The secretory granule peptides 7B2 and CCB are sensitive biochemical markers of neuro‐endocrine bronchial tumours in man

Abstract

Bronchial tumours are the most frequent cause of the ectopic ACTH syndrome. Two types of tumours are classically responsible: the relatively benign carcinoids and the highly aggressive small cell carcinomas. Both have neuro-endocrine features and are thought to originate from the endocrine component of the bronchial tree. Our objective was to assess the sensitivity of 7B2 and secretogranin 1 as new biochemical markers of neuro-endocrine differentiation in these tumours in comparison with gastrin releasing peptide. Tissue concentration of 7B2, secretogranin 1 fragments (GAWK and CCB), gastrin releasing peptide and beta-endorphin were measured in normal human lung (n = 4), bronchial carcinoid tumours with (n = 5) and without (n = 15) the ectopic ACTH syndrome, small cell carcinomas (n = 2), squamous cell carcinomas (n = 11) and adenocarcinomas (n = 6). Molecular weight forms of immunoreactive--ACTH, -GAWK, -gastrin releasing peptide, and -7B2 were also examined using gel exclusion chromatography and Western blot analysis. We detected 7B2 immunoreactivity in 19 of 22 neuro-endocrine lung tumours (with values ranging from less than 5 to 555 fmol/mg wet weight tissue), CCB immunoreactivity in 20 of 22 tumours with neuro-endocrine features (with values ranging from less than 5 to 19,875 fmol mg wet weight tissue) and gastrin releasing peptide immunoreactivity in 10 of 22 neuro-endocrine lung tumors (with values ranging from less than 5 to 11,132 fmol/mg wet weight tissue). Immunoreactive 7B2 and CCB were detected neither in tumours with non-endocrine features, nor in the four normal lung specimens. Differing molecular weight forms of immunoreactive 7B2 in two bronchial carcinoids associated with the ectopic ACTH syndrome showed a predominant signal corresponding to a molecular weight of 22 kDa; in addition, a second signal of 19 kDa was also present. The differing molecular weight forms of immunoreactive ACTH related peptides in the five tumours responsible for the ectopic ACTH syndrome showed, in addition to ACTH1-39, the constant presence in variable proportions of corticotrophin-like intermediary lobe peptide (or ACTH18-39). The differing molecular weight forms of immunoreactive GAWK showed heterogeneous results with materials eluting at Kav of 0, 0.3 and 0.4 respectively. In the three bronchial carcinoids studied, two immunoreactive gastrin releasing peptide molecular weight forms were always found at Kav of 0.5 and 0.85 corresponding to gastrin releasing peptide and its fragment 14-27 respectively. Our results show that 7B2 and the two fragments of secretogranin 1 (GAWK and CCB) are the best biochemical markers of neuro-endocrine differentiation in human lung tumours.