Determination of Tight Junction Integrity in Brain Endothelial Cells Based on Tight Junction Protein Expression

Blood-brain barrier (BBB) dysfunction and hyperpermeability that occurs following traumatic and ischemic insults lead to various downstream ill effects such as cerebral edema and elevation of intracranial pressure. The inter-endothelial tight junctions that consist of tight junction proteins are critical regulators of BBB dysfunctions and hyperpermeability. The major tight junction-associated proteins of the BBB are occludin, claudins, and junctional adhesion molecules that are intracellularly linked to the adaptor protein zonula occludens-1 (ZO-1). Quantitative measurement of tight junction-associated proteins provides valuable insight into barrier integrity and mechanisms that regulate microvascular hyperpermeability. Western blot analysis is a commonly used method to separate and identify proteins in a mixture using gel electrophoresis. Understanding the changes in the expression of one or more of these proteins is critical to evaluating barrier integrity and permeability in health and disease. Furthermore, studying them will provide insight into the associated downstream signaling pathways and evaluation of therapeutic approaches for regulating BBB permeability. Herein, we have described the protocol for immunoblot analysis of ZO-1 as an indicator of tight junction integrity in brain microvascular endothelial cells.

Evaluation of Tight Junction Integrity in Brain Endothelial Cells Using Confocal Microscopy

The blood-brain barrier (BBB) is a highly complex and dynamic microvascular barrier that protects the brain parenchyma from the entry of pathogens, toxins, and other macromolecules and is a critical structure that helps to maintain brain homeostasis. The BBB is formed mainly by brain capillary endothelial cells and perivascular astrocytes and pericytes. One of the primary properties of the BBB is a tight regulation of paracellular permeability due to the presence of tight junctional complexes (also, adherens and gap junctions) between the neighboring microvascular endothelial cells. Alterations in the assembly of the tight junctions impair BBB properties, particularly influenced barrier integrity and permeability. The tight junctions of the BBB are mainly composed of proteins including claudins, occludin, and zonula occludens-1 (ZO-1). Zonula occludens-1 binds to the actin cytoskeleton, and its localization provides valuable information on the status of BBB integrity and permeability. Immunofluorescence localization of ZO-1 and/or other tight junction proteins is a reliable indicator of barrier integrity and permeability in microvascular endothelial cells. In microvascular endothelial cells, f-actin stress fiber formation significantly influences the rate and size of the inter-endothelial cell gap that form as cells retract from their borders. Rhodamine phalloidin is a popular conjugate used as a fluorescent label for f-actin. Herein, we describe the procedures for ZO-1 immunofluorescence and f-actin labeling followed by confocal microscopic imaging to determine barrier integrity and tight junction organization in brain microvascular endothelial cells in vitro.

Abstract 1069: OBT076, a clinical-stage ADC, displays synergy with oxaliplatin and cisplatin in preclinical gastric cancer models

CD205 is a transmembrane glycoprotein, robustly expressed in malignancies from varied histotypes, making it an ideal target for Antibody Drug Conjugate (ADC) therapy. OBT076 is a novel and selective clinical stage ADC with potent activity against CD205-positive liquid and solid tumors. We explored the cellular cytotoxicity profile of combination chemotherapy with OBT076 and two standard-of-care platinum-based compounds, Oxaliplatin (Ox) and Cisplatin (Cis), in preclinical gastric, pancreatic and colorectal cancer models.

A panel of gastric cancer and other solid tumor cell lines were selected, based on mRNA data, for CD205 expression. This was confirmed using flow cytometry. The cell lines were assessed for susceptibility to monotherapy with OBT076, Ox and Cis. Cells lines displaying positive cytotoxic responses were assessed for susceptibility to combination chemotherapy by first treating cells with a single dose of OBT076 for 72 hours, leading to 20% growth inhibition (IC20), and subsequently with either Ox or Cis for 48 hours (OBT-Ox and OBT-CIS, respectively). The ATP-dependent fluorescence-based cellular viability system cell titer-glo was used as the cytotoxic readout.

In our preclinical gastric cancer model, pre-treatment with OBT076 followed by either Ox or Cis displayed synergistic combination effects, reducing the half-maximal inhibitory concentration (IC50) of Ox and Cis by 40- and 10-fold respectively. The resultant cellular cytotoxicity of OBT-Ox and OBT-Cis combination therapy was higher compared to monotherapy with either agent. Moreover, while monotherapy with Ox was less potent than with Cis, OBT-Ox achieved similar potency to OBT076-Cis. For colorectal and pancreatic cancer models, the effects were less pronounced: OBT076-combination therapy increased Platinum sensitivity by 2 to 5 times. No synergistic effects were observed when the treatment order was reversed. These results and those from ongoing in vivo studies in gastric cancer models will be discussed.

In summary OBT076, a clinical stage ADC displays synergistic anti-tumor effects in preclinical gastric cancer models, when used in combination with Ox or Cis. OBT076 is currently being evaluated in the gastric clinical population where Platinum-based therapies remain the mainstay of treatment.

Citation Format: Arnima Bisht, Murray Cox, Chander Sekhar Peddaboina, Michael Crocamo, Abderrahim Fandi, Christian Rohlff. OBT076, a clinical-stage ADC, displays synergy with oxaliplatin and cisplatin in preclinical gastric cancer models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1069.

