Discovery of Orally Bioavailable Purine-Based Inhibitors of the Low-Molecular-Weight Protein Tyrosine Phosphatase

Obesity-associated insulin resistance plays a central role in the pathogenesis of type 2 diabetes. A promising approach to decrease insulin resistance in obesity is to inhibit the protein tyrosine phosphatases that negatively regulate insulin receptor signaling. The low-molecular-weight protein tyrosine phosphatase (LMPTP) acts as a critical promoter of insulin resistance in obesity by inhibiting phosphorylation of the liver insulin receptor activation motif. Here, we report development of a novel purine-based chemical series of LMPTP inhibitors. These compounds inhibit LMPTP with an uncompetitive mechanism and are highly selective for LMPTP over other protein tyrosine phosphatases. We also report the generation of a highly orally bioavailable purine-based analogue that reverses obesity-induced diabetes in mice.

Serine-Threonine Kinase TAO3-Mediated Trafficking of Endosomes Containing the Invadopodia Scaffold TKS5α Promotes Cancer Invasion and Tumor Growth

Invadopodia are actin-based proteolytic membrane protrusions required for invasive behavior and tumor growth. In this study, we used our high-content screening assay to identify kinases whose activity affects invadopodia formation. Among the top hits selected for further analysis was TAO3, an STE20-like kinase of the GCK subfamily. TAO3 was overexpressed in many human cancers and regulated invadopodia formation in melanoma, breast, and bladder cancers. Furthermore, TAO3 catalytic activity facilitated melanoma growth in three-dimensional matrices and in vivo. A novel, potent catalytic inhibitor of TAO3 was developed that inhibited invadopodia formation and function as well as tumor cell extravasation and growth. Treatment with this inhibitor demonstrated that TAO3 activity is required for endosomal trafficking of TKS5α, an obligate invadopodia scaffold protein. A phosphoproteomics screen for TAO3 substrates revealed the dynein subunit protein LIC2 as a relevant substrate. Knockdown of LIC2 or expression of a phosphomimetic form promoted invadopodia formation. Thus, TAO3 is a new therapeutic target with a distinct mechanism of action. SIGNIFICANCE: An unbiased screening approach identifies TAO3 as a regulator of invadopodia formation and function, supporting clinical development of this class of target.

Discovery of β-Arrestin Biased, Orally Bioavailable, and CNS Penetrant Neurotensin Receptor 1 (NTR1) Allosteric Modulators

Neurotensin receptor 1 (NTR1) is a G protein coupled receptor that is widely expressed throughout the central nervous system where it acts as a neuromodulator. Neurotensin receptors have been implicated in a wide variety of CNS disorders, but despite extensive efforts to develop small molecule ligands there are few reports of such compounds. Herein we describe the optimization of a quinazoline based lead to give 18 (SBI-553), a potent and brain penetrant NTR1 allosteric modulator.

Diabetes reversal by inhibition of the low-molecular-weight tyrosine phosphatase

Obesity-associated insulin resistance plays a central role in type 2 diabetes. As such, tyrosine phosphatases that dephosphorylate the insulin receptor (IR) are potential therapeutic targets. The low-molecular-weight protein tyrosine phosphatase (LMPTP) is a proposed IR phosphatase, yet its role in insulin signaling in vivo has not been defined. Here we show that global and liver-specific LMPTP deletion protects mice from high-fat diet-induced diabetes without affecting body weight. To examine the role of the catalytic activity of LMPTP, we developed a small-molecule inhibitor with a novel uncompetitive mechanism, a unique binding site at the opening of the catalytic pocket, and an exquisite selectivity over other phosphatases. This inhibitor is orally bioavailable, and it increases liver IR phosphorylation in vivo and reverses high-fat diet-induced diabetes. Our findings suggest that LMPTP is a key promoter of insulin resistance and that LMPTP inhibitors would be beneficial for treating type 2 diabetes.

