Small Molecule Mcl-1 Inhibitors Research Articles

Abstract 1970: Novel Mcl-1 inhibitor effectively restores in vivo regorafenib sensitivity in resistant colorectal cancer

Abstract Colorectal cancer (CRC) is one of deadliest malignancies and approximately 25% of patients present with metastatic disease at the time of diagnosis, necessitating efficacious therapeutic options. Treatment of CRC has been greatly improved by targeted therapies such as the FDA-approved multi-kinase inhibitor, regorafenib, which elicits its anti-cancer effects by inducing apoptosis. Ours and other studies identified the anti-apoptotic Mcl-1 protein as a significant resistance factor to regorafenib treatment in CRC, associated with inactivating mutations in the tumor suppressor F-box and WD repeat domain-containing 7 (FBW7). These mutations result in abrogated Mcl-1 degradation, which contributes to survival of cancer cells and ineffective regorafenib induced apoptosis. Therefore, there is sound rationale for Mcl-1 inhibition to circumvent FBW7 inactivity and restore the efficacy of regorafenib. Our group has discovered and developed several classes of selective small molecule Mcl-1 inhibitors that bind in the conserved BH3 groove. In HCT116 colon cancer cells, the lead compound, 483LM, engages endogenous Mcl-1 as demonstrated by a CETSA assay and leads to a rapid accumulation of Mcl-1 protein levels, indicative of protein stabilization. 483LM induces BAX/BAK dependent apoptosis in cancer cells, upregulates the pro-apoptotic protein, Noxa, and displays favorable in vivo DMPK properties. Using a genetic Mcl-1 knock-in (KI) CRC cell line to mimic the effect of FBW7 loss, we confirmed the in vitro resistance of these KI cells to single agent regorafenib treatment and restored apoptosis when treated in combination with 483LM. Importantly, the in vivo combination treatment of 483LM and regorafenib completely overcome Mcl-1-mediated regorafenib resistance in HCT116 KI CRC xenograft tumors. Pharmacodynamic evaluation of tumor samples revealed significant caspase-3 activation in 483LM treated tumors. The proximity ligation assay revealed the ability of 483LM to induce significant disruption of PUMA:Mcl-1 complexes in treated tumor samples. These data confirm the previous reports of the involvement of Mcl-1 in regorafenib resistance in CRC and provides rationale for further investigation into the clinical application of pharmacological Mcl-1 inhibition in combination therapies to combat resistance. In addition, these results provide evaluation and characterization of a novel Mcl-1 selective small molecule inhibitor with potent in vivo activity and potential to treat various malignancies. Citation Format: Karson J. Kump, Jingshan Tong, Ahmed S. Mady, Lei Miao, Siwei Li, Duxin Sun, Jian Yu, Lin Zhang, Zaneta Nikolovska-Coleska. Novel Mcl-1 inhibitor effectively restores in vivo regorafenib sensitivity in resistant colorectal cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1970.

BAX-BAK heterodimer as a pharmacodynamic biomarker of on-target drug action of Mcl-1 inhibitors to evaluate in-vivo effectiveness.

2582Background: Clinical development of promising small molecule Mcl-1 inhibitors is underway. The Mcl-1 inhibitors act by disrupting complexes of Mcl-1 with pro-apoptotic proteins such as BAK/BIM/...

Small-molecule Mcl-1 inhibitors: Emerging anti-tumor agents

The anti-apoptotic members of B-cell lymphoma-2 (Bcl-2) proteins family, such as Bcl-2 and myeloid cell leukemia-1 (Mcl-1), are the key regulators of the intrinsic pathway of apoptosis and overexpressed in many tumor cells, which have been confirmed as potential drug targets for cancers. A number of Bcl-2 proteins inhibitors have been developed and conducted clinical trials, but no Mcl-1 inhibitors are presented in the clinics. In addition, Mcl-1 is an important reason for the resistance to radio- and chemotherapies, including inhibitors that target other Bcl-2 family members. For example, the recently launched Bcl-2-selective inhibitor ABT-199 displays highly potency in the treatment of chronic lymphocytic leukemia (CLL), but it cannot induce the apoptosis controlled by Mcl-1 in some tumor cell lines. Therefore, developing potent Mcl-1 inhibitors become urgently needed in clinical therapy. This review briefly introduces the structure of Mcl-1 protein, the role in cancers and focuses on the progress of small-molecule Mcl-1 inhibitors from 2012 to 2017.

Recent Advances in Cancer Drug Development: Targeting Induced Myeloid Cell Leukemia-1 (Mcl-1) Differentiation Protein.

