Small Molecule Inhibitor Of Bcl-2 Research Articles

Abstract 1805: Characterization of pyoluteorin derivatives as Mcl-1 antagonists

Abstract The evasion of apoptosis is considered to be a hallmark of cancers and a cause of resistance to anti-cancer therapies. Consistently, aberrant overexpression of anti-apoptotic Bcl-2 family proteins (e.g., Bcl-2, Bcl-xL, Mcl-1) is associated with tumorigenesis and increased resistance to chemotherapy in multiple malignancies. To date, several small-molecule Bcl-2 inhibitors that bind the BH3-binding pocket of the protein have entered clinical trials. These BH3 mimetics are known to induce apoptosis by disrupting the interactions between pro- and anti-apoptotic Bcl-2 family proteins. The most well characterized selective agents are the Bcl-2 inhibitor ABT-737 and its orally active analog ABT-263 which inhibit Bcl-2 and Bcl-XL but not Mcl-1. Consequently, cancers with elevated Mcl-1 do not respond to these drugs. Moreover, Mcl-1 is frequently upregulated in cancer cells and compensates for the inhibition of Bcl-2 function by ABT-737, thereby mediating resistance to the drug. Thus, there is an urgent need to develop Mcl-1-specific inhibitors for the treatment of Mcl-1-dependent human cancers. We have recently identified and characterized the natural product marinopyrrole A (maritoclax) as a novel Mcl-1 inhibitor, which induces apoptosis by targeting Mcl-1 for proteasomal degradation without significant effects on mRNA levels. To determine the pharmacophore of maritoclax, we systematically altered or removed portions of the molecule to identify regions essential for inhibition of Mcl-1 and induction of apoptosis. To date, we synthesized over 40 derivatives of maritoclax and evaluated their inhibitory actions toward Mcl-1 and cytotoxicity in cell lines of human hematological malignancies. As a result, we have identified several pharmacophore sites in maritoclax that are required for biological activity and two pyoluteorin derivatives, KS04 and KS18, which bind to a similar site(s) in Mcl-1 as maritoclax, as determined by NMR titration experiments. Like maritoclax, KS04 or KS18 markedly reduced the half-life of Mcl-1 protein, induced apoptosis selectively in Mcl-1-dependent but not Bcl-2-dependent K562 cells, and acted synergistically with ABT-737 to enhance apoptosis in ABT-737 resistant HL60 cells. Moreover, the combination treatment of KS18 (10 mg/kg/d) and ABT-737 (20 mg/kg/d) significantly suppressed the growth of ABT-737-resistant HL60 xenografts in nude mice. Thus, further studies are warranted to develop pyoluteorin derivatives as a novel class of Mcl-1 inhibitors. Citation Format: Kenichiro Doi, Krishne Gowda, Qiang Liu, Shen-Shu Sung, Jyh Ming Lin, Shantu Amin, Thomas P. Loughran, Hong-Gang Wang. Characterization of pyoluteorin derivatives as Mcl-1 antagonists. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1805. doi:10.1158/1538-7445.AM2014-1805

PI3K and Bcl-2 inhibition primes glioblastoma cells to apoptosis through downregulation of Mcl-1 and Phospho-BAD.

Glioblastoma multiforme (GBM) is a highly malignant human brain neoplasm with limited therapeutic options. GBMs display a deregulated apoptotic pathway with high levels of the antiapoptotic Bcl-2 family of proteins and overt activity of the phosphatidylinositol 3-kinase (PI3K) signaling pathway. Therefore, combined interference of the PI3K pathway and the Bcl-2 family of proteins is a reasonable therapeutic strategy. ABT-263 (Navitoclax), an orally available small-molecule Bcl-2 inhibitor, and GDC-0941, a PI3K inhibitor, were used to treat established glioblastoma and glioblastoma neurosphere cells, alone or in combination. Although GDC-0941 alone had a modest effect on cell viability, treatment with ABT-263 displayed a marked reduction of cell viability and induction of apoptotic cell death. Moreover, combinatorial therapy using ABT-263 and GDC-0941 showed an enhanced effect, with a further decrease in cellular viability. Furthermore, combination treatment abrogated the ability of stem cell-like glioma cells to form neurospheres. ABT-263 and GDC-0941, in combination, resulted in a consistent and significant increase of Annexin V positive cells and loss of mitochondrial membrane potential compared with either monotherapy. The combination treatment led to enhanced cleavage of both initiator and effector caspases. Mechanistically, GDC-0941 depleted pAKT (Serine 473) levels and suppressed Mcl-1 protein levels, lowering the threshold for the cytotoxic actions of ABT-263. GDC-0941 decreased Mcl-1 in a posttranslational manner and significantly decreased the half-life of Mcl-1 protein. Ectopic expression of human Mcl-1 mitigated apoptotic cell death induced by the drug combination. Furthermore, GDC-0941 modulated the phosphorylation status of BAD, thereby further enhancing ABT-263-mediated cell death. Combination therapy with ABT-263 and GDC-0941 has novel therapeutic potential by specifically targeting aberrantly active, deregulated pathways in GBM, overcoming endogenous resistance to apoptosis.

