Jonathan Alexander Terrett

Heterogeneity of Prostate-Specific Membrane Antigen (PSMA) Expression in Prostate Carcinoma with Distant Metastasis

Prostate-specific membrane antigen (PSMA) is a transmembrane protein that is overexpressed in advanced stage prostate adenocarcinomas. As a novel target for in vivo prognostic and therapeutic approaches, the distribution pattern of PSMA in primary and metastatic tumors is of significant interest. In this study we addressed the cellular distribution and heterogeneity of PSMA expression. Paraffin-embedded sections of 51 patients with primary prostate carcinoma and distant metastases were evaluated. Immunohistochemistry was used to determine the cellular localization, staining intensity and positive cell fraction which were related to tumor type and growth pattern. We demonstrated differences in the intracellular localization of the PSMA immunostaining which seem to be related to the tumor differentiation pattern. A significant number of the primary tumors (7/51) and metastases (6/51) presented with highly heterogeneous PSMA expression and in further 2 primary, and 8 metastatic tumors the staining was in the negative range (<10% positive tumor cells). A direct correlation between histological parameters and PSMA expression could not be demonstrated. Our findings clearly support the feasibility but also direct to potential failures of PSMA-targeted in vivo diagnostic and therapeutic approaches in prostate cancer patients with distant metastasis.

Abstract 3646: Characterization of the novel antibody drug conjugate MEN1309 and its target antigen Ly75

Ly75 (CD205, DEC-205) is a type I transmembrane glycoprotein and a C-type lectin receptor involved in antigen uptake and processing, mainly expressed by antigen presenting cells (APC). The short cytoplasmic tail contains motifs for amino acid-based endocytosis, making this receptor an ideal target antigen for an antibody drug conjugate (ADC)-based antitumoral therapy. MEN1309 is a novel fully humanized ADC which binds to Ly75 with high affinity as shown by ELISA and FACS analysis. The antibody is conjugated to a maytansinoid DM4, a potent tubulin inhibitor, through a cleavable linker.The ability of Ly75 to internalize the antibody after binding was determined using an immunoflourescence assay that showed a rapid, efficient, and near complete internalization over a one hour time course.The expression of Ly75 mRNA and protein was investigated in human cancer cell lines derived from different histotypes and revealed high expression in pancreas, bladder, triple negative breast cancer (TNBC) cells and in diffuse large B-cell lymphoma (DLBCL). Indeed, MEN1309 shows a powerful (pM range) in vitro cytotoxic activity on different cancer cell lines expressing Ly75, whereas it exerts a weaker effect on antigen-negative cells. Besides the mechanism of action (MoA) of MEN1309 as an ADC, the putative efficacy of the antibody to drive an ADCC response was investigated through in vitro binding and functional assays. In spite of a high binding affinity of MEN1309 to FcγRIIIa, no ADCC response was observed, suggesting that the high internalization rate of the antigen could hamper the triggering of NK responses.Moreover, in order to characterize the functional role of Ly75 in cancer cell lines, its expression was downregulated by siRNA demonstrating an inhibition of the proliferation rate in cells from different histotypes.Finally, we investigated if some cancer cell lines could show a higher expression of two intergenically spliced forms derived from Ly75 and DCL-1 genes recently reported in literature. We found that the intergenically spliced forms were expressed on average 30 fold less than CD205 mRNA in all the cancer cell lines analyzed, suggesting that these variants derive just from an intergenic readthrough without a specific transcriptional regulation. Citation Format: Alessandro Bressan, Alessio Fiascarelli, Giuseppe Merlino, Corrado Carrisi, Daniela Bellarosa, Rachel Dusek, Rahel Awdew, Sudha Swaminathan, Arnima Bisht, To Uyen T. Do, San Lin Lou, Dee Aud, Jonathan Terrett, Keith Wilson, Christian Rohlff, Monica Binaschi. Characterization of the novel antibody drug conjugate MEN1309 and its target antigen Ly75 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3646. doi:10.1158/1538-7445.AM2017-3646

Abstract 2975: Development of a probody drug conjugate (PDC) targeting CD71 for the treatment of solid tumors and lymphomas

