Interaction between the hydrophobic Bak BH3-binding groove and the BH3 domain of activator proteins is a key step in initiating Bak oligomerization and activation.

Key Points• BCL2 mutations in FL correlate with activationinduced cytidine deaminase expression and frequently alter the amino acid sequence of the protein.• Mutations in the BCL2 coding sequence at diagnosis are associated with shortened time to transformation and earlier death due to lymphoma.Follicular lymphoma (FL), an indolent neoplasm caused by a t(14;18) chromosomal translocation that juxtaposes the BCL2 gene and immunoglobulin locus, has a variable clinical course and frequently undergoes transformation to an aggressive lymphoma. Although BCL2 mutations have been previously described, their relationship to FL progression remains unclear. In this study, we evaluated the frequency and nature of BCL2 mutations in 2 independent cohorts of grade 1 and 2 FLs, along with the correlation between BCL2 mutations, transformation risk, and survival. The prevalence of BCL2 coding sequence mutations was 12% in FL at diagnosis and 53% at transformation (P < .0001). The presence of these BCL2 mutations at diagnosis correlated with an increased risk of transformation (hazard ratio 3.6; 95% CI, 2.0-6.2; P < .0001) and increased risk of death due to lymphoma (median survival of 9.5 years with BCL2 mutations vs 20.4 years without; P 5 .012).In a multivariate analysis, BCL2 mutations and high FL international prognostic index were independent risk factors for transformation and death due to lymphoma. Some mutant Bcl-2 proteins exhibited enhanced antiapoptotic capacity in vitro. Accordingly, BCL2 mutations can affect antiapoptotic Bcl-2 function, are associated with increased activationinduced cytidine deaminase expression, and correlate with increased risk of transformation and death due to lymphoma. (Blood. 2015;125(4):658-667) Introduction Follicular lymphoma (FL) has a highly variable clinical course. [1][2][3] Although some patients do well for decades, often with limited therapy, at some point 30% to 50% of patients experience histologic transformation to a more aggressive lymphoma, usually diffuse large B-cell lymphoma (DLBCL). [4][5][6][7][8][9][10][11] This transformation, which is thought to reflect the acquisition of new genetic abnormalities leading to further genomic instability, [12][13][14][15][16] has generally been associated with a poor clinical outcome. 17 Retrospective analyses from the prerituximab era have reported a median survival of only 1 to 2 years after transformation, 18,19 although a recent prospective observational study suggests somewhat better survival after transformation in the rituximab era. 20 At the present time, the FL international prognostic index (FLIPI), which integrates patient characteristics at diagnosis, is the gold standard for predicting FL clinical outcome. 21,22 There is, however, considerable interest in identifying characteristics of the FL cells themselves that might also impact prognosis. 22,23 The BCL2 gene is critical for FL pathogenesis. 24,25 Originally identified because of its translocation to the immunoglobulin heavy chain (IGH) locus as a part of the t(14;18) ...