Anti-apoptotic members of the Bcl-2 family of proteins are upregulated in a majority of cancers and are potential therapeutic targets. Fragment-based design led to the development of clinical candidates that target Bcl-xL/Bcl-2. Although these BclxL/ Bcl-2 inhibitors showed promise in pre-clinical studies, resistance to several Bcl-xL inhibitors was observed, when used alone. This is attributed to the over-expression of Mcl-1, another member of the Bcl-2 family of proteins. Indeed, Mcl-1 is highly amplified in numerous cancers, suggesting that it may contribute to malignant cell growth and evasion of apoptosis. Therefore, significant efforts have been made toward the development of direct Mcl-1 inhibitors for cancer therapy. Following an extensive search of peer-reviewed articles on the development of Mcl-1-selective inhibitors, the literature retrieved is chronologically arranged and discussed in this review article. We have included 147 articles in this review; including articles that describe the development of stapled peptides with improved binding affinity as Mcl-1-selective BH3 mimetics, those describing fragment-based and structure-based design of small molecule Mcl-1 inhibitors by various research groups, and those detailing the use of natural products and their derivatives as potential Mcl-1 inhibitors. The therapeutic potential of targeting the Mcl-1 protein for cancer drug discovery is vast. Stapling BH3 peptides, as well as the development of small molecule inhibitors as BH3 mimetics, are viable strategies to develop selective Mcl-1 inhibitors. With no clinically approved candidate in hand, additional modes of perturbing the biological function of this protein will aid drug discovery efforts.

Abstract 1173: A novel selective Mcl-1 inhibitor exhibits in vitro and in vivo efficacy in melanoma

Abstract Metastatic melanoma is the deadliest form of skin cancer that still has limited treatment options and dismal 5-year year survival rates as low as 15%. Only recently has there been significant progress in the treatment of metastatic melanoma, advent by molecular targeted drugs and immunotherapy, but their limitations are exposed as these cancers are quickly able to develop resistance. Dysregulation of apoptotic machinery in melanoma allows the cancer cells to evade cell death and contributes to treatment resistance. Up-regulation of Mcl-1, a member of the Bcl-2 family of anti-apoptotic proteins, has been correlated with melanoma progression and metastasis. Mcl-1 amplification is one of the most common genetic aberrations found in human cancers and has been labeled as a marker of aggressive oncogenesis and poor patient prognosis. Previous studies have pointed to Mcl-1 as a viable therapeutic target for the treatment of melanoma and conclude that small molecule Mcl-1 inhibitors may appeal this unmet medical need. We have discovered and characterized a new class of selective small molecule Mcl-1 inhibitors using various biochemical, functional, and cell based assays; further development of these compounds allowed us to achieve potent low-nanomolar binding affinity for Mcl-1 and more than 300-fold selectivity over Bcl-2/Bcl-xL. Our most potent inhibitor, 483-LM, was screened across a panel of human melanoma cell lines using a cell proliferation assay and revealed varying levels of sensitivity. A BH3 profiling assay demonstrates that C8161, the cell line most sensitive to our inhibitor, solely relies on Mcl-1 for survival. The Mcl-1 dependence of C8161 might contribute to the known metastatic nature of this cell line. Mechanistic studies revealed that 483-LM effectively engaged the endogenous Mcl-1 protein after treatment of C8161, as determined by a CETSA assay, and prompted disruption of protein-protein interactions between Mcl-1 and several pro-apoptotic proteins, including Bax, Bak and Bim. This was followed by induction of Bax/Bak dependent apoptosis and activation of hallmarks of the intrinsic apoptotic pathway, including mitochondrial outer membrane depolarization, caspase activation, and PARP cleavage. Importantly, treatment with 483-LM caused massive up-regulation of the pro-apoptotic BH3-only protein Noxa, an effect apparent after an 8 hour treatment, which contributes to the induction of cell death. The in vivo efficacy studies with 483-LM showed significant effect on tumor growth and caspase-3 activation in tumor samples. Overall, our data indicate that Mcl-1 inhibitors are a promising treatment option for aggressive metastatic melanoma and warrant further preclinical investigation of 483-LM as a promising selective Mcl-1 inhibitor to be used as a single agent and in combination with chemotherapy and immunotherapy. Citation Format: Karson J. Kump, Lei Miao, Ahmed S. Mady, Katherine Lev, William Giblin, Mary E. Skinner, David B. Lombard, Zaneta Nikolovska-Coleska. A novel selective Mcl-1 inhibitor exhibits in vitro and in vivo efficacy in melanoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1173. doi:10.1158/1538-7445.AM2017-1173

