Myeloid Cell Leukemia-1 Expression Research Articles

Abstract PO2-14-10: A selective MCL-1 inhibitor AZD5991 showed tumor regression in a triple-negative inflammatory breast cancer xenograft model

Abstract Background Triple-negative breast cancer (TNBC) accounts for 15-20% of all breast cancer diagnoses but up to 30% of breast cancer-related deaths. Similarly, Inflammatory breast cancer (IBC) accounts for 2-4% of breast cancer diagnosis but causes 8%–10% of all breast cancer-related deaths. The myeloid cell leukemia-1 (MCL-1) is a member of the BCL-2 family of proteins, which is highly amplified in numerous human cancers and associated with cell immortalization, transformation, and chemoresistance. In fact, MCL-1 is amplified in 55% of TNBC after preoperative chemotherapy. Amongst the MCL-1 inhibitors that have been developed, AZD5991 showed high selectivity and affinity for MCL-1. In myeloma and acute myeloid leukemia cells AZD5991 induces apoptosis and showed anti-tumor effects in in vivo models. In the present study, we evaluated the biological role of the MCL-1 inhibitor AZD5991 in IBC and TNBC in vitro and in vivo models. Materials and methods The expression of the MCL-1 gene was analyzed in the World Consortium IBC patient dataset. Next, we screened a panel of TNBC and IBC cell lines for MCL-1 expression by western blot analysis. The effect of AZD5991 on TNBC and IBC cells was analyzed via cell titer-blue proliferation, clonogenic assays and soft agar assay. To further validate these findings, we used siRNA to knockdown MCL-1 and performed cell proliferation, clonogenic and migration assays. To identify signaling pathways involved in MCL-1 Inhibitor’s effects we performed a proteome profiler human apoptosis array in TNBC cells in the presence of AZD5991. The anti-tumor effect of the MCL-1 inhibitor was evaluated using a SUM-149 (TN-IBC) orthotopic xenograft mouse model. The mice were treated with AZD5991 at doses of 15 and 30mg/kg once weekly via tail vein injection for a duration of 4 weeks. Results The mean expression level of MCL-1 was higher in patients with TNBC than in those with non-TNBC. Further, compared to the patients with ER positive, HER-2 negative tumors those with TNBC showed an increased in the mean expression of MCL-1 gene (p value= 0.05). We screened a panel of TNBC and IBC cell lines in which most of the cell lines showed high levels of MCL-1. The cell proliferation assay showed IC50 ranging from 0.27 – 19.6 μM. The SUM149, SUM190, FCIBC02, MDA-IBC3 and MDA-MB-468 cells showed high sensitivity and showed significant decrease in the proliferation rate while BCX010, KPL4, MDA-MB-231, 4T1.2 and E0771 cells as well as the normal breast cells MCF10A exhibited resistance with no significant decrease in proliferation. The clonogenic and soft agar assays with these sensitive and resistant cell lines showed similar results. Further, these findings were validated via genetic knockdown of MCL-1 which resulted in a significant decrease in cell proliferation, colony formation and migration capability of the TNBC cells. To identify signaling pathways involved in MCL-1 Inhibitor’s phenotypic changes, we performed a proteome profiler human apoptosis array which showed a decreased in BCLx expression, and an increase in expression of BAX and phospho-Rad17 proteins in the AZD5991 treated TN-IBC cells. Finally, in a SUM-149 (TN-IBC) orthotopic xenograft mouse model, mice injected with 30mg/kg showed a significant tumor regression compared to the vehicle-treated mice (vehicle vs 30 mg/kg, p value=0.0006). Conclusions and Future directions Our data demonstrates that AZD5991 inhibits tumorigenesis in an inflammatory breast cancer xenograft model. We are currently validating several significant targets to understand the biological mechanisms related to our candidate drug. Our long-term goal is to develop MCL-1 targeted therapy in combination with standard-of-care treatment for inflammatory and triple-negative breast cancers. Citation Format: Mohd Mughees, Moises Tacam, Alex Tan, Michael White, Bisrat Debeb, Emilly Villodre, Xiaoding Hu, Debu Tripathy, Wendy Woodward, Rachel Layman, Geoffrey Bartholomeusz, Chandra Bartholomeusz. A selective MCL-1 inhibitor AZD5991 showed tumor regression in a triple-negative inflammatory breast cancer xenograft model [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO2-14-10.

Anlotinib Inhibits Cisplatin Resistance in Non-Small-Cell Lung Cancer Cells by Inhibiting MCL-1 Expression via MET/STAT3/Akt Pathway.

Anlotinib is an effective targeted therapy for advanced non-small-cell lung cancer (NSCLC) and has been found to mediate chemoresistance in many cancers. However, the underlying molecular mechanism of anlotinib mediates cisplatin (DDP) resistance in NSCLC remains unclear. Cell viability was assessed by the cell counting kit 8 assay. Cell proliferation, migration, and invasion were determined using the colony formation assay and transwell assay. The mRNA expression levels of mesenchymal-epithelial transition factor (MET) and myeloid cell leukemia-1 (MCL-1) were measured by quantitative real-time PCR. Protein expression levels of MET, MCL-1, and STAT3/Akt pathway-related markers were examined using western blot analysis. Our data showed that anlotinib inhibited the DDP resistance of NSCLC cells by regulating cell proliferation and metastasis. Moreover, MET and MCL-1 expression could be decreased by anlotinib treatment. Silencing of MET suppressed the activity of the STAT3/Akt pathway and MCL-1 expression. Furthermore, MET overexpression reversed the inhibitory effect of anlotinib on the DDP resistance of NSCLC cells, and this effect could be eliminated by MCL-1 knockdown or ACT001 (an inhibitor for STAT3/Akt pathway). Our results confirmed that anlotinib inhibited DDP resistance in NSCLC cells, which might decrease MCL-1 expression via mediating the MET/STAT3/Akt pathway.

