We recently described a carrier-mediated nuclear transport system for tRNA in Xenopus laevis oocytes. A natural human tRNAimet variant with a G to T transversion in position 57 is defective in transport across the nuclear membrane. In addition, processing of the primary transcript of the variant gene is much less efficient than the wild type. We now describe the nuclear transport and processing phenotypes of 30 different point mutants generated by in vitro mutagenesis of a wild-type human tRNAimet gene. The effects of each nucleotide change on processing and transport were analyzed in X. laevis oocytes following nuclear microinjection of each mutant gene. Mutants exhibiting transport-defective behavior were further characterized by measuring transport kinetics of the purified mature tRNA. Our studies demonstrate that many mutations affect tRNAimet nuclear transport, although those with the most deleterious effects are clustered in the highly conserved D stem-loop and T stem-loop regions.

Concomitant chemoradiotherapy with cisplatin and vinorelbine is feasible. The recommended phase II dose is cisplatin 80 mg/m2 every 3 weeks with vinorelbine 15 mg/m2 given twice over 3 weeks on a day 1/day 8 schedule. Esophagitis is the DLT, with neutropenia occurring at higher dose levels. A Cancer and Leukemia Group B (CALGB) phase II trial is currently underway to evaluate further the efficacy and toxicities of this regimen in unresectable stage III NSCLC.

Ifosfamide plus paclitaxel is an active treatment regimen in advanced non-small-cell lung cancer, and compares favorably with the results of cisplatin-based chemotherapy. A phase II study is in progress by the Cancer and Leukemia Group B, in an effort to better characterize the tolerance of the regimen, as well as its effect on tumor response and survival.

Myelosuppression is the DLT of this regimen with no major subjective toxicities. With tolerable toxicity and an encouraging 1-year survival rate of 48%, further investigation of this new vinorelbine schedule is warranted in this and other combination regimens.

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(1) This intensive multimodality regimen can be given with aggressive supportive care incorporating GCSF. The recommended phase II doses for a 4-week cycle are cisplatin 50 mg/m2 week 1, and 100 mg/m2 week 2, IFN 2.5 MU, HU 500 mg every 12 h x 11 and 5-FU 800 mg/m2 per day with single fraction radiotherapy during weeks 1-3 and GCSF during weeks 1, 3, and 4. (2) GCSF can be safely administered and provides effective support of neutrophils when administered simultaneously with IFN, cisplatin, and chest radiotherapy. (3) There is synergistic renal toxicity when high doses of IFN and cisplatin are given together. (4) Hyperfractionated radiotherapy decreases the severity of esophagitis but increases thrombocytopenia. (5) Although highly toxic, response rates, time to progression and survival figures with this regimen are encouraging and support its investigation in the phase II setting.

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