Expression Of Bcl-2 Family Members Research Articles

Synergistic drug interactions of the histone deacetylase inhibitor givinostat (ITF2357) in CRLF2-rearranged pediatric B-cell precursor acute lymphoblastic leukemia identified by high-throughput drug screening

Combining multiple drugs broadens the window of therapeutic opportunities and is crucial for diseases that are currently lacking fully curative treatments. A powerful emerging tool for selecting effective drugs and combinations is the high-throughput drug screening (HTP). The histone deacetylase inhibitor (HDACi) givinostat (ITF2357) has been shown to act effectively against CRLF2-rearranged pediatric B-cell precursor acute lymphoblastic leukemia (BCP-ALL), a subtype characterized by poor outcome and enriched in children with Down Syndrome, very fragile patients with a high susceptibility to treatment-related toxicity. The aim of this study is to investigate possible synergies with givinostat for these difficult-to-treat patients by performing HTP screening with a library of 174 drugs, either approved or in preclinical studies. By applying this approach to the CRLF2-r MHH-CALL-4 cell line, we identified 19 compounds with higher sensitivity in combination with givinostat compared to the single treatments. Next, the synergy between givinostat and the promising candidates was further validated in CRLF2r cell lines with a broad matrix of concentrations. The combinations with trametinib (MEKi) or venetoclax (BCL2i) were found to be the most effective and with the greatest synergy across three metrics (ZIP, HAS, Bliss). Their efficacy was confirmed in primary blasts treated ex vivo at concentration ranges with a safe profile on healthy cells. Finally, we described givinostat-induced modifications in gene expression of MAPK and BCL-2 family members, supporting the observed synergistic interactions. Overall, our study represents a model of drug repurposing strategy using HTP screening for identifying synergistic, efficient, and safe drug combinations.

Artesunate promotes cervical cancer cell apoptosis by regulating Bcl2 family molecules and reducing the mitochondrial membrane potential.

Artesunate (ART), an antimalarial drug, has a broad spectrum of antitumour effects in cancer types such as esophageal and gastric cancer. However, evidence demonstrating the role of ART in cervical cancer cells is limited. In the present study, the inhibitory effect of ART on the growth of cervical cancer cells through the modulation of the cell cycle and apoptosis was investigated. The growth-inhibitory effect of ART on a cervical cancer cell line (SiHa) was detected using a Cell Counting Kit-8 assay after treatment with ART for 24 h, after which the half-maximal inhibitory concentration (IC50) was calculated. Using flow cytometry assays, apoptosis, the cell cycle, the levels of reactive oxygen species (ROS) and calcium (Ca2+) ions, as well as the mitochondrial membrane potential were evaluated in SiHa cells following treatment with ART for 24 and 48 h. The mRNA expression levels of Bcl2, Bcl-xl, (myeloid cell leukaemia 1) Mcl-1, Bcl2-like protein 11 (BIM), (Bcl2-related ovarian killer protein) Bok, Bax and (Bcl2 homologous antagonist/killer) Bak in SiHa cells were detected using reverse transcription-quantitative PCR. ART inhibited the growth of SiHa cells in a dose-dependent manner. The IC50 of ART in SiHa cells was 26.32 µg/ml. According to the IC50 value, 15, 30 and 100 µg/ml ART were selected for further experiments, and normal saline (0 µg/ml ART) was used as the control group. The results indicated that treatment with 15, 30 and 100 µg/ml ART for 24 and 48 h induced apoptosis, increased the levels of ROS, the levels of Ca2+ and the mRNA expression levels of BIM, Bok, Bax and Bak, but decreased the cell proliferation indices, the mitochondrial membrane potential and the mRNA expression levels of Bcl2, Bcl-xl and Mcl-1 in a dose- and time-dependent manner. In conclusion, ART inhibited the growth of SiHa cells and induced apoptosis via a mechanism associated with the regulation of Bcl2 family member expression, which was associated with the increase of the levels of ROS and Ca2+ and the reduction of the mitochondrial membrane potential.

Ajania pacifica (Nakai) K. Bremer and Humphries Extract Limits MYC Expression to Induce Apoptosis in Diffuse Large B Cell Lymphoma.

The proto-oncogene MYC is frequently dysregulated in patients with diffuse large B-cell lymphoma (DLBCL) and plays a critical role in disease progression. To improve the clinical outcomes of patients with DLBCL, the development of strategies to target MYC is crucial. The use of medicinal plants for developing anticancer drugs has garnered considerable attention owing to their diverse mechanisms of action. In this study, 100 plant extracts of flora from the Republic of Korea were screened to search for novel agents with anti-DLBCL effects. Among them, Ajania pacifica (Nakai) K. Bremer and Humphries extract (APKH) efficiently suppressed the survival of DLBCL cells, while showing minimal toxicity toward normal murine bone marrow cells. APKH suppressed the expression of anti-apoptotic BCL2 family members, causing an imbalance between the pro-apoptotic and anti-apoptotic BCL2 members. This disrupted mitochondrial membrane potential, cytochrome c release, and pro-caspase-3 activation and eventually led to DLBCL cell death. Importantly, MYC expression was markedly downregulated by APKH and ectopic expression of MYC in DLBCL cells abolished the pro-apoptotic effects of APKH. These results demonstrate that APKH exerts anti-DLBCL effects by inhibiting MYC expression. Moreover, when combined with doxorubicin, an essential component of the CHOP regimen (cyclophosphamide, doxorubicin, vincristine, and prednisone), APKH synergistically enhanced the therapeutic effect of doxorubicin. This indicates that APKH may overcome drug resistance, which is common in patients with refractory/relapsed DLBCL. To identify compounds with anti-DLBCL activities in APKH, the chemical profile analysis of APKH was performed using UPLC-QTOF/MSe analysis and assessed for its anticancer activity. Based on the UPLC-QTOF/MSe chemical profiling, it is conceivable that APKH may serve as a novel agent targeting MYC and sensitizing drug-resistant DLBCL cells to CHOP chemotherapy. Further studies to elucidate how the compounds in APKH exert tumor-suppressive role in DLBCL are warranted.

