Roles of nitric oxide synthase inhibition and vascular endothelial growth factor receptor-2 inhibition on vascular morphology and function in an in vivo model of pancreatic cancer

Gasotransmitters in the tumor microenvironment: Impacts on cancer chemotherapy (Review)

Nitric oxide, carbon monoxide and hydrogen sulfide are three endogenous gasotransmitters that serve a role in regulating normal and pathological cellular activities. They can stimulate or inhibit cancer cell proliferation and invasion, as well as interfere with cancer cell responses to drug treatments. Understanding the molecular pathways governing the interactions between these gases and the tumor microenvironment can be utilized for the identification of a novel technique to disrupt cancer cell interactions and may contribute to the conception of effective and safe cancer therapy strategies. The present review discusses the effects of these gases in modulating the action of chemotherapies, as well as prospective pharmacological and therapeutic interfering approaches. A deeper knowledge of the mechanisms that underpin the cellular and pharmacological effects, as well as interactions, of each of the three gases could pave the way for therapeutic treatments and translational research.

The Role of Nitric Oxide in Cancer: Master Regulator or NOt?

Nitric oxide (NO) is a key player in both the development and suppression of tumourigenesis depending on the source and concentration of NO. In this review, we discuss the mechanisms by which NO induces DNA damage, influences the DNA damage repair response, and subsequently modulates cell cycle arrest. In some circumstances, NO induces cell cycle arrest and apoptosis protecting against tumourigenesis. NO in other scenarios can cause a delay in cell cycle progression, allowing for aberrant DNA repair that promotes the accumulation of mutations and tumour heterogeneity. Within the tumour microenvironment, low to moderate levels of NO derived from tumour and endothelial cells can activate angiogenesis and epithelial-to-mesenchymal transition, promoting an aggressive phenotype. In contrast, high levels of NO derived from inducible nitric oxide synthase (iNOS) expressing M1 and Th1 polarised macrophages and lymphocytes may exert an anti-tumour effect protecting against cancer. It is important to note that the existing evidence on immunomodulation is mainly based on murine iNOS studies which produce higher fluxes of NO than human iNOS. Finally, we discuss different strategies to target NO related pathways therapeutically. Collectively, we present a picture of NO as a master regulator of cancer development and progression.

Arginine metabolism: a potential target in pancreatic cancer therapy

ABSTRACT

Pancreatic ductal adenocarcinoma (PDAC) is an extremely malignant disease, which has an extremely low survival rate of <9% in the United States. As a new hallmark of cancer, metabolism reprogramming exerts crucial impacts on PDAC development and progression. Notably, arginine metabolism is altered in PDAC cells and participates in vital signaling pathways. In addition, arginine and its metabolites including polyamine, creatine, agmatine, and nitric oxide regulate the proliferation, growth, autophagy, apoptosis, and metastasis of cancer cells. Due to the loss of argininosuccinate synthetase 1 (ASS1) expression, the key enzyme in arginine biosynthesis, arginine deprivation is regarded as a potential strategy for PDAC therapy. However, drug resistance develops during arginine depletion treatment, along with the re-expression of ASS1, metabolic dysfunction, and the appearance of anti-drug antibody. Additionally, arginase 1 exerts crucial roles in myeloid-derived suppressor cells, indicating its potential targeting by cancer immunotherapy. In this review, we introduce arginine metabolism and its impacts on PDAC cells. Also, we discuss the role of arginine metabolism in arginine deprivation therapy and immunotherapy for cancer.

Reprogramming of Amino Acid Metabolism in Pancreatic Cancer: Recent Advances and Therapeutic Strategies

Pancreatic ductal adenocarcinoma (PDAC) is one of the most fatal malignancies with an extremely poor prognosis. Energy metabolism reprogramming, an emerging hallmark of cancer, has been implicated in the tumorigenesis and development of pancreatic cancer. In addition to well-elaborated enhanced glycolysis, investigating the role of reprogramming of amino acid metabolism has sparked great interests in recent years. The rewiring amino acid metabolism orchestrated by genetic alterations contributes to pancreatic cancer malignant characteristics including cell proliferation, invasion, metastasis, angiogenesis and redox balance. In the unique hypoperfused and nutrient-deficient tumor microenvironment (TME), the interactions between cancer cells and stromal components and salvaging processes including autophagy and macropinocytosis play critical roles in fulfilling the metabolic requirements and supporting growth of PDAC. In this review, we elucidate the recent advances in the amino acid metabolism reprogramming in pancreatic cancer and the mechanisms of amino acid metabolism regulating PDAC progression, which will provide opportunities to develop promising therapeutic strategies.