Characterization of Potent SMAC Mimetics that Sensitize Cancer Cells to TNF Family-Induced Apoptosis

Members of the Inhibitor of APoptosis (IAP) protein family suppress apoptosis within tumor cells, particularly in the context of immune cell-mediated killing by the tumor necrosis factor (TNF) superfamily cytokines. Most IAPs are opposed endogenously by the second mitochondrial activator of caspases (SMAC), which binds to selected baculovirus IAP repeat (BIR) domains of IAPs to displace interacting proteins. The development of SMAC mimetics as novel anticancer drugs has gained impetus, with several agents now in human clinical trials. To further understand the cellular mechanisms of SMAC mimetics, we focused on IAP family members cIAP1 and cIAP2, which are recruited to TNF receptor complexes where they support cell survival through NF-κB activation while suppressing apoptosis by preventing caspase activation. We established fluorescence polarization (FP) assays for the BIR2 and BIR3 domains of human cIAP1 and cIAP2 using fluorochrome-conjugated SMAC peptides as ligands. A library of SMAC mimetics was profiled using the FP assays to provide a unique structure activity relationship (SAR) analysis compared to previous assessments of binding to XIAP. Potent compounds displayed mean inhibitory binding constants (K_i) of 9 to 27 nM against the BIR3 domains of cIAP1 and cIAP2, respectively. Selected compounds were then characterized using cytotoxicity assays in which a cytokine-resistant human tumor cell line was sensitized to either TNF or lymphotoxin-α (LT-α). Cytotoxicity correlated closely with cIAP1 and cIAP2 BIR3 binding activity with the most potent compounds able to reduce cell viability by 50%. Further testing demonstrated that active compounds also inhibit RIP1 binding to BIR3 of cIAP1 and cIAP2 in vitro and reduce steady-state cIAP1 protein levels in cells. Altogether, these data inform the SAR for our SMAC mimetics with respect to cIAP1 and cIAP2, suggesting that these IAP family members play an important role in tumor cell resistance to cytotoxicity mediated by TNF and LT-α.

Identification of a selective inhibitor of murine intestinal alkaline phosphatase (ML260) by concurrent ultra-high throughput screening against human and mouse isozymes

Alkaline phosphatase (AP) isozymes are present in a wide range of species from bacteria to man and are capable of dephosphorylation and transphosphorylation of a wide spectrum of substrates in vitro. In humans, four AP isozymes have been identified-one tissue-nonspecific (TNAP) and three tissue-specific-named according to the tissue of their predominant expression: intestinal (IAP), placental (PLAP) and germ cell (GCAP) APs. Modulation of activity of the different AP isozymes may have therapeutic implications in distinct diseases and cellular processes. For instance, changes in the level of IAP activity can affect gut mucosa tolerance to microbial invasion due to the ability of IAP to detoxify bacterial endotoxins, alter the absorption of fatty acids and affect ectopurinergic regulation of duodenal bicarbonate secretion. To identify isozyme selective modulators of the human and mouse IAPs, we developed a series of murine duodenal IAP (Akp3-encoded dIAP isozyme), human IAP (hIAP), PLAP, and TNAP assays. High throughput screening and subsequent SAR efforts generated a potent inhibitor of dIAP, ML260, with specificity for the Akp3-, compared to the Akp5- and Akp6-encoded mouse isozymes.

Small-molecule IAP antagonists sensitize cancer cells to TRAIL-induced apoptosis: roles of XIAP and cIAPs

TNF-related apoptosis-inducing ligand (TRAIL) is a promising anticancer agent because it shows apoptosis-inducing activity in transformed, but not in normal, cells. As with most anticancer agents, however, its clinical use is restricted by either inherent or acquired resistance by cancer cells. We demonstrate here that small-molecule SMAC mimetics that antagonize the inhibitor of apoptosis proteins (IAP) potently sensitize previously resistant human cancer cell lines, but not normal cells, to TRAIL-induced apoptosis, and that they do so in a caspase-8-dependent manner. We further show that the compounds have no cytotoxicity as single agents. Also, we demonstrate that several IAP family members likely participate in the modulation of cellular sensitivity to TRAIL. Finally, we note that the compounds that sensitize cancer cells to TRAIL are the most efficacious in binding to X-linked IAP, and in inducing cellular-IAP (cIAP)-1 and cIAP-2 degradation. Our studies thus describe valuable compounds that allow elucidation of the signaling events occurring in TRAIL resistance, and demonstrate that these agents act as potent TRAIL-sensitizing agents in a variety of cancer cell lines.

