Enhanced cloning efficiency of murine rhabdomyosarcoma cells after chlorozotocin treatment: relationship with enhanced lung metastasis

The effect of chlorozotocin [(CZT) CAS: 54749-90-5; 2-(3-(2-chloroethyl)-3-nitrosoureido)-D-gluco-pyranose] was studied on a series of tumor cells, cultured or extracted fresh primary or transplanted tumors, by means of clonogenic assay. The ability of most rat rhabdomyosarcoma cells to form colonies in soft agar was enhanced when exposed to the water-soluble nitrosourea chloride CZT. The tumor cells tested were derived from a) several primary tumors induced in WAG rats by colloidal nickel, then cultured and exposed to CZT early during in vitro passage; b) the 9-4 tumor, also Ni-induced but maintained in long-term culture; and c) the Ni-induced 9-4/0 tumor, maintained by transplantation in syngeneic rats. No inhibition of colony formation was observed in any of the cell lines even at high concentrations of CZT. Adriamycin, chosen as a control treatment, strongly inhibited the cloning efficiency (CE) of the tumor cells. In vivo, the weekly injection of 10 mg CZT/kg body weight into syngeneic rats bearing transplanted tumors led to an enhancement of lung metastasis formation. The CZT enhancement of CE of tumor cells and its relationship to increased in vivo tumor metastasis is discussed.