, we developed a single therapeutic agent based on a bovine serum albumin nanocarrier that can co-deliver the anti-angiogenic drug Sorafenib ("S") and the photosensitizer Ce6 ("C") along with a molecular oxygen supply based on MnO2 ("M") as a convenient one-pot formulated nanoscale agent (SCM@BSA). Compared with anti-angiogenesis monotherapy, SCM@BSA can not only improve upon the solubility and therapeutic effects of anti-angiogenesis agents, but it also reshapes the immunosuppressive TME during anti-angiogenic therapy. Together, these results point out that SCM@BSA synthesized via a very simple method can solve the shortcomings usually experienced during long-term anti-angiogenic therapy.

Resistance to Anti-angiogenic Therapies: A Mechanism Depending on the Time of Exposure to the Drugs

Angiogenesis, the formation of new blood vessels from preexisting one, represents a critical process for oxygen and nutrient supply to proliferating cells, therefore promoting tumor growth and metastasis. The Vascular Endothelial Growth Factor (VEGF) pathway is one of the key mediators of angiogenesis in cancer. Therefore, several therapies including monoclonal antibodies or tyrosine kinase inhibitors target this axis. Although preclinical studies demonstrated strong antitumor activity, clinical studies were disappointing. Antiangiogenic drugs, used to treat metastatic patients suffering of different types of cancers, prolonged survival to different extents but are not curative. In this review, we focused on different mechanisms involved in resistance to antiangiogenic therapies from early stage resistance involving mainly tumor cells to late stages related to the adaptation of the microenvironment.

Resistance Mechanisms to Anti-angiogenic Therapies in Cancer

Tumor growth and metastasis rely on tumor vascular network for the adequate supply of oxygen and nutrients. Tumor angiogenesis relies on a highly complex program of growth factor signaling, endothelial cell (EC) proliferation, extracellular matrix (ECM) remodeling, and stromal cell interactions. Numerous pro-angiogenic drivers have been identified, the most important of which is the vascular endothelial growth factor (VEGF). The importance of pro-angiogenic inducers in tumor growth, invasion and extravasation make them an excellent therapeutic target in several types of cancers. Hence, the number of anti-angiogenic agents developed for cancer treatment has risen over the past decade, with at least eighty drugs being investigated in preclinical studies and phase I-III clinical trials. To date, the most common approaches to the inhibition of the VEGF axis include the blockade of VEGF receptors (VEGFRs) or ligands by neutralizing antibodies, as well as the inhibition of receptor tyrosine kinase (RTK) enzymes. Despite promising preclinical results, anti-angiogenic monotherapies led only to mild clinical benefits. The minimal benefits could be secondary to primary or acquired resistance, through the activation of alternative mechanisms that sustain tumor vascularization and growth. Mechanisms of resistance are categorized into VEGF-dependent alterations, non-VEGF pathways and stromal cell interactions. Thus, complementary approaches such as the combination of these inhibitors with agents targeting alternative mechanisms of blood vessel formation are urgently needed. This review provides an updated overview on the pathophysiology of angiogenesis during tumor growth. It also sheds light on the different pro-angiogenic and anti-angiogenic agents that have been developed to date. Finally, it highlights the preclinical evidence for mechanisms of angiogenic resistance and suggests novel therapeutic approaches that might be exploited with the ultimate aim of overcoming resistance and improving clinical outcomes for patients with cancer.

Pathological complete response by advanced hepatocellular carcinoma with massive macrovascular invasion to hepatic arterial infusion chemotherapy: a case report

Background

Advanced hepatocellular carcinoma (HCC) with macrovascular invasion has an extremely dismal prognosis. We report a rare case of multiple HCC with tumor thrombosis in the portal vein and inferior vena cava that was initially treated with hepatic arterial infusion chemotherapy (HAIC); later resection revealed pathological complete response.

Case presentation

A 75-year-old man presented with HCC in his right liver, with tumor thrombosis growing to the right portal vein and the inferior vena cava, and bilateral intrahepatic liver metastases. He underwent HAIC (5-fluorouracil [170 mg/m²] + cisplatin [7 mg/m²]) via an indwelling port. Although the tumor shrank and tumor marker levels decreased rapidly, we abandoned HAIC after one cycle because of cytopenia. We resumed HAIC 18 months later because of tumor progression, using biweekly 5-fluorouracil only [1000 mg] due to renal dysfunction. However, after 54 months, the HAIC indwelling port was occluded. The patient therefore underwent a right hepatectomy to resect the residual lesion. Histopathological findings showed complete necrosis with no viable tumor cells. The patient has been doing well without postoperative adjuvant therapy for more than 10 years after initially introducing HAIC and 6 years after the resection, without evidence of tumor recurrence.

Conclusions

HAIC can be an effective alternative treatment for advanced HCC with macrovascular invasion.

Tumor vasculature remolding by thalidomide increases delivery and efficacy of cisplatin

Background

A promising strategy to overcome the chemoresistance is the tumor blood vessel normalization, which restores the physiological perfusion and oxygenation of tumor vasculature. Thalidomide (Thal) has been shown to increase the anti-tumor effect of chemotherapy agents in solid tumors. However, it is not yet known whether the synergistic effect of Thal combined with other cytotoxic drugs is attributable to tumor vascular normalization.

Methods

We used two homograft mice models (4 T1 breast tumor model and CT26 colorectal tumor model) to investigate the effect of Thal on tumor growth, microvessel density, vascular physiology, vascular maturity and function, drug delivery and chemosensitivity. Immunofluorescence, immunohistochemistry and scanning electron microscopy were performed to determine the vessel changes. Protein array assay, qPCR and western blotting were used to detect the molecular mechanism by which Thal regulates tumor vascular.