Design, synthesis and evaluation of inhibitor of apoptosis protein (IAP) antagonists that are highly selective for the BIR2 domain of XIAP

We recently reported the systematic ligand-based rational design and synthesis of monovalent Smac mimetics that bind preferentially to the BIR2 domain of the anti-apoptotic protein XIAP. Expanded structure-activity relationship (SAR) studies around these peptidomimetics led to compounds with significantly improved selectivity (>60-fold) for the BIR2 domain versus the BIR3 domain of XIAP. The potent and highly selective IAP antagonist 8q (ML183) sensitized TRAIL-resistant prostate cancer cells to apoptotic cell death, highlighting the merit of this probe compound as a valuable tool to investigate the biology of XIAP.

Expedient synthesis of highly potent antagonists of inhibitor of apoptosis proteins (IAPs) with unique selectivity for ML-IAP

A series of novel, potent antagonists of the inhibitor of apoptosis proteins (IAPs) were synthesized in a highly convergent and rapid fashion (≤6 steps) using the Ugi four-component reaction as the key step, thus enabling rapid optimization of binding potency. These IAP antagonists compete with caspases 3, 7, and 9 for inhibition by X chromosome-linked IAP (XIAP) and bind strongly (nanomolar binding constants) to several crucial members of the IAP family of cancer pro-survival proteins to promote apoptosis, with a particularly unique selectivity for melanoma IAP (ML-IAP). Experiments in cell culture revealed powerful cancer cell growth inhibitory activity in multiple (breast, ovarian, and prostate) cell lines with single agent toxicity at low nanomolar levels against SKOV-3 human ovarian carcinoma cells. Administration of the compounds to human foreskin fibroblast cells revealed no general toxicity to normal cells. Furthermore, computational modeling was performed, revealing key contacts between the IAP proteins and antagonists, suggesting a structural basis for the observed potency.

Design, synthesis and evaluation of monovalent Smac mimetics that bind to the BIR2 domain of the anti-apoptotic protein XIAP

We report the systematic rational design and synthesis of new monovalent Smac mimetics that bind preferentially to the BIR2 domain of the anti-apoptotic protein XIAP. Characterization of compounds in vitro (including 9i; ML101) led to the determination of key structural requirements for BIR2 binding affinity. Compounds 9h and 9j sensitized TRAIL-resistant breast cancer cells to apoptotic cell death, highlighting the value of these probe compounds as tools to investigate the biology of XIAP.

LGD-5552, an antiinflammatory glucocorticoid receptor ligand with reduced side effects, in vivo

Treatment of inflammation is often accomplished through the use of glucocorticoids. However, their use is limited by side effects. We have examined the activity of a novel glucocorticoid receptor ligand that binds the receptor efficiently and strongly represses inflammatory gene expression. This compound has potent antiinflammatory activity in vivo and represses the transcription of the inflammatory cytokine monocyte chemoattractant protein-1 and induces the antiinflammatory cytokine IL-10. The compound demonstrates differential gene regulation, compared with commonly prescribed glucocorticoids, effectively inducing some genes and repressing others in a manner different from the glucocorticoid prednisolone. The separation between the antiinflammatory effects of LGD-5552 and the side effects commonly associated with glucocorticoid treatment suggest that this molecule differs significantly from prednisolone and other steroids and may provide a safer therapeutic window for inflammatory conditions now commonly treated with steroidal glucocorticoids.

Agonist and antagonist of retinoic acid receptors cause similar changes in gene expression and induce senescence-like growth arrest in MCF-7 breast carcinoma cells

Biological effects of retinoids are mediated via retinoic acid (RA) receptors (RAR) and retinoid X receptors (RXR). The best-characterized mechanism of retinoid action is stimulation of transcription from promoters containing RA response elements (RARE). Retinoids induce senescence-like growth arrest in MCF-7 breast carcinoma cells; this effect is associated with the induction of several growth-inhibitory genes. We have now found that these genes are induced by RAR-specific but not by RXR-specific ligands. Genome-scale microarray analysis of gene expression was used to compare the effects of two pan-RAR ligands, one of which is a strong agonist of RARE-dependent transcription, whereas the other induces such transcription only weakly and antagonizes the inducing effect of RAR agonists. Both RAR ligands, however, produced very similar effects on gene expression in MCF-7 cells, suggesting that RARE-dependent transcription is only a minor component of retinoid-induced changes in gene expression. The effects of RAR ligands on gene expression parallel changes associated with damage-induced senescence, and both ligands induced G(1) arrest and the senescent phenotype in MCF-7 cells. The RAR ligands up-regulated many tumor-suppressive genes and down-regulated multiple genes with oncogenic activities. Genes that are strongly induced by RAR ligands encode secreted bioactive proteins, including several tumor-suppressing factors. In agreement with these observations, retinoid-treated MCF-7 cells inhibited the growth of retinoid-insensitive MDA-MB-231 breast carcinoma cells in coculture. These results indicate that RARE-independent transcriptional effects of RAR ligands lead to senescence-like growth arrest and paracrine growth-inhibitory activity in MCF-7 breast carcinoma cells.

