THE FREQUENCY OF ILLEGITIMATE V(D)J RECOMBINASE-MEDIATED MUTATIONS INCHILDREN TREATED WITH ETOPOSIDE-CONTAINING ANTILEUKEMIC THERAPY

Etoposide is among the most widely used anti-cancer drugs. Its use, ho wever, has been associated with increased risk of secondary acute myel oid leukemia (AML) which is characterized by chromosomal translocation s suggesting involvement of recombination-associated motifs at the bre akpoints. A PCR-based assay was developed to quantitate the frequency of two illegitimate V(D)J recombinase-mediated genomic rearrangements- a 20-kb deletion in the hprt gene and the bcl2/IgH translocation (t(14 ;18)) found in non-Hodgkin's lymphoma. We examined both lymphocyte and non-lymphocyte blood cell DNA of children with acute lymphoblastic le ukemia (ALL) for changes in the frequencies of these biomarkers during etoposide therapy to determine the level of illegitimate V(D)J recomb ination changes during therapy. A low level of t(14;18) was found in t he lymphocytes before etoposide treatment, which was significantly red uced during etoposide therapy. In before-etoposide samples, no t(14;18 ) were found among 7.72 x 10(7) non-lymphocytes; during treatment none were found among 1.87 x 10(9) non-lymphocytes. Deletions were not fou nd before etoposide treatment in either the lymphocytes (6.67 x 10(7)) or non-lymphocytes (5.43 x 10(7)) and were non-significantly elevated during etoposide therapy (1 in 1.4 x 10(8) lymphocytes and 1 in 1.39 x 10(8) non-lymphocytes). It is interesting to note the one patient wi th an hprt deletion mutation in non-lymphocytes; V(D)J recombination i s not normally found in this cell type, but is the cell type from whic h AML derives. Several patients had clones of t(14;18)-bearing cells a s determined by DNA sequence analysis. These results suggest that this etoposide-based chemotherapy was ineffective in producing genomic rea rrangements mediated by illegitimate V(D)J recombination in these pati ents. (C) 1998 Elsevier Science B.V. All rights reserved.