Abstract 4316: MCL-1 inhibition ameliorates the expansion of human leukemia in a dose dependent fashion

Abstract Myeloid cell leukemia-1 (MCL-1) is a prosurvival BCL-2 family member protein commonly overexpressed in cancer, including hematologic malignancies. The successful use of BH3 mimetics against other anti-apoptotic proteins has validated the potential of this line of therapy in hematologic malignancies. However, targeting BCL-2 family members, like MCL-1, with a small molecule inhibitor is challenging because these inhibitors mediate their effects through protein-protein interactions. Recently, we discovered potent (sub nM), selective small molecule MCL-1 inhibitors that exhibit cell-based activity and slow the growth of tumors in multiple mouse models. To determine tumor cell dependence on specific BCL2-family members, we employed BH3 profiling on a panel of myeloid tumor cells to reveal mitochondrial outer membrane permeablization (MOMP) in a cytochrome C release assay. Additionally, we determined growth inhibition of these cell lines in the presence of the potent MCL-1 inhibitor. These assays indicated MV-411 cells were dependent on MCL-1 and sensitive to MCL-1 inhibition with a GI50 <100nM. After cell line profiling, we began in vivo studies with the MCL-1 inhibitor in a systemic AML xenograft model. NSGS mice were sublethally irradiated and administered MV-411 cells intravenously. Engrafted mice received the MCL-1 inhibitor in 3 different doses (vehicle vs 10, 25 and 75mg/kg) daily via intraperitoneal injection. During treatment, the kinetics of MV-411 expansion was monitored via flow cytometry for the detection of human AML in the blood. At approximately 4 weeks after transplant, the vehicle mice became moribund, and all experimental groups were sacrificed for analysis of chimerism. Significant decreases in leukemic expansion were evident in the bone marrow (25 and 75mg/kg vs vehicle, P= .01, P <.001) and spleen (vehicle vs. 75mg/kg, P<.001) of treated mice in a dose-dependent fashion. MCL-1 blockade also eliminated splenomegaly in MCL-1 inhibitor treated mice. Successful use of the BCL-2 inhibitor, venetoclax, as a single agent and in combination with DNA methyltransferase inhibitors or low dose ara-C has proven the powerful role BH3 mimetics may play in AML therapy. However, mediation of resistance via alternative BCL-2 family antiapoptotic proteins remains a concern, and development of suitable inhibitors of MCL-1 and BCL-XL is important. These data show that we have developed a potent MCL-1 inhibitor, with in vivo efficacy in an AML mouse model. Further studies can determine the potential use of this drug to overcome resistance in the clinic. In addition, we will employ dynamic BH3 profiling of patient samples to determine the combination and sequencing of therapeutically applied BH3 mimetics. Citation Format: Haley E. Ramsey, Melissa A. Fischer, Taekyu Lee, Agnieszka E. Gorska, Pia Arrate, John Sensintaffer, Leah Hogdal, Edward Olejniczak, Stephen Fesik, Michael R. Savona. MCL-1 inhibition ameliorates the expansion of human leukemia in a dose dependent fashion [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4316. doi:10.1158/1538-7445.AM2017-4316

Mcl-1 Degradation Is Required for Targeted Therapeutics to Eradicate Colon Cancer Cells.

The Bcl-2 family protein Mcl-1 is often degraded in cancer cells subjected to effective therapeutic treatment, and defective Mcl-1 degradation has been associated with intrinsic and acquired drug resistance. However, a causal relationship between Mcl-1 degradation and anticancer drug responses has not been directly established, especially in solid tumor cells where Mcl-1 inhibition alone is insufficient to trigger cell death. In this study, we present evidence that Mcl-1 participates directly in determining effective therapeutic responses in colon cancer cells. In this setting, Mcl-1 degradation was induced by a variety of multikinase inhibitor drugs, where it relied upon GSK3β phosphorylation and FBW7-dependent ubiquitination. Specific blockade by genetic knock-in (KI) abolished apoptotic responses and conferred resistance to kinase inhibitors. Mcl-1-KI also suppressed the antiangiogenic and anti-hypoxic effects of kinase inhibitors in the tumor microenvironment. Interestingly, these same inhibitors also induced the BH3-only Bcl-2 family protein PUMA, which is required for apoptosis. Degradation-resistant Mcl-1 bound and sequestered PUMA from other prosurvival proteins to maintain cell survival, which was abolished by small-molecule Mcl-1 inhibitors. Our findings establish a pivotal role for Mcl-1 degradation in the response of colon cancer cells to targeted therapeutics, and they provide a useful rational platform to develop Mcl-1-targeting agents that can overcome drug resistance. Cancer Res; 77(9); 2512-21. ©2017 AACR.

