Abstract 1780: TCR-T and CAR-T cells targeting HLA-A2/MAGEA4 demonstrate differential tumor control, reflecting co-stimulatory signaling requirements

The clinical success of cancer immunotherapy, including engineered T cell therapies, has revolutionized treatment paradigms and patient outcomes. While hematological tumors have benefited most from cell therapy approaches, the treatment of solid tumors remains a challenge in part due to the limited availability of abundant and tumor-specific cell-surface antigens. Peptides derived from intracellular tumor-specific proteins, such as cancer-testis antigens (CTAs), that are presented via HLA (pHLA) enable a therapeutic opportunity to target tumors while sparing normal tissue. Surface-accessible pHLA complexes may be targeted with engineered T cell receptors or TCR mimetic antibodies reformatted to chimeric antigen receptors (CARs). Using MAGE-A4 as a model CTA, we compared engineered human TCR- and CAR-T cells head-to-head to understand how to best deploy these modalities. To this end, we generated fully-human, HLA-A2/MAGE-A4(230-239)-specific TCR and CARs harboring CD28/CD3z or 41BB/CD3z signaling domains. TCR and CAR-T cells demonstrated similar robust on-target reactivity, cytokine release, and target cell lysis in vitro. In vivo, each of these modalities showed potent, dose-dependent anti-tumor efficacy against human xenograft tumors expressing low, endogenous levels (~500 cell-surface copies) of the MAGE-A4 peptide. However, differences emerged when we examined the in vivo kinetics and durability of tumor suppression. MAGE-A4 CD28/z CAR-T demonstrated the most rapid and potent tumor clearance, while the 41BB/z CAR-T showed delayed but ultimately complete efficacy. TCR-T cells induced tumor regressions during the first 2 weeks of treatment, but this response was transient and followed by tumor relapse. These differential responses correlated with early, modest accumulation of CD28/z CAR-T in line with fast tumor clearance. 41BB/z CAR-T showed a remarkable ~800-fold expansion in the tumor versus limited in vivo TCR-T proliferation. Mechanistically, the MAGE-A4 TCR induced strong CD3 proximal signaling associated with a greater induction of T cell dysfunction markers and limited cytotoxic potential in vitro. However, stimulating 41BB signaling pathways in the MAGE-A4 TCR T cells augmented long-term cytotoxicity. These data demonstrate that tumor-specific pHLA complexes can be potently targeted by both TCR and CAR-T cells, and that co-stimulatory signaling is necessary to mediate durable anti-tumor activity.

Citation Format: Corinne E. Decker, Jacqueline Idun, Katja Mohrs, Thomas Meagher, Kevin Bray, Iryna Petriv, Jonathon Golas, Timothy Helms, Dharani Ajithdoss, Gavin Thurston, John Lin, Jessica R. Kirshner, David J. DiLillo. TCR-T and CAR-T cells targeting HLA-A2/MAGEA4 demonstrate differential tumor control, reflecting co-stimulatory signaling requirements [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 1780.

Anti-Extra Domain B Splice Variant of Fibronectin Antibody-Drug Conjugate Eliminates Tumors with Enhanced Efficacy When Combined with Checkpoint Blockade

Extra domain B splice variant of fibronectin (EDB+FN) is an extracellular matrix protein (ECM) deposited by tumor-associated fibroblasts, and is associated with tumor growth, angiogenesis, and invasion. We hypothesized that EDB+FN is a safe and abundant target for therapeutic intervention with an antibody-drug conjugate (ADC). We describe the generation, pharmacology, mechanism of action, and safety profile of an ADC specific for EDB+FN (EDB-ADC). EDB+FN is broadly expressed in the stroma of pancreatic, non-small cell lung (NSCLC), breast, ovarian, head and neck cancers, whereas restricted in normal tissues. In patient-derived xenograft (PDX), cell-line xenograft (CLX), and mouse syngeneic tumor models, EDB-ADC, conjugated to auristatin Aur0101 through site-specific technology, demonstrated potent antitumor growth inhibition. Increased phospho-histone H3, a pharmacodynamic biomarker of response, was observed in tumor cells distal to the target site of tumor ECM after EDB-ADC treatment. EDB-ADC potentiated infiltration of immune cells, including CD3+ T lymphocytes into the tumor, providing rationale for the combination of EDB-ADC with immune checkpoint therapy. EDB-ADC and anti-PD-L1 combination in a syngeneic breast tumor model led to enhanced antitumor activity with sustained tumor regressions. In nonclinical safety studies in nonhuman primates, EDB-ADC had a well-tolerated safety profile without signs of either on-target toxicity or the off-target effects typically observed with ADCs that are conjugated through conventional conjugation methods. These data highlight the potential for EDB-ADC to specifically target the tumor microenvironment, provide robust therapeutic benefits against multiple tumor types, and enhance activity antitumor in combination with checkpoint blockade.

