Amiloride inhibition of angiogenesis in vitro

Amiloride reduces fructosamine-3-kinase expression to restore sunitinib sensitivity in renal cell carcinoma

The kidney is a vital organ responsible for water and sodium metabolism, while the primary function of amiloride is to promote the excretion of water and sodium. We investigated amiloride enhanced the sunitinib sensitivity in RCC. We found both sunitinib and amiloride displayed cytotoxicity and exerted the synergy effect in RCC cells in vivo and in vitro arrays. Protein expression profiles were screened via MS/TMT, revealing that FN3K was upregulated in the sunitinib group, and rescued in amiloride and the combination administration. Exogenous FN3K could promote proliferation, invasion and metastasis and decrease the sensitivity of Caki-1 cells to sunitinib, also, exogenous FN3K up-regulated VEGFR2 expression and activated AKT/mTOR signal pathway. More FN3K and VEGFR2 accumulated in R-Caki-1 cells and rescued by amiloride treatment. Co-IP and IF confirmed the interaction between FN3K and VEGFR2. In conclusion, FN3K depletion mediated VEGFR2 disruption promotes amiloride synergized the anti-RCC activity of sunitinib.

Towards an Integral Therapeutic Protocol for Breast Cancer Based upon the New H+-Centered Anticancer Paradigm of the Late Post-Warburg Era

A brand new approach to the understanding of breast cancer (BC) is urgently needed. In this contribution, the etiology, pathogenesis, and treatment of this disease is approached from the new pH-centric anticancer paradigm. Only this unitarian perspective, based upon the hydrogen ion (H+) dynamics of cancer, allows for the understanding and integration of the many dualisms, confusions, and paradoxes of the disease. The new H+-related, wide-ranging model can embrace, from a unique perspective, the many aspects of the disease and, at the same time, therapeutically interfere with most, if not all, of the hallmarks of cancer known to date. The pH-related armamentarium available for the treatment of BC reviewed here may be beneficial for all types and stages of the disease. In this vein, we have attempted a megasynthesis of traditional and new knowledge in the different areas of breast cancer research and treatment based upon the wide-ranging approach afforded by the hydrogen ion dynamics of cancer. The concerted utilization of the pH-related drugs that are available nowadays for the treatment of breast cancer is advanced.

The impact of tumour pH on cancer progression: strategies for clinical intervention

Dysregulation of cellular pH is frequent in solid tumours and provides potential opportunities for therapeutic intervention. The acidic microenvironment within a tumour can promote migration, invasion and metastasis of cancer cells through a variety of mechanisms. Pathways associated with the control of intracellular pH that are under consideration for intervention include carbonic anhydrase IX, the monocarboxylate transporters (MCT, MCT1 and MCT4), the vacuolar-type H⁺-ATPase proton pump, and the sodium-hydrogen exchanger 1. This review will describe progress in the development of inhibitors to these targets.

Synergy Between Low Dose Metronomic Chemotherapy and the pH-centered Approach Against Cancer

Low dose metronomic chemotherapy (MC) is becoming a mainstream treatment for cancer in veterinary medicine. Its mechanism of action is anti-angiogenesis by lowering vascular endothelial growth factor (VEGF) and increasing trombospondin-1 (TSP1). It has also been adopted as a compassionate treatment in very advanced human cancer. However, one of the main limitations of this therapy is its short-term effectiveness: 6 to 12 months, after which resistance develops. pH-centered cancer treatment (pHT) has been proposed as a complementary therapy in cancer, but it has not been adopted or tested as a mainstream protocol, in spite of existing evidence of its advantages and benefits. Many of the factors directly or indirectly involved in MC and anti-angiogenic treatment resistance are appropriately antagonized by pHT. This led to the testing of an association between these two treatments. Preliminary evidence indicates that the association of MC and pHT has the ability to reduce anti-angiogenic treatment limitations and develop synergistic anti-cancer effects. This review will describe each of these treatments and will analyze the fundamentals of their synergy.

