Soluble phosphorylated fms-like tyrosine kinase III. FLT3 protein in patients with acute myeloid leukemia (AML)

Patterns of molecular response to and relapse after combination of sorafenib, idarubicin, and cytarabine in patients with FLT3 mutant acute myeloid leukemia

BACKGROUND

FMS-like tyrosine kinase 3 (FLT3) is a class III receptor tyrosine kinase involved in hematopoietic progenitor cell development. Mutations of FLT3 have been reported in about a third of patients with acute myeloid leukemia (AML), and inhibitors of FLT3 are of clinical interest. Sorafenib is an orally active multikinase inhibitor with potent activity against FLT3 and the Raf/ERK/MEK kinase pathway.

METHODS

We studied the patterns of molecular response and relapse in 18 patients with mutated FLT3 treated with the combination of sorafenib, idarubicin, and cytarabine.

RESULTS

The median follow-up was 9 months. Sixteen patients achieved complete remission (CR), and the other 2 patients achieved CR but lacked platelet recovery for an overall response rate of 100%. Ten patients had their FLT3-mutated clone eradicated, with 6 patients who showed some residual FLT3-mutated cells, and 2 patients who showed persistent FLT3-mutated cells. The elimination of FLT3-mutated population at the time of morphologic CR, however, was not predictive of relapse. After a median follow-up of 9 months (range, 1-16 months), 10 (55%) patients had relapsed, with a median CR duration of 8.8 months (range, 1-9.5 months). By DNA sequencing, there was no evidence of an acquired FLT3 point mutation at the time of relapse in 7 patients tested, which suggested the presence of other mechanisms of sorafenib resistance.

CONCLUSION

Sorafenib, combined with chemotherapy, is effective in attaining CR, but relapses still occur.

Clinical relevance of FLT3 receptor protein expression in Indian patients with acute leukemia

AIM

FLT3 is a receptor tyrosine kinase that plays an important role in the pathogenesis of leukemia. The present study aimed to evaluate the role of FLT3 protein in patients with acute leukemia.

METHOD

FLT3 protein was quantified by flow cytometry on leukemic blasts using CD135 antibody in 160 patients with acute leukemia.

RESULTS

We demonstrated FLT3 protein expression (>20%) in 82% of acute myeloid leukemia (AML), 60% of B-lineage acute lymphoblastic leukemia (B-ALL), 23% of T-lineage acute lymphoblastic leukemia (T-ALL) and 80% of biphenotypic leukemia. Further, FLT3 expression was seen to be significantly higher in AMLM2, M4, and M5 than in AMLM3. In B-ALL, FLT3 was found to be higher in pro-B-ALL and lower in early B-ALL. A CD34 expression >20% was associated with FLT3 positive B-ALL. When correlated with disease status, all patients in the relapsed AML group had FLT3 > 20% at diagnosis. Unlike AML, the relapsed group of B-ALL showed a lower incidence of FLT3 than the remission group.

CONCLUSION

In summary, our data imply that there is frequent overexpression of the FLT3 protein in AML and B-ALL patients of Indian origin. In future, the FLT3 protein level may be used to select patients for whom FLT3 inhibitor therapy may be indicated.

Phase I/II study of combination therapy with sorafenib, idarubicin, and cytarabine in younger patients with acute myeloid leukemia

PURPOSE To determine the efficacy and toxicity of the combination of sorafenib, cytarabine, and idarubicin in patients with acute myeloid leukemia (AML) younger than age 65 years. PATIENTS AND METHODS In the phase I part of the study, 10 patients with relapsed AML were treated with escalating doses of sorafenib with chemotherapy to establish the feasibility of the combination. We then treated 51 patients (median age, 53 years; range, 18 to 65 years) who had previously untreated AML with cytarabine at 1.5 g/m(2) by continuous intravenous (IV) infusion daily for 4 days (3 days if > 60 years of age), idarubicin at 12 mg/m(2) IV daily for 3 days, and sorafenib at 400 mg orally twice daily for 7 days. RESULTS Overall, 38 (75%) patients have achieved a complete remission (CR), including 14 (93%) of 15 patients with mutated FMS-like tyrosine kinase-3 (FLT3; the 15th patient had complete remission with incomplete platelet recovery [CRp]) and 24 (66%) of 36 patients with FLT3 wild-type (WT) disease (three additional FLT3-WT patients had CRp). FLT3-mutated patients were more likely to achieve a CR than FLT3-WT patients (P = .033). With a median follow-up of 54 weeks (range, 8 to 87 weeks), the probability of survival at 1 year is 74%. Among the FLT3-mutated patients, 10 have relapsed and five remain in CR with a median follow-up of 62 weeks (range, 10 to 76 weeks). Plasma inhibitory assay demonstrated an on-target effect on FLT3 kinase activity. CONCLUSION Sorafenib can be safely combined with chemotherapy, produces a high CR rate in FLT3-mutated patients, and inhibits FLT3 signaling.