UMI-77 primes glioma cells for TRAIL-induced apoptosis by unsequestering Bim and Bak from Mcl-1.

Malignant glioma is the most common and aggressive form of brain tumor with poor prognosis of survival. Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a promising anticancer agent but is insufficient of inducing apoptosis in some types of gliomas. In this study, we showed that the small-molecule Mcl-1 inhibitor UMI-77 sensitized glioma cells to TRAIL treatment, as evidenced by cell viability assay, Annexin V stainingand JC-1 staining. Combination of UMI-77 and TRAIL in glioma cells led to the activation of caspase-8 and Bid, cleavage of caspase-3 and poly-ADP ribose polymerase (PARP), accumulation of tBid in the mitochondriaand release of cytochrome c into the cytosol. UMI-77 alone or in combination with TRAIL untethered pro-apoptotic Bcl-2 proteins Bim and Bak from the sequestration of Mcl-1 and promoted the conformational activation of Bak. Small hairpin RNA (shRNA) of Bid attenuated the cleavage of caspase-8, Bid, caspase-3and PARP, and reduced the cytotoxicity of UMI-77 plus TRAIL as compared with control shRNA cells, indicating this synergy entails the crosstalk between extrinsic and intrinsic apoptotic signaling. Taken together, UMI-77 enhances TRAIL-induced apoptosis by unsequestering Bim and Bak, which provides a novel therapeutic strategy for the treatment of gliomas.

Mutant BRAF upregulates MCL-1 to confer apoptosis resistance that is reversed by MCL-1 antagonism and cobimetinib in colorectal cancer.

603 Background: Oncogenic BRAFV600E mutations activate MAP kinase signaling and are associated with treatment resistance and poor prognosis in patients with colorectal cancer (CRC). In BRAFV600E mutant CRCs, treatment failure may be related to BRAFV600E-mediated apoptosis resistance that occurs by an as yet undefined mechanism. Methods: BRAF isogenic RKO CRC cells and RKO, HT29, WiDr cell lines were treated with cobimetinib ± the small molecule MCL-1 inhibitor, A-1210477. Apoptosis was measured by Annexin V staining and caspase cleavage. Gene knockdown or overexpression was achieved by lentivirus; ERK siRNA was utilized. Competitive RT-PCR was performed for MCL-1 mRNA expression. HT-29 cells with control or MCL-1 shRNA were xenografted into SCID mice, treated with cobimetinib or vehicle, and tumor volume was measured. Results: We found that BRAFV600E can upregulate anti-apoptotic MCL-1 in a gene dose-dependent manner using CRC cell lines isogenic for BRAF. BRAFV600E-induced MCL-1 upregulation was confirmed by ectopic BRAFV600E expression that activated MEK/ERK signaling to phosphorylate (MCL-1Thr163) and stabilize MCL-1. Upregulation of MCL-1 was mediated by MEK/ERK shown by ERK siRNA that suppressed MCL-1. Stabilization of MCL-1 by phosphorylation was shown by a phosphorylation-mimicking mutant and an unphosphorylated MCL-1 mutant that decreased or increased MCL-1 protein turnover, respectively.MEK /ERK inhibition by cobimetinib suppressed MCL-1 expression/phosphorylation and induced pro-apoptotic BIM to a greater extent than did vemurafenib in BRAFV600E cell lines. MCL-1 knockdown vs control shRNA significantly enhanced cobimetinib-induced apoptosis in vitro and in HT29 colon cancer xenografts. A-1210477 also enhanced cobimetinib-induced apoptosis in vitrothat was due to disruption of the interaction of MCL-1 with pro-apoptotic BAK and BIM. Knockdown of BIM attenuated BAX, but not BAK, activation by cobimetinib plus A-1210477. Conclusions: BRAFV600E-mediated MEK/ERK activation can upregulate MCL-1 by phosphorylation/stabilization to confer apoptosis resistance that can be reversed by MCL-1 antagonism.