Glycolysis, tumor metabolism, cancer growth and dissemination. A new pH-based etiopathogenic perspective and therapeutic approach to an old cancer question

Cancer cells acquire an unusual glycolytic behavior relative, to a large extent, to their intracellular alkaline pH (pHi). This effect is part of the metabolic alterations found in most, if not all, cancer cells to deal with unfavorable conditions, mainly hypoxia and low nutrient supply, in order to preserve its evolutionary trajectory with the production of lactate after ten steps of glycolysis. Thus, cancer cells reprogram their cellular metabolism in a way that gives them their evolutionary and thermodynamic advantage. Tumors exist within a highly heterogeneous microenvironment and cancer cells survive within any of the different habitats that lie within tumors thanks to the overexpression of different membrane-bound proton transporters. This creates a highly abnormal and selective proton reversal in cancer cells and tissues that is involved in local cancer growth and in the metastatic process. Because of this environmental heterogeneity, cancer cells within one part of the tumor may have a different genotype and phenotype than within another part. This phenomenon has frustrated the potential of single-target therapy of this type of reductionist therapeutic approach over the last decades. Here, we present a detailed biochemical framework on every step of tumor glycolysis and then proposea new paradigm and therapeutic strategy based upon the dynamics of the hydrogen ion in cancer cells and tissues in order to overcome the old paradigm of one enzyme-one target approach to cancer treatment. Finally, a new and integral explanation of the Warburg effect is advanced.

Cariporide and other new and powerful NHE1 inhibitors as potentially selective anticancer drugs--an integral molecular/biochemical/metabolic/clinical approach after one hundred years of cancer research

In recent years an increasing number of publications have emphasized the growing importance of hydrogen ion dynamics in modern cancer research, from etiopathogenesis and treatment. A proton [H⁺]-related mechanism underlying the initiation and progression of the neoplastic process has been recently described by different research groups as a new paradigm in which all cancer cells and tissues, regardless of their origin and genetic background, have a pivotal energetic and homeostatic disturbance of their metabolism that is completely different from all normal tissues: an aberrant regulation of hydrogen ion dynamics leading to a reversal of the pH gradient in cancer cells and tissues (↑pH_i/↓pH_e, or “proton reversal”). Tumor cells survive their hostile microenvironment due to membrane-bound proton pumps and transporters, and their main defensive strategy is to never allow internal acidification because that could lead to their death through apoptosis. In this context, one of the primary and best studied regulators of both pH_i and pH_e in tumors is the Na⁺/H⁺ exchanger isoform 1 (NHE1). An elevated NHE1 activity can be correlated with both an increase in cell pH and a decrease in the extracellular pH of tumors, and such proton reversal is associated with the origin, local growth, activation and further progression of the metastatic process. Consequently, NHE1 pharmaceutical inhibition by new and potent NHE1 inhibitors represents a potential and highly selective target in anticancer therapy. Cariporide, being one of the better studied specific and powerful NHE1 inhibitors, has proven to be well tolerated by humans in the cardiological context, however some side-effects, mainly related to drug accumulation and cerebrovascular complications were reported. Thus, cariporide could become a new, slightly toxic and effective anticancer agent in different human malignancies.

Anti-tumour/metastasis effects of the potassium-sparing diuretic amiloride: an orally active anti-cancer drug waiting for its call-of-duty?

Amiloride.HCl is clinically used as an oral potassium-sparing diuretic, but multiple studies in biochemical, cellular and animal models have shown that the drug also possesses anti-tumour and anti-metastasis activities. The additional effects appear to arise through inhibition of two discrete targets: (i) the sodium-hydrogen exchanger 1 (NHE1), a membrane protein responsible for the characteristically low extracellular pH of tumours and (ii) the urokinase-type plasminogen activator (uPA), a serine protease mediator of cell migration, invasion and metastasis and well-known marker of poor prognosis in cancer. This mini-review summarises for the first time the reported anti-tumour/metastasis effects of amiloride in experimental models, discusses the putative molecular mechanisms responsible for these effects and concludes by commenting on the pros and cons of trialling amiloride or one of its structural analogues as potential new anti-tumour/metastasis drugs.

