Jeanette Marjorie Wood

Structure-based design of aliskiren, a novel orally effective renin inhibitor

Hypertension is a major risk factor for cardiovascular diseases such as stroke, myocardial infarction, and heart failure, the leading causes of death in the Western world. Inhibitors of the renin-angiotensin system (RAS) have proven to be successful treatments for hypertension. As renin specifically catalyses the rate-limiting step of the RAS, it represents the optimal target for RAS inhibition. Several peptide-like renin inhibitors have been synthesized previously, but poor pharmacokinetic properties meant that these compounds were not clinically useful. We employed a combination of molecular modelling and crystallographic structure analysis to design renin inhibitors lacking the extended peptide-like backbone of earlier inhibitors, for improved pharmacokinetic properties. This led to the discovery of aliskiren, a highly potent and selective inhibitor of human renin in vitro, and in vivo; once-daily oral doses of aliskiren inhibit renin and lower blood pressure in sodium-depleted marmosets and hypertensive human patients. Aliskiren represents the first in a novel class of renin inhibitors with the potential for treatment of hypertension and related cardiovascular diseases.

Blockade of Vascular Endothelial Cell Growth Factor Receptor Signaling Is Sufficient to Completely Prevent Retinal Neovascularization

Retinal vasculogenesis and ischemic retinopathies provide good model systems for study of vascular development and neovascularization (NV), respectively. Vascular endothelial cell growth factor (VEGF) has been implicated in the pathogenesis of retinal vasculogenesis and in the development of retinal NV in ischemic retinopathies. However, insulin-like growth factor-I and possibly other growth factors also participate in the development of retinal NV and intraocular injections of VEGF antagonists only partially inhibit retinal NV. One possible conclusion from these studies is that it is necessary to block other growth factors in addition to VEGF to achieve complete inhibition of retinal NV. We recently demonstrated that a partially selective kinase inhibitor, PKC412, that blocks phosphorylation by VEGF and platelet-derived growth factor (PDGF) receptors and several isoforms of protein kinase C (PKC), completely inhibits retinal NV. In this study, we have used three additional selective kinase inhibitors with different selectivity profiles to explore the signaling pathways involved in retinal NV. PTK787, a drug that blocks phosphorylation by VEGF and PDGF receptors, but not PKC, completely inhibited retinal NV in murine oxygen-induced ischemic retinopathy and partially inhibited retinal vascularization during development. CGP 57148 and CGP 53716, two drugs that block phosphorylation by PDGF receptors, but not VEGF receptors, had no significant effect on retinal NV. These data and our previously published study suggest that regardless of contributions by other growth factors, VEGF signaling plays a critical role in the pathogenesis of retinal NV. Inhibition of VEGF receptor kinase activity completely blocks retinal NV and is an excellent target for treatment of proliferative diabetic retinopathy and other ischemic retinopathies.

AEE788: a dual family epidermal growth factor receptor/ErbB2 and vascular endothelial growth factor receptor tyrosine kinase inhibitor with antitumor and antiangiogenic activity.

