A nearby transiting rocky exoplanet that is suitable for atmospheric investigation.

Spectroscopy of transiting exoplanets can be used to investigate their atmospheric properties and habitability. Combining radial velocity (RV) and transit data provides additional information on exoplanet physical properties. We detect a transiting rocky planet with an orbital period of 1.467 days around the nearby red dwarf star Gliese 486. The planet Gliese 486 b is 2.81 Earth masses and 1.31 Earth radii, with uncertainties of 5%, as determined from RV data and photometric light curves. The host star is at a distance of ~8.1 parsecs, has a J-band magnitude of ~7.2, and is observable from both hemispheres of Earth. On the basis of these properties and the planet's short orbital period and high equilibrium temperature, we show that this terrestrial planet is suitable for emission and transit spectroscopy.

Reversal of a novel multidrug resistance mechanism in human colon carcinoma cells by fumitremorgin C.

We selected a human colon carcinoma cell line in increasing concentrations of mitoxantrone to obtain a resistant subline, S1-M1-3.2, with the following characteristics: profound resistance to mitoxantrone; significant cross-resistance to doxorubicin, bisantrene, and topotecan; and very low levels of resistance to Taxol, vinblastine, colchicine, and camptothecin. This multidrug resistance (MDR) phenotype, which was not reversed by verapamil or another potent P-glycoprotein (Pgp) inhibitor, CL 329,753, was dependent, in part, upon an energy-dependent drug efflux mechanism. Pgp and the multidrug resistance protein (MRP) were not elevated in the resistant cells relative to the drug-sensitive parent, suggesting that resistance was mediated by a novel pathway of drug transport. A cell-based screen with S1-M1-3.2 cells was used to identify agents capable of circumventing this non-Pgp, non-MRP MDR. One of the active agents identified was a mycotoxin, fumitremorgin C. This molecule was extremely effective in reversing resistance to mitoxantrone, doxorubicin, and topotecan in multidrug-selected cell lines showing this novel phenotype. Reversal of resistance was associated with an increase in drug accumulation. The compound did not reverse drug resistance in cells with elevated expression of Pgp or MRP. We suggest that fumitremorgin C is a highly selective chemosensitizing agent for the resistance pathway we have identified and can be used as a specific pharmacological probe to distinguish between the diverse resistance mechanisms that occur in the MDR cell.

A new antiestrogen, 2-(4-hydroxy-phenyl)-3-methyl-1-[4-(2-piperidin-1-yl-ethoxy)-benzyl]-1H-indol-5-ol hydrochloride (ERA-923), inhibits the growth of tamoxifen-sensitive and -resistant tumors and is devoid of uterotropic effects in mice and rats.

PURPOSE: Tamoxifen is an antiestrogen used in women who have estrogen receptor (ER)-alpha-positive breast cancer. Unfortunately, resistance to tamoxifen is common in women with metastatic disease and side effects, including increased risk of endometrial cancer, exist. Here we describe the activity of a new selective ER modulator, ERA-923, in preclinical models focused on these limitations. EXPERIMENTAL DESIGN: The ability of ERA-923, 4-OH tamoxifen, or raloxifene to inhibit estrogen-stimulated growth was evaluated in cell-based and xenograft assays with tumor cells that are sensitive or resistant to tamoxifen. Uterine effects of selective ER modulators were compared in rodents. RESULTS: ERA-923 potently inhibits estrogen binding to ER-alpha (IC(50), 14 nM). In ER-alpha-positive human MCF-7 breast carcinoma cells, ERA-923 inhibits estrogen-stimulated growth (IC(50), 0.2 nM) associated with cytostasis. In vitro, a MCF-7 variant with inherent resistance to tamoxifen (10-fold) or 4-OH tamoxifen (>1000-fold) retains complete sensitivity to ERA-923. Partial sensitivity to ERA-923 exists in MCF-7 variants that have acquired profound tamoxifen resistance. In tumor-bearing animals, ERA-923 (10 mg/kg/day given p.o.) inhibits 17beta-estradiol-stimulated growth in human tumors derived from MCF-7, EnCa-101 endometrial, or BG-1 ovarian carcinoma cells, including a MCF-7-variant that is inherently resistant to tamoxifen. Raloxifene is inactive in the MCF-7 xenograft model. Unlike tamoxifen, droloxifene, or raloxifene, ERA-923 is not uterotropic in immature rats or ovariectomized mice. Consistent with this, tamoxifen, but not ERA-923, stimulates the growth of EnCa-101 tumors. CONCLUSIONS: In preclinical models, ERA-923 has an improved efficacy and safety compared with tamoxifen. Clinical trials with ERA-923 are in progress.