Evaluation of EDB Fibronectin in Plasma, Patient-Derived Xenograft Formalin-Fixed Paraffin-Embedded and Fresh Frozen Tumor Tissues Using Immunoaffinity LC-MS/MS

The fibronectin (FN) isoform including the extradomain B (EDB) segment (EDB + FN) is a promising tumor target and is highly expressed in some tumor types, such as breast, head, and neck cancer. To date, mostly immunohistochemistry (IHC) and Western blot have been used for the analysis of EDB + FN. However, complete quantitative measurements of EDB + FN expression in a tumor and circulation are important for the development of anti-EDB therapeutics. To this end, a method using protein enrichment followed by online antipeptide antibody enrichment coupled with a nanoflow LC-MS/MS was developed to quantify EDB + FN in human and cynomolgus plasma, patient-derived xenograft (PDX) tumors, and PDX formalin-fixed paraffin-embedded (FFPE) samples. Mouse plasma EDB + FN was analyzed using a protein immunoaffinity method followed by nanoflow LC-MS/MS. EDB + FN concentrations were 63.1 pmol/g in PDX breast cancer tumor and 49.6 pmol/g in PDX head and neck tumor. Mean plasma concentration was 1.1 nM (pmol/mL, 47.4 ng/mL) in normal healthy humans and 0.35 nM (15.1 ng/mL) in naive cynomolgus. The assay sensitivity was 0.018 nM based on calibration with recombinant human EDB + FN (rhEDB + FN).

NOTCH3-targeted antibody drug conjugates regress tumors by inducing apoptosis in receptor cells and through transendocytosis into ligand cells

Aberrant NOTCH3 signaling and overexpression is oncogenic, associated with cancer stem cells and drug resistance, yet therapeutic targeting remains elusive. Here, we develop NOTCH3-targeted antibody drug conjugates (NOTCH3-ADCs) by bioconjugation of an auristatin microtubule inhibitor through a protease cleavable linker to two antibodies with differential abilities to inhibit signaling. The signaling inhibitory antibody rapidly induces ligand-independent receptor clustering and internalization through both caveolin and clathrin-mediated pathways. The non-inhibitory antibody also efficiently endocytoses via clathrin without inducing receptor clustering but with slower lysosomal co-localization kinetics. In addition, DLL4 ligand binding to the NOTCH3 receptor mediates transendocytosis of NOTCH3-ADCs into ligand-expressing cells. NOTCH3-ADCs internalize into receptor and ligand cells independent of signaling and induce cell death in both cell types representing an atypical mechanism of ADC cytotoxicity. Treatment of xenografts with NOTCH3-ADCs leads to sustained tumor regressions, outperforms standard-of-care chemotherapy, and allows targeting of tumors that overexpress NOTCH3 independent of signaling inhibition.

NOTCH3 receptor is overexpressed in breast, lung, and ovarian tumors

Newly generated NOTCH3-targeted antibody drug conjugates are efficacious and safe

NOTCH3 antibodies internalize through different routes depending on signaling status

NOTCH3 antibody intercellular trafficking occurs by transendocytosis into ligand cells

PF-06804103, A Site-specific Anti-HER2 Antibody-Drug Conjugate for the Treatment of HER2-expressing Breast, Gastric, and Lung Cancers

The approval of ado-trastuzumab emtansine (T-DM1) in HER2⁺ metastatic breast cancer validated HER2 as a target for HER2-specific antibody-drug conjugates (ADC). Despite its demonstrated clinical efficacy, certain inherent properties within T-DM1 hamper this compound from achieving the full potential of targeting HER2-expressing solid tumors with ADCs. Here, we detail the discovery of PF-06804103, an anti-HER2 ADC designed to have a widened therapeutic window compared with T-DM1. We utilized an empirical conjugation site screening campaign to identify the engineered ĸkK183C and K290C residues as those that maximized in vivo ADC stability, efficacy, and safety for a four drug-antibody ratio (DAR) ADC with this linker-payload combination. PF-06804103 incorporates the following novel design elements: (i) a new auristatin payload with optimized pharmacodynamic properties, (ii) a cleavable linker for optimized payload release and enhanced antitumor efficacy, and (iii) an engineered cysteine site-specific conjugation approach that overcomes the traditional safety liabilities of conventional conjugates and generates a homogenous drug product with a DAR of 4. PF-06804103 shows (i) an enhanced efficacy against low HER2-expressing breast, gastric, and lung tumor models, (ii) overcomes in vitro- and in vivo-acquired T-DM1 resistance, and (iii) an improved safety profile by enhancing ADC stability, pharmacokinetic parameters, and reducing off-target toxicities. Herein, we showcase our platform approach in optimizing ADC design, resulting in the generation of the anti-HER2 ADC, PF-06804103. The design elements of identifying novel sites of conjugation employed in this study serve as a platform for developing optimized ADCs against other tumor-specific targets.

Multidimensional Coculture System to Model Lung Squamous Carcinoma Progression

Tumor-stroma interactions play a critical role in the development of lung squamous carcinoma (LUSC). However, understanding how these dynamic interactions contribute to tissue architectural changes observed during tumorigenesis remains challenging due to the lack of appropriate models. In this protocol, we describe the generation of a 3D coculture model using a LUSC primary cell culture known as TUM622. TUM622 cells were established from a LUSC patient-derived xenograft (PDX) and have the unique property to form acinar-like structures when seeded in a basement membrane matrix. We demonstrate that TUM622 acini in 3D coculture recapitulate key features of tissue architecture during LUSC progression as well as the dynamic interactions between LUSC cells and components of the tumor microenvironment (TME), including the extracellular matrix (ECM) and cancer-associated fibroblasts (CAFs). We further adapt our principal 3D culturing protocol to demonstrate how this system could be utilized for various downstream analyses. Overall, this organoid model creates a biologically rich and adaptable platform that enables one to gain insight into the cell-intrinsic and extrinsic mechanisms that promote the disruption of epithelial architectures during carcinoma progression and will aid the search for new therapeutic targets and diagnostic markers.