Navtemadlin, a Novel MDM2 Inhibitor, Potentiated Venetoclax-Induced Antitumor Efficacy in TP53 Wild-Type Acute Myeloid Leukemia (AML)

Introduction: The tumor suppressor p53 ( TP53) maintains genomic integrity, and nearly 50% of cancers are characterized by a loss or mutation in the TP53 gene. Murine double minute 2 (MDM2) negatively regulates p53 expression and promotes oncogenesis in TP53 wild-type ( TP53 WT) tumors. Navtemadlin (nvtm) is a potent, selective, orally available MDM2 inhibitor that overcomes MDM2 dysregulation by restoring p53 activity and inducing apoptosis in TP53 WT tumors. AML is a heterogeneous hematological malignancy resulting from the transformation of stem cells and is characterized by poor therapy response. Thus, combination therapies are required to avoid tumor escape mechanisms, such as alterations in apoptotic machinery and metabolism. Venetoclax (ven), a BCL-2 inhibitor, is a promising therapy in AML. Overexpression of anti-apoptotic members of the BCL-2 family, including myeloid cell leukemia-1 (MCL-1) limits ven response, thus requiring MCL-1 inhibitors to further improve sensitivity. A proof-of-concept study with idasanutlin (idasa), a first-generation MDM2 inhibitor and ven demonstrated manageable safety and encouraging efficacy in relapsed/refractory AML patients (Daver et al. Blood 2023). Here, we present a preclinical evaluation of nvtm alone and in combination with ven in the setting of TP53 WT AML, with a focus on metabolic pathways, pro-survival signaling, and bone marrow (BM) niche. Methods: AML-derived cell line, MOLM-13 ( TP53 WT, FLT3-ITD) was cultured alone, with HS5 AML stromal cells or with cytokines. Cultures were treated with DMSO, nvtm (0.1-1.5 μM), or ven (0.5 μM) for short-term (4-8 hrs) or long-term (48-72 hrs) and analyzed for changes in cell cycle progression, viability, clonogenicity potential, and metabolism (glycolysis and mitochondrial oxidative phosphorylation by analyzing extracellular acidification rate (ECAR) and oxygen consumption rate (OCR) respectively). Primary AML BM mononuclear cells (MNCs) were cultured in cytokine support media. Results: In MOLM-13 cells, short-termnvtm (0.5 µM) treatment rapidly restored p53 expression and phosphorylation, with greater efficacy than idasa. Long-term treatment significantly induced apoptosis in a dose-dependent manner from 0.25 μM (p<0.01) with 80% cytotoxicity at 0.75 μM (p<0.001). Cell cycle analysis at 48 hr showed that nvtm significantly arrested cells in the sub-G0-G1 phase. Clonogenicity potential was significantly lowered in nvtm-treated cells. Metabolic alterations in the Mito Stress and Glycostress tests showed nvtm significantly lowered EACR, OCR, and mitochondrial membrane potential, as compared to idasa. We next evaluated the effects of nvtm in ven-treated MOLM-13 cells. Combination treatment significantly lowered the metabolism, cell viability, and clonogenicity potential of MOLM-13 cells, compared to nvtm or ven treatment. Immunoblotting analysis revealed a reduction in key anti-apoptosis proteins (BCL-2, MCL-1, PARP). Strikingly, nvtm downregulated ven-induced MCL-1 expression in a dose-dependent manner. Culturing MOLM-13 cells in HS5-conditioned media, transwells overlying HS5 cells, or with HS5 cells increased MOLM-13 cell resistance to nvtm. However, in HS5 co-cultures, a combination of nvtm and ven strongly re-sensitized MOLM-13 cells for apoptosis. Nvtm also significantly blocked the cytoprotective effects of AML-relevant cytokines (IL-6, SCF, FLT3 ligand, TPO, and GM-SCF). In cultures of primary AML BM-MNCs (n=11), nvtm alone at clinically relevant concentrations reduced viability (14-40%), and a combination nvtm and ven significantly enhanced AML cytotoxicity (30-52%). Conclusions: Nvtm, a potent second-generation MDM2 inhibitor, rapidly restored p53 function, induced apoptosis in p53 WT AML MOLM-13 by impeding cell cycle, viability, clonogenicity potential, and reducing both glycolysis and oxidative phosphorylation. Nvtm combined with ven significantly enhanced these effects. Importantly, this combination blocked stromal cell-mediated (contact and soluble factors) cytoprotection. These encouraging results provide a mechanistic basis for the evaluation of this combination in vivo and as a therapeutic strategy to overcome documented ven resistance mechanisms in TP53 WT AML patients.