A phase I study of pevonedistat, azacitidine, and venetoclax in patients with relapsed/refractory acute myeloid leukemia.

Azacitidine/venetoclax is an active regimen in patients with newly diagnosed acute myeloid leukemia (AML). However, primary or secondary resistance to azacitidine/venetoclax is an area of unmet need and overexpression of MCL1 is suggested to be a potential resistance mechanism. Pevonedistat inhibits MCL1 through activation of NOXA, and pevonedistat/azacitidine has previously shown activity in AML. To assess the tolerability and efficacy of adding pevonedistat to azacitidine/ venetoclax in relapsed/refractory AML, we conducted a phase I, multicenter, open-label study in 16 adults with relapsed/ refractory AML. Patients were treated with azacitidine, venetoclax along with pevonedistat intravenously on days 1, 3 and 5 of each 28-day cycle at doses of 10, 15 or 20 mg/m2 in successive cohorts in the dose escalation phase. The impact of treatment on protein neddylation as well as expression of pro-apoptotic BCL2 family members was assessed. The recommended phase II dose of pevonedistat was 20 mg/m2. Grade 3 or higher adverse events included neutropenia (31%), thrombocytopenia (13%), febrile neutropenia (19%), anemia (19%), hypertension (19%) and sepsis (19%). The overall response rate was 46.7% for the whole cohort including complete remission in five of seven (71.4%) patients who had not previously been treated with the hypomethylating agent/venetoclax. No measurable residual disease was detected in 80.0% of the patients who achieved complete remission. The median time to best response was 50 (range, 23-77) days. Four patients were bridged to allogeneic stem cell transplantation. The combination of azacitidine, venetoclax and pevonedistat is safe and shows encouraging preliminary activity in patients with relapsed/refractory AML. (NCT04172844).

Abstract 4605: AZD4573 in combination with CHOP increases combination benefit in preclinical peripheral T-cell lymphoma models

Abstract Peripheral T-cell Lymphoma (pTCL) makes up about 10% of non-Hodgkin's lymphoma in the United States. Patients with relapsed/refractory pTCL have limited treatment options and poor prognosis. Current standard of care for pTCL revolves around the chemotherapy regimens CHOP/E. Here we examine the efficacy of CDK9 inhibition for the treatment of pTCL. CDK9 regulates transcription through phosphorylation of RNA polymerase II. AZD4573 is a highly potent and selective CDK9 inhibitor; acute inhibition with AZD4573 downregulates short-lived proteins such as MCL-1, BFL-1, and c-MYC, which are often overexpressed in hematologic tumors. It has been shown that the expression pattern of the anti-apoptotic BCL-2 family members in pTCL cell line models closely resembled the expression patterns in pTCL patient samples (Koch et al. 2019). Expression of BCL-2 family members is highly heterogeneous in pTCL, with MCL-1 being the most universally expressed. Using MCL-1 inhibitor AZD5991, we showed statistically significant benefit in survival when combined with CHOP in MCL-1 dependent preclinical pTCL PDX models (Koch et al. 2019). In addition, we have previously reported the importance of the anti-apoptotic protein BFL-1 in cell survival in NHL, including a subset of pTCL (Boiko et al 2021). AZD4573 treatment showed a range of activity across the panel of 18 human pTCL cell lines, in a 6-hour caspase-3/7 activation assay. 14 of the cell lines were sensitive, with EC50 values less than 100 nM, and 13 reached a max caspase activation of over 40%. pTCL subtypes that responded to AZD4573 treatment included ALCL, NK-TCL, and PTCL-NOS and CTCL. Acute AZD4573 treatment resulted in decreased pSer2-RNAP2 and reduced protein levels of c-MYC and MCL-1. To determine what was driving the apoptotic phenotype, we used ribonucleoprotein (RNP) mediated CRISPR knock out (KO) of MYC and MCL1 genes. While pTCL cell lines were dependent on c-MYC and MCL-1 for viability after KO, only MCL-1 KO impaired AZD4573 treatment, suggesting that efficacy is mediated through MCL-1 in ALCL pTCL cell lines assessed. To determine if combining AZD4573 with CHOP improved efficacy, we tested 5 pTCL cell lines in a 6x6 combination dosing matrix and measured viability after 24-72 hours using RealTime-Glo after 24hr exposure to CHOP with AZD4573 added for the last 6hrs. Adding AZD4573 to CHOP in vitro increased the efficacy in pTCL ALCL cell lines with MCL-1 dependency, but not in CTCL cell line with BCL-xL dependency and resistance to AZD4573. CHOP treatment in vitro resulted in a decrease in c-MYC levels but not MCL-1, suggesting that combination benefit may be driven through c-MYC. This data suggests that treatment with AZD4573 as a monotherapy or in combination with CHOP regimen would be an effective therapeutic strategy in pTCL. Citation Format: Danielle Sinead Potter, India Ott, Jamal Saeh, Richard Olsson, Stephen Fawell, Lisa Drew, Justine Roderick. AZD4573 in combination with CHOP increases combination benefit in preclinical peripheral T-cell lymphoma models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 4605.