Evidences supporting the vascular etiology of post-double balloon enteroscopy pancreatitis: Study in porcine model

Double balloon enteroscopy (DBE) is an endoscopic technique broadly used to diagnose and treat small bowel diseases. Among the associated complications of the oral DBE, post-procedure pancreatitis has taken the most attention due to its gravity and the thought that it might be associated to the technique itself and anatomical features of the pancreas. However, as the etiology has not been clarified yet, this paper aims to review the published literature and adds new results from a porcine animal model. Biochemical markers, histological sections and the vascular perfusion of the pancreas were monitored in the pig during DBE practice. A reduced perfusion of the pancreas and bowel, the presence of defined hypoxic areas and disseminated necrotic zones were found in the pancreatic tissue of pigs. All these evidences contribute to support a vascular distress as the most likely etiology of the post-DBE pancreatitis.

Early Actions of Anti-Vascular Endothelial Growth Factor/Vascular Endothelial Growth Factor Receptor Drugs on Angiogenic Blood Vessels

Tumors induce their heterogeneous vasculature by secreting vascular endothelial growth factor (VEGF)-A. Anti-VEGF/VEGF receptor (VEGFR) drugs treat cancer, but the underlying mechanisms remain unclear. An adenovirus expressing VEGF-A (Ad-VEGF-A¹⁶⁴) replicates the tumor vasculature in mice without tumor cells. Mother vessels (MV) are the first angiogenic vessel type to form in tumors and after Ad-VEGF-A¹⁶⁴. Multiday treatments with a VEGF trap reverted MV back to normal microvessels. We now show that, within hours, a single dose of several anti-VEGF drugs collapsed MV to form glomeruloid microvascular proliferations (GMP), accompanied by only modest endothelial cell death. GMP, common in many human cancers but of uncertain origin, served as an intermediary step in MV reversion to normal microvessels. The vasodisruptive drug combretastatin CA4 also targeted MV selectively but acted differently, extensively killing MV endothelium. Antivascular changes were quantified with a novel Evans blue dye assay that measured vascular volumes. As in tumors, Ad-VEGF-A¹⁶⁴ strikingly increased endothelial nitric oxide synthase (eNOS) expression. The eNOS inhibitor N(G)-Nitro-l-arginine methyl ester mimicked anti-VEGF/VEGFR drugs, rapidly collapsing MV to GMP. Inhibition of eNOS reduces synthesis of its vasodilatory product, nitric oxide, leading to arterial contraction. Patients and mice receiving anti-VEGF/VEGFR drugs develop hypertension, reflecting systemic arterial contraction. Together, anti-VEGF/VEGFR drugs act in part by inhibiting eNOS, causing vasocontraction, MV collapse to GMP, and subsequent reversion of GMP to normal microvessels, all without extensive vascular killing.

NO• and Pancreatic Cancer: A Complex Interaction with Therapeutic Potential

SIGNIFICANCE

Pancreatic tumors express high level of nitric oxide synthases (NOSs) in particular inducible (iNOS/NOS2) and endothelial (eNOS/NOS3) forms. However, the role of nitric oxide (NO^•) in the development and progression of pancreatic cancer is not clearly defined. Delineating the NO^•-induced signaling in pancreatic cancer and its potential contribution in disease aggressiveness may provide therapeutic targets to improve survival in this lethal malignancy. Recent Advances: An increased expression of NOS2/iNOS in tumors is associated with poorer survival in early stage resected patients with pancreatic ductal adenocarcinoma (PDAC). Furthermore, genetic deletion of NOS2 enhanced survival in mice with autochthonous PDAC. Additionally, targeting NOS3/eNOS reduced the abundance of precursor lesions in mice, which trended toward improved survival.

CRITICAL ISSUES

The extremely poor prognosis in pancreatic cancer is due to the late diagnosis and lack of effective therapy in advanced disease. One of the most critical issues is to decipher the underlying mechanism of disease aggressiveness and therapeutic resistance for identifying potential therapeutic target and effective treatment. Given the evidence of a strong association between inflammation and pancreatic cancer and clinical evidence, which suggests an association between NOS2 and disease aggressiveness, it is critical to define the role of NO^• signaling in this lethal malignancy.

FUTURE DIRECTIONS

Recent preclinical and clinical evidences indicate a potential therapeutic significance of targeting NO^• signaling in pancreatic cancer. With the emergence of new preclinical models, including the patient-derived organoids, further preclinical evaluation using clinically tested NOS inhibitors is needed for designing future clinical investigation. Antioxid. Redox Signal. 26, 1000-1008.

