Analysis of expression of TGF-β1 receptor (ALK-1) in normal and tumor tissues by tissue microarrays

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e22044 Background: TGF-β1 is an important angiogenic factor involved in different aspects of angiogenesis and vessel maintenance. TGF-β1 receptors consist of class I, class II and accessory receptors. Activin-like kinase I (ALK-1) is a class I TGF- β1 receptor which is almost exclusively expressed on endothelial cells. Hereditary hemorrhagic telangiectasia (HHT) is caused by mutations in the ALK-1 gene. Knock-out mice for ALK-1 die during gestation due to vascular malformation. ALK-1 may thus represent an attractive target for anti-angiogenic therapy. A therapeutic monoclonal antibody (PF-03446962) against ALK-1 has been developed which is currently in phase I testing. Here we describe target validation in normal and tumor tissue using tissue micro-arrays (TMAs). Methods: Normal tissue arrays comprised of 609 individual histological samples representing 76 human tissues. Multi-tumor arrays consisted of 3923 individual tumor samples from 87 tumor types. Consecutive sections of tissue arrays were stained for ALK-1 and CD31. CD31 immunohistology (IHC) was performed to ensure presence of vessels within tissue samples. ALK-1 staining was graded 0=absent, 1=weak, 2= moderate and 3=strong by an experienced pathologist blinded to tissue type. Results: ALK-1 staining of vessels in normal tissues was generally weak (mostly grade 1 and rarely grade 2) and was detectable in lymphatic tissues including tonsil, lymph nodes, thymus and spleen, lung, the entire GI tract including parotid, submandibular and sublingual glands as well as pancreas. ALK-1 positive vessels were also found within the female genital tract including placenta, uterus and ovary. In human tumor vessels ALK-1 expression showed high variability between tumor types. The highest ALK-1 expression rate was found in lung cancer (NSCLC 49%, SCLC 83%), neuroendocrine pancreas tumor (71%), colon cancer (50%), chondrosarcoma 50%, angiosarcoma 40% and NHL (44%). Conclusions: TMAs are an excellent tool to verify target expression in normal and tumor tissues. Results may be used to predict side effects of targeted therapy and to direct phase II testing of innovative agents in patients likely to respond. [Table: see text]