5(Z)-Benzylidene-1,2-dihydro-9-hydroxy-10-methoxy-2,2,4-trimethyl-5H-1-aza-6-oxa-chrysenes as non-steroidal glucocorticoid receptor modulators

A series of 5-benzylidene-1,2-dihydro-2,2,4-trimethyl-5H-1-aza-6-oxa-chrysenes was synthesized and profiled for their ability to act as selective glucocorticoid receptor modulators (SGRMs). The synthesis and structure-activity relationships for this series of compounds are presented.

Biological characterization of a heterodimer-selective retinoid X receptor modulator: potential benefits for the treatment of type 2 diabetes

Specific retinoid X receptor (RXR) agonists, such as LG100268 (LG268), and the thiazolidinedione (TZD) PPARgamma agonists, such as rosiglitazone, produce insulin sensitization in rodent models of insulin resistance and type 2 diabetes. In sharp contrast to the TZDs that produce significant increases in body weight gain, RXR agonists reduce body weight gain and food consumption. Unfortunately, RXR agonists also suppress the thyroid hormone axis and generally produce hypertriglyceridemia. Heterodimer-selective RXR modulators have been identified that, in rodents, retain the metabolic benefits of RXR agonists with reduced side effects. These modulators bind specifically to RXR with high affinity and are RXR homodimer partial agonists. Although RXR agonists activate many heterodimer partners, these modulators selectively activate RXR:PPARalpha and RXR:PPARgamma, but not RXR:RARalpha, RXR:LXRalpha, RXR:LXRbeta, or RXR:FXRalpha. We report the in vivo characterization of one RXR modulator, LG101506 (LG1506). In Zucker fatty (fa/fa) rats, LG1506 is a potent insulin sensitizer that also enhances the insulin-sensitizing activities of rosiglitazone. Administration of LG1506 reduces both body weight gain and food consumption and blocks the TZD-induced weight gain when coadministered with rosiglitazone. LG1506 does not significantly suppress the thyroid hormone axis in rats, nor does it elevate triglycerides in Sprague Dawley rats. However, LG1506 produces a unique pattern of triglycerides elevation in Zucker rats. LG1506 elevates high-density lipoprotein cholesterol in humanized apolipoprotein A-1-transgenic mice. Therefore, selective RXR modulators are a promising approach for developing improved therapies for type 2 diabetes, although additional studies are needed to understand the strain-specific effects on triglycerides.

Conversion of human-selective PPARα agonists to human/mouse dual agonists: a molecular modeling analysis

To understand the species selectivity in a series of alpha-methyl-alpha-phenoxy carboxylic acid PPARalpha/gamma dual agonists (1-11), structure-based molecular modeling was carried out in the ligand binding pockets of both human and mouse PPARalpha. This study suggested that interaction of both 4-phenoxy and phenyloxazole substituents of these ligands with F272 and M279 in mouse PPARalpha leads to the species-specific divergence in ligand binding. Insights obtained in the molecular modeling studies of these key interactions resulted in the ability to convert a human-selective PPARalpha agonist to a human and mouse dual agonist within the same platform.

Design and Synthesis of α-Aryloxy-α-methylhydrocinnamic Acids: A Novel Class of Dual Peroxisome Proliferator-Activated Receptor α/γ Agonists

The design and synthesis of the dual peroxisome proliferator activated receptor (PPAR) alpha/gamma agonist (S)-2-methyl-3-[4-[2-(5-methyl-2-thiophen-2-yl-oxazol-4-yl)ethoxy]phenyl]-2-phenoxypropionic acid (2) for the treatment of type 2 diabetes and associated dyslipidemia are described. 2 possesses a potent dual hPPAR alpha/gamma agonist profile (IC(50) = 28 and 10 nM; EC(50) = 9 and 4 nM, respectively, for hPPARalpha and hPPARgamma). In preclinical models, 2 substantially improves insulin sensitivity and potently reverses diabetic hyperglycemia while significantly improving overall lipid homeostasis.