Aberrant epidermal growth factor receptor (EGFR) and ErbB2 expression are associated with advanced disease and poor patient prognosis in many tumor types (breast, lung, ovarian, prostate, glioma, gastric, and squamous carcinoma of head and neck). In addition, a constitutively active EGFR type III deletion mutant has been identified in non-small cell lung cancer, glioblastomas, and breast tumors. Hence, members of the EGFR family are viewed as promising therapeutic targets in the fight against cancer. In a similar vein, vascular endothelial growth factor (VEGF) receptor kinases are also promising targets in terms of an antiangiogenic treatment strategy. AEE788, obtained by optimization of the 7H-pyrrolo[2,3-d]pyrimidine lead scaffold, is a potent combined inhibitor of both epidermal growth factor (EGF) and VEGF receptor tyrosine kinase family members on the isolated enzyme level and in cellular systems. At the enzyme level, AEE788 inhibited EGFR and VEGF receptor tyrosine kinases in the nm range (IC(50)s: EGFR 2 nm, ErbB2 6 nm, KDR 77 nm, and Flt-1 59 nm). In cells, growth factor-induced EGFR and ErbB2 phosphorylation was also efficiently inhibited (IC(50)s: 11 and 220 nm, respectively). AEE788 demonstrated antiproliferative activity against a range of EGFR and ErbB2-overexpressing cell lines (including EGFRvIII-dependent lines) and inhibited the proliferation of epidermal growth factor- and VEGF-stimulated human umbilical vein endothelial cells. These properties, combined with a favorable pharmacokinetic profile, were associated with a potent antitumor activity in a number of animal models of cancer, including tumors that overexpress EGFR and or ErbB2. Oral administration of AEE788 to tumor-bearing mice resulted in high and persistent compound levels in tumor tissue. Moreover, AEE788 efficiently inhibited growth factor-induced EGFR and ErbB2 phosphorylation in tumors for >72 h, a phenomenon correlating with the antitumor efficacy of intermittent treatment schedules. Strikingly, AEE788 also inhibited VEGF-induced angiogenesis in a murine implant model. Antiangiogenic activity was also apparent by measurement of tumor vascular permeability and interstitial leakage space using dynamic contrast enhanced magnetic resonance imaging methodology. Taken together, these data indicate that AEE788 has potential as an anticancer agent targeting deregulated tumor cell proliferation as well as angiogenic parameters. Consequently, AEE788 is currently in Phase I clinical trials in oncology.Aberrant epidermal growth factor receptor (EGFR) and ErbB2 expression are associated with advanced disease and poor patient prognosis in many tumor types (breast, lung, ovarian, prostate, glioma, gastric, and squamous carcinoma of head and neck). In addition, a constitutively active EGFR type III deletion mutant has been identified in non-small cell lung cancer, glioblastomas, and breast tumors. Hence, members of the EGFR family are viewed as promising therapeutic targets in the fight against cancer. In a similar vein, vascular endothelial growth factor (VEGF) receptor kinases are also promising targets in terms of an antiangiogenic treatment strategy. AEE788, obtained by optimization of the 7H-pyrrolo[2,3-d]pyrimidine lead scaffold, is a potent combined inhibitor of both epidermal growth factor (EGF) and VEGF receptor tyrosine kinase family members on the isolated enzyme level and in cellular systems. At the enzyme level, AEE788 inhibited EGFR and VEGF receptor tyrosine kinases in the nm range (IC50s: EGFR 2 nm, ErbB2 6 nm, KDR 77 nm, and Flt-1 59 nm). In cells, growth factor-induced EGFR and ErbB2 phosphorylation was also efficiently inhibited (IC50s: 11 and 220 nm, respectively). AEE788 demonstrated antiproliferative activity against a range of EGFR and ErbB2-overexpressing cell lines (including EGFRvIII-dependent lines) and inhibited the proliferation of epidermal growth factor- and VEGF-stimulated human umbilical vein endothelial cells. These properties, combined with a favorable pharmacokinetic profile, were associated with a potent antitumor activity in a number of animal models of cancer, including tumors that overexpress EGFR and or ErbB2. Oral administration of AEE788 to tumor-bearing mice resulted in high and persistent compound levels in tumor tissue. Moreover, AEE788 efficiently inhibited growth factor-induced EGFR and ErbB2 phosphorylation in tumors for >72 h, a phenomenon correlating with the antitumor efficacy of intermittent treatment schedules. Strikingly, AEE788 also inhibited VEGF-induced angiogenesis in a murine implant model. Antiangiogenic activity was also apparent by measurement of tumor vascular permeability and interstitial leakage space using dynamic contrast enhanced magnetic resonance imaging methodology. Taken together, these data indicate that AEE788 has potential as an anticancer agent targeting deregulated tumor cell proliferation as well as angiogenic parameters. Consequently, AEE788 is currently in Phase I clinical trials in oncology.

