Lymphoma Patient-derived Xenograft Research Articles

ABBV-319: A CD19-targeting glucocorticoid receptor modulator antibody-drug conjugate therapy for B-cell malignancies

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).

Abstract 1027: Immunohistochemistry (IHC) to assess tumor cell-associated OX40 expression in lymphoma PDXs

Abstract Background. Tumor necrosis factor receptor superfamily member 4, or OX40, is an immunostimulatory receptor usually expressed in activated T-cells. The OX40-OX40L (ligand of OX40) interaction plays a crucial role in the enhancement of T-cell proliferation, survival, and cytokine production, including those in tumor microenvironment (TME) leading to increased anti-tumor immunity1. OX40 agonist antibodies have been widely tested for immunotherapy for solid tumors2,3. Interestingly, in the treatment of lymphoma, the situation may become more complicate, where OX40 could also be found to be expressed on lymphoma cells, in addition to TME. This phenomenon might or might not impact OX40 agonist therapy. This report aims at developing an immunohistochemistry (IHC) assay to assess tumor-associated OX40 by utilizing morphology approach to understand OX40 expression in lymphoma cells, as opposed on tumor-infiltrate T-lymphocytes (TILs) present in TME. FFPE samples from patient-derived xenografts (PDXs), recapitulating the main pathological features of the original tumors, but exclusive of human TILs, were used as the first stage of the assay development, avoiding TIL interference prior to human sample testing. Methods. Ninety leukemia and lymphoma PDXs are comprehensively annotated, including RNAseq and histopathology (HuBaseTM: https://hubase.crownbio.com). IHC staining of PDX FFPE slides or TMA (tissue microarray) of various cancers was performed using a commercial OX40 antibody (CST, #61637) and Bond RX Automated IHC/ISH Staining System (Leica Biosystems), followed by whole slide imaging by NanoZoomer NDP2.0-HT Digital Slide System (Hamamatsu) and quantitative analysis by HALOTM image analysis software (Indica labs). OX40 IHC scores were also compared to the RNA expression determined by RNAseq. Results. A total of 90 leukemia and lymphoma PDXs were comprehensively evaluated. RNASeq data (human mRNA) indeed revealed OX40 gene expression (cutoff as Log2 (FPKM)>3) in 8.9% of models (8/90 models); on the other hand, IHC data also confirmed these OX40 protein expression; and the IHC scores largely correlated with the RNA data. Together, our data firmly confirmed the expression of OX40 in certain hematological cancers, beyond just in TME. The ongoing studies is investigating the characteristics of the OX40 positive lymphoma/leukemia, and the preliminary data will be presented in the annual conference. Furthermore, we are also using the same assay to explore other cancer types beyond hematological cancers. Conclusion. A tumor associated OX40 expression IHC workflow was preliminarily established and validated to facility the OX40 immunotherapy development. Citation Format: Jie Lin, Xiaolong Tu, Likun Zhang, Hongjiang Yu, Cheng JIang, Tao Yang, Henry Qixiang Li. Immunohistochemistry (IHC) to assess tumor cell-associated OX40 expression in lymphoma PDXs [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 1027.

Abstract 2836: Assessment of therapeutic antibody efficacy without the interference of murine Fc receptors allows for investigation of human antibody-dependent cellular cytotoxicity mediated by NK cells in the FcResolv™ hIL-15 NOG mouse model

Abstract Targeted antibody therapy is applied to treat various cancer types. In addition to the primary mode of action (MOA), which involves direct binding to the tumor antigen, indirect MOA acting through the constant region (Fc) of the antibody can enhance anti-tumor efficacy. Indirect mechanisms engage the innate immune system, mediated by both the complement system (complement-dependent cytotoxicity (CDC)) and immune cells (antibody-dependent cellular phagocytosis (ADCP) and antibody-dependent cellular cytotoxicity (ADCC)). These indirect mechanisms can complicate the evaluation and accurate assessment of antibody-induced ADCC by human NK cells in current mouse models. In immune-deficient mouse strains (e.g. NOG), false positives and/or negatives may occur due to interactions with murine Fc receptors. These can either result in anti-tumor responses via activation of the murine innate immune system or can interfere with the human-targeted therapy's primary MOA. To study the response to anti-cancer antibodies without the interference of these murine Fc receptor interactions and to investigate ADCC mediated by human NK cells, a novel mouse model deficient in Fc receptors and expressing human IL-15 (FcResolv™ hIL-15 NOG) was employed for testing antibody therapies. Methods: Patient-derived xenograft (PDX) tumor models were transplanted into hIL-15 NOG and FcResolv™ hIL-15 NOG mice. A human head and neck squamous cell carcinoma and a lung adenocarcinoma PDX model were both treated with cetuximab. Treatment with pertuzumab and trastuzumab was applied in a breast ductal carcinoma PDX model. Rituximab treatment was tested in two diffuse large B cell lymphoma PDX models. Based on growth kinetics, the lung cancer PDX model was chosen for further testing of ADCC in the NK cell-humanized FcResolv™ hIL-15 NOG mouse. Results and Conclusion: There was no difference in percent tumor growth inhibition between the FcResolv™ hIL-15 NOG and hIL-15 NOG mice with regards to cetuximab treatment in the lung and head and neck cancer or for trastuzumab treatment of breast ductal carcinoma. However, pertuzumab treatment revealed a false positive efficacy, with the false positive effect more pronounced in hIL-15 NOG mice than in FcResolv™ hIL-15 NOG mice. In one of the lymphoma models, a false negative result was observed. Here, rituximab did not show notable tumor inhibition in the hIL-15 NOG mice but did in the FcResolv™ hIL-15 NOG mice. These results demonstrate that FcResolv™ hIL-15 NOG mice serve as a suitable mouse model for a more accurate assessment of the therapeutic efficacy of anti-tumor antibodies. Additionally, evaluation of human-mediated ADCC of therapeutic antibodies in NK cell-humanized FcResolv™ hIL-15 NOG allows detection of effects specifically mediated by human NK cells. Citation Format: Simone Rhein, Maria Stecklum, Monika Buczek, Janell Richardson, Jens Hoffmann. Assessment of therapeutic antibody efficacy without the interference of murine Fc receptors allows for investigation of human antibody-dependent cellular cytotoxicity mediated by NK cells in the FcResolv™ hIL-15 NOG mouse model [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 2836.