Abstract 818: NG-HER2 ADC (PF-06804103) is superior to trastuzumab emtansine in a mouse 'avatar' head-to-head clinical trial

Patient-derived xenografts (PDXs) are resected human tumors engrafted into mice and represent personalized murine ‘avatars' of those tumors. PDXs are valuable tumor models for drug development since they recapitulate the complexity of the human tumor microenvironment more extensively than cell line xenografts (CLXs). Unlike CLXs, PDXs are never passaged in vitro, and therefore they more faithfully recapitulate native tumor biology and response to therapeutics. Thus, PDXs may more accurately predict clinical activity of therapeutic compounds than traditional CLXs. We are developing a next generation (NG)-HER2 antibody-drug conjugate (ADC), PF-06804103, that employs a proprietary site-specific conjugation technology that chemically links the clinically-validated linker-payload “ValCit-Aur0101” to an anti-HER2 antibody. The site-specific conjugation enables enhanced exposures and reduced off-target toxicities as previously described. We utilized our PDX collection to evaluate the breadth-of-efficacy of PF-06804103 versus trastuzumab emtansine (T-DM1), an FDA-approved ADC for metastatic breast cancer patients with high HER2 expression. Efficient cleavage of the ‘ValCit' linker and payload release in the early endosome is not impacted by the rapid recycling properties of the HER2 receptor, unlike T-DM1 which requires catabolism in the within the lysosomal milieu to efficiently release its payload. To date, we have enrolled >20 HER2-expressing breast, gastric and non-small cell lung cancer PDXs, with varying low to high HER2 expression levels, in a head-to-head ‘mouse avatar clinical trial' comparing activity of a single cycle of T-DM1 (6 mg/kg) to PF-06804103 (3 mg/kg). Impressively, PF-06804103 had more durable complete responses and a higher objective response rate (ORR) than T-DM1 (84% vs. 4%), including in low-moderate HER2 expressers. PF-06804103 prolonged median overall survival (OS) of mice with HER2-expressing tumors compared to T-DM1 (100 vs 45 days). Biomarker analysis showed that tumors at all levels of HER2 expression were more likely to receive more benefit with PF-06804103 than T-DM1 (HR < 0.45). By leveraging our novel PDX ‘avatar' clinic, we were able to demonstrate that PF-06804103 displays superior in vivo breadth-of-efficacy compared to T-DM1.

Citation Format: Matthew S. Sung, Christine Hopf, Erik Upeslacis, Jonathon Golas, Mark Kaplan, Kiran Khandke, Manoj Charati, Frank Kotch, Frank Loganzo, Ken Geles, Judy Lucas, Hans-Peter Gerber, Puja Sapra, Edward Rosfjord. NG-HER2 ADC (PF-06804103) is superior to trastuzumab emtansine in a mouse 'avatar' head-to-head clinical trial [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 818.

Abstract 2113: Caveolae-mediated endocytosis as a novel mechanism of resistance to T-DM1 ADC

Trastuzumab emtansine (T-DM1) is an antibody-drug conjugate (ADC) comprised of the HER2-targeting antibody trastuzumab and DM1, a microtubule depolymerizing agent covalently attached via a non-cleavable thioether linker. T-DM1 has demonstrated clinical benefit for patients with metastatic breast cancer, however activity may be limited by inherent or acquired resistance during prolonged treatment periods. The molecular mechanisms that drive clinical resistance to T-DM1, especially in HER2 positive tumors, are not well understood. We used the HER2+ cell line N87 to develop a model of T-DM1 resistance utilizing a cyclical dosing schema in which cells received T-DM1 in an “on-off” routine until a T-DM1 resistant population of N87 cells (N87-TM) was generated. N87-TM cells displayed 103-fold resistance toward T-DM1 treatment compared to the parental N87 cells. The N87-TM cells were cross-resistant to a panel of trastuzumab-ADCs (T-ADCs) with non-cleavable-linked auristatins. N87-TM cells do not have a decrease in HER2 protein levels or an increase in drug efflux pump (e.g. MDR1) protein expression compared to parental N87 cells. Comparative proteomic profiling suggested an enrichment in proteins (e.g. caveolin-1, CAV1) that mediate caveolae formation and endocytosis in the N87-TM cells. Indeed, N87-TM cells internalize ADCs into intracellular CAV1+ puncta and alter their trafficking to the lysosome compared to N87 cells. Intriguingly, T-ADCs utilizing auristatin payloads attached via an enzymatically cleavable linker (i.e. ValCit linker) overcome T-DM1 resistance in N87-TM cells. Importantly, N87-TM cells implanted into athymic mice in vivo formed T-DM1 refractory tumors which remain sensitive to T-ADCs with cleavable-linked auristatin payloads. When comparing antigen positive patient-derived xenograft models that were refractory to T-DM1 yet responded to T-ADCs with ValCit linker-payloads, CAV1 was found to be a predictive protein biomarker identifying T-DM1 refractory tumors. These data implicate caveolae-mediated endocytosis in ADC biology and suggest that alterations in this pathway may impact a tumor's response profile to ADCs with non-cleavable linkers. We also propose CAV1 as a novel protein biomarker whose high tumoral expression predicts a refractory response to the T-DM1 ADC.