Results

Here we report that Thal potently suppressed tumor growth, angiogenesis, hypoxia, and vascular permeability in animal models. Thal also induced a regular monolayer of endothelial cells in tumor vessels, inhibiting vascular instability, and normalized tumor vessels by increasing vascular maturity, pericyte coverage and endothelial junctions. The tumor vessel stabilization effect of Thal resulted in a decrease in tumor vessel tortuosity and leakage, and increased vessel thickness and tumor perfusion. Eventually, the delivery of cisplatin was highly enhanced through the normalized tumor vasculature, thus resulting in profound anti-tumor and anti-metastatic effects. Mechanistically, the effects of Thal on tumor vessels were caused in part by its capability to correct the imbalance between pro-angiogenic factors and anti-angiogenic factors.

Conclusions

Our findings provide direct evidence that Thal remodels the abnormal tumor vessel system into a normalized vasculature. Our results may lay solid foundation for the development of Thal as a novel candidate agent to maximize the therapeutic efficacy of chemotherapeutic drugs for solid tumors.

Electronic supplementary material

The online version of this article (10.1186/s13046-019-1366-x) contains supplementary material, which is available to authorized users.

Stem Cell Plasticity and Dormancy in the Development of Cancer Therapy Resistance

Cancer treatment with either standard chemotherapy or targeted agents often results in the emergence of drug-refractory cell populations, ultimately leading to therapy failure. The biological features of drug resistant cells are largely overlapping with those of cancer stem cells and include heterogeneity, plasticity, self-renewal ability, and tumor-initiating capacity. Moreover, drug resistance is usually characterized by a suppression of proliferation that can manifest as quiescence, dormancy, senescence, or proliferative slowdown. Alterations in key cellular pathways such as autophagy, unfolded protein response or redox signaling, as well as metabolic adaptations also contribute to the establishment of drug resistance, thus representing attractive therapeutic targets. Moreover, a complex interplay of drug resistant cells with the micro/macroenvironment and with the immune system plays a key role in dictating and maintaining the resistant phenotype. Recent studies have challenged traditional views of cancer drug resistance providing innovative perspectives, establishing new connections between drug resistant cells and their environment and indicating unexpected therapeutic strategies. In this review we discuss recent advancements in understanding the mechanisms underlying drug resistance and we report novel targeting agents able to overcome the drug resistant status, with particular focus on strategies directed against dormant cells. Research on drug resistant cancer cells will take us one step forward toward the development of novel treatment approaches and the improvement of relapse-free survival in solid and hematological cancer patients.

Recruited bone marrow derived cells, local stromal cells and IL-17 at the front line of resistance development to anti-VEGF targeted therapies

Although anti-angiogenic agents targeting VEGF have shown affordable beneficial outcomes in several human cancer types, in most pre-clinical and clinical studies, these effects are transient and followed by rapid relapse and tumor regrowth. Recently, it has been suggested that recruited bone marrow derived cells (BMDCs) to the tumor-microenvironment together with stromal cells play an important role in development of resistance to anti-VEGF therapies. Additionally, acquired resistance to anti-VEGF therapies has shown to be mediated partly through overexpression of different pro-angiogenic cytokines and growth factors including G-CSF, IL-6, IL-8, VEGF and FGF by these cells. Alongside, IL-17, a pro-inflammatory cytokine, mostly secreted by infiltrated CD4⁺ T helper cells, has shown to mediate resistance to anti-VEGF therapies, through recruiting BMDCs and modulating stromal cells activities including endothelial cells, tumor associated macrophages and cancer associated fibroblasts. Here, we examined the role of BMDCs, tumor stromal cells, IL-17 and their negotiation in development of resistance to anti-VEGF targeted therapies.

Antiangiogenic therapy: Markers of response, "normalization" and resistance

Currently in cancer treatment, one premise is to use antiangiogenic therapies in association with chemotherapy or radiotherapy to augment their efficacy by benefiting from the vascular "normalization" induced by antiangiogenic therapy. This concept defines the time during which the tumor blood vessels adopt normal-like morphology and functionality, i.e. the blood vessels become more mature, the perfusion augments and hypoxia decreases. To date, there is such a diversity of treatment protocols where the type of antiangiogenic to adopt, its dose and duration of administration are different, that knowing when and how to treat is problematic. In this review, we analyzed thoroughly preclinical and clinical studies that use antiangiogenic treatments to benefit from the "normalization" and showed that the effects depend on the type of antiangiogenic administrated (anti-VEGF, anti-VEGFR, Multi-Kinase Inhibitor) and on the duration of treatment. Finally, biomarkers of "normalization" and resistance that could be used in the clinic are presented.

Upregulated WEE1 protects endothelial cells of colorectal cancer liver metastases

Surgical resection of colorectal cancer liver metastases (CLM) can be curative, yet 80% of patients are unsuitable for this treatment. As angiogenesis is a determinant of CLM progression we isolated endothelial cells from CLM and sought a mechanism which is upregulated, essential for angiogenic properties of these cells and relevant to emerging therapeutic options. Matched CLM endothelial cells (CLMECs) and endothelial cells of normal adjacent liver (LiECs) were superficially similar but transcriptome sequencing revealed molecular differences, one of which was unexpected upregulation and functional significance of the checkpoint kinase WEE1. Western blotting confirmed that WEE1 protein was upregulated in CLMECs. Knockdown of WEE1 by targeted short interfering RNA or the WEE1 inhibitor AZD1775 suppressed proliferation and migration of CLMECs. Investigation of the underlying mechanism suggested induction of double-stranded DNA breaks due to nucleotide shortage which then led to caspase 3-dependent apoptosis. The implication for CLMEC tube formation was striking with AZD1775 inhibiting tube branch points by 83%. WEE1 inhibitors might therefore be a therapeutic option for CLM and could be considered more broadly as anti-angiogenic agents in cancer treatment.

