Fludarabine induces declines in Mcl-1 protein levels in B-CLLs in vitro. Representative immunoblot data are presented for CLL specimens that exhibited in vitro resistance (IC₅₀ > 10⁻⁵ mol/L) (R) or sensitivity (IC₅₀ < 10⁻⁵ mol/L) (S) to fludarabine. CLLs were cultured at 2 × 10⁶ cells/mL with or without 1 μmol/L fludarabine, then lysed in 1% Triton X-100–containing solution, and subjected to SDS-PAGE/immunoblot assay after normalization of samples for total protein content (25 μg/lane). The same blot was incubated with antibodies specific for Mcl-1 (top), BAG-1 (middle), and Bcl-2 (bottom).