Abstract
The fusion of ABL1 with BCR results in the hybrid BCR-ABL1 oncogene that encodes the constitutively active Bcr-Abl tyrosine kinase encountered in the majority of patients with chronic myeloid leukemia (CML) and in approximately 30% of pts with B-cell acute lymphoblastic leukemia (B-ALL). Recently, the episomal amplification of ABL1 has been described in 6% of pts with T-ALL (Nat Genet2004;36:1084–9). Molecular analysis demonstrated the oncogenic fusion of ABL1 with the nuclear pore complex protein NUP214 (NUP214-ABL1). We screened 29 pts with T-cell lymphoblastic lymphoma (T-LBL) and T-ALL for the presence of the NUP214-ABL1 fusion transcript by RT-PCR using specific primers for the 5 different transcripts thus far described. Three (10%) pts were found to express this fusion transcript, including 2 with T lymphoblastic lymphoma (NUP214 exon 31) and 1 with T-ALL (NUP214 exon 29). This was confirmed by direct sequencing in all cases. All pts received therapy with hyperCVAD and achieved a complete remission (CR). However, 2 of them died 6 and 9 months into therapy, respectively. One other pt remains in CR (19+ months) by morphologic and flow cytometry criteria. However, NUP214-ABL1 is still detectable in peripheral blood by nested PCR, thus suggesting minimal residual disease (MRD). We then studied the activity of the tyrosine kinase inhibitors imatinib and nilotinib in the NUP214-ABL1-expressing cell lines PEER and BE-13. Although PEER and BE-13 cell viability was reduced with both agents, the IC50 was almost 10-fold higher for imatinib (643 nM) than for nilotinib (68 nM) (F test, p<0.001), which parallels the 10− to 30− fold higher Abl kinase inhibitory activity of nilotinib compared to imatinib in BCR-ABL-expressing cells. Nilotinib also potently inhibited the cell proliferation of BE-13 cells (IC50 131 nM). In contrast, Jurkat cells, a T-ALL cell line which does not carry NUP214-ABL1, were remarkably resistant to both imatinib and nilotinib with an IC50 values greater than 5 μM indicating that the cytotoxicity mediated by both TKIs is not related to a general toxic effect on T-ALL cell lines. The inhibition of cellular proliferation by imatinib and nilotinib was associated with a dose- and time-dependent induction of apoptosis in both PEER and BE-13 cells. In Western blotting, higher inhibition of phospho-Abl and phospho-CRKL (a surrogate of Bcr-Abl kinase status) was observed in PEER cells upon exposure to nilotinib as compared with imatinib at their respective IC50 concentrations for cell growth inhibition.
We conclude that NUP214-ABL1 can be detected in 10% of pts with T-cell malignancies and its detection can be used as a sensitive marker of MRD. Imatinib and nilotinib potently inhibits the growth of NUP214-ABL1-expressing cells. Given the higher Abl kinase inhibitory activity of nilotinib with respect to imatinib, this agent must be further investigated in clinical studies targeting patients with T-ALL and T-LBL expressing the NUP214-ABL1 fusion kinase.
Heterogeneity of T-cell lymphoblastic malignancies
