Abstract Immunotherapy has revolutionized cancer therapy by activating the host immune system to attack the cancer. While immune checkpoint inhibitors that predominantly target T-cells have induced durable clinical responses across multiple tumor types, a large majority of patients do not respond, and resistance/relapse is frequently observed, highlighting the needs for new therapeutic approaches. The innate immune system also holds promise to trigger an anti-tumor immune response. Amongst the cell type of the innate immune system, Dendritic Cells (DCs) stand out as critical sentinels for the immune system as well as the bridge between the innate and adaptive immune responses. Indeed, conventional type 1 DCs (cDC1s) have emerged as critical mediators of anti-tumor immunity due to their ability to cross-prime CD8 T-cells. However, within the tumor microenvironment (TME) cDC1s are often dysfunctional but the mechanisms tumors utilize to disrupt their functions are poorly understood. Recently, serotonin (5-HT), the widely known neurotransmitter, and its downstream metabolites have emerged as immune modulators of anti-tumor immunity, but the involvement of cDC1s is unknown. To address this, we leveraged human and mouse tumor bioinformatics, which uncovered high levels of the 5-HT7 (also called HTR7) serotonin receptor in the DC compartment, specifically in cDC1s in several tumor types. Consistent with this, individually deleting all 5-HT receptors in mouse bone marrow derived DC1s (BMDC1s) indicated loss of 5-HT7 dramatically enhanced BMDC1 function and cross priming. We then leveraged our proprietary chemical library to identify compounds likely to antagonize 5-HT7, and subsequent medicinal chemistry efforts led to the discovery of A-911, a potent 5-HT7 antagonist. Phenocopying 5-HT7 deletion, A-911 enhanced BMDC1 IL-12 production, CD8 T-cell cross-priming, and antigen specific T-cell killing. A-911 has suitable properties for oral administration, exhibits low brain exposure relative to plasma and tumor, and is well tolerated in mice. Daily oral dosing inhibited tumor growth in B16-OVA and Pan02 immunocompetent tumor models and induced combination activity with anti-PD-1 or anti-CTLA-4 antibodies, respectively. A-911 also induced DC1 activation in the TME and downstream T-cell activation and cytolytic activity. These findings elucidate a mechanism by which 5-HT signaling through 5-HT7 within the TME can constrain anti-tumor immunity and identify 5-HT7 as a potential cDC1 therapeutic target for cancer immunotherapy.AbbVie Disclosure Statement: 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. Citation Format: Kenneth D. Bromberg, Jacob Gorman, Jun Guo, Douglas E. Kline, Daniel T. Cohen, Paul Ellis, David Peetz, Luis Rodriguez, Sven Malchow, Cara Hrusch, Ryan Duggan, Min Cheng, Todd Hopkins, Bailin Shaw, Val Manaves, Danli Towne, Sujatha Gopalakrishnan. Discovery of A-911, a potent, orally bioavailable 5-HT7 antagonist that promotes DC1-mediated T-cell cross-priming and anti-tumor immunity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(8_Suppl):Abstract nr LB253.

Epcoritamab, a subcutaneous CD3xCD20 bispecific antibody approved for relapsed/refractory diffuse large B-cell lymphoma (DLBCL) and follicular lymphoma, is being evaluated in regimens containing CD20-targeted monoclonal antibodies (e.g. rituximab plus cylophosphamide, doxorubicin, vincristine, and prednisone [R-CHOP]). To demonstrate combinability of epcoritamab with CD20 monoclonal antibodies (mAbs), potential interference of rituximab or obinutuzumab with epcoritamab was investigated. While there was dose-dependent binding interference between CD20 mAbs and epcoritamab through steric hindrance, ex vivo assays using tumor cell lines, R-CHOP-treated patient samples, and an animal model showed this did not impair tumor cell killing. In a pharmacokinetic model, >90% maximal cytotoxicity was predicted after the first full epcoritamab dose in the presence of therapeutic rituximab concentrations due to effective tumor-epcoritamab-T-cell trimer formation. Immunoprofiling of R-CHOP-treated DLBCL patient samples showed emergence of less-differentiated CD8 memory T cells, further supporting the feasibility of the combination in ongoing studies of epcoritamab with rituximab-containing chemoimmunotherapy.

