Effect of R115777 on FT-dependent processing of prelamin A and HDJ-2 in K562 cells in vitro and in leukemic bone marrow samples in situ.

(A) Log-phase K562 cells were incubated for 24 hours with diluent (lane 1) or concentrations of R115777 ranging from 0.78 to 100 nM in 2-fold increments (lanes 2-11). At the completion of the incubation, samples were sedimented at 200g, washed once in serum-free RPMI 1640, and prepared for analysis as described in “Patients, materials, and methods.” R115777 causes a dose-dependent increase in signals for prelamin A and HDJ-2. (B) Bone marrow samples harvested before therapy (day 0) or at weekly intervals during therapy with the indicated dose of R115777 were prepared for immunoblotting as described in “Patients, materials, and methods.” Inhibition of prelamin A and pre–HDJ-2 processing at the 100 and 300 mg bid doses was not detected. Prelamin A appeared in some samples obtained from patients during treatment with 600 and 900 mg (eg, LO and MH, lanes 8-13). In samples from other patients, lamin A was undetectable before treatment (MIT, lanes 14-17) or disappeared during the course of treatment (eg, MIR, lanes 18-21), making it impossible to use prelamin A as a marker of FT inhibition. In contrast, an increase in pre–HDJ-2 was detectable in many of these same samples, as illustrated in lanes 14-21 and summarized in Table 4. The median blast count for the day 1 samples shown in this figure was 90%.