Stroma-derived HGF drives metabolic adaptation of colorectal cancer to angiogenesis inhibitors

The role of paracrine Hepatocyte Growth Factor (HGF) in the resistance to angiogenesis inhibitors (AIs) is hidden in xenograft models because mouse HGF fails to fully activate human MET. To uncover it, we compared the efficacy of AIs in wild-type and human HGF knock-in SCID mice bearing orthotopic human colorectal tumors. Species-specific HGF/MET signaling dramatically impaired the response to anti-angiogenic agents and boosted metastatic dissemination. In cell-based assays mimicking the consequences of anti-angiogenic therapy, colorectal cancer cells were completely resistant to hypoxia but extremely sensitive to nutrient deprivation. Starvation-induced apoptosis could be prevented by HGF, which promoted GLUT1-mediated glucose uptake, sustained glycolysis and activated autophagy. Pharmacological inhibition of GLUT1 in the presence of glucose killed tumor cells as effectively as glucose deprivation, and this effect was antagonized by HGF. Concomitant targeting of GLUT1 and HGF potently suppressed growth and dissemination of AI-resistant human tumors in human HGF knock-in SCID mice without exacerbating tumor hypoxia. These data suggest that stroma-derived HGF protects CRC cells against glucose starvation-induced apoptosis, promoting resistance to both AIs and anti-glycolytic agents. Combined inhibition of glucose metabolism and HGF/MET signaling (‘anti-METabolic therapy’) may represent a more effective CRC treatment compared to utterly blocking tumor blood supply.

Etoposide-Bevacizumab a new strategy against human melanoma cells expressing stem-like traits

Tumors contain a sub-population of self-renewing and expanding cells known as cancer stem cells (CSCs). Putative CSCs were isolated from human melanoma cells of a different aggressiveness, Hs294T and A375 cell lines, grown under hypoxia using “sphere-forming assay”, CD133 surface expression and migration ability. We found that a cell sub-population enriched for P1 sphere-initiating ability and CD133 expression also express larger amount of VEGF-R2. Etoposide does not influence phenotype of this sub-population of melanoma cells, while a combined treatment with Etoposide and Bevacizumab significantly abolished P1 sphere-forming ability, an effect associated with apoptosis of this subset of cells. Hypoxic melanoma cells sorted for VEGF-R2/CD133 positivity also undergo apoptosis when exposed to Etoposide and Bevacizumab. When Etoposide and Bevacizumab-treated hypoxic cells were injected intravenously into immunodeficient mice revealed a reduced capacity to induce lung colonies, which also appear with a longer latency period. Hence, our study indicates that a combined exposure to Etoposide and Bevacizumab targets melanoma cells endowed with stem-like properties and might be considered a novel approach to treat cancer-initiating cells.

Tumor refractoriness to anti-VEGF therapy

Vascular endothelial growth factor (VEGF) has been identified as the most potent cytokine involved in tumor angiogenesis and metastasis formation. Clinical results of anti-angiogenic therapies targeting VEGF and its receptors are very modest, resulting in a moderate improvement of overall survival. The clinical outcome is associated with the development of resistance and the increased risk of invasion and metastasis. In this article, I have analyzed the principal mechanisms of resistance to VEGF pathway inhibitors, including normalization of tumor blood vessels, hypoxia, recruitment of inflammatory cells and immature myeloid cells, alternative mechanisms of tumor vessel formation, genomic instability of tumor endothelial cells. In this context, the concept and strategies of anti-angiogenic therapies should be extensively re-considered and re-evaluated. In particular, rational combinations of anti-angiogenic agents based on pharmacokinetic and pharmacodynamics data are needed to overcome resistance and it is extremely important to determine the optimal duration and scheduling of anti-VEGF agents.

Tumor refractoriness to endostatin anti-angiogenesis is associated with the recruitment of CD11b+Gr1+ myeloid cells and inflammatory cytokines

Aims and background

A major challenge in developing antiangiogenic therapies is tumor intrinsic refractoriness and the emergence of treatment-induced resistance. Recently, such resistance is considered to be associated with inflammatory changes in the tumor microenvironment. However, no information has been acquired about the effect of endostatin on tumor microenvironment in this field. We established two tumor models refractory to endostatin treatment and sought to determine the role of inflammatory changes in the development of tumor refractoriness to antiangiogenic therapy.

Methods

Three xenograft tumor murine models were treated with low-dose endostatin or high-dose endostatin for 10 days. The effect of endostatin on tumor growth was observed, and tumors refractory to endostatin treatment were defined. Flow cytometry were carried out to assess the presence of CD11b+Gr1+ myeloid cells in the peripheral blood and in the tumor. Inflammatory cytokine levels in peripheral blood were measured using the enzyme-linked immunosorbent assay. The expression of NF-κB, versican and hypoxia-inducible factor-1α in the tumor was evaluated using immunohistochemistry.

Results

LLC and B16F1 tumors were defined as animal models of refractoriness to endostatin treatment. CD11b+Gr1+ myeloid cells were inherently recruited into the peripheral blood and the tumor microenvironment in the LLC tumor-bearing mice, and levels of serum G-CSF and TNF-α were increased along with the progression of tumor growth. In the B16F1 tumor-bearing mice, CD11b+Gr1+ myeloid cells were acquiredly recruited by endostatin into the peripheral blood and the tumor microenvironment. Additionally, high levels of G-CSF and TNF-α in serum and high expression of NF-κB, versican and hypoxia-inducible factor-1α in tumor tissue were found in B16F1 tumor-bearing mice after endostatin administration.

Conclusions

A tumor can grow inherently or acquiredly with refractoriness to endostatin treatment in vivo. Recruitment of CD11b+Gr1+ myeloid cells and inflammatory cytokines may play an important role in the development of tumor refractoriness to endostatin anti-angiogenesis.