Abstract 4673: Therapeutic potential of polatuzumab vedotin for the treatment of diffuse large B-cell lymphoma

Abstract Background Diffuse large B-cell lymphoma (DLBCL) is typically treated with rituximab, cyclophosphamide, doxorubicin, vincristine, and prednisone (R-CHOP). Although most patients can be cured with R-CHOP, up to one-third of them relapses with a dismal outcome in most cases. Numerous approaches have been attempted to improve the treatment outcomes with R-CHOP. Polatuzumab vedotin is an antibody-drug conjugate targeting CD79b, which is ubiquitously expressed on over 90% of B-cell NHL malignancies, including DLBCL. To determine the potential of polatuzumab vedotin as a therapeutic agent, we evaluate its potency across a series of DLBCL patient derived xenograft (PDX) models. Method We established and characterized a series of DLBCL lymphoma PDX models. Eight DLBCL PDX models were selected for polatuzumab vedotin efficacy study, of which three are GCB DLBCL. Gene expression analysis of these lymphoma PDX models was performed using an Illumina NovaSeq 6000 system following Illumina-provided protocols for 2 × 150 paired-end sequencing. The expression status of CD79b on these DLBCL PDX models was also evaluated by IHC. Conclusion Our data showed that a single dose of polatuzumab vedotin at just 2 mg/kg could reached a comparable effect with R-CHOP and no significant body weight loss was observed. Our result showed that there is no apparent correlation between polatuzumab vedotin responses (TGI) and the CD79b expression (IHC Score). Although polatuzumab vedotin demonstrated encouraging activity in the treatment of DLBCL, some of the PDX models are also resistant to polatuzumab vedotin treatment. To further investigate the molecular parameters of the relative sensitivity of polatuzumab vedotin. Gene expression profiling of those PDX models and their sensitivity to polatuzumab vedotin were conducted, we found that the expression level of BCL-XL was correlated with reduced sensitivity to polatuzumab vedotin. Citation Format: Hui Qi, Fuyang Wang, Bingrui Han, Xiaomin Wang, Xiangnan Qiang, Zhixiang Zhang, Qiangyang Gu. Therapeutic potential of polatuzumab vedotin for the treatment of diffuse large B-cell lymphoma. [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 4673.

Generation of a humanized afucosylated BAFF-R antibody withbroad activity against human B-cell malignancies.

B-cell activating factor receptor (BAFF-R) is a mature B-cell survival receptor, which is highly expressed in a wide variety of B-cell malignancies but with minimal expression in immature B cells. These properties make BAFF-R an attractive target for therapy of B-cell lymphomas. We generated a novel humanized anti BAFF-R monoclonal antibody (mAb) with high specificity and potent invitro and invivo activity against B-cell lymphomas and leukemias. The humanized variants of an original chimeric BAFF-R mAb retained BAFF-R binding affinity and antibody-dependent cellular cytotoxicity (ADCC) against a panel of human cell lines and primary lymphoma samples. Furthermore, 1 humanized BAFF-R mAb clone and its afucosylated version, glycoengineered to optimize the primary mechanism of action, prolonged survival of immunodeficient mice bearing human tumor cell lines or patient-derived lymphoma xenografts in 3 separate models, compared with controls. Finally, the tissue specificity of this humanized mAb was confirmed against a broad panel of normal human tissues. Taken together, we have identified a robust lead-candidate BAFF-R mAb for clinical development.

JAK and mTOR inhibitors prevent cytokine release while retaining T cell bispecific antibody in vivo efficacy

BackgroundT cell engaging therapies, like chimeric antigen receptor T cells and T cell bispecific antibodies (TCBs), efficiently redirect T cells towards tumor cells, facilitating the formation of a cytotoxic synapse...

