Synthesis of [H-3]- and [C-14]-labeled elagolix.

Gonadotropin-releasing hormone (GnRH) receptor antagonists are an important class of compounds designed to block the pituitary gland from synthesizing follicle-stimulating hormone and luteinizing hormone for the treatment of sex hormone dependent disorders. Elagolix (ABT-620) is currently approved for the treatment of pain associated with endometriosis and as a combination with estradiol and norethindrone acetate is approved for management of heavy menstrual bleeding due to uterine fibroids. In order to support the development of elagolix, we prepared [3 H]elagolix for preclinical metabolism studies and [14 C]elagolix for environmental risk assessment studies.

Iniparib nonselectively modifies cysteine-containing proteins in tumor cells and is not a bona fide PARP inhibitor.

PURPOSE: PARP inhibitors are being developed as therapeutic agents for cancer. More than six compounds have entered clinical trials. The majority of these compounds are ß-nicotinamide adenine dinucleotide (NAD(+))-competitive inhibitors. One exception is iniparib, which has been proposed to be a noncompetitive PARP inhibitor. In this study, we compare the biologic activities of two different structural classes of NAD(+)-competitive compounds with iniparib and its C-nitroso metabolite. EXPERIMENTAL DESIGN: Two chemical series of NAD(+)-competitive PARP inhibitors, iniparib and its C-nitroso metabolite, were analyzed in enzymatic and cellular assays. Viability assays were carried out in MDA-MB-436 (BRCA1-deficient) and DLD1(-/-) (BRCA2-deficient) cells together with BRCA-proficient MDA-MB-231 and DLD1(+/+) cells. Capan-1 and B16F10 xenograft models were used to compare iniparib and veliparib in vivo. Mass spectrometry and the (3)H-labeling method were used to monitor the covalent modification of proteins. RESULTS: All NAD(+)-competitive inhibitors show robust activity in a PARP cellular assay, strongly potentiate the activity of temozolomide, and elicit robust cell killing in BRCA-deficient tumor cells in vitro and in vivo. Cell killing was associated with an induction of DNA damage. In contrast, neither iniparib nor its C-nitroso metabolite inhibited PARP enzymatic or cellular activity, potentiated temozolomide, or showed activity in a BRCA-deficient setting. We find that the nitroso metabolite of iniparib forms adducts with many cysteine-containing proteins. Furthermore, both iniparib and its nitroso metabolite form protein adducts nonspecifically in tumor cells. CONCLUSIONS: Iniparib nonselectively modifies cysteine-containing proteins in tumor cells, and the primary mechanism of action for iniparib is likely not via inhibition of PARP activity.

Pharmacological MRI in awake rats predicts selective binding of alpha4beta2 nicotinic receptors.

Neuronal nicotinic receptors are the subject of intensive research focused on developing novel therapies for drug abuse, neurocognitive disorders, neurodegenerative diseases, and pain. In this study, we have applied pharmacological magnetic resonance imaging (phMRI) in awake rats to map functional brain responses to the selective alpha(4)beta(2) nicotinic receptor agonists, A-85380, and ABT-594. Moreover, we have validated our methods by comparison with autoradiography using [(3)H]-A-85380 and [(3)H]-ABT-594. Under awake conditions (no anesthesia during scanning) where rats were habituated to the imaging environment, both compounds increased regional cerebral blood volume (rCBV) across multiple brain regions that closely matched regional brain receptor distribution with the same tritiated compounds. In addition, regional ABT-594-induced rCBV changes under awake conditions were also derived and characterized using a pharmacological model. Area-under-curve and maximum rCBV changes in brain were found to be dose-related and region-specific, and corresponded well with the known preclinical behavioral profile of this drug. In contrast, under conditions of alpha-chloralose anesthesia where physiological variables were maintained within normal ranges, increases in rCBV induced by ABT-594 were primarily restricted to some cortical areas and did not agree well with autoradiography data. Our data demonstrate the utility of using phMRI in awake animals to characterize selective pharmacological action but also highlight an important confound (anesthesia) that is rarely considered in preclinical phMRI studies.

Detection of multiple H3 receptor affinity states utilizing [3H]A-349821, a novel, selective, non-imidazole histamine H3 receptor inverse agonist radioligand.

1. A-349821 is a selective histamine H3 receptor antagonist/inverse agonist. Herein, binding of the novel non-imidazole H3 receptor radioligand [3H]A-349821 to membranes expressing native or recombinant H3 receptors from rat or human sources was characterized and compared with the binding of the agonist [3H]N--methylhistamine ([3H]NMH). 2. [3H]A-349821 bound with high affinity and specificity to an apparent single class of saturable sites and recognized human H3 receptors with 10-fold higher affinity compared to rat H3 receptors. [3H]A-349821 detected larger populations of receptors compared to [3H]NMH. 3. Displacement of [3H]A-349821 binding by H3 receptor antagonists/inverse agonists was monophasic, suggesting recognition of a single binding site, while that of H3 receptor agonists was biphasic, suggesting recognition of both high- and low-affinity H3 receptor sites. 4. pKi values of high-affinity binding sites for H3 receptor competitors utilizing [3H]A-349821 were highly correlated with pKi values obtained with [3H]NalphaMH, consistent with labelling of H3 receptors by [3H]A-349821. 5. Unlike assays utilizing [3H]NMH, addition of GDP had no effect on saturation parameters measured with [3H]A-349821, while displacement of [3H]A-349821 binding by the H3 receptor agonist histamine was sensitive to GDP. 6. In conclusion, [3H]A-349821 labels interconvertible high- and low-affinity states of the H3 receptor, and displays improved selectivity over imidazole-containing H3 receptor antagonist radioligands. [3H]A-349821 competition studies showed significant differences in the proportions and potencies of high- and low-affinity sites across species, providing new information about the fundamental pharmacological nature of H3 receptors.