AZD4573 in Combination with CHOP Increases Combination Benefit in Preclinical Peripheral T-Cell Lymphomas Models

Peripheral T-cell Lymphoma (pTCL) make up about 10% of non-Hodgkin's lymphoma in the United States. Patients with relapsed/refractory pTCL have limited treatment options and poor outcomes to standard of care therapy. Current standard of care for pTCL revolves around the chemotherapy regimens CHOP/E and for CD30-postive pTCLs, brentuximab vedotin is approved. CDK9 regulates transcription elongation through phosphorylation of RNA polymerase II. AZD4573 is a highly potent and selective CDK9 inhibitor, acute inhibition with AZD4573 downregulates short-lived proteins such as MCL-1, BFL-1, and c-MYC, which are frequently overexpressed in haematologic tumours. It has been previously shown that the expression pattern of the anti-apoptotic BCL-2 family members in pTCL cell line models closely resembled the expression patterns in pTCL patient samples (Koch et al. 2019). Expression and dependencies of the anti-apoptotic BCL-2 family members is highly heterogeneous in pTCL; however MCL-1 is the most universally expressed BCL-2 family member. Using the MCL-1 inhibitor AZD5991, we have shown statistically significant benefit in survival when combined with CHOP in 2 MCL-1 dependent preclinical pTCL PDX models (Koch et al. 2019). In addition to MCL-1, we have previously reported the importance of the anti-apoptotic protein BFL-1 in mediating cell survival in NHL, including a subset of pTCL (Boiko et al 2021). Consistent with these findings, AZD4573 treatment exhibited a range of activity across the panel of 18 human TCL cell lines, in a 6-hour caspase-3/7 activation assay. 14 of the cell lines were sensitive, having EC 50 values < 100 nM, and 13 reached a max caspase-3/7 activation of greater than 40%. pTCL cell lines that responded to AZD4573 treatment including ALCL, NK-TCL, and PTCL-NOS and CTCL subtypes. Acute AZD4573 treatment of pTCL cell lines resulted in decreased p-SerRNApoll II and reduced levels of c-MYC and MCL-1 protein levels. To determine if MCL-1 or c-MYC was driving the apoptotic phenotype, we used ribonucleoprotein (RNP) mediated CRISPR knock out (KO) of MYC and MCL1 genes. While pTCL cell lines were dependent on c-MYC and MCL-1 after long term KO, only MCL-1 KO impaired AZD4573 treatment, suggesting that AZD4573 efficacy is mediated through MCL-1, in ALCL pTCL cell lines tested. To determine if combining AZD4573 with CHOP improved efficacy, we tested 5 pTCL cell lines in a 6x6 combination dosing matrix and assessed for viability after 24-72 hours using RealTime-Glo after 18hr exposure to CHOP and AZD4573 added for the last 6hrs. Adding AZD4573 treatment to CHOP schedule in vitro increased the combination benefit in pTCL ALCL cell lines that show MCL-1 dependency, but not in CTCL cell line which show a BCL-xL dependency and resistance to AZD4573. CHOP treatment in vitro resulted in a decrease in c-MYC levels at 24-48 hours, but not MCL-1 suggesting that combination benefit may be driven through decreased c-MYC levels, as KO of c-MYC resulted is loss of cell viability in these models. These data suggested that treatment with AD4573 either as a monotherapy or in combination with CHOP, would be an effective therapeutic strategy in pTCL. AZD4573 monotherapy is currently being evaluated in a phase 2 study (NCT05140382) to assess the efficacy, safety, and PK in patients with relapsed/refractory pTCL.

BCL-W makes only minor contributions to MYC-driven lymphoma development.

The BH3-mimetic drug Venetoclax, a specific inhibitor of anti-apoptotic BCL-2, has had clinical success for the treatment of chronic lymphocytic leukaemia and acute myeloid leukaemia. Attention has now shifted towards related pro-survival BCL-2 family members, hypothesising that new BH3-mimetic drugs targeting these proteins may emulate the success of Venetoclax. BH3-mimetics targeting pro-survival MCL-1 or BCL-XL have entered clinical trials, but managing on-target toxicities is challenging. While increasing evidence suggests BFL-1/A1 is a resistance factor for diverse chemotherapeutic agents and BH3-mimetic drugs in haematological malignancies, few studies have explored the role of BCL-W in the development, expansion, and therapeutic responses of cancer. Previously, we found that BCL-W was not required for the ongoing survival and growth of various established human Burkitt lymphoma and diffuse large B cell lymphoma cell lines. However, questions remained about whether BCL-W impacts lymphoma development. Here, we show that BCL-W appears dispensable for MYC-driven lymphomagenesis, and such tumours arising in the absence of BCL-W show no compensatory changes to BCL-2 family member expression, nor altered sensitivity to BH3-mimetic drugs. These results demonstrate that BCL-W does not play a major role in the development of MYC-driven lymphoma or the responses of these tumours to anti-cancer agents.

NOXA Accentuates Apoptosis Induction by a Novel Histone Deacetylase Inhibitor.