CD38 x ICAM1 Bispecific Antibody Is a Novel Approach for Treating Multiple Myeloma and Lymphoma

Targeting cluster of differentiation 38 (CD38) with monoclonal antibodies has resulted in outstanding responses in patients with multiple myeloma (MM). However, a significant portion of patients failed to respond and nearly all patients eventually relapsed. Furthermore, daratumumab, an anti-CD38 antibody, only showed limited monotherapy activity in relapsed/refractory Non-Hodgkin lymphoma (NHL) patients in a phase 2 study. One of the mechanisms of resistance has been partially attributed to lower CD38 expression. Intercellular adhesion molecule 1 (ICAM1), an immunoglobulin (Ig)-like cell adhesion molecule, is highly expressed in multiple myeloma and lymphoma. Antibody against ICAM1, bersanlimab (BI505, BioInvent), was well-tolerated, but only showed limited clinical efficacy in MM patients. Here, we generated bispecific CD38 x ICAM1 antibody to target ICAM1 + tumor types with low to medium CD38 expression. RNA sequencing (RNAseq) results from the Cancer Cell Line Encyclopedia (CCLE) database showed that ICAM1 is highly expressed on myeloma and lymphoma cell lines. ICAM1 expression levels for selected myeloma and lymphoma cell lines were then validated using flow cytometry. The CD38 x ICAM1 bispecific antibody was constructed by paring a novel CD38 antibody and a novel ICAM1 antibody through an asymmetric three chain knob-into-hole format. The bispecific antibody showed potent in vitro antibody-dependent cellular cytotoxicity (ADCC) activities on ICAM1 + tumor cells with medium to low CD38 levels, where daratumumab has low or minimal effect. The bispecific antibody also showed potent in vitro antibody-dependent cellular phagocytosis (ADCP) activities on cell lines with a range of CD38 expression. The CD38 x ICAM1 bispecific antibody further demonstrated potent tumor inhibition activities in in vivo myeloma and lymphoma cell line-derived xenograft (CDX) models, including cell lines with low to medium CD38 expression. We then evaluated CD38 and ICAM1 expressions in lymphoma patient-derived xenograft (PDX) samples by RNAseq. Among the 37 PDX samples, 27 of them showed ICAM1 expression above 2 5 fragments per kilobase of transcript per million map reads (FPKM). On the contrary, there is a wide range of CD38 expression levels with only 6 samples having CD38 expression above 2 5 FPKM. The ICAM1 and CD38 expressions in the selected PDX samples were further validated with IHC staining. Most importantly, the CD38 x ICAM1 bispecific antibody showed complete tumor inhibition in a rituximab-resistant lymphoma PDX model, whereas daratumumab only showed minimal efficacy. In conclusion, the CD38 x ICAM1 bispecific antibody demonstrated improved efficacy and specificity toward CD38 + and ICAM1 + tumor cells and represents a novel approach for treating multiple myeloma and lymphoma. DisclosuresNo relevant conflicts of interest to declare.

Bio-P-05 - Cutaneous T-cell lymphoma patient-derived xenografts retain molecular characteristics across passages

<h3>Introduction:</h3> Cutaneous T-cell lymphomas (CTCLs) are a clinically heterogeneous array of clonal neoplasms of skin-homing CD4+ T-helper lymphocytes. Mycosis fungoides (MF) is the most common subtype of CTCL. Its clinical course varies significantly. Median survival times range from over fifteen years in its mildest form to under two in its most severe. Elucidation of MF pathogenesis and drug development are hampered by the dearth of CTCL laboratory models. Models examined in the literature are largely derived from leukemic CTCL, many of which have been shown to be confounded by HTLV-1 virus positivity. Additionally, recent models demonstrate phenotypic divergence even in the context of stable TCR clonality across passages. Here we molecularly characterize patient-derived xenografts (PDX) from six MF patients, compare their features to known CTCL characteristics and examine their stability over passages. <h3>Materials and methods:</h3> We established and analyzed ten PDX lines from six MF patients. Patient tumor cells were obtained from peripheral blood or lymph node fine needle aspirate and engrafted into NSG mice (P0). Subsequent passages (P1/2) were made by engrafting cells from P0/1 spleens in naive NSG mice. Peripheral blood mononuclear cells (PBMCs) from a subset of patients were collected for comparison to PDXs. Whole exome sequencing (WES) data was used for mutational and copy number analysis. Three PDX lines were also transcriptionally characterized using RNA sequencing. <h3>Results:</h3> WES analysis demonstrates the presence of canonical CTCL driver events in all samples. In all PDXs with patient PBMCs available for comparison, we find that subsets of these driver events were maintained through grafting. Strikingly, PDXs established from tumor cells collected at later points in clinical disease progression reflect tumor evolution. We identify genomic features that may show associations with successful engraftments. Through RNA-seq analysis, we observe that PDX transcriptional phenotypes harbored similarities to primary patient samples in the literature. We also demonstrate the transcriptional stability of one PDX into P1. <h3>Conclusion:</h3> Overall, we demonstrate that we have established PDXs that faithfully retain genomic and transcriptional features of CTCL across passages. Our results have implications not only for use of the models described here, but also for development of future xenografts by similar methods. We predict that employing molecularly stable CTCL PDXs in preclinical experiments could have significant benefits for the elucidation of CTCL pathophysiology and the development of novel CTCL treatments.

