Carboxyamido-Triazole (CAI)-a Novel “static” Signal Transduction Inhibitor Induces Apoptosis in Human B-Cell Chronic Lymphocytic Leukemia Cells

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Abstract
Signal transduction is a key mechanism by which both proliferative and apoptotic processes of B-cell chronic lymphocytic leukemia (CLL) cells are mediated. Carboxyamido-triazole (CAI) is a cytostatic signal transduction inhibitor currently being tested in phase II clinical trials. Based on this, we investigated the in vitro activity of CAI in mononuclear cell isolates from patients with B-CLL (n = 11). Viability, utilizing the MTT assay, was assessed at varying concentrations (0.01–100 μM) of CAI for 4 days. The CAI concentration required for 50% inhibition of cell viability (LC50), determined by the tetrazolium dye (MTT) assay, at 4 days was 53.5 μM (range 29–74.6; 95% CI × 14.8). Cells from 6 of 11 patients (3 of whom were clinically fludarabine refractory) had a 27 percent (range 11–43) mean decline in viability at 10 μM after a 4 day drug exposure, a concentration readily attainable in humans. To assess if loss of viability was due to apoptosis, we incubated cells from 4 additional CLL patients with media or CAI (10 μM) for 4 days. Annexin-V/propidium iodine labeling subsequently demonstrated CAI significantly (p = 0.049) induces apoptosis (40.1%; 95% CI × 18.1) as compared to media matched control cells (18.3%; 95% CI × 11.2). These data provide evidence that CAI can induce apoptosis in human CLL cells in vitro at drug concentrations attainable in vivo. These findings justify phase n studies of CAI in patients with B-CLL.