Amiloride improves locomotor recovery after spinal cord injury

Amiloride is a drug approved by the United States Food and Drug Administration, which has shown neuroprotective effects in different neuropathological conditions, including brain injury or brain ischemia, but has not been tested in spinal cord injury (SCI). We tested amiloride's therapeutic potential in a clinically relevant rat model of contusion SCI inflicted at the thoracic segment T10. Rats receiving daily administration of amiloride from 24 h to 35 days after SCI exhibited a significant improvement in hindlimb locomotor ability at 21, 28, and 35 days after injury, when compared to vehicle-treated SCI rats. Rats receiving amiloride treatment also exhibited a significant increase in myelin oligodendrocyte glycoprotein (MOG) levels 35 days after SCI at the site of injury (T10) when compared to vehicle-treated controls, which indicated a partial reverse in the decrease of MOG observed with injury. Our data indicate that higher levels of MOG correlate with improved locomotor recovery after SCI, and that this may explain the beneficial effects of amiloride after SCI. Given that amiloride treatment after SCI caused a significant preservation of myelin levels, and improved locomotor recovery, it should be considered as a possible therapeutic intervention after SCI.

Inhibitory effects of amiloride on the current mediated by native GABA(A) receptors in cultured neurons of rat inferior colliculus

1. The diuretic amiloride is known to modulate the activity of several types of ion channels and membrane receptors in addition to its inhibitory effects on many ion transport systems. However, the effects of amiloride on some important ion channels and receptors, such as GABA(A) receptors, in the central nervous system have not been characterized. 2. In the present study, we investigated the functional action of amiloride on native GABA(A) receptors in cultured neurons of rat inferior colliculus using whole-cell patch-clamp recordings. 3. Amiloride reversibly inhibited the amplitude of the GABA-induced current (I(GABA)) in a concentration-dependent manner (IC(50) 454 +/- 24 micromol/L) under conditions of voltage-clamp with a holding potential at -60 mV. The inhibition depended on drug application mode and was independent of membrane potential. Amiloride did not change the reversal potential of I(GABA). Moreover, amiloride induced a parallel right-ward shift in the concentration-response curve for I(GABA) without altering the maximal value and Hill coefficient. 4. The present study shows that amiloride competitively inhibits the current mediated by native GABA(A) receptors in the brain region, probably via a direct action on GABA-binding sites on the receptor. The findings suggest that the functional actions of amiloride on GABA(A) receptors may result in possible side-effects on the central nervous system in the case of direct application of this drug into the cerebrospinal fluid for treatment of diseases such as brain tumours.

Amiloride derivatives induce apoptosis by depleting ER Ca(2+) stores in vascular endothelial cells

BACKGROUND AND PURPOSE

Amiloride derivatives are blockers of the Na(+)/H(+) exchanger (NHE) and at micromolar concentrations have protective effects on cardiac and brain ischaemia/reperfusion injury but at higher concentrations also induce apoptosis. Here, we aimed to elucidate the mechanism related to this cytotoxic action.

EXPERIMENTAL APPROACH

We quantified the expression of genes associated with endoplasmic reticulum (ER) stress and measured changes in luminal ER Ca(2+) concentration ([Ca(2+)](ER)) with a 'cameleon' indicator, D1ER.

KEY RESULTS

Amiloride derivatives induced apoptosis in vascular endothelial cells, an effect that increased at alkaline extracellular pH. The potency order for cytotoxicity was 5-(N,N-hexamethylene)-amiloride (HMA) > 5-(N-methyl-N-isobutyl) amiloride > 5-(N-ethyl-N-isopropyl) amiloride (EIPA) >> amiloride. HMA dose-dependently increased the transcription of the ER stress genes GADD153 and GADD34 and rapidly depleted [Ca(2+)](ER), mimicking the effects of the sarco/endoplasmic reticulum ATPase (SERCA) inhibitor thapsigargin. The NHE1-specific inhibitor HOE 694 inhibited NHE activity by 87% but did not alter [Ca(2+)](ER). The decrease in [Ca(2+)](ER) evoked by amiloride derivatives was also observed in HeLa cells and was mirrored by an increase in cytosolic Ca(2+) concentration.

