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Dual bromodomain BET inhibitors that bind with similar affinities to the first and second bromodomains across BRD2, BRD3, BRD4, and BRDT have displayed modest activity as monotherapy in clinical trials. Thrombocytopenia, closely followed by symptoms characteristic of gastrointestinal toxicity, have presented as dose-limiting adverse events that may have prevented escalation to higher dose levels required for more robust efficacy. ABBV-744 is a highly selective inhibitor for the second bromodomain of the four BET family proteins. In contrast to the broad antiproliferative activities observed with dual bromodomain BET inhibitors, ABBV-744 displayed significant antiproliferative activities largely although not exclusively in cancer cell lines derived from acute myeloid leukemia and androgen receptor positive prostate cancer. Studies in acute myeloid leukemia xenograft models demonstrated antitumor efficacy for ABBV-744 that was comparable with the pan-BET inhibitor ABBV-075 but with an improved therapeutic index. Enhanced antitumor efficacy was also observed with the combination of ABBV-744 and the BCL-2 inhibitor, venetoclax compared with monotherapies of either agent alone. These results collectively support the clinical evaluation of ABBV-744 in AML (Clinical Trials.gov identifier: NCT03360006).

Background Breast and colon cancer rank second and third, respectively, in world-wide prevalence of malignancies and present a large unmet medical need. The correlation between lymphocyte infiltration into the tumor microenvironment and efficacy of anti-cancer immunotherapies has been established. Therefore, relevant and cost-saving pre-clinical models are needed for developing new treatment approaches to predominant human tumor types. HuCD34NCG mice facilitate studying human immune responses in vivo elicited by experimental therapeutic antibodies. We characterized growth kinetics and human immune responses to checkpoint blockade in human breast and colon tumor-bearing HuCD34NCG mice. Aging, non tumor-bearing HuCD34NCG mice were also monitored for indicators of spontaneous hematopoietic cancer formation. Methods HSC engraftment was quality controlled prior to inoculating HuCD34NCG mice with either colon adenocarcinoma (COLO 205) or triple negative breast cancer (MDA-MB-436) cells (both purchased from American Type Culture Collection, Manassas, VA). Mice were randomized into treatment groups based on tumor size, and checkpoint inhibitor antibodies were dosed twice weekly (anti-human PD-1, BioXcell clone: RMP1-14 or Keytruda; anti-human CTLA-4, BioXcell clone: BN13; and combination therapy). Body weights, general health status and survival were monitored. Peripheral blood (PB) and selected tissues were analyzed for the presence and composition of human immune cells by acoustic focusing flow cytometry. Non tumor-bearing aged HuCD34NCG mice (27 weeks post-engraftment) were sampled biweekly over ten weeks for lymphoma immunophenotyping. Results Both tumor-bearing models showed significant anti-hPD-1 and anti-hCTLA-4 responses, but combination therapy only enhanced growth reduction significantly in MDA-MB-436 tumors. Flow cytometric analysis identified viable human leukocytes in tumor and spleen at study termination. These tumor-infiltrating lymphocytes (TIL) and splenocytes from surviving COLO 205 and MDA-MB-436 mice consisted of a total T-cell phenotype (CD3+) with proliferating (Ki67+), CD4+, CD8+ and Treg subsets. Additionally, myeloid cells (CD11b+, CD11c+) and M1/M2 macrophages were detected within these infiltrates. Splenic and tumor-infiltrating T-cells readily secreted human cytokines (IFN-γ, IL-2, TNF-α) and granzyme B upon ex vivo activation exhibiting polyfunctional and cytotoxic capabilities in all treatment groups. Baseline murine and human cytokine levels were distinguished in plasma from aging, non tumor-bearing HuCD34NCGs. Their phenotypes also showed no conclusive indicators of abnormal blood cells developing or graft failure. Conclusions Breast and colon tumor cell-line derived models were established in HuCD34NCG mice. Standard checkpoint inhibitor treatment promoted human T-cell infiltration into tumor microenvironments inhibiting growth. These results demonstrate that HuCD34NCG are a robust and relevant host for various human cell xenotransplants to advance preclinical immuno-oncology drug development. Ethics Approval Animal studies were executed in compliance with local Charles River IACUC guidelines, IACUC number I-033.