A prostate tumor cell line (PC3M-A2/beta 2M) was inoculated subcutaneously in the right flank of CD34-humanized NSG mice. Mice were treated intravenously at indicated time points with either vehicle or with an ABBV-184 precursor molecule, and tumor size was monitored. Tumors experienced transient regression and growth inhibition prior to harvest for analysis of tumor-infiltrating immune cells.

Glucocorticoids are key components of the current standard-of-care regimens (e.g., R-CHOP, EPOCH-R, Hyper-CVAD) for treatment of B-cell malignancy. However, systemic glucocorticoid treatment is associated with several adverse events. CD19 displays restricted expression in normal B-cells and is up-regulated in B-cell malignancies. ABBV-319 is a CD19-targeting antibody-drug conjugate (ADC) engineered to reduce glucocorticoid-associated toxicities while possessing three distinct mechanisms of action (MOA) to increase therapeutic efficacy: (1) antibody-mediated delivery of glucocorticoid receptor modulator (GRM) payload to activate apoptosis, (2) inhibition of CD19 signaling, and (3) enhanced Fc-mediated effector function via afucosylation of the antibody backbone. ABBV-319 elicited potent GRM-driven anti-tumor activity against multiple malignant B-cell lines in vitro as well as in cell line-derived xenografts (CDXs) and patient-derived xenografts (PDXs) in vivo. Remarkably, a single-dose of ABBV-319 induced sustained tumor regression and enhanced anti-tumor activity compared to repeat dosing of systemic prednisolone at the maximum tolerated dose (MTD) in mice. The unconjugated CD19 monoclonal antibody (mAb) also displayed anti-proliferative activity on a subset of B-cell lymphoma cell lines through the inhibition of PI3K signaling. Moreover, afucosylation of the CD19 mAb enhanced Fc-mediated antibody-dependent cellular cytotoxicity (ADCC), and this activity was maintained after conjugation with GRM payloads. Notably, ABBV-319 displayed superior efficacy compared to afucosylated CD19 mAb in human CD34+ PBMC-engrafted NSG-tg(Hu-IL15) transgenic mice, demonstrating enhanced anti-tumor activity when multiple MOAs are enabled. ABBV-319 also showed durable anti-tumor activity across multiple B-cell lymphoma PDX models, including non-germinal center B-cell (GCB) DLBCL and relapsed lymphoma post R-CHOP treatment. Collectively, these data support the ongoing evaluation of ABBV-319 in Phase I clinical trial (NCT05512390).