P-glycoprotein mediates profound resistance to bisantrene.

Bisantrene, mitoxantrone, and anthracyclines are anthracene derivatives that interact with DNA and are used for the treatment of cancers. The mechanisms of resistance to bisantrene are unknown. Here we show that cells that overexpress low levels of P-glycoprotein or are transfected with human MDR1 have approximately 10-fold greater resistance to bisantrene compared to vinblastine, doxorubicin, or colchicine. Furthermore, bisantrene can be used to select for high-level P-glycoprotein-mediated multiple drug resistance in a human colon carcinoma cell line, LS 174T, and the drug blocks photoaffinity labeling of P-glycoprotein. The data suggest that bisantrene is an excellent substrate for P-glycoprotein. These findings could influence subsequent clinical evaluation of bisantrene for the treatment of cancer.

alpha-(3,4-dimethyoxyphenyl)-3,4-dihydro-6,7-dimethoxy-alpha- [(4-methylphenyl)thio]-2(1H)-isoquinolineheptanenitrile (CL 329,753): a novel chemosensitizing agent for P-glycoprotein-mediated resistance with improved biological properties compared with verapamil and cyclosporine A.

Agents that inhibit P-glycoprotein may restore sensitivity to some antitumor drugs in cancer patients. Optimization of the specificity and potency of one class of chemosensitizing agents related to verapamil has led to the identification of alpha-(3,4-dimethyoxyphenyl)-3,4-dihydro-6, 7-dimethoxy-alpha-[(4-methylphenyl) thio]-2(1H)-isoquinolineheptanenitrile, designated CL 329,753. In vitro, 0.1 to 2.0 microM CL 329,753 restored sensitivity to drugs in the multidrug resistance (MDR) phenotype in cell lines that overexpress P-glycoprotein. CL 329,753 was greater than 10-fold more potent and efficacious than cyclosporine A or verapamil in vitro, particularly in cells that express high levels of P-glycoprotein. The enhanced activity of CL 329,753 may be related to its inability to be transported by P-glycoprotein, since low drug accumulation of cyclosporine or verapamil but not CL 329,753 was found in P-glycoprotein-containing cells, yet all three agents inhibited vinblastine binding to membranes containing P-glycoprotein and inhibited photoaffinity labeling of P-glycoprotein. In vivo, CL 329,753 resensitized drug-resistant tumors to vinblastine or doxorubicin in an ascitic or solid tumor model, respectively. No alteration in the plasma pharmacokinetic profile of doxorubicin by CL 329,753 has been found. Furthermore, the compound had 70-fold less calcium channel antagonistic activity compared with verapamil.

Functional evidence that transmembrane 12 and the loop between transmembrane 11 and 12 form part of the drug-binding domain in P-glycoprotein encoded by MDR1.

Human MDR1 encodes an ATP-binding cassette transporter, P-glycoprotein, that mediates multiple drug resistance (MDR) to antitumor agents. It has been previously shown that photoaffinity drug-labeling sites reside within, or near, the last transmembrane loop of each cassette within P-glycoprotein (transmembrane domains (TM) 5-6 and 11-12). A genetic approach was used to determine if the drug-labeling site in the second cassette contains functionally important amino acids. Since human MDR3 is 77% identical to MDR1 but does not mediate MDR, the region from TM10 to the C terminus of MDR1 was replaced with the corresponding sequences from MDR3. The resultant chimeric protein was expressed but not functional. By using progressively smaller replacements, we show that replacements limited to TM12 markedly impaired resistance to actinomycin D, vincristine, and doxorubicin, but not to colchicine. The phenotype was associated with an impaired ability to photoaffinity label the chimeric P-glycoprotein with [125I]iodoaryl azidoprazosin. In contrast, replacement of the loop between TM11 and 12 appears to create a more efficient drug pump for actinomycin D, colchicine, and doxorubicin, but not vincristine. These results suggest that, similar to voltage-gated ion channels, amino acids within and immediately N-terminal to the last transmembrane domain of P-glycoprotein compose part of the drug-binding pocket and are in close proximity to photoaffinity drug-labeling domains.