Oncolytic Activity of Canine Distemper Virus in Human Ductal Breast Carcinoma Cells

Introduction: Oncolytic virotherapy is a novel strategy for cancer treatment in humans and companion animals. Canine distemper virus (CDV) is known to induce apoptosis in tumor cells, thus serving as a potential candidate for oncolytic therapy. However, the mechanism of viral oncolytic activity is less studied and varies depending on the type of cancer and cell lines. Methods: In the present study, the susceptibility of the MCF-7 cell line to CDV infection was assessed using the CDV strain, which was confirmed previously through sequence analysis in the Vero cell line. The impact of CDV infection on cell proliferation and apoptosis was studied by evaluating the expression of four target genes including the myeloid cell leukemia 1 (MCL-1), phosphoinositide-3-kinase regulatory subunit 1 (PIK3R1), transcription factor (SP1), and DNA (cytosine-5)-methyltransferase 3A (DNMT3A). Results: CDV replication in the cells induced cytopathic effect and decreased in the cell proliferation rates compared to the uninfected control. MCL-1, SP1, and PIK3R1 gene expression was down-regulated, while the expression of DNMT3A was up-regulated 3 days post-infection. The expression levels of the target genes suggest that CDV may be inducing the intrinsic apoptotic pathway in the cancer cell line. Conclusion: Overall, the results strongly propose CDV strain as a potential candidate for cancer therapy after detailed studies.

Myeloid Cell Leukemia 1 Small Molecule Inhibitor S63845 Synergizes with Cisplatin in Triple-Negative Breast Cancer.

Triple-negative breast cancer (TNBC) is an aggressive cancer that lacks specific molecular targets that are often used for therapy. The refractory rate of TNBC to broad-spectrum chemotherapy remains high; however, the combination of newly developed treatments with the current standard of care has delivered promising anti-tumor effects. One mechanism employed by TNBC to avoid cell death is the increased expression of the anti-apoptotic protein, myeloid cell leukemia 1 (MCL1). Multiple studies have demonstrated that increased MCL1 expression enables resistance to platinum-based chemotherapy. In addition to suppressing apoptosis, we recently demonstrated that MCL1 also binds and negatively regulates the transcriptional activity of TP73. TP73 upregulation is a critical driver of cisplatin-induced DNA damage response, and ultimately, cell death. We therefore sought to determine if the coadministration of an MCL1-targeted inhibitor with cisplatin could produce a synergistic response in TNBC. This study demonstrates that the MCL1 inhibitor, S63845, combined with cisplatin synergizes by inducing apoptosis while also decreasing proliferation in a subset of TNBC cell lines. The use of combined MCL1 inhibitors with cisplatin in TNBC effectively initiates TAp73 anti-tumor effects on cell cycle arrest and apoptosis. This observation provides a molecular profile that can be exploited to identify sensitive TNBCs.

Characterization of MCL-1 in patients with colorectal cancer (CRC): Expression, molecular profiles, and outcomes.

3085 Background: Myeloid cell leukemia 1 (MCL-1) is a member of the BCL-2 protein family and is anti-apoptotic/pro-survival in function. Dysregulation of MCL-1 expression has been reported in several solid tumors, including lung and breast cancer. In CRC, MCL-1 has been associated with resistance to chemotherapeutic drugs and multi-kinase inhibitor regorafenib. Our study aimed to characterize the molecular features associated with MCL-1 gene expression in CRC. Methods: 28,576 CRC samples were analyzed by Caris Life Sciences (Phoenix, AZ) with WTS (Illumina NovaSeq) and NextGen DNA sequencing (NextSeq, 592 Genes and NovaSEQ, WES). MCL-1 expression was stratified by quartiles where top quartile transcripts per million (TPM) were considered high (Q4) and bottom quartile low (Q1). Cell infiltration (CI) in the tumor microenvironment (TME) was estimated by RNA deconvolution analysis using QuantiSEQ. Interferon-gamma and T-cell inflamed signatures were also calculated from RNA data. X2 and Fisher-Exact tests were used, and statistical significance was determined as a P-value adjusted for multiple comparisons ( q < 0.05). Real world survival was obtained from insurance claims data and Kaplan-Meier estimates were calculated for molecularly defined patients. Results: MCL-1 expression was significantly increased in rectal tumors compared to other primary tumor sites (median TPM [mTPM] 20.8 vs 18.9 vs 18.7, in rectal vs left-sided vs right-sided, respectively, q < 0.0001). MCL-1 high tumors were associated with increased rate of PD-L1 IHC levels (Q1 vs Q4: 4.2% vs 9.7% [all CRC]; 3.7% vs 8.9% [pMMR/MSS], q < 0.0001), while MCL-1-low showed marginally increased rates of TMB-high (8.0% vs 7.0% [all CRC]; 3.3% vs 2.6% [pMMR/MSS], P < 0.05). MCL-1-high expression was associated with a higher T-cell inflamed signature and IFN score ( q < 0.0001). MCL-1 high was associated with higher mutation rates of CDKN2A, BRCA2, KRAS and GNAS, while lower mutation rates of TP53, PIK3CA, PTEN, BRAF, APC, FBXW7, AMER1, SOX9, and SMAD2 and copy number amplifications in several genes ( q < 0.05). MCL-1 high TME had higher CI of M1 and M2 macrophages, monocytes, B cells, NK cells, and T-reg infiltration, while dendritic cells and CD4+ T-cell were lower ( q < 0.05). Patients with high MCL-1 expressing CRC had longer survival (Q4 vs Q1: 33.5 vs 24.8 months, HR 0.72, 95% CI 0.67-0.77, P < 0.0001) and longer time-on-treatment with regorafenib although with limited clinical benefit (Q4 vs Q1: 2.03 vs 1.06 months, HR: 0.67, 95% CI: 0.50-0.89, P = 0.005). Conclusions: Our data show a strong correlation between distinct immune biomarkers, TME cell infiltration and MCL-1 expression in CRC. Furthermore, increased tumor MCL-1 expression improved patient prognosis and treatment outcomes. These findings suggest a key clinical role for MCL-1 as an important modulator of anti-tumor immunity and TME and a potential biomarker in CRC.