Background Bladder cancer is the fifth most common cancer in the US, and the ninth most common cancer worldwide. Treatment of bladder cancer has evolved over time to encompass traditional modalities of chemotherapy and surgery, but has been particularly impacted by the recent use of immunotherapy. Modern immunotherapy has focused on checkpoint protein inhibitors that impede immune function. The inhibitors for several checkpoint targets (programmed death-ligand 1 [PD-L1], programmed cell death protein1 [PD-1], and cytotoxic T-lymphocyte-associated protein 4 [CTLA4]) were either approved or in late-stage development. In this study we examined the effect of PD-1 inhibitor pembrolizumab and cisplatin in a panel of bladder patient-derived xenografts (PDX) with distinct patterns of PD-L1 expression in CD34+ stem cell humanized NCG (HuCD34NCG) mice. Methods Three bladder PDX models PNX0428, PNX0434 and PNX1028 have been established under informed consent from the patients at the Fox Chase Cancer Center, Philadelphia. These models have been profiled for the levels of PD-L1 protein using immunohistochemical staining with SP263 antibody (Ventana) and used to establish the growth kinetics and sensitivity to the PD-1 check point inhibitor pembrolizumab and standard of care chemotherapeutic agent cisplatin in female HuCD34NCG and standard NCG mice from Charles River Laboratories. Results We have established the ability of three bladder PDX models to grow in both the HuCD34NCG and standard NCG mice. The tumor growth kinetics of these models was slightly delayed in HuCD34NCG animals compared to NCG. We observed variable responses to cisplatin and pembrolizumab treatments among the PDX models that did not correlate with the level of PD-L1 expression in these tumors. Despite the presence of ~70% PD-L1 positive cells in the PNX0428 model, these tumors produced minor responses to pembrolizumab in HuCD34NCG mice that correspond to progressive disease in patients. Interestingly, pembrolizumab treatment in the PNX1028 model and even more significantly in the PNX0434 model in HuCD34NCG mice produced strong statistically significant tumor growth inhibition that correlates with stable disease in patients despite negative staining for PD-L1 protein in these tumors. The standard of care treatment cisplatin produced significant tumor growth inhibition in all three PDX models in both HuCD34NCG and standard NCG mice. Conclusions Our data indicates that abundant expression of PD-L1 protein in tumors should not be used as the only biomarker for patient stratification for the treatment with PD-1/PD-L1 check point inhibitors. The HuCD34NCG mouse model is an effective tool for supporting tumor growth and evaluating immunotherapies. Ethics Approval Animal studies were approved by Nexus Pharma, IACUC number 08-22.Three bladder PDX models PNX0428, PNX0434 and PNX1028 have been established under informed consent from the patients at the Fox Chase Cancer Center, Philadelphia, IRB protocol 11-866.

Background: In vivo syngeneic models continue to be an important tool in cancer biology research. Charles River C57BL/6 and Balb/c mice, two frequently used inbred strains, can be implanted with different murine tumor cell lines. One aspect of syngeneic model development is to characterize the extent and composition of infiltrating leukocytes (TIL) of tumor-bearing mice. The ability to analyze TILs is a relevant factor in preclinical model selection for studying immunomodulatory responses. Study Details: We evaluated growth rates and basal infiltrates in syngeneic models of solid mouse tumors. In four separate studies 7-week-old Charles River mice were implanted subcutaneously on the flank with either MC38 or B16F10 cells (C57BL/6) or with either RENCA or EMT6 cells (Balb/c), respectively. Mice were treated with isotype control IgG1 antibody (BioXcell clone MOPC-21) when tumors reached sizes of ~50-100 mm3. Surviving mice were euthanized when tumor burden reached or exceeded 2000 mm3 in line with internal IACUC guidelines. Spleen and tumors were then processed into single cell suspensions for immunophenotyping by multicolor acoustic-assisted flow cytometry. Results: Growth kinetics of all four tumor cell lines, MC38, B16F10, RENCA and EMT6, were monitored throughout each study. At study termination murine leukocyte infiltration was found in all models. These TILs were immune profiled to determine the frequencies and composition of murine immune cells in the lymphoid and myeloid compartments. Phenotyping data confirmed the presence of viable CD45+ cells with total T-cells (CD3+), T-cell subsets (CD4+, CD8+ and Treg) and myeloid populations (CD11b+) including M1 and M2 TAMs as well as CD11c+ cells. M1/M2 TAM, CD8/Treg and CD4/CD8 ratios were also calculated, and tumor models were assessed based on their baseline TIL composition. Conclusions: Four different allograft models of solid mouse tumors could be established using Charles River C57BL/6 and Balb/c mice. Their basal immune microenvironments could be characterized and therefore can be useful as pharmacodynamic readouts in efficacy studies of potential anti-cancer therapeutics. Citation Format: Christoph S. Eberle, Jenny Rowe, Ann Fiore, Robert Mihalek, Stephen Festin. Evaluation of tumor growth and baseline leukocyte infiltration in Charles River C57BL/6 and Balb/c mice engrafted with MC38, B16F10, RENCA and EMT6 cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2770.