Introduction: Glucocorticoids are key components of standard-of-care treatment regimens (e.g., R-CHOP, Hyper-CVAD) for several B-cell malignancies. However, prolonged systemic glucocorticoid treatment results in glucocorticoid-associated adverse events and acquired resistance that limit its therapeutic potential. ABBV-319 is a novel CD19-targeting ADC engineered to reduce glucocorticoid-associated toxicity observed with systemic glucocorticoids while possessing three distinct mechanisms of action (MoA) to increase efficacy: 1) antibody-mediated delivery of GRM to activate glucocorticoid receptor (GR) induced cell death in cancer cells, 2) inhibition of CD19 signaling, and 3) enhanced Fc-mediated cancer cell killing via afucosylation of the antibody backbone. Results: We identified a GRM agonist that is 15 and 150 times more potent at driving GR transcriptional activation and cell death compared to clinical glucocorticoids dexamethasone and prednisolone, respectively. The conjugation of GRM agonist as the payload on ABBV-319 enables potent GRM-driven anti-cancer activity against malignant B-cell lines in vitro as well as in cell-line and patient derived xenograft (CDX and PDX) models in vivo. Remarkably, a single-dose of ABBV-319 induced sustained tumor regression and enhanced anti-tumor activity compared to repeat dosing of systemic glucocorticoids (e.g., prednisolone) at its maximum tolerated dose in mice. The CD19 monoclonal antibody (mAb) also reduced proliferation of a subset of B-cell malignant cell lines through inhibition of the PI3K/AKT pathway. Moreover, afucosylation of the CD19 mAb in ABBV-319 enhanced Fc-mediated antibody-dependent cellular cytotoxicity (ADCC), and this activity was maintained after conjugation with GRM payloads. ABBV-319 bound similarly to both V158 (high-affinity) and F158 (low-affinity) FcγRIIIa allotypes and mediated potent ADCC in co-culture assays with human peripheral blood mononuclear cells (PBMCs). Notably, ABBV-319 displayed superior efficacy compared to afucosylated CD19 mAb in human CD34+ hematopoietic stem cell-engrafted NSG-Tg(Hu-IL15) mice, demonstrating that the three MoA (GR-driven cell death, CD19 signaling inhibition, and ADCC) collectively contribute to anti-tumor activity in vivo. ABBV-319 also displayed on-target depletion of normal human B-cells but did not affect peripheral NK cell counts in mice. Furthermore, CITE-seq profiling revealed that ABBV-319 treatment of human PBMCs activated GRM-induced signature genes restricted to B-cells, demonstrating the specificity of CD19-mediated delivery of GRM. Conclusion: ABBV-319 has potent anti-tumor activity from three distinct MoA and exhibits safety improvements compared to systemic glucocorticoids, supporting its recent progression into Phase I clinical trial. Citation Format: Chewei Anderson Chang, Ethan Emberley, Aloma L. D'Souza, Weilong Zhao, Cormac Cosgrove, Axel Hernandez Jr, Anatol Oleksijew, Paul Ellis, Luis Rodriguez, Gail Bukofzer, David Peetz, Wissam Assaily, Raghuveer Singh Mali, Wei Liu, Danqing Xu, Gregory K. Potts, Shaun McLoughlin, Kimberley McCarthy, Zhaomei Zhang, Jos Campbell, Isabella Sturdevant, Gloria Zhang, Tyler Curran, Jon D. Williams, Erwin Boghaert, Milan Bruncko, Christopher C. Marvin, Adrian Hobson, Michael Mcpherson, Tamar Uziel, Marybeth Pysz, Xi Zhao, Alex Bankovich, Kevin J. Freise, Susan Morgan-Lappe, James W. Purcell. Preclinical development of ABBV-319: a CD19-targeting glucocorticoid receptor modulator (GRM) agonist antibody-drug conjugate (ADC) for the treatment of B-cell malignancies. [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 6308.

Supplementary figures S1-S6, tables 1 and 2. Table S1. Body weight loss and health observations in HeyA8 xenograft tumor-bearing mice treated with PARP inhibitors or TMZ alone or in combination. Table S2. Summary of PK parameters in HeyA8 xenograft tumor-bearing mice. Figure S1. PARP inhibitors potentiate the activity of alkylating agents in vitro. Figure S2. Equilibrium binding of PARP inhibitors to PARP1. Figure S3. Analysis of PARP1-DNA binding kinetics by BLI. Figure S4. Michaelis-Menten analysis of the mode of inhibition of different PARP inhibitors. Figure S5. γH2AX levels by cell cycle phase in HeyA8 cells treated with MMS and PARP inhibitors alone and in combination. Figure S6. Pharmacokinetics and pharmacodynamics in HeyA8 xenograft tumor-bearing mice.

Abstract CD3 bispecific T-cell engagers (TCE), comprised of a tumor-targeting domain linked to a CD3 binding domain, function by bridging target-positive tumors and CD3-expressing effector T cells enabling redirected T cell–mediated killing of tumor cells. Although the majority of CD3 bispecific molecules in clinical development incorporate tumor-targeting antibody-based binding domains, many tumor-associated antigens derive from intracellular proteins and are not accessible to targeting via antibody. Intracellular proteins processed into short peptide fragments and presented on the cell surface by MHC proteins are recognized by T-cell receptors (TCR) on the surface of T cells. Here we describe the generation and preclinical evaluation of ABBV-184, a novel TCR/anti-CD3 bispecific composed of a highly selective soluble TCR that binds a peptide derived from the oncogene survivin (BIRC5) bound to the class I MHC allele human leukocyte antigen (HLA)-A*02:01 expressed on tumor cells, linked to a specific binder to the CD3 receptor on T cells. ABBV-184 drives an optimal distance between T cell and target cell thereby enabling sensitive recognition of low-density peptide/MHC targets. Consistent with the expression profile of survivin across a broad range of both hematologic and solid tumors, treatment of acute myeloid leukemia (AML) and non–small cell lung cancer (NSCLC) cell lines with ABBV-184 results in T-cell activation, proliferation, and potent redirected cytotoxicity of HLA-A2–positive target cell lines, both in vitro and in vivo, including patient-derived AML samples. These results indicate that ABBV-184 is an attractive clinical candidate for the treatment of patients with AML and NSCLC.