CONCLUSIONS AND IMPLICATIONS

Amiloride derivatives disrupt ER and cytosolic Ca(2+) homeostasis by a mechanism unrelated to NHE inhibition, most likely by interfering with the activity of SERCA. We propose that ER Ca(2+) depletion and subsequent ER stress provide a rationale framework for the apoptotic effects of amiloride derivatives.

Antiangiogenic effects of spironolactone and other potassium-sparing diuretics in human umbilical vein endothelial cells and in fibrin gel chambers implanted in rats

OBJECTIVE

Potassium-sparing diuretics have different effects on angiogenesis that may mediate some abilities to treat cardiovascular diseases. The aim of the current study was to compare the effects of spironolactone and an active metabolite, canrenone, or a derivative, eplerenone, and amiloride, a diuretic without affecting mineralocorticoid activity, on the proliferation of human umbilical vein endothelial cells (HUVEC) and on angiogenesis in fibrin gel chambers implanted in rats.

MATERIALS AND METHODS

We measured the effects of spironolactone, canrenone, eplerenone, and amiloride on the proliferation of HUVEC in the presence or absence of vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF). We also examined the effects of these compounds on migration and capillary tube formation by HUVEC. Finally, the effects of the compounds on neovessel formation in vivo were investigated by implanting Wistar rats for 14 days with perforated Plexiglas chambers containing rat fibrin.

RESULTS

Spironolactone and amiloride inhibited the proliferation of HUVEC, but canrenone and eplerenone had no effect. The inhibitory effect of spironolactone was not prevented by VEGF or bFGF. Aldosterone had no effect on spironolactone-induced inhibition of HUVEC proliferation. Spironolactone induced a dose-dependent reduction of both cell chemotaxis and capillary tube formation. In fibrin gel chambers, spironolactone and amiloride significantly reduced the numbers of both peripheral and central neovessels. Canrenone and eplerenone, in contrast, had no antiangiogenic effect.

CONCLUSION

Spironolactone and amiloride significantly inhibited angiogenesis in vitro and in the fibrin gel chamber in vivo. Spironolactone antiangiogenic effects are unrelated to antimineralocorticoid activity.

Antinociceptive, antiedematogenic and antiangiogenic effects of benzaldehyde semicarbazone

Semicarbazones induce an anticonvulsant effect in different experimental models. As some anticonvulsant drugs also have anti-inflammatory activity, the effects of benzaldehyde semicarbazone (BS) on models of nociception, edema and angiogenesis were investigated. BS (10, 25 or 50 mg/kg, i.p.) markedly inhibited the second phase of nociceptive response induced by formaldehyde (0.34%, 20 microl) in mice, but only the highest dose inhibited the first phase of this response. The thermal hyperalgesia and mechanical allodynia induced by carrageenan (1%, 50 microl, i.pl.) in rats were also inhibited by BS (50 mg/kg, i.p.). However, treatment of mice with BS did not induce an antinociceptive effect in the hot-plate model. The paw edema induced by carrageenan (1%, 50 microl, i.pl.) in rats was inhibited by BS (25 or 50 mg/kg, i.p.). Treatment of mice with BS (0.25, 0.5 or 2.5 mg/kg/day, i.p., 7 days) also inhibited angiogenesis induced by subcutaneous implantation of a sponge disc. It is unlikely that the antinociceptive effect induced by BS results from motor incoordination or a muscle relaxing effect, as the mice treated with this drug displayed no behavioral impairment in the rotarod apparatus. In conclusion, we demonstrated that BS presents antinociceptive, antiedematogenic and antiangiogenic activities. An extensive investigation of the pharmacological actions of BS and its derivatives is justified and may lead to the development of new clinically useful drugs.