Phase 1 dose-expansion study of oral TP-1287, a cyclin-dependent kinase 9 (CDK9) inhibitor, in patients with Ewing sarcoma (EWS).

TPS11589 Background: Cyclin-dependent kinase 9 (CDK9) blockade inhibits tumor growth and progression by impairing the transcription of key oncogenes, such as myeloid cell leukemia-1 (MCL-1) and c-MYC. CDK9 overexpression has been observed in sarcoma patients (pts), and CDK9 has emerged as a potential therapeutic target in pts with sarcoma. TP-1287 is an investigational orally delivered phosphate prodrug of the CDK9 inhibitor alvocidib. In preclinical studies, TP-1287 has been shown to decrease MCL-1 expression and phosphorylation of RNA polymerase II (RPB1), and inhibit tumor growth in an Ewing sarcoma (EWS) mouse model. Phase 1 dose-escalation in solid tumors has completed and TP-1287 is being investigated in a dose expansion cohort in pts with EWS (NCT03604783). The design of the expansion part of the trial in pts with EWS is herein described. Methods: Up to thirty pts with EWS will be enrolled in this dose expansion cohort. Key eligibility criteria are age ≥18 years (≥12 years, if weight ≥40 kg); histologically confirmed locally advanced or metastatic unresectable EWS; received 1 to 5 prior lines of treatment including an anthracycline; one or more measurable tumors per the RECIST v1.1; ECOG performance status of ≤1; acceptable liver and renal function, and acceptable hematologic and coagulation status; no treatment with surgery, chemotherapy, or investigational therapy within 28 days or 5 half-lives. Eligible pts will be treated with oral TP-1287 monotherapy RP2D established from the dose escalation part (11 mg BID, continuous dosing in a 28-day treatment cycle) and will continue treatment until treatment-related adverse event or disease progression. Assessments will be performed on Day 1 and Day 15 of each cycle. Tumor response assessment will be done after Cycle 2 and at the end of every other cycle thereafter. The primary objectives are objective response rate (ORR) and clinical benefit rate (CBR) ; secondary objectives are median progression-free survival (PFS), PFS rate at 16-weeks and 24-weeks and safety; and exploratory objectives include evaluation of systemic exposure and pharmacodynamics. Safety data will be reviewed on an ongoing basis and a Bayesian approach will be used to assess the efficacy data. Statistical analysis for safety and efficacy parameters will be primarily descriptive in nature. EWS dose expansion cohort is currently recruiting in the United States. Clinical trial information: NCT03604783 .

Abstract 2530: DELE1 loss and dysfunctional integrated stress signaling in TP53 mutated AML is a novel pathway for venetoclax resistance

Abstract Background: Venetoclax (ven) in combination with hypomethylating agents or low dose cytarabine leads to rapid and durable remission in patients (pts) with acute myeloid leukemia (AML) unfit for intensive chemotherapy (IC), however, pts with TP53 mutations (TP53mut) exhibit adverse prognosis. Here, we identify dysregulation of the integrated stress response (ISR) pathway in pts with TP53mut, specifically through the actions of DAP3 binding cell death enhancer 1 (DELE1) and its activating protease OMA1. Methods: RNA sequencing was performed on pre-treatment bone marrow-derived mononuclear cells (BMMCs) from pts with AML ineligible for IC across four clinical trials (NCT02993523, NCT02203773, NCT03069352, and NCT02287233). CRISPR-Cas9 editing of TP53-intact AML cell lines was used to generate TP53-/-, TP53mut, DELE1-/-, OMA1-/- and TP53/DELE1 double deficient cell lines. Quantification of BCL2 and Myeloid cell leukemia 1 (MCL1) complexes with BCL2 interacting mediator (BIM) was performed using chemiluminescence assays. A drug screen to assess viability and gene expression was performed in cells treated with ven in combination with 63 drugs. Results: In total 401 pts were included in the analyses, of which 17% harbored TP53mut and 83% were TP53wt. Analysis of genes differentially expressed (DE) between pts with TP53mut and TP53wt AML revealed 19 DE genes shared across all trials. DELE1, an ISR adaptor, was associated with genes mapping to the ISR-related eukaryotic initiation factor-α (eIF2α) in TP53mut AML BMMCs. Deletion of DELE1 or OMA1 in AML cell lines blocked eIF2α activation and induction of the transcription factor ATF4, a critical ISR effector, in response to the mitochondrial stressor FCCP, ven, and azacitidine, and resulted in ven resistance similar to that of TP53 deficient cells. All modified AML cell lines exhibited a concomitant decrease in the pro-apoptotic regulator PMAIP1, encoding NOXA, and a 14-18-fold increase in MCL1-BIM complexes following ven treatment, as well as increased MCL1 expression, compared to parental lines. Further screening of these cell lines for ven sensitizing activity revealed the BH3 mimetic S63845, which targets MCL1, as the top hit, suggesting that combined BH3 mimetics may overcome ven resistance during ISR pathway defects. As DELE1 is located on chromosome 5 (CH); the frequent loss of CH 5q among TP53mut AML may contribute to low DELE1 expression. Conclusions: These data suggest that defective ISR signaling may be a factor in TP53mut AML treatment outcome and point to DELE1 dysregulation as a driver of ISR inactivation in pts with TP53mut AML. The ISR induces the expression of NOXA, which displaces MCL1 from BIM and lowers the apoptotic threshold. Our data identify p53, DELE1, and OMA1 as regulators of NOXA expression post ven treatment and indicate that co-targeting MCL1 in pts with TP53mut AML may be beneficial to overcome ven resistance. Citation Format: David Sharon, Paul Jung, Yan Sun, Weiguo Feng, Ziping Yang, Valerie Robinson, Diya Mitra, Wei Liu, Pingping Zheng, Tamar Uziel, Lloyd Lam, Mark D. Minden, Jeremy Ross, Wellington Mendes, Jalaja Potluri, Andrew H. Wei, Marina Konopleva, Monique Dail, Brenda Chyla, PK Epling-Burnette. DELE1 loss and dysfunctional integrated stress signaling in TP53 mutated AML is a novel pathway for venetoclax resistance [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2530.