Current Challenges of Cancer Anti-angiogenic Therapy and the Promise of Nanotherapeutics

With growing interest in cancer therapeutics, anti-angiogenic therapy has received considerable attention and is widely administered in several types of human cancers. Nonetheless, this type of therapy may induce multiple signaling pathways compared with cytotoxics and lead to worse outcomes in terms of resistance, invasion, metastasis, and overall survival (OS). Moreover, there are important challenges that limit the translation of promising biomarkers into clinical practice to monitor the efficiency of anti-angiogenic therapy. These pitfalls emphasize the urgent need for discovering alternative angiogenic inhibitors that target multiple angiogenic factors or developing a new drug delivery system for the current inhibitors. The great advantages of nanoparticles are their ability to offer effective routes that target the biological system and regulate different vital processes based on their unique features. Limited studies so far have addressed the effectiveness of nanoparticles in the normalization of the delicate balance between stimulating (pro-angiogenic) and inhibiting (anti-angiogenic) factors. In this review, we shed light on tumor vessels and their microenvironment and consider the current directions of anti-angiogenic and nanotherapeutic treatments. To the best of our knowledge, we consider an important effort in the understanding of anti-angiogenic agents (often a small volume of metals, nonmetallic molecules, or polymers) that can control the growth of new vessels.

Contribution of Adipose Tissue to Development of Cancer

Solid tumor growth and metastasis require the interaction of tumor cells with the surrounding tissue, leading to a view of tumors as tissue-level phenomena rather than exclusively cell-intrinsic anomalies. Due to the ubiquitous nature of adipose tissue, many types of solid tumors grow in proximate or direct contact with adipocytes and adipose-associated stromal and vascular components, such as fibroblasts and other connective tissue cells, stem and progenitor cells, endothelial cells, innate and adaptive immune cells, and extracellular signaling and matrix components. Excess adiposity in obesity both increases risk of cancer development and negatively influences prognosis in several cancer types, in part due to interaction with adipose tissue cell populations. Herein, we review the cellular and noncellular constituents of the adipose "organ," and discuss the mechanisms by which these varied microenvironmental components contribute to tumor development, with special emphasis on obesity. Due to the prevalence of breast and prostate cancers in the United States, their close anatomical proximity to adipose tissue depots, and their complex epidemiologic associations with obesity, we particularly highlight research addressing the contribution of adipose tissue to the initiation and progression of these cancer types. Obesity dramatically modifies the adipose tissue microenvironment in numerous ways, including induction of fibrosis and angiogenesis, increased stem cell abundance, and expansion of proinflammatory immune cells. As many of these changes also resemble shifts observed within the tumor microenvironment, proximity to adipose tissue may present a hospitable environment to developing tumors, providing a critical link between adiposity and tumorigenesis. © 2018 American Physiological Society. Compr Physiol 8:237-282, 2018.

Macrophage depletion through colony stimulating factor 1 receptor pathway blockade overcomes adaptive resistance to anti-VEGF therapy

Anti-angiogenesis therapy has shown clinical benefit in patients with high-grade serous ovarian cancer (HGSC), but adaptive resistance rapidly emerges. Thus, approaches to overcome such resistance are needed. We developed the setting of adaptive resistance to anti-VEGF therapy, and performed a series of in vivo experiments in both immune competent and nude mouse models. Given the pro-angiogenic properties of tumor-associated macrophages (TAMs) and the dominant role of CSF1R in macrophage function, we added CSF1R inhibitors following emergence of adaptive resistance to anti-VEGF antibody. Mice treated with a CSF1R inhibitor (AC708) after anti-VEGF antibody resistance had little to no measurable tumor burden upon completion of the experiment while those that did not receive a CSF1R inhibitor still had abundant tumor. To mimic clinically used regimens, mice were also treated with anti-VEGF antibody and paclitaxel until resistance emerged, and then a CSF1R inhibitor was added. The addition of a CSF1R inhibitor restored response to anti-angiogenesis therapy, resulting in 83% lower tumor burden compared to treatment with anti-VEGF antibody and paclitaxel alone. Collectively, our data demonstrate that the addition of a CSF1R inhibitor to anti-VEGF therapy and taxane chemotherapy results in robust anti-tumor effects.

Macrophage depletion through colony stimulating factor 1 receptor pathway blockade overcomes adaptive resistance to anti-VEGF therapy

Anti-angiogenesis therapy has shown clinical benefit in patients with high-grade serous ovarian cancer (HGSC), but adaptive resistance rapidly emerges. Thus, approaches to overcome such resistance are needed. We developed the setting of adaptive resistance to anti-VEGF therapy, and performed a series of in vivo experiments in both immune competent and nude mouse models. Given the pro-angiogenic properties of tumor-associated macrophages (TAMs) and the dominant role of CSF1R in macrophage function, we added CSF1R inhibitors following emergence of adaptive resistance to anti-VEGF antibody. Mice treated with a CSF1R inhibitor (AC708) after anti-VEGF antibody resistance had little to no measurable tumor burden upon completion of the experiment while those that did not receive a CSF1R inhibitor still had abundant tumor. To mimic clinically used regimens, mice were also treated with anti-VEGF antibody and paclitaxel until resistance emerged, and then a CSF1R inhibitor was added. The addition of a CSF1R inhibitor restored response to anti-angiogenesis therapy, resulting in 83% lower tumor burden compared to treatment with anti-VEGF antibody and paclitaxel alone. Collectively, our data demonstrate that the addition of a CSF1R inhibitor to anti-VEGF therapy and taxane chemotherapy results in robust anti-tumor effects.

Macrophage depletion through colony stimulating factor 1 receptor pathway blockade overcomes adaptive resistance to anti-VEGF therapy

Anti-angiogenesis therapy has shown clinical benefit in patients with high-grade serous ovarian cancer (HGSC), but adaptive resistance rapidly emerges. Thus, approaches to overcome such resistance are needed. We developed the setting of adaptive resistance to anti-VEGF therapy, and performed a series of in vivo experiments in both immune competent and nude mouse models. Given the pro-angiogenic properties of tumor-associated macrophages (TAMs) and the dominant role of CSF1R in macrophage function, we added CSF1R inhibitors following emergence of adaptive resistance to anti-VEGF antibody. Mice treated with a CSF1R inhibitor (AC708) after anti-VEGF antibody resistance had little to no measurable tumor burden upon completion of the experiment while those that did not receive a CSF1R inhibitor still had abundant tumor. To mimic clinically used regimens, mice were also treated with anti-VEGF antibody and paclitaxel until resistance emerged, and then a CSF1R inhibitor was added. The addition of a CSF1R inhibitor restored response to anti-angiogenesis therapy, resulting in 83% lower tumor burden compared to treatment with anti-VEGF antibody and paclitaxel alone. Collectively, our data demonstrate that the addition of a CSF1R inhibitor to anti-VEGF therapy and taxane chemotherapy results in robust anti-tumor effects.