The mammalian target of rapamycin (mTOR) plays crucial roles in proliferative and antiapoptotic signaling in lymphoid malignancies. Rapamycin analogs, which are allosteric mTOR complex 1 (mTORC1) inhibitors, are active in mantle cell lymphoma and other lymphoid neoplasms, but responses are usually partial and short-lived. In the present study we compared the effects of rapamycin with the dual mTORC1/mTORC2 inhibitor OSI-027 in cell lines and clinical samples representing divers lymphoid malignancies. In contrast to rapamycin, OSI-027 markedly diminished proliferation and induced apoptosis in a variety of lymphoid cell lines and clinical samples, including specimens of B-cell acute lymphocytic leukemia (ALL), mantle cell lymphoma, marginal zone lymphoma and Sezary syndrome. Additional analysis demonstrated that OSI-027-induced apoptosis depended on transcriptional activation of the PUMA and BIM genes. Overexpression of Bcl-2, which neutralizes Puma and Bim, or loss of procaspase 9 diminished OSI-027-induced apoptosis in vitro. Moreover, OSI-027 inhibited phosphorylation of mTORC1 and mTORC2 substrates, upregulated Puma, and induced regressions in Jeko xenografts. Collectively, these results not only identify a pathway that is critical for the cytotoxicity of dual mTORC1/mTORC2 inhibitors, but also suggest that simultaneously targeting mTORC1 and mTORC2 might be an effective anti-lymphoma strategy in vivo. (Blood. 2012;119(2):476-487) IntroductionDespite being considered among the most treatable malignancies, lymphomas and lymphocytic leukemias continue to account for more than 27 000 deaths annually in the US 1 These statistics highlight the continued need for improved therapy.Over the past 6 years, rapamycin and its derivatives temsirolimus and everolimus (collectively called rapalogs) have shown promising activity in a wide range of lymphoma subtypes. 2 These agents are allosteric inhibitors of the mammalian target of rapamycin (mTOR), a highly conserved serine/threonine kinase that integrates signaling from the phosphoinositide-3-kinase (PI3K)/ Akt and AMP kinase pathways as well as others (reviewed in Bjornsti and Houghton, 3 Dowling et al, 4 and Sengupta et al 5 ). Through its involvement in 2 distinct complexes, mTOR complex 1 (mTORC1) and mTORC2, mTOR modulates several processes, including mRNA translation, cell cycle progression, survival and motility. 4,6 In particular, the raptor-containing mTORC1 phosphorylates p70 S6 kinase and eukaryotic initiation factor 4E binding protein 1 (4E-BP1), thereby regulating translation of certain messages that are critical for progression from G 1 into S phase (cyclin D1, c-myc) and, in some cells, survival . 4,7 In addition, the rictor-containing mTORC2 phosphorylates Akt on Ser 473 , affecting Akt-mediated survival signaling, and AGC family kinases, 4,6 thereby modulating cell motility.The effects of rapalogs on signaling are complex. After rapamycin initially binds to the cytosolic protein FKBP12, the resulting complex interacts with the FK-rapamycin binding domain o...

Background: PARP inhibitors and topoisomerase I poisons (Top1p) synergize by an unknown mechanism. Results: Although Parp1 deletion fails to increase Top1p sensitivity, transfection with catalytically inactive PARP1 or its isolated DNA binding domain does sensitize. Conclusion: PARP inhibitors poison PARP1 to diminish repair of topoisomerase I-triggered DNA damage. Significance: These results predict that tumors with elevated PARP1 will be particularly sensitive to Top1p/PARP inhibitor combinations.

Purpose Incorporation of cytarabine into DNA activates checkpoint kinase 1 (Chk1), which stabilizes stalled replication forks, induces S-phase slowing, and diminishes cytarabine cytotoxicity. The selective Chk1 inhibitor SCH 900776 abrogates cytarabine-induced S-phase arrest and enhances cytarabine cytotoxicity in acute leukemia cell lines and leukemic blasts in vitro. To extend these findings to the clinical setting, we have conducted a phase I study of cytarabine and SCH 900776. Experimental Design Twenty-four adults with relapsed and refractory acute leukemias received timed sequential, continuous infusion cytarabine 2 g/m2 over 72 hours (667 mg/m2/24 hours) beginning on day 1 and again on day 10. SCH 900776 was administered as a 15- to 30-minute infusion on days 2, 3, 11, and 12. The starting dose of SCH 900776 was 10 mg/m2/dose. Results Dose-limiting toxicities consisting of corrected QT interval prolongation and grade 3 palmar-plantar erythrodysesthesia occurred at 140 mg flat dosing (dose level 5, equivalent to 80 mg/m2). Complete remissions occurred in 8 of 24 (33%) patients, with 7 of 8 at 40 mg/m2 or higher. SCH 900776 did not accumulate at any dose level. Marrow blasts obtained pretreatment and during therapy showed increased phosphorylation of H2Ax after SCH 900776 beginning at 40 mg/m2, consistent with unrepaired DNA damage. Conclusions These data support a randomized phase II trial of cytarabine +/− SCH 900776 at a recommended flat dose of 100 mg (equivalent to 56 mg/m2) for adults with poor-risk leukemias. The trial (SP P05247) was registered at www.clinicaltrials.gov as NCT #00907517.