Estrogen-dependent activation of NCOA3 couples with p300 and NF-κB to mediate antiapoptotic genes in ER-positive breast cancer cells

Circumvention of apoptosis by the elevation of antiapoptotic proteins is an important cause of carcinogenesis. The induction of antiapoptotic genes, including B-cell CLL/lymphoma 2 (BCL2), BCL2 related protein A1 (BCL2A1), BCL2 like 1 (BCL2L1), BCL2L2, and myeloid cell leukemia 1 (MCL1), has been observed in multiple cancers, including breast cancer. However, the underlying mechanisms of their overexpression are still being investigated. Here, we revealed that BCL2, BCL2A1, BCL2L2, and MCL1 but not BCL2L1 were overexpressed in estrogen receptor (ER)-positive breast cancer cells and clinical biopsies. Stimulation with estrogen in ER-positive cell lines resulted in a dose-dependent increase in BCL2, BCL2A1, BCL2L2, and MCL1 mRNA levels. Molecular investigation revealed that nuclear factor kappa B (NF-κB) recruited histone acetyltransferase p300 and nuclear receptor coactivator 3 (NCOA3) to form a transcriptional complex. This complex docked the promoters of BCL2, BCL2A1, BCL2L2, and MCL1 and activated their expression. Interestingly, estrogen exposure dose-dependently activated NCOA3. Depletion of the NCOA3-p300-NF-κB components or blockage of NCOA3 function with inhibitors (gossypol and bufalin) in ER-positive cells suppressed BCL2, BCL2A1, BCL2L2, and MCL1 expression, while also decreasing cell viability, colony formation, cell invasion, and tumor growth. Collectively, our results demonstrate an upstream signaling that activates four antiapoptotic genes in ER-positive breast cancer cells. Importantly, our results also imply that targeting NCOA3 or blocking the assembly of the NCOA3-p300-NF-κB complex may be promising therapeutic strategies for treating ER-positive breast cancer.

FBXW7 affects autophagy through MCL1 in oral squamous cell carcinoma.

Oral cancer is associated with high risk of morbidity and mortality. However, effective treatment for oral cancer is urgently required in clinics. In this study, we aimed to determine whether F-box/WD repeat-containing protein 7 (FBXW7), an essential tumor suppressor gene, can regulate autophagy and improve the prognosis in oral squamous cell carcinoma (OSCC). mRNA levels of FBXW7 and myeloid cell leukemia 1 (MCL-1) in OSCC tissues and adjacent normal tissues were measured by qRT-PCR. FBXW7 and MCL-1 were overexpressed in OSCC cell line using lentivirus containing FBXW7 and MCL-1, respectively. Protein expression was determined by Western blot. The mRNA and protein levels of FBXW7 were decreased in patients with OSCC, whereas the mRNA and protein levels of MCL-1 were increased. Moreover, the mRNA coding for autophagy proteins was reduced in patients with OSCC. Additionally, it was found that overexpression of FBXW7 significantly reduced MCL-1 expression and upregulated autophagy-related proteins, including Beclin1, autophagy related 7, and microtubule-associated protein light chain 3. Our results suggest that FBXW7 affects autophagy through MCL1 in OSCC.

Abstract 2309: CDK9 as a potential therapeutic target in sarcomas

Abstract Sarcomas are a heterogeneous group of over 80 different tumors which arise from mesenchymal or connective tissue, accounting for 1% of adult malignancies. The annual incidence of soft tissue sarcoma (STS) is approximately 11,000 cases in the United States and STS is among the top five causes of cancer deaths for those under 20 years old. Cyclin-dependent kinase 9 (CDK9) is a serine/threonine protein kinase involved in transcription elongation through phosphorylation and activation of RNA polymerase II (RPB1), which increases the levels of key oncogenic genes like myeloid cell leukemia-1 (MCL-1) and c-Myc. CDK9 inhibition reduces their expression, leading to cell cycle arrest and apoptosis. TP-1287 is an orally delivered phosphate pro-drug of alvocidib, a potent CDK9 inhibitor. We hypothesized that alvocidib, the pharmaceutically active form of TP-1287, can inhibit the CDK9 signaling pathway and suppress tumor growth of sarcoma cells. Alvocidib demonstrated the suppression of the phosphorylation of RPB1 (p-RPB1) and MCL-1 expression in an A-673 Ewing sarcoma cell line and U-2 OS and MG-63 osteosarcoma cell lines after 6-hr treatment. In U-2 OS cells, 24-hr treatment with alvocidib induced the cleavage of PARP-1, an indicator of apoptosis, whereas less than 6-hr treatment with alvocidib failed to induce PARP-1 cleavage, suggesting that long-term CDK9 suppression would be necessary for the apoptosis induction in sarcoma cells. In cell viability assays using CellTiter-Glo, alvocidib demonstrated an IC50 of around 100 nM: 32 - 90 nM in sarcoma cell lines after 4-day treatment and 24 - 174 nM in sarcoma cells, which were obtained from patient derived xenograft (PDX) models, after 6-day treatment. In the sarcoma cells from PDX models, MCL-1 mRNA expression was moderately correlated with alvocidib sensitivity. Further bioinformatic analysis to predict alvocidib sensitivity is currently underway. In immunofluorescence analysis, alvocidib induced the activation of caspase-3/7, another indicator of apoptosis, after 2-day treatment in the sarcoma cells from PDX models. In an in vivo pharmacodynamic (PD) study using BALB/c mice, p-RPB1 and MCL-1 suppression in peripheral blood mononuclear cells (PBMCs) was observed after single administration of TP-1287. In an in vivo efficacy study using the A-673 model, TP-1287 showed a trend of tumor growth inhibition (TGI) at 2.5 mg/kg (QD), but not at 7.5 mg/kg (Q3D). These in vivo studies suggest that CDK9 signaling pathway was inhibited after TP-1287 administration in vivo and that continuous CDK9 inhibition would be needed for TGI in sarcoma models. In vivo efficacy and PD studies using sarcoma PDX models are currently ongoing. Taken together, alvocidib has shown activity in inhibiting the growth of sarcoma cells and TP-1287 could be a viable therapeutic option targeting the CDK9 pathway in sarcomas. TP-1287 is being investigated for solid tumors including sarcomas (clinicaltrials.gov, NCT03604783). Citation Format: Yuta Matsumura, Hiroki Umehara, Jun Oishi, Adam Siddiqui, Jason M. Foulks, Setsuko Yamamoto, Steven L. Warner. CDK9 as a potential therapeutic target in sarcomas [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 2309.