Abstract 3005: Establishment and characterization of a series of lymphoma PDX models representing varied clinical behaviors and treatment responses

Abstract Background: Lymphomas are comprised of a heterogeneous group of hematologic malignancies based on different origins with diverse patterns of clinical behavior and treatment response. Pathologically, lymphomas are divided into two main subtypes, Hodgkin (HL) and non-Hodgkin (NHL), which account for around 10% and 90% of cases, respectively. NHL is further divided into B cell, T cell and natural killer (NK) cell subtypes. Besides histopathology, cancer is increasingly recognized as a genetic disease with specific molecular alterations, such as ALK translocation in anaplastic large cell lymphoma, MYC/BCL2/BCL6 translocation in B cell lymphoma (often referred to as ‘double-hit' or ‘triple-hit') and other specific mutations or overexpression. Current clinical therapeutic options for lymphoma therefore need to consider not only the histological type, clinical aggressiveness and cancer stage, but also the molecular markers, cytokine signaling, epigenetic aberrations and lymphoma microenvironment. Preclinical modeling with diverse types of lymphomas and deep characterization are important for the drug discovery of new lymphoma treatments. Methods: We have established and characterized a number of different subtypes of lymphoma patient-derived xenograft (PDX) models including both mature T/NK cell neoplasms and B cell neoplasms. Immunodeficient mice were used for establishment of these lymphoma PDX models with subcutaneous or tail vein engraftment. Model classification and characterization were determined by histopathology and IHC, as well as genomic profiling by next-generation sequencing (NGS) and response to chemo- or targeted therapies. Results: We have developed and characterized a large panel of lymphoma PDX models with various subtypes, including mantle cell lymphoma, angioimmunoblastic T cell lymphoma, ALK negative anaplastic large cell lymphoma, adult T cell leukemia/lymphoma, peripheral T cell lymphoma, extranodal NK/T cell lymphoma and also other common B cell lymphomas such as DLBCL and follicular lymphoma. Histopathology analysis of these models is in line with clinical pathology diagnosis. Additionally, cancer type-specific biomarkers, such as CD3, CD20, BCL2, BCL6 and MYC, were used for characterization of these lymphoma models by IHC. The response to subtype-specific chemotherapy or targeted therapies, such as CHOP, BTK inhibitors, CD38 antibodies etc., are now tested in some of these lymphoma PDX models and will be presented at the meeting. Conclusions: Lymphomas have diverse subtypes, represented by different clinical features and treatment responses. We have established and characterized a series of lymphomas with varied types including a large cohort of B cell lymphoma and T/NK cell lymphoma PDX models for drug evaluation. Citation Format: Jessie J. Wang, Yanrui Song, Jitai Zheng, Guiqing Wu, Likun Zhang, Henry Q.X. Li, Davy Xuesong Ouyang. Establishment and characterization of a series of lymphoma PDX models representing varied clinical behaviors and treatment responses [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 3005.

Abstract 2957: A novel circulating tumor DNA (ctDNA) assay enables monitoring of disease progression and treatment response in disseminated preclinical hematologic cancer models

Abstract We have established a novel assay to assess circulating tumor DNA (ctDNA) in mice engrafted with disseminated cell line and patient-derived xenografts (PDX) of hematologic malignancies. Disseminated models recapitulate many features of human disease, but engraftment in multiple tissues makes monitoring of disease and treatment response difficult. Existing assays also lack the sensitivity required to assess minimal residual disease (MRD). This novel ddPCR assay targets highly conserved human-specific regions of LINE-1 and HERV-K repeat elements resulting in exceptionally sensitive detection of shed human ctDNA. Initial data shows sensitivity of 0.8 haploid genome equivalents (one haploid genome is ~3.3pg of human DNA), whereas ctDNA monitoring assays currently on the market require 1,000 times more input DNA to reach a sensitivity of just 2-9 genome equivalents. Serial dilution experiments confirm this assay is suitable to detect increases in ctDNA over several orders of magnitude, while also establishing a minimum plasma input of 40uL. To validate the assay we assessed the ability of ctDNA to detect disease alongside traditional histology, bioluminescence imaging, and flow cytometry assays in 10 leukemia and lymphoma models. Levels of ctDNA correlated well with disease progression across models engrafting in bone marrow, spleen, liver, blood and other tissues. In all cases where early stage disease was analyzed, the ctDNA assay was able to detect disease earlier relative to other methods due to its increased sensitivity, and these data can be effectively used for randomization into treatment groups. We also assessed the utility of ctDNA for determining drug treatment response in mice engrafted with a disseminated mantle cell lymphoma PDX. Baseline ctDNA assessment was completed on day 11 post-engraftment confirming ctDNA levels above baseline, at which point mice were divided into 7 treatment groups: Vehicle, Acalabrutinib, and 5 combination arms of Acalabrutinib plus clinically used agents. After 4 weeks of treatment disease burden was assessed by flow cytometry of the bone marrow (femur) compared to ctDNA detected in plasma. Efficacy readouts from both assays agreed for all groups, while the ctDNA assay was able to identify a significant difference between the two best responding arms which appeared to have near complete responses when assessed by flow cytometry alone. The fold difference between the two best responding arms was 1.1 fold by flow cytometry and 3.6 fold by ctDNA, illuminating a greater disparity in MRD and relapse potential between these 2 groups. This novel ctDNA assay allows for robust experimental designs to answer questions about the depth and durability of treatment responses, as well as to identify early stage disease. Work is ongoing to explore extended monitoring for relapse and application to solid tumor models. Citation Format: Amanda L. Christie, Paul Labrousse, Courtney L. Andersen, Justine E. Roderick, Jacob Gordon, Deborah Lawson, Denise Hughes, Kimberly Maratea, Daniel Stetson, Brandon Willis, Andrew Bloecher, Corinne Reimer, Brian Dougherty. A novel circulating tumor DNA (ctDNA) assay enables monitoring of disease progression and treatment response in disseminated preclinical hematologic cancer models [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 2957.

