Beatriz Kanterewicz

Glutamate-induced neuron death requires mitochondrial calcium uptake.

We have investigated the role of mitochondrial calcium buffering in excitotoxic cell death. Glutamate acts at NMDA receptors in cultured rat forebrain neurons to increase the intracellular free calcium concentration. Although concurrent inhibition of mitochondrial calcium uptake substantially enhanced this cytoplasmic calcium increase, it significantly reduced glutamate-stimulated neuronal cell death. Mitochondrial inhibition did not affect nitric oxide production or MAP kinase phosphorylation, which have been proposed to mediate excitotoxicity. These results indicate that very high levels of cytoplasmic calcium are not necessarily toxic to forebrain neurons, and that potential-driven uptake of calcium into mitochondria is required to trigger NMDA-receptor-stimulated neuronal death.

Synaptic localization of a functional NADPH oxidase in the mouse hippocampus.

Superoxide has been shown to be critical for hippocampal long-term potentiation (LTP) and hippocampus-dependent memory function. A possible source for the generation of superoxide during these processes is NADPH oxidase. The active oxidase consists of two membrane proteins, gp91phox and p22phox, and four cytosolic proteins, p40phox, p47phox, p67phox, and Rac. Upon stimulation, the cytosolic proteins translocate to the membrane to form a complex with the membrane components, which results in production of superoxide. Here, we determined the presence, localization, and functionality of a NADPH oxidase in mouse hippocampus by examining the NADPH oxidase proteins as well as the production of superoxide. All of the NADPH oxidase proteins were present in hippocampal homogenates and enriched in synaptoneurosome preparations. Immunocytochemical analysis of cultured hippocampal neurons indicated that all NADPH oxidase proteins were localized in neuronal cell bodies as well as dendrites. Furthermore, double labeling analysis using antibodies to p67phox and the presynaptic marker synaptophysin suggest a close association of the NADPH oxidase subunits with synaptic sites. Finally, stimulation of hippocampal slices with phorbol esters triggered translocation of the cytoplasmic NADPH oxidase proteins to the membrane and an increase in superoxide production that was blocked by inhibitors of NADPH oxidase. Taken together, our data suggest that NADPH oxidase is present in mouse hippocampus and might be the source of superoxide production required for LTP and memory function.

Regulation of Endogenous Gene Expression in Human Non–Small Cell Lung Cancer Cells by Estrogen Receptor Ligands

Estrogen receptor (ER) agonists and antagonists elicit distinct responses in non-small cell lung cancer (NSCLC) cells. To determine how such responses are generated, the expression of ERalpha, ERbeta, and ER coregulators in human lung fibroblasts and human NSCLC cell lines was evaluated by immunoblot. Ligand-dependent estrogenic responses in NSCLC cells are probably generated via ERbeta and the p160 coactivator GRIP1/TIF2, because expression of these proteins was detected, but not full-length ERalpha or the p160 coactivator SRC-1. ERbeta and GRIP1/TIF2 are shown to interact in vitro in a ligand-dependent manner and thus may form functional transcription complexes in NSCLC cells. Furthermore, the capacity of ER ligands to regulate gene expression in NSCLC cells was explored using gene miniarrays. Expression profiles were examined after treatment with ER agonist 17-beta-estradiol (E2), the pure ER antagonist ICI 182,780 (fulvestrant, Faslodex), or epidermal growth factor, which served as a positive control for an alternative growth stimulus. E-cadherin and inhibitor of differentiation 2 were differentially regulated by E2 versus ICI 182,780 in 201T and 273T NSCLC cell lines. Epidermal growth factor also stimulated proliferation of these cells but had no effect on expression of E-cadherin and inhibitor of differentiation 2, suggesting they are specific targets of ER signaling. These data show that NSCLC cells respond to estrogens/antiestrogens by altering endogenous gene expression and support a model in which ICI 182,780 reduces proliferation of NSCLC cells via its ability to disrupt ER signaling. ICI 182,780 may therefore have therapeutic benefit in NSCLC.