Translationally Controlled Tumor Protein-Mediated Stabilization of Host Antiapoptotic Protein MCL-1 Is Critical for Establishment of Infection by Intramacrophage Parasite Leishmania donovani.

In the early phase of infection, the intramacrophage pathogen Leishmania donovani protects its niche with the help of the antiapoptotic protein myeloid cell leukemia-1 (MCL-1). Whether Leishmania could exploit MCL-1, an extremely labile protein, at the late phase is still unclear. A steady translational level of MCL-1 observed up to 48 h postinfection and increased caspase-3 activity in MCL-1-silenced infected macrophages documented its importance in the late hours of infection. The transcript level of MCL-1 showed a sharp decline at 6 h postinfection, and persistent MCL-1 expression in cyclohexamide-treated cells negates the possibility of de novo protein synthesis, thereby suggesting infection-induced stability. Increased ubiquitination, a prerequisite for proteasomal degradation of MCL-1, was also found to be absent in the late hours of infection. Lack of interaction with its specific E3 ubiquitin ligase MULE (MCL-1 ubiquitin ligase E3) and specific deubiquitinase USP9X prompted us to search for blockade of the ubiquitin-binding site in MCL-1. To this end, TCTP (translationally controlled tumor protein), a well-known binding partner of MCL-1 and antiapoptotic regulator, was found to be strongly associated with MCL-1 during infection. Phosphorylation of TCTP, a requirement for MCL-1 binding, was also increased in infected macrophages. Knockdown of TCTP decreased MCL-1 expression and short hairpin RNA-mediated silencing of TCTP in an infected mouse model of visceral leishmaniasis showed decreased parasite burden and induction of liver cell apoptosis. Collectively, our investigation revealed a key mechanism of how L. donovani exploits TCTP to establish infection within the host.

Myeloid cell leukemia-1 expression in cancers of the oral cavity: a scoping review.

BackgroundB cell lymphoma-2 (Bcl-2) family members play important roles in cell survival as well as cell death. The role of myeloid cell leukemia-1 (Mcl-1), an important member of the Bcl-2 family, is well established in hematopoietic malignancies. However, the association between Mcl-1 and oral cavity, cancers is not clearly defined.MethodsA scoping review was conducted until June 30, 2021, using four major databases, PubMed, Scopus, Web of Science, and Embase. Medical subject headings keywords for Mcl-1, along with its other identifiers, and head and neck cancers (only oral cavity tumors) were used to evaluate the expression, function, molecular association, and therapeutic approach of Mcl-1 in oral cavity cancers and precancers.FindingsMcl-1 expression was associated with the progression of oral cavity cancers. The molecular mechanism and pathways of Mcl-1 in oral cavity cancers established via experimental results have been highlighted in this review. Moreover, the various synthetic and naturally derived therapeutic agents targeting Mcl-1 have been documented.Novelty/ImprovementBased on our present review, Mcl-1 appears to be an effective anticancer target that can be used in the therapeutic management of oral cancers.

Interplay between protein acetylation and ubiquitination controls MCL1 protein stability.

SUMMARYThe anti-apoptotic myeloid cell leukemia 1 (MCL1) protein belongs to the pro-survival BCL2 family and is frequently amplified or elevated in human cancers. MCL1 is highly unstable, with its stability being regulated by phosphorylation and ubiquitination. Here, we identify acetylation as another critical post-translational modification regulating MCL1 protein stability. We demonstrate that the lysine acetyltransferase p300 targets MCL1 at K40 for acetylation, which is counteracted by the deacetylase sirtuin 3 (SIRT3). Mechanistically, acetylation enhances MCL1 interaction with USP9X, resulting in deubiquitination and subsequent MCL1 stabilization. Therefore, ectopic expression of acetylation-mimetic MCL1 promotes apoptosis evasion of cancer cells, enhances colony formation potential, and facilitates xenografted tumor progression. We further demonstrate that elevated MCL1 acetylation sensitizes multiple cancer cells to pharmacological inhibition of USP9X. These findings reveal that acetylation of MCL1 is a critical post-translational modification enhancing its oncogenic function and provide a rationale for developing innovative therapeutic strategies for MCL1-dependent tumors.