MYC-Dependent PI3K and MCL-1 Feedbacks Attenuate BET Inhibitors Activity in Diffuse Large B-Cell Lymphoma

MYC overexpression is a poor prognostic predictor in Diffuse Large B-Cell Lymphoma (DLBCL). MYC-targeting with bromodomain and extraterminal protein family (BET) inhibitors is a promising strategy for the treatment of MYC-driven cancers, including lymphomas. However, preclinical and emerging data from early clinical trials demonstrated a modest antiproliferative activity in vitro and in vivo. We hypothesized that BET inhibition may induce feedback survival mechanisms preventing or attenuating cell death that could be exploited for designing future, more effective, combination strategies. In a high-throughput combinatorial drug screening experiment, we found that phosphatidylinositol 3-kinase (PI3K) pathway inhibitors enhanced the antiproliferative effects of BET inhibitors (JQ1, I-BET 151, CPI-203) with a strong class effect. JQ1 upregulated the mRNA expression of several upstream components of the PI3K pathway, including PIK3CA, PIK3R1, PDK1 in a large panel of DLBCL and Burkitt lymphoma cell lines. These effects translated in increased pathway activation as demonstrated by increased levels of the phosphorylated forms of downstream targets GSK3α/β, TSC2, P70S6K, and by increased concentrations of chemokines known to be regulated by PI3K in cell culture supernatants (CCL3 and CCL4). This effect was reversed by submicromolar doses of the PI3K inhibitor BKM-120. MYC silencing recapitulated the effects of BET inhibitors on PI3K pathway gene expression, activation and chemokine secretion. These data indicate that BET inhibition induces PI3K activation by a MYC-dependent feedback. We also observed transcriptional upregulation of the antiapoptotic gene Myeloid Leukemia 1 (MCL-1) following BET inhibition or MYC depletion, suggesting a second MYC-dependent mechanism. RNAi-mediated MCL-1 silencing or co-treatment with a small molecule MCL-1 inhibitor (UMI-77) enhanced the effects of BET inhibitors in DLBCL cell lines by inducing apoptosis. Using SILAC-based quantitative mass spectrometry, we found that BET inhibitors at submicromolar doses downregulated several E2 ubiquitin conjugating enzymes including UBE2C. RNAi mediated UBE2C knockdown induced MCL-1 upregulation in DLBCL cells. The enhanced in vitro effect of combining BETi and PI3Ki was reproduced in TMD8 mouse xenografts. To our knowledge, this is the first study demonstrating MYC-dependent regulation of the PI3K pathway, MCL-1 and the ubiquitin system upon BET inhibition. Our study revealed previously unknown mechanisms of action of BET inhibitors uncovering novel MYC-dependent survival feedback loops, and providing a framework for future combination strategies. DisclosuresZelenetz:Gilead Sciences: Research Funding.

S63845, an MCL-1 Selective BH3 Mimetic: Another Arrow in Our Quiver

A recent study reports a novel small molecule inhibitor of MCL-1 with efficacy in killing MCL-1-dependent cancer cells invitro and invivo. With the advent of S63845, the targeting of BCL-2, BCL-XL, and MCL-1 is now possible invivo, but optimal clinical use is yet to be determined.

Mutant BRAF Upregulates MCL-1 to Confer Apoptosis Resistance that Is Reversed by MCL-1 Antagonism and Cobimetinib in Colorectal Cancer.

Oncogenic BRAFV600E mutations activate MAPK signaling and are associated with treatment resistance and poor prognosis in patients with colorectal cancer. In BRAFV600E-mutant colorectal cancers, treatment failure may be related to BRAFV600E-mediated apoptosis resistance that occurs by an as yet undefined mechanism. We found that BRAFV600E can upregulate anti-apoptotic MCL-1 in a gene dose-dependent manner using colorectal cancer cell lines isogenic for BRAF BRAFV600E-induced MCL-1 upregulation was confirmed by ectopic BRAFV600E expression that activated MEK/ERK signaling to phosphorylate (MCL-1Thr163) and stabilize MCL-1. Upregulation of MCL-1 was mediated by MEK/ERK shown by the ability of ERK siRNA to suppress MCL-1. Stabilization of MCL-1 by phosphorylation was shown by a phosphorylation-mimicking mutant and an unphosphorylated MCL-1 mutant that decreased or increased MCL-1 protein turnover, respectively. MEK/ERK inhibition by cobimetinib suppressed MCL-1 expression/phosphorylation and induced proapoptotic BIM to a greater extent than did vemurafenib in BRAFV600E cell lines. MCL-1 knockdown versus control shRNA significantly enhanced cobimetinib-induced apoptosis in vitro and in HT29 colon cancer xenografts. The small-molecule MCL-1 inhibitor, A-1210477, also enhanced cobimetinib-induced apoptosis in vitro that was due to disruption of the interaction of MCL-1 with proapoptotic BAK and BIM. Knockdown of BIM attenuated BAX, but not BAK, activation by cobimetinib plus A-1210477. In summary, BRAFV600E-mediated MEK/ERK activation can upregulate MCL-1 by phosphorylation/stabilization to confer apoptosis resistance that can be reversed by MCL-1 antagonism combined with cobimetinib, suggesting a novel therapeutic strategy against BRAFV600E-mutant CRCs. Mol Cancer Ther; 15(12); 3015-27. ©2016 AACR.