Stimulation of p42 and p44 mitogen-activated protein kinases by reactive oxygen species and nitric oxide in hippocampus

Abstract: Reactive oxygen species (ROS) have been suggested to act as cellular messengers that mediate signal transduction cascades in various cell types. However, little is known about their role in this capacity in the nervous system. We have begun to investigate the role of ROS, and that of nitric oxide (NO), in mediating mitogen‐activated protein kinase (MAPK) signaling in rat hippocampal slices. Our studies have revealed that direct exposure of hippocampal slices to hydrogen peroxide, xanthine/xanthine oxidase (a superoxide‐generating system), sodium nitroprusside (an NO donor compound), S‐nitroso‐N‐acetylpenicillamine (an NO donor compound), or 3‐morpholinosydnonimine (a compound that produces NO and superoxide) results in an enhancement in tyrosine phosphorylation of several proteins, including proteins with apparent molecular masses of 42 and 44 kDa. We investigated the possibility that these proteins correspond to the active forms of p42 MAPK and p44 MAPK. Hippocampal slices exposed to various ROS and NO donors resulted in increases in levels of the active forms of both p42 MAPK and p44 MAPK. The ROS‐ and NO‐enhanced tyrosine phosphorylation and activation of p42 MAPK and p44 MAPK were inhibited by pretreatment with the antioxidant N‐acetyl‐l‐cysteine. Our observations indicate that ROS and NO can mediate protein tyrosine phosphorylation and MAPK signaling in the hippocampus via a redox‐sensitive mechanism and suggest a potential cellular mechanism for their effects in the nervous system.

CYP24, the enzyme that catabolizes the antiproliferative agent vitamin D, is increased in lung cancer

1α,25‐Dihydroxyvitamin D3 (1,25D3) displays potent antiproliferative activity in a variety of tumor model systems and is currently under investigation in clinical trials in cancer. Studies were initiated to explore its potential in nonsmall cell lung cancer (NSCLC), as effective approaches to the treatment of that disease are needed. In evaluating factors that may affect activity in NSCLC, the authors found that CYP24 (25‐hydroxyvitamin D3‐24‐hydroxylase), the enzyme that catabolizes 1,25D3, is frequently expressed in NSCLC cell lines but not in the nontumorigenic bronchial epithelial cell line, Beas2B. CYP24 expression by RT‐PCR was also detected in 10/18 primary lung tumors but in only 1/11 normal lung tissue specimens. Tumor‐specific CYP24 upregulation was confirmed at the protein level via immunoblot analysis of patient‐matched normal lung tissue and lung tumor extracts. Enzymatically active CYP24 is expected to desensitize NSCLC cells to 1,25D3. The authors therefore implemented a high performance liquid chromatography‐tandem mass spectrometry (HPLC‐MS/MS) assay for 1,25D3 and its CYP24‐generated metabolites to determine whether NSCLC cells express active enzyme. Analysis of NSCLC cell cultures revealed time‐dependent loss of 1,25D3 coincident with the appearance of CYP24‐generated metabolites. MK‐24(S)‐S(O)(NH)‐Ph‐1, a specific inhibitor of CYP24, slowed the loss of 1,25D3 and increased 1,25D3 half‐life. Furthermore, combination of 1,25D3 with MK‐24(S)‐S(O)(NH)‐Ph‐1 resulted in a significant decrease in the concentration of 1,25D3 required to achieve maximum growth inhibition in NSCLC cells. These data suggest that increased CYP24 expression in lung tumors restricts 1,25D3 activity and support the preclinical evaluation of CYP24 inhibitors for lung cancer treatment.

Vorinostat increases carboplatin and paclitaxel activity in non-small cell lung cancer cells