Cardiovascular toxicity of angiogenesis inhibitors in treatment of malignancy: A systematic review and meta-analysis

BACKGROUND

The cardiovascular risk of angiogenesis inhibitors is not well-quantified. We hypothesized that, compared to direct vascular endothelial growth factor (VEGF) inhibitors (anti-VEGF antibodies or decoy receptors), small molecule agents have higher risk due to their less specific mechanism.

METHODS

We searched the MEDLINE, EMBASE, and Cochrane Central Register of Controlled Trials for phase III randomised controlled trials comparing angiogenesis inhibitor-based therapy to other systemic therapy. Outcomes evaluated were hypertension, severe hypertension, cardiac dysfunction, congestive heart failure, cardiac ischemia, arterial thromboembolism, venous thromboembolism, and fatal cardiovascular events. Data were pooled using Mantel-Haenszel random effects method to generate odds ratios (OR).

RESULTS

We identified 77 studies meeting inclusion criteria. Compared to routine care, angiogenesis inhibitors were associated with a higher risk of hypertension (OR 5.28 [4.53-6.15], number needed to harm [NNH] 6), severe hypertension (OR 5.59 [4.67-6.69], NNH 17), cardiac ischemia (OR 2.83 [1.72-4.65], NNH 85) and cardiac dysfunction (OR 1.35 [1.06-1.70], NNH 139). VEGF inhibitors were associated with an increased risk of arterial thromboembolism (OR 1.52 [1.17-1.98], NNH 141). No significant interaction was observed between the two drug subgroups for any outcomes. We identified no significant increase in the risk of the other outcomes evaluated.

CONCLUSION

Angiogenesis inhibitors increase the risk of hypertension, arterial thromboembolism, cardiac ischemia and cardiac dysfunction. There was no significant difference in cardiovascular risk between direct VEGF inhibitors and small molecule agents.

Antagonist antibodies to vascular endothelial growth factor receptor 2 (VEGFR-2) as anti-angiogenic agents

Interaction of numerous signaling pathways in endothelial and mesangial cells results in exquisite control of the process of physiological angiogenesis, with a central role played by vascular endothelial growth factor receptor 2 (VEGFR-2) and its cognate ligands. However, deregulated angiogenesis participates in numerous pathological processes. Excessive activation of VEGFR-2 has been found to mediate tissue-damaging vascular changes as well as the induction of blood vessel expansion to support the growth of solid tumors. Consequently, therapeutic intervention aimed at inhibiting the VEGFR-2 pathway has become a mainstay of treatment in cancer and retinal diseases. In this review, we introduce the concepts of physiological and pathological angiogenesis, the crucial role played by the VEGFR-2 pathway in these processes, and the various inhibitors of its activity that have entered the clinical practice. We primarily focus on the development of ramucirumab, the antagonist monoclonal antibody (mAb) that inhibits VEGFR-2 and has recently been approved for use in patients with gastric, colorectal, and lung cancers. We examine in-depth the pre-clinical studies using DC101, the mAb to mouse VEGFR-2, which provided a conceptual foundation for the role of VEGFR-2 in physiological and pathological angiogenesis. Finally, we discuss further clinical development of ramucirumab and the future of targeting the VEGF pathway for the treatment of cancer.

Mechanisms of Cardiotoxicity of Cancer Chemotherapeutic Agents: Cardiomyopathy and Beyond

Tremendous strides have been made in the treatment of various oncological diseases such that patients are surviving longer and are having better quality of life. However, the success has been tainted by the iatrogenic cardiac toxicities. This is especially concerning in the younger population who are facing cardiac disease such as heart failure in their 30s and 40s as the consequence of the anthracycline's side effects (used for childhood leukemia and lymphoma). This resulted in the awareness of cardiotoxic effects of anticancer drugs and emergence of a new discipline: oncocardiology. Since then, numerous anticancer drugs have been correlated to cardiomyopathy. Additionally, other cardiovascular effects have been identified, which includes but is not limited to myocardial infarction, thrombosis, hypertension, arrhythmias, and pulmonary hypertension. In this review we examine some of the anticancer agents that mitigate cardiotoxicity and present current knowledge of molecular mechanism(s). The aim of the review is to ignite awareness of emerging cardiotoxic effects as new generations of anticancer agents are being tested in clinical trials and introduced as part of the therapeutic armamentarium to our oncological patients.

