The Discovery and Preclinical Development of ASG-5ME, an Antibody-Drug Conjugate Targeting SLC44A4-Positive Epithelial Tumors Including Pancreatic and Prostate Cancer

Here, we report the development of an antibody-drug conjugate, ASG-5ME, which targets the solute carrier receptor SLC44A4. SLC44A4 is a member of a family of putative choline transporters that we show to be markedly upregulated in a variety of epithelial tumors, most notably prostate and pancreatic cancer. SLC44A4 is normally expressed on the apical surface of secretory epithelial cells, but in cancer we show expression is not restricted to the luminal surface in advanced and undifferentiated tumors. ASG-5ME consists of a human IgG2 anti-SLC44A4 antibody conjugated through a cleavable linker to the microtubule-disrupting agent monomethylauristatin E. It has potent antitumor activity in both cell line - and patient-derived xenograft models of pancreatic and prostate cancers. Combination studies with ASG-5ME and nab-paclitaxel demonstrated combination effect in both pancreatic and prostate tumor models. Altogether, the data presented here suggest that ASG-5ME may have the potential to offer a new therapeutic option for the treatment of pancreatic and prostate cancers. Mol Cancer Ther; 15(11); 2679-87. ©2016 AACR.

Discoidin domain receptor 1 contributes to tumorigenesis through modulation of TGFBI expression

Discoidin domain receptor 1 (DDR1) is a member of the receptor tyrosine kinase family. The receptor is activated upon binding to its ligand, collagen, and plays a crucial role in many fundamental processes such as cell differentiation, adhesion, migration and invasion. Although DDR1 is expressed in many normal tissues, upregulated expression of DDR1 in a variety of human cancers such as lung, colon and brain cancers is known to be associated with poor prognosis. Using shRNA silencing, we assessed the oncogenic potential of DDR1. DDR1 knockdown impaired tumor cell proliferation and migration in vitro and tumor growth in vivo. Microarray analysis of tumor cells demonstrated upregulation of TGFBI expression upon DDR1 knockdown, which was subsequently confirmed at the protein level. TGFBI is a TGFβ-induced extracellular matrix protein secreted by the tumor cells and is known to act either as a tumor promoter or tumor suppressor, depending on the tumor environment. Here, we show that exogenous addition of recombinant TGFBI to BXPC3 tumor cells inhibited clonogenic growth and migration, thus recapitulating the phenotypic effect observed from DDR1 silencing. BXPC3 tumor xenografts demonstrated reduced growth with DDR1 knockdown, and the same xenograft tumors exhibited an increase in TGFBI expression level. Together, these data suggest that DDR1 expression level influences tumor growth in part via modulation of TGFBI expression. The reciprocal expression of DDR1 and TGFBI may help to elucidate the contribution of DDR1 in tumorigenesis and TGFBI may also be used as a biomarker for the therapeutic development of DDR1 specific inhibitors.

Abstract 2650: Ags67e, an anti-cd37 monomethyl auristatin e antibody (mmae) drug conjugate as a potential therapeutic for non-hodgkin's lymphoma, chronic lymphocytic leukemia and acute myeloid leukemia

We have developed AGS67E, an antibody drug conjugate that targets CD37, a tetraspanin highly expressed on malignant B cells, for the potential treatment of non-Hodgkin's lymphoma (NHL), chronic lymphocytic leukemia (CLL) and acute myeloid leukemia (AML). AGS67E is a fully human anti-CD37 monoclonal IgG2 antibody conjugated to the potent microtubule-disrupting agent, MMAE, via reduced cysteines and the protease cleavable linker, maleimidocaproyl-valine-citrulline-p-aminobenzoyloxycarbonyl.

AGS67E exhibits potent in vitro binding, internalization and cytotoxicity on a variety of NHL, CLL and AML models and patient-derived samples, including CD34+CD38- leukemic stem cells. AGS67E also demonstrates potent anti-tumor responses, including complete tumor regressions in a variety of NHL, CLL and AML xenografts, including Rituxan refractory models and patient-derived samples. In general, CD37 was highly expressed across all models and a strong correlation was observed between the in vitro and in vivo efficacy of AGS67E.

