Effects of physiological oxygen environment on drug-induced cell lethality of multicellular tumor spheroids from human lung cancer.

Advanced malignant tumors of certain histological types contain a hypoxic and necrotic core. Multicellular tumor spheroids (MTS) have the characteristics of chronically hypoxic cells in the center. We studied the effects of physiological oxygen environment on MTS growth and the cell lethality produced by doxorubicin (DXR) and cisplatin (DDP). MTS were made from 2 human lung cancer cell lines; PC-6 small cell and PC-10 squamous cell carcinoma, and grown for 2, 3 or 4 weeks; either in 5% CO2/air or 5% 02/5% CO2/90% N2. They were exposed to graded concentrations of DXR for 1 hr and cell lethality was determined by clonogenic assay. In the physiological oxygen environment MTS growth was retarded for both cell lines. PC-6 MTS grown in physiological oxygen environment were more sensitive to DXR than those developed in air. The differential sensitivity was most pronounced with the 2 week old MTS and gradually narrowed with increasing MTS size. In contrast, PC-10 MTS developed in the physiological oxygen environment were more resistant to DXR than those in air; the differences were again most pronounced in 2 week old MTS. There were little differences in cell kill effects of DDP, irrespective of cells being in monolayer or in MTS and growing in air or in physiological oxygen environment. These observations are consistent with the interpretation that cells in PC-6 MTS are scarcely affected by the physiological oxygen environment but easily affected by DXR, whereas cells in PC-10 MTS responded vice versa.