Targeting Bfl-1 via acute CDK9 inhibition overcomes intrinsic BH3-mimetic resistance in lymphomas

AbstractBH3 mimetics like venetoclax target prosurvival Bcl-2 family proteins and are important therapeutics in the treatment of hematological malignancies. We demonstrate that endogenous Bfl-1 expression can render preclinical lymphoma tumor models insensitive to Mcl-1 and Bcl-2 inhibitors. However, suppression of Bfl-1 alone was insufficient to fully induce apoptosis in Bfl-1–expressing lymphomas, highlighting the need for targeting additional prosurvival proteins in this context. Importantly, we demonstrated that cyclin-dependent kinase 9 (CDK9) inhibitors rapidly downregulate both Bfl-1 and Mcl-1, inducing apoptosis in BH3-mimetic–resistant lymphoma cell lines in vitro and driving in vivo tumor regressions in diffuse large B-cell lymphoma patient-derived xenograft models expressing Bfl-1. These data underscore the need to clinically develop CDK9 inhibitors, like AZD4573, for the treatment of lymphomas using Bfl-1 as a selection biomarker.

Cytarabine nanotherapeutics with increased stability and enhanced lymphoma uptake for tailored highly effective therapy of mantle cell lymphoma

Mantle cell lymphoma (MCL) is a rare subtype of B-cell non-Hodgkin lymphoma (B-NHL) with chronically relapsing clinical course. Implementation of cytarabine (araC) into induction and salvage regimen became standard of care for majority of MCL patients. In this study, tailored N-(2-hydroxypropyl)methacrylamide (HPMA)-based polymer nanotherapeutics containing covalently bound araC (araC co-polymers) were designed, synthesized and evaluated for their anti-lymphoma efficacy in vivo using a panel of six patient-derived lymphoma xenografts (PDX) derived from newly diagnosed and relapsed / refractory (R/R) MCL. While free araC led to temporary inhibition of growth of MCL tumors, araC co-polymers induced long-term disappearance of the engrafted lymphomas with no observed toxicity even in the case of PDX models derived from patients, who relapsed after high-dose araC-based treatments. The results provide sound preclinical rationale for the use of HPMA-based araC co-polymers in induction, salvage or palliative therapy of MCL patients.

Overcoming resistance to rituximab in relapsed non-Hodgkin lymphomas by antibody-polymer drug conjugates actively targeted by anti-CD38 daratumumab

B-cell non-Hodgkin lymphomas (B-NHL) represent the most common type of hematologic malignancies in the Western hemisphere. The therapy of all B-NHL is based on the combination of different genotoxic cytostatics and anti-CD20 monoclonal antibody (mAb) rituximab. Unfortunately, many patients relapse after the mentioned front-line treatment approaches. The therapy of patients with relapsed/refractory (R/R) B-NHL represents an unmet medical need. We designed, developed and tested novel actively targeted hybrid mAb-polymer-drug conjugate (APDC) containing anti-CD20, anti-CD38 or anti-CD19 mAbs. Biocompatible copolymers based on N-(2-hydroxypropyl)methacrylamide (HPMA) with cytostatic agent doxorubicin attached via stimuli-sensitive hydrazone bond were employed for the mAb grafting. Anti-lymphoma efficacy of the APDC nanotherapeutics was evaluated in vivo on a panel of three patient-derived lymphoma xenografts derived from two patients with R/R B-NHL and one patient with so far untreated B-NHL. In both PDX models derived from patients with R/R B-NHL, the targeting with anti-CD38 antibody daratumumab demonstrated highly improved anti-lymphoma efficacy compared to the targeting with anti-CD20 rituximab, two experimental anti-CD19 antibodies and non-targeted controls. The results represent a proof-of-concept of a new algorithm of personalized anti-tumor therapy based on highly innovative APDC biomaterials.

Abstract 5631: Leukaemia and lymphoma patient-derived xenografts (PDX) engraft on humanized mice and respond to immune therapy with check point inhibitors

Abstract Background The preclinical evaluation of novel immune therapies for cancer remains a challenge, as models require both, engraftment of human tumor cells and a matching human immune cell population. In previous experiments, we have demonstrated, that we can use either peripheral blood mononuclear cells (PBMC) or hematopoietic stem cells (HSC) to establish a humanized immune system on highly immunodeficient mice. In this study, we transplanted patient-derived xenografts (PDX) from leukaemia and lymphoma on these humanized mice. Further, we validated the models by evaluating treatments with checkpoint inhibitors Nivolumab (Nivo) and Ipilimumab (Ipi) or standard of care therapies. Methods HSC were transplanted i.v. on immunodeficient mice. Engraftment of human immune cells was monitored by FACS analysis of blood samples. Three lymphoma PDX and one acute myeloid leukaemia (AML) model were s.c. transplanted on humanized mice. To model systemic leukaemia, three AML models were transplanted i.v. on humanized mice. Engraftment of the PDX was compared to growth on non-humanized mice. After successful engraftment, mice were treated with Nivo, Ipi or in combination with standard therapies and irradiation. Results We confirmed successful engraftment of HSC in the humanized mice. Within 14 weeks after HSC inoculation, FACS analysis revealed an established functional human immune system with up to 20% T-cells, characterized by a high PD-1 expression. The s.c. transplanted leukaemia and lymphoma PDX engrafted on the humanized mice and tumor growth was measured with calipers. Engraftment of i.v. transplanted AML models was confirmed by FACS measurement of human CD33+ AML cells in the blood of the humanized mice. Treatment with Ipi or Nivo alone or in combination led to a minor growth delay. FACS analysis confirmed an increased percentage of activated T-cells in the blood and in the s.c. tumors. Response to checkpoint inhibitors was in correlation to PD-L1 expression on the lymphoma and AML cells. Combination of check point inhibitors with radiotherapy provided additive effects in our models. Conclusions We developed a humanized immune-PDX model for different blood cancers enabling appropriate preclinical translational research on tumor immune biology and the evaluation of new therapies and combinations, as well as the identification and validation of biomarkers for immune therapy. These novel model are currently optimized for the preclinical evaluation of new bispecific immune cell engagers (BITE) and cell therapies (CART). Citation Format: Maria Stecklum, Annika Wulf-Goldenberg, Antje Siegert, Bernadette Brzezicha, Anja Sterner-Kock, Wolfgang Walther, Jens Hoffmann. Leukaemia and lymphoma patient-derived xenografts (PDX) engraft on humanized mice and respond to immune therapy with check point inhibitors [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 5631.

