Inhibition of macromolecular synthesis in tumors by L-1-tosylamido-2-phenylethyl chloromethyl ketone.

L-1-tosylamido-2-phenylethyl chloromethyl ketone was observed to inhibit the incorporation of ³H] amino acids into protein and ³H] thymidine incorporation into DNA in Novikoff hepatoma ascites cells $\text{in vitro}$ Similar effects were seen with several Morris hepatomas and a transplanted colon tumor in rats, and were accompanied by decreased uptake of isotope into acid soluble tissue fractions. Under the same conditions, there was no significant inhibition in regenerating liver and there was an increased uptake of ³H] amino acids in the livers of normal and tumor bearing rats.