PD-0332991, a potent and selective inhibitor of cyclin-dependent kinase 4/6, demonstrates inhibition of proliferation in renal cell carcinoma at nanomolar concentrations and molecular markers predict for sensitivity.

BACKGROUND: PD-0332991 is an inhibitor of cyclin-dependent kinases (CDK) 4 and 6, and was evaluated to determine its anti-proliferative effects in 25 renal cell carcinoma (RCC) cell lines. MATERIALS AND METHODS: Half-maximal inhibitory concentrations (IC50) of PD-0332991 were determined with cell line proliferation assays, as were its effects on the cell cycle, apoptosis, and retinoblastoma (RB) phosphorylation. Molecular markers for response prediction, including p16, p15, cyclin D1 (CCND1), cyclin E1 (CCNE1), E2F transcription factor 1 (E2F1), RB, CDK4 and CDK6, were studied using array comparative genomic hybridization (CGH) and gene expression. RESULTS: IC50 values for PD-0332991 ranged from 25.0 nM to 700 nM, and the agent demonstrated G0/G1 cell-cycle arrest, induction of late apoptosis, and blockade of RB phosphorylation. Through genotype and expression data p16, p15 and E2F1 were identified as having significant association between loss and sensitivity to PD-0332991: p16 (p=0.021), p15 (p=0.047), and E2F1 (p=0.041). CONCLUSION: PD-0332991 has antiproliferative activity in RCC cell lines, and molecular markers predict for sensitivity to this agent.

First report of a de novo 18q11.2 microdeletion including GATA6 associated with complex congenital heart disease and renal abnormalities.

Deletions of the long arm of chromosome 18 have been previously reported in many patients. Most cases involve the more distal regions of the long arm (18q21.1->qter). However, proximal interstitial deletions involving 18q11.2 are extremely rare. Here we report on a 14-month-old female with a 4.7 Mb (19,667,062-24,401,876 hg19) de novo interstitial deletion within chromosomal band 18q11.2, which includes GATA6 and 24 other RefSeq genes. The clinical features of our patient include complex congenital heart defects, a double outlet right ventricle, a subaortic ventricular septal defect, D-malposed great arteries, an atrial septal defect, a dysplastic aortic valve and patent ductus arteriosus. In addition, she had renal anomalies-a duplicated collecting system on the left and mild right hydronephrosis. These heart and renal defects are not reported in other patients with 18q proximal interstitial deletions. Heterozygous point mutations in GATA6, encoding for a zinc finger transcription factor, have been shown to cause congenital heart defects. Given the well-established biological role of GATA6 in cardiac development, a deletion of GATA6 is very likely responsible for our patient's complex congenital heart defects. This is the smallest and most proximal 18q11.2 deletion involving GATA6 that is associated with complex congenital heart disease and renal anomalies.

Atypical rearrangement involving 3'-IGH@ and a breakpoint at least 400 Kb upstream of an intact MYC in a CLL patient with an apparently balanced t(8;14)(q24.1;q32) and negative MYC expression.

The t(8;14)(q24.1;q32), the cytogenetic hallmark of Burkitt's lymphoma, is also found, but rarely, in cases of chronic lymphocytic leukemia (CLL). Such translocation typically results in a MYC-IGH@ fusion subsequently deregulating and overexpressing MYC on der 14q32. In CLL, atypical rearrangements resulting in its gain or loss, within or outside of IGH@ or MYC locus, have been reported, but their clinical significance remains uncertain. Herein, we report a 67 year-old male with complex cytogenetic findings of apparently balanced t(8;14) and unreported complex rearrangements of IGH@ and MYC loci. His clinical, morphological and immunophenotypic features were consistent with the diagnosis of CLL.Interphase FISH studies revealed deletions of 11q22.3 and 13q14.3, and an extra copy of IGH@, indicative of rearrangement. Karyotype analysis showed an apparently balanced t(8;14)(q24.1;q32). Sequential GPG-metaphase FISH studies revealed abnormal signal patterns: rearrangement of IGH break apart probe with the 5'-IGH@ on derivative 8q24.1 and the 3'-IGH@ retained on der 14q; absence of MYC break apart-specific signal on der 8q; and, the presence of unsplit 5'-MYC-3' break apart probe signals on der 14q. The breakpoint on 8q24.1 was found to be at least 400 Kb upstream of 5' of MYC. In addition, FISH studies revealed two abnormal clones; one with 13q14.3 deletion, and the other, with concurrent 11q deletion and atypical rearrangements. Chromosome microarray analysis (CMA) detected a 7.1 Mb deletion on 11q22.3-q23.3 including ATM, a finding consistent with FISH results. While no significant copy number gain or loss observed on chromosomes 8, 12 and 13, a 455 Kb microdeletion of uncertain clinical significance was detected on 14q32.33. Immunohistochemistry showed co-expression of CD19, CD5, and CD23, positive ZAP-70 expression and absence of MYC expression. Overall findings reveal an apparently balanced t(8;14) and atypical complex rearrangements involving 3'-IGH@ and a breakpoint at least 400 Kb upstream of MYC, resulting in the relocation of the intact 5'-MYC-3' from der 8q, and apposition to 3'-IGH@ at der 14q. This case report provides unique and additional cytogenetic data that may be of clinical significance in such a rare finding in CLL. It also highlights the utility of conventional and sequential metaphase FISH in understanding complex chromosome anomalies and their association with other clinical findings in patients with CLL. To the best of our knowledge, this is the first CLL reported case with such an atypical rearrangement in a patient with a negative MYC expression.

