A phase II study of intravenous exatecan mesylate (DX-8951f) administered daily for 5 days every 3 weeks to patients with advanced ovarian, tubal or peritoneal cancer resistant to platinum, taxane and topotecan.

BACKGROUND: DX-8951f is a water-soluble camptothecin derivative with greater in vivo and in vitro activity than topotecan or irinotecan. The objectives of this phase II study were to determine the antitumor activity, safety and pharmacokinetic profile of DX-8951f administered intravenously for five consecutive days, every 3 weeks in patients with advanced ovarian, tubal and peritoneal cancer resistant to platinum, taxane and topotecan. METHODS: Enrolled in the study at The University of Texas M. D. Anderson Cancer Center were 16 patients with measurable cancer resistant to platinum, taxane and topotecan. All 16 patients were assessable for safety and 15 for efficacy analyses. Treatment consisted of a daily infusion of DX-8951f at 0.3 mg/m(2) per day (except for one minimally pretreated patient who started at 0.5 mg/m(2) per day) over 30 min for five consecutive days every 3 weeks. The pharmacokinetic and excretory profiles of DX-8951, the anhydrous form of DX-8951f, were also characterized. RESULTS: Disease was stable in 7 of 16 patients (44%) (4 minor response and 3 stable disease). The median time to tumor progression was 43 days (95% CI 37-92 days). The median overall survival was 117 days (95% CI 90-279 days). The main toxic effect was neutropenia and leukopenia with 50% of patients experiencing grade 3 or 4 neutropenia and leukopenia. One episode of neutropenic fever was observed. Grade 3 or more anemia and thrombocytopenia were seen in 25% and 13% of patients, respectively. Grade 3 nonhematologic side effects included nausea (25% of patients) and fatigue (19%). Other side effects were not more than grade 2, and included gastrointestinal dysfunction, stomatitis, dermatitis, alopecia, liver dysfunction and drug fever. DX-8951 displayed linear pharmacokinetic characteristics at the doses administered. The average plasma clearance, total volume of distribution, and terminal elimination half-life were 2.1 l/h per m(2), 20 l/m(2) and 9.5 h, respectively. CONCLUSIONS: DX-8951f administered parenterally as a single agent daily at a dose of either 0.5 or 0.3 mg/m(2) per day for 5 days is feasible in patients with advanced ovarian, tubal and peritoneal cancer resistant to platinum, taxane and topotecan. Although no responses were observed, a significant number of patients had stable disease with a decrease in CA-125 levels. In this heavily pretreated population, DX-8951f has clinically relevant hematologic and gastrointestinal toxicities in about 25% of patients. DX-8951 appeared to have linear pharmacokinetic characteristics on the basis of multiple administrations.

Characterization of a fluorescent conjugate of the rabbit angiotensin AT(1) receptor.

1. The rabbit AT(1) receptor (AT(1)R) for angiotensin II (A(II)) has been conjugated to the yellow fluorescent protein (YFP) in order to establish the pharmacological profile of such a fusion protein and to facilitate the study of ligand-induced regulation. 2. A(II) bound AT(1)R-YFP (K(D) 8.1 nM in transiently transfected cells) and stimulated HEK 293 cells expressing the fusion protein at concentration ranges similar to the ones that stimulate the contraction of the isolated rabbit aorta. Antagonists found to be insurmountable in the latter assay (candesartan and EXP-3174 being the most extreme cases) were also insurmountable in the phospholipase A(2) assay applied to cells expressing AT(1)R-YFP, whereas losartan appeared to be surmountable in both assays. 3. Cells expressing AT(1)R-YFP exhibited a membrane-associated fluorescence that was partly and reversibly translocated into intracellular structures upon A(II) stimulation (confocal microscopy); the nonpeptide antagonists were not active in this respect, but prevented the effect of the agonist. 4. A(II) treatment increased the quantity of the fusion protein in cells, and phorbol 12-myristate 13-acetate (PMA) treatment even more so (immunoblot, confocal microscopy) but, unlike the agonist, the latter drug did not induce receptor endocytosis. A protein kinase C (PKC) inhibitor prevented the effect of either A(II) or PMA on AT(1)R-YFP abundance. 5. The conjugate AT(1)R-YFP retains the pharmacological properties of the parent rabbit AT(1)R. Agonist-induced downregulation was not documented using this system; to the contrary, we have observed a PKC-mediated increased expression AT(1)R-YFP likely to be the result of a decreased breakdown rate of the fusion protein.

Agonist-induced translocation of the kinin B(1) receptor to caveolae-related rafts.

The kallikrein-kinin system, activated during inflammatory conditions and the regulation of specific cardiovascular and renal functions, includes two G protein-coupled receptors for bradykinin (BK)-related peptides. The B(1) receptor (B(1)R) subtype is not believed to undergo agonist-induced phosphorylation and endocytosis. A conjugate made of the rabbit B(1)R fused with the yellow variant of green fluorescent protein (YFP) was expressed in mammalian cells. In COS-1 or human embryonic kidney (HEK) 293 cells, the construction exhibited a nanomolar affinity for the agonist radioligand [(3)H]Lys-des-Arg(9)-BK or the antagonist ligand [(3)H]Lys-[Leu(8)]des-Arg(9)-BK and a pharmacological profile virtually identical to that of wild-type B(1)R. Lys-des-Arg(9)-BK stimulation of HEK 293 cells stably expressing B(1)R-YFP but not stimulation of untransfected cells released [(3)H]arachidonate in a phospholipase A(2) assay. B(1)R-YFP was visualized as a continuous labeling of the plasma membranes in stably transfected HEK 293 cells (confocal microscopy). Addition of Lys-des-Arg(9)-BK (1-100 nM) rapidly concentrated the receptor-associated fluorescence into multiple aggregates that remained associated with the plasma membrane (no significant internalization) and colocalized with caveolin-1. This reaction was slowly reversible upon agonist washing at 37 degrees C and prevented pretreatment with a B(1)R antagonist. beta-Cyclodextrin treatment, which extracts cholesterol from membranes and disrupts caveolae-related rafts, prevented agonist-induced redistribution of B(1)R-YFP but not the PLA(2) activation mediated by this receptor. The agonist radioligand copurified with caveolin-1 to a greater extent than the tritiated antagonist in buoyant fractions of HEK 293 cells treated with the ligands. Agonist-induced cellular translocation of the kinin B(1)R to caveolae-related rafts without endocytosis is a novel variation on the theme of G protein-coupled receptor adaptation.