Identification of Linoleic and Arachidonic Acids as the Factors in Hyperlipemic Blood That Increase [3H]Thymidine Incorporation in Hepatoma 7288CTC Perfused in Situ1

Tumor growth and the incorporation of |'H]thymidine into tumor DNA in vivo are increased about 3 times in adult rats (greater than 250 g) after 1 to 2 days of starvation or the induction of diabetes with streptozotocin. These tumor growth responses require hyperlipemia and are reversed by refeeding or insulin treatment, respectively. They do not occur in young tumor-bearing rats (less than about 150 g) that lack appreciable fat stores. A direct relationship between the increased rates of both |-'H)thy midine incorporation and tumor growth and host hyperli pemia suggests that tumor cell renewal in vivo in fed rats is limited by substances that are present in hyperlipemic blood. In this study we used a procedure for perfusion of solid tumors in situ to measure the sensitivity of tumor [3H]thymidine incorporation to hy perlipemic blood and to identify the rate-limiting substances. Tissueisolated Morris hepatomas (7288CTQ growing in young or adult Buffalo rats were perfused with blood from donor rats. Hyperlipemic blood for perfusion was obtained from 2-day starved tumor-bearing (Buffalo) or non-tumor-bearing (Buffalo or Lewis) rats. At the end of the perfusions the tumors were labeled with a pulse of |'H|th>midinc (2 pCi/g estimated tumor wet weight). | 'H]Thymidine incorporation in tumors growing in fed adult rats was increased from 80 ±5 (SD) dpm/Mg DNA at zero time (before perfusion) to 209 ±9 dpm/Mg DNA (n = 3) after perfusion for 3 h. Tumors growing in fed or starved young rats showed similar responses, and hyperlipemic blood from non-tumor-bearing rats was as effective as hyperlipemic blood from tumor-bearing rats. Perfusion of tumors growing in starved rats with normolipemic blood from fed adult rats decreased | 'H)thymidinc incorporation from 211 ±13 dpm/Mg DNA before perfu sion to 68 ±9 