Comparison of mibefradil and derivative NNC 55-0396 effects on behavior, cytochrome P450 activity, and tremor in mouse models of essential tremor.

NNC 55-0396 [(1S,2S)-2-(2-(N-[(3-benzimidazol-2-yl)propyl]-N-methylamino)ethyl)-6-fluoro-1,2, 3,4-tetrahydro-1-isopropyl-2-naphtyl cyclopropanecarboxylate dihydrochloride], is a mibefradil derivative that retains potent in vitro T-type calcium channel antagonist efficacy. We compared the two compounds for behavioral toxicity, effects on cytochrome P450 activity, and efficacy against tremor in the γ-aminobutyric acid type A (GABAA) receptor subunit α1-null mouse, and the harmaline tremor model of essential tremor in wild-type mice. NNC 55-0396 was better tolerated than mibefradil in the horizontal wire test of sedation/motor function, with 3/6 failing at 300 and 30mg/kg respectively. To assess for a potential interaction with harmaline, mice were given the drugs, followed by harmaline or vehicle, and tested 30min later in the inverted wire grid test. Mibefradil exacerbated, whereas NNC 55-0396 ameliorated harmaline-induced test deficits. In mouse liver microsomes, NNC 55-0396 was a less potent inhibitor of harmaline O-demethylation than mibefradil (Ki: 0.95 and 0.29µM respectively), and also less potent at inhibiting testosterone 6-ß-hydroxylation (Ki: 0.71 and 0.12µM respectively). In the GABAA α1-null model, NNC 55-0396 but not mibefradil, (each at 20mg/kg), suppressed tremor while NNC 55-0396 at 12.5mg/kg suppressed harmaline-induced tremor by half by 20-100min, whereas mibefradil at the same dose did not significantly affect tremor. In contrast to mibefradil, NNC 55-0396 is well tolerated and suppresses tremor, and exerts less cytochrome P450 inhibition. These results suggest potential clinical utility for NNC 55-0396 or similar derivatives as a T-type calcium antagonist.

Fatty acid hydroperoxides support cytochrome P450 2S1-mediated bioactivation of benzo[a]pyrene-7,8-dihydrodiol.

In the accompanying report (p. 1031), we showed that a novel dioxin-inducible cytochrome P450, CYP2S1, efficiently metabolizes benzo[a]pyrene-trans-7,8-dihydrodiol (BaP-7,8-diol) into the highly mutagenic and carcinogenic benzo[a]pyrene-r-7,t-8-dihydrodiol-t-9,10-epoxide (BaP-diol-t-epoxide), using cumene hydroperoxide in lieu of NADPH/O(2). Lipid hydroperoxide-supported P450 oxidation has been reported in several cases. However, it has not yet been described for the bioactivation of BaP-7,8-diol. In this report, we demonstrate that CYP2S1 can use various fatty acid hydroperoxides to support epoxidation of BaP-7,8-diol at a much higher rate than with cumene hydroperoxide. Kinetic analyses with several fatty acid hydroperoxides revealed that 13S-hydroperoxy-9Z,11E-octadecadienoic acid (13-HpODE) was the most potent oxidant tested (K(m), 3.4 +/- 0.8 microM; turnover, 4.51 +/- 0.13 min(-1)), followed by 12S-hydroperoxy-5Z,8Z,10E,14Z-eicosatetraenoic acid (K(m), 2.8 +/- 0.7 microM; turnover, 3.7 +/- 0.1 min(-1)), 5S-hydroperoxy-6E,8Z,11Z,14Z-eicosatetraenoic acid (K(m), 2.7 +/- 0.8 microM; turnover, 3.69 +/- 0.09 min(-1)), and 15S-hydroperoxy-5Z,8Z,10E,14Z-eicosatetraenoic acid (K(m), 11.6 +/- 0.3 microM; turnover, 0.578 +/- 0.030 min(-1)). The antioxidant butylated hydroxyanisole inhibited CYP2S1-catalyzed epoxidation by 100%, suggesting that epoxidation proceeds by a free radical mechanism. Other cytochromes P450, including CYP1A1, CYP1B1, CYP1A2, and CYP3A4, were also able to epoxidize BaP-7,8-diol using various fatty acid hydroperoxides, although at slower rates than CYP2S1. The cytotoxicity of BaP-7,8-diol significantly increased in mammalian cells overexpressing CYP2S1, and BaP-diol-t-epoxide formation in these cells also increased in the presence of 13-HpODE. Together, these results suggest that fatty acid hydroperoxides can serve as physiological cofactors in supporting in vivo CYP2S1-catalyzed oxidation of BaP-7,8-diol, and that fatty acid hydroperoxides and CYP2S1 may play important roles in benzo[a]pyrene-induced carcinogenesis.