Phase I study of ABT-199 (GDC-0199) in patients with relapsed/refractory (R/R) non-Hodgkin lymphoma (NHL): Responses observed in diffuse large B-cell (DLBCL) and follicular lymphoma (FL) at higher cohort doses.

8522 Background: The anti-apoptotic protein Bcl-2 is a highly expressed in NHL and contributes to chemotherapy resistance. ABT-199 is a selective, orally bioavailable, small molecule Bcl-2 inhibitor that is a promising agent for the treatment of patients (pts) with NHL. Methods: Objectives of this Phase I, dose-escalation study include evaluations of safety, pharmacokinetics (PK), and preliminary efficacy in pts with R/R NHL. ABT-199 was given on Week 1 Day -7 (W1D-7), followed by continuous, once-daily dosing from W1D1 until progressive disease or unacceptable toxicity. A 2 to 3 week lead-in period with stepwise dose titration was implemented. Final cohort doses of 200 - 900 mg have been evaluated. Results: As of December 4, 2013, 44 pts have been enrolled, 15 (35%) with mantle cell lymphoma (MCL), 11 (26%) with FL, 10 (23%) with DLBCL, 4 (9%) with Waldenstrom macroglobulinemia (WM), 2 (5%) with marginal zone (MZL), 1 (2%) with primary mediastinal B-cell lymphoma (PMBCL), and 1 (2%) with multiple myeloma...

Randomized phase II study of carboplatin and etoposide with or without obatoclax mesylate in extensive-stage small cell lung cancer

ObjectiveThis randomized phase II study assessed the efficacy and safety of obatoclax mesylate, a small-molecule Bcl-2 inhibitor, added to carboplatin/etoposide chemotherapy as initial treatment for extensive-stage small-cell lung cancer (ES-SCLC). Materials and methodsChemotherapy-naïve subjects with ES-SCLC and Eastern Cooperative Oncology Group performance status (ECOG PS) 0–2 received carboplatin/etoposide with (CbEOb) or without (CbE) obatoclax for up to six cycles. Responders to CbEOb could receive maintenance obatoclax until disease progression. The primary endpoint was objective response rate (ORR). Results155 subjects (median age 62, 58% male, 10% ECOG PS 2) were treated with CbEOb (n=77) or CbE (n=78); 65% and 59% of subjects, respectively, completed six cycles. ORR was 62% with CbEOb versus 53% with CbE (1-sided p=0.143). Clinical benefit (ORR+ stable disease) trended better with CbEOb (81% versus 68%; p=0.054). Median progression-free survival (PFS) and overall survival (OS) were 5.8 months (95% confidence interval [CI]: 5.3–6.5) and 10.5 months (8.9–13.8) with CbEOb and 5.2 months (95% CI: 4.1–5.7) and 9.8 months (7.2–11.2) with CbE. Median OS was 10.5 months (95% CI: 8.9–13.8) and 9.8 months (7.2–11.2) with a nonsignificant hazard ratio for OS, 0.823; 1-sided p=0.121. Grade 3/4 adverse events (AEs) were primarily hematologic and similar in frequency between treatment arms. Obatoclax-related somnolence and euphoria were grade 1/2, transient, and did not require treatment discontinuation. ConclusionObatoclax was well tolerated when added to carboplatin/etoposide in first-line treatment of ES-SCLC, but failed to significantly improve ORR, PFS, or OS.

The pro-death role of autophagy and apoptosis in cell death induced by the BH3 mimetic gossypol

Gossypol has been identified as a natural BH3 mimetic and a small-molecule inhibitor of Bcl-2 that can induce apoptosis in various cancer cell lines. In this study, we evaluated the effect of gossypol on apoptosis-proficient (wild-type [WT] mouse embryonic fibroblasts, MEFs) and apoptosis-deficient cells (Bax–/–/Bak–/– MEFs) in order to determine whether apoptosis indeed plays an essential death-promoting role in gossypol-mediated cell death. Unexpectedly, we found that Bax–/–/Bak–/– double-knockout (DKO) MEFs were more sensitive than the WT cells to gossypol-induced cell death. Gossypol caused progressive emergence of both apoptotic and necrotic cells in DKO MEFs; this result suggests that gossypol induces Bax/Bak-independent apoptosis. Conversely, fluorescence-activated cell sorting profiles showed no apoptotic cell death in WT MEFs. Rather, incubation of WT MEFs with gossypol markedly induced autophagy, as evidenced by punctate patterns of LC3 immunoreactivity, indicative of apoptosis-independent autophagic cell death. Nonetheless, there was only limited induction of autophagy in DKO MEFs. No significant differences between WT and DKO MEFs were observed in cell cycle profiles. Gossypol caused a weak increase of the percentage of cells at the G2/M checkpoint in the two cell lines, with a concomitant small decrease in the number of cells in the S phase. Taken together, our results suggest that apoptotic cell death is induced by gossypol in DKO MEFs, whereas autophagy plays a death-promoting role in gossypol-mediated death of WT MEFs cells.