Cell-Demanded Liberation of VEGF121 From Fibrin Implants Induces Local and Controlled Blood Vessel Growth

Abstract— Although vascular endothelial growth factor (VEGF) has been described as a potent angiogenic stimulus, its application in therapy remains difficult: blood vessels formed by exposure to VEGF tend to be malformed and leaky. In nature, the principal form of VEGF possesses a binding site for ECM components that maintain it in the immobilized state until released by local cellular enzymatic activity. In this study, we present an engineered variant form of VEGF, &agr;2PI1–8- VEGF121, that mimics this concept of matrix-binding and cell-mediated release by local cell–associated enzymatic activity, working in the surgically-relevant biological matrix fibrin. We show that matrix-conjugated &agr;2 PI1–8- VEGF121 is protected from clearance, contrary to native VEGF121 mixed into fibrin, which was completely released as a passive diffusive burst. Grafting studies on the embryonic chicken chorioallantoic membrane (CAM) and in adult mice were performed to assess and compare the quantity and quality of neovasculature induced in response to fibrin implants formulated with matrix-bound &agr;2 PI1–8- VEGF121 or native diffusible VEGF121. Our CAM measurements demonstrated that cell-demanded release of &agr;2 PI1–8- VEGF121 increases the formation of new arterial and venous branches, whereas exposure to passively released wild-type VEGF121 primarily induced chaotic changes within the capillary plexus. Specifically, our analyses at several levels, from endothelial cell morphology and endothelial interactions with periendothelial cells, to vessel branching and network organization, revealed that &agr;2 PI1–8- VEGF121 induces vessel formation more potently than native VEGF121 and that those vessels possess more normal morphologies at the light microscopic and ultrastructural level. Permeability studies in mice validated that vessels induced by &agr;2 PI1–8- VEGF121 do not leak. In conclusion, cell-demanded release of engineered VEGF121 from fibrin implants may present a therapeutically safe and practical modality to induce local angiogenesis.

Structure-based drug design: the discovery of novel nonpeptide orally active inhibitors of human renin

BACKGROUND The aspartic proteinase renin plays an important physiological role in the regulation of blood pressure. It catalyses the first step in the conversion of angiotensinogen to the hormone angiotensin II. In the past, potent peptide inhibitors of renin have been developed, but none of these compounds has made it to the end of clinical trials. Our primary aim was to develop novel nonpeptide inhibitors. Based on the available structural information concerning renin-substrate interactions, we synthesized inhibitors in which the peptide portion was replaced by lipophilic moieties that interact with the large hydrophobic S1/S3-binding pocket in renin. RESULTS Crystal structure analysis of renin-inhibitor complexes combined with computational methods were employed in the medicinal-chemistry optimisation process. Structure analysis revealed that the newly designed inhibitors bind as predicted to the S1/S3 pocket. In addition, however, these compounds interact with a hitherto unrecognised large, distinct, sub-pocket of the enzyme that extends from the S3-binding site towards the hydrophobic core of the enzyme. Binding to this S3(sp) sub-pocket was essential for high binding affinity. This unprecedented binding mode guided the drug-design process in which the mostly hydrophobic interactions within subsite S3(sp) were optimised. CONCLUSIONS Our design approach led to compounds with high in vitro affinity and specificity for renin, favourable bioavailability and excellent oral efficacy in lowering blood pressure in primates. These renin inhibitors are therefore potential therapeutic agents for the treatment of hypertension and related cardiovascular diseases.

Antagonism of Sphingosine-1-Phosphate Receptors by FTY720 Inhibits Angiogenesis and Tumor Vascularization

FTY720, a potent immunomodulator, becomes phosphorylated in vivo (FTY-P) and interacts with sphingosine-1-phosphate (S1P) receptors. Recent studies showed that FTY-P affects vascular endothelial growth factor (VEGF)-induced vascular permeability, an important aspect of angiogenesis. We show here that FTY720 has antiangiogenic activity, potently abrogating VEGF- and S1P-induced angiogenesis in vivo in growth factor implant and corneal models. FTY720 administration tended to inhibit primary and significantly inhibited metastatic tumor growth in a mouse model of melanoma growth. In combination with a VEGFR tyrosine kinase inhibitor PTK787/ZK222584, FTY720 showed some additional benefit. FTY720 markedly inhibited tumor-associated angiogenesis, and this was accompanied by decreased tumor cell proliferation and increased apoptosis. In transfected HEK293 cells, FTY-P internalized S1P1 receptors, inhibited their recycling to the cell surface, and desensitized S1P receptor function. Both FTY720 and FTY-P apparently failed to impede VEGF-produced increases in mitogen-activated protein kinase activity in human umbilical vascular endothelial cells (HUVEC), and unlike its activity in causing S1PR internalization, FTY-P did not result in a decrease of surface VEGFR2 levels in HUVEC cells. Pretreatment with FTY720 or FTY-P prevented S1P-induced Ca2+ mobilization and migration in vascular endothelial cells. These data show that functional antagonism of vascular S1P receptors by FTY720 potently inhibits angiogenesis; therefore, this may provide a novel therapeutic approach for pathologic conditions with dysregulated angiogenesis.