Design and synthesis of novel RXR-selective modulators with improved pharmacological profile

New RXR-selective modulators possessing a 6-fluoro trienoic acid moiety (6Z olefin) or a fluorinated/heterocyclic-substituted benzene core ring, were synthesized in an expedient and selective way. A subset of these compounds was evaluated for their metabolic properties (exposure in IRC male mice) and show a dramatic increase of exposure compared to our reference compound, 3 (LG101506).

Design, synthesis, and structure-activity relationship studies of novel 6,7-locked-[7-(2-alkoxy-3,5-dialkylbenzene)-3-methylocta]-2,4,6-trienoic acids

Retinoid X receptor:peroxisome proliferative-activated receptor (RXR:PPAR) heterodimers play a critical role in the regulation of glucose (RXR/PPARgamma) and lipid metabolism (RXR/PPARalpha). Previously, we described a concise structure-activity relationship study of selective RXR modulators possessing a (2E,4E,6Z)-3-methyl-7-(3,5-dialkyl-6-alkoxyphenyl)-octa-2,4,6-trienoic acid scaffold. These studies were focused on the 2-position alkoxy side chain. We describe here the design and synthesis of a novel series of RXR selective modulators possessing the same aromatic core structure with the addition of a ring locked 6-7-Z-olefin on the trienoic acid moiety. The synthesis and structure-activity relationship studies of these 6,7-locked cyclopentenyl, phenyl, thienyl, furan, and pyridine-trienoic acid derivatives is presented herein.

Novel (2E,4E,6Z)-7-(2-alkoxy-3,5-dialkylbenzene)-3-methylocta-2,4,6-trienoic acid retinoid X receptor modulators are active in models of type 2 diabetes

Previous data have shown that RXR-selective agonists (e.g., 3 and 4) are insulin sensitizers in rodent models of non-insulin-dependent diabetes mellitus (NIDDM). Unfortunately, they also produce dramatic increases in triglycerides and profound suppression of the thyroid hormone axis. Here we describe the design and synthesis of new RXR modulators that retain the insulin-sensitizing activity of RXR agonists but produce substantially reduced side effects. These molecules bind selectively and with high affinity to RXR and, unlike RXR agonists, do not activate RXR homodimers. To further evaluate the antidiabetic activity of these RXR modulators, we have designed a concise and systematic structure-activity relationship around the 2E,4E,6Z-7-aryl-3-methylocta-2,4,6-trienoic acid scaffold. Selected compounds have been evaluated using insulin-resistant rodents (db/db mice) to characterize effects on glucose homeostasis. Our studies demonstrate the effectiveness of RXR modulators in lowering plasma glucose in the db/db mouse model.

A tailored therapy for the metabolic syndrome: the dual peroxisome proliferator-activated receptor-alpha/gamma agonist LY465608 ameliorates insulin resistance and diabetic hyperglycemia while improving cardiovascular risk factors in preclinical models

A novel nonthiazolidinedione dual peroxisome proliferator- activated receptor (PPAR)-alpha/gamma agonist, LY465608, was designed to address the major metabolic disturbances of type 2 diabetes. LY465608 altered PPAR-responsive genes in liver and fat of db/db mice and dose-dependently lowered plasma glucose in hyperglycemic male Zucker diabetic fatty (ZDF) rats, with an ED(50) for glucose normalization of 3.8 mg small middle dot kg(-1) small middle dot day(-1). Metabolic improvements were associated with enhanced insulin sensitivity, as demonstrated in female obese Zucker (fa/fa) rats using both oral glucose tolerance tests and hyperinsulinemic-euglycemic clamps. Further characterization of LY465608 revealed metabolic changes distinct from a selective PPAR-gamma agonist, which were presumably due to the concomitant PPAR-alpha agonism, lower respiratory quotient, and less fat accumulation, despite a similar impact on glycemia in male ZDF rats. In addition to these alterations in diabetic and insulin-resistant animals, LY465608 dose-dependently elevated HDL cholesterol and lowered plasma triglycerides in human apolipoprotein A-I transgenic mice, demonstrating that this compound significantly improves primary cardiovascular risk factors. Overall, these studies demonstrate that LY465608 beneficially impacts multiple facets of type 2 diabetes and associated cardiovascular risk, including those facets involved in the development of micro- and macrovascular complications, which are the major sources for morbidity and mortality in these patients.