Background Prolactin receptor (PRLR) is an attractive antibody therapeutic target with expression across a broad population of breast cancers. Antibody efficacy, however, may be limited to subtypes with either PRLR overexpression and/or those where estradiol no longer functions as a mitogen and are, therefore, reliant on PRLR signaling for growth. In contrast a potent PRLR antibody-drug conjugate (ADC) may provide improved therapeutic outcomes extending beyond either PRLR overexpressing or estradiol-insensitive breast cancer populations. Methods We derived a novel ADC targeting PRLR, ABBV-176, that delivers a pyrrolobenzodiazepine (PBD) dimer cytotoxin, an emerging class of warheads with enhanced potency and broader anticancer activity than the clinically validated auristatin or maytansine derivatives. This agent was tested in vitro and in vivo cell lines and patient derived xenograft models. Results In both in vitro and in vivo assays, ABBV-176 exhibits potent cytotoxicity against multiple cell line and patient-derived xenograft breast tumor models, including triple negative and low PRLR expressing models insensitive to monomethyl auristatin (MMAE) based PRLR ADCs. ABBV-176, which cross links DNA and causes DNA breaks by virtue of its PBD warhead, also demonstrates enhanced anti-tumor activity in several breast cancer models when combined with a poly-ADP ribose polymerase (PARP) inhibitor, a potentiator of DNA damage. Conclusions Collectively the efficacy and safety profile of ABBV-176 suggest it may be an effective therapy across a broad range of breast cancers and other cancer types where PRLR is expressed with the potential to combine with other therapeutics including PARP inhibitors.

Novel biologics that redirect cytotoxic T lymphocytes (CTLs) to kill tumor cells bearing a tumor associated antigen hold great promise in the clinic. However, the ability to safely and potently target CD3 on CTL toward tumor associated antigens (TAA) expressed on tumor cells remains a challenge of both technology and biology. Herein we describe the use of a Half DVD-Ig format that can redirect CTL to kill tumor cells. Notably, Half DVD-Ig molecules that are monovalent for each specificity demonstrated reduced non-specific CTL activation and conditional CTL activation upon binding to TAA compared to intact tetravalent DVD-Ig molecules that are bivalent for each specificity, while maintaining good drug like properties and appropriate PK properties.

2556 Background: Owing to the role of PARPs in DNA damage repair, PARP inhibitors (PARPi) are under clinical investigation as anticancer therapies with a focus on tumors with impaired homologous recombination or regimens containing DNA damaging chemotherapies. Pre-clinical evidence indicates that PARPi potentiate the cytotoxicity of platinums. A recent Phase II study suggested evidence of a benefit in both progression and survival when veliparib was added to carboplatin and paclitaxel in the treatment of advanced NSCLC. Methods: In vitroefficacy was evaluated in GFP-overexpressing cell lines cultured as 3D spheroids. In vivo efficacy was determined in xenograft tumor-bearing SCID mice. PARP1 trapping was evaluated by cellular fractionation and immunoblotting. Bone marrow toxicity was determined with CFU assays. Results: We have developed a method to monitor the growth of 3D spheroids in vitro in real time. In this system, veliparib potentiated the activity of platinums in numerous models. Likewise, veliparib potentiated the activity of platinums in multiple xenograft models in vivo. PARP trapping was undetectable when PARPi were combined with cisplatin. PARPi differed in the extent to which catalytic inhibition and trapping could be resolved. PARPi with more potent trapping activity induced greater cytotoxicity in bone marrow CFU assays than equipotent inhibitors with weaker trapping activity. Conclusions: Veliparib potentiates the activity of platinum agents in vitro and in vivo; however the mechanisms underlying this activity remain unclear. PARP trapping is a recently characterized mechanism central to the synergistic cytotoxicity of PARPi and temozolomide. In contrast, our results suggest that PARP trapping is not required for the combination activity of PARPi and cisplatin. Our observation that potent trapping activity is associated with cytotoxicity towards myeloid and erythroid progenitors suggests that trapping may contribute to the anemia and myelosuppression observed in patients treated with PARPi. As such, PARPi capable of catalytic inhibition at concentrations where trapping is undetectable may be more suitable for combination regimens in which trapping is not required for activity.