Multiple components of the spliceosome regulate Mcl1 activity in neuroblastoma

Cancer treatments induce cell stress to trigger apoptosis in tumor cells. Many cancers repress these apoptotic signals through alterations in the Bcl2 proteins that regulate this process. Therapeutics that target these specific survival biases are in development, and drugs that inhibit Bcl2 activities have shown clinical activity for some cancers. Mcl1 is a survival factor for which no effective antagonists have been developed, so it remains a principal mediator of therapy resistance, including to Bcl2 inhibitors. We used a synthetic-lethal screening strategy to identify genes that regulate Mcl1 survival activity using the pediatric tumor neuroblastoma (NB) as a model, as a large subset are functionally verified to be Mcl1 dependent and Bcl2 inhibitor resistant. A targeted siRNA screen identified genes whose knockdown restores sensitivity of Mcl1-dependent NBs to ABT-737, a small molecule inhibitor of Bcl2, BclXL and BclW. Three target genes that shifted the ABT-737 IC50 >1 log were identified and validated: PSMD14, UBL5 and PRPF8. The latter two are members of a recently characterized subcomplex of the spliceosome that along with SART1 is responsible for non-canonical 5′-splice sequence recognition in yeast. We showed that SART1 knockdown similarly sensitized Mcl1-dependent NB to ABT-737 and that triple knockdown of UBL5/PRPF8/SART1 phenocopied direct MCL1 knockdown, whereas having no effect on Bcl2-dependent NBs. Both genetic spliceosome knockdown or treatment with SF3b-interacting spliceosome inhibitors like spliceostatin A led to preferential pro-apoptotic Mcl1-S splicing and reduced translation and abundance of Mcl1 protein. In contrast, BN82865, which inhibits the second transesterification step in terminal spliceosome processing, did not have this effect. These findings demonstrate a prominent role for the spliceosome in mediating Mcl1 activity and suggest that drugs that target either the specific UBL5/PRPF8/SART1 subcomplex or SF3b functions may have a role as cancer therapeutics by attenuating the Mcl1 survival bias present in numerous cancers.

The Single-Agent Bcl-2 Inhibitor ABT-199 (GDC-0199) In Patients With Relapsed/Refractory (R/R) Non-Hodgkin Lymphoma (NHL): Responses Observed In All Mantle Cell Lymphoma (MCL) Patients

