CEA, EpCAM, αvβ6 and uPAR Expression in Rectal Cancer Patients with a Pathological Complete Response after Neoadjuvant Therapy

Rectal cancer patients with a complete response after neoadjuvant therapy can be monitored with a watch-and-wait strategy. However, regrowth rates indicate that identification of patients with a pathological complete response (pCR) remains challenging. Targeted near-infrared fluorescence endoscopy is a potential tool to improve response evaluation. Promising tumor targets include carcinoembryonic antigen (CEA), epithelial cell adhesion molecule (EpCAM), integrin αvβ6, and urokinase-type plasminogen activator receptor (uPAR). To investigate the applicability of these targets, we analyzed protein expression by immunohistochemistry and quantified these by a total immunostaining score (TIS) in tissue of rectal cancer patients with a pCR. CEA, EpCAM, αvβ6, and uPAR expression in the diagnostic biopsy was high (TIS > 6) in, respectively, 100%, 100%, 33%, and 46% of cases. CEA and EpCAM expressions were significantly higher in the diagnostic biopsy compared with the corresponding tumor bed (p < 0.01). CEA, EpCAM, αvβ6, and uPAR expressions were low (TIS < 6) in the tumor bed in, respectively, 93%, 95%, 85%, and 62.5% of cases. Immunohistochemical evaluation shows that CEA and EpCAM could be suitable targets for response evaluation after neoadjuvant treatment, since expression of these targets in the primary tumor bed is low compared with the diagnostic biopsy and adjacent pre-existent rectal mucosa in more than 90% of patients with a pCR.

Abstract 291: Synergistic inhibition of cancer invasion and metastasis by combined anti-PD1-TRC105-mediated Endoglin targeting on cancer-associated fibroblasts and endothelial cells

Cancer-associated fibroblasts (CAFs) are the major component of the tumor microenvironment in colorectal cancer (CRC) and play an important role in tumor progression and metastasis, partly through the transforming growth factor-β (TGF-β) signaling pathway. Recently, we showed that a subset of CAFs characterized by the expression of the TGF-β family co-receptor endoglin, selectively localized at the invasive borders of CRC tissues. Moreover, CAF-specific endoglin expression increased with higher tumor stage and predicted metastasis-free survival of stage-II CRC patients (n= 140, p&lt;0.05). Targeting endoglin on CAFs using TRC105 (carotuximab), an endoglin neutralizing antibody currently in clinical development, inhibits endoglin dependent signaling and metastatic colonization when CRC cells and CAFs are co-injected into mice. We further investigated these anti-tumor effects in four different models of CRC (chemically-induced model of early CRC, subcutaneous MC38 and CT26 syngeneic mouse CRC models, and orthotopic MC38 model). TRC105 treatment inhibited tumor initiation (early stage CRC), growth, and progression. Therapeutic effects of TRC105 therapy were dependent on antibody dependent cytotoxicity (ADCC) and CD8+ T-cells, as no therapeutic benefit from TRC105 was observed in Fc-y I-IV receptor knockout mice or CD8+ cell depleted mice. Since therapeutic TRC105 activity was immune cell dependent, we combined TRC105 with anti-programmed cell death (PD-1 immunotherapy). We observed synergistic inhibition of tumor initiation and growth in all four tumor models, leading to delayed tumor outgrowth, increased survival and cure rates up to 60% in the combination treated mice bearing palpable tumors. Combined treatment also induced memory responses, as shown by resistance to repeated tumor challenge. Anti-tumor responses were accompanied by enhanced immune cell activation including an increased number of tumor-specific T-cells, NK cells, decreased number of tumor-infiltrating neutrophils and increased granzyme B production. CD8+ cytotoxic T-cells were instrumental in these synergistic therapeutic responses, as their depletion abolished the effects. Taken together, our data indicate significant therapeutic effects of targeting endoglin by affecting signaling and multiple immune related components in the tumor microenvironment. These results are currently being translated in a clinical trial combining TRC105 with nivolumab in patients with non-small cell lung cancer (NCT03181308).

Citation Format: Mark JA Schoonderwoerd, Madelon Paauwe, Ricardo Angela, Maaike Koops, Tom Harryvan, Cornelis Sier, Marieke Fransen, Charles Theuer, Lukas JAC Hawinkels. Synergistic inhibition of cancer invasion and metastasis by combined anti-PD1-TRC105-mediated Endoglin targeting on cancer-associated fibroblasts and endothelial cells [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 291.

Correlation of glutathione S-transferases with overall survival in patients with gastric carcinoma

Glutathione S-transferases (GST) are enzymes involved in the detoxification of xenobiotics and are divided into four subclasses, Alpha, Mu, Pi, and Theta. Most human gastrointestinal tumors contain increased amounts of GST Pi and GST enzyme activity. The relationship between GST parameters and tumor and patient characteristics, including overall survival, were studied retrospectively in normal and malignant gastric tissue from 49 patients with primary gastric carcinoma. Twelve patients (24%) were alive at the end of the study with a mean follow-up time of 4.1+/-0.4 years. Levels of GST Alpha, Mu, Pi and GST enzyme activity were not related to tumor stage, localization and diameter of the tumor, number of eosinophils in the tumor, presence of intestinal metaplasia in normal gastric mucosa, or gender and age of the patient. Optimal dichotomization and uni- and multivariate analyses were done with the Cox proportional hazard model. None of the clinicopathological parameters were associated with survival, except the number of eosinophils in the tumor. In contrast, high levels of GST Pi in both normal mucosa (Hazard ratio 3.0, p=0.02) and in gastric carcinoma (HR 2.2, p=0.05) and the presence of GST Mu in normal (HR 0.4, p=0.05) and malignant (HR 0.3, p=0.009) gastric tissue were found to have a significant prognostic value, independent from the clinicopathological parameters, when added separately to a Cox model. In conclusion, the levels of GST Mu and Pi in both normal or carcinomatous gastric tissue have an independent prognostic impact on overall survival.

High performance density gradient electrophoresis of subcellular organelles, protein complexes and proteins

A density gradient electrophoresis (DGE) apparatus (2.2 x, 14 cm) was constructed for the rapid separation of milligram quantities of proteins. By using binary buffers according to Bier (Electrophoresis 1993, 14, 1011-1018) proteins were rate-zonally separated in less than 60 min. Acidic proteins were separated in a pH 8.6, 56 microS/cm buffer, and basic proteins in a pH 5.4, 76 microS/cm buffer. Thus the A (pI 5.15) and B (pI 5.30) forms of beta-lactoglobulin as well as the sialylated glycoforms of apotransferrin were well separated at pH 8.6. The isoforms of myoglobin (pI 6.9 and 7.35, respectively), RNAse A (pI 9.45) and cytochrome c (pI 10.0) and lysozyme (pI 11) were separated at pH 5.4 within 80 min. On a 7 cm DGE column, subcellular organelles derived from HeLa cells were separated in standard electrophoresis buffer (655 microS/cm) for 90 min at 10 mA. Using a new low conductivity buffer (193 microS/cm) 20 min was sufficient to separate late endosomes, lysosomes, endoplasmic reticulum, early endosomes, plasma membrane, clathrin-coated pits, proteasomes, and clathrin-coated vesicles within a single run directly from a postnuclear supernatant.