Epigenetic modifiers of the histone deacetylase (HDAC) family are often dysregulated in cancer cells. Experiments with small molecule HDAC inhibitors (HDACi) have proven that HDACs are a vulnerability of transformed cells. We evaluated a novel hydroxamic acid-based HDACi (KH16; termed yanostat) in human pancreatic ductal adenocarcinoma (PDAC) cells, short- and long-term cultured colorectal cancer (CRC) cells, and retinal pigment epithelial cells. We show that KH16 induces cell cycle arrest and apoptosis, both time and dose dependently in PDAC and CRC cells. This is associated with altered expression of BCL2 family members controlling intrinsic apoptosis. Recent data illustrate that PDAC cells frequently have an altered expression of the pro-apoptotic BH3-only protein NOXA and that HDACi induce an accumulation of NOXA. Using PDAC cells with a deletion of NOXA by CRISPR-Cas9, we found that a lack of NOXA delayed apoptosis induction by KH16. These results suggest that KH16 is a new chemotype of hydroxamic acid HDACi with superior activity against solid tumor-derived cells. Thus, KH16 is a scaffold for future research on compounds with nanomolar activity against HDACs.

The comprehensive expression of BCL2 family genes determines the prognosis of diffuse large B-cell lymphoma

Diffuse large B-cell lymphoma (DLBCL) is a prevalent and aggressive non-Hodgkin's lymphoma, and 40% of patients succumb to death. Despite numerous clinical trials aimed at developing treatment strategies beyond the conventional R–CHOP (rituximab, cyclophosphamide, doxorubicin, vincristine, and prednisone) regimen, there have been no positive results thus far. Although the selective BCL2 inhibitor venetoclax has shown remarkable efficacy in chronic lymphocytic leukemia, its therapeutic effect in DLBCL was limited. We hypothesized that the limited therapeutic effect of venetoclax in DLBCL may be attributed to the complex expression and interactions of BCL2 family members, including BCL2. Therefore, we aimed to comprehensively analyze the expression patterns of BCL2 family members in DLBCL. We analyzed 157 patients with de novo DLBCL diagnosed at Asan Medical Center and Ajou University Hospital. The mRNA expression levels of BCL2 family members were quantified using the NanoString technology. BCL2 family members showed distinct heterogeneous expression patterns both intra- and inter-patient. Using unsupervised hierarchical cluster analysis, we were able to classify patients with similar BCL2 family expression pattern and select groups with clear prognostic features, C1 and C6. In the group with the best prognosis, C1, the expression of pro-apoptotic and pro-apoptotic BH3-only group gene expressions were increased, while anti-apoptotic group expression was significantly increased in both C1 and C6. Based on this, we generated the BCL2 signature score using the expression of pro-apoptotic genes BOK and BCL2L15, and anti-apoptotic gene BCL2. The BCL2 signature score 0 had the best prognosis, score 1/2 had intermediate prognosis, and score 3 had the worst prognosis (EFS, p = 0.0054; OS, p = 0.0011). Multivariate analysis, including COO and IPI, showed that increase in the BCL2 signature score was significantly associated with poor prognosis for EFS, independent of COO and IPI. The BCL2 signature score we proposed in this study provides information on BCL2 family deregulation based on the equilibrium of pro-versus anti-apoptotic BCL2 family, which can aid in the development of new treatment strategies for DLBCL in the future.

Anti-apoptotic protein BCL-XL as a therapeutic vulnerability in gastric cancer.

New therapeutic targets are needed to improve the outcomes for gastric cancer (GC) patients with advanced disease. Evasion of programmed cell death (apoptosis) is a hallmark of cancer cells and direct induction of apoptosis by targeting the pro-survival BCL2 family proteins represents a promising therapeutic strategy for cancer treatment. Therefore, understanding the molecular mechanisms underpinning cancer cell survival could provide a molecular basis for potential therapeutic interventions. Here we explored the role of BCL2L1 and the encoded anti-apoptotic BCL-XL in GC. Using Droplet Digital PCR (ddPCR) technology to investigate the DNA amplification of BCL2L1 in GC samples and GC cell lines, the sensitivity of GC cell lines to selective BCL-XL inhibitors A1155463 and A1331852, pan-inhibitor ABT-263, and VHL-based PROTAC-BCL-XL was analyzed using (CellTiter-Glo) CTG assay in vitro. Western Blot (WB) was used to detect the protein expression of BCL2 family members in GC cell lines and the manner in which PROTAC-BCL-XL kills GC cells. Co-immunoprecipitation (Co-IP) was used to investigate the mechanism of A1331852 and ABT-263 kills GC cell lines. DDPCR, WB, and real-time PCR (RTPCR) were used to investigate the correlation between DNA, RNA, protein levels, and drug activity. The functional assay showed that a subset of GC cell lines relies on BCL-XL for survival. In gastric cancer cell lines, BCL-XL inhibitors A1155463 and A1331852 are more sensitive than the pan BCL2 family inhibitor ABT-263, indicating that ABT-263 is not an optimal inhibitor of BCL-XL. VHL-based PROTAC-BCL-XL DT2216 appears to be active in GC cells. DT2216 induces apoptosis of gastric cancer cells in a time- and dose-dependent manner through the proteasome pathway. Statistical analysis showed that the BCL-XL protein level predicts the response of GC cells to BCL-XL targeting therapy and BCL2L1 gene CNVs do not reliably predict BCL-XL expression. We identified BCL-XL as a promising therapeutic target in a subset of GC cases with high levels of BCL-XL protein expression. Functionally, we demonstrated that both selective BCL-XL inhibitors and VHL-based PROTAC BCL-XL can potently kill GC cells that are reliant on BCL-XL for survival. However, we found that BCL2L1 copy number variations (CNVs) cannot reliably predict BCL-XL expression, but the BCL-XL protein level serves as a useful biomarker for predicting the sensitivity of GC cells to BCL-XL-targeting compounds. Taken together, our study pinpointed BCL-XL as potential druggable target for specific subsets of GC.

Dual targeting of BCL-2 and MCL-1 in the presence of BAX breaks venetoclax resistance in human small cell lung cancer.