IntroductionNew treatment options are needed for patients (pts) with R/R NHL, particularly in MCL where there are no curative options. Dysregulation of the anti-apoptotic protein Bcl-2 is a hallmark of NHL pathogenesis and contributes to chemotherapy resistance. ABT-199 is a selective, potent, orally bioavailable small molecule Bcl-2 inhibitor that is a promising agent for the treatment of pts with NHL. MethodsThe primary objectives of this phase I, dose-escalation study were to evaluate the safety and pharmacokinetics (PK), and to determine a maximum tolerated dose (MTD) and recommended phase 2 dose (RP2D) of ABT-199. Secondary objectives were to assess the efficacy of ABT-199 and to explore biomarkers for response. Adult pts requiring therapy, with ECOG performance status ≤1 and adequate marrow function (ANC ≥1.0 x 109/L, Plt ≥50 x 109/L) received ABT-199 on Week 1 Day -7 (W1D-7), followed by continuous, once-daily dosing from W1D1 until progressive disease or unacceptable toxicity. A 2 to 3 week lead-in period with stepwise escalation starting with lower doses to final cohort doses of 200, 300, 400, 600, and 900 mg was implemented. Evaluations include adverse events (AE; NCI-CTCAE-V4), PK parameters and disease responses (IWG 2007 criteria). ResultsAs of July 4, 2013, 32 pts were enrolled, 11 (34%) with follicular (FL), 8 (25%) with MCL, 8 (25%) with diffuse large B-cell (DLBCL), 1 (3%) with marginal zone (MZL), 3 (9%) with Waldenström macroglobulinemia (WM), and 1 (3%) multiple myeloma (MM). The median age was 68 (range 35-85), 63% were male with a median of 3.5 prior therapies (range 1-7), and the median time on study was 6.0 months (range 0.5-15.0). 44% of the pts had bulky disease ≥5 cm, including ≥10 cm in 16%. 22 pts have discontinued (D/C) drug: 18 due to progressive disease, 2 due to AEs, and 2 who proceeded to stem cell transplant in ongoing response. The most common AEs of any grade (G) occurring in ≥20% of pts were nausea (41%), diarrhea (31%), vomiting (22%), fatigue (22%), and upper respiratory tract infection (22%). G 3/4 AEs occurring in >3 pts were anemia (15%), neutropenia (13%), and thrombocytopenia (13%). G 3/4 thrombocytopenia was not dose-dependent or dose-limiting. Two of 10 pts in cohort 5 experienced a DLT (G3 febrile neutropenia and G4 neutropenia) at the target dose of 600 mg. G3 laboratory tumor lysis syndrome was seen after the initial dose in 1 pt with bulky MCL (elevations in phosphate and potassium only) and 1 pt with DLBCL (elevations in phosphate and uric acid only). After a single dose with food, ABT-199 had Tmax and T1/2 of approximately 8 and 15 hours, respectively. Food increased ABT-199 bioavailability by 3-4 fold. Preliminary efficacy data are summarized in the table. ConclusionsABT-199 showed anti-tumor activity as monotherapy for several NHL subtypes, with an overall response rate of 53% in this R/R population. Anti-tumor activity was seen in all MCL and WM pts treated across the range of ABT-199 cohort doses, and responses in DLBCL and FL pts were observed at doses ≥600 mg. Dose escalation is continuing to determine the MTD and RP2D. Biomarker studies are also underway in various NHL subtypes to explore a potential correlation with response. Disclosures:Seymour:Genentech: Consultancy, Membership on an entity's Board of Directors or advisory committees. Gerecitano:AbbVie: Research Funding; Genentech: Research Funding. Kahl:AbbVie, Inc.: Research Funding; Genentech: Consultancy, Research Funding. Wierda:AbbVie, Inc.: Research Funding; Genentech: Consultancy, Research Funding, Speakers Bureau. Anderson:Genentech: Research Funding; AbbVie, Inc.: Research Funding; Walter and Eliza Hall Institute of Medical Research: Employee, which recieves commercial income related to ABT-199, Employee, which recieves commercial income related to ABT-199 Other. Rudersdorf:AbbVie, Inc.: Employment, Stock Other. Gressick:AbbVie, Inc: Employment, Stock Other. Montalvo:AbbVie, Inc.: Employment, Stock Other. Yang:AbbVie, Inc.: Employment, Stock Other. Busman:AbbVie, Inc.: Employment, Stock Other. Dunbar:AbbVie, Inc.: Employment, Stock Other. Cerri:AbbVie, Inc.: Employment, Stock Other. Enschede:AbbVie, Inc.: Employment, Stock Other. Humerickhouse:AbbVie, Inc.: Employment, Stock Other. Roberts:AbbVie, Inc.: Research Funding; Genentech: Research Funding; Walter and Eliza Hall Institute of Medical Research: Employee, recieves commercial income related to ABT-199, Employee, recieves commercial income related to ABT-199 Other, Employment.

Primary T-Prolymphocytic Leukemia (T-PLL) Cells Are Sensitive To BCL-2 and HDAC Inhibitors: Results From High-Throughput Ex Vivo Drug Testing