Citation Format: Matthew S. Sung, Xingzhi Tan, Christine Hosselet, Michael Cinque, Erik Upeslacis, Jonathon Golas, Fang Wang, Bingwen Lu, Laurie Tylaska, Lindsay King, Jeremy Myers, Edward Rosfjord, Judy Lucas, Hans-Peter Gerber, Frank Loganzo. Caveolae-mediated endocytosis as a novel mechanism of resistance to T-DM1 ADC. [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 2113.

Abstract B010: Pharmacodynamics and mechanisms of drug action for bispecific redirected T cell immunotherapy against P-cadherin

Utilizing pharmacodynamic immunohistochemistry (PD-IHC) for in situ & quantitative measures, we explored the mechanism of action of a Dual-Affinity Re-Targeting (DART®) bispecific recombinant antibody engineered with enhanced pharmacokinetic properties to extend in vivo half-life. This bispecific, designated P-cadherin LP-DART, is designed to engage and activate polyclonal T cell populations via the CD3 complex in the presence of P-cadherin expressing tumors. Following administration in mice bearing established human tumors and implanted with human T-cells we examined the localization of P-cadherin LP-DART within the tumor xenografts, P-cadherin expression, quantitation and immunophenotyping of tumor infiltrating lymphocytes (TILs), downstream biomarkers of T-cell effector function and immunoregulatory mechanisms. Cell surface P-cadherin expression was maintained on the established tumor xenografts after the administration of single and multiple doses of the bispecific molecule. Furthermore, we detected P-cadherin LP-DART in the tumors more than one week after administration. Pan lymphocyte IHC and digital image analysis demonstrated P-cadherin LP-DART mediated CD3+ T-cell infiltration, resulting in nearly half of the viable cells in the tumor being TILs. Conversely, we did not detect infiltrating CD3+ human T-cells in normal organs, confirming a specific target mediated T-cell response at the tumor site. Elevated proximal and downstream mediators of drug action (granzyme B and cleaved caspase 3) further support that P-cadherin LP-DART localized within the tumor induces T-cell mediated growth inhibition and sustained regression. Additionally, to study the the tumor response to redirected T-cell mediated killing we measured the up-regulation of critical immune check point pathways after treatment P-cadherin LP-DART. In the in vivo tumor models examined, tumor cells acutely and robustly induced expression of immunoregulatory pathways in response to effector T-cell activity. Taken together, we demonstrate the utility of in situ kinetic PD-IHC methodologies to demonstrate target expression, drug localization, downstream biomarkers of drug action, and provide insights into potential immunoregulatory mechanisms in response to T-cell mediated bispecific immunotherapy.

Citation Format: Justin Lucas, Andrea T. Hooper, Jonathon Golas, Bryan Peano, Alan Opsahl, Leslie Obert, Maria Gavriil, Timothy Fisher, Anton Xavier, Michael Cinque, Roger Conant, Judy Lucas, Adam Root, Lioudmila Tchistiakova, Hans Peter Gerber, Chad May. Pharmacodynamics and mechanisms of drug action for bispecific redirected T cell immunotherapy against P-cadherin. [abstract]. In: Proceedings of the CRI-CIMT-EATI-AACR Inaugural International Cancer Immunotherapy Conference: Translating Science into Survival; September 16-19, 2015; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(1 Suppl):Abstract nr B010.

Epigenetic reprogramming by tumor-derived EZH2 gain-of-function mutations promotes aggressive 3D cell morphologies and enhances melanoma tumor growth

In addition to genetic alterations, cancer cells are characterized by myriad epigenetic changes. EZH2 is a histone methyltransferase that is over-expressed and mutated in cancer. The EZH2 gain-of-function (GOF) mutations first identified in lymphomas have recently been reported in melanoma (~2%) but remain uncharacterized. We expressed multiple EZH2 GOF mutations in the A375 metastatic skin melanoma cell line and observed both increased H3K27me3 and dramatic changes in 3D culture morphology. In these cells, prominent morphological changes were accompanied by a decrease in cell contractility and an increase in collective cell migration. At the molecular level, we observed significant alteration of the axonal guidance pathway, a pathway intricately involved in the regulation of cell shape and motility. Furthermore, the aggressive 3D morphology of EZH2 GOF-expressing melanoma cells (both endogenous and ectopic) was attenuated by EZH2 catalytic inhibition. Finally, A375 cells expressing exogenous EZH2 GOF mutants formed larger tumors than control cells in mouse xenograft studies. This study not only demonstrates the first functional characterization of EZH2 GOF mutants in non-hematopoietic cells, but also provides a rationale for EZH2 catalytic inhibition in melanoma.

