A pentapeptide with analgesic activity has been isolated from human lung squamous cell carcinoma and from three other types of propagated tumors of human lung small-cell carcinoma (SCC), adenoma (AD) and large-cell carcinoma (LCC) in nude mice. The amino acid sequence of the peptide has been revealed to be H-Thr-Ser-Lys-Tyr-Arg-OH, which is exactly the same as that of neo-kyotorphin, an analgesic peptide originally isolated from bovine brain [(1982) Life Sci. 31, 17331. No neo-kyotorphin could be isolated from normal lung tissue using the same procedures as those used for carcinomas. The results suggest that the presence of neo-kyotorphin in the lung carcinoma may represent the ectopic expression of peptide hormone.Our findings constitute the first example of a human lung carcinoma producing analgesic peptide.

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A biologically active peptide designated hLCP has been isolated and purified to homogeneity from human lung carcinoma by means of acidic extraction and successive chromatography on Sephadex G-50, Toyopearl HW-40 F and reverse-phase high performance liquid chromatography columns. Analysis showed that peptide consists of thirteen amino acids. Primary structure of hLCP has been deduced by double-coupling Edman degradation combined with enzyme digestion as H-Ser-Pro-Pro-Asp-Gly-Lys-Lys-Glx-Ser-Ala-Asp-Val-Lys-OH. hLCP possessed significant excitatory activity on an electrical stimulation induced contraction. No hLCP could be detected in normal lung tissue. The possibility of using hLCP as a biochemical marker in the clinic for the early detection of lung carcinoma is being investigated.