Loss of miR-1469 expression mediates melanoma cell migration and invasion.

Tumor ulceration is considered one of the most prognostically significant findings in primary cutaneous melanoma, associated with decreased disease-free and overall survival. However, the unique features associated with ulcerated melanoma that contribute to a poor prognosis in affected patients remain poorly defined. microRNAs are small, non-coding RNAs that function to inhibit expression of specific gene targets, therefore altering the functions of cells in which they are expressed. miR-1469 is a novel miR with significantly decreased expression in ulcerated melanoma tissue relative to non-ulcerated tumors. We hypothesized that loss of miR-1469 expression in melanoma contributes to altered tumor cell functions mediating disease progression. Transfection of a miR-1469 mimic resulted in a significant reduction in the migratory and invasive capacity of the CHL1 and MEL39 melanoma cell lines (>58.1% reduction, p < 0.0332), as well as the invasive capacity of the A375 melanoma cell line (>50% reduction, p < 0.0021). Expression of myeloid cell leukemia-1 (MCL1), a miR-1469 target gene, was reduced in the A375 and MEL39 cell lines by immunoblot. No significant differences in viability, resistance to apoptotic stimuli, or proliferation were observed following transfection. These findings together demonstrate how migration and invasion are specific functions through which miR-1469 expression in melanoma cells can contribute to the differences in disease progression associated with tumor ulceration.

CircPVT1 promotes gallbladder cancer growth by sponging miR-339-3p and regulates MCL-1 expression

Circular RNAs (circRNAs) have been implicated in modulating biological processes in some tumors. However, the contributions and molecular mechanisms of circRNAs to gallbladder cancer (GBC) remain largely unknown. In the present study, our results showed circPVT1 expression was significantly upregulated in GBC tissues and cells. Higher circPVT1 expression was correlated with lymph node metastasis, advanced TNM stage, and poor overall survival (OS) in patients with GBC. Subsequently, knockdown of circPVT1 significantly impeded GBC cell proliferation, migration, invasion, while induced cell apoptosis in vitro. However, upregulated circPVT1 had the opposite effects. In vivo, we also demonstrated that knockdown of circPVT1 inhibited tumor growth. Furthermore, we confirmed that circPVT1 could regulate Myeloid cell leukemia-1 (MCL-1) expression by sponging to miR-339-3p, which affected tumor progression in GBC cells. In summary, our findings indicated that circPVT1 may serve as a promising prognostic marker and therapeutic target for GBC.

Abstract 1959: CDK9 inhibition combined with hypomethylating agents target MCL-1 dependency in MDS and AML

Abstract Myelodysplastic syndrome (MDS) is a heterogeneous group of hematopoietic stem cell disorders. Approximately 70% of patients diagnosed with higher-risk (HR) MDS progress to acute myeloid leukemia (AML). Cyclin-dependent kinase 9 (CDK9) influences transcription through phosphorylation and activation of RNA polymerase II (RPB1), which increases the levels of key oncogenic survival genes like myeloid cell leukemia-1 (MCL-1). MCL-1 dependent malignancies can be identified through a functional assay by adding a NOXA mimetic MCL-1 antagonist peptide to patient samples and measuring the subsequent induction of apoptosis. The assay has been tested in bone marrow mononuclear cells (BMMCs) from AML and MDS patients to examine MCL-1 dependency prior to therapy with alvocidib. Approximately 25% of AML patient BMMCs and 60% of MDS patient BMMCs are MCL-1 dependent (data not shown). We hypothesized that the hypomethylating agents (HMAs) azacitidine and decitabine, which are currently approved for treatment of MDS, can increase MCL-1 dependency through re-expression of pro-apoptotic proteins like NOXA, normally repressed through DNA methylation in malignancies. In the MV-4-11 AML cell line and primary CD34+ MDS BMMCs, alvocidib treatment resulted in a dose dependent reduction in p-RPB1 and MCL-1. In cell viability assays using CellTiter-Glo, treatment with alvocidib and azacitidine resulted in IC50 values of ~100 nM and ~3000 nM, respectively in both cell types. Treatment with HMAs increased NOXA expression and alvocidib suppressed MCL-1 expression, whereas sequential treatment of azacitidine and alvocidib showed both NOXA induction and MCL-1 suppression. Sequential treatment of azacitidine and alvocidib showed synergistic apoptosis induction compared with either treatment alone. Azacitidine treatment sensitized MV-4-11 and MDS BMMCs to MCL-1 inhibition in an MCL-1 dependency assay. In an in vivo efficacy study using the MOLM13 AML xenograft model, the combination of alvocidib and azacitidine or decitabine inhibited tumor growth 71% and 84%, respectively. Alvocidib, azacitidine and decitabine alone showed 51%, 5.7% and 19% tumor growth inhibition (TGI), respectively. Pharmacodynamic analysis in a Phase 1 trial with alvocidib (clinicaltrials.gov, NCT03593915) showed DNA methylation of NOXA gene locus was reduced and NOXA gene expression was upregulated, while MCL-1 gene expression was suppressed in peripheral blood mononuclear cells (PBMCs) after azacitidine and alvocidib treatment. These pre-clinical and clinical data suggest that an alvocidib/HMA combination may constitute a viable therapeutic regimen whose rationale focuses on hypertargeting of NOXA/MCL-1. Taken together, these studies indicate that the combination of alvocidib and HMAs drives AML/MDS cells toward MCL-1 dependent apoptosis. Citation Format: Yuta Matsumura, Ethika Tyagi, Satya Pathi, Dan D. Vo, Tianxiang Zhu, Suman Verma, Clifford J. Whatcott, Stephen P. Anthony, Adam Siddiqui, Jason M. Foulks, David J. Bearss, Steven L. Warner. CDK9 inhibition combined with hypomethylating agents target MCL-1 dependency in MDS and AML [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1959.