Abstract 4544: Multifaceted mechanism of action of DuoHexaBody-CD37 involves both complement- and Fc gamma receptor-mediated cytotoxicity in pre-clinical B-cell lymphoma models

Abstract CD37 is a tetraspanin expressed on mature B cells where it orchestrates plasma membrane organization, receptor signaling, cell migration and adhesion. As CD37 is abundantly expressed on many mature B cell-derived malignancies, it represents an attractive target for new antibody therapies. DuoHexaBody®-CD37 is a novel biparatopic bispecific CD37 antibody with an Fc domain engineered to enhance antibody hexamerization upon binding to CD37 on the plasma membrane. DuoHexaBody-CD37 was shown to induce potent complement-dependent cytotoxicity (CDC) of malignant B-cell lines and primary chronic lymphocytic leukemia and non-Hodgkin lymphoma patient samples (Oostindie et al., Blood 2018 132:4170; van der Horst et al., Blood 2018 132:4179). Here, we demonstrate that the DuoHexaBody-CD37 mechanism of action also encompasses FcγR-mediated effector functions, including antibody-dependent cellular cytotoxicity (ADCC) and antibody-dependent cellular phagocytosis (ADCP). Daudi and Raji cells opsonized with DuoHexaBody-CD37 induced FcγRIIa and FcγRIIIa signaling in luciferase reporter assays. In agreement with efficient FcγR engagement, opsonization with DuoHexaBody-CD37 resulted in dose-dependent ADCC and ADCP by human healthy donor peripheral blood mononuclear cells (PBMCs) and monocyte-derived macrophages (MDMs), respectively. In a 4-hour Chromium-51 release assay, DuoHexaBody-CD37 induced ADCC in Daudi cells with PMBCs from 11 out of 12 tested donors (average EC50 of 9.87 [±9.98] ng/mL; maximum kill 20.4 [±9.2]%), and in Raji cells with 1 out of 3 donors. Image- and flow cytometry-based assays with MDMs illustrated that in presence of DuoHexaBody-CD37, Daudi cells were efficiently engulfed by effector cells from 3 different donors (average percentage phagocytic macrophages 29.7 ± 7.6%) resulting in target cell depletion (maximum depletion 75.9 [±18.0]%). Potent anti-tumor activity of DuoHexaBody-CD37 in vivo was reported in a screening approach using B-cell lymphoma patient-derived xenograft (PDX) models with single-mouse treatment groups. Two weekly doses of 5 mg/kg DuoHexaBody-CD37 resulted in strong tumor growth inhibition (tumor stasis or tumor regression) in 3/9 models compared to untreated tumors. Follow-up cohort PDX studies with eight mice per group confirmed potent, dose-dependent anti-tumor activity of DuoHexaBody-CD37 at doses as low as 1 mg/kg. In summary, DuoHexaBody-CD37 induces efficient tumor cell kill through CDC, ADCC and ADCP in vitro and shows potent anti-tumor activity in B-cell lymphoma PDX models in vivo. These data further strengthen the rationale for exploring the safety and efficacy of DuoHexaBody-CD37 in B-cell malignancy patients. Citation Format: Laurens P. Kil, Simone C. Oostindie, Kristin Strumane, Hilma J. van der Horst, Berris van Kessel, Marije B. Overdijk, Andreas Lingnau, Marcel Brandhorst, Jeroen van den Brakel, Margaret A. Lindorfer, Ronald P. Taylor, Martine E. Chamuleau, Tuna Mutis, A. Kate Sasser, Janine Schuurman, Paul W. Parren, Frank J. Beurskens, Esther C. Breij. Multifaceted mechanism of action of DuoHexaBody-CD37 involves both complement- and Fc gamma receptor-mediated cytotoxicity in pre-clinical B-cell lymphoma models [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 4544.