Gasotransmitters in cancer: from pathophysiology to experimental therapy

The three endogenous gaseous transmitters - nitric oxide (NO), carbon monoxide (CO) and hydrogen sulfide (H2S) - regulate a number of key biological functions. Emerging data have revealed several new mechanisms for each of these three gasotransmitters in tumour biology. It is now appreciated that they show bimodal pharmacological character in cancer, in that not only the inhibition of their biosynthesis but also elevation of their concentration beyond a certain threshold can exert anticancer effects. This Review discusses the role of each gasotransmitter in cancer and the effects of pharmacological agents - some of which are in early-stage clinical studies - that modulate the levels of each gasotransmitter. A clearer understanding of the pharmacological character of these three gases and the mechanisms underlying their biological effects is expected to guide further clinical translation.

Improved efficacy of a novel anti-angiogenic drug combination (TL-118) against colorectal-cancer liver metastases; MRI monitoring in mice

BACKGROUND

The poor prognosis of patients with colorectal-cancer liver metastases (CRLM) and the insufficiency of available treatments have raised the need for alternative curative strategies. We aimed to assess the therapeutic potential of TL-118, a new anti-angiogenic drug combination, for CRLM treatment, in a mouse model.

METHODS

The therapeutic potential of TL-118 was evaluated and compared with B20-4.1.1 (B20; anti-VEGF antibody) and rapamycin in CRLM-bearing mice. Tumour progression and the vascular changes were monitored by MRI. Additionally, mice survival, cell proliferation, apoptosis and vessel density were evaluated.

RESULTS

This study demonstrated an unequivocal advantage to TL-118 therapy by significantly prolonging survival (threefold) and reducing metastasis perfusion and vessel density (ninefold). The underlying mechanism for TL-118-treatment success was associated with hepatic perfusion attenuation resulting from reduced nitric-oxide (NO) serum levels as elucidated by using hemodynamic response imaging (HRI, a functional MRI combined with hypercapnia and hyperoxia). Further, systemic hepatic perfusion reduction during the initial treatment phase by adding NO inhibitor has proven to be essential for reaching maximal therapeutic effects for both TL-118 and B20.

CONCLUSION

TL-118 harbours a potential clinical benefit to CLRM patients. Moreover, the reduction of hepatic perfusion at early stages of anti-angiogenic therapies by adding NO inhibitor is crucial for achieving maximal anti-tumour effects.

Targeting eNOS in pancreatic cancer

Mortality from pancreatic ductal adenocarcinoma cancer (PDAC) is among the highest of any cancer and frontline therapy has changed little in years. Activation of endothelial nitric oxide synthase (eNOS, NOS3, or NOS III) has been implicated recently in the pathogenesis of PDACs. In this study, we used genetically engineered mouse and human xenograft models to evaluate the consequences of targeting eNOS in PDACs. Genetic deficiency in eNOS limited the development of preinvasive pancreatic lesions and trended toward an extended lifespan in mice with advanced pancreatic cancer. These effects were also observed upon oral administration of the clinically evaluated NOS small molecule inhibitor N(G)-nitro-L-arginine methyl ester (l-NAME). Similarly, other transgenic models of oncogenic KRas-driven tumors responded to l-NAME treatment. Finally, these results were recapitulated in xenograft models of human pancreatic cancer, in which l-NAME was found to broadly inhibit tumorigenic growth. Taken together, our findings offer preclinical proof-of-principle to repurpose l-NAME for clinical investigations in treatment of PDACs and possibly other KRas-driven human cancers.

Beyond antiangiogenesis: vascular modulation as an anticancer therapy-a review

This review attempts to move beyond the traditional borders of antiangiogenesis and toward the dynamic, evolving strategies of vascular modulation. This repositioning entails a two-fold paradigm shift: conceptually, to a view of antiangiogenesis as only one part of a larger story, and therapeutically, to approaches which attempt to modulate tumor blood flow instead of simply inhibiting it. Three vascular modulation strategies-provascular, antivascular, and redistributive-are presented with representative compounds. These vascular modulation strategies are described in specific measurable characteristics (blood vessel maturity and type, effect on blood flow, microenvironmental target, molecular target, angiogenic biomarker, and imaging biomarkers) that will help define the tumor types that are more susceptible to a particular vascular modulation strategy thereby guiding therapeutic agent selection and enabling a personalized medicine approach.

Identification of cancer stem cells in human gastrointestinal carcinoid and neuroendocrine tumors

BACKGROUND & AIMS

Metastatic gastrointestinal neuroendocrine tumors (NETs) frequently are refractory to chemotherapy. Chemoresistance in various malignancies has been attributed to cancer stem cells (CSCs). We sought to identify gastrointestinal neuroendocrine CSCs (N-CSCs) in surgical specimens and a NET cell line and to characterize novel N-CSC therapeutic targets.