IntroductionT-PLL is a rare mature post-thymic T-cell neoplasm with an aggressive clinical course and median overall survival of less than one year. Almost 75% of T-PLL cases harbor chromosome 14 translocations involving the T-cell receptor A/D locus resulting in aberrant activation of the proto-oncogenes TCL1A or MTCP1. T-PLL patients are difficult to treat as the leukemic cells are often resistant to most available chemotherapeutic drugs. Due to the rareness and aggressive nature of the disease, large clinical trials are difficult to execute. We therefore aimed to discover novel potential therapeutic targets using a high-throughput ex vivo drug sensitivity and resistance testing (DSRT) platform covering 306 approved and investigational oncology drugs. MethodsPrimary T-PLL cells were available from two patients. The first patient had a double positive CD4+CD8+CD3+ Vβ.14+ T-cell phenotype (patient 1) and cells underwent DSRT twice during a 5-month time-period (no treatment during that time). The second patient had a CD4+CD3+ phenotype (patient 2) and the cells were assayed once by DSRT. Fresh blood mononuclear cells (MNCs) were separated by Ficoll centrifugation from the patient samples (over 85 % leukemic cells in the MNC fraction) and healthy controls. Cells were seeded in 384-well plates and 306 active substances were tested using a 10,000-fold concentration range resulting in a dose-response curve for each compound. Cell viability was measured after 72 h incubation and differential drug sensitivity scores (DSS), representing leukemia-specific responses, were calculated by comparing patient samples with those obtained from healthy donors. In addition, both exome and RNA sequencing was performed from T-PLL cells (patient 1). ResultsBoth patient samples showed high sensitivity to small molecule BCL2-inhibitors navitoclax (EC50 values 44nM and 10nM) and ABT-199 (EC50 23nM and 20nM) (Fig. 1 and 2). HDAC-inhibitors (quisinostat, belinostat and panobinostat) also showed high sensitivity in both patients in low nM concentrations (EC50 values 1-80nM). As AKT1/mTOR pathway is activated in most T-PLL patients due to the TCL1 oncoprotein, it was interesting to observe that neither of the patient samples showed any response to an AKT1 inhibitor (MK-2206 EC50 values >1000 nM) nor to mTOR inhibitors (temsirolimus and everolimus)(Fig. 1). Furthermore, T-PLL cells were resistant to corticosteroids such as prednisolone and methylprednisolone. [Display omitted] [Display omitted] To further elucidate the molecular mechanism behind the drug responses, exome and RNA sequencing was performed from T-PLL cells (patient 1). No deletion was found in the ATM gene, but instead a homozygous missense mutation K2413Q was detected. This particular mutation is in the region coding for the FAT domain and while it has not been described earlier in T-PLL, it is in a cancer mutation hotspot region of ATM, suggesting that it is inactivating. No mutations directly linked to the BCL2-family genes were observed. In the RNA sequencing analysis, TCL1A was overexpressed when compared to the healthy CD4+ cells as expected. Similarly, AKT1 was overexpressed. The expression of BCL-2 and BCL-XL did not differ from those observed in healthy CD4+ cells while pro-apoptotic BCL-2 family members BID and BAD were elevated compared to the healthy control. ConclusionsPrimary T-PLL cells showed sensitivity to BCL-2 and HDAC inhibitors in a systematic high-throughput ex vivo drug sensitivity testing across a range of clinical and investigational drugs. The BCL-2 inhibitor sensitivity was not related to increased BCL-2 expression or activating mutations in the BCL-2 family genes, and further studies are needed to clarify the mechanism of action. However, the results suggest that BCL-2 inhibitors could be a novel promising candidate drug for T-PLL-patients and warrant further clinical development in this group of patients. In contrast, inhibitors of AKT and mTOR, kinases known to be activated by TCL1, showed no efficacy ex vivo in this assay. Disclosures:Porkka:BMS: Consultancy, Research Funding, Speakers Bureau; Novartis: Consultancy, Research Funding, Speakers Bureau. Mustjoki:Novartis: Consultancy, Speakers Bureau; BMS: Consultancy, Speakers Bureau.

Abstract A12: Small molecule inhibitor of BCL2 in combination with RCHOP is effective in CD20 negative DLBCL.

Abstract Rituximab alone or in combination with chemotherapeutics is the first-line therapy for diffuse large B cell lymphomas (DLBCL). Although the complete response rate is quite impressive, vast majority of patient presents recurrent disease. The association between CD20 expression and clinical outcome in patients strongly suggests that reduced CD20 expression leads to inferior response to RCHOP (rituximab, cyclophosphamide, vincristine, doxorubicin and prednisone). In order to understand how loss of CD20 leads to development of RCHOP resistance, we developed rituximab resistant DoHH2 model in vivo by chronic exposure to rituximab. Characterization of several resistant in vivo xenografts revealed one model that maintained resistance to an acute dose of rituximab and demonstrated loss of CD20. Further characterization of the model demonstrated a loss of CD20 is associated with over expression of BCL2 and BIM. In vivo efficacy studies showed resistant line is insensitive to acute dose of RCHOP and treatment with an inhibitor of BCL2 (ABT199) in combination with chemotherapy resulted in better efficacy than RCHOP alone. We have identified an in vivo model of DLBCL where loss of CD20 and over expression of anti-apoptotic protein BCL2 leads to RCHOP resistance. These data suggest the addition of BCL2 inhibitor to chemotherapy might be effective in treating CD20 negative lymphomas. Citation Information: Mol Cancer Ther 2013;12(11 Suppl):A12. Citation Format: Chaitali Dutta, Michele Mayo, Mike Collins, Christopher Brueckner, Deborah Lawson, Zhongwu Lai, Larry Bao, Corinne Reimer. Small molecule inhibitor of BCL2 in combination with RCHOP is effective in CD20 negative DLBCL. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr A12.