To confirm binding of AGS67E in a variety of normal and patient-derived NHL, CLL and AML samples, we developed flow cytometry and immunohistochemistry (IHC) assays which have confirmed reported CD37 expression data in NHL & CLL. In normal hematopoietic cells, AGS67E bound strongly to B cells and to a much lesser extent to monocytes, T cells, neutrophils and NK cells. AGS67E also bound with high and similar affinity to cynomolgus monkey B cells and was equally cytotoxic to these and human B cells. In other normal tissues, AGS67E binding was only evident where lymphoid structures were apparent such as in the spleen and lymph node. With respect to CD37 expression in NHL, CLL and AML, AGS67E was found to bind to >80% of NHL and 100% of CLL and AML samples.

Taken together, our findings suggest that AGS67E may serve as a potential therapeutic for NHL, CLL and AML. To our knowledge, this body of work is also the first demonstration that CD37 is well expressed and potentially drug-able in AML.

Citation Format: Daniel S. Pereira, Claudia Guevara, Alla Verlinsky, Cyrus Virata, J Hsu Ssucheng, Zili An, Chungying Zhang, Nick Dinh, Hector Avina, Lisa Do, Sher Karki, Joseph Abad, Peng Yang, Jimmy Ou, Karen Morrison, Sing-Ju Moon, Faisal Malik, Liqing Jin, Michael Choi, Christina Wu, Banmeet Anand, Scott Cooper, Ingrid Joseph, Xiao-Chi Jia, Kendall Morrison, Pia Challita-Eid, Fernando Donate, Thomas Kipps, John Dick, David Stover. Ags67e, an anti-cd37 monomethyl auristatin e antibody (mmae) drug conjugate as a potential therapeutic for non-hodgkin's lymphoma, chronic lymphocytic leukemia and acute myeloid leukemia. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2650. doi:10.1158/1538-7445.AM2014-2650

Abstract 1314: Molecular profiling and characterization of patient-derived human pancreatic tumor xenograft models, and application for drug discovery and preclinical development of cancer therapeutics

A major obstacle that has hampered the development and assessment of novel anticancer therapies is the inability of the conventional xenograft models to reliably predict clinical efficacy. This is in part due the fact that the cell lines used for these studies are cultured on plastic for extensive passages and lack the human extracellular matrix component that is critical for cancer-stromal cell interactions. Models are needed which more accurately reflect tumor heterogeneity and interaction with the tumor microenvironment in order to more accurately reflect tumor complexity and predict response to therapies in the clinic. This has led to the development of models by directly engrafting cancer patient-derived tumor tissues into immunodeficient mice with the aim of retaining histopathological features and molecular characteristics of the original tumor. A vital question relating to patient-derived tumor xenografts is whether tumor characteristics are maintained during passaging. We have established a number of proprietary pancreatic cancer patient-derived xenografts. Studies were performed to molecularly characterize the xenograft models and to confirm they retain similarity to the original tumors. Original patient tumors and corresponding serial xenograft passages were examined for growth, histopathological features and protein expression, as well as genomic and tumor biomarker status. Examination of these patient-derived xenograft models demonstrated that tumor morphology is maintained upon passaging. Immunohistochemical and qPCR analysis of targets of interest showed that expression levels are consistent between tumors and xenograft passages. Although slight differences were observed in genomic profiles for some individual models after engraftment in mice, whole genome profiling by microarray and aCGH revealed that individual tumor models retain organ-specific characteristics and that xenografts remain stable throughout passaging. Core sets of significantly expressed genes and genomic aberrations were maintained, with some additional changes observed during passaging. Retention of the characteristics of the original donor tumors within the xenograft models, such as tumor architecture and molecular signatures will afford the use of models which more accurately reflect patient tumor biology. Comprehensive molecular characterization of our models was utilized to investigate differential response to our proprietary drug candidates. Expanded testing in multiple models can potentially provide important pre-clinical translational information to help guide clinical trial design regarding patient subpopulations that may be more likely to respond to therapy.

