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TRAIL can activate cell surface death receptors, resulting in potent tumor cell death via induction of the extrinsic apoptosis pathway. Eftozanermin alfa (ABBV-621) is a second generation TRAIL receptor agonist engineered as an IgG1-Fc mutant backbone linked to two sets of trimeric native single-chain TRAIL receptor binding domain monomers. This hexavalent agonistic fusion protein binds to the death-inducing DR4 and DR5 receptors with nanomolar affinity to drive on-target biological activity with enhanced caspase-8 aggregation and death-inducing signaling complex formation independent of FcγR-mediated cross-linking, and without clinical signs or pathologic evidence of toxicity in nonrodent species. ABBV-621 induced cell death in approximately 36% (45/126) of solid cancer cell lines in vitro at subnanomolar concentrations. An in vivo patient-derived xenograft (PDX) screen of ABBV-621 activity across 15 different tumor indications resulted in an overall response (OR) of 29% (47/162). Although DR4 (TNFSFR10A) and/or DR5 (TNFSFR10B) expression levels did not predict the level of response to ABBV-621 activity in vivo, KRAS mutations were associated with elevated TNFSFR10A and TNFSFR10B and were enriched in ABBV-621–responsive colorectal carcinoma PDX models. To build upon the OR of ABBV-621 monotherapy in colorectal cancer (45%; 10/22) and pancreatic cancer (35%; 7/20), we subsequently demonstrated that inherent resistance to ABBV-621 treatment could be overcome in combination with chemotherapeutics or with selective inhibitors of BCL-XL. In summary, these data provide a preclinical rationale for the ongoing phase 1 clinical trial (NCT03082209) evaluating the activity of ABBV-621 in patients with cancer. Significance: This study describes the activity of a hexavalent TRAIL-receptor agonistic fusion protein in preclinical models of solid tumors that mechanistically distinguishes this molecular entity from other TRAIL-based therapeutics.

Herein we describe the discovery of A-1331852, a first-in-class orally active BCL-XL inhibitor that selectively and potently induces apoptosis in BCL-XL-dependent tumor cells. This molecule was generated by re-engineering our previously reported BCL-XL inhibitor A-1155463 using structure-based drug design. Key design elements included rigidification of the A-1155463 pharmacophore and introduction of sp3-rich moieties capable of generating highly productive interactions within the key P4 pocket of BCL-XL. A-1331852 has since been used as a critical tool molecule for further exploring BCL-2 family protein biology, while also representing an attractive entry into a drug discovery program.

MCL-1 is one of the most frequently amplified genes in cancer, facilitating tumor initiation and maintenance and enabling resistance to anti-tumorigenic agents including the BCL-2 selective inhibitor venetoclax. The expression of MCL-1 is maintained via P-TEFb-mediated transcription, where the kinase CDK9 is a critical component. Consequently, we developed a series of potent small-molecule inhibitors of CDK9, exemplified by the orally active A-1592668, with CDK selectivity profiles that are distinct from related molecules that have been extensively studied clinically. Short-term treatment with A-1592668 rapidly downregulates RNA pol-II (Ser 2) phosphorylation resulting in the loss of MCL-1 protein and apoptosis in MCL-1-dependent hematologic tumor cell lines. This cell death could be attenuated by either inhibiting caspases or overexpressing BCL-2 protein. Synergistic cell killing was also observed between A-1592668 or the related analog A-1467729, and venetoclax in a number of hematologic cell lines and primary NHL patient samples. Importantly, the CDK9 inhibitor plus venetoclax combination was well tolerated in vivo and demonstrated efficacy superior to either agent alone in mouse models of lymphoma and AML. These data indicate that CDK9 inhibitors could be highly efficacious in tumors that depend on MCL-1 for survival or when used in combination with venetoclax in malignancies dependent on MCL-1 and BCL-2.

