Overexpression of BCL2 and BAX following BFM induction therapy predicts ch-ALL patients' poor response to treatment and short-term relapse

Abstract

Purpose: The identification of childhood acute lymphoblastic leukemia (ch-ALL) patients who are at a higher risk of chemotherapy resistance and relapse is essential for successful treatment decisions, despite the application of novel therapies. The aim of the study is the evaluation of BCL2 and BAX expression for the prognosis of ch-ALL patients treated with Berlin-Frankfurt-Münster (BFM) backbone protocol.

Methods: Bone marrow specimens were obtained at the time of diagnosis and on day 33 following BFM treatment induction from 82 ch-ALL patients, as well as from 63 healthy children. Following extraction, total RNA was reverse transcribed and BCL2 and BAX expression levels were determined by qPCR.

Results: BCL2 expression and BCL2/BAX ratio were strongly upregulated in ch-ALL compared to healthy children and were correlated with favorable prognostic disease features. Increased levels of BCL2 and BAX expression were associated with disease remission, as ch-ALL patients with lower expression ran a significantly higher risk of M2-M3 response, positive MRD and poor survival outcome. Moreover, the upregulation of BCL2 and BAX following BFM treatment induction was shown to represent an independent predictor of patients' short-term relapse, which was further confirmed in ch-ALL patients with favorable prognostic markers.

Conclusions: In conclusion, BCL2 and BAX could be effectively used for an enhanced prediction of BFM-treated patients' outcome.

Keywords: Apoptosis; Berlin–Frankfurt–Münster treatment protocol; Chemotherapy resistance; Childhood acute lymphoblastic leukemia (ch-ALL); Molecular tumor markers.

Fig. 1

BCL2 expression and BCL2/BAX ratio are significantly upregulated in ch-ALL patients and correlated with favorable prognostic markers of the disease. a Box plots presenting the BCL2 and BAX expression levels, as well as BCL2/BAX ratio in bone marrow specimens of ch-ALL patients and healthy controls. b ROC curve analysis of BCL2 expression, BAX expression and BCL2/BAX ratio for the discrimination of ch-ALL patients from healthy children. c–f Box plots presenting the BCL2 and BAX expression levels, as well as BCL2/BAX ratio in bone marrow specimens of ch-ALL patients according to immunophenotype (c), WBC count (d), high hyperdiploidy (>50 chromosomes) (e) and presence of TEL-AML1 rearrangement (f). p values calculated by Mann–Whitney U test (a, d–f), Hanley and McNeil test (b) and Kruskal–Wallis test (c)

Fig. 2

ch-ALL patients with reduced BCL2 and BAX expression levels at disease diagnosis run a significantly higher risk of poor response to BFM treatment and short-term relapse. a–c Box plots presenting the BCL2 expression, BAX expression and BCL2/BAX ratio in bone marrow specimens of ch-ALL patients according to bone marrow response (blasts percentage) on day 15 (a), MRD on day 33 (b) and patients’ risk stratification (c). d–g Kaplan–Meier curves of ch-ALL patients’ disease-free survival (DFS; d, f) and cancer-specific survival (CSS; e, g) according to BCL2 and BAX expression levels at disease diagnosis. p values calculated by Mann–Whitney U test (a–c) and log-rank test (d–g)

Fig. 3

BFM-treated patients with increased BCL2 and BAX expression levels compared to diagnosis suffer from significantly shorter disease-free and cancer-specific survival. a–d Kaplan–Meier curves of ch-ALL patients’ disease-free survival (DFS; a, c) and cancer-specific survival (CSS; b, d) according to BCL2 and BAX expression change following BFM treatment induction (day 33). p values calculated by log-rank test (a–f)

Fig. 4

Overexpression of BCL2 and BAX following BFM protocol induction increases the risk of disease short-term relapse of ch-ALL patients with favorable prognostic features. (a–d) Kaplan–Meier disease-free survival (DFS) curves of 1–10 years of age (a), <50,000 WBC/μl (b), M1 response (<5 % blasts) (c) and “standard- and intermediate-risk” (d) patients’ groups according to BCL2 and BAX expression change following BFM treatment induction (day 33). p values calculated by log-rank test (a–f)