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 1314. doi:1538-7445.AM2012-1314

Abstract 1086: Discoidin domain receptor 1 contributes to tumorigenesis through modulation of TGFBI expression

Discoidin domain receptor 1 (DDR1) is a member of the receptor tyrosine kinase family. It is activated by binding to its ligand, collagen and plays a key role in cell survival, adhesion, migration and invasion. Although DDR1 is present in several normal tissues, it is overexpressed in various cancer types, including lung, colon, ovary and breast tumors as well as in gliomas, where it is known to be associated with poor prognosis. The significance of DDR1 in cancer was illustrated using shRNA silencing, which impaired tumor cell growth, both in vitro and in vivo. Using microarray analysis of tumor cells with DDR1 knockdown, we identified an upregulation of TGFBI expression, which was subsequently confirmed at the protein level. TGFBI is a TGFβ induced extracellular matrix protein secreted by tumor cells and has been reported to act as either a tumor promoter or suppressor, depending upon tumor type. Exogenous addition of recombinant TGFBI to tumor cells inhibited clonogenic growth, recapitulating shRNA data. When grown in vivo as xenografts, the DDR1 knockdown cell lines demonstrated a similar phenotype of reduced growth and tumors exhibited an increase in TGFBI protein levels. In summary, our data suggests that DDR1 expression levels influences tumor growth in part through modulation of TGFBI expression. Ongoing studies will help to understand how DDR1 and TGFBI are linked and contribute to tumorigenesis.

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 1086. doi:1538-7445.AM2012-1086

Abstract 4566: AGS-1C4D4: A fully human anti-PSCA antibody inhibits tumor formation and metastasis in orthotopic models of pancreatic cancer

Prostate stem cell antigen (PSCA) is a cysteine-rich cell surface glycoprotein expressed in about 50% of pancreatic and prostate cancers. AGS-PSCA is a hybridoma-derived fully human IgG1κ monoclonal antibody (MAb) targeting PSCA previously reported to have anti-tumor efficacy in prostate and pancreatic tumor models. AGS-1C4D4 is a CHO-derived antibody generated from the same gene as AGS-PSCA, with similar specificity and binding affinity to PSCA (Kd = 2.0 × 10-10M). Since hybridoma and CHO-derived MAbs displayed disparate glycosylation patterns by mass spectroscopy, we further evaluated their MAb effector functions. AGS-1C4D4 was found to have more potent ADCC activity in vitro on PSCA-expressing pancreatic cell lines, HPAC and Panc0203, using human PBMCs from multiple normal donors. However, both MAbs were similarly effective in mediating CDC on PSCA-expressing recombinant B300.19 cells. Deglycosylation greatly reduced the relative ADCC and CDC activities of both MAbs compared to their intact versions. Additional studies to elucidate the role of the effector functions of AGS-1C4D4 are currently being conducted in vivo using intact and deglycosylated MAbs and will be presented. While neither intact antibody had any direct cytotoxic activity on HPAC cells in vitro, both MAbs significantly inhibited tumor formation, local invasion and metastases to distant sites in orthotopic HPAC xenograft tumor models in vivo. In addition, AGS-1C4D4 significantly inhibited the growth and metastasis of established orthotopic HPAC tumors in combination with Gemcitabine. AGS-1C4D4 is currently being evaluated in a Phase 2 clinical study for pancreatic cancer in combination with Gemcitabine.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 4566. doi:10.1158/1538-7445.AM2011-4566

Inhibition of HIV-1 replication using a mutated tRNALys-3 primer

Cellular tRNALys-3 serves as the primer for reverse transcription of human immunodeficiency virus, type 1 (HIV-1). tRNALys-3 interacts directly with HIV-1 reverse transcriptase, is packaged into viral particles and anneals to the primer-binding site (PBS) of the HIV-1 genome to initiate reverse transcription. Therefore, the priming step of reverse transcription is a potential target for antiviral strategies. We have developed a mutant tRNALys-3 derivative with mutations in the PBS-binding region such that priming specificity was re-directed to the highly conserved TAR stem-loop region. This mutant tRNA retains high-affinity binding to HIV-1 reverse transcriptase, viral encapsidation, and is able to prime at both the targeted TAR sequence and at the viral PBS. Constitutive expression of mutant tRNA in T-cells results in marked inhibition of HIV-1 replication, as determined by measurements of viral infectivity, syncytium formation, and p24 production. Inhibition of retroviral replication through interference with the normal process of priming constitutes a new anti-retroviral approach and also provides a novel tool for dissecting molecular aspects of priming.