METHODS

Human gastrointestinal NETs were evaluated for CSCs using the Aldefluor (Stemcell Technologies, Vancouver, Canada) assay. An in vitro, sphere-forming assay was performed on primary NET cells. CNDT2.5, a human midgut carcinoid cell line, was used for in vitro (sphere-formation) and in vivo (tumorigenicity assays) CSC studies. N-CSC protein expression was characterized using Western blotting. In vivo, systemic short interfering RNA administration targeted Src.

RESULTS

By using the Aldefluor assay, aldehyde dehydrogenase-positive (ALDH+) cells comprised 5.8% ± 1.4% (mean ± standard error of the mean) of cells from 19 patient samples. Although many primary cell lines failed to grow, CNDT96 ALDH+ cells formed spheres in anchorage-independent conditions, whereas ALDH- cells did not. CNDT2.5 ALDH+ cells formed spheres, whereas ALDH- cells did not. In vivo, ALDH+ CNDT2.5 cells generated more tumors, with shorter latency than ALDH- or sham-sorted cells. Compared with non-CSCs, ALDH+ cells demonstrated increased expression of activated Src, Erk, Akt, and mammalian target of rapamycin (mTOR). In vivo, anti-Src short interfering RNA treatment of ALDH+ tumors reduced tumor mass by 91%.

CONCLUSIONS

CSCs are present in NETs, as shown by in vitro sphere formation and in vivo tumorigenicity assays. Src was activated in N-CSCs and represents a potential therapeutic target in gastrointestinal NETs.

Evaluation of wedged arterial injection as a new technique for delivery of experimental therapeutic substances into the porcine pancreas

OBJECTIVES

To prospectively evaluate the technical feasibility and efficacy of wedged arterial injection (WAI) as a potential route for experimental selective therapy to the pancreas of healthy pigs.

MATERIALS AND METHODS

Selective angiographies were completed in ten pigs under general anaesthesia. By superselective angiography, the catheter was inserted and wedged into the major pancreatic artery, blocking the blood flow. In order to evaluate the efficacy of the WAI method, a DNA-specific fluorescent dye (Hoechst 33258) was used.

RESULTS

Histological study revealed a uniform distribution of the fluorescent dye within the nuclei of the endocrine and exocrine pancreatic cells. Pancreatic and liver enzymes as well as histopathology of the pancreas were normal.

CONCLUSION

WAI is a highly effective minimally invasive methodology to target the porcine pancreas. The findings suggest that WAI may contribute to developing preclinical assays of pancreas gene or cell-transfer therapies in swine model.

The transfusion problem: role of aberrant S-nitrosylation

Protein S-nitrosylation (the binding of a nitric oxide [NO] group to a cysteine thiol) is a major mechanism through which the ubiquitous cellular influence of NO is exerted. Disruption of S-nitrosylation is associated with a wide range of pathophysiologic conditions. Hemoglobin (Hb) exemplifies both of these concepts. It is the prototypical S-nitrosylated protein in that it binds, activates, and deploys NO. Within red blood cells (RBCs), Hb is S-nitrosylated during the respiratory cycle and thereby conveys NO bioactivity that may be dispensed to regulate local blood flow in the physiologic response known as hypoxic vasodilation. Hb thus both delivers oxygen directly and delivers vasoactivity to potentially optimize tissue perfusion in concert with local metabolic demand. Accordingly, decreased levels of S-nitrosylated Hb (also known as S-nitrosohemoglobin) and/or impaired delivery of RBC-derived NO bioactivity have been observed in a variety of disease states that are characterized by tissue hypoxemia. It has been shown recently that storage of blood depletes S-nitrosylated Hb, accompanied by reduced ability of RBCs to induce vasodilation. This defect appears to account in significant part for the impaired ability of banked RBCs to deliver oxygen. Renitrosylation can correct this impairment and thus may offer a means to ameliorate the disruptions in tissue perfusion produced by transfusion.

The role of tumour-derived iNOS in tumour progression and angiogenesis

Background:

Progressive tumour growth is dependent on the development of a functional tumour vasculature and highly regulated by growth factors and cytokines. Nitric oxide (NO) is a free radical, produced both by tumour and host cells, and functions as a signalling molecule downstream of several angiogenic factors. Both pro- and antitumourigenic properties have been attributed to NO.

Methods:

The expression of the inducible isoform of NO synthase (iNOS) was knocked down in the C6 glioma cell line using constitutive expression of antisense RNA, and the effect of tumour-derived NO on tumour progression and angiogenesis was investigated.

