SEQUENTIAL TREATMENT OF HUMAN CHRONIC LYMPHOCYTIC-LEUKEMIA WITH BRYOSTATIN-1 FOLLOWED BY 2-CHLORODEOXYADENOSINE - PRECLINICAL STUDIES

We have previously reported that bryostatin 1 (Bryo 1) induces differe ntiation of chronic lymphocytic leukemia (CLL) in vitro to a hairy cel l (HC) stage, This study tests the hypothesis that Bryo 1-differentiat ed CLL cells are more susceptible to 2-chlorodeoxyadenosine (2-CdA) th an parent CLL cells, A recently established EBV-negative CLL line (WSU -CLL) from a patient resistant to chemotherapy including fludarabine w as used to test this hypothesis, Both Bryo 1 (10-1000 nM) and 2-CdA (5 .6-22.4 mu M) exhibited a dose-dependent growth inhibitory effect on t he WSU-CLL cell line, In vitro, the sequential exposure to Bryo 1 (100 nM for 72 h) followed by 2-CdA (11.2 mu M) resulted in significantly higher rates of growth inhibition than either agent alone, Changes in immunophenotype, enzymes, lipids, proteins, and the DNA of WSU-CLL cel ls were studied before and after Bryo 1 treatment, Bryo 1 induced a po sitive tartrate-resistant acid phosphatase reaction and two important markers, CD11c and CD25, after 72 h of culture, confirming the differe ntiation of CLL to HC, The Fourier transformation infrared spectroscop ic analysis showed that the amount of membrane lipids significantly in creased in Bryo 1-treated cells compared to controls after 24 h, where as the protein content, as well as the DNA content, decreased, This fi nding supports the change of CLL to HC, To evaluate the in vivo effica cy of Bryo 1 and 2-CdA, we used a xenograft model of CLL in WSU-CLL-be aring mice with severe combined immune deficiency, s.c. tumors were de veloped by injection of 10(7) WSU-CLL cells, and fragments were then t ransplanted into a new batch of severe combined immunodeficient mice, Bryo 1 and 2-CdA at the maximum tolerated doses (75 mu g/kg i.p. and 3 0 mg/kg s.c., respectively) were administered to the mice at different combinations and schedules, The survival in days, the tumor growth in hibition ratio, the tumor growth delay, and the log(10) kill of the mi ce treated with Bryo 1 followed by 2-CdA were significantly better tha n the control and other groups, We conclude that the sequential treatm ent with Bryo 1 followed by 2-CdA resulted in higher antitumor activit y and improved animal survival.