Theranostic Performance of Acoustic Nanodroplet Vaporization-Generated Bubbles in Tumor Intertissue

Solid tumors with poorly perfused regions reveal some of the treatment limitations that restrict drug delivery and therapeutic efficacy. Acoustic droplet vaporization (ADV) has been applied to directly disrupt vessels and release nanodroplets, ADV-generated bubbles (ADV-Bs), and drugs into tumor tissue. In this study, we investigated the in vivo behavior of ADV-Bs stimulated by US, and evaluated the possibility of moving intertissue ADV-Bs into the poorly perfused regions of solid tumors. Intravital imaging revealed intertissue ADV-B formation, movement, and cavitation triggered by US, where the distance of intertissue ADV-B movement was 33-99 µm per pulse. When ADV-Bs were applied to tumor cells, the cell membrane was damaged, increasing cellular permeability or inducing cell death. The poorly perfused regions within solid tumors show enhancement due to ADV-B accumulation after application of US-triggered ADV-B. The intratumoral nanodroplet or ADV-B distribution around the poorly perfused regions with tumor necrosis or hypoxia were demonstrated by histological assessment. ADV-B formation, movement and cavitation could induce cell membrane damage by mechanical force providing a mechanism to overcome treatment limitations in poorly perfused regions of tumors.

Concurrent anti-vascular therapy and chemotherapy in solid tumors using drug-loaded acoustic nanodroplet vaporization

Drug-loaded nanodroplets (NDs) can be converted into gas bubbles through ultrasound (US) stimulation, termed acoustic droplet vaporization (ADV), which provides a potential strategy to simultaneously induce vascular disruption and release drugs for combined physical anti-vascular therapy and chemotherapy. Doxorubicin-loaded NDs (DOX-NDs) with a mean size of 214nm containing 2.48mg DOX/mL were used in this study. High-speed images displayed bubble formation and cell debris, demonstrating the reduction in cell viability after ADV. Intravital imaging provided direct visualization of disrupted tumor vessels (vessel size <30μm), the extravasation distance was 12μm in the DOX-NDs group and increased over 100μm in the DOX-NDs+US group. Solid tumor perfusion on US imaging was significantly reduced to 23% after DOX-NDs vaporization, but gradually recovered to 41%, especially at the tumor periphery after 24h. Histological images of the DOX-NDs+US group revealed tissue necrosis, a large amount of drug extravasation, vascular disruption, and immune cell infiltration at the tumor center. Tumor sizes decreased 22%, 36%, and 68% for NDs+US, DOX-NDs, and DOX-NDs+US, respectively, to prolong the survival of tumor-bearing mice. Therefore, this study demonstrates that the combination of physical anti-vascular therapy and chemotherapy with DOX-NDs vaporization promotes uniform treatment to improve therapeutic efficacy.

STATEMENT OF SIGNIFICANCE

Tumor vasculature plays an important role for tumor cell proliferation by transporting oxygen and nutrients. Previous studies combined anti-vascular therapy and drug release to inhibit tumor growth by ultrasound-stimulated microbubble destruction or acoustic droplet vaporization. Although the efficacy of combined therapy has been demonstrated; the relative spatial distribution of vascular disruption, drug delivery, and accompanied immune responses within solid tumors was not discussed clearly. Herein, our study used drug-loaded nanodroplets to combined physical anti-vascular and chemical therapy. The in vitro cytotoxicity, intravital imaging, and histological assessment were used to evaluate the temporal and spatial cooperation between physical and chemical effect. These results revealed some evidences for complementary action to explain the high efficacy of tumor inhibition by combined therapy.

Linking metabolic reprogramming to therapy resistance in cancer

Metabolic rearrangements are essential to satisfy the different requirements of cancer cells during tumorigenesis and recent studies have highlighted a role for such metabolic reprogramming in response and adaptation to therapies. However, therapy-resistant experimental models have been described to be either glycolysis-dependent or OXPHOS-addicted. Here we discuss the recent literature on metabolic reprogramming of cancer in therapy resistance with a plausible explanation of the observed differences which collectively indicate that dis-regulated metabolic pathways could be considered potential therapeutic targets in tumors resistant to conventional therapy.

Improving cancer therapies by targeting the physical and chemical hallmarks of the tumor microenvironment

Tumors are highly heterogeneous at the patient, tissue, cellular, and molecular levels. This multi-scale heterogeneity poses significant challenges for effective therapies, which ideally must not only distinguish between tumorous and healthy tissue, but also fully address the wide variety of tumorous sub-clones. Commonly used therapies either leverage a biological phenotype of cancer cells (e.g. high rate of proliferation) or indiscriminately kill all the cells present in a targeted volume. Tumor microenvironment (TME) targeting represents a promising therapeutic direction, because a number of TME hallmarks are conserved across different tumor types, despite the underlying genetic heterogeneity. Historically, TME targeting has largely focused on the cells that support tumor growth (e.g. vascular endothelial cells). However, by viewing the intrinsic physical and chemical alterations in the TME as additional therapeutic opportunities rather than barriers, a new class of TME-inspired treatments has great promise to complement or replace existing therapeutic strategies. In this review we summarize the physical and chemical hallmarks of the TME, and discuss how these tumor characteristics either currently are, or may ultimately be targeted to improve cancer therapies.

Alternative scheduling of pulsatile, high dose sunitinib efficiently suppresses tumor growth

Background

Increased exposure to multitargeted kinase inhibitor sunitinib is associated with improved outcome, emphasizing the importance of maintaining adequate dosing and drug levels. The currently approved schedule (50 mg daily, four weeks on, two weeks off) precludes further dose-intensification. Recent data suggest that sunitinib, although initially developed as an antiangiogenic agent, has direct antitumor activity.