Abstract 1469: Patient derived xenograft (PDX) models: improving predictability of experimental cancer therapies

Clinical development of cancer therapies is associated with attrition rates as high as 80-95%. This high attrition suggests that standard preclinical pharmacology models do not accurately reflect clinical responses. The development of more predictive preclinical models requires several considerations; the relevance of the in vivo model, the administration of test agent, and the interpretation of efficacy data. PDX are cancer models developed from the direct transfer of patient tumor tissue into immunocompromised mice. A collection of PDX models, by retaining the genetic and histologic characteristics of the patients from which they were derived, represents the complexity and heterogeneity of human cancer. To minimize the clinical attrition rates of oncology compounds, we are developing hundreds of PDX models in seven major cancer indications. The collection is being molecularly profiled by RNAseq, WES, and proteomics. Profiling has identified models with robust expression of target proteins or mutant oncogenes that are likely to respond in preclinical efficacy tests. Conversely, the PDX models may provide an understanding of resistance, for example evaluating models with good target expression that fail to respond to therapy. Patient and tumor information, if known, has been collected for each PDX model including age, sex, cancer stage and grade, diagnosis, primary or metastatic site, and prior treatments. In addition to the improvements provided by the PDX models, a preclinical paradigm shift away from treatment with maximally tolerated dose towards clinically relevant dose (CRD), taking into consideration such aspects as exposure, formulation, route and schedule, is critical when attempting to predict clinical outcome from preclinical data. Also essential is the incorporation of clinically meaningful endpoints (regression) when assessing preclinical activity. We have initiated studies on cohorts of non small cell lung and breast PDX models to predict the likely clinical efficacy of candidate compounds for clinical development and to determine the CRD for standard of care (SOC) regimens required to define the most promising Phase II/III combination therapies. Anti-tumor activities were characterized using RECIST criteria of progressive disease (PD), stable disease (SD), partial response (PR), and complete response (CR). Target expression was evaluated by RNA, proteomics and immunohistochemistry. Preliminary results demonstrate a spectrum of responses against experimental therapeutics, including Phase I ADCs and are defining the CRD required for combination treatments with SOC. Identification of the most critical parameters of PDX models predicting clinical outcome will help in validating the utility of ‘n of 1′ studies with the PDX collection, inform patient enrollment strategies, guide combination therapies, and provide insight for identifying new tumor indications.

Citation Format: Edward Rosfjord, Xin Han, Danielle Leahy, Erik Upeslacis, Justin Lucas, Jonathon Golas, Andrea Hooper, Fred Immermann, Bingwen Lu, Jeremy Myers, Zhengyan Kan, James Hardwick, Eric Powell, Puja Sapra, Paul Rejto, Hans-Peter Gerber, Judy Lucas. Patient derived xenograft (PDX) models: improving predictability of experimental cancer therapies. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1469. doi:10.1158/1538-7445.AM2015-1469

Abstract 564: The expression of fetal oncogene 5T4 in CTCs obtained from NSCLC patients is discordant with the expression measured in the primary tumor

The fetal oncogene 5T4 is a cell surface protein, with over-expression observed in a variety of cancers as compared to normal adult tissue. Recent studies have shown that expression of 5T4 appears to be associated with the undifferentiated state and the epithelial-mesenchymal transition (EMT), and thus has been associated with a more invasive phenotype. We have developed assays to measure the expression of the fetal oncogene, 5T4, in both the primary tumor compartment and in the circulating tumor cell compartment. These assays were then used to investigate 5T4 expression in a small cohort of patients with NSCLC. We obtained matched primary tumor and blood samples, with the blood being obtained prior to resection of the primary tumor. The expression of 5T4 was found to be robust and measurable in both the primary and circulating tumor compartments. We observed expression of 5T4 in both adenocarcinoma and squamous cell carcinoma, in all stages and grades of tumor, with no specific correlation between expression and stage, grade or pathology. We further observed robust enumeration of CTCs in NSCLC samples. The expression of 5T4 was heterogeneous in the CTC compartment with no correlation to grade, stage or pathology. Finally, we observed no concordance between 5T4 expression in the primary tumor and the circulating tumor cell compartment. We discuss the current utility of target expression in predicting response to targeted therapy in the context of antibody based therapy, and the role that CTCs may have in the clinic.

Citation Format: Steven R. Pirie-Shepherd, Shibing Deng, Jonathon Golas, Pamela Vizcarra, Eric Tucker, Dena Marrinuci, Hans-Peter Gerber, Eric L. Powell. The expression of fetal oncogene 5T4 in CTCs obtained from NSCLC patients is discordant with the expression measured in the primary tumor. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 564. doi:10.1158/1538-7445.AM2015-564

Reciprocal regulation of amino acid import and epigenetic state through Lat1 and EZH2

Lat1 (SLC7A5) is an amino acid transporter often required for tumor cell import of essential amino acids (AA) including Methionine (Met). Met is the obligate precursor of S-adenosylmethionine (SAM), the methyl donor utilized by all methyltransferases including the polycomb repressor complex (PRC2)-specific EZH2. Cell populations sorted for surface Lat1 exhibit activated EZH2, enrichment for Met-cycle intermediates, and aggressive tumor growth in mice. In agreement, EZH2 and Lat1 expression are co-regulated in models of cancer cell differentiation and co-expression is observed at the invasive front of human lung tumors. EZH2 knockdown or small-molecule inhibition leads to de-repression of RXRα resulting in reduced Lat1 expression. Our results describe a Lat1-EZH2 positive feedback loop illustrated by AA depletion or Lat1 knockdown resulting in SAM reduction and concomitant reduction in EZH2 activity. shRNA-mediated knockdown of Lat1 results in tumor growth inhibition and points to Lat1 as a potential therapeutic target.