Abstract 5156: Targeting N-myristoylation in B-cell lymphomas as a therapeutic strategy

Abstract Myristoylation is the N-terminal modification of proteins with the fatty acid myristate. This process is mediated by two ubiquitously expressed N-myristoyltransferases, NMT1 and NMT2, and is critical for membrane targeting and cell signaling. Because NMT expression is increased in some cancers, we used three robotic screens to evaluate the potential of the potent pan-NMT inhibitor PCLX-001 on 300 cancer cell lines spanning the spectrum of human cancers. We discovered a marked increase in the sensitivity of hematological cancer cell lines, including B-cell lymphomas, to myristoylation inhibition. PCLX-001 consistently reduced both lymphoma cell proliferation and viability at concentrations lower than those needed to inhibit the growth of or to kill benign immortalized B cells. In lymphoma cell lines, PCLX-001 treatment inhibited early B-cell receptor (BCR) signaling events by disrupting membrane targeting of several myristoylated Src family kinases and promoted their ubiquitin-mediated degradation. Unexpectedly, PCLX-001 also promoted the degradation of non-myristoylated transcriptional activators P-ERK, c-Myc, NFκB and CREB downstream in the BCR signaling cascade, leading to loss of survival signals and apoptosis. Furthermore, compared to clinically approved drugs dasatinib and ibrutinib, PCLX-001 was more potent in vitro at inhibiting B-cell signaling, had a wider breadth of efficacy, and had greater selectivity thus sparing normal B cells. PCLX-001 treatment reduced tumor size in a time and concentration dependent manner in three B-cell lymphoma xenograft models and resulted in complete disease regression in two of these models, including an R-CHOP refractory lymphoma patient-derived xenograft. To investigate the potential mechanisms responsible for the sensitivity of hematological cancers to PCLX-001, we examined the NMT expression levels in cancer cells using publically available databases. Contrary to the reported NMT overexpression in some cancers, we found that hematological cancer cell lines and tumors both display significant reduction in NMT2 expression. The decreased NMT2 expression is significantly correlated with lower EC50 and poorer patient prognosis. Using the CRISPR-based genetic alteration Cancer Dependency Map, we discovered that cancer cells are highly dependent on functional NMT1, and that NMT1 dependency increases with low NMT2 expression. PCLX-001 treatment may mimic the effect of genetic alteration of NMT1 in hematological cancer cells low in NMT2 by pharmacologically inhibiting the remaining NMT1 in these cells. This results in an effect reminiscent of synthetic lethality since the vast majority of normal cells express both NMTs and PCLX-001 selectively kills NMT2-deficient cancer cells while sparing normal cells. Our findings support the ongoing development and eventual clinical trials of PCLX-001 as a therapy for hematological cancers. Citation Format: Erwan Beauchamp, Megan C. Yap, Maneka A. Perinpanayagam, Jay M. Gamma, Krista M. Vincent, Raymond Lai, Wei-Feng Dong, Manikandan Lakshmanan, Anandhkumar Raju, Vinay Tergaonkar, Soo Yong Tan, Soon Thye Lim, Lynne Postovit, Kevin D. Read, David W. Gray, Paul G. Wyatt, John R. Mackey, Luc G. Berthiaume. Targeting N-myristoylation in B-cell lymphomas as a therapeutic strategy [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 5156.

A Novel JAK1 Mutant Breast Implant-Associated Anaplastic Large Cell Lymphoma Patient-Derived Xenograft Fostering Pre-Clinical Discoveries.

Breast implant-associated lymphoma (BIA-ALCL) has recently been recognized as an independent peripheral T-cell lymphoma (PTCL) entity. In this study, we generated the first BIA-ALCL patient-derived tumor xenograft (PDTX) model (IL89) and a matching continuous cell line (IL89_CL#3488) to discover potential vulnerabilities and druggable targets. We characterized IL89 and IL89_CL#3488, both phenotypically and genotypically, and demonstrated that they closely resemble the matching human primary lymphoma. The tumor content underwent significant enrichment along passages, as confirmed by the increased variant allele frequency (VAF) of mutations. Known aberrations (JAK1 and KMT2C) were identified, together with novel hits, including PDGFB, PDGFRA, and SETBP1. A deep sequencing approach allowed the detection of mutations below the Whole Exome Sequencing (WES) sensitivity threshold, including JAK1G1097D, in the primary sample. RNA sequencing confirmed the expression of a signature of differentially expressed genes in BIA-ALCL. Next, we tested IL89’s sensitivity to the JAK inhibitor ruxolitinib and observed a potent anti-tumor effect, both in vitro and in vivo. We also implemented a high-throughput drug screening approach to identify compounds associated with increased responses in the presence of ruxolitinib. In conclusion, these new IL89 BIA-ALCL models closely recapitulate the primary correspondent lymphoma and represent an informative platform for dissecting the molecular features of BIA-ALCL and performing pre-clinical drug discovery studies, fostering the development of new precision medicine approaches.

Cytarabine Nanotherapeutics with Increased Stability and Enhanced Lymphoma Uptake for Tailored Highly Effective Therapy of Mantle Cell Lymphoma

Mantle cell lymphoma (MCL) is a rare subtype of B-cell non-Hodgkin lymphoma (B-NHL) with chronically relapsing clinical course. Implementation of cytarabine (araC) into induction and salvage regimen became standard of care for majority of MCL patients. In this study, tailored N-(2-hydroxypropyl)methacrylamide (HPMA)-based polymer nanotherapeutics containing covalently bound araC (araC co-polymers) were designed, synthesized and evaluated for their anti-lymphoma efficacy in vivo using a panel of six patient-derived lymphoma xenografts (PDX) derived from newly diagnosed and relapsed / refractory (R/R) MCL. While free araC led to temporary inhibition of growth of MCL tumors, araC co-polymers induced long-term disappearance of the engrafted lymphomas with no observed toxicity even in the case of PDX models derived from patients, who relapsed after high-dose araC-based treatments. The results provide sound preclinical rationale for the use of HPMA-based araC co-polymers in induction, salvage or palliative therapy of MCL patients.