Abstract 1975: Potential novel Immuno-oncology mechanism revealed during translational phase I Immuno-blood profiling of experimental ADC medicine OBT076 in a gastric cancer patient

CD205 is a type I transmembrane glycoprotein, with unique characteristics that make it an ideal target for Antibody Drug Conjugate (ADC) therapy. Here we report on a potential novel immuno-oncology mechanism revealed during the Translational Phase I (NCT04064359) immuno-blood profiling of a chemo-refractory patient treated with OBT076, an experimental CD205-directed ADC.

A chemo-refractory advanced gastric cancer patient with 60% CD205 expression in the primary tumor via IHC and having previously undergone 2 lines of chemotherapy treatment (Docetaxel/cisplatin/5FU and Ramucirumab/Paclitaxel), received five 21-day cycles of OBT076 (one at 2.5mg/kg and four cycles at 2.0 mg/kg) followed by 1 cycle of Pembrolizumab (PZ; 200mg) ~4 weeks later. Clinical response was evaluated and immunological markers (CD45, CD205, CD4, CD8, and PD1) in peripheral blood cells were quantified using flow cytometry.

After 2 OBT076 cycles at 2.0 mg/kg, there was an ~40% shrinkage in the primary gastric tumor size and resolution of ascites and lymph node metastases were observed. Following 2 further cycles and PZ, complete response was achieved for the primary tumor. Flow cytometry showed (1) an initial decrease in the absolute numbers of dendritic cells by day 8, followed by a 2-fold increase in numbers by day 21 after treatment; (2) a near total decrease in the population of CD8+ CD205+ cells by day 8, no recovery in levels were observed; (3) a 3-fold increase in CD4+ and CD8+ T-cell numbers between days 8 and 21 and (4) an initial decrease in CD4+ PD1+ and CD8+ PD1+ T-cell numbers followed by an ~4-fold increase between days 8 and 21.

In summary our results show that increases in PD1+ T-cells, T-cell induction, and decreases in immuno-suppressive CD4+ CD205+ and CD8+ CD205+ cells occur simultaneously; coinciding with rapid resolution of the primary tumor, lymph node metastases and ascites. These findings suggest that OBT076 activates the patient’s immune response against the tumor through a potentially novel mechanism: drug-induced depletion of CD8+ CD205+ immuno-suppressive cells and subsequent T-cell activation. Additionally, our data support the use of immune checkpoint inhibitors in conjunction with OBT076 to achieve favorable clinical outcomes.

Citation Format: Christian Rohlff, Solmaz Sahebjam, Alain Mita, Rosen Lee, Chander Sekhar Peddaboina, Arnima Bisht, Lindsey Hudson, Wolf Fridman, Abderrahim Fandi, Olivier Rixe. Potential novel Immuno-oncology mechanism revealed during translational phase I Immuno-blood profiling of experimental ADC medicine OBT076 in a gastric cancer patient [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1975.

Abstract 5167: Identification and validation of a novel immuno-oncology target and selection of a therapeutic antibody candidate with a pharmacologically beneficial activity profile

Identification of novel targets in cancer immunotherapy is needed to address the significant number of patients that either do not respond to current therapies or encounter unacceptable toxicities. The first two generations of immuno-oncology drugs have been antagonist antibodies against immune checkpoint proteins, such as cytotoxic T lymphocyte protein 4 (CTLA-4) and programmed cell death protein 1 (PD-1). Moving forward, there has been progress in targeting co-stimulatory receptors like inducible T cell co-stimulator (ICOS), OX40 and CD137 with agonist antibodies. At Oxford BioTherapeutics, in-depth expression profiling of membrane proteins from intact tumors collected in the proprietary OGAP database revealed novel IO targets in primary tumor-derived lymphocytes (TILs). Proteomic and flow cytometry analysis of TILs and PBMCs establish that OX003R is a novel co-stimulatory IO target. It is expressed on naïve T and B cells; however, higher expression is observed in TILs and activated or exhausted T cells. OX003R expression is observed by immunohistochemistry in infiltrating lymphocytes in a variety of solid tumor types. A Fab phage display library was screened by FACS for binding to target on the cell surface. All the Fabs were also profiled by an interferon gamma release assay for T cell activation. Five best binders demonstrating T cell activation were reformatted into full-length chimeric mAbs and expressed in mammalian Expi 293 cells. Recombinant antibodies were extensively screened for T cell activation in an ex vivo 3D tumor culture system developed in-house using fresh non-small cell lung and colorectal carcinomas. Interferon gamma release was assessed by ELISpot assay and expression of the target was confirmed by immunohistochemistry on the corresponding tumor samples. Chimeric antibody 1B3 robustly activated T cells in most of the tumor samples in a dose-dependent manner as compared to isotype control and was chosen as the lead therapeutic antibody for humanization. The lead therapeutic antibody was tested for the propensity to facilitate the undesirable cytokine storm in whole blood and did not induce the release of dangerous levels of cytokines.

Conclusion: OX003R is a validated immuno-oncology target and chimeric 1B3 is being developed as a promising therapeutic antibody with agonistic TIL activity, specifically in the tumor microenvironment.

Citation Format: Arnima Bisht, Angelo Kaplan, Livija Deban, Chander Sekhar Peddaboina, Murray Cox, Lindsey Hudson, James Ackroyd, Nickolas Attanasio, San Lin Lou, Jason Allen, Martin Barnes, Robert Boyd, Eugene Zhukovsky, Abderrahim Fandi, Christian Rohlff. Identification and validation of a novel immuno-oncology target and selection of a therapeutic antibody candidate with a pharmacologically beneficial activity profile [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 5167.