Results:

Tumours in which iNOS expression was decreased displayed significantly reduced growth rates compared with tumours derived from parental C6 cells. Quantitative non-invasive magnetic resonance imaging and fluorescence microscopy of tumour uptake of Hoechst 33342, and haematoxylin and eosin staining, revealed significantly impaired vascular development and function in antisense iNOS tumours compared with control in vivo, primarily associated with the more necrotic tumour core. Decreased iNOS expression had no effect on tumour VEGF expression.

Conclusion:

Nitric oxide derived from tumour iNOS is an important modulator of tumour progression and angiogenesis in C6 gliomas and further supports the therapeutic strategy of inhibiting iNOS for the treatment of cancer.

Ambulatory monitoring detects sorafenib-induced blood pressure elevations on the first day of treatment

PURPOSE

Hypertension is a mechanism-based toxicity of sorafenib and other cancer therapeutics that inhibit the vascular endothelial growth factor (VEGF) signaling pathway. This prospective, single-center, cohort study characterized ambulatory blood pressure monitoring as an early pharmacodynamic biomarker of VEGF signaling pathway inhibition by sorafenib.

EXPERIMENTAL DESIGN

Fifty-four normotensive advanced cancer patients underwent 24-hour ambulatory blood pressure monitoring before and between days 6 and 10 of sorafenib therapy. After blood pressure changes were detected among the first cohort within 10 days, ambulatory blood pressure monitoring was done during the first 24 hours of treatment for the second cohort.

RESULTS

For the entire patient population, the blood pressure increase [mean systolic, +10.8 mm Hg; 95% confidence interval (95% CI), 8.6-13.0; range, -5.2 to +28.7 mm Hg; mean diastolic, +8.0 mm Hg; 95% CI, 6.3-9.7; range, -4.4 to +27.1 mm Hg] was detected between days 6 and 10 (P < 0.0001 for both) and plateaued thereafter. Variability in blood pressure change did not associate with: age, body size, sex, self-reported race, baseline blood pressure, or steady-state sorafenib plasma concentrations. In the second cohort, the blood pressure elevation was detected during the first 24 hours (mean systolic, +8.2 mm Hg; 95% CI, 5.0-11.3; mean diastolic, +6.5 mm Hg; 95% CI, 4.7-8.3; P < 0.0001 for both).

CONCLUSIONS

Ambulatory blood pressure monitoring detects the blood pressure response to VEGF signaling pathway inhibition by sorafenib during the first 24 hours of treatment. The magnitude of blood pressure elevation is highly variable and unpredictable but could be important in optimizing the therapeutic index of VEGF signaling pathway inhibitor therapy.

Cardiovascular toxicities: clues to optimal administration of vascular endothelial growth factor signaling pathway inhibitors

Several angiogenesis inhibitors have been approved for commercial use and many additional agents are under development for the treatment of various malignancies. Cardiovascular toxicities have been increasingly recognized as effects of this entire class of new anticancer therapeutics. There is a limited but growing understanding of the mechanism of action of these drugs in the human cancer patient and the factors affecting the therapeutic index. In addition to reviewing current concepts for the cardiovascular toxicities of angiogenesis inhibitors, we discuss how better understanding the pharmacologic basis for these effects could optimize their use for individual patients.

Apoptosis-inducing high (.)NO concentrations are not sustained either in nascent or in developed cancers

Nitric oxide ((.)NO) induces apoptosis at high concentrations by S-nitrosating proteins such as glyceraldehyde-3-phosphate dehydrogenase. This literature analysis revealed that failure to sustain high (.)NO concentrations is common to all cancers. In cervical, gastric, colorectal, breast, and lung cancer, the cause of this failure is the inadequate expression of inducible nitric oxide synthase (iNOS), resulting from the inhibition of iNOS expression by TGF-beta1 at the mRNA level. In bladder, renal, and prostate cancer, the reason for the insufficient (.)NO levels is the depletion of arginine, resulting from arginase overexpression. Arginase competes with iNOS for arginine, catalyzing its hydrolysis to ornithine and urea. In gliomas and ovarian sarcomas, low (.)NO levels are caused by inhibition of iNOS by N-chlorotaurine, produced by infiltrating neutrophils. Stimulated neutrophils express myeloperoxidase, catalyzing H2O2 oxidation of Cl- to HOCl, which N-chlorinates taurine at its concentration of 19 mM in neutrophils. In squamous cell carcinomas of the skin, ovarian cancers, lymphomas, Hodgkin's disease, and breast cancers, low (.)NO concentrations arise from the inhibition of iNOS by N-bromotaurine, produced by eosinophil-peroxidase-expressing infiltrating eosinophils. Eosinophil peroxidase catalyzes the H2O2 oxidation of Br- to HOBr, which N-brominates taurine to N-bromotaurine at its concentration of 15 mM in eosinophils. In microvascularized tumors, the (.)NO concentration is further depleted; (.)NO is rapidly consumed by red blood cells (RBCs) through S-nitrosation of RBC glutathione and hemoglobin, and by oxidation to nitrate by RBC oxyhemoglobin. Angiogenesis-inhibiting antibodies are currently used to treat cancers; their mode of action is not, as previously thought, reduction of the tumor O2 or nutrient supply. They actually decrease the loss of (.)NO to RBCs.

