NOTCH1 activation clinically antagonizes the unfavorable effect of PTEN inactivation in BFM-treated children with precursor T-cell acute lymphoblastic leukemia

Abstract

Despite improvements in treatment results for pediatric T-cell acute lymphoblastic leukemia, approximately 20% of patients relapse with dismal prognosis. PTEN inactivation and NOTCH1 activation are known frequent leukemogenic events but their effect on outcome is still controversial. We analyzed the effect of PTEN inactivation and its interaction with NOTCH1 activation on treatment response and long-term outcome in 301 ALL-BFM treated children with T-cell acute lymphoblastic leukemia. We identified PTEN mutations in 52 of 301 (17.3%) of patients. In univariate analyses this was significantly associated with increased resistance to induction chemotherapy and a trend towards poor long-term outcome. By contrast, patients with inactivating PTEN and activating NOTCH1 mutations showed marked sensitivity to induction treatment and excellent long-term outcome, which was similar to patients with NOTCH1 mutations only, and more favorable than in patients with PTEN mutations only. Notably, in the subgroup of patients with a prednisone- and minimal residual disease (MRD)-response based medium risk profile, PTEN-mutations without co-existing NOTCH1-mutations represented an MRD-independent highly significant high-risk biomarker. Mutations of PTEN highly significantly indicate a poor prognosis in T-ALL patients who have been stratified to the medium risk group of the BFM-protocol. This effect is clinically neutralized by NOTCH1 mutations. Although these results have not yet been explained by an obvious molecular mechanism, they contribute to the development of new molecularly defined stratification algorithms. Furthermore, these data have unexpected potential implications for the development of NOTCH1 inhibitors in the treatment of T-cell acute lymphoblastic leukemia in general, and in those with a combination of PTEN and NOTCH1 mutations in particular.

Figure 1.

Univariate analysis shows a trend towards poor long-term outcome in children with T-ALL. Kaplan-Meier estimate of pEFS (A) and pCIR (B) in PTEN mutated and PTEN-non-mutated patients treated on the ALL-BFM 2000 protocol

Figure 2.

Effect of PTEN inactivation and NOTCH1 activation on early treatment response in children with T-ALL. (A) Prednisone response: prednisone good response (PGR; <1000 blasts/μL of peripheral blood at Day 8), Prednisone poor response (PPR; ≥1000 blasts/μL of peripheral blood at Day 8). (B) MRD response on Day 33: an unfavorable MRD status (≥10⁻⁴) was defined by the presence of at least one leukemic cell in 10⁴ cells, whereas a favorable MRD status (<10⁻⁴) was defined as the absence of detectable leukemic cells in 10⁴ cells (C) MRD response on Day 78: an unfavorable MRD status (≥10⁻⁴) was defined by the presence of at least one leukemic cell in 10⁴ cells, whereas a favorable MRD status (<10⁻⁴) was defined as the absence of detectable leukemic cells in 10⁴ cells. The number of patients is indicated on top of the columns.

Figure 3.

NOTCH1 activation neutralizes the unfavorable effect of PTEN inactivation on long-term outcome in children with T-ALL. Kaplan-Meier estimate of pEFS (A) and pCIR (B) in PTEN mutated and NOTCH1 non-mutated patients compared to the rest of the cohort.

Figure 4.

PTEN only mutated patients in the BFM-2000 medium-risk group show the worst long-term outcome. (A) Kaplan-Meier estimate of pEFS in the four different combinations of PTEN, NOTCH1 genotypes (total cohort n=301). (B) pCIR in the four different combinations of PTEN, NOTCH1 genotypes (total cohort n=301) (C) Kaplan-Meier estimate of pEFS in NOTCH1 and PTEN mutated, NOTCH1 and PTEN non-mutated, and NOTCH1 non-mutated and PTEN mutated patients stratified into the medium risk group (n=154) (D) Kaplan-Meier estimate of pEFS in NOTCH1 andPTEN mutated, NOTCH1 and PTEN non-mutated, and NOTCH1 non-mutated and PTEN mutated patients stratified into the high-risk group (n=53).