12P Individualized breast cancer therapy using Mcl-1 inhibition based combination

Background Breast cancer (BC)isleadingcauseofcancer-relatedmortalityinwomen. Anti-apoptotic Bcl-2 family members including Bcl-2, Bcl-xL and myeloid cell leukemia-1(Mcl-1) controltheintrinsicpathwayofapoptosis.ElevatedMcl-1levels have been correlated with poor prognosis. The aim of this study is to evaluate a rationally-derived combination of Mcl-1-inhibitor with Bcl-2 or Bcl-xL inhibitors as well as with conventional BC treatment and to provide the derived rationale to therapeutically target Mcl-1. Methods The anti-BC cell-activity of the novel small molecule Mcl-1 inhibitor EU5346 was evaluated alone or in combination with other antiapoptotic agents, hormone therapy, targeted therapy, or chemotherapy using proliferation and spheroid forming assays as well as immunoblotting in different BC cell lines. Synergistic activity of combination therapies was determined by the Chou-Talalay method. Results Using protein profiling Mcl-1 is consistently overexpressed in all BC subtypes while Bcl-2 and Bcl-xL are variably expressed. We then performed selective treatments with Mcl-1/Bcl-2/Bcl-xL inhibitors. As expected, cell proliferation was significantly reduced in correspondence to the protein levels of antiapoptotic Bcl-2 family member, thereby indicating the rational combination of Mcl-1 inhibitor with Bcl-2/Bcl-xL inhibitors. Importantly, Bak, Bim and Noxa protein levels predict the IC50 of EU-5346 in all BC subtypes. We then demonstrated that a protein level-based drug combination Mcl-1 inhibitor with Bcl-2/Bcl-xL inhibitors, induces synergistic anti- BC cell activity. Moreover, not only the combination of EU-5346 with tamoxifen, trastuzumab as well as paclitaxel triggers synergistic anti- BC cell activity, but also inhibiting Mcl-1 overcomes resistance to paclitaxel in paclitaxel-resistant TNBC cells. Conclusions Our data demonstrate an important role of Mcl-1 in BC cell survival, and provide the preclinical framework for the individualized, clinical use of Mcl-1-inhibitor- based drug combinations with antiapoptotic, antihormonal or chemotherapies to improve patient outcome in BC. Legal entity responsible for the study Klaus Podar Funding Eutropics Pharmaceuticals, Inc, Disclosure M.H.Bashari: received research support from EUTROPICS. M. H. Cardone: employee of Eutropics, Inc. All other authors have declared no conflicts of interest.

Anticancer drugs: Breaking up a pro-survival interaction.

A paper in Nature describes a highly specific and potent small molecule inhibitor of MCL1 that has single-agent activity and good tolerability in several cancer models.

Anticancer drugs: Breaking up a pro-survival interaction.

A paper inNaturedescribes a highly specific and potent small molecule inhibitor of MCL1 that has single-agent activity and good tolerability in several cancer models.

Abstract 2115: MEK/ERK and MCL-1 inhibition synergistically reverse apoptosis resistance in colon cancer cells with BRAF(V600E)-mediated MCL-1-upregulation