Inhibitory effect of nifedipine on tumor necrosis factor alpha-induced neovascularization in cultured choroidal explants of streptozotocin-diabetic rat

We have previously reported that the Nepsilon (carboxymethyl)lysine (CML) adduct, a major structure of an advanced glycation end product, facilitates proliferation of CD34+ endothelial progenitor cells budded from cultured choroidal explants and produces immature vessel-like structures in fibrin gel. The CML adduct is accumulated and facilitates immature neovascularization in cultured choroidal explants of streptozotocin (STZ)-induced diabetic rat. The CML-enhanced neovascularization activity is associated with the actions of tumor necrosis factor (TNF) alpha, vascular endothelial growth factor and platelet-derived growth factor released from the choroidal explant (Kobayashi et al., Biol. Pharm. Bull., 27, 1382-1387 (2004); 27, 1565-1571 (2004)). The present study was investigated an inhibitory effect of a dihydropyridine calcium antagonist nifedipine on TNF alpha-induced choroidal neovascularization in the STZ-diabetic rat. TNF alpha (1-100 ng/ml) increased neovascularization of cultured choroidal explants in the age-matched normal rat but did not increase it in the diabetic rat. Anti-TNF alpha antibody (1 : 1000) decreased the neovascularization in the diabetic rat but not in the normal rat. Nifedipine (1 microM) inhibited TNF alpha-induced neovascularization of the normal choroidal explant in a non-competitive manner. Nifedipine (1 microM) also inhibited the diabetic state-induced neovascularization and its inhibitory action was reversed by TNF alpha (1-10 ng/ml). In conclusion, STZ-diabetic state facilitated choroidal neovascularization through the release of TNF alpha. Nifedipine inhibited the action of TNF alpha probably by blocking voltage-dependent Ca2+ channels in the endothelial progenitor cells of the diabetic choroid.

Aldosterone signaling modifies capillary formation by human bone marrow endothelial cells

We investigated the regulation of the epithelial sodium channel (ENaC) in human bone marrow endothelial cells (HBMEC) responding to mineralocorticoid hormones and other accessory effectors. The message for both the mineralocorticoid receptor (MCR) and the alpha subunit of ENaC was expressed in HBMEC as predicted bands of 838 and 521 bp, respectively. In Western blots, the MCR of about 107 kDa was localized primarily in the cytoplasmic compartment but migrated to the nucleus when cell cultures were exposed to exogenous aldosterone. On the other hand, the alphaENaC was revealed as a membrane-bound protein of approximately 82 kDa, whose abundance increased after aldosterone treatment. Confocal microscopy confirmed the presence of both the MCR and ENaC as nucleocytoplasmic and membrane-bound proteins, respectively, and both colocalized with tubulin in situ. On Matrigel, the mineralocorticoid aldosterone, by itself, did not influence capillary formation by HBMEC, but the diuretic amiloride reduced the organization of HBMEC into capillary-like networks; curiously, aldosterone further exacerbated this inhibitory effect of amiloride. On the fibrin matrix, aldosterone had no influence at all on the length of the newly formed capillaries, but the capillary diameter was highly increased over the control. Aldosterone-mediated capillary swelling was totally reversed by amiloride, which, by itself, also inhibited capillary elongation by HBMEC. Thus, cell signaling by mineralocorticoid hormones in HBMEC appears to proceed in a manner very similar to that in the epithelial cell, thereby leading to an increase in the endothelial cell volume, which may underline the hypertensive state and which may also modify angiogenesis.

A novel early chorioallantoic membrane assay demonstrates quantitative and qualitative changes caused by antiangiogenic substances

The chicken chorioallantoic membrane (CAM) has been extensively used in the study of angiogenesis. However, the CAM assay can be difficult and time-consuming to quantify, provides poor quality images of the results, and is not very reproducible. In this study, a novel early CAM assay was developed: It was found to be quantitative through relatively simple methods, enabled high-quality imaging of results, and was reproducible. Additionally, unique qualitative changes in vessel structure were observed, and it was possible to measure veins and arteries separately. Treatment of the CAM on days 4 and 5 with SU5614, suramin, fumagillin, amiloride, and PI-88 reduced blood-vessel growth. SU5614 (4 microg) resulted in significant reductions in artery but not vein length (60% and 111%, respectively, vs control). Suramin tended to increase CAM vasculature at 50 microg but caused dramatic reductions both in vessel length and CAM growth at 100 microg. As with SU5614, the effect was greater with regard to arterial compared with venous length (49% and 74%, respectively, vs control). PI-88 (20 microg) also decreased artery and vein length (66% and 80%, respectively, vs control). In contrast, fumagillin (5 microg) and amiloride (20 microg) both reduced arterial growth slightly less than venous growth (67% and 54% and 50% and 44%, respectively, vs control). Each antiangiogenic substance caused a different qualitative pattern of change in vessel branching and structure. The early CAM assay will be useful in the screening of antiangiogenic substances. Further study of the qualitative effects of antiangiogenic treatments may be a valuable tool to increase our understanding of the angiogenic process itself.