Abstract 2059: In situ imaging of antibody drug conjugate (ADC) binding and pharmacodynamic biomarkers of response in models of human cancer

Antibody drug conjugates (ADCs) are clinically validated as a modality for targeted therapy of solid and hematological cancer due to advancements in target selection, conjugation chemistry and linker technology. However, much about mechanism of action (MoA) is yet to be fully understood. Our goal was to interrogate ADC pharmacokinetics and pharmacodynamics establishing proof of mechanism (PoM) of drug action with a diverse panel of ADCs. Herein, we describe the development of novel immunohistochemical (IHC) methods for in situ visualization of ADCs binding to target expressing cells and their cognate downstream biomarkers of response in formalin fixed paraffin embedded cells/tissues. We demonstrate specific binding of 4 different ADCs spanning 2 solid tumor targets and an endothelial cell target using IHC with anti-human IgG in human tumor xenograft models expressing the respective targets. ADC binding to target is observed as early as 20 minutes after a single dose of ADC at 3 mg/kg. Utilizing an anti-microtubule inhibitor (MTI) payload-specific antibody we additionally detect ADC binding to tumor cells by monitoring the cytotoxic payload. The cell type where the antibodies and payload localized was identified by double and triple IHC. Pharmacodynamic biomarkers of response for two payload classes (DNA damaging agents and MTIs) were detected with antibodies against phospho-Histone H2AX and phospho-Histone H3, respectively - confirming the expected ADC MoAs. Downstream apoptosis of target cells was detected with cleaved caspase 3 IHC. The kinetics of biomarker response and downstream cellular impact was quantified via image analysis with biomarkers evident as early as 24 hours after a single dose for both tumor cell and vascular targets. Furthermore, we observed a correlation between biomarkers of response and efficacy of the ADCs as measured by statistically significant tumor growth inhibition for the 4 ADCs we studied. These data suggest that IHC interrogations of drug action should be used to further the clinical development of ADCs via demonstration of pharmacodynamic activities at the cellular level, establishing PoM data, and enabling predictive preclinical oncology models in order to reduce clinical attrition of ADCs.

Citation Format: Jonathon Golas, Andrea T. Hooper, Justin Lucas, Heather Jones, Timothy Nichols, Kiran Khandke, Manoj Charati, Roger Conant, Michael Cinque, Judy Lucas, Marc Damelin, Ken Geles, Caiazzo Teresa, Frank Loganzo, Puja Sapra, Hans-Peter Gerber, Chad May. In situ imaging of antibody drug conjugate (ADC) binding and pharmacodynamic biomarkers of response in models of human cancer. [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 2059. doi:10.1158/1538-7445.AM2014-2059

Abstract 5144: Epigenetic reprogramming by tumor-derived EZH2 gain of function mutants leads to aggressive 3D-cell morphologies in both epithelial and melanoma cells

In addition to numerous genetic changes underlying cellular transformation, cancer cells are also characterized by epigenetic changes that are likely to play important roles in disease progression. EZH2 is an epigenetic repressor that plays well-established roles in development. In addition to widespread overexpression in a variety of tumors, the discovery of gain of function (GOF) mutations of EZH2 in diffuse large B-cell lymphoma (DLBCL), follicular lymphoma, and melanoma strongly suggests an important function for this histone methyltransferase in cancer. To ascertain the function of elevated EZH2 catalytic activity, we expressed either wild-type EZH2 (WT) or EZH2 GOF mutants in both non-tumorigenic (immortalized epithelial cells) and tumorigenic (melanoma cells) settings. In both systems, EZH2 GOF mutants greatly increased global levels of H3K27me3 and decreased H3K27me2 levels, similar to the epigenetic pattern seen in DLBCL cell lines with endogenous EZH2 GOF mutations.

In epithelial cells, expression of an EZH2 GOF mutant caused striking changes in 3D-morphology and gene changes that are indicative of cells that have undergone an epithelial to mesenchymal transition. In the disease relevant melanoma cells, several distinct EZH2 GOF mutants (but not EZH2 WT) caused prominent branching morphology in 3D-culture. Interestingly, these GOF mutants did not affect 2D-cell morphology or proliferation of melanoma cells. Furthermore, catalytic inhibition of EZH2 GOF mutants with a commercially available tool compound attenuated the 3D-phenotype. Importantly, EZH2 inhibition in melanoma cells expressing an endogenous GOF mutation also caused similar changes in 3D-morphology. RNA-seq analysis revealed genes involved in processes such as cell adhesion and axonal guidance that were down-regulated by EZH2 GOF mutants. Finally, melanoma cells expressing ectopic EZH2 GOF mutants formed larger tumors than control cells in mouse xenograft studies. Collectively, these results suggest that EZH2 GOF mutants may alter the interaction of tumor cells with their microenvironment and in this way provide a selective advantage to such tumors.