Cell death can be initiated through activation of the extrinsic and intrinsic apoptotic signaling pathways. Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL), a member of the TNF superfamily of cytokines, preferentially triggers the extrinsic apoptotic pathway by binding as a trimer to two closely related cell surface death receptors, TRAIL-R1 (DR4) and TRAIL-R2 (DR5). Receptor trimerization leads to the formation of the death-inducing signaling complex (DISC) to recruit and activate downstream caspases that ultimately leads to apoptotic cell death. Because TRAIL signaling induces apoptosis, several TRAIL receptor agonists have been developed for the treatment of cancer. ABBV-621 is a novel, second generation TRAIL receptor agonist that is an engineered fusion protein consisting of an IgG1-Fc linked to a single chain trimer of TRAIL subunits resulting in a total of six death receptor binding sites per molecule to maximize receptor clustering that is currently being tested in Phase I clinical trials (NCT03082209). To expand upon the potential therapeutic utility of ABBV-621, we tested the combinatorial activity of ABBV-621 with numerous standard-of-care (SoC) therapeutics and targeted agents in diffuse large B-cell lymphoma (DLBCL), acute myeloid leukemia (AML) and multiple myeloma (MM) cell lines. Thein vitroresults led to selection of agents to combine with ABBV-621 forin vivostudies. In DLBCL cell line-derived xenograft (CDX) preclinical models, we observed combination activity of ABBV-621 with pevonedistat (PEV) a selective NEDD8 inhibitor. Additionally, synergistic activity was observed with ABBV-621 with either bendamustine (BED) or rituximab (RTX) alone, or BED/RTX together. In AML, we observed compelling combination activity of ABBV-621 with PEV in cell line-derived xenograft (CDX) models. In MM, combination of ABBV-621 plus bortezomib (BTZ) resulted in deeper anti-tumorigenic activity than either agent alone in several CDX models. The pre-clinical data presented here support expanding the indications and settings where ABBV-621 may have utility. A clinical trial assessing the activity of ABBV-621 in combination with bortezomib and dexamethasone in R/R MM patients is planned. Disclosures: All authors are employees of AbbVie. The design, study conduct, and financial support for this research were provided by AbbVie. AbbVie participated in the interpretation of data, review, and approval of the publication. Disclosures Smith: AbbVie:Current Employment, Current equity holder in publicly-traded company.Jin:AbbVie:Current Employment, Current equity holder in publicly-traded company.Chen:AbbVie:Current Employment, Current equity holder in publicly-traded company.Zhang:AbbVie:Current Employment, Current equity holder in publicly-traded company.Huska:AbbVie:Current Employment, Current equity holder in publicly-traded company.Widomski:AbbVie:Current Employment, Current equity holder in publicly-traded company.Bontcheva:AbbVie:Current Employment, Current equity holder in publicly-traded company.Buchanan:AbbVie:Current Employment, Current equity holder in publicly-traded company.Morgan-Lappe:AbbVie:Current Employment, Current equity holder in publicly-traded company.Phillips:AbbVie:Current Employment, Current equity holder in publicly-traded company.Tahir:AbbVie:Current Employment, Current equity holder in publicly-traded company.

Background Venetoclax (ABT-199), a first-in-class orally bioavailable BCL-2-selective inhibitor, was recently approved by the FDA for use in patients with 17p-deleted chronic lymphocytic leukemia who have received prior therapy. It is also being evaluated in numerous clinical trials for treating patients with various hematologic malignancies. As with any targeted cancer therapy, it is critically important to identify potential mechanisms of resistance, both for patient stratification and developing strategies to overcome resistance, either before it develops or as it emerges. Methods In order to gain a more comprehensive insight into the nature of venetoclax resistance mechanisms, we evaluated the changes in the BCL-2 family members at the genetic and expression levels in seven different venetoclax-resistant derived leukemia and lymphoma cell lines. Results Gene and protein expression analyses identified a number of different alterations in the expression of pro- and anti-apoptotic BCL-2 family members. In the resistant derived cells, an increase in either or both the anti-apoptotic proteins BCL-XL or MCL-1, which are not targeted by venetoclax was observed, and either concomitant or exclusive with a decrease in one or more pro-apoptotic proteins. In addition, mutational analysis also revealed a mutation in the BH3 binding groove (F104L) that could potentially interfere with venetoclax-binding. Not all changes may be causally related to venetoclax resistance and may only be an epiphenomenon. For resistant cell lines showing elevations in BCL-XL or MCL-1, strong synergistic cell killing was observed when venetoclax was combined with either BCL-XL- or MCL-1-selective inhibitors, respectively. This highlights the importance of BCL-XL- and MCL-1 as causally contributing to venetoclax resistance. Conclusions Overall our study identified numerous changes in multiple resistant lines; the changes were neither mutually exclusive nor universal across the cell lines tested, thus exemplifying the complexity and heterogeneity of potential resistance mechanisms. Identifying and evaluating their contribution has important implications for both patient selection and the rational development of strategies to overcome resistance. Electronic supplementary material The online version of this article (doi:10.1186/s12885-017-3383-5) contains supplementary material, which is available to authorized users.

A-1155463, a highly potent and selective BCL-XL inhibitor, was discovered through nuclear magnetic resonance (NMR) fragment screening and structure-based design. This compound is substantially more potent against BCL-XL-dependent cell lines relative to our recently reported inhibitor, WEHI-539, while possessing none of its inherent pharmaceutical liabilities. A-1155463 caused a mechanism-based and reversible thrombocytopenia in mice and inhibited H146 small cell lung cancer xenograft tumor growth in vivo following multiple doses. A-1155463 thus represents an excellent tool molecule for studying BCL-XL biology as well as a productive lead structure for further optimization.