The targets of Antibody Drug Conjugates (ADCs) have typically been selected by identifying transmembrane antigens that are highly expressed in tumors but are low or absent in normal tissues. The number of potential ADC targets meeting these requirements is limited, either because expression in tumors is not high enough for optimal efficacy, or because expression in normal tissues is too high, leading to toxicity. Probody (TM) therapeutics are antibody prodrugs designed to remain inactive until proteolytically activated in the tumor microenvironment. Probody technology therefore has the potential to enable targeting of more desirable tumor antigens with higher, more persistent and more homogeneous expression in tumors, while limiting toxicity due to interaction with these antigens in normal tissues. CD71 (transferrin receptor) is an example of a highly desirable ADC target, because of its well-characterized ability to efficiently internalize and deliver an ADC payload intracellularly. Further, CD71 is expressed at homogeneously high levels (3+ expression by IHC) in almost all tumor types, including in metastatic disease. However, because CD71 is also expressed on multiple normal cell types, including many progenitor hematological cells, we reasoned that a CD71-targeted ADC would be challenging to develop. To enable targeting of CD71, we have developed an anti-CD71 Probody Drug Conjugate (PDC) CX-2005, which can be activated by multiple proteases in the tumor microenvironment, but which remains in a relatively inactive form while in circulation and in normal tissues. CX-2005 produces complete tumor regressions at therapeutic doses in mouse models of lymphoma, breast cancer and lung cancer. Consistent with our hypothesis that it would be difficult to develop an anti-CD71 ADC, treatment of cynomolgus monkeys with an anti-CD71 ADC at doses that were efficacious in mouse tumor models caused life-threatening depletion of CD71-expressing hematopoietic cells, including neutrophils, lymphocytes and RBCs. In contrast, these toxicities were not observed in monkeys treated with the same dose of the anti-CD71 PDC, consistent with the Probody therapeutic avoiding interaction with these normal cells. Our data demonstrate that, in preclinical studies, Probody drug conjugates can safely and effectively target attractive tumor antigens like CD71 which have been difficult to effectively approach with traditional ADCs due to their expression on critical normal tissues. Further, our data support the development of Probody therapeutics directed against CD71 in multiple different cancers. PROBODY is a trademark of CytomX Therapeutics, Inc. Citation Format: Shweta Singh, Amy DuPage, Annie Yang Weaver, Jason Sagert, Clayton White, Michael Krimm, Yuanhui Huang, Linnea Diep, Kim Tipton, Shouchun Liu, Jennifer Richardson, W. Michael Kavanaugh, Jonathan A. Terrett, Luc R. Desnoyers. Development of a probody drug conjugate (PDC) targeting CD71 for the treatment of solid tumors and lymphomas. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2975.

Abstract 661: Proteomics and selecting the right combination of target and toxin for antibody-drug-conjugate (ADC) development

With the successes of Kadcyla and Adcetris, and the emerging data from early phase trials of many other ADCs our understanding of the critical attributes for target selection and ADC development has improved significantly. Clinical experience indicates that the dose-limiting toxicities observed are predominately off-target and thus are similar across ADCs using the same linker and drug combinations and independent of the target antigen. Furthermore, the maximum tolerated doses (MTDs) in humans, monkeys, and mice for many ADCs seem to be very similar regardless of the protein being targeted. Thus, the therapeutic index of new ADCs using the current drug/linker technologies (tubulin and DNA targeting toxins) will be driven predominately by efficacy, specifically the ability to achieve antitumor activity at exposure levels below the MTD. Therefore, the focus of future target selection should be on efficacy within the therapeutic window rather than on antigen-dependent (i.e. on-target) toxicity arising from normal tissue expression. We have selected targets and toxins for ADC development based on the likelihood of robust potency against cancer cells. The properties favored are : 1) high expression and high prevalence in selected malignancies, 2) normal tissue expression profiles known to be tolerable for ADCs ( e.g. her2neu, gpnmb, nectin4), 3) targets enabling rapid intracellular delivery of ADC and release of active toxin, 4) clinical indications sensitive to the toxin of choice. This process and its success are demonstrated here through the development of two ADCs. Firstly, Ox-1476 for triple negative breast cancer (TNBC). The target was selected based on consistent high expression in TNBC, the MAb selected from a large screen of greater than 1000 candidates based on activity as an actual ADC, and the toxin selected based on the positive experience with maytansine in breast cancer (Kadcyla) and the preclinical data presented here. The Ox-1476 ADC shows greater and broader activity than Kadcyla in vitro and an initial toxicity profile consistent with pursuing clinical development. Secondly, Ox-1425 is being developed for small cell lung cancer (SCLC). The target and MAb were selected by the same processes but for Ox-1425 the toxin screen resulted in the selection of a DNA alkylating agent. Our proteomics database has provided a unique data set of candidate cell surface targets for the development of antibodies compatible with the current state of the art ADC payloads. The selected targets show high and prevalent expression in cancers, are in protein families shown to internalize efficiently, and have normal tissue expression profiles similar to other proteins already being targeted by clinical stage ADCs. The preclinical safety and activity data shown here is supportive of our strategy for selecting ADC targets. Citation Format: Jonathan A. Terrett, Rachel Dusek, Dee Aud, Rahel Awdew, Sudha Swaminathan, San Lin Lou, Michael Trang, Arnima Bisht, Mary Do, Jim Ackroyd, Robert Boyd, Lindsey Hudson, Phuoc Pham, Nickolas Attanasio, Ami Antani, Carmel Lynch, Christian Rohlff. Proteomics and selecting the right combination of target and toxin for antibody-drug-conjugate (ADC) development. [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 661. doi:10.1158/1538-7445.AM2014-661