Methods

In this study, we tested whether a chemotherapy-like schedule of pulsatile high dose sunitinib would result in improved antitumor activity.

Results

In vitro, a single exposure to 20 μM sunitinib for 6-9 h resulted in complete inhibition of tumor cell growth and cell death conveyed through activation of caspases and autophagy upregulation. Notably, repeated exposure of tumor cells to pulses of high concentrations of sunitinib did not induce resistance. In vivo, once-weekly treatment with high dose sunitinib of tumors growing on the chorioallantoic membrane (CAM) of the chicken embryo significantly impaired tumor growth by 57 % compared to vehicle, outperforming the daily, standard scheduling.

Conclusions

These results prompted the initiation of a phase I clinical trial, where intermittent, high dose sunitinib is being investigated in patients with advanced solid tumors (registration number and date: NCT02058901, 30 September 2013, respectively). The trial is actively recruiting patients and promising preliminary indications of antitumor activity have been observed.

Scopoletin, an active principle of tree tobacco (Nicotiana glauca) inhibits human tumor vascularization in xenograft models and modulates ERK1, VEGF-A, and FGF-2 in computer model

We recently reported the antineovascularization effect of scopoletin on rat aorta and identified its potential anti-angiogenic activity. Scopoletin could be useful as a systemic chemotherapeutic agent against angiogenesis-dependent malignancies if its antitumorigenic activity is investigated and scientifically proven using a suitable human tumor xenograft model. In the present study, bioassay-guided (anti-angiogenesis) phytochemical investigation was conducted on Nicotiana glauca extract which led to the isolation of scopoletin. Further, anti-angiogenic activity of scopoletin was characterized using ex vivo, in vivo and in silico angiogenesis models. Finally, the antitumorigenic efficacy of scopoletin was studied in human colorectal tumor xenograft model using athymic nude mice. For the first time, an in vivo anticancer activity of scopoletin was reported and characterized using xenograft models. Scopoletin caused significant suppression of sprouting of microvessels in rat aortic explants with IC50 (median inhibitory concentration) 0.06μM. Scopoletin (100 and 200mg/kg) strongly inhibited (59.72 and 89.4%, respectively) vascularization in matrigel plugs implanted in nude mice. In the tumor xenograft model, scopoletin showed remarkable inhibition on tumor growth (34.2 and 94.7% at 100 and 200mg/kg, respectively). Tumor histology revealed drastic reduction of the extent of vascularization. Further, immunostaining of CD31 and NG2 receptors in the histological sections confirmed the antivascular effect of scopoletin in tumor vasculature. In computer modeling, scopoletin showed strong ligand affinity and binding energies toward the following angiogenic factors: protein kinase (ERK1), vascular endothelial growth factor A (VEGF-A), and fibroblast growth factor 2 (FGF-2). These results suggest that the antitumor activity of scopoletin may be due to its strong anti-angiogenic effect, which may be mediated by its effective inhibition of ERK1, VEGF-A, and FGF-2.

Enhanced angiogenesis, hypoxia and neutrophil recruitment during Myc-induced liver tumorigenesis in zebrafish

Angiogenesis, hypoxia and immune cells are important components in tumor microenvironment affecting tumor growth. Here we employed a zebrafish liver tumor model to investigate the effect of Myc expression on angiogenesis, hypoxia and tumor-infiltrated neutrophils during the tumor initiation stage. We found that induced Myc expression in the liver caused a dramatic increase of liver size with neoplastic features. The tumorigenic liver was accompanied by enhanced angiogenesis and inhibition of angiogenesis by an inhibitor (SU5416 or sunitinib) hindered the tumorigenic growth, suggesting an essential role of angiogenesis in tumorigenic growth of liver tumor in this zebrafish model. Myc induction also caused hypoxia, which could be further enhanced by hypoxia activator, ML228, to lead to a further enlargement of tumorigenic liver. Furthermore, Myc overexpression incurred an increase of liver-infiltrated neutrophils and the increase could be suppressed by angiogenesis inhibitors or by morpholino knockdown inhibition of neutrophil differentiation, leading to a suppression of growth of tumorigenic livers. Finally, the enhanced angiogenesis, hypoxia and tumor-infiltrated neutrophils by Myc overexpression were validated by RT-qPCR examination of expression of relevant biomarker genes. In sum, the current study demonstrated that the Myc-induced liver tumor model in zebrafish provides an excellent platform for study of tumor microenvironment.

[Resistance to anti-angiogenic therapy: a clinical and scientific current issue]

Although the use of anti-angiogenic agents has been considered a promising strategy to block tumor growth and improve the bioavailability of drugs into the tumor, the use of most of them in clinical trials is limited. The development of resistance to some anti-angiogenic agents and their high toxicity are currently under investigations. However, the approach is still valid since this therapeutic tool has lengthened survival of patients with colon, breast, kidney, lungs and liver cancers. The identification of biomarkers in response to this family of drugs is an important area of investigation.

Prognostic Significance of Intratumoral Metabolic Heterogeneity on 18F-FDG PET/CT in Pathological N0 Non-Small Cell Lung Cancer

PURPOSE

The aim of the study was to evaluate the prognostic significance of intratumoral metabolic heterogeneity on pretreatment F-FDG PET/CT in patients with lung cancer who were pathologically N0 (pN0) after curative surgical resection.

METHODS

We examined 119 patients (M/F = 79/40; mean age, 64.6 ± 9.0 years) who had undergone pretreatment F-FDG PET/CT and were diagnosed as pN0 after curative surgery for adenocarcinoma (ADC; n = 67) or squamous cell carcinoma (SQCC; n = 52). Heterogeneity factor (HF) and other metabolic parameters (SUVmax, metabolic tumor volume [MTV] and total lesion glycolysis [TLG]) for the primary lesions were measured, and the results were analyzed for recurrence. The HF, defined as the derivative of the volume-threshold function from 20% to 80%, was computed for primary lesions. Univariate and multivariate analyses for recurrence were performed using the Kaplan-Meier method and using the Cox proportional hazards model.