Abstract Poly(ADP-ribose) polymerases (PARP1, -2, and -3) play important roles in DNA damage repair. As such, a number of PARP inhibitors are undergoing clinical development as anticancer therapies, particularly in tumors with DNA repair deficits and in combination with DNA-damaging agents. Preclinical evidence indicates that PARP inhibitors potentiate the cytotoxicity of DNA alkylating agents. It has been proposed that a major mechanism underlying this activity is the allosteric trapping of PARP1 at DNA single-strand breaks during base excision repair; however, direct evidence of allostery has not been reported. Here the data reveal that veliparib, olaparib, niraparib, and talazoparib (BMN-673) potentiate the cytotoxicity of alkylating agents. Consistent with this, all four drugs possess PARP1 trapping activity. Using biochemical and cellular approaches, we directly probe the trapping mechanism for an allosteric component. These studies indicate that trapping is due to catalytic inhibition and not allostery. The potency of PARP inhibitors with respect to trapping and catalytic inhibition is linearly correlated in biochemical systems but is nonlinear in cells. High-content imaging of γH2Ax levels suggests that this is attributable to differential potentiation of DNA damage in cells. Trapping potency is inversely correlated with tolerability when PARP inhibitors are combined with temozolomide in mouse xenograft studies. As a result, PARP inhibitors with dramatically different trapping potencies elicit comparable in vivo efficacy at maximum tolerated doses. Finally, the impact of trapping on tolerability and efficacy is likely to be context specific. Implications: Understanding the context-specific relationships of trapping and catalytic inhibition with both tolerability and efficacy will aid in determining the suitability of a PARP inhibitor for inclusion in a particular clinical regimen. Mol Cancer Res; 13(11); 1465–77. ©2015 AACR.

Poly(ADP-ribose) polymerases (PARP1, -2, and -3) play important roles in DNA damage repair. As such, a number of PARP inhibitors are undergoing clinical development as anticancer therapies, particularly in tumors with DNA repair deficits and in combination with DNA-damaging agents. Preclinical evidence indicates that PARP inhibitors potentiate the cytotoxicity of DNA alkylating agents. It has been proposed that a major mechanism underlying this activity is the allosteric trapping of PARP1 at DNA single-strand breaks during base excision repair; however, direct evidence of allostery has not been reported. Here the data reveal that veliparib, olaparib, niraparib, and talazoparib (BMN-673) potentiate the cytotoxicity of alkylating agents. Consistent with this, all four drugs possess PARP1 trapping activity. Using biochemical and cellular approaches, we directly probe the trapping mechanism for an allosteric component. These studies indicate that trapping is due to catalytic inhibition and not allostery. The potency of PARP inhibitors with respect to trapping and catalytic inhibition is linearly correlated in biochemical systems but is nonlinear in cells. High-content imaging of gH2Ax levels suggests that this is attributable to differential potentiation of DNA damage in cells. Trapping potency is inversely correlated with tolerability when PARP inhibitors are combined with temozolomide in mouse xenograft studies. As a result, PARP inhibitors with dramatically different trapping potencies elicit comparable in vivo efficacy at maximum tolerated doses. Finally, the impact of trapping on tolerability and efficacy is likely to be context specific. Implications:Understanding the context-specific relationships of trapping and catalytic inhibition with both tolerability and efficacy will aid in determining the suitability of a PARP inhibitor for inclusion in a particular clinical regimen. Mol Cancer Res; 13(11); 1–