No targeted drugs are currently available against small cell lung cancer (SCLC). BCL-2 family members are involved in apoptosis regulation and represent therapeutic targets in many malignancies. Expression of BCL-2 family members in 27 SCLC cell lines representing all known four SCLC molecular subtypes was assessed by qPCR, Western blot and mass spectrometry-based proteomics. BCL-2 and MCL-1 inhibition (venetoclax and S63845, respectively) was assessed by MTT assay and flow cytometry and in mice bearing human SCLC tumours. Drug interactions were calculated using the Combenefit software. Ectopic BAX overexpression was achieved by expression plasmids. The highest BCL-2 expression levels were detected in ASCL1- and POU2F3-driven SCLC cells. Although sensitivity to venetoclax was reflected by BCL-2 levels, not all cell lines responded consistently despite their high BCL-2 expression. MCL-1 overexpression and low BAX levels were both characteristic for venetoclax resistance in SCLC, whereas the expression of other BCL-2 family members did not affect therapeutic efficacy. Combination of venetoclax and S63845 resulted in significant, synergistic in vitro and in vivo anti-tumour activity and apoptosis induction in double-resistant cells; however, this was seen only in a subset with detectable BAX. In non-responding cells, ectopic BAX overexpression sensitised to venetoclax and S63845 and, furthermore, induced synergistic drug interaction. The current study reveals the subtype specificity of BCL-2expression and sheds light on the mechanism of venetoclax resistance in SCLC. Additionally, we provide preclinical evidence that combined BCL-2 and MCL-1 targeting is an effective approach to overcome venetoclax resistance in high BCL-2-expressing SCLCs with intact BAX.

Bcl-2 Family (Bcl-2, Mcl-1, Bim and Bax) and Btk Expression in B-Cell Chronic Lymphocytic Leukemia (B-CLL) Lymphocytes in Different Lymphoid Compartments and Changes during Btk Inhibitor Therapies (ibrutinib or acalabrutinib)

B-cell chronic lymphocytic leukemia (B-CLL) is characterized with variable infiltration by B -CLL lymphocytes of various lymphoid compartments, i.e peripheral blood (PB), bone marrow (BM) and lymph nodes (LN) and lymphoid organs. Interactions with various microenvironments may result in different disease activity and resistance to apoptosis. Novel agents targeting Btk and Bcl-2 show remarkable activity in B-CLL. However, they may have different activity in different lymphoid compartments while Btk inhibitors also may cause significant B-CLL lymphocyte redistribution between compartments. Aim of this study was to evaluate: 1) is there a different expression of Bcl-2 family of anti- and pro-apoptotic proteins (Bcl-2, Bax, Bim, mcl-1) and Btk in B-CLL lymphocytes from different lymphoid compartments; 2) relationship of observed expressions to disease parameters (TTM, TD, stage, B2MG, LDH); 3) changes during treatment with Btk inhibitors. We have included 28 B-CLL patients (18/10 M/F, median age 71 yr, range 48-85) treated with Btk inhibitors (ibrutinib 24, acalabrutinib 4). There were 15 previously treated patients and 13 treatment naïve patients. All evaluated patients had samples from PB and BM before treatment while 19 patients had also LN samples. At least one follow-up sample from PB had 20 patients. Median TTM score was 10.2 (range 3.4-23.9) and TD score was 0.68. Rai stage III/IV had 8 patients. Expression of Bcl-2, Mcl-1, Bim, Bax and Btk was determined by flow cytometry in CD19+CD5+ lymphocytes from fresh samples taken simultaneously by venipuncture (PB) or fine needle aspiration (BM and LN). There is higher expression of Bcl-2, Mcl-1 in LN compared to PB and BM (p<0.05), while there is no change in follow-up PB during ibrutinib/acalbrutinib treatment. There is no significant difference in Bim expression between compartments, while there is trend for higher expression in PB follow-up sample (p=0.054). There is no significant difference in Bax expression between PB, BM and LN compartments, while there is significant drop in Bax expression in PB follow-up sample during treatment (p<0.05). p-Btk has higher expression in LN compared to PB and BM (p<0.05). Follow-up PB p-Btk expression is comparable to pretreatment expression in PB (despite redistribution). We haven't found significant correlation of Bcl-2 family expression and p-Btk expression to the parameters of tumor mass (TTM) and tumor distribution (TD). In conclusion, there is a different pattern of expression of anti-apoptotic and pro-apoptotic Bcl-2 family members and Btk between lymphoid compartments. Our results may indicate higher BCR signaling and higher antiapoptotic activity in B-CLL lymphocytes in lymph node microenvironment. With redistribution during Btk inhibitor treatment B-CLL lymphocytes assume PB phenotype with downregulation of Btk and anti-apoptotic Bcl-2 and Mcl-1 proteins. Downregulation of pro-apoptotic Bax and possible upregulation of Bim protein indicate that there may be more complex interplay between various proteins resulting in different disease course. These results again emphasize the role of LN microenvironment in pathogenesis of B-CLL and may provide insights for treatment strategies combining targeted agents (Btk inhibitors and Bcl-2 antagonists).