Proteins in the B cell CLL/lymphoma 2 (BCL-2) family are key regulators of the apoptotic process. This family comprises proapoptotic and prosurvival proteins, and shifting the balance toward the latter is an established mechanism whereby cancer cells evade apoptosis. The therapeutic potential of directly inhibiting prosurvival proteins was unveiled with the development of navitoclax, a selective inhibitor of both BCL-2 and BCL-2-like 1 (BCL-X(L)), which has shown clinical efficacy in some BCL-2-dependent hematological cancers. However, concomitant on-target thrombocytopenia caused by BCL-X(L) inhibition limits the efficacy achievable with this agent. Here we report the re-engineering of navitoclax to create a highly potent, orally bioavailable and BCL-2-selective inhibitor, ABT-199. This compound inhibits the growth of BCL-2-dependent tumors in vivo and spares human platelets. A single dose of ABT-199 in three patients with refractory chronic lymphocytic leukemia resulted in tumor lysis within 24 h. These data indicate that selective pharmacological inhibition of BCL-2 shows promise for the treatment of BCL-2-dependent hematological cancers.

Platelets are relatively short-lived, anucleated cells that are essential for proper hemostasis. The regulation of platelet survival in the circulation remains poorly understood. The process of platelet activation and senescence in vivo is associated with processes similar to those observed during apoptosis in nucleated cells, including loss of mitochondrial membrane potential, caspase activation, phosphatidylserine (PS) externalization, and cell shrinkage. ABT-737, a potent antagonist of Bcl-2, Bcl-X(L), and Bcl-w, induces apoptosis in nucleated cells dependent on these proteins for survival. In vivo, ABT-737 induces a reduction of circulating platelets that is maintained during drug therapy, followed by recovery to normal levels within several days after treatment cessation. Whole body scintography utilizing ([111])Indium-labeled platelets in dogs shows that ABT-737-induced platelet clearance is primarily mediated by the liver. In vitro, ABT-737 treatment leads to activation of key apoptotic processes including cytochrome c release, caspase-3 activation, and PS externalization in isolated platelets. Despite these changes, ABT-737 is ineffective in promoting platelet activation as measured by granule release markers and platelet aggregation. Taken together, these data suggest that ABT-737 induces an apoptosis-like response in platelets that is distinct from platelet activation and results in enhanced clearance in vivo by the reticuloendothelial system.

The Bcl-2 family inhibitors venetoclax and navitoclax demonstrated potent antitumor activity in chronic lymphocytic leukemia patients, notably in reducing marrow load and adenopathy. Subsequent trials with venetoclax have been initiated in non-Hodgkin's lymphoma and multiple myeloma patients. Traditional preclinical models fall short either in faithfully recapitulating disease progression within such compartments or in allowing the direct longitudinal analysis of systemic disease. We show that intravenous inoculation of engineered RS4;11 (acute lymphoblastic leukemia) and Granta 519 (mantle cell lymphoma) bioluminescent reporter cell lines result in tumor engraftment of bone marrow, with additional invasion of the central nervous system in the case of Granta 519. Importantly, apoptosis induction and response of these systemically engrafted tumors to Bcl-2 family inhibitors alone or in combination with standard-of-care agents could be monitored longitudinally with optical imaging, and was more accurately reflective of the observed clinical response.

Myeloid cell leukemia 1 (MCL-1) is a BCL-2 family protein that has been implicated in the progression and survival of multiple tumor types. Herein we report a series of MCL-1 inhibitors that emanated from a high throughput screening (HTS) hit and progressed via iterative cycles of structure-guided design. Advanced compounds from this series exhibited subnanomolar affinity for MCL-1 and excellent selectivity over other BCL-2 family proteins as well as multiple kinases and GPCRs. In a MCL-1 dependent human tumor cell line, administration of compound 30b rapidly induced caspase activation with associated loss in cell viability. The small molecules described herein thus comprise effective tools for studying MCL-1 biology.