Abstract 3869: Proteomics highlights which G-protein coupled receptors are candidates for ADC development

Proceedings: AACR 103rd Annual Meeting 2012‐‐ Mar 31‐Apr 4, 2012; Chicago, IL Antibody-drug conjugates (ADCs) are a recent and exciting development for targeted therapy of cancer. Their efficacy is governed by ADC-intrinsic characteristics such as avidity, drug load and linker chemistry, and mechanisms of activation and action, which can be controlled or clarified in the early stages of ADC development. In contrast, the properties that define a promising ADC target are still somewhat unclear. OGAP is a unique proteomic database that integrates information at the tissue, disease and protein isoform level across diseases, indications, and normal tissues to clarify protein expression levels and profiles. Specifically, it currently holds information on ∼2,000,000 human protein peptide sequences, ∼16,000 human proteins sequenced, ∼7,000 cancer membrane proteins, ∼50 tissues/organs, and ∼60 diseases. Building on OGAP and a proprietary sample preparation and processing workflow that relies on state-of-the-art high-throughput mass spectrometry and data processing to provide quantitative information on over 4,000 membrane-enriched proteins from ∼ 15,000 unique peptide sequences per analysis, we have established a novel predictive tool to establish each proteins potential to serve as a target for ADC development. The tool considers proteomic and target-specific information on antigenicity, structure, function, expression level, regulation, and tissue distribution in order to highlight the most suitable candidates for ADC development. We will demonstrate the utility of this process for the protein family of G-protein coupled receptors (GPCRs), which according to a recent bioinformatics prediction encompasses 899 distinct members in the human genome. These cell surface receptors are the target of more than one third of conventional drugs, yet their potential for ADCs is largely unexplored. Here we show that proteomics in the context of the OGAP database can highlight which of this large family of receptors have the potential to become true ADC targets. 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 3869. doi:1538-7445.AM2012-3869

Abstract 1683: High throughput membrane proteomics for the discovery of oncology targets ideally suited for the development of antibody drug conjugates (ADCs)

Proceedings: AACR 102nd Annual Meeting 2011‐‐ Apr 2‐6, 2011; Orlando, FL Antibody Drug Conjugates (ADCs) are showing tremendous promise for cancer patients as recently demonstrated by the dramatic responses reported in breast cancer and Hodgkins Lymphoma clinical trials to the ADCs T-DM1 and SGN-35. We have developed proteomics methods to enrich for membrane proteins that are expressed preferentially in cancer cells over normal cells. Potential ADC targetable proteins are then validated using the proprietary OGAP database as well as conventional expression analysis tools. The proteomics processes have identified novel cancer specific proteins as well as cancer specific isoforms of known proteins. These targets are then combined with large panels of antibodies to discover potential therapeutics with properties desirable for the development of ADCs. Antibodies are selected which : a) preferentially bind to tumor cells over normal cells, b) have good specificity and affinity, c) show high prevalence in target cancer indications by IHC, d) internalize on antigen binding, e) bind to relevant tox species tissues as they bind to human tissues. Here we describe the proteomics processes and use of the OGAP database and demonstrate the development of candidate therapeutic antibodies with the potential to become ADCs, which are directed to novel targets and cancer specific isoforms. 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 1683. doi:10.1158/1538-7445.AM2011-1683