Interrogation of novel CDK2/9 inhibitor fadraciclib (CYC065) as a potential therapeutic approach for AML

Over the last 50 years, there has been a steady improvement in the treatment outcome of acute myeloid leukemia (AML). However, median survival in the elderly is still poor due to intolerance to intensive chemotherapy and higher numbers of patients with adverse cytogenetics. Fadraciclib (CYC065), a novel cyclin-dependent kinase (CDK) 2/9 inhibitor, has preclinical efficacy in AML. In AML cell lines, myeloid cell leukemia 1 (MCL-1) was downregulated following treatment with fadraciclib, resulting in a rapid induction of apoptosis. In addition, RNA polymerase II (RNAPII)-driven transcription was suppressed, rendering a global gene suppression. Rapid induction of apoptosis was observed in primary AML cells after treatment with fadraciclib for 6–8 h. Twenty-four hours continuous treatment further increased efficacy of fadraciclib. Although preliminary results showed that AML cell lines harboring KMT2A rearrangement (KMT2A-r) are more sensitive to fadraciclib, we found that the drug can induce apoptosis and decrease MCL-1 expression in primary AML cells, regardless of KMT2A status. Importantly, the diversity of genetic mutations observed in primary AML patient samples was associated with variable response to fadraciclib, confirming the need for patient stratification to enable a more effective and personalized treatment approach. Synergistic activity was demonstrated when fadraciclib was combined with the BCL-2 inhibitor venetoclax, or the conventional chemotherapy agents, cytarabine, or azacitidine, with the combination of fadraciclib and azacitidine having the most favorable therapeutic window. In summary, these results highlight the potential of fadraciclib as a novel therapeutic approach for AML.

Oncolytic virotherapy promotes radiosensitivity in soft tissue sarcoma by suppressing anti-apoptotic MCL1 expression.

Soft tissue sarcoma (STS) is a rare cancer that develops from soft tissues in any part of the body. Despite major advances in the treatment of STS, patients are often refractory to conventional radiotherapy, leading to poor prognosis. Enhancement of sensitivity to radiotherapy would therefore improve the clinical outcome of STS patients. We previously revealed that the tumor-specific, replication-competent oncolytic adenovirus OBP-301 kills human sarcoma cells. In this study, we investigated the radiosensitizing effect of OBP-301 in human STS cells. The in vitro antitumor effect of OBP-301 and ionizing radiation in monotherapy or combination therapy was assessed using highly radiosensitive (RD-ES and SK-ES-1) and moderately radiosensitive (HT1080 and NMS-2) STS cell lines. The expression of markers for apoptosis and DNA damage were evaluated in STS cells after treatment. The therapeutic potential of combination therapy was further analyzed using SK-ES-1 and HT1080 cells in subcutaneous xenograft tumor models. The combination of OBP-301 and ionizing radiation showed a synergistic antitumor effect in all human STS cell lines tested, including those that show different radiosensitivity. OBP-301 was found to enhance irradiation-induced apoptosis and DNA damage via suppression of anti-apoptotic myeloid cell leukemia 1 (MCL1), which was expressed at higher levels in moderately radiosensitive cell lines. The combination of OBP-301 and ionizing radiation showed a more profound antitumor effect compared to monotherapy in SK-ES-1 (highly radiosensitive) and HT1080 (moderately radiosensitive) subcutaneous xenograft tumors. OBP-301 is a promising antitumor reagent to improve the therapeutic potential of radiotherapy by increasing radiation-induced apoptosis in STS.

MiR-26a Reverses Multidrug Resistance in Osteosarcoma by Targeting MCL1.

The multidrug resistance (MDR) acquired in human osteosarcoma is a huge obstacle for effective chemotherapy. Recently, microRNA-26a (miR-26a) has been associated with the pathogenesis and progression of osteosarcoma. However, whether it regulates MDR in osteosarcoma is unknown. We show here that miR-26a expression declines in chemoresistant osteosarcoma after neoadjuvant chemotherapy, and its expression correlates with clinical outcome. In addition, compared with sensitive parental cells, miR-26a expression also declines in osteosarcoma MDR cells, together suggesting a negative correlation between miR-26a expression and MDR development in osteosarcoma. We also show that the enforced expression of miR-26a reverses MDR in osteosarcoma cells, and conversely, miR-26a knockdown confers MDR in chemosensitive osteosarcoma cells treated with doxorubicin, methotrexate, or cisplatin. Mechanistically, miR-26a directly targets the pro-survival protein myeloid cell leukemia 1 (MCL1), and in turn, the enforced expression of MCL1 markedly antagonizes miR-26a-decreased MDR in osteosarcoma MDR cells, therefore demonstrating that miR-26a reverses MDR in osteosarcoma by targeting MCL1. Lastly, miR-26a reverses resistance to doxorubicin in osteosarcoma MDR cells xenografted in nude mice. Collectively, these results reveal a negative role and the underlying mechanism of miR-26a in the regulation of MDR in human osteosarcoma, implying a potential tactic of manipulating miR-26a for overcoming MDR in osteosarcoma chemotherapy.