Nuclear injection of anti-pigpen antibodies inhibits endothelial cell division

Endothelial cell proliferation is required for angiogenesis in both embryonic and adult tissues. In rat brain tumors, it has recently been shown that the nuclear protein pigpen is expressed selectively in endothelial cells of developing microvasculature but not in the established peritumoral vessels (Blank, M., Weinschenk, T., Priemer, M., and Schluesener, H. (2001) J. Biol. Chem. 276, 16464-16468). This finding suggests that pigpen may be important for promoting the undifferentiated, or "angiogenic" endothelial cell phenotype. Our studies show that pigpen protein and mRNA are expressed in actively dividing endothelial cells and down-regulated as they become confluent. Protein distribution is regulated in a cell cycle-dependent manner. We conclude that this expression pattern is important for and not simply ancillary to proliferation because nuclear microinjection of anti-pigpen Fab fragments inhibited endothelial cell division. Moreover, expression of the proliferating cell marker Ki67 was inhibited in antibody-injected cells. The absence of Ki67 suggests exit from rather than arrest within (for example, at the G(1)/S interface) the cell cycle. Together with earlier observations on the structure and expression of this molecule, our data support the hypothesis that pigpen helps regulate endothelial cell differentiation state.

Differential roles of ICAM-1 and E-selectin in polymorphonuclear leukocyte-induced angiogenesis

Ets-1, which stimulates metalloproteinase gene transcription, has a key role in angiogenesis. We first examined whether activated polymorphonuclear leukocytes (PMNs) enhanced angiogenesis through the induction of Ets-1. Addition of activated PMNs to endothelial cells stimulated both in vitro angiogenesis in collagen gel and Ets-1 expression. Both angiogenesis and Ets-1 expression induced by PMNs were reduced by ets-1 antisense oligonucleotide, suggesting that Ets-1 is an important factor in PMN-induced angiogenesis. Although intercellular adhesion molecule (ICAM)-1 and E-selectin are involved in PMN-induced angiogenesis, the mechanisms underlying their roles in angiogenesis have yet to be elucidated. PMN-induced Ets-1 expression was reduced by a monoclonal antibody against ICAM-1 but not E-selectin despite the inhibition of PMN-induced angiogenesis by both antibodies. Moreover, the stimulation of angiogenesis by H(2)O(2) without PMNs was inhibited by a monoclonal antibody to E-selectin but not ICAM-1. These findings suggested that ICAM-1 in endothelial cells may act as a signaling receptor to induce Ets-1 expression, whereas E-selectin seems to function in the formation of tubelike structures in vascular endothelial cell cultures.

Local anti-angiogenic brain tumor therapies

The critical role of angiogenesis in the growth of solid tumors, including neoplasms of the central nervous system, has provided the impetus for research leading to the discovery of inhibitors of tumor neovascularization. The therapeutic potential of systemically administered antiangiogenic drugs for brain tumors, however, is limited by a variety of anatomic and physiologic barriers to drug delivery. Implantable controlled-release polymers for local drug administration directly into the tumor parenchyma have therefore been developed to achieve therapeutic concentrations of these drugs within the brain while minimizing systemic toxicity. With use of these polymers, successful antiangiogenic therapy for treatment of experimental intracranial malignancies has been achieved. This has been demonstrated with a variety of otherwise unrelated drugs -- including the angiostatic steroids, tetracycline derivatives, and amiloride -- which modulate collagenase activity, and thus, basement membrane and interstitial matrix metabolism. Controlled-release polymers provide a clinically practicable method of achieving sustained antiangiogenic therapy which can be readily used in combination with other treatment modalities such as cytoreductive surgery, radiation, and cytotoxic chemotherapy.