Therapeutic targeting of Id2 reduces growth of human colorectal carcinoma in the murine liver

During development inhibitor of DNA-bind-2 (Id2) regulates proliferation and differentiation. Id2 expression has been detected in cancer cells, yet its cellular function and validity as a therapeutic target remains largely unknown. Immunohistochemical analysis of colorectal cancer (CRC) specimens revealed that Id2 was undetectable in normal colonic mucosa, but occurs in 40% of primary tumors and in most CRC liver metastases (P<0.0001). Additionally, Id2 was expressed in all CRC cell lines assayed. CRC cells with reduced Id2 expression demonstrated reduced proliferation. Analysis of CRC cell cycle regulatory proteins showed that reducing Id2 levels reduces cyclin D1 levels and increased p21 levels. Reduction of Id2 expression also enhanced tumor cell apoptosis, increasing levels of the pro-apoptotic protein Bim/Bod, and cleavage of caspase-7 and poly (ADP-ribose) polymerase. In vivo studies show tumors derived from cells with decreased Id2 levels formed smaller tumors with fewer metastases compared with tumors with normal levels (P<0.05). Furthermore, intraperitoneal administration of Id2 small interfering RNA (siRNA) conjugated with the neutral liposome 1,2-dioleoyl-sn-glycero-3-phosphatidylcholine decreased tumor burden in mice compared with control treatment (P=0.006). We conclude that Id2 is upregulated in CRC, and is important in promoting cell survival. In vivo targeting of Id2 by siRNA establishes that it is a valid therapeutic target where its expression occurs.

VEGF-targeted therapy: mechanisms of anti-tumour activity

Several vascular endothelial growth factor (VEGF)-targeted agents, administered either as single agents or in combination with chemotherapy, have been shown to benefit patients with advanced-stage malignancies. VEGF-targeted therapies were initially developed with the notion that they would inhibit new blood vessel growth and thus starve tumours of necessary oxygen and nutrients. It has become increasingly apparent, however, that the therapeutic benefit associated with VEGF-targeted therapy is complex, and probably involves multiple mechanisms. A better understanding of these mechanisms will lead to future advances in the use of these agents in the clinic.

Therapeutic targeting of neuropilin-2 on colorectal carcinoma cells implanted in the murine liver

BACKGROUND

Neuropilin-2 (NRP2) is a high-affinity kinase-deficient receptor for vascular endothelial growth factor (VEGF) and semaphorin 3F. We investigated its function in human colorectal cancers.

METHODS

Immunohistochemistry and immunoblotting were used to assess NRP2 expression levels in colorectal tumors and colorectal cancer cell lines, respectively. HCT-116 colorectal cancer cells stably transfected with short hairpin RNA (shRNAs) against NRP2 or control shRNAs were assayed for proliferation by the tetrazolium salt 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and for activation of the VEGFR1 pathway by immunoblotting. Soft agar assays, Annexin V staining, and Boyden chamber assays were used to examine anchorage-independent growth, apoptosis in response to hypoxia, and cell migration/invasion, respectively, in HCT-116 transfectants. Tumor growth and metastasis were analyzed in mice (groups of 10) injected with shRNA-expressing HCT-116 cells. The effect of in vivo targeting of NRP2 by small interfering RNA (siRNA) on the growth of hepatic colorectal tumors derived from luciferase-expressing HCT-116 cells was assessed by measuring changes in bioluminescence and final tumor volumes. All statistical tests were two-sided.

RESULTS

NRP2 expression was substantially higher in tumors than in adjacent mucosa. HCT-116 transfectants with reduced NRP2 levels had reduced VEGFR1 signaling, but proliferation was unchanged. Anchorage-independent growth, survival under hypoxic conditions, and motility/invasiveness were also reduced. In vivo, HCT-116 transfectants with reduced NRP2 demonstrated decreased tumor growth, fewer metastases, and increased apoptosis compared with control cells. Hepatic colorectal tumors in mice treated with NRP2 siRNAs were statistically significantly smaller than those in mice treated with control siRNAs (at 28 days after implantation, mean control siRNAs = 420 mm3, mean NRP2 siRNAs = 36 mm3, NRP2 vs control: difference = 385 mm3, 95% confidence interval = 174 mm3 to 595 mm3, P = .005).