Pharmacology and pharmacokinetics of a novel nonpeptide angiotensin II receptor antagonist--DMP 811

DMP 811 exhibited high binding affinity for the angiotensin II subtype receptor AT1 in rat adrenal tissues with an IC50 of 6 nM, but not for the subtype receptor AT2. In the isolated rabbit aorta, DMP 811 inhibited the contractile response to angiotensin II selectively and noncompetitively with a KB value of 0.1 nM. In conscious renal hypertensive rats, DMP 811 decreased blood pressure with i.v. and p.o. ED30s of 0.005 and 0.03 mg/kg, respectively (p.o. ED30 for losartan = 0.59 mg/kg). In conscious furosemide-treated dogs, DMP 811 given either at 0.3 or 1 mg/kg p.o. decreased blood pressure. DMP 811 has oral bioavailabilities of 7 and 29% in rats and dogs, respectively, after a solution dose and 8 and 13%, respectively, after a suspension or capsule dosing. Our study indicates that DMP 811 is a selective and insurmountable AT1 receptor antagonist and is a 20-fold more potent orally-active antihypertensive agent than losartan.

Angiotensin II receptor heterogeneity

The possibility of receptor heterogeneity in the angiotensin II (AII) system has been suggested previously, based on differences in Kd values or sensitivity to thiol reagents. One of our earliest indications was the frequent observation of incomplete inhibition of the binding of AII to adrenal cortical membranes. Autoradiographic studies demonstrated that all of the labeling of the rat adrenal was blocked by unlabeled AII or saralasin, but not by DuP 753. The predominant receptor in the rat adrenal cortex (80%) is sensitive to dithiothreitol (DTT) and DuP 753, and is designated AII-1. The residual sites in the adrenal cortex and almost all of the sites in the rat adrenal medulla are insensitive to both DTT and DuP 753, but were blocked by EXP655. These sites have been confirmed by ligand binding studies and are designated AII-2. The rabbit adrenal cortex is unique in yielding a nonuniform distribution of AII-2 sites around the outer layer of glomerulosa cells. In the rabbit kidney, the sites on the glomeruli are AII-1, but the sites on the kidney capsule are AII-2. Angiotensin III appears to have a higher affinity for AII-2 sites since it inhibits the binding to the rabbit kidney capsule but not the glomeruli. Elucidation of the distribution and function of these diverse sites should permit the development of more selective and specific therapeutic strategies.

Functional studies of nonpeptide angiotensin II receptor subtype-specific ligands: DuP 753 (AII-1) and PD123177 (AII-2)

DuP 753 and PD123177 are two nonpeptide angiotensin II (AII)-specific ligands, which show high affinities for two respective and distinct subtypes of AII binding sites, i.e., AII-1 and AII-2 sites, respectively, in the rat adrenal gland, brain and uterus. The objective of this study is to identify the functions of these subtype binding sites in the adrenal, sympathetic ganglia, brain and vascular smooth muscle. In conscious rats, DuP 753 at 1, 3 and 10 mg/kg i.v. but not PD123177 at 30 and 100 mg/kg i.v. inhibited the AII-induced aldosterone increase. In the isolated perfused rat adrenal gland, DuP 753 at 10(-6) and 10(-4) M but not PD123177 at 10(-3) M blocked the AII-induced epinephrine secretion. In control and chemically sympathectomized pithed rats, the pressor and tachycardiac responses to AII were blocked by DuP 753 at 10 mg/kg i.v. but not by PD123177 at 100 mg/kg i.v. In conscious rats, DuP 753 at 10 mg/kg s.c. but not PD123177 at 100 mg/kg s.c. inhibited the AII-induced water drinking. In the rabbit aorta, DuP 753 at 10(-6) M but not PD123177 at 10(-4) M inhibited the contractile effect of AII. In conscious renal artery-ligated hypertensive rats, DuP 753 but not PD123177 at 0.1 to 10 mg/kg i.v. lowered blood pressure. In summary, a function of the PD123177-sensitive AII binding site (AII-2) has not yet been identified. However, the DuP 753-sensitive site (AII-1) appears to mediate the AII-induced responses such as adrenal aldosterone and catecholamine secretion, release of catecholamine from sympathetic ganglia, drinking and vasoconstriction.