Immunotherapy is revolutionizing cancer treatment. As a consequence, there is an urgent need for predictive preclinical models to support compound development with the aim of bringing optimal drug candidates into clinical trials. Patient-derived xenografts (PDX) are the gold-standard in cancer drug development. One major drawback of PDX is the lack of an immunological competent host. To overcome this hurdle triple immunodeficient mice are humanized with hematopoietic stem cells (HSC) to enable the interaction between human immune cells and human tumor cells in a rodent host. The current study uses HSC humanized NCG (NOD-Prkdcem26Cd52Il2rgem26Cd22/NjuCrl) mice, HuCD34NCG, to evaluate the sensitivity of five NSCLC PDX models towards anti CTLA-4 (Ipilimumab), anti-PD-1 (Nivolumab) and the combination thereof. We identified one predicted responder and one non-responder and in a single mouse trial approach (SMT) and confirmed the results in a conventional experimental set-up with n=5 per treatment arm. Infiltration of human immune cells was detected by flow cytometry in tumor tissue (TIL) and hematopoietic organs. Serum of tumor bearing animals was analyzed for human and mouse cytokine secretion pre- and post-treatment. The NCG mouse strain was genetically characterized by whole exome sequencing (WES) and the mutational profile compared to other common mouse strains. The mutational profile showed the highest overlap with the genome data from other triple immune compromised mice and with NOD/SCID indicating their close hereditary relationship. Non-tumor bearing HuCD34NCG mice depicted engraftment of human CD45+ cells in peripheral blood of >25% and >60% in bone marrow and spleen after 8-12 wks post injection. Thus, they fulfilled enrollment criteria for conducting a drug screen for immune modulating compounds. The five NSCLC PDX models showed a distinct sensitivity profile ranging from partial remission (tumor growth inhibition, TGI, of 87.5% compared to untreated control) to progression (no TGI). In all models the combination treatment was the most active therapy (TGI: 60%), followed by Ipilimumab (TGI: 55%) and Nivolumab (TGI: 48%). Nevertheless, in selected models anti-CTLA-4 treatment was the most efficacious therapy. The two models examined in more detail LXFE 397 (=responder, TGI 55% in both formats) and LXFA 400 (non-responder, TGI 2%SMTvs 5%, n=5/group) displayed the same sensitivity pattern in the conventional set-up as compared to the SMT screening approach. The TIL analysis revealed a pronounced rise in the CD3+ subset and increased CD4+/CD8+ ratio in the most effective treatment arms. Subsequent serum analyses will help identify possible biomarkers predicting drug response towards checkpoint inhibition. Taken together our study proves that the HuCD34NCG mouse is a fully functional drug development tool. In combination with highly predictive PDX tumor models this in vivo platform provides a further step to support the development of new drugs targeting the host immune response. Citation Format: Julia Schüler, Jenny Rowe, Eva Oswald, Stephen Festin. The single mouse trial format predicts the sensitivity towards checkpoint inhibitor treatment in NSCLC PDX models in HuCD34NCG/CRL mice, an innovative triple immune deficient mouse strain [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 5634.