The ability of a cancer cell to avoid apoptosis is crucial to tumorigenesis and can also contribute to chemoresistance. The Bcl-2 family of prosurvival proteins (Bcl-2, Bcl-XL, Bcl-w, Mcl-1, and A1) plays a key role in these processes. We previously reported the discovery of ABT-263 (navitoclax), a potent small-molecule inhibitor of Bcl-2, Bcl-XL, and Bcl-w. While navitoclax exhibits single-agent activity in tumors dependent on Bcl-2 or Bcl-XL for survival, the expression of Mcl-1 has been shown to confer resistance to navitoclax, most notably in solid tumors. Thus, therapeutic agents that can downregulate or neutralize Mcl-1 are predicted to synergize potently with navitoclax. Here, we report the activity of navitoclax in combination with 19 clinically relevant agents across a panel of 46 human solid tumor cell lines. Navitoclax broadly enhanced the activity of multiple therapeutic agents in vitro and enhanced efficacy of both docetaxel and erlotinib in xenograft models. The ability of navitoclax to synergize with docetaxel or erlotinib corresponded to an altered sensitivity of the mitochondria toward navitoclax, which was associated with the downmodulation of Mcl-1 and/or upregulation of Bim. These data provide a rationale to interrogate these combinations clinically. Mol Cancer Ther; 10(12); 2340–9. ©2011 AACR.

ABT-737 and ABT-263 are potent inhibitors of the BH3 antiapoptotic proteins, Bcl-x(L) and Bcl-2. This class of putative anticancer agents invariantly contains an acylsulfonamide core. We have designed and synthesized a series of novel quinazoline-based inhibitors of Bcl-2 and Bcl-x(L) that contain a heterocyclic alternative to the acylsulfonamide. These compounds exhibit submicromolar, mechanism-based activity in human small-cell lung carcinoma cell lines in the presence of 10% human serum. This comprises the first successful demonstration of a quinazoline sulfonamide core serving as an effective benzoylsulfonamide bioisostere. Additionally, these novel quinazolines comprise only the second known class of Bcl-2 family protein inhibitors to induce mechanism-based cell death.

ABT-199 is a first-in-class orally bioavailable BCL-2 selective inhibitor that is currently being testing in clinical trials. Clinical activity has been reported in chronic lymphocytic leukemia and NHL patients treated with ABT-199 as a monotherapy. As with any targeted cancer therapy, it is important to identify the potential mechanisms of resistance, not only to inform patient selection but also to develop strategies to circumvent resistance as it emerges. In this study, we generated resistant variants from ABT-199-sensitive cell lines of different leukemia and lymphoma subtypes (two diffuse large B-cell lymphomas, two follicular lymphomas, one leukemia line, and two mantle cell lymphomas) by increasing exposure to ABT-199 in a stepwise manner over time. Compared to the parental cell lines, the variants were 10 to >100-fold less sensitive to ABT-199. The ABT-199-resistant variants were also resistant to ABT-263 (navitoclax), a BCL-2/BCL-XL inhibitor, as well as to other standard-of-care cancer agents. Gene and protein expression analyses revealed multiple alterations in the expression of BCL-2 family members in the resistant variants; however, not all of the changes were universal. Alterations included changes in the levels of the target protein BCL-2, reduction of the pro-apoptotic proteins BAX, BIM or NOXA, or increases in the anti-apoptotic proteins BCL-XL or MCL-1. In some but not all cases, the changes to gene and protein expression levels were accompanied by changes in DNA copy number. To determine whether changes in the anti-apoptotic BCL-2 family members were causally related to ABT-199 resistance, we tested ABT-199 in combination with BCL-XL and MCL-1 selective inhibitors. Co-treating with ABT-199 and either a BCL-XL or MCL-1 selective compound was synergistic in killing the ABT-199-resistant variants, suggesting these proteins can both contribute directly to ABT-199 resistance. Under appropriate selection pressure, intrinsic traits that mitigate the effects of anticancer drugs can lead to the enrichment of a resistant tumor population. In ABT-199-resistant RS4;11 cells we observed a complete and permanent loss of BAX, one of the ultimate effectors of mitochondrial mediated apoptosis. FACS analysis revealed that there was a pre-existing population of RS4;11 cells lacking this protein. It is likely that these cells had a selective advantage over those expressing BAX when treated with ABT-199. Overall our data indicate that there are distinct mechanisms of resistance to ABT-199, either innate or acquired, which will have important implications for both patient selection and developing strategies to overcome resistance. Disclosures: All authors are employees of AbbVie. The design, study conduct, and financial support for the research were provided by AbbVie. AbbVie participated in the interpretation of data, review, and approval of the publication. Citation Format: Stephen K. Tahir, Morey L. Smith, Paul Hessler, Lisa Roberts-Rapp, Joel D. Leverson, Lloyd T. Lam. Mechanisms of resistance to ABT-199 in leukemia and lymphoma cell lines. [abstract]. In: Proceedings of the AACR Precision Medicine Series: Drug Sensitivity and Resistance: Improving Cancer Therapy; Jun 18-21, 2014; Orlando, FL. Philadelphia (PA): AACR; Clin Cancer Res 2015;21(4 Suppl): Abstract nr B30.