We observed a 53% response rate in non‐small cell lung cancer (NSCLC) patients treated with vorinostat plus paclitaxel/carboplatin in a Phase I trial. Studies were undertaken to investigate the mechanism (s) underlying this activity. Growth inhibition was assessed in NSCLC cells by MTT assay after 72 hr of continuous drug exposure. Vorinostat (1 μM) inhibited growth by: 17% ± 7% in A549, 28% ± 6% in 128‐88T, 39% ± 8% in Calu1 and 41% ± 7% in 201T cells. Vorinostat addition to carboplatin or paclitaxel led to significantly greater growth inhibition than chemotherapy alone in all 4 cell lines. Vorinostat (1 μM) synergistically increased the growth inhibitory effects of carboplatin/paclitaxel in 128‐88T cells. When colony formation was measured after drug withdrawal, vorinostat significantly increased the effects of carboplatin but not paclitaxel. The % colony formation was control 100%; 1 μM vorinostat, 83% ± 10%; 5 μM carboplatin, 41% ± 11%; carboplatin/vorinostat, 8% ± 4%; 2 nM paclitaxel, 53% ± 11%; paclitaxel/vorinostat, 46% ± 21%. In A549 and 128‐88T, vorinostat potentiated carboplatin induction of gamma‐H2AX (a DNA damage marker) and increased α‐tubulin acetylation (a marker for stabilized mictrotubules). In A549, combination of vorinostat with paclitaxel resulted in a synergistic increase in α‐tubulin acetylation, which reversed upon drug washout. We conclude that vorinostat interacts favorably with carboplatin and paclitaxel in NSCLC cells, which may explain the provocative response observed in our clinical trial. This likely involves a vorinostat‐mediated irreversible increase in DNA damage in the case of carboplatin and a reversible increase in microtubule stability in the case of paclitaxel.

CYP24 inhibition preserves 1α,25-dihydroxyvitamin D3 anti-proliferative signaling in lung cancer cells

Human lung tumors aberrantly express the 1α,25-dihydroxyvitamin D(3) (1,25(OH)(2)D(3))-catabolizing enzyme, CYP24. We hypothesized that CYP24 reduces 1,25(OH)(2)D(3)-mediated transcription and allows lung cancer cells to escape its growth-inhibitory action. To test this, H292 lung cancer cells and the CYP24-selective inhibitor CTA091 were utilized. In H292 cells, CTA091 reduces 1,25(OH)(2)D(3) catabolism, significantly increases 1,25(OH)(2)D(3)-mediated growth inhibition, and increases 1,25(OH)(2)D(3) effects on induced and repressed genes in gene expression profiling studies. Pathway mapping of repressed genes uncovered cell cycle as a predominant 1,25(OH)(2)D(3) target. In H292 cells, 1,25(OH)(2)D(3) significantly decreases cyclin E2 levels and induces G(0)/G(1) arrest. A broader set of cyclins is down-regulated when 1,25(OH)(2)D(3) is combined with CTA091, and cell cycle arrest further increases. Effects of CTA091 on 1,25(OH)(2)D(3) signaling are vitamin D receptor-dependent. These data provide evidence that CYP24 limits 1,25(OH)(2)D(3) anti-proliferative signaling in cancer cells, and suggest that CTA091 may be beneficial in preserving 1,25(OH)(2)D(3) action in lung cancer.

A local effect of CYP24 inhibition on lung tumor xenograft exposure to 1,25-dihydroxyvitamin D3 is revealed using a novel LC–MS/MS assay

The vitamin D(3) catabolizing enzyme, CYP24, is frequently over-expressed in tumors, where it may support proliferation by eliminating the growth suppressive effects of 1,25-dihydroxyvitamin D(3) (1,25(OH)(2)D(3)). However, the impact of CYP24 expression in tumors or consequence of CYP24 inhibition on tumor levels of 1,25(OH)(2)D(3)in vivo has not been studied due to the lack of a suitable quantitative method. To address this need, an LC-MS/MS assay that permits absolute quantitation of 1,25(OH)(2)D(3) in plasma and tumor was developed. We applied this assay to the H292 lung tumor xenograft model: H292 cells eliminate 1,25(OH)(2)D(3) by a CYP24-dependent process in vitro, and 1,25(OH)(2)D(3) rapidly induces CYP24 expression in H292 cells in vivo. In tumor-bearing mice, plasma and tumor concentrations of 1,25(OH)(2)D(3) reached a maximum of 21.6 and 1.70ng/mL, respectively, following intraperitoneal dosing (20μg/kg 1,25(OH)(2)D(3)). When co-administered with the CYP24 selective inhibitor CTA091 (250μg/kg), 1,25(OH)(2)D(3) plasma levels increased 1.6-fold, and tumor levels increased 2.6-fold. The tumor/plasma ratio of 1,25(OH)(2)D(3) AUC was increased 1.7-fold by CTA091, suggesting that the inhibitor increased the tumor concentrations of 1,25(OH)(2)D(3) independent of its effects on plasma disposition. Compartmental modeling of 1,25(OH)(2)D(3) concentration versus time data confirmed that: 1,25(OH)(2)D(3) was eliminated from plasma and tumor; CTA091 reduced the elimination from both compartments; and that the effect of CTA091 on tumor exposure was greater than its effect on plasma. These results provide evidence that CYP24-expressing lung tumors eliminate 1,25(OH)(2)D(3) by a CYP24-dependent process in vivo and that CTA091 administration represents a feasible approach to increase tumor exposure to 1,25(OH)(2)D(3).