Naringenin에 의한 인체혈구암세포의 apoptosis 유발에 미치는 pro-apoptotic Bcl-2의 영향

감귤류에 많이 함유되어 있는 naringenin은 항암화학요법제로서 중요한 가능성을 가지고 있으나 항암활성에 대한 분자생물학적 기전에 대해서는 명확히 밝혀져 있지 않다. 본 연구에서는 인체 혈구암세포인 U937 세포에서 naringenin이 유발하는 항암효과 및 항암기전을 조사하였다. Naringenin 처리에 의한 U937 세포의 증식억제는 apoptosis 유발과 연관성이 있었으며, 이러한 현상은 caspases 활성화와 밀접한 관련이 있었다. 그러나 pan-caspase inhibitor인 z-VAD-fmk의 선처리에 의하여 U937 세포에서 naringenin이 유발하는 apoptosis가 억제되는 것으로 나타났으므로 caspases가 apoptosis 유발의 중요한 조절자라는 것을 알 수 있었다. 또한 U937 세포에 naringenin을 처리하였을 경우 pro-apoptotic Bcl-2 및 anti-apoptotic Bax의 발현에는 아무런 변화가 나타나지는 않았지만 Bcl-2가 과발현된 U937/Bcl-2 세포에서 naringenin에 의한 apoptosis가 억제되었다. 하지만 small-molecule Bcl-2 inhibitor인 HA14-1 및 naringenin을 같이 처리하였을 경우에는 XIAP 발현감소, Bid 단편화 및 caspase-3 활성화를 통하여 다시 apoptosis가 유발되었다. 따라서 HA14-1 및 naringenin에 의한 apoptosis 상승효과는 death receptor-mediated apoptosis pathway를 경유한다는 것을 제시하는 결과이다. Naringenin, a naturally occurring citrus flavonone, is a potentially valuable candidate for cancer chemotherapy. However, the cellular and molecular mechanisms responsible for its anticancer activity are largely unknown. In the present study, we attempted to elucidate the mechanisms responsible for naringenin-induced apoptosis in human leukemic U937 cells. We found that naringenin markedly inhibited the growth of U937 cells by decreasing cell proliferation and inducing apoptosis, which was associated with the activation of caspases. A pan-caspase inhibitor, z-VAD-fmk, significantly inhibited naringenin-induced U937 cell apoptosis, indicating that caspases are key regulators of apoptosis in response to naringenin in U937 cells. Although the levels of antiapoptotic Bcl-2 and proapoptotic Bax proteins remained unchanged in naringenin-treated U937 cells, Bcl-2 overexpression attenuated naringenin-induced apoptosis. Furthermore, combined treatment with naringenin and HA14-1, a small-molecule Bcl-2 inhibitor, effectively increased the apoptosis through enhancement of XIAP down-regulation, Bid cleavage, and caspase activation, suggesting that the synergistic effect was at least partially mediated through the death receptor-mediated apoptosis pathway.

Targeting apoptosis to induce stable mixed hematopoietic chimerism and long-term allograft survival without myelosuppressive conditioning in mice

AbstractInduction of mixed hematopoietic chimerism results in donor-specific immunological tolerance by apoptosis-mediated deletion of donor-reactive lymphocytes. A broad clinical application of this approach is currently hampered by limited predictability and toxicity of the available conditioning protocols. We developed a new therapeutic approach to induce mixed chimerism and tolerance by a direct pharmacological modulation of the intrinsic apoptosis pathway in peripheral T cells. The proapoptotic small-molecule Bcl-2 inhibitor ABT-737 promoted mixed chimerism induction and reversed the antitolerogenic effect of calcineurin inhibitors by boosting the critical role of the proapoptotic Bcl-2 factor Bim. A short conditioning protocol with ABT-737 in combination with costimulation blockade and low-dose cyclosporine A resulted in a complete deletion of peripheral donor-reactive lymphocytes and was sufficient to induce mixed chimerism and robust systemic tolerance across full major histocompatibility complex barriers, without myelosuppression and by using moderate doses of bone marrow cells. Thus, immunological tolerance can be achieved by direct modulation of the intrinsic apoptosis pathway in peripheral lymphocytes—a new approach to translate immunological tolerance into clinically applicable protocols.

Induction of Apoptosis by Fucoidan in Human Leukemia U937 Cells through Activation of p38 MAPK and Modulation of Bcl-2 Family

The present study investigated possible mechanisms on the apoptosis induction of human leukemic cells by fucoidan, a sulfated polysaccharide found in marine algae. Fucoidan treatment of cells resulted in inhibition of growth and induction of apoptosis, as measured by 3-(4,5-dimetylthiazol-2-yl)-2,5-diphenyl-tetrazolium (MTT) assay, fluorescence microscopy, DNA fragmentation, and flow cytometry analysis. The increase in apoptosis was associated with the proteolytic activation of caspases, Bid cleavage, insertion of pro-apoptotic Bax into the mitochondria, release of cytochrome c from mitochondria to cytosol, and loss of mitochondria membrane potential (MMP) in U937 cells. However, apoptosis induced by fucoidan was attenuated by caspase inhibitors, indicating that fucoidan-induced apoptosis was dependent on the activation of caspases. Furthermore, fucoidan treatment effectively activated the p38 mitogen-activated protein kinase (MAPK) and p38 MAPK inhibitor, SB203580, and significantly reduced fucoidan-induced apoptosis through inhibition of Bax translocation and caspases activation, suggesting that the activation of p38 MAPK may play a key role in fucoidan-induced apoptosis. In addition, the authors found fucoidan-induced significantly attenuated in Bcl-2 overexpressing U937 cells, and pretreatment with fucoidan and HA 14-1, a small-molecule Bcl-2 inhibitor, markedly increased fucoidan-mediated apoptosis in Bcl-2 overexpressing U937 cells. Our findings imply that we may attribute some of the biological functions of p38 MAPK and Bcl-2 to their ability to inhibit fucoidan-induced apoptosis.