Background: Checkpoint blockade inhibitors targeting PD-1 and CTLA-4 pathways are clinically approved therapies for multiple cancer types. The performance of targeted interventions has been effective, but clinical response rates vary. In vivo models of human immunity in human tumor bearing mice (TBM) is an important tool for studying mechanisms of targeted therapies and developing new and effective treatments. The NCG (NOD-Prkdcem26Cd52Il2rgem26Cd22/NjuCrl), a recently developed triple immunodeficient mouse strain, is a stable host for both human immune cells and tumors for the study of immuno-oncology-based therapeutics. Study Details: We evaluated the anti-tumor effects of immune checkpoint inhibitors (anti-human PD-1, including Pembrolizumab, and CTLA-4) on colon epithelial carcinoma (RKO) and basal lung cell adenocarcinoma (A549) cell lines in a human donor immune cell-humanized NCG/CRL mouse model (HuCD34NCG). In separate studies Charles River humanized NCG (HuCD34NCG) mice were implanted subcutaneously on the flank with either RKO or A549 tumors. Group randomization occurred when the average tumor size reached a volume of ~100mm3 (A549) or 30-60mm3 (RKO). Control mice were treated with isotype control IgG antibodies. RKO TBM were treated with anti-PD-1 antibody alone, while A549 TBM were dosed with anti-PD1-1 and anti-CTLA-4 antibodies independently and in combination therapy. Results: Human immune cell engraftment levels were confirmed in the peripheral blood, spleen and tumor (hCD45, hCD3, hCD4, hCD8, hCD19, NK, myeloid, macrophages; markers vary based on study) of HuCD34NCG humanized mice. Tumor growth kinetics were monitored throughout the study. Inhibition of RKO and A549 tumor growth upon anti-PD-1 monotherapy was significant. Human T-cell infiltration was observed in A549 and RKO tumors with the majority of live T-cells responsive post infiltration. Human cytokines (IFN-γ, IL-2 and TNF-α) were released by tumor-infiltrating total T-cells (CD3+) and subsets (CD4+ and CD8+), as demonstrated by intracellular cytokine staining following PMA/Ionomycin stimulation. Polyfunctional T-cell responses were detected in all treatment groups at study termination. Conclusions: The results from these studies demonstrate significant immunomodulatory anti-tumor response to immune checkpoint inhibitors. The newly developed HuCD34NCG humanized mouse model showed robust and sustained engraftment of human immune cell populations and demonstrated infiltration of T-cells into tissues and tumors making this mouse model ideal for immuno-oncology studies. Citation Format: JENNY ROWE, Christoph Eberle, Elizabeth Reap, Ann Fiore, Anya Avrutskaya, Paula Miliani de Marval, Robert Mihalek, Stephen Festin. Evaluation of in vivo anti-tumor response of solid tumors in a novel immune cell-humanized NOD-Prkdcem26Cd52Il2rgem26Cd22/NjuCrl mouse model [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 5625.

Acute myeloid leukemia (AML) co-clinical modeling has been optimized with peripheral blood mononuclear cells (PBMCs) collected from low volume (14 mL) patient samples to establish an algorithm for efficiently co-clinically modeling AML patients. Methods: PBMCs were ficoll gradient purified and viably cryopreserved. Intrahepatic (i.h.) inoculation of AML PBMCs in neonate NOD/Shi-scid-IL2rγnull (NOG) mice and intravenous (i.v.) inoculation in both juvenile NOG mice and juvenile human transgenic IL-3/GMCSF NOD/Shi-scid-IL2rγnull mice (NOG-EXL) were evaluated. Bone marrow (BM) aspirates, splenocytes and PBMCs from mice were evaluated by fluorescence-activated cell sorting (FACS) at 12 weeks post AML inoculation for engraftment as determined by % ratio of human CD33+ cells to total CD45+ cells (human + murine cells). Humerus bones from inoculated animals were also evaluated by human CD33 immunohistochemistry (IHC). Results: Cells from 2/6 AML patient samples (CTG-2224 and CTG-2357) successfully engrafted into neonate mice. Animals were dosed with vehicle, cytarabine, ABBV-075 (clinical trial-staged BET family bromodomain (BD) inhibitor), or ABBV-744 (a preclinical BDII selective inhibitor) and evaluated for tumor burden six weeks post drug treatment initiation. ABBV-075 and ABBV-744 treated animals had lower tumor burden in the CTG-2224 model, 17% (p Citation Format: Neal C. Goodwin, Daniel H. Albert, Angela M. Davies, Jenny Rowe, Gerold Feuer, Michael Boyiadzis, Kathleen A. Dorritie, Maria Mancini, Regina Gandour-Edwards, Warren M. Kati, Mark D. McKee, Keith F. McDaniel, David J. Frost. Acute myeloid leukemia human/mouse co-clinical trial feasibility study optimized in human transgenic IL-3/GMCSF NOD/Shi-scid-IL2rγnull mice [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 1150.