Cystacyclin, a novel microbial metabolite with NGF mimetic activity

Nerve growth factor (NGF) is known to have key roles in neural protection and repair of central and peripheral neurons.¹ NGF was reported to ameliorate several neuronal dysfunction and injury in animal models,^{2, 3} and has been applied to clinical trial.⁴ Because of its protein property, NGF is thought unsuitable for oral administration and insufficient for blood–brain barrier penetration. So far low-molecular-weight compounds having NGF mimetic activity have been screened and neurite-inducing compounds such as lactacystin⁵ and K-252a⁶ were isolated from microbial resources. A chemically synthesized compound of AIT-012 was reported to enhance NGF-induced neurite outgrowth and has been applied to clinical trail.⁷ In this report we describe isolation of a novel NGF mimetic compound and show its physico-chemical properties and biological activities of the compound named as cystacyclin.

Rat pheochromocytoma cell line of PC12 was known to form neurite in response to NGF. For screening PC12 cells were inoculated into 96-well microplate and microbial cultured broths were applied. After 2 days incubation, neurite formation of the cells was observed visually with microscope. From about 30 000 microbial cultured broths, 40 positive samples were selected. Human leukemia cell line of TF-1 was known to proliferate dependently on the factors such as NGF, granulocyte macrophage colony-stimulating factor or interlukin-3 in the medium.⁸ TF-1 cells were washed three times with the factor-deficient medium and inoculated into 96-well microplate with the same medium. The 40 samples selected in the PC12 cell assay were applied to the TF-1 cells and cellular proliferation was monitored with ³H-thymidine uptake activity. As a result, one positive sample that elicited the uptake activity was selected and a producing microbial strain was assigned to Streptomyces endus.

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