Breast cancer-derived M543V mutation in helix 12 of estrogen receptor α inverts response to estrogen and SERMs

We have isolated from human breast cancers several mutations in the Helix 12 component of activation function 2 (AF-2) in the estrogen receptor alpha (ERα). We used a novel approach to detect changes in the hormone-binding domain of ERα, based on the evidence that antiestrogens, such as 4-hydroxytamoxifen (ZOHT) and ICI 182,780, block the function of ERα by binding and folding the AF-2 transcriptional domain in a way that inhibits its association with coactivator proteins. We have identified a Helix 12 mutation, M543V, which leads to greater ERα transcription with ZOHT and other antiestrogens (including 1,1-dichloro-2,2,3-triarylcyclopropanes, DTACs) than with 17-β estradiol (E2). We also found an independent mutation at the same position, M543I, which did not show this inverted ligand phenotype. In comparison to further Helix 12 mutations made in vitro, it appears that relative hydrophobicity of the amino acid side chains on the inner face of Helix 12 is key to maintaining the transcriptionally active, agonist conformation with bound E2. This active conformation can be induced, resulting in increased transcription, by adding excess p160 coactivator AIB1 in transcriptional assays with E2-bound receptors, while the ZOHT-bound receptors were not further activated by AIB1. Other experiments show that the cross talk between ERα and AP-1 protein from AP-1-binding sites is not dependent on Helix 12 integrity. We show that two alleles containing a proline substitution in Helix 12 that inactivate AF-2 function of ERα at EREs have little negative effect on function through AP-1 elements, supporting a prominent role for the N-terminal AF-1 of ERα in AP-1/ERα transcriptional cross talk.

Preclinical Evidence for Combined Use of Aromatase Inhibitors and NSAIDs as Preventive Agents of Tobacco-Induced Lung Cancer

Introduction: A hormonal role in NSCLC development is well documented. We previously showed that the aromatase inhibitor (AI) anastrozole decreased development of tobacco carcinogen‐induced lung tumors in a murine lung cancer prevention model and that aromatase and estrogen receptor were expressed in pulmonary inflammatory cells. Methods: We utilized a tobacco carcinogen–induced lung tumor mouse model by treatment with 4‐(methylnitrosoamino)‐1‐(3‐pyridyl)‐1‐butanone (NNK), to determine whether an AI combined with nonsteroidal anti‐inflammatory drugs results in greater lung tumor prevention effects compared to single‐agent treatment. Results: Combination of anastrozole (0.1 mg/kg/d) with aspirin (25 mg/kg/d) after NNK exposure resulted in significantly fewer and smaller lung tumors than did single‐agent treatments and was accompanied by maximum decreases in circulating &bgr;‐estradiol (E2) and interleukin‐6, tumor‐infiltrating macrophages, and tumoral Ki67, phospho–mitogen‐activated protein kinase, phospho–signal transducer and activator of transcription 3, and interleukin‐17A expression. Preneoplasia arising after combination treatment showed the lowest Sox‐2 expression, suggesting an inhibitory effect on proliferative capacity in the airways by blocking both E2 and inflammation. Anastrozole combined with ibuprofen instead of aspirin also showed enhanced antitumor effects. Moreover, male mice treated with NNK that received E2 in their drinking water showed greater levels of pulmonary macrophages and inflammatory markers than did the control, confirming an E2 effect on inflammation in the microenvironment. Conclusions: Our results suggest a benefit to joint targeting of the estrogen and inflammatory pathways for NSCLC prevention. Combining AIs with nonsteroidal anti‐inflammatory drugs reduces circulating E2, proinflammatory cytokines, and macrophage recruitment in the lung microenvironment after tobacco exposure. This strategy could be particularly effective in women who have underlying pulmonary inflammatory diseases.