Pharmacological profile of valsartan: a potent, orally active, nonpeptide antagonist of the angiotensin II AT1-receptor subtype

1 The pharmacological profile of valsartan, (S)‐N‐valeryl‐N‐{[2′‐(1H‐tetrazol‐5‐yl)biphenyl‐4‐yl]‐methyl}‐valine, a potent, highly selective, and orally active antagonist at the angiotensin II (AII) AT1‐receptor, was studied in vitro and in vivo. 2 Valsartan competed with [125I]‐AII at its specific binding sites in rat aortic smooth muscle cell membranes (AT1‐receptor subtype) with a Ki of 2.38 nm, but was about 30,000 times less active in human myometrial membranes (AT2‐receptor subtype). 3 In rabbit aortic rings incubated for 5 min with valsartan, at concentrations of 2, 20 and 200 nm, the concentration‐response curve of AII was displaced to the right and the maximum response was reduced by 33%, 36% and 40%, respectively. Prolongation of the incubation time with valsartan to 1 h or 3 h, further reduced the maximum response by 48% or 59% (after 20 nm) and by 59% or 60% (after 200 nm) respectively. After 3 h incubation an apparent pKB value of 9.26 was calculated. Contractions induced by noradrenaline, 5‐hydroxytryptamine, or potassium chloride were not affected by valsartan. No agonistic effects were observed in the rabbit aorta at concentrations of valsartan up to 2 μm. 4 In bovine adrenal glomerulosa, valsartan inhibited All‐stimulated aldosterone release without affecting the maximum response (pA2 8.4). 5 In the pithed rat, oral administration of valsartan (10 mg kg−1) shifted the All‐induced pressor response curves to the right, without affecting responses induced by the electrical stimulation of the sympathetic outflow or by noradrenaline. Animals treated with valsartan 24 h before pithing also showed significant inhibition of the response to AII. 6 In conscious, two‐kidney, one‐clip renal hypertensive rats (2K1C), valsartan decreased blood pressure in a dose‐dependent manner after single i.v. or oral administration. The respective ED30 values were 0.06 mg kg−1 (i.v.) and 1.4 mg kg−1 (p.o.). The antihypertensive effect lasted for at least 24 h after either route of administration. After repeated oral administration for 4 days (3 and 10 mg kg−1 daily), in 2K1C renal hypertensive rats, systolic blood pressure was consistently decreased, but heart rate was not significantly affected. 7 In conscious, normotensive, sodium‐depleted marmosets, valsartan decreased mean arterial pressure, measured by telemetry, after oral doses of 1–30 mg kg−1. The hypotensive effect persisted up to 12 h after 3 and 10 mg kg−1 and up to 24 h after 30 mg kg−1. 8 In sodium‐depleted marmosets, the hypotensive effect of valsartan lasted longer than that of losartan (DuP 753). In renal hypertensive rats, both agents had a similar duration (24 h), but a different onset of action (valsartan at 1 h, losartan between 2 h and 24 h). 9 These results demonstrate that valsartan is a potent, specific, highly selective antagonist of AII at the AT1‐receptor subtype and does not possess agonistic activity. Furthermore, it is an efficacious, orally active, blood pressure‐lowering agent in conscious renal hypertensive rats and in conscious normotensive, sodium‐depleted primates.