Structure-activity relationship of quinoline carboxylic acids. A new class of inhibitors of dihydroorotate dehydrogenase

The novel anticancer drug candidate brequinar sodium [DuP 785, NSC 368390, 6-fluoro-2-(2'-fluoro-1,1'-biphenyl-4-yl)-3-methyl-4-quinoline carboxylic acid sodium salt] inhibits dihydroorotate dehydrogenase, the fourth enzyme in the de novo pyrimidine biosynthetic pathway leading to the formation of UMP. Sixty-nine quinoline 4-carboxylic acid analogs were analyzed as inhibitors of L1210 dihydroorotate dehydrogenase. This structure-activity relationship study identified three critical regions of brequinar sodium and its analogs, where specific substitutions are required for the inhibition of the activity of dihydroorotate dehydrogenase. The three principal regions are: (i) the C(2) position where bulky hydrophobic substituents are necessary, (ii) the C(4) position which has a strict requirement for the carboxylic acid and its corresponding salts, and (iii) the benzo portion of the quinoline ring with appropriate substitutions. These results will be useful in the elucidation of the precise nature of the interaction between brequinar sodium and dihydroorotate dehydrogenase.

Identification of angiotensin II receptor subtypes

We have demonstrated the existence of two distinct subtypes of the angiotensin II receptor in the rat adrenal gland using radioligand binding and tissue section autoradiography. The identification of the subtypes was made possible by the discovery of two structurally dissimilar, nonpeptide compounds, DuP 753 and EXP655, that show reciprocal selectivity for the two subtypes. In the rat adrenal cortex, DuP 753 inhibited 80% of the total AII binding with an IC50 value on the sensitive sites of 2 x 10(-8) M, while EXP655 displaced only 20%. In the rat adrenal medulla, EXP655 gave 90% inhibition of AII binding with an IC50 value of 3.0 x 10(-8) M, while DuP 753 was essentially inactive. The combination of the two compounds completely inhibited AII binding in both tissues.

Activity of a novel 4-quinolinecarboxylic acid, NSC 368390 [6-fluoro-2-(2'-fluoro-1,1'-biphenyl-4-yl)-3-methyl-4-quinolinecarb oxylic acid sodium salt], against experimental tumors

A novel, substituted 4-quinolinecarboxylic acid (NSC 339768) demonstrated antitumor activity against L1210 leukemia and B16 melanoma in the National Cancer Institute's Developmental Therapeutics Program. An extensive analogue synthesis program was initiated; over 200 derivatives were synthesized and tested for anticancer activity. One of these compounds, 6-fluoro-2-(2'-fluoro-1,1'-biphenyl-4-yl)-3-methyl-4-quinolinecarboxylic acid sodium salt, NSC 368390 (DuP-785), was selected for further investigation because of its efficacy against a spectrum of human solid tumors and its water solubility. In initial studies with L1210 leukemia, the compound caused an increase in life span of greater than 80%. The activity was schedule dependent, and the compound was equally efficacious when administered i.p., i.v., s.c., or p.o. In tests against human tumors xenografted under the renal capsule of nude mice, NSC 368390 when injected i.p. in doses of 20-40 mg/kg daily for 9 days inhibited the growth of the MX-1 breast, LX-1 lung, BL/STX-1 stomach, and CX-1 colon carcinomas by greater than 90%. NSC 368390 also inhibited the growth of three distinct human colon carcinomas, the HCT-15, clone A, and DLD-2 tumors, growing s.c. in nude mice. An i.p. dose of 25 mg/kg given daily for 9 days inhibited the growth of the DLD-2 colon cancer by 98%. 1-beta-D-Arabinofuranosylcytosine and Adriamycin were ineffective, and fluorouracil was only moderately effective against these colon tumors. Because of its good activity against human colon tumors and other human carcinomas and its water solubility, NSC 368390 (DuP-785) is being developed as a Phase 1 anticancer agent.