Citation Format: Robert A. Rollins, Anthony M. Barsotti, Michael Ryskin, Wenyan Zhong, Wei-Guo Zhang, Andreas Giannakou, Christine Loreth, Veronica Diesl, Maximillian T. Follettie, Jonathon Golas, Michelle Lee, Timothy Nichols, Conglin Fan, Gary Li, Stephen Dann, Paul A. Rejto, Kim T. Arndt, Dominique Verhelle. Epigenetic reprogramming by tumor-derived EZH2 gain of function mutants leads to aggressive 3D-cell morphologies in both epithelial and melanoma cells. [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 5144. doi:10.1158/1538-7445.AM2014-5144

Abstract 2669: Targeting the tumor vasculature with antibody drug conjugates

Clinical use of vascular targeting antibody drug conjugates (VT-ADCs) has not yet been explored. Herein, we preclinically demonstrate utility, mechanisms and advantages of VT-ADCs as targeted cancer therapeutics. A monoclonal human IgG1 antibody selective for murine VEGFR2 (B3) is non-VEGF-A neutralizing and traffics to the lysosome. B3 was conjugated to a proprietary auristatin microtubule inhibitor with a non-cleavable maleimidocaproyl linker, resulting in the proof-of-concept VT-ADC, B3-mcMTI. In vitro, free-payload and anti-VEGFR2-mcMTI selectively inhibit proliferating endothelial cells (ECs) with pM and low nM IC50s - suggesting that even with a broadly expressed, low-level target, a VT-ADC should be potent and tumor specific. To test this in vivo, we treated three cell line xenografts (CLX, HT29, Ls174T, A498) and a colorectal carcinoma patient derived xenograft (CRC PDX) with B3-mcMTI at 3 mg/kg q4d, resulting in tumor stasis in four models. In the HT29 colon carcinoma CLX and the CRC PDX model, B3-mcMTI was superior to VEGF-neutralizing antibody G6-31 (anti-VEGF mAb). In standard-of-care (SOC) chemotherapy (irinotecan and 5-FU) combination studies in HT29, B3-mcMTI had improved anti-tumor activity over SOC alone, and, moreover, was as effective in inhibiting tumor growth as a single agent ADC as anti-VEGF mAb combined with SOC. In the 4T1 orthotopic anti-VEGF resistant breast carcinoma setting, B3-mcMTI outperformed anti-VEGF mAb, and when combined with SOC (paclitaxel) demonstrated improved activity over single agent without an increase in metastases. B3-mcMTI internalization in endothelial cells is VEGFR2-mediated, with antibody binding and active payload releasing in normal and tumor tissues at concentrations above the in vitro IC50s; however, payload activity as measured by quantitative image analysis of pharmacodynamic biomarkers such as phospho-Histone H3 and cleaved caspase 3 is overwhelmingly localized to tumor ECs. Targeted vessels are smooth muscle invested, suggesting that VT-ADCs may target vasculature that contributes to anti-VEGF resistance. In conclusion, VT-ADCs are effective both as single agents and when combined with SOC, and VT-ADCs may overcome resistance mechanisms to standard anti-angiogenics. Taken together, these data suggest that payloads selective for proliferating ECs enable ADC-mediated targeting of widely expressed EC surface proteins, supporting the clinical pursuit of VT-ADCs.

Citation Format: Andrea T. Hooper, Chao-Pei Betty Chang, Kimberly Marquette, Jonathon Golas, Justin Lucas, Timothy Nichols, Judy Lucas, Gavriil Maria, Edward Rosfjord, Anton Xavier, Nathan Scott, Sadhana Jain, Wei Cao, Mauricio Leal, Andreas Maderna, Magali Guffroy, Xiang Zheng, Lioudmila Tchistiakova, Frank Loganzo, Hans-Peter Gerber, Chad May. Targeting the tumor vasculature with antibody drug conjugates. [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 2669. doi:10.1158/1538-7445.AM2014-2669

Abstract 4752: Preclinical development and translational research on a novel antibody-drug conjugate that targets 5T4, an oncofetal antigen expressed on tumor-initiating cells

Antibody-drug conjugates (ADCs) represent a promising therapeutic modality for the clinical management of cancer. We sought to develop a novel ADC that targets 5T4 (TPBG), an oncofetal antigen expressed on tumor-initiating cells (TICs), which comprise the most aggressive cell population in the tumor. We optimized an anti-5T4 ADC (A1mcMMAF) by sulfydryl-based conjugation of the humanized A1 antibody to the tubulin inhibitor monomethylauristatin F (MMAF) via a maleimidocaproyl linker. A1mcMMAF exhibited potent in vivo anti-tumor activity in a variety of tumor models and induced long-term regressions for up to 100 days after the last dose. Strikingly, animals showed pathological complete response in each model. In a non-small cell lung cancer patient-derived xenograft in which 5T4 is preferentially expressed on the less differentiated tumor cells, A1mcMMAF treatment resulted in sustained tumor regressions and reduced TIC frequency. These results highlight the potential of ADCs that target the most aggressive cell populations within tumors. An optimized pharmacokinetic/pharmacodynamic (PK/PD) model of tumor growth and drug kill was used to characterize the ADC concentration response relationship in mouse. A holistic secondary parameter, tumor static concentration (TSC), was derived from model parameters to quantify efficacy and support early clinical trial design. Tumor static concentrations [80% confidence] of A1mcMMAF ranged from 1.1[0.9 -1.4] μg/ml to 11.6 [9.6 - 14.1] μg/ml across tumor models. For comparison, in the clinic T-DM1 has an average concentration of 14 μg/ml at an efficacious dose of 3.6 mg/kg Q3wk (HER+ breast cancer) (Krop et al. 2010) and Brentuximab-vedotin has an average concentration of 3.65 μg/ml at an efficacious dose of 1.8 mg/kg Q 3wk (HL/ ALCL) (Younes et al. 2010). Taken together, the preclinical data established a promising therapeutic index that supports clinical testing of A1mcMMAF. Expression analysis profiling using clinical and preclinical data indicated that lung and breast tumors demonstrated differentially high expression of 5T4 in comparison to normal tissues. An IHC assay developed in house confirmed the hypothesis that a broad range of 5T4 expression was measurable in NSCLC patient tumor samples. Additionally, we developed an assay that measures 5T4 expression on circulating tumor cells (CTCs) and used this assay to measure and characterize a broad range of 5T4 expression in CTCs obtained from the blood of NSCLC patients. We intend to deploy these co-developed immunoassays to guide A1mcMMAF clinical development.