Abstract 5339: BCL2A1 is expressed in myelofibrosis specimens and JAK2-mutated UKE-1 cells, yet does not inhibit synergistic cell killing by BCL-XL inhibitor navitoclax plus JAK1/2 inhibitors, including ruxolitinib

Abstract Myelofibrosis (MF) is driven by mutually exclusive mutations in JAK2, CALR, and MPL in hematopoietic stem cells, leading to constitutively active JAK-STAT signaling and consequently, increased proliferation and cell survival. The JAK1/2 inhibitor ruxolitinib (Rux) is standard of care in front line patients; however, JAK inhibition alone does not induce long-term remission or disease-modifying effects. The BCL-2 family pro-survival proteins BCL-XL and MCL-1 have been implicated in resistance to Rux, and combined activity between the BCL-XL/BCL-2 inhibitor navitoclax (Nav) and JAK2 inhibition has been described in preclinical models. The combination of Nav + Rux resulted in clinically meaningful responses (e.g., improvements in spleen volume, constitutional symptoms, anemia, and bone marrow fibrosis) in patients with suboptimal response to, or progression while on, Rux (Harrison et al., EHA 2021, EP1087). Nav does not have strong affinity for MCL-1 or BCL2A1. BCL2A1 has garnered recent attention given its potential role in tumor survival and drug resistance; however, its role in MF is unknown. Given the potential of Nav + Rux in MF, we evaluated the expression of BCL-2 pro-survival proteins, including BCL2A1, in MF patient specimens and assessed the ability of BCL2A1 to serve as a resistance factor to Nav + Rux in vitro. DNA/RNA was extracted from PBMCs from healthy donors (n=15), JAK1/2-inhibitor naïve patients with MF (n=18), and suboptimal responders or progressors (R/R MF) currently on stable dose of Rux (n=72). When compared to healthy donors, expression of BCL2L1, MCL1 and BCL2A1, but not BCL2, was higher in naïve and R/R MF patients, with greatest increase observed in BCL2L1. Increase in median expression in naïve patients vs healthy donors for BCL2L1, MCL1, and BCL2A1 was ~4-, 1.5-, and 2-fold, respectively. A similar trend was observed with R/R MF patients vs healthy donors. We next evaluated BCL-2 family expression in in vitro models of MPN. Notably, MCL1 expression was high in UKE-1, SET-2 and HEL cell lines, while high expression of BCL2A1 was only observed in UKE-1. The combination of Nav plus either Rux, fedratinib or momelitinib induced synergistic cell killing in all lines. These data suggest that although MCL1 and BCL2A1 are expressed in JAK2-mutated cells and other malignancies characterized by constitutive JAK/STAT signaling, they do not confer resistance to a Nav + JAK-inhibitor combination. In summary, our data demonstrate dysregulated pro-survival BCL-2 family member expression, including MCL1 and BCL2A1, in MF patient samples and JAK2-mutated cell lines, and further implicate BCL-XL as a major survival factor in both naïve and Rux-treated R/R MF patients. Together these data support a Nav/JAK1/2-inhibitor combination for both JAK1/2-inhibitor naïve patients, as well as those no longer benefiting from Rux therapy. Citation Format: Marion Refici, Ziping Yang, Jacob Riehm, Darren Phillips, Andrew Souers, Jason Harb. BCL2A1 is expressed in myelofibrosis specimens and JAK2-mutated UKE-1 cells, yet does not inhibit synergistic cell killing by BCL-XL inhibitor navitoclax plus JAK1/2 inhibitors, including ruxolitinib [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5339.

Increased apoptotic sensitivity of glioblastoma enables therapeutic targeting by BH3-mimetics

Glioblastoma (GBM) is the most prevalent malignant primary brain tumour in adults. GBM typically has a poor prognosis, mainly due to a lack of effective treatment options leading to tumour persistence or recurrence. We investigated the therapeutic potential of targeting anti-apoptotic BCL-2 proteins in GBM. Levels of anti-apoptotic BCL-xL and MCL-1 were consistently increased in GBM compared with non-malignant cells and tissue. Moreover, we found that relative to their differentiated counterparts, patient-derived GBM stem-like cells also displayed higher expression of anti-apoptotic BCL-2 family members. High anti-apoptotic BCL-xL and MCL-1 expression correlated with heightened susceptibility of GBM to BCL-2 family protein-targeting BH3-mimetics. This is indicative of increased apoptotic priming. Indeed, GBM displayed an obligate requirement for MCL-1 expression in both tumour development and maintenance. Investigating this apoptotic sensitivity, we found that sequential inhibition of BCL-xL and MCL-1 led to robust anti-tumour responses in vivo, in the absence of overt toxicity. These data demonstrate that BCL-xL and MCL-1 pro-survival function is a fundamental prerequisite for GBM survival that can be therapeutically exploited by BH3-mimetics.

Primary plasma cell leukemias displaying t(11;14) have specific genomic, transcriptional, and clinical features

AbstractPrimary plasma cell leukemia (pPCL) is an aggressive form of multiple myeloma (MM) that has not benefited from recent therapeutic advances in the field. Because it is very rare and heterogeneous, it remains poorly understood at the molecular level. To address this issue, we performed DNA and RNA sequencing of sorted plasma cells from a large cohort of 90 newly diagnosed pPCL and compared with MM. We observed that pPCL presents a specific genomic landscape with a high prevalence of t(11;14) (about half) and high-risk genomic features such as del(17p), gain 1q, and del(1p32). In addition, pPCL displays a specific transcriptome when compared with MM. We then wanted to characterize specifically pPCL with t(11;14). We observed that this subentity displayed significantly fewer adverse cytogenetic abnormalities. This translated into better overall survival when compared with pPCL without t(11;14) (39.2 months vs 17.9 months, P = .002). Finally, pPCL with t(11;14) displayed a specific transcriptome, including differential expression of BCL2 family members. This study is the largest series of patients with pPCL reported so far.