Cancer treatment with inhibitors of urokinase-type plasminogen activator and plasmin

The urokinase-type plasminogen activator-plasmin system plays an important role in many normal physiological processes including clot lysis, wound healing, embryogenesis and tissue remodelling. It is also involved in the pathogenesis of human malignancy through its ability to mediate tumour cell growth, invasion and metastatic dissemination. Interfering with this system is an appealing approach for experimental therapy of malignancy for several reasons. This concept is supported by a wealth of preclinical data. Evidence exists suggesting a role for this system in several major human tumour types. Preliminary evidence suggests that agents which block this pathway are effective in therapeutic doses that are already defined and relatively non-toxic. This form of treatment is not likely to carry cross-resistance with other types of cancer therapy and should be applicable to both localised and advanced tumours. Since heterogeneity in responsiveness among various tumour types is expected, clinical effects in given tumours would provide a basis for interpreting mechanisms of tumour progression in vivo and for future development of drugs with improved efficacy. Inhibition of the urokinase-type plasminogen activator-plasmin system remains a promising, but largely untested, area of experimental cancer therapeutics.

Inhibition of angiogenesis by blockers of volume-regulated anion channels

Osmotic cell swelling activates an outwardly rectifying Cl(-) current in endothelial cells that is mediated by volume-regulated anion channels (VRACs). In the past, we have shown that serum-induced proliferation of endothelial cells is arrested in the presence of compounds that potently block the endothelial VRACs. Here we report on the effects of four chemically distinct VRAC blockers [5-nitro-2-(3-phenylpropylamino)benzoic acid] (NPPB), mibefradil, tamoxifen, and clomiphene-on several models of experimental angiogenesis. Mibefradil (20 microM), NPPB (100 microM), tamoxifen (20 microM), and clomiphene (20 microM) inhibited tube formation by rat microvascular endothelial cells plated on matrigel by 42.9 +/- 8.8%, 25.3 +/- 10.4%, 32.2 +/- 4.5%, and 20 +/- 5.8%, respectively (p < 0.05). Additionally, NPPB (50-100 microM) and mibefradil (10-30 microM) significantly inhibited bFGF (10 ng/ml) + TNFalpha (2.5 ng/ml)-stimulated microvessel formation by human microvascular endothelial cells plated on fibrin by 30-70%. Furthermore, NPPB, mibefradil, and clomiphene concentration dependently inhibited spontaneous microvessel formation in the rat aorta-ring assay and vessel development in the chick chorioallantoic membrane assay. These results suggest that VRAC blockers are potent inhibitors of angiogenesis and thus might serve as therapeutic tools in tumor growth and other angiogenesis-dependent diseases.

A comparison of two controlled-release delivery systems for the delivery of amiloride to control angiogenesis

The diuretic amiloride has been reported to inhibit both Na+-H+ antiport and the urokinase-type plasminogen activator. As a consequence of these inhibitions, neovascularization may also be inhibited. We hypothesized that if amiloride could be effectively delivered in a site-specific manner, a system might be developed that could inhibit localized angiogenesis. In order to evaluate this possibility we conducted a study that compared two different controlled-release systems into which amiloride had been incorporated. The effectiveness of amiloride release from each delivery system was determined by quantitating angiogenic patterns in a chick chorioallantoic membrane (CAM) system using a fractal analysis software program. The two delivery systems compared were sucrose acetate isobutyrate (SAIB) and calcium alginate. Initial HPLC laboratory tests confirmed that amiloride could be released from both SAIB and calcium alginate in vitro in a sustained manner for 72 h. The CAM studies confirmed that neither SAIB nor calcium alginate alone promoted or inhibited angiogenesis when compared to nontreated controls. The release of amiloride from each delivery vehicle resulted in a significant (P < 0.05) inhibition of angiogenesis following both 24 and 48 h of release compared to controls. There was no difference in inhibition of angiogenesis, however, when comparing SAIB + amiloride treated CAMs with calcium alginate + amiloride treated CAMs. These data suggest that both SAIB and calcium alginate may be useful delivery vehicles for the localized application of amiloride to control angiogenesis. Such a system could potentially control tumor angiogenesis without systemic effects.

