A 24-mer (antisense) phosphorothioate oligonucleotide (ODN) corresponding to the codons 2-9 of the c-myb gene was evaluated for its effects on the growth of a human Burkitt lymphoma cell line (Raji) in vitro. Raji cells incubated with different concentrations of c-myb antisense ODN (5-15 mu g/ml) for 24-72 h showed a significant dose-dependent decrease in growth. The same concentrations of control (sense) or scrambled c-myb phosphorothioate ODNs did not inhibit Raji cell growth. The c-myb antisense ODN, but not the control ODNs, significantly decreased c-myb mRNA levels in treated cells as determined by RT-PCR. Additionally, the c-myb antisense ODN induced apoptosis of Raji cells as demonstrated by i) flow cytometry to enumerate the A(o) (apoptotic cell population) population of propidium iodide stained cells; ii) electron microscopy to evaluate the cell morphology; and iii) DNA fragmentation pattern. Thus, an antisense c-myb ODN causes significant growth inhibition of Burkitt lymphoma cells, and one mechanism of growth inhibition is the induction of apoptosis of the lymphoma cells. In addition, antisense c-myb ODN did not reduce CFU-GM or BFU-e colony-forming ability of normal hematopoietic stem/progenitor cells. Because the inhibition is sequence-specific and Burkitt lymphoma cell selective, evaluation of the therapeutic effects of c-myb antisense ODN against Burkitt lymphoma is warranted.

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