Pharmacology of imatinib (STI571)

Deregulation of protein kinase activity has been shown to play a central role in the pathogenesis of human cancer. The molecular pathogenesis of chronic myelogenous leukemia (CML) in particular, depends on formation of the bcr-abl oncogene, leading to constitutive expression of the tyrosine kinase fusion protein, Bcr-Abl. Based on these observations, imatinib was developed as a specific inhibitor for the Bcr-Abl protein tyrosine kinase. The expanding understanding of the basis of imatinib-mediated tyrosine kinase inhibition has revealed a spectrum of potential new antitumor applications beyond the powerful activity already reported in the treatment of CML. Imatinib has shown activity in vivo against PDGF-driven tumor models including glioblastoma, dermatofibrosarcoma protuberans and chronic myelomonocytic leukemia. Antiangiogenic effects have been demonstrated by inhibition of PDGF-, VEGF (vascular endothelial growth factor)- and bFGF- (basic fibroblast growth factor) induced angiogenesis in vivo, and by inhibition of angiogenesis and tumor growth in an experimental bone metastasis model. Imatinib has been shown to reduce interstitial fluid pressure in an experimental colonic carcinoma model by blocking PDGF-mediated effects on tumor-associated blood vessels and stromal tissue. It is also a potent inhibitor of the Kit receptor tyrosine kinase, and has demonstrated activity clinically against the Kit-driven gastrointestinal stromal tumor (GIST) and experimentally in small-cell lung cancer cell lines. The pharmacology of imatinib and its activity in various tumor models is discussed.

mTOR Inhibitor RAD001 (Everolimus) Has Antiangiogenic/Vascular Properties Distinct from a VEGFR Tyrosine Kinase Inhibitor

Purpose: Comparison of the antiangiogenic/vascular properties of the oral mammalian target of rapamycin (mTOR) inhibitor RAD001 (everolimus) and the vascular endothelial growth factor receptor (VEGFR) inhibitor vatalanib (PTK/ZK). Experimental Design: Antiproliferative activity against various tumor histotypes and downstream effects on the mTOR pathway were measured in vitro. In vivo, antitumor activity, plasma, and tumor RAD001 levels were measured. Activity in several different angiogenic/vascular assays in vitro and in vivo was assessed and compared with PTK/ZK. Results: RAD001 inhibited proliferation in vitro (IC50 values <1 nmol/L to >1 μmol/L), and in sensitive and insensitive tumor cells, pS6 kinase and 4E-BP1 were inhibited. Activity in vitro did not correlate with activity in vivo and significant responses were seen in tumors with IC50 values >10-fold higher than tumor RAD001 concentrations. In vitro, RAD001 inhibited the proliferation of VEGF-stimulated and fibroblast growth factor-stimulated human endothelial cells but not dermal fibroblasts and impaired VEGF release from both sensitive and insensitive tumor cells but did not inhibit migration of human endothelial cells. In vivo, in tumor models derived from either sensitive or insensitive cells, RAD001 reduced Tie-2 levels, the amount of mature and immature vessels, total plasma, and tumor VEGF. RAD001 did not affect blood vessel leakiness in normal vasculature acutely exposed to VEGF nor did it affect tumor vascular permeability (Ktrans) as measured by dynamic contrast-enhanced magnetic resonance imaging. However, the pan-VEGFR inhibitor PTK/ZK inhibited endothelial cell migration and vascular permeability but had less effect on mature vessels compared with RAD001. Conclusions: VEGFR and mTOR inhibitors show similar but also distinct effects on tumor vascular biology, which has implications for their clinical activity alone or in combination.

Dissection of angiogenic signaling in zebrafish using a chemical genetic approach

Striking homology between signaling molecules in zebrafish and humans suggests that compounds known to inhibit human kinases may enable a chemical genetic approach to dissect signaling pathways in the zebrafish embryo. We tested this hypothesis using a vascular endothelial growth factor receptor inhibitor, PTK787/ZK222584. Zebrafish embryos treated with this compound lacked all major blood vessels. Overexpression of AKT/PKB, a putative effector of vascular endothelial growth factor signaling, allowed blood vessels to form in the presence of drug. Endothelial cell apoptosis induced by the drug is prevented by increasing AKT/PKB activity, thus establishing the physiological relevance of AKT/PKB in the angiogenic process. This approach allowed us to examine the effects of blood flow and the role of endothelial signals in organogenesis.