Time and dose dependency of the suppression of pulmonary metastases of rat mammary cancer by amiloride

Amiloride is an inhibitor of urokinase plasminogen activator (uPA), an essential component of the plasminogen/plasmin enzyme system. Inhibition of uPA prevents the conversion of plasminogen to tumor cell surface bound plasmin which is required for initiation of the metastatic process. MATB rat mammary cancer cells were introduced into the jugular venous system of 80 Fisher 344 female rats. Amiloride at high and low dosages was administered in the drinking water at the time of, prior to or several days following the tumor cell inoculation and continued daily for 10 days post inoculation. Control rats were maintained on water alone. The middle lobe of the right lung was examined microscopically for numbers of metastases. Suppression of metastases was significant at high amiloride dosages in all groups, and at low dosage when administered prior to inoculation. We conclude that amiloride suppresses induced metastases of rat mammary cancer, the effect being dose- and time-dependent.

Ion channels in vascular endothelium

The functional impact of ion channels in vascular endothelial cells (ECs) is still a matter of controversy. This review describes different types of ion channels in ECs and their role in electrogenesis, Ca2+ signaling, vessel permeability, cell-cell communication, mechano-sensor functions, and pH and volume regulation. One major function of ion channels in ECs is the control of Ca2+ influx either by a direct modulation of the Ca2+ influx pathway or by indirect modulation of K+ and Cl- channels, thereby clamping the membrane at a sufficiently negative potential to provide the necessary driving force for a sustained Ca2+ influx. We discuss various mechanisms of Ca2+ influx stimulation: those that activate nonselective, Ca(2+)-permeable cation channels or those that activate Ca(2+)-selective channels, exclusively or partially operated by the filling state of intracellular Ca2+ stores. We also describe the role of various Ca(2+)- and shear stress-activated K+ channels and different types of Cl- channels for the regulation of the membrane potential.

Tumour vasculature--a potential therapeutic target

The tumour vasculature is vital for the establishment, growth and metastasis of solid tumours. Its physiological properties limit the effectiveness of conventional anti-cancer strategies. Therapeutic approaches directed at the tumour vasculature are reviewed, suggesting the potential of anti-angiogenesis and the targeting of vascular proliferation antigens as cancer treatments.

Amiloride and harmaline are potent inhibitors of NhaB, a Na+/H+ antiporter from Escherichia coli

The diuretic drug amiloride is a specific inhibitor of sodium transporting proteins in several cell types. Attempts to inhibit this activity in membrane vesicles derived from various bacteria, did not yield clear results. Therefore, we tested the effect of amiloride and its derivatives on the purified Na+/H+ antiporters of E. coli reconstituted in functional form in proteoliposomes. Whereas NhaA is not inhibited by amiloride, both amiloride and harmaline are potent inhibitors of NhaB with K0.5 of 6 and 15 microM, respectively. The pattern of inhibition by amiloride derivatives is different from that reported for mammalian antiporters but similar to that reported for the Na+/H+ antiporter of D. salina [Katz, A., Kleyman, T.R. and Pick, U. (1994) Biochemistry 33, 2389-2393]. Clonidine is a poor inhibitor (K0.5 = 200 microM) while cimetidine had no effect on the antiporter up to concentration of 1 mM. These new potent inhibitors provide us with important tools for the study of the mechanism of action of NhaB.

Angiogenesis inhibition: a review

In this review we discuss the concept of anti-angiogenesis, which is the inhibition of neovascularization. Anti-angiogenic agents are viewed from the standpoint of their effect on various elements of the angiogenic process, including induction of vascular discontinuity, endothelial cell movement, endothelial cell proliferation, and three-dimensional restructuring of patent vessels. An effort is made to place the many different approaches to anti-angiogenesis research into a comprehensible structure, in order to identify problems of evaluation and interpretation, thereby providing a clearer basis for determining promising and needed directions for further investigation.