MLN4924 (pevonedistat), an inhibitor of the Nedd8 activating enzyme (NAE), has exhibited promising clinical activity in acute myelogenous leukemia (AML). Here we demonstrate that MLN4924 induces apoptosis in AML cell lines and clinical samples via a mechanism distinct from those observed in other malignancies. Inactivation of E3 cullin ring ligases (CRLs) through NAE inhibition causes accumulation of the CRL substrate c-Myc, which transactivates the PMAIP1 gene encoding Noxa, leading to increased Noxa protein, Bax and Bak activation, and subsequent apoptotic changes. Importantly, c-Myc knockdown diminishes Noxa induction; and Noxa siRNA diminishes MLN4924-induced killing. Because Noxa also neutralizes Mcl-1, an anti-apoptotic Bcl-2 paralog often upregulated in resistant AML, further experiments have examined the effect of combining MLN4924 with BH3 mimetics that target other anti-apoptotic proteins. In combination with ABT-199 or ABT-263 (navitoclax), MLN4924 exerts a synergistic cytotoxic effect. Collectively, these results provide new insight into MLN4924-induced engagement of the apoptotic machinery that could help guide further exploration of MLN4924 for AML.

The release of cytochrome c from mitochondria, which leads to activation of the intrinsic apoptotic pathway, is regulated by interactions of Bax and Bak with antiapoptotic Bcl-2 family members. The factors that regulate these interactions are, at the present time, incompletely understood. Recent studies showing preferences in binding between synthetic Bcl-2 homology domain 3 and antiapoptotic Bcl-2 family members in vitro have suggested that the antiapoptotic proteins Mcl-1 and Bcl-x L , but not Bcl-2, restrain proapoptotic Bak from inducing mitochondrial membrane permeabilization and apoptosis. Here we show that Bak protein has a much higher affinity than the 26-amino acid Bak Bcl-2 homology domain 3 for Bcl-2, that some naturally occurring Bcl-2 allelic variants have an affinity for full-length Bak that is only 3-fold lower than that of Mcl-1, and that endogenous levels of these Bcl-2 variants (which are as much as 40-fold more abundant than Mcl-1) restrain part of the Bak in intact lymphoid cells. In addition, we demonstrate that Bcl-2 variants can, depending on their affinity for Bak, substitute for Mcl-1 in protecting cells. Thus, the ability of Bcl-2 to protect cells from activated Bak depends on two important contextual variables, the identity of the Bcl-2 present and the amount expressed.The release of cytochrome c from mitochondria, which leads to activation of the intrinsic apoptotic pathway, is regulated by Bcl-2 family members (1-5). This group of proteins consists of three subgroups: Bax and Bak, which oligomerize upon death stimulation to form a putative pore in the outer mitochondrial membrane, thereby allowing efflux of cytochrome c and other mitochondrial intermembrane space components; Bcl-2, Bcl-x L , Mcl-1, and other antiapoptotic homologs, which antagonize the effects of Bax and Bak; and BH3-only proteins 2 such as Bim, Bid, and Puma, which are proapoptotic Bcl-2 family members that share only limited homology with the other two groups in a single 15-amino acid domain (the BH3 domain, see Ref. 6). Although it is clear that BH3-only proteins serve as molecular sensors of various stresses and, when activated, trigger apoptosis (3, 6 -11), the mechanism by which they do so remains incompletely understood. One current model suggests that BH3-only proteins trigger apoptosis solely by binding and neutralizing antiapoptotic Bcl-2 family members, thereby causing them to release the activated Bax and Bak that are bound (reviewed in Refs. 9 and 10; see also Refs. 12 and 13), whereas another current model suggests that certain BH3-only proteins also directly bind to and activate Bax (reviewed in Ref.3; see also Refs. 14 -17). Whichever model turns out to be correct, both models agree that certain antiapoptotic Bcl-2 family members can inhibit apoptosis, at least in part, by binding and neutralizing activated Bax and Bak before they permeabilize the outer mitochondrial membrane (13,18,19).Much of the information about the interactions between pro-and antiapoptotic Bcl-2 family members has been derived f...

Background:The chemokine receptor CXCR4 plays a role in AML. Results: SDF-1, the ligand of CXCR4, induces apoptosis in AML cell lines and patient samples via modulation of Bcl-2 family members. Conclusion: SDF-1 induces apoptosis of AML cells via up-regulation of Bak and Noxa and down-regulation of Bcl-X L . Significance: SDF-1/CXCR4 signaling could induce AML cell apoptosis if bone marrow survival cues can be disrupted.