Abstract 1069: New panel of patient derived lymphoma xenografts (PDX) for preclinical research and immune oncology

Abstract Lymphomas represent a very heterogeneous group of hematologic malignancies and pose an important challenge in the clinical routine. They frequently develop resistance to the treatment with standard-of-care (SoC) drugs and have a high incidence of disease recurrence. Recent progress in molecular high throughput profiling has helped to identify genetic drivers and genetic subtypes of diffuse large B-cell lymphomas (DLBCL). Further target validation and drug development projects are highly dependent on corresponding preclinical models representing the different clinical subtypes. Therefore, we started to establish and characterize new patient derived xenografts (PDX) of non-Hodgkin (NHL) and Hodgkin lymphomas (HL) for drug development, translational and immune oncology research. All lymphoma PDX were derived from peripheral blood, lymph node extirpations or core needle biopsies, and were usually transplanted subcutaneously into immunodeficient mice. For further characterization, established lymphoma PDX models were treated with SoC and investigational drugs. In addition, the growth of lymphoma PDX on humanized mice was evaluated to establish new models for the evaluation of novel immune therapy approaches. To gain a deeper insight in the molecular biology of the lymphoma models, RNA sequencing of all was performed. More than 20 new PDX models from NHL (including 8 DLBCL) and HL have been successfully established and characterized. Heterogeneous individual responses to the treatments were observed. Explorative analysis of RNA sequencing data confirmed the representation of the clinical lymphoma subgroups in our panel of models. Likewise, genetic subtypes of DLBCL COO classes could be confirmed by PCA and hierarchical clustering methods. Patterns of genetic driver mutations as revealed by recently published large genomic studies were identified. Our newly and extensively characterized lymphoma PDX model panel allows the evaluation on novel targeted and immune therapies in preclinical phase II trial settings. They provide an exceptional platform for the identification and validation of new targets and allow the preclinical screening of new combinations in translational research projects. Citation Format: Bernadette Brzezicha, Michael Becker, Maria Stecklum, Teresia Conrad, Martin Janz, Aitomi Bittner, Clemens Schmitt, Ulrich Keilholz, Jens Hoffmann. New panel of patient derived lymphoma xenografts (PDX) for preclinical research and immune oncology [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1069.

Abstract 3702: Establishment and characterization of a novel MYC/BCL2 double-hit high-grade B-cell lymphoma cell line HLA-3

Abstract The majority of MYC/BCL2 double hit lymphoma (DHL) morphologically resembles diffuse large B-cell lymphoma (DLBCL) or unclassified B-cell lymphoma, with intermediate features of DLBCL and Burkitt’s lymphoma. DHL also typically results in shorter survival time than other lymphomas. To further understand DHL’s biology and identify potential effective agents against DHL, we established a unique MYC/BCL2 high-grade B-cell lymphoma cell line with morphological DLBCL features. The HLA-3 DHL cell line was derived from a MYC/BCL2 high-grade B-cell lymphoma patient-derived xenograft (PDX) model. We performed flow cytometry immunophenotypic analysis and established the HLA-3 cell line after 7 months of continuous culture. We utilized molecular and cellular techniques, including flow cytometry and polymerase chain reaction (PCR) analysis, to characterize the HLA-3 cell line. We performed reverse phase protein array (RPPA) analysis to determine its protein signaling profile. To identify agents with anti-DHL activity, we screened the effects of a panel of agents alone and in combination with ibrutinib on the cell viability of this newly established cell line. The HLA-3 cell line was optimally maintained at a density between 1 and 2 × 106 cells/mL and successfully proliferated in a single-cell suspension without cellular clump formation. The HLA-3 cells were EBV-negative and possessed a germinal center B cell immunophenotype. Moreover, the immunophenotypes of the primary patient tumor cells and HLA-3 cells were virtually identical. The HLA-3 cells were positive for CD19, CD45, CD35, CD10 and HLA-ABC, negative for CD3, CD5, CD40, CD34 and TdT, and were dim for CD22, CD56, CD8, CD4 and CD23. Representative flow cytometry histograms showed 99% of the HLA-3 cells were positive for CD19 and CD45, with no detectable surface kappa and lambda light chains. The HLA-3 cells expressed a high level of CD38, an indicator of MYC rearrangement. Similar to the original lymphoma cells, the HLA-3 cells showed dim/low CD20 expression. Based on RPPA data, we constructed a diagram showing activation of the ATM/Chk2 DNA repair and the IGF1R/PI3K/mTOR signaling pathways in the HLA-3 cells. In support of this upregulated activity, we found that 5/7 tested commercial PI3K/mTOR inhibitors significantly reduced the viability of the HLA-3 cells in a dose-dependent manner, with AZD8055 the most sensitive of the tested inhibitors against the cell line. Further, DNA repair pathway inhibitors BMN673 and RG7112 were effective against the HLA-3 cell line. The newly characterized high-grade B-cell lymphoma cell line will provide useful in vitro and in vivo models for biological studies related to human DHL, which is refractory to current therapies and urgently needs novel therapeutic approaches. This work suggests the PI3K/mTOR and DNA repair pathways may be therapeutic targets for MYC/BCL2 double-hit high-grade B-cell lymphoma. Citation Format: Hui Guo, Hui Zhang, Krystle Nomie, Liang Zhang, Kelley P. Murfin, Michael Wang. Establishment and characterization of a novel MYC/BCL2 double-hit high-grade B-cell lymphoma cell line HLA-3 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3702.