A novel missense mutation of ABCA1 in transmembrane alpha-helix in a Japanese patient with Tangier disease.

Tangier disease (TD) is a hereditary disorder characterized by the severe deficiency or absence of high-density lipoprotein cholesterol (HDL-C). TD is caused by mutations in the ATP-binding cassette transporter A1 (ABCA1) gene, most of which are located in the extracellular loops and nucleotide-binding domains. Here we describe the first case of TD carrying a missense mutation in a transmembrane alpha-helix of ABCA1. A 31-year-old Japanese woman had an extremely low level of HDL-C (1mg/dl) and yellowish tonsillar swelling, leading to the diagnosis of TD. The proband was homozygous for a point mutation of T4978C in exon 37, which results in the substitution of cysteine-1660 to arginine (C1660R) in the 8th transmembrane segment of ABCA1. Her parents, grandmother, and brother were found to be heterozygous for the same mutation. Both peripheral blood leukocytes from the patient and HEK293 cells transfected with T4978C-mutated ABCA1 normally expressed ABCA1 on the plasma membrane and had normal apolipoprotein A-I-binding ability. However, apolipoprotein A-I-mediated efflux of cholesterol and phospholipids was markedly diminished in HEK293 cells transfected with T4978C-mutated ABCA1. These results suggest that this mutant is normally translated and exists as a stable product with normal localization, yet is functionally defective. Cysteine-1660 appears to be a critical residue for cholesterol transport of ABCA1.

Schedule-dependent interactions between pemetrexed and cisplatin in human carcinoma cell lines in vitro.

The combination of pemetrexed and cisplatin shows good clinical activity against mesothelioma and lung cancer. In order to study the potential cellular basis for this, and provide leads as to how to optimize the combination, we studied the schedule-dependent cytotoxic effects of pemetrexed and cisplatin against four human cancer cell lines in vitro. Tumor cells were incubated with pemetrexed and cisplatin for 24 h at various schedules. The combination effects after 5 days were analyzed by the isobologram method. Both simultaneous exposure to pemetrexed and cisplatin for 24 h and sequential exposure to cisplatin for 24 h followed by pemetrexed for 24 h produced antagonistic effects in human lung cancer A549, breast cancer MCF7, and ovarian cancer PA1 cells and additive effects in colon cancer WiDr cells. Pemetrexed for 24 h followed by cisplatin for 24 h produced synergistic effects in MCF7 cells, additive/synergistic effects in A549 and PA1 cells, and additive effects in WiDr cells. Cell cycle analysis of MCF7 and PA1 cells supported these findings. Our results suggest that the simultaneous clinical administration of pemetrexed and cisplatin may be suboptimal. The optimal schedule of pemetrexed in combination with cisplatin at the cellular level is the sequential administration of pemetrexed followed by cisplatin and this schedule is worthy of clinical investigations.