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F. Diop et al.
In order to assess whether BIRC3 mutations interfere with apoptosis, primary CLL cells were treated with vene- toclax. Venetoclax treatment resulted in a similar reduc- tion of cell viability in BIRC3-mutated cells, TP53-mutated cells and BIRC3/TP53-wildtype cells (Figure 4C, D). Such divergent sensitivity to fludarabine and venetoclax of BIRC3-mutated CLL cells indirectly suggests that BIRC3 mutations likely affect the upstream DNA damage response pathway rather than downstream apoptosis as a mechanism of inducing cell death.
Patients harboring BIRC3 mutations are at risk of FCR failure
In order to confirm in vivo in patients that BIRC3 muta- tions confer resistance to fludarabine-based chemoim- munotherapy, we correlated the BIRC3 mutation status with PFS of CLL patients treated with FCR. Mutational profiling was performed in 287 patients who received first-line FCR. The baseline features of the study cohort were consistent with progressive, previously untreated CLL (Table 1). The median follow-up was 6.8 years, with
AB
a median PFS and overall survival of 4.6 and 11.7 years, respectively (Table 1) consistent with observations in clinical trial cohorts.15 As expected, SF3B1 and NOTCH1 were the most frequently mutated genes identified in 13.9% and in 13.6% of patients, respectively, followed by TP53 in 9.4% and ATM in 6.9% of patients. BIRC3 was mutated in 3.1% of patients, reflecting the data reported in previous studies.6,7,13 Overall, 154/287 (53.6%) cases harbored at least one non-synonymous somatic mutation in one of the 24 CLL genes included in our panel (range, 1-5 mutation per patient), which is con- sistent with the typical mutational spectrum of CLL requiring first-line treatment (Figure 5, Online Supplementary Table S5).6,7,16
By univariate analysis adjusted for multiple compar- isons, among the genes analyzed in our panel, only TP53 mutations (median PFS of 2.6 years; P<0.0001) and BIRC3 mutations (median PFS of 2.2 years; P<0.001) (Figure 6A) were associated with significantly shorter PFS (Table 2). Following FCR treatment, the PFS of BIRC3-mutated patients was similar to that of cases har-
CDE
Figure 3. The non-canonical nuclear factor-κB pathway is not switched off by ibrutinib in BIRC3-mutated cell lines. Western blot showing p100/p52 expression in (A) MEC1 and (B) VL51 cell lines that harbor BIRC3 mutations. (C) MAVER-1 and (D) Z-138 cell lines, known to be affected by non-canonical NF-κB pathway gene mutations and resistant to ibrutinib were used as positive controls. (E) The JEKO-1 cell line, known to be devoid of NF-κB pathway gene mutations and sensitive to ibrutinib, was used as a negative control. All cell lines were treated with different concentrations of ibrutinib for 72 and 96 h. DMSO: dimethylsulfoxide.
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haematologica | 2020; 105(2)