Functional characterization of human cytochrome P450 2S1 using a synthetic gene-expressed protein in Escherichia coli.

Human cytochrome P450 2S1 was recently identified and shown to be inducible by 2,3,7,8-tetrachlorodibenzo-p-dioxin and hypoxia. It is highly expressed in epithelial cells of tissues that are exposed to the environment and in many tumors of epithelial origin. The biological function of CYP2S1 has not yet been determined, although its possible role in carcinogen metabolism has been suggested. In this report, we investigated its ability to metabolize carcinogens. To obtain a large quantity of active enzyme for substrate screening, we overexpressed CYP2S1 in Escherichia coli (200 nM culture), using a synthetic gene approach. High-level expression allowed us to achieve purification of CYP2S1 with high specific content and purity (16 nmol/mg). Despite high-level expression, we found that CYP2S1 was not readily reduced by cytochrome P450 reductase, and thus no activity was found using NADPH. However, the oxidative activity of CYP2S1 was supported by cumene hydroperoxide or H(2)O(2), such that CYP2S1 oxidized many important environmental carcinogens, including benzo[a]pyrene, 9,10-dihydro-benzo[a]pyrene, 7,12-dimethylbenz[a]anthracene, benzo[a]pyrene-7,8-dihydrodiol, aflatoxin B1, naphthalene, and styrene, with high turnover. Most substrates tested were converted to detoxification products, except in the case of benzo[a]pyrene-7,8-dihydrodiol, which was converted into the very potent carcinogenic metabolite 7,8-dihydrodiol-trans-9,10-epoxide at a relatively efficient rate (K(m) = 12.4 +/- 2 microM, turnover = 2.3 min(-1)). This metabolite formation was also supported both in vitro and in vivo by fatty acid hydroperoxides described in the accompanying report (p. 1044). Together, these data indicate that CYP2S1 contributes to the metabolism of environmental carcinogens via an NADPH independent activity.

The mibefradil derivative NNC55-0396, a specific T-type calcium channel antagonist, exhibits less CYP3A4 inhibition than mibefradil.

A novel mibefradil derivative, NNC55-0396, designed to be hydrolysis-resistant, was shown to be a selective T-type Ca(2+) channel inhibitor without L-type Ca(2+) channel efficacy. However, its effects on cytochromes P450 (P450s) have not previously been examined. We investigated the inhibitory effects of NNC55-0396 toward seven major recombinant human P450s--CYP3A4, CYP2D6, CYP1A2, CYP2C9, CYP2C8, CYPC19, and CYP2E1--and compared its effects with those of mibefradil and its hydrolyzed metabolite, Ro40-5966. Our results show that CYP3A4 and CYP2D6 are the two P450s most affected by mibefradil, Ro40-5966, and NNC55-0396. Mibefradil (IC(50) = 33 +/- 3 nM, K(i) = 23 +/- 0.5 nM) and Ro40-5966 (IC(50) = 30 +/- 7.8 nM, K(i) = 21 +/- 2.8 nM) have a 9- to 10-fold greater inhibitory activity toward recombinant CYP3A4 benzyloxy-4-trifluoromethylcoumarin-O-debenzylation activity than NNC55-0396 (IC(50) = 300 +/- 30 nM, K(i) = 210 +/- 6 nM). More dramatically, mibefradil (IC(50) = 566 +/- 71 nM, K(i) = 202 +/- 39 nM) shows 19-fold higher inhibition of CYP3A-associated testosterone 6beta-hydroxylase activity in human liver microsomes compared with NNC55-0396 (IC(50) = 11 +/- 1.1 microM, K(i) = 3.9 +/- 0.4 microM). Loss of testosterone 6beta-hydroxylase activity by recombinant CYP3A4 was shown to be time- and concentration-dependent with both compounds. However, NNC55-0396 (K(I) = 3.87 microM, K(inact) = 0.061/min) is a much less potent mechanism-based inhibitor than mibefradil (K(I) = 83 nM, K(inact) = 0.048/min). In contrast, NNC55-0396 (IC(50) = 29 +/- 1.2 nM, K(i) = 2.8 +/- 0.3 nM) and Ro40-5966 (IC(50) = 46 +/- 11 nM, K(i) = 4.5 +/- 0.02 nM) have a 3- to 4-fold greater inhibitory activity toward recombinant CYP2D6 than mibefradil (IC(50) = 129 +/- 21 nM, K(i) = 12.7 +/- 0.9 nM). Our results suggest that NNC55-0396 could be a more favorable T-type Ca(2+) antagonist than its parent compound, mibefradil, which was withdrawn from the market because of strong inhibition of CYP3A4.