Abstract Background. Oncogenic BRAFV600E mutations in colorectal cancer (CRC) are associated with poor prognosis and treatment resistance. BRAF mutations activate MAP kinase signaling and may confer apoptosis resistance by upregulating anti-apoptotic BCL-2/BCL-XL/MCL-1 proteins. Results. Ectopic expression of mutant BRAFV600E was shown to potently activate MEK/ ERK that mediated the phosphorylation (T163) and upregulation of MCL-1, but not BCL-2 or BCL-XL. MEK/ERK-mediated phosphorylation of MCL-1 (T163) increased its protein stability, shown by an MCL-1 phospho-mimic mutant. In human colon cancers, mutant vs wild-type BRAF was associated with increased MCL-1 expression by IHC. MEK/ERK inhibition by cobimetinib induced pro-apoptotic BIM in BRAF mutant CRC cell lines (HT-29, RKO), and suppressed phospho-MCL-1/MCL-1 proteins as did ERK siRNA. Suppression of MCL-1 by shRNA or using a small molecule MCL-1 inhibitor (A-1210477) synergistically enhanced cobimetinib-induced apoptosis (Table) that was associated with BAK/BAX activation. A-1210477 antagonized MCL-1 by disrupting its interaction with BAK and BIM proteins, shown by immunoprecipitation. Conclusion. BRAF/MEK/ERK induces upregulation of MCL-1 via phosphorylation/stabilization to confer apoptosis resistance that can be overcome by combined ERK and MCL-1 inhibition, suggesting a novel therapeutic strategy against BRAF mutant CRCs. Drug-induced apoptosis (annexin V) in CRC cell linesDrugsHT-29 % apoptosisRKO % apoptosisDMSO16.842.11A-1210477 (2.5 μM)29.5222.88Cobimetinib(5 μM)28.0421.05Combination53.2250.93 Citation Format: Hisato Kawakami, Shengbing Huang, Frank A. Sinicrope. MEK/ERK and MCL-1 inhibition synergistically reverse apoptosis resistance in colon cancer cells with BRAF(V600E)-mediated MCL-1-upregulation. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2115.

Abstract 3727: Small molecule Mcl-1 inhibitors induce apoptosis and death in multiple cancer subtypes in vitro

Abstract Mcl-1 is a member of the Bcl-2 family of proteins that play a major role in conferring resistance to apoptosis in cancer cells. Inhibiting Mcl-1 using peptides or RNAi has been shown to induce apoptosis in a broad array of cancer cell lines in numerous studies, making Mcl-1 a compelling target for anticancer therapy. We have discovered potent and selective small molecule Mcl-1 inhibitors that bind to the BH3 binding site of Mcl-1 with sub nanomolar affinities. These agents rapidly induced apoptosis in the Mcl-1 dependent NCI-H929 myeloma cell line, as demonstrated by mitochondrial membrane depolarization, caspase activation, and decreased viability. We measured the anti-proliferative activity of our compounds in cell lines from several cancer subtypes and found a broad spectrum of sensitivity to Mcl-1 inhibition. In cell lines that were resistant to Mcl-1 antagonists, combination with the dual Bcl-2/Bcl-xL inhibitor ABT-263 (navitoclax) greatly enhanced the activity of both compounds. These findings demonstrate that pharmacologic inhibition of Mcl-1 as a single agent or in combination with other cancer therapeutic agents is an effective way to modulate the intrinsic apoptotic pathway and promote cell death in cancer cells. Citation Format: John L. Sensintaffar, Allison Arnold, Craig Goodwin, Leah Hogdal, Subrata Shaw, James C. Tarr, Taekyu Lee, Edward Olejniczak, Stephen W. Fesik. Small molecule Mcl-1 inhibitors induce apoptosis and death in multiple cancer subtypes in vitro. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 3727.

Abstract 4331: Discovery of potent 2-Indole-acylsulfonamide Mcl-1 inhibitors using structure guided fragment-based methods

Abstract Mcl-1 (Myeloid cell leukemia 1), a member of the Bcl-2 family of proteins, is overexpressed and amplified in various cancers and is one of the major acquired resistance mechanisms for many anticancer therapies. Targeting Mcl-1 with small molecules is very challenging because Mcl-1 exerts its effects through protein-protein interactions. Here we describe our continuing efforts in the discovery of potent and selective Mcl-1 inhibitors using fragment-based methods and structure-based design. We previously described the discovery of small-molecule Mcl-1 inhibitors containing a 2-indole-carboxylic core that primarily bind to the P2 pocket. In order to enhance potency, we extend our molecules to occupy the entire BH3 binding interface. A number of P4 site hits were identified using a fragment-based screening while the P2 pocket of Mcl-1 was saturated with our previously reported lead. P4 site ligands were then linked to our initial lead guided by the ternary Mcl-1 structure containing both P2 and P4 units using an acylsulfonamide as a synthetic handle that retained the critical charged-charged interaction with R263. X-ray co-crystal structures of new inhibitors occupying both P2 and P4 sites bound Mcl-1 provided detailed information on how these small-molecules bind to the target and guided subsequent potency optimization. From the efforts, we discovered a novel series of 2-indole-acylsulfonamide containing Mcl-1 inhibitors that exhibit low nanomolar binding affinities to the target and greater than 500-fold selectivity over Bcl-xL. These compounds represent useful starting points for the discovery of clinically useful Mcl-1 inhibitors for the treatment of a wide variety of cancers. Citation Format: Subrata Shaw, James Chris Tarr, Nicholas Pelz, Zhiguo Bian, Johannes Belmar, Bin Zhao, Craig Goodwin, Allison Arnold, John Sensintaffar, Olivia Rossanese, Taekyu Lee, Edward Olejniczak, Stephen Fesik. Discovery of potent 2-Indole-acylsulfonamide Mcl-1 inhibitors using structure guided fragment-based methods. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4331.