Abstract The Aurora kinases are a family of serine/threonine kinases that mediate essential functions in cell division. Aurora A depletion results in accumulation of cells in the G2/M phase and apoptosis. Inhibition of Aurora B/C results in abnormal cell division, polyploidy, resulting in apoptosis, therefore, Aurora kinases present an attractive target for chemotherapy. Cells treated with aurora inhibitors enter mitosis with normal kinetics but fail to undergo cytokinesis due to mitotic spindle checkpoint disruption. ABT-348 is a novel adenosine triphosphate (ATP)-competitive inhibitor of Aurora A, Aurora B, and Aurora C (Enzyme IC50 A=116, B=5, C= 1 nM) and a potent inhibitor of all members of the VEGF and PDGF family of receptor tyrosine kinases (RTKs). Despite significant advances in the epidemiological, genetic and biological understanding of acute myeloid leukemia (AML) and myelodysplastic syndrome (MDS), the basic therapeutic approach has not substantially changed for the last 10-15 years, so most patients still die of this disease. Here we demonstrate profound in vivo efficacy (with regressions) of ABT-348 in both AML (MV-4-11, FLT3 mutant expressing the internal tandem duplication with constitutive kinase activation) and MDS (SKM-1) xenograft models. MV-4-11 tumor-bearing SCID mice were treated at 6.25, 12.5 and 25 mg/kg/day, p.o., q7d x 3 (%TGI ratios on day 30 were 80, 86 and 94%, respectively). SKM-1 tumor-bearing SCID mice were treated at 6.25, 12.5 and 25 mg/kg/day, p.o., q7d x 3 (% tumor growth inhibition or TGI ratios on day 30 were 38, 59 and 80%, respectively). In addition, ABT-348 provided additive effects when combined with cytarabine, decitabine or doxorubicin compared to cytotoxic monotherapies. The treatments were well tolerated with no animal health concerns observed indicating the feasibility of ABT-348 combination strategies in the clinic. Currently ABT-348 is being evaluated (monotherapy and in combination with cytotoxic therapies) in the HL-60 acute promyelocytic leukemia xenograft model in vivo. Dose/scheduling studies for combination therapies in the SKM-1 and HL-60 xenografts are ongoing. Pharmacokinetic/pharmacodynamic biomarker analyses in these xenograft models were evaluated using phospho-H3 (an Aurora B substrate, proliferation) and cleaved caspase-3 (apoptosis) by IHC at various timepoints post single dose (1/2 hr to 5 days). A general decrease in proliferation and increase in apoptosis consistent with the mechanism of action was observed which coincided with the potent in vivo efficacy in xenograft models. Overall, ABT-348 is a potent, oral Aurora kinase inhibitor, demonstrating robust in antitumor activity in AML and MDS xenograft models with a good safety profile that warrants investigation in the clinic. ABT-348 is currently undergoing Phase I clinical trials in advanced hematologic malignancies. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 858. doi:1538-7445.AM2012-858

Abstract The Aurora kinases (Aurora A, B, and C) play essential roles in regulating cell division in mammalian cells and their over-expression in diverse tumor types makes them appealing oncology targets. ABT-348 is a novel, ATP-competitive, multi-targeted kinase inhibitor that exhibits potent activity in multiple solid tumor-derived and leukemia cell lines. ABT-348 is active against Aurora B (IC50 7 nM) and Aurora C (IC50 1 nM), Aurora A (IC50 120 nM). The activity against Aurora B is demonstrated by inhibition of histone H3 phosphorylation and induction of polyploidy. ABT-348 is also active against Aurora-B Y156H, a mutant resistant to other Aurora-B inhibitors. In addition, ABT-348 potently inhibits most members of the VEGFR and PDGFR family of receptor tyrosine kinases, which play a critical role in stromal angiogenesis. In contrast to other Aurora kinase inhibitors, the cellular efficacy of ABT-348 is retained in cells over-expressing P-glycoprotein (Pgp) or breast cancer resistant protein (BCRP), indicating that ABT-348 is not a substrate for these commonly upregulated ATP-binding cassette drug transporters. Consistent with these in vitro studies, ABT-348 was broadly efficacious as a single agent against a wide range of tumor types in vivo, including 3 multi-drug resistant xenograft models. In summary, the potent activity and unique kinase selectivity of ABT-348 against the Aurora kinases and VEGF and PDGF receptor tyrosine kinases, engender its ability to block multiple mechanisms of tumor progression. In addition, our data provide evidence that ABT-348 may be active in tumors resistant to other well-characterized inhibitors targeting Aurora-B. ABT-348 is presently under clinical evaluation in adult patients with advanced solid and hematological neoplasms. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1818. doi:1538-7445.AM2012-1818