Induction of apoptosis and antitumor effects of a small molecule inhibitor of Bcl-2 and Bcl-xl, gossypol acetate, in multiple myeloma in vitro and in vivo

Gossypol is a naturally occurring polyphenolic compound extracted from cotton plants. Recent studies revealed that gossypol is a non-peptidic small molecule inhibitor of Bcl-2/Bcl-xl. The aim of the present study was to investigate the induction of apoptosis and antitumor effects of gossypol acetate in multiple myeloma and the possible mechanism(s) of action. Our results showed that gossypol acetate resulted in a dose- and time-dependent inhibition of multiple myeloma cell proliferation, with an IC50 value to both U266 and Wus1 cells at 2.4, 2.2µM at 48h after treatment. Gossypol acetate effectively induced the apoptosis of multiple myeloma cells as demonstrated by typical morphological changes, DNA ladder formation and increase in the percentage of cells in subdiploid peak. Furthermore, colorimetric assays showed activation of both caspase-3 and caspase-9. Bcl-2 and Bcl-xl expression was decreased by 86.5±1.2% and 35.9±3.6%, respectively, after treatment with gossypol acetate at 25µmol/l for 24h. Preliminary studies invivo showed that a growth inhibition (T/C) of 30.9% (gossypol acetate 40mg/kg) was obtained in Balb/C mice bearing Wus1 cells. In addition, there was no body weight loss for the treated group in comparison with the vehicle mice. Our results demonstrated that the potent inhibitor of Bcl-2 and Bcl-xl gossypol acetate had significant antiproliferative and antiapoptotic effects on multiple myeloma cells invitro and invivo. Gossypol acetate may represent a promising new anticancer agent with a novel molecular mechanism and warrants further investigation as a single agent, or in combination with other chemotherapeutics, for human multiple myeloma with Bcl-2 overexpression.

Abstract 1720: Maritoclax, a selective Mcl-1 inhibitor, sensitizes melanoma cells to the Bad BH3-mimetic ABT-737.

Abstract Melanoma is the most aggressive form of skin cancer. Despite the development of the therapies it remains one of the most invasive and highly drug resistance cancers. The dysregulation of apoptosis are thought to be one barrier to effective systemic treatment of melanoma. The overexpression of anti-apoptotic Bcl-2 family proteins has been associated with inferior survival, poor prognosis and chemoresistance of several cancers including malignant melanoma. ABT-737, a small-molecule inhibitor of Bcl-2, Bcl-xL and Bcl-w, has demonstrated efficacy in several forms of hematological and non-hematological cancers. However, the efficacy of ABT-737 is diminished in cancer cells with high levels of Mcl-1, another anti-apoptotic member of the Bcl-2 family. The overexpression of Mcl-1 is frequently observed in melanoma and therefore, specifically targeting of Mcl-1 may overcome the resistance of ABT-737. In this study, we investigated the effects of Maritoclax, a novel Mcl-1-selective inhibitor, alone and in combination with ABT-737, on the survival of human melanoma cells. The treatments of Maritoclax reduce the cell viabilities of melanoma cells with an IC50 of between 2.2-5.0μM. Further, treatment of melanoma cells with 2.5 μM Maritoclax for 24 h showed significant decrease in Mcl-1 expression. We found that Maritoclax is able to induce apoptosis in melanoma cells in a caspase-dependent manner. Moreover, Maritoclax induces Mcl-1 degradation via the proteasome system, which is associated with its pro-apoptotic activity. Importantly, Maritoclax markedly enhances the efficacy of ABT-737 against melanoma cells. As a single agent, ABT-737 was not efficient in killing UACC 903 cells with IC50 values of >30 μm. However, in combination with a sub-optimal dose of Maritoclax (2.5μM), the efficacy of ABT-737 was enhanced (IC50 1.3 μm). Similarly, Maritoclax potentiated apoptotic effects of ABT-737 from 20%-71% and 18%-62% when measured by Live and Dead and annexin-V assay, respectively. Taken together, these results suggest that targeting of Mcl-1 by Maritoclax may represent a new therapeutic strategy to sensitize melanoma cells to ABT-737-induced apoptosis. Citation Format: Manoj K. Pandey, Krishne Gowda, Kenichiro Doi, Arun Sharma, Hong-Gang Wang, Shantu Amin. Maritoclax, a selective Mcl-1 inhibitor, sensitizes melanoma cells to the Bad BH3-mimetic ABT-737. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1720. doi:10.1158/1538-7445.AM2013-1720

Abstract SY24-02: Remarkable early clinical activity with the Bcl-2 selective inhibitor ABT-199: Proving the concept.