RESULTS

SUVmax, MTV, TLG, and HF were statistically different between patients with ADC and SQCC. Forty-one (34.5%) of 119 patients experienced recurrence (ADC, 25/67 = 37.3% vs. SQCC, 16/52 = 30.8%). Results of univariate analysis indicate that SUVmax, MTV, TLG, and HF in ADC and TLG and HF in SQCC were predictors for recurrence. After adjusting for sex, age, and histological grade in multivariate analysis, high SUVmax, MTV, TLG, and HF in ADC exhibited an association with increased risk of recurrence.

CONCLUSIONS

Metabolic parameters and heterogeneity of primary tumor on pretreatment F-FDG PET/CT can predict recurrence in pN0 NSCLC patients of ADC type who have undergone curative surgery but not in patients of SQCC type.

A Phase I Clinical, Pharmacokinetic, and Pharmacodynamic Study of Weekly or Every Three Week Ixabepilone and Daily Sunitinib in Patients with Advanced Solid Tumors

PURPOSE

To evaluate the safety, MTD, pharmacokinetics/pharmacodynamics, and early clinical activity of ixabepilone given either weekly or every 3 weeks in combination with daily sunitinib in patients with advanced solid tumors.

EXPERIMENTAL DESIGN

Eligible patients received either weekly (schedule A) or every 3 weeks (schedule B) ixabepilone at escalating doses (schedule A: 7.5, 15, or 20 mg/m(2); schedule B: 20, 30, or 40 mg/m(2)), and oral sunitinib (37.5 mg daily), starting on day 8 of cycle 1. Dose-limiting toxicities (DLT) were assessed during cycle 1.

RESULTS

The ixabepilone and sunitinib combination was fairly well tolerated. DLTs were observed in 3 subjects (1 in schedule 3A and 2 in schedule 3B). The most common grade 3-4 hematologic and nonhematologic adverse events were leukopenia and fatigue, respectively. Four patients (3 in schedule A) achieved a partial response, while 13 patients had stable disease. Nine of 17 heavily pretreated colorectal cancer patients had clinical benefit. Coadministration of sunitinib with ixabepilone on a weekly (but not every 3 week) schedule was associated with a significant increase in the half-life and a significant decrease in the clearance of ixabepilone. Correlative studies demonstrated a significant association between higher baseline plasma angiogenic activity (PAA) and clinical benefit in schedule A patients. Weekly, but not every 3 weeks, ixabepilone led to a significant decrease in PAA postbaseline.

CONCLUSIONS

Coadministration of ixabepilone with sunitinib has acceptable toxicity and encouraging clinical activity in heavily pretreated patients, particularly in patients with metastatic colorectal cancer. Clin Cancer Res; 22(13); 3209-17. ©2016 AACR.

Autophagy, a double-edged sword in anti-angiogenesis therapy

Autophagy is a highly conservative cell behavior to keep the intracellular homeostasis and is frequently activated when cells encounter disgusting conditions, such as nutrition or growth factor deprive, hypoxia and cytotoxic agents. However, the precise role of autophagy under various conditions may be opposite, differ from protect cells survival to promote cells death, and the mechanism of this conditional-dependent role is still unclear. Anti-angiogenesis agents, such as bevacizumab, sorafenib and sunitinib, could reduce tumor microvascular density and increase tumor hypoxia, thus up-regulating autophagy activation of tumor cells, but the function of autophagy induced by anti-angiogenesis agents is still divergent and is considered to play a cytoprotective role in most cases. In this review, we mainly discuss the relationship between anti-angiogenesis therapy-induced hypoxia and autophagy, and pay special attention on the exact role of anti-angiogenesis agents induced autophagy in the process of anti-angiogenesis treatment.

Strong Notch activation hinders bevacizumab efficacy in advanced colorectal cancer

AIM

To assess the role of Notch activation in predicting bevacizumab efficacy in colorectal cancer (CRC).

MATERIALS & METHODS

Notch activation was evaluated by immunohistochemistry (IHC) on 65 CRC enrolled within randomized clinical trials assessing first-line bevacizumab-based chemotherapy and on 21 CRC treated with chemotherapy alone.

RESULTS

Strong Notch (IHC 3+) activation was negatively associated with response (18 vs 62% in low Notch cases [IHC 0, 1, 2+]; p = 0.016), progression-free survival (4.9 vs 12.1 months; p = 0.002) and overall survival (19.3 vs 30.4 months; p = 0.039). No correlation was found between Notch activation and clinical outcome in CRC treated with chemotherapy alone.

CONCLUSION

A potential role of Notch activation in the antitumor activity of bevacizumab could be hypothesized.

Compensatory angiogenesis and tumor refractoriness

Since the establishment of tumor angiogenesis as a therapeutic target, an excitement in developing the anti-angiogenic agents was resulted in tailoring a humanized monoclonal antibody (Bevacizumab) against vascular endothelial growth factor (VEGF): a key factor in recruiting angiogenesis. The past three decades' research in the area of angiogenesis also invented a series of novel and effective anti-angiogenic agents targeting the VEGF signaling axis. Despite the demonstrable clinical benefits of anti-angiogenic therapy, the preclinical and clinical data of the current therapeutic settings clearly indicate the transient efficacy, restoration of tumor progression and aggressive recurrence of tumor invasion after the withdrawal of anti-angiogenic therapy. Therefore, the impact of this therapeutic regime on improving overall survival of patients has been disappointing in clinic. The recent advances in pathophysiology of tumor angiogenesis and related molecular and cellular underpinnings attributed the conspiracy of compensatory angiogenic pathways in conferring evasive and intrinsic tumor resistance to anti-angiogenic agents. The understandings of how these pathways functionally cross-talk for sustaining tumor angiogenesis during VEGF blockade is essential and perhaps may act as a basic prerequisite for designing novel therapeutic strategies to combat the growing arrogance of tumors toward anti-angiogenic agents. The present review offers a discourse on major compensatory angiogenic pathways operating at cellular and molecular levels and their attributes with resistance to anti-angiogenic agents along with strategic opinions on future setting in targeting tumor angiogenesis.