Abstract P5-13-06: Exploratory biomarker analysis in VERONICA, a phase 2 study of venetoclax + fulvestrant versus fulvestrant in patients with estrogen receptor (ER)-positive HER2-negative metastatic breast cancer (mBC)

Abstract BACKGROUND: Venetoclax (VEN) is a potent and selective inhibitor of the anti-apoptotic protein, BCL2. Preclinical studies have implicated the BCL2 family members, BCLXL and MCL1, in VEN resistance, and clinical studies in hematological malignancies have demonstrated subgroups with high ratios of BCL2/BCLXL and BCL2/MCL1 have the greatest VEN antitumor activity. The randomized phase 2 VERONICA study (NCT03584009) evaluated VEN in combination with fulvestrant (F) vs F alone in ER-positive, HER2-negative MBC pts who experienced disease recurrence/progression during or after a CDK4/6 inhibitor. Previously reported results from VERONICA (Lindeman et al. ASCO 2021) did not show an improved clinical benefit rate or progression-free survival (PFS) with VEN+F vs F alone. Here we present exploratory biomarker analyses of the expression of BCL2 family members and genomic alterations in circulating tumor DNA (ctDNA) and association with clinical outcomes from VEN+F vs F. METHODS: Tumor specimens were obtained during screening from 103 patients enrolled in the study, and expression levels of BCL2, BCLXL and MCL1 were analyzed by IHC. Baseline plasma-derived ctDNA was evaluated using the FoundationOne® Liquid assay. Expression of BCL2, BCLXL, MCL1 and mutations in ctDNA were correlated with PFS from VEN+F vs F based on the primary analysis (cutoff: Aug 5, 2020). RESULTS: In the overall population, protein levels of BCL2, BCLXL and MCL1 were similar between the VEN+F vs F arms. Patients whose tumors were BCL2 3+ trended towards having the greatest difference in median (m) PFS (3.9 months [mo] in VEN+F vs 1.7 mo in F; hazard ratio [HR] 0.38 [95% CI 0.09, 1.62]) albeit in a small sample size (n=13). Similarly, subgroup analysis suggested a trend for increasing mPFS and improved HR in VEN+F vs F alone in patients with the lowest BCLXL expression. mPFS in patients with a BCL2/BCLXL ratio ≥1 was 3.7 mo for VEN+F vs 1.8 mo for F (HR 0.67 [95% CI 0.3-1.49]) whereas patients with a BCL2/BCLXL ratio &amp;lt;1 had no difference in mPFS between the arms (2.0 mo in both arms, HR 1.21 [95% CI 0.7-2.1]). In the ctDNA-evaluable population, ESR1 (42.6%), TP53 (41.5%) and PIK3CA (35%) were the most prevalent genomic alterations observed and well-controlled between arms. PFS was similar between the ESR1 wildtype (wt) and mutant (mut) subgroups. TP53 mut status was a poor prognostic factor in both treatment arms. The PIK3CA wt subgroup had increased mPFS with VEN+F vs F alone (HR 0.66 [95% 0.38-1.17]) compared to PIK3CA mut (HR 1.59 [95% 0.74-3.34]). Patients with PIK3CA wt and BCL2 high tumors had the largest difference in mPFS between VEN+F (3.7 mo) vs F alone (1.9 mo) (HR 0.58 [95%CI 0.28-1.19]), compared to PIK3CA wt-BCL2 low tumors (2.4 vs 1.9 mo; HR 0.67 [95%CI 0.26-1.72]). CONCLUSION: Our data suggest that a high ratio of BCL2 to BCLXL conferred a trend towards a greater benefit to VEN+F compared to F alone, consistent with other clinical studies evaluating VEN. These analyses highlight the need to profile BCL2 and its family members to identify the VEN-sensitive subgroups, especially in indications where high expression of BCLXL or MCL1 may be observed. The ctDNA profile of VERONICA patients indicate a heavily pretreated patient population. The benefit observed in PIK3CA wt patients from VEN+F suggest increased dependence on BCL2 in this subgroup, while PIK3CA mut tumors likely rely on PI3K/AKT/mTOR survival programs or other BCL2 family members to evade apoptosis. Exploratory biomarker analyses are ongoing to further understand the VERONICA patient population. Citation Format: Geoffrey J. Lindeman, Tharu M. Fernando, Rebecca Bowen, Ching-Wei Chang, Rupal Desai, Kushagra Gupta, Aulde Fléchais, Timothy R. Wilson, Aditya Bardia. Exploratory biomarker analysis in VERONICA, a phase 2 study of venetoclax + fulvestrant versus fulvestrant in patients with estrogen receptor (ER)-positive HER2-negative metastatic breast cancer (mBC) [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P5-13-06.

Abstract P4-02-06: Exploiting ceramide homeostasis to target endocrine therapy-resistant breast cancer