CONCLUSION

NRP2 on colorectal carcinoma cells is important for tumor growth and is a potential therapeutic target in human cancers where it is expressed.

Overexpression of PDGF-BB decreases colorectal and pancreatic cancer growth by increasing tumor pericyte content

We hypothesized that overexpression of PDGF-BB in colorectal cancer (CRC) and pancreatic cancer cells would result in increased pericyte coverage of ECs in vivo, rendering the tumor vasculature more resistant to antiangiogenic therapy. We stably transfected the cDNA for the PDGF-B into HT-29 human CRC and FG human pancreatic cancer cells. Surprisingly, when HT-29 or FG parental and transfected cells were injected into mice (subcutaneously and orthotopically), we observed marked inhibition of tumor growth in the PDGF-BB-overexpressing clones. In the PDGF-BB-overexpressing tumors, we observed an increase in pericyte coverage of ECs. Treatment of PDGF-BB-overexpressing tumors with imatinib mesylate (PDGFR inhibitor) resulted in increased growth and decreased total pericyte content compared with those in untreated PDGF-BB-overexpressing tumors. In vitro studies demonstrated the ability of VSMCs to inhibit EC proliferation by approximately 50%. These data show that increasing the pericyte content of the tumor microenvironment inhibits the growth of angiogenesis-dependent tumors. Single-agent therapy targeting PDGF receptor must be used with caution in tumors when PDGFR is not the target on the tumor cell itself.

Effect of nitric-oxide synthesis on tumour blood volume and vascular activity: a phase I study

BACKGROUND

Nitric oxide has been implicated in tumour angiogenesis and in the maintaining of vasodilator tone of tumour blood vessels. The tumour vascular effects of inhibition of nitric-oxide synthesis have not been investigated in patients with cancer.

METHODS

Seven women and 11 men (12 with non-small-cell lung cancer, five prostate cancer, and one cervical cancer) were recruited onto a phase I dose-escalation study and received a single dose of the nitric oxide synthase inhibitor, N-nitro-L-arginine (L-NNA). Dose escalation was done by a modified Fibonacci scale with three patients at each dose level, starting with 0.1 mg/kg. Changes in dynamic contrast-enhanced CT measures of tumour relative blood volume and transfer constant (K) were measured at 1 h and 24 h after L-NNA administration.

FINDINGS

In the 18 patients, toxic effects were self-limiting cardiovascular changes: three patients had Common Toxicity Criteria version 2.0 grade 1 hypertension; two had grade 1 sinus bradycardia; and one had grade 1 palpitation. L-NNA area under the curve (AUC) increased linearly with dose from 163 micromol min(-1) L(-1) at 0.1 mg/kg L-NNA to 2150 micromol min(-1) L(-1) at 0.9 mg/kg L-NNA. In eight patients that underwent dynamic CT scanning, tumour blood volume decreased 1 h after L-NNA treatment (mean 42.9% [range 12.0-62.1]; paired t test p=0.0070), which was sustained for up to 24 h (mean 33.9% [range 6.5-64.9]; p=0.035). This decrease in blood volume was associated with an increase in the number of non-perfused pixels from 7.3% (SD 5.5) at baseline to 25.1% (15.3; p=0.0089) at 1 h, and 18.2% (12.9; p=0.050) at 24 h. There was a significant correlation between L-NNA plasma AUC and the reduction in tumour blood volume at 24 h after L-NNA (r=0.83; p=0.010).

INTERPRETATION

We have shown in vivo in patients with cancer that nitric oxide has a role in maintaining tumour blood supply, and we provide early clinical evidence that inhibition of nitric-oxide synthesis has tumour antivascular activity.

The role of nitric oxide in mediating tumour blood flow

Nitric oxide (NO) is a ubiquitous molecule with a myriad of physiological and pathophysiological roles. It has numerous direct and indirect effects on tumour vasculature as both a regulatory and effector molecule. NO affects tumour blood flow through its effects on tumour angiogenesis, vascular tone and vascular permeability, partly via its interaction with vascular endothelial growth factor. In this review, the authors examine the basic tenants of NO biology, the association of NO with tumour progression, and the role NO plays in mediating alterations in vascular functions in tumours.