Bcl-2/Bax ratios in chronic lymphocytic leukaemia and their correlation with in vitro apoptosis and clinical resistance

Impaired nodal shrinkage and apoptosis define the independent adverse outcome of NOTCH1 mutated patients under ibrutinib therapy in chronic lymphocytic leukaemia

The introduction of agents inhibiting the B-cell receptor-associated kinases such as ibrutinib has dramatically changed treatments algorithms of chronic lymphocytic leukemia (CLL) as well as the role of different adverse prognosticators. We evaluated the efficacy of ibrutinib as a single agent, in a real-life context, in 180 patients with CLL mostly pretreated, recruited from three independent cohorts from Italy. Patients received 420 mg oral ibrutinib once daily until progression or occurrence of unacceptable side effects. Seventy-three patients discontinued ibrutinib for progression or for adverse events. NOTCH1 mutations (NOTCH1 M) were correlated with a reduced redistribution lymphocytosis, calculated at 3 months on ibrutinib (P=0.022). Moreover, NOTCH1 M patients showed inferior nodal response at 6 months on ibrutinib compared to NOTCH1 wild-type patients (P<0.0001). Significant shorter progression free survival (PFS) and overall survival (OS) were observed in NOTCH1 M patients (P=0.00002 and P=0.001). Interestingly, NOTCH1 M plus a lower BAX/BCL-2 ratio identified a CLL subset showing the worst PFS and OS (P=0.0002 and P=0.005). In multivariate analysis of PFS and OS, NOTCH1 M were confirmed an independent prognosticator (P=0.00006 and P=0.0039). In conclusion, NOTCH1 M are strongly associated with a lower BAX/BCL-2 ratio, consistent with defective apoptosis, lower redistribution lymphocytosis and lower nodal shrinkage under ibrutinib treatment, this last paramter being responsible for partial responses, subsequent relapses, as well as shorter PFS and OS. Either new small molecule combination approaches or antibodies targeting NOTCH1 could be future therapeutic options for NOTCH1 M patients.

GAB2 inhibits chondrocyte apoptosis through PI3K-AKT signaling in osteoarthritis

Cartilage degeneration is considered the main pathologic feature of osteoarthritis (OA). Cumulative evidence indicates that chondrocyte apoptosis is associated with cartilage degradation. However, the underlying molecular mechanism of chondrocyte apoptosis remains unclear. Growth factor receptor-bound protein 2 (GAB2), an adaptor protein, belongs to the Gab family and is involved in various biologic processes. Here, we explored the role of GAB2 in the pathogenesis of osteoarthritis (OA). GAB2 expression was markedly increased in OA articular cartilage. GAB2 expression was also increased in an in vitro model of TNFα-induced apoptosis. GAB2 depletion by siRNA promoted expression of the apoptosis markers, PARP and caspase-3, and increased the number of apoptotic cells, indicating that GAB2 might have an anti-apoptotic effect in chondrocytes. Moreover, GAB2 knockdown inhibited AKT phosphorylation, increased BAX expression, and decreased BCL2 expression, which indicated that GAB2 regulates chondrocyte apoptosis through PI3K-AKT signaling. Taken together, our study indicates that GAB2 plays a vital role in chondrocyte apoptosis and provides a new therapeutic target for OA.

Clinical significance of bax/bcl-2 ratio in chronic lymphocytic leukemia

In chronic lymphocytic leukemia the balance between the pro-apoptotic and anti-apoptotic members of the bcl-2 family is involved in the pathogenesis, chemorefractoriness and clinical outcome. Moreover, the recently proposed anti-bcl-2 molecules, such as ABT-199, have emphasized the potential role of of bcl-2 family proteins in the context of target therapies. We investigated bax/bcl-2 ratio by flow cytometry in 502 patients and identified a cut off of 1.50 to correlate bax/bcl-2 ratio with well-established clinical and biological prognosticators. Bax/bcl-2 was 1.50 or over in 263 patients (52%) with chronic lymphocytic leukemia. Higher bax/bcl-2 was associated with low Rai stage, lymphocyte doubling time over 12 months, beta-2 microglobulin less than 2.2 mg/dL, soluble CD23 less than 70 U/mL and a low risk cytogenetic profile (P<0.0001). On the other hand, lower bax/bcl-2 was correlated with unmutated IGHV (P<0.0001), mutated NOTCH1 (P<0.0001) and mutated TP53 (P=0.00007). Significant shorter progression-free survival and overall survival were observed in patients with lower bax/bcl-2 (P<0.0001). Moreover, within IGHV unmutated (168 patients) and TP53 mutated (37 patients) subgroups, higher bax/bcl-2 identified cases with significant longer PFS (P=0.00002 and P=0.039). In multivariate analysis of progression-free survival and overall survival, bax/bcl-2 was an independent prognostic factor (P=0.0002 and P=0.002). In conclusion, we defined the prognostic power of bax/bcl-2 ratio, as determined by a flow cytometric approach, and highlighted a correlation with chemoresistance and outcome in chronic lymphocytic leukemia. Finally, the recently proposed new therapies employing bcl-2 inhibitors prompted the potential use of bax/bcl-2 ratio to identify patients putatively resistant to these molecules.

An antiapoptotic BCL-2 family expression index predicts the response of chronic lymphocytic leukemia to ABT-737

The antiapoptotic BCL-2 proteins regulate lymphocyte survival and are over-expressed in lymphoid malignancies, including chronic lymphocytic leukemia. The small molecule inhibitor ABT-737 binds with high affinity to BCL-2, BCL-XL, and BCL-W but with low affinity to MCL-1, BFL-1, and BCL-B. The active analog of ABT-737, navitoclax, has shown a high therapeutic index in lymphoid malignancies; developing a predictive marker for it would be clinically valuable for patient selection or choice of drug combinations. Here we used RT-PCR as a highly sensitive and quantitative assay to compare expression of antiapoptotic BCL-2 genes that are known to be targeted by ABT-737. Our findings reveal that the relative ratio of MCL-1 and BFL-1 to BCL-2 expression provides a highly significant linear correlation with ABT-737 sensitivity (r = 0.6, P < .001). In contrast, antiapoptotic transcript levels, used individually or in combination for high or low affinity ABT-737-binding proteins, could not predict ABT-737 sensitivity. The (MCL-1 + BFL-1)/BCL-2 ratio was validated in a panel of leukemic cell lines subjected to genetic and pharmacologic manipulations. Changes after ABT-737 treatment included increased expression of BFL-1 and BCL-B that may contribute to treatment resistance. This study defines a highly significant BCL-2 expression index for predicting the response of CLL to ABT-737.