Polyamine depletion of the MTW9 mammary tumor and subsequent elevation of spermidine in the sera of tumor-bearing rats as a biochemical marker of tumor regression.

Polyamine levels were measured in livers, tumors, sera, and tumor interstitial fluids of rats with growing mammary tumors, as well as in rats at various times after the initiation of tumor regression obtained by hormonal deprivation. Although there were traces of putrescine and spermine in the sera of tumor-bearing animals, spermidine was the only polyamine that could be found consistently in measurable amounts. Decreases in both liver and tumor levels of spermidine parallel the elevation of spermidine in the serum. The period of maximal tumor regression, i.e., within 48 hr of removal of hormonal support, corresponds with the time of the highest levels of spermidine in serum and in tumor interstitial fluid. These data indicate that intracellular spermidine levels, which increase during tumor growth, are lowered by excretion during regression and that spermidine levels in the serum reflect tumor cell death.