Abstract Estrogen receptor (ER)-positive breast cancer accounts for the majority of breast cancer-related deaths. Current treatment includes endocrine therapy (ET), which most women respond to at first. However, up to 40% of women will eventually experience a relapse. Recurrent tumors tend to retain ER expression but no longer respond to ET. There have been multiple genomic and proteomic profiling studies between ET-sensitive and ET-resistant breast cancer cells, but lipidomic studies have been lacking. We have performed targeted and non-targeted lipidomic profiling of ET-sensitive and two models of ET-resistant MCF-7 breast cancer cells and found differences in their sphingolipid profiles, suggesting our overarching hypothesis that ceramide homeostasis is altered in ET-resistance. The current study is designed to understand the functional role of ceramides and their metabolites in ET-resistant breast cancer, with an overall goal to improve the current treatment regimens and quality of life in breast cancer patients. Detection of ceramides and other sphingolipid levels were analyzed by reverse-phase chromatography and LC-QToF-MS. C1P levels were detected by LC-QqQ-MS. Hoechst-PI staining was performed to measure cell death and Annexin-PI staining to detect apoptosis. All cytometric data analyses were performed using a Celigo cytometer. RT-qPCR was performed to analyze mRNA expression. Fold changes were calculated using the ΔΔCt method with multiple housekeeping controls. While numerous changes were observed in lipid species, the most pronounced changes were seen in the sphingolipidome. More specifically, ET-resistant breast cancer cells had lower levels of ceramides and di-hydroceramides. Along with a depletion of ceramides, we have also observed an increase in ceramide-1-phosphate (C1P) levels in the ET-resistant cells. C1P, which is produced by phosphorylation of ceramides by ceramide kinase (CERK), is known to promote cell survival and proliferation. This observation suggests that ET-resistant cells may rely on a higher degree of ceramide turnover to C1P compared to their ET-sensitive counterpart. To test this hypothesis, CERK was inhibited with a small molecule inhibitor (NVP-231), which resulted in increased apoptosis in ET-resistant cells but not in ET-sensitive cells, suggesting ET-resistant cells are more sensitive to CERK inhibition. Although NVP-231 treatment increased ceramide levels in both ET-sensitive and ET-resistant cells, only ET-resistant cells were dependent on ceramide turnover to C1P. To further understand the molecular underpinnings of the differential sensitivity to CERK inhibition, we have investigated the expression of several BCL2 family members, as evidence from the literature suggests that sphingolipids play a critical role in apoptosis by interacting with several BCL2 family members by mechanisms that are not thoroughly understood. We have observed a high positive correlation between BCL2 expression and NVP-231 sensitivity, as well as an inverse correlation between MCL-1 and NVP-231 sensitivity. This suggests that loss of BCL2 in the ET-resistant cells may be a factor for increased sensitivity to CERK inhibition and elevated MCL-1 fails to compensate for that loss. Together, our findings suggest that ET-resistant breast cancer cells have a unique ceramide homeostasis dependence, i.e., rely on a higher degree of ceramide turnover to C1P. Additionally, BCL2 family proteins may play a critical role in determining the sensitivity to CERK inhibition. The dependence of ET-resistant breast cancer cells on C1P production for survival can therefore offer a unique opportunity to increase the therapeutic efficacy and improve patient outcome for women with ET-resistant breast cancer. Citation Format: Purab Pal, Alec Millner, Ekin Atilla-Gokcumen, Jonna Frasor. Exploiting ceramide homeostasis to target endocrine therapy-resistant breast cancer [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P4-02-06.

Identification of Small Molecules Inhibiting Cardiomyocyte Necrosis and Apoptosis by Autophagy Induction and Metabolism Reprogramming.

Improvement of anticancer treatments is associated with increased survival of cancer patients at risk of cardiac disease. Therefore, there is an urgent need for new therapeutic molecules capable of preventing acute and long-term cardiotoxicity. Here, using commercial and home-made chemolibraries, we performed a robust phenotypic high-throughput screening in rat cardiomyoblast cell line H9c2, searching for small molecules capable of inhibiting cell death. A screen of 1600 compounds identified six molecules effective in preventing necrosis and apoptosis induced by H2O2 and camptothecin in H9c2 cells and in rat neonatal ventricular myocytes. In cells treated with these molecules, we systematically evaluated the expression of BCL-2 family members, autophagy progression, mitochondrial network structure, regulation of mitochondrial fusion/fission, reactive oxygen species, and ATP production. We found that these compounds affect autophagy induction to prevent cardiac cell death and can be promising cardioprotective drugs during chemotherapy.

Inhibition of MCL1 induces apoptosis in anaplastic large cell lymphoma and in primary effusion lymphoma

Overexpression of antiapoptotic BCL2 family proteins occurs in various hematologic malignancies and contributes to tumorigenesis by inhibiting the apoptotic machinery of the cells. Antagonizing BH3 mimetics provide an option for medication, with venetoclax as the first drug applied for chronic lymphocytic leukemia and for acute myeloid leukemia. To find additional hematologic entities with ectopic expression of BCL2 family members, we performed expression screening of cell lines applying the LL-100 panel. Anaplastic large cell lymphoma (ALCL) and primary effusion lymphoma (PEL), 2/22 entities covered by this panel, stood out by high expression of MCL1 and low expression of BCL2. The MCL1 inhibitor AZD-5991 induced apoptosis in cell lines from both malignancies, suggesting that this BH3 mimetic might be efficient as drug for these diseases. The ALCL cell lines also expressed BCLXL and BCL2A1, both contributing to survival of the cells. The combination of specific BH3 mimetics yielded synergistic effects, pointing to a novel strategy for the treatment of ALCL. The PI3K/mTOR inhibitor BEZ-235 could also efficiently be applied in combination with AZD-5991, offering an alternative to avoid thrombocytopenia which is associated with the use of BCLXL inhibitors.

Yeast as a tool to decipher the molecular mechanisms underlying the functions of Bcl-2 family.

The budding yeast Saccharomyces cerevisiae, a favorite model in biology, does not contain any protein of the Bcl-2 family. From initial experiments with two-hybrid systems to the heterologous expression of human Bcl-2 family members, and the characterization of several forms of yeast programmed cell death, it has however always been a powerful tool to gain information on the mechanisms of apoptosis in general and on Bcl-2 family in particular. This is a short survey of 25 years of experiments that have provided, and at times initiated, insights into the molecular mechanisms underlying the function of Bcl-2 family members.