Thrombospondin-1 mimetic peptide inhibitors of angiogenesis and tumor growth: design, synthesis, and optimization of pharmacokinetics and biological activities.

The heptapeptide 1, NAc-Gly-Val-DIle-Thr-Arg-Ile-ArgNHEt, a structurally modified fragment derived from the second type-1 repeat of thrombospondin-1 (TSP-1), is known to possess antiangiogenic activity. However, therapeutic utility could not be demonstrated because this peptide has a very short half-life in rodents. To optimize the PD/PK profile of 1, we initiated a systematic SAR study. The initial structural modifications were performed at positions 5 and 7 of peptide 1 and at the N- and C-termini. Out of several hundred peptides synthesized, the nonapeptide 5 (ABT-526) emerged as a promising lead. ABT-526 inhibited VEGF-induced HMVEC cell migration and tube formation in the nanomolar range and increased apoptosis of HUAEC cells. ABT-526 showed acceptable PK in rodents, dog, and monkey. ABT-526, when incorporated in an angiogenic pellet implanted in the rat cornea at 10 microM, reduced neovascularization by 92%. Substitution of DalloIle in place of DIle in ABT-526 provided nonapeptide 6 (ABT-510), which was 30-fold less active than ABT-526 in the EC migration but 20-fold more active in the tube formation assay. In comparison to ABT-526, ABT-510 has increased water solubility and slower clearance in dog and monkey. Radiolabeled ABT-510 demonstrated saturable binding to HMVEC cells at 0.02-20 nM concentrations and was displaceable by TSP-1. ABT-510 and ABT-526 were shown to significantly increase apoptosis of HUAEC cells. ABT-510 was effective in blocking neovascularization in the mouse Matrigel plug model and inhibited tumor growth in the mouse Lewis lung carcinoma model. Previous studies had shown that ABT-510 was effective in inhibiting the outgrowth of murine melanoma metastases in syngeneic mice and in blocking the growth of human bladder carcinoma implanted in nude mice. It had been also shown that ABT-510 could regress tumor lesions in pet dogs or cause unexpected stabilization of the disease in advanced canine cancer. ABT-526 and ABT-510 are the first compounds in the class of potent inhibitors of angiogenesis that mimic the antiangiogenic function of TSP-1. ABT-510 is currently in phase II clinical studies.

[3H] A-369508 ([2-[4-(2-cyanophenyl)-1-piperazinyl]-N-(3-methylphenyl) acetamide): an agonist radioligand selective for the dopamine D4 receptor.

Tritiation of the dopamine D(4) receptor selective agonist A-369508 ([2-[4-(2-cyanophenyl)-1-piperazinyl]-N-(3-methylphenyl) acetamide) has provided a radioligand for the characterization of dopamine D(4) receptors. [(3)H] A-369508 binds with high affinity to the major human dopamine D(4) receptor variants D(4.2), D(4.4) and D(4.7) (K(d)=1.7, 4, and 1.2 nM, respectively). It also binds to the rat dopamine D(4) receptor, (K(d)=4.4 nM), implying similar binding affinity across human and rat receptors. A-369508 shows >400-fold selectivity over D(2L), >350-fold selectivity over 5-HT(1A) and >700-1,000-fold selectivity over all other receptors tested. Agonist activity determined by inhibition of forskolin-induced cAMP in Chinese hamster ovary cells transfected with the human dopamine D(4.4) receptor (EC(50)=7.5 nM, intrinsic activity=0.71) indicates that A-369508 is a potent agonist at the human dopamine D(4) receptor. Similar data was observed in other functional assays. [(3)H] A-369508 binds to a single, high affinity site on membranes containing the human dopamine D(4.4) receptor. When compared to the D(2)-like antagonist [(3)H] spiperone, competition binding for agonists like dopamine and apomorphine were 2-10-fold more potent with [(3)H] A-369508, while the antagonists clozapine, haloperidol and L-745870 bind with similar affinity to both ligands. Binding to rat brain regions demonstrated that the most abundant area was cerebral cortex (51.2 fmol/mg protein) followed by hypothalamus, hippocampus, striatum and cerebellum. [(3)H] A-369508 is a useful tool to define the localization and physiological role of dopamine D(4) receptors in central nervous system and can facilitate measuring accurate affinities (K(i)) for structure/activity relationship studies designed to identify dopamine D(4) receptor selective agonists.