The Aurora kinases are a family of serine/threonine kinases that mediate multiple essential functions in cell division. Aurora A depletion results in accumulation of cells in the G2/M phase and apoptosis. Inhibition of Aurora B/C results in abnormal cell division, polyploidy, followed by apoptosis, therefore, Aurora kinases present an attractive target for chemotherapy. Cells treated with aurora inhibitors enter mitosis with normal kinetics but fail to undergo cytokinesis due to a disruption of the mitotic spindle checkpoint. ABT-348 is a novel adenosine triphosphate (ATP)-competitive inhibitor of Aurora A, Aurora B, and Aurora C (Enzyme IC50 A=116, B=5, C= 1 nM) and a potent inhibitor of all members of the VEGF and PDGF family of receptor tyrosine kinases (RTK). Here we demonstrate profound in vivo efficacy (with regressions) in a broad spectrum of histological types (breast, colon, NSCLC, HNSCC, melanoma, ovarian, pancreatic, prostate, leukemia, lymphoma and renal; 50–94% TGI, tumor growth inhibition). The treatment was well tolerated with no animal health concerns observed. In addition, ABT-348 was also efficacious in tumor xenografts overexpressing P-gp and provided significant in vivo efficacy in comparison to competitor compounds in colon, NSCLC and ovarian xenograft models. Various dosing schemes to achieve optimal efficacy (IV, OMP and PO) were investigated. The anti-tumor efficacy of ABT-348 was not affected by the route of administration. Similar efficacy was achieved by IV, OMP or PO administration, once weekly in a dose-dependent manner. Pharmacokinetic/pharmacodynamic biomarker analysis in select tumor xenograft models were evaluated by phospho-H3 (an Aurora B substrate, proliferation marker) and cleaved caspase-3 (apoptosis marker) by IHC at various timepoints post single dose (6 hr to 9 days). Significant levels of ABT-348 were detected in the plasma and tumor. A general decrease in proliferation and increase in apoptosis consistent with the mechanism of action was observed and coincide with the potent in vivo efficacy in xenograft models. Overall, ABT-348 is a potent, oral Aurora kinase inhibitor, demonstrating robust in vitro and in vivo antitumor activity with a good safety profile that warrants investigation in the clinic. ABT-348, is currently undergoing Phase I clinical trials in both solid and hematologic malignancies. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr B231.