Abstract SY24-02: Remarkable early clinical activity with the Bcl-2 selective inhibitor ABT-199: Proving the concept.

A small molecule inhibitor of Bcl-2, HA14-1, also inhibits ceramide glucosyltransferase

HA14-1 is a Bcl-2 inhibitor that is widely used for studies of apoptosis. In the course of searching for a ceramide glucosyltransferase inhibitor that catalyzes the first glycosylation step of glycosphingolipid synthesis, we unexpectedly found that HA-14-1 also has the ability to inhibit ceramide glucosyltransferase. The IC50 value of HA14-1 against ceramide glucosyltransferase is 4.5μM, which is lower than that reported for Bcl-2 in vitro. Kinetic analyses revealed that HA14-1 is a competitive and mixed-type inhibitor with respect to C6-NBD-ceramide and UDP-glucose, respectively.

ABT-199: Taking Dead Aim at BCL-2

ABT-199 is a new selective small molecule inhibitor of BCL-2 that appears to spare platelets while achieving potent antitumor activity. Assays that can predict the efficacy of ABT-199 in individual tumors will be critical in determining how best to incorporate this promising agent into the armamentarium of cancer therapies.

Synergistic Bcl-2 inhibition by ABT-737 and cyclosporine A

Survival of lymphocytes and melanocyte stem cells critically depends on B cell lymphoma 2 (Bcl-2). In T lymphocytes, a basal calcineurin activity maintains Bcl-2 expression in naïve cells, and the activation of the calcineurin pathway orchestrates the regulation of the intrinsic apoptosis pathway after antigen recognition. Therefore, calcineurin inhibitors might potentiate the pro-apoptotic effect of pharmacological Bcl-2 inhibitors on lymphatic cells. In vitro, a reduced Bcl-2 expression in lymphocytes exposed to calcineurin inhibitors increased their sensitivity to the small molecule Bcl-2 inhibitor ABT-737. This correlated with an augmented pro-apoptotic activity of ABT-737 on lymphocytes in combination with cyclosporine A in naïve mice in vivo. Interestingly, similar processes were observed in melanocytes. ABT-737 induced a fur depigmentation at the site of injection, and this effect was expanded to a generalized depigmentation in combination with cyclosporine A. Thus, inhibiting calcineurin increases the pro-apoptotic potency of ABT-737 in cells depending on Bcl-2 for survival. The increased efficacy of Bcl-2 inhibitors in combination with cyclosporine A might be relevant to exploit their anti-neoplastic and immuno-modulatory properties.

Structure-based design of potent Bcl-2/Bcl-xL inhibitors with strong in vivo antitumor activity.

Bcl-2 and Bcl-xL are key apoptosis regulators and attractive cancer therapeutic targets. We have designed and optimized a class of small-molecule inhibitors of Bcl-2 and Bcl-xL containing a 4,5-diphenyl-1H-pyrrole-3-carboxylic acid core structure. A 1.4 Å resolution crystal structure of a lead compound, 12, complexed with Bcl-xL has provided a basis for our optimization. The most potent compounds, 14 and 15, bind to Bcl-2 and Bcl-xL with subnanomolar K(i) values and are potent antagonists of Bcl-2 and Bcl-xL in functional assays. Compounds 14 and 15 inhibit cell growth with low nanomolar IC(50) values in multiple small-cell lung cancer cell lines and induce robust apoptosis in cancer cells at concentrations as low as 10 nM. Compound 14 also achieves strong antitumor activity in an animal model of human cancer.

Design of Bcl-2 and Bcl-xL inhibitors with subnanomolar binding affinities based upon a new scaffold.

Employing a structure-based strategy, we have designed a new class of potent small-molecule inhibitors of the anti-apoptotic proteins Bcl-2 and Bcl-xL. An initial lead compound with a new scaffold was designed based upon the crystal structure of Bcl-xL and U.S. Food and Drug Administration (FDA) approved drugs and was found to have an affinity of 100 μM for both Bcl-2 and Bcl-xL. Linking this weak lead to another weak-affinity fragment derived from Abbott's ABT-737 led to an improvement of the binding affinity by a factor of >10 000. Further optimization ultimately yielded compounds with subnanomolar binding affinities for both Bcl-2 and Bcl-xL and potent cellular activity. The best compound (21) binds to Bcl-xL and Bcl-2 with K(i) < 1 nM, inhibits cell growth in the H146 and H1417 small-cell lung cancer cell lines with IC(50) values of 60-90 nM, and induces robust cell death in the H146 cancer cell line at 30-100 nM.