Anti-angiogenic Effects of Bumetanide Revealed by DCE-MRI with a Biodegradable Macromolecular Contrast Agent in a Colon Cancer Model

PURPOSE

To assess the antiangiogenic effect of bumetanide with dynamic contrast enhanced (DCE)-MRI and a biodegradable macromolecular MRI contrast agent.

METHODS

A new polydisulfide containing macrocyclic gadolinium (Gd(III)) chelates, poly([(Gd-DOTA)-DETA]-co-DTBP) (GODP), was synthesized as a safe biodegradable macromolecular MRI contrast agent for DCE-MRI. Nude mice bearing flank HT29 colon cancer xenografts were then treated daily with either bumetanide or saline for a total of 3 weeks. DCE-MRI was performed before and after the treatment weekly. The DCE-MRI data were analyzed using the adiabiatic approximation to the tissue homogeneity (AATH) model to assess the change of tumor vascularity in response to the treatment. Immunohistochemistry (IHC) and western blot were performed to study tumor angiogenic biomarkers and hypoxia.

RESULTS

DCE-MRI with GODP revealed that bumetanide reduced vascular permeability and plasma volume fraction by a significantly greater extent than the saline control therapy after 3 weeks of therapy. These changes were verified by the significant decline of CD31 and VEGF expression in the bumetanide treatment group. Despite a significant regression in vascularity, the tumors remained highly proliferative. Overexpression of the transcription factor HIF-1α in response to elevated hypoxia is thought to be the driving force behind the uninterrupted tumor expansion.

CONCLUSION

This study demonstrated the effectiveness of DCE-MRI with GODP in detecting vascular changes following the administration of bumetanide. Bumetanide has the potential to curtail growth of the tumor vasculature and can be employed in future therapeutic strategies.

Enhanced Anti-Angiogenic Effect of Low Molecular Weight Heparin-Bile Acid Conjugates by Co-Administration of a Selective COX-2 Inhibitor

PURPOSE

To overcome definite limitations of angiogenesis inhibitors such as insufficient therapeutic efficacy as a single drug and resisting or conflicting effect under chronic treatment, it is required to develop a new regimen to improve the therapeutic effect.

METHODS

The combination effect of a multi-targeting angiogenesis inhibitor (LHT7) and a selective cyclooxygenase-2 inhibitor (celecoxib) on neovascularization in tumor growth was studied both in vitro and vivo experiments.

RESULTS

While hypoxia-mediated COX-2 overexpression and macrophage recruitment were observed at LHT7-treated tumor tissues, it was well-controlled by the combination of celecoxib and LHT7. On the other hand, the in vitro tube formation and the in vivo tumor vessel formation and structure were inhibited by either LHT7 or celecoxib, but the inhibition effect was further enhanced by using them together. However, the combination therapy did not further enhance the inhibitory effect on tumor growth in terms of volume compared to single drug uses, which attributed not to increased cellular apoptosis but to decreased cell proliferation.

CONCLUSIONS

COX-2 inhibition could enhance the therapeutic effect of anti-angiogenic drugs both by inhibiting the inflammatory reactions induced by hypoxia and by altering the vascular stabilization that is mediated by an assembly with mural cells.

HIF-1α/GPER signaling mediates the expression of VEGF induced by hypoxia in breast cancer associated fibroblasts (CAFs)

INTRODUCTION

Carcinoma-associated fibroblasts (CAFs) play a pivotal role in cancer progression by contributing to invasion, metastasis and angiogenesis. Solid tumors possess a unique microenvironment characterized by local hypoxia, which induces gene expression changes and biological features leading to poor outcomes. Hypoxia Inducible Factor 1 (HIF-1) is the main transcription factor that mediates the cell response to hypoxia through different mechanisms that include the regulation of genes strongly associated with cancer aggressiveness. Among the HIF-1 target genes, the G-protein estrogen receptor (GPER) exerts a stimulatory role in diverse types of cancer cells and in CAFs.

METHODS

We evaluated the regulation and function of the key angiogenic mediator vascular endothelial growth factor (VEGF) in CAFs exposed to hypoxia. Gene expression studies, Western blotting analysis and immunofluorescence experiments were performed in CAFs and breast cancer cells in the presence of cobalt chloride (CoCl₂) or cultured under low oxygen tension (2% O₂), in order to analyze the involvement of the HIF-1α/GPER signaling in the biological responses to hypoxia. We also explored the role of the HIF-1α/GPER transduction pathway in functional assays like tube formation in human umbilical vein endothelial cells (HUVECs) and cell migration in CAFs.

RESULTS

We first determined that hypoxia induces the expression of HIF-1α and GPER in CAFs, then we ascertained that the HIF-1α/GPER signaling is involved in the regulation of VEGF expression in breast cancer cells and in CAFs exposed to hypoxia. We also assessed by ChIP assay that HIF-1α and GPER are both recruited to the VEGF promoter sequence and required for VEGF promoter stimulation upon hypoxic condition. As a biological counterpart of these findings, conditioned medium from hypoxic CAFs promoted tube formation in HUVECs in a HIF-1α/GPER dependent manner. The functional cooperation between HIF-1α and GPER in CAFs was also evidenced in the hypoxia-induced cell migration, which involved a further target of the HIF-1α/GPER signaling like connective tissue growth factor (CTGF).

CONCLUSIONS

The present results provide novel insight into the role elicited by the HIF-1α/GPER transduction pathway in CAFs towards the hypoxia-dependent tumor angiogenesis. Our findings further extend the molecular mechanisms through which the tumor microenvironment may contribute to cancer progression.