Citation Format: Puja Sapra, Marc Damelin, Kimberly Marquette, Kenneth G. Geles, Jonathon Golas, Maureen Dougher, Bitha Narayanan, Andreas Giannakou, Kiran Khandke, Russell Dushin, Elana Ernstoff, Judy Lucas, Mauricio Leal, George Hu, Alison Betts, Nahor Haddish-Berhane, Eric Powell, Steven Pirie-Shepherd, Christopher O'Donnell, Lioudmila Tchistiakova, Hans-Peter Gerber, Dena Marrinucci, Eric Tucker. Preclinical development and translational research on a novel antibody-drug conjugate that targets 5T4, an oncofetal antigen expressed on tumor-initiating cells. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4752. doi:10.1158/1538-7445.AM2013-4752

Abstract 1235: p120ctn is a key effector of Ras-PKC∈-mediated oncogenic signaling

Within the family of protein kinase C (PKC) molecules only the novel isoform member PRKCE (PKC∈) acts as a bona fide oncogene in in-vitro and in-vivo models of tumorigenesis. Previous studies have reported cancer-specific misexpression of PKC∈ at levels well above that of normal adjacent tissue in breast, prostate and lung tumors. We find that oncogenic Ras signaling promotes PKC∈ expression and results in hyperphosphorylation of CTNND1/p120-catenin (p120ctn). In this context, loss of PKC∈ by genetic or pharmacological means results in normalization of morphology and signaling responses. In a KRasD13-dependent breast cancer model loss of PKC∈ function results in growth inhibition in 2-dimensional (2D) and 3-dimensional (3D) culture systems as well as in orthotopic xenografts concomitant with the normalization of a subset of Ras-induced signaling responses. Using phospho-proteomic profiling analysis we observe that CTNND1 (p120ctn) phosphorylation at serine 268 (S268) occurs in a strictly PKC∈ dependent manner. Treatment with a specific PKC∈ inhibitor, PF-5263555, recapitulates the genetic loss of function phenotype and interferes with breast cancer cell growth in-vitro and in-vivo. We also show that PKC∈-mediated phosphorylation at S268 further stabilizes additional p120ctn phosphorylation sites and total protein levels of β-catenin. We demonstrate that p120ctn phosphorylation at S268 represents a specific readout for PKC∈ activity and as such can serve as a suitable biomarker for PKC∈ dysregulation in human cancer and for monitoring therapeutic response.

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 1235. doi:1538-7445.AM2012-1235

Delineation of a cellular hierarchy in lung cancer reveals an oncofetal antigen expressed on tumor-initiating cells

Poorly differentiated tumors in non-small cell lung cancer (NSCLC) have been associated with shorter patient survival and shorter time to recurrence following treatment. Here, we integrate multiple experimental models with clinicopathologic analysis of patient tumors to delineate a cellular hierarchy in NSCLC. We show that the oncofetal protein 5T4 is expressed on tumor-initiating cells and associated with worse clinical outcome in NSCLC. Coexpression of 5T4 and factors involved in the epithelial-to-mesenchymal transition were observed in undifferentiated but not in differentiated tumor cells. Despite heterogeneous expression of 5T4 in NSCLC patient-derived xenografts, treatment with an anti-5T4 antibody-drug conjugate resulted in complete and sustained tumor regression. Thus, the aggressive growth of heterogeneous solid tumors can be blocked by therapeutic agents that target a subpopulation of cells near the top of the cellular hierarchy.

Abstract 475: Delineation of a cellular hierarchy in lung cancer reveals an oncofetal antigen expressed on tumor-initiating cells

Poorly differentiated tumors in non-small cell lung cancer (NSCLC) are refractory to chemotherapy and associated with short survival time. Here we integrate multiple experimental models with clinicopathological analysis of patient tumors to delineate a cellular hierarchy in NSCLC. We demonstrate that the oncofetal protein 5T4 is expressed on tumor-initiating cells and associated with worse clinical outcome in NSCLC. Coexpression of 5T4 and factors involved in the epithelial-to-mesenchymal transition was observed in undifferentiated but not in differentiated tumor cells. Despite heterogeneous expression of 5T4 in NSCLC patient-derived xenografts, treatment with an anti-5T4 antibody-drug conjugate resulted in complete and sustained tumor regression. Thus, the aggressive growth of heterogeneous solid tumors can be blocked by therapeutic agents that target a subpopulation of cells near the top of the cellular hierarchy.

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 475. doi:10.1158/1538-7445.AM2011-475