Mcl-1 confers protection of Her2-positive breast cancer cells to hypoxia: therapeutic implications.

BackgroundMolecular mechanisms leading to the adaptation of breast cancer (BC) cells to hypoxia are largely unknown. The anti-apoptotic Bcl-2 family member myeloid cell leukemia-1 (Mcl-1) is frequently amplified in BC; and elevated Mcl-1 levels have been correlated with poor prognosis. Here we investigated the pathophysiologic role of Mcl-1 in Her2-positive BC cells under hypoxic conditions.MethodsRNA interference and a novel small molecule inhibitor, EU-5346, were used to examine the role of Mcl-1 in Her2-positive BC cell lines and primary BC cells (sensitive or intrinsically resistant to Her2 inhibitors) under hypoxic conditions (using a hypoxic incubation chamber). Mechanisms-of-action were investigated by RT-PCR, mitochondrial isolation, as well as immunoprecipitation/blotting analysis, and microscopy. The specificity against Mcl-1 of the novel small molecule inhibitor EU5346 was verified in Mcl-1Δ/nullversus Mcl-1wt/wt Murine Embryonic Fibroblasts (MEFs). Proliferation, survival, and spheroid formation were assessed in response to Mcl-1 and Her2 inhibition.ResultsWe demonstrate for a strong correlation between high Mcl-1 protein levels and hypoxia, predominantly in Her2-positive BC cells. Surprisingly, genetic depletion of Mcl-1 decreased Her2 and Hif-1α levels followed by inhibition of BC cell survival. In contrast, Mcl-1 protein levels were not downregulated after genetic depletion of Her2 indicating a regulatory role of Mcl-1 upstream of Her2. Indeed, Mcl-1 and Her2 co-localize within the mitochondrial fraction and form a Mcl-1/Her2- protein complex. Similar to genetically targeting Mcl-1 the novel small molecule Mcl-1 inhibitor EU-5346 induced cell death and decreased spheroid formation in Her2-positive BC cells. Of interest, EU-5346 induced ubiquitination of Mcl-1- bound Her2 demonstrating a previously unknown role for Mcl-1 to stabilize Her2 protein levels. Importantly, targeting Mcl-1 was also active in Her2-positive BC cells resistant to Her2 inhibitors, including a brain-primed Her2-positive cell line.ConclusionOur data demonstrate a critical role of Mcl-1 in Her2-positive BC cell survival under hypoxic conditions and provide the preclinical framework for the therapeutic use of novel Mcl-1- targeting agents to improve patient outcome in BC.Electronic supplementary materialThe online version of this article (doi:10.1186/s13058-016-0686-4) contains supplementary material, which is available to authorized users.

Structure-based design of N-substituted 1-hydroxy-4-sulfamoyl-2-naphthoates as selective inhibitors of the Mcl-1 oncoprotein

Structure-based drug design was utilized to develop novel, 1-hydroxy-2-naphthoate-based small-molecule inhibitors of Mcl-1. Ligand design was driven by exploiting a salt bridge with R263 and interactions with the p2 pocket of the protein. Significantly, target molecules were accessed in just two synthetic steps, suggesting further optimization will require minimal synthetic effort. Molecular modeling using the Site-Identification by Ligand Competitive Saturation (SILCS) approach was used to qualitatively direct ligand design as well as develop quantitative models for inhibitor binding affinity to Mcl-1 and the Bcl-2 relative Bcl-xL as well as for the specificity of binding to the two proteins. Results indicated hydrophobic interactions in the p2 pocket dominated affinity of the most favourable binding ligand (3bl: Ki = 31 nM). Compounds were up to 19-fold selective for Mcl-1 over Bcl-xL. Selectivity of the inhibitors was driven by interactions with the deeper p2 pocket in Mcl-1 versus Bcl-xL. The SILCS-based SAR of the present compounds represents the foundation for the development of Mcl-1 specific inhibitors with the potential to treat a wide range of solid tumours and hematological cancers, including acute myeloid leukemia.