Growth status significantly affects the response of human lung cancer cells to antitumor polyamine-analogue exposure

Human solid tumors frequently have a relatively small growth fraction, which interferes with the action of many chemotherapeutic agents that target actively cycling cells. Several polyamine analogues are currently being developed for clinical application against human solid tumors including N¹, N¹¹-bis(ethyl)norspermine. Therefore, an effort was made to examine the effects of growth rate on polyamine-analogue efficacy. Low growth fraction (LGF) cell cultures of the human non-small cell lung cancer cell line NCI-H157 were generated to partially mimic solid tumors with low mitotic indices. Log-phase cells were compared with LGF cells with respect to cell survival and biochemical effects after exposure to polyamine analogues. The results demonstrate generally that LGF NCI-H157 cells were sensitive to analogue treatment. However, the dose necessary to elicit a response in LGF cells was an order of magnitude higher than the dose needed in log-phase cells. Additionally, the biochemical effects of analogues were similar between log phase and LGF cells with regard to a down-regulation of polyamine biosynthesis as measured by ornithine decarboxylase activity and an increase in polyamine catabolism as indicated by an increase in spermidine/spermine N¹-acetyltransferase activity. However, biochemical effects were less dramatic in the LGF cells than those observed in the log-phase cells. The overall results of these studies suggest that the growth status of solid tumors can significantly affect the response to antitumor polyamine analogues, and growth fraction must be considered in the continued development and use of the polyamine analogues.