Abstract PARP's role in DNA damage recognition/repair makes PARP inhibition an attractive cancer therapeutic target. Veliparib (ABT-888) is a potent PARP inhibitor with excellent oral bioavailability that readily crosses the blood-brain barrier and is currently in Phase 2 clinical trials. Veliparib has shown significant ability to potentiate multiple DNA damaging agents (cisplatin, carboplatin, cyclophosphamide, irinotecan, radiation and temozolomide) in a spectrum of tumors from multiple histological types. In studies using cytotoxic combinations with veliparib (cisplatin, cyclophosphamide, TMZ) there was a marked increase in efficacy over cytotoxic monotherapies, especially in the MX-1 breast model. Since DNA repair deficiencies (e.g. HR-defective) are known to render cells very sensitive to PARP inhibition, we genotyped the MX-1 breast line and found it to be HR-deficient. Subsequent studies with both the MX-1 (BRCA1-deleted and BRCA2-mutated breast line) and the Capan-1 (BRCA2-deficient pancreatic cancer cell line), showed that veliparib (25 mg/kg/day, p.o., b.i.d.×5) demonstrated enhancement of TMZ (50 mg/kg/day, p.o., q.d.×5) activity, with regressions compared to TMZ alone (81–97% TGI, tumor growth inhibition). Continuous dosing at 4×-8× higher doses (100 and 200 mg/kg/day, p.o., b.i.d.×21) demonstrated a significant single agent, dose-responsive activity (26–87% TGI). Similar results were observed with single agent veliparib treatment of BRCA isogenic cell lines in vitro. Further, the combination treatment of veliparib (100 and 200 mg/kg/day, p.o., b.i.d.×21) with carboplatin, carbotaxol, radiation, gemcar, cyclophosphamide, topotecan and TMZ also demonstrated a measurable advantage over either veliparib or cytotoxic agent alone. Both high dose single agent veliparib and the cytotoxic combination therapy were well tolerated and there were no observable animal health concerns; this indicated the feasibility of using the single agent and cytotoxic combination regimen in the clinic. Analysis of tumors for the reduction of PAR after veliparib treatment demonstrated a correlative and significant reduction by western blot indicating the ability of veliparib to inhibit PARP activity in vivo. Altogether, our studies show the strong activity of veliparib as a single agent in BRCA-deficient xenografts as well as the enhanced activity and tolerability of veliparib in combination with various cytotoxic agents. These results warrant investigation of single agent therapy and cytotoxic combination regimens in BRCA-deficient patients to further the clinical development of veliparib. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr B62.

We have developed a series of phenylpyrrolidine- and phenylpiperidine-substituted benzimidazole carboxamide poly(ADP-ribose) polymerase (PARP) inhibitors with excellent PARP enzyme potency as well as single-digit nanomolar cellular potency. These efforts led to the identification of (S)-2-(2-fluoro-4-(pyrrolidin-2-yl)phenyl)-1H-benzimidazole-4-carboxamide (22b, A-966492). Compound 22b displayed excellent potency against the PARP-1 enzyme with a K(i) of 1 nM and an EC(50) of 1 nM in a whole cell assay. In addition, 22b is orally bioavailable across multiple species, crosses the blood-brain barrier, and appears to distribute into tumor tissue. It also demonstrated good in vivo efficacy in a B16F10 subcutaneous murine melanoma model in combination with temozolomide and in an MX-1 breast cancer xenograft model both as a single agent and in combination with carboplatin.

Aurora kinase B inhibitors induce apoptosis secondary to polyploidization and have entered clinical trials as an emerging class of neocytotoxic chemotherapeutics. We demonstrate here that polyploidization neutralizes Mcl-1 function, rendering cancer cells exquisitely dependent on Bcl-XL/-2. This “addiction” can be exploited therapeutically by combining aurora kinase inhibitors and the orally bioavailable BH3 mimetic, ABT-263, which inhibits Bcl-XL, Bcl-2, and Bcl-w. The combination of ABT-263 with aurora B inhibitors produces a synergistic loss of viability in a range of cell lines of divergent tumor origin and exhibits more sustained tumor growth inhibition in vivo compared with aurora B inhibitor monotherapy. These data demonstrate that Bcl-XL/-2 is necessary to support viability during polyploidization in a variety of tumor models and represents a druggable molecular vulnerability with potential therapeutic utility.

Small molecule inhibitors of PARP-1 have been pursued by various organizations as potential therapeutic agents either capable of sensitizing cytotoxic treatments or acting as stand-alone agents to combat cancer. As one of the strategies to expand our portfolio of PARP-1 inhibitors, we pursued unsaturated heterocycles to replace the saturated cyclic amine derivatives appended to the benzimidazole core. Not only did a variety of these new generation compounds maintain high enzymatic potency, many of them also displayed robust cellular activity. For example, the enzymatic IC(50) and cellular EC(50) values were as low as 1 nM or below. Compounds 24 (EC(50) = 3.7 nM) and 44 (EC(50) = 7.8 nM), featuring an oxadiazole and a pyridine moiety, respectively, demonstrated balanced potency and PK profiles. In addition, these two molecules exhibited potent oral in vivo efficacy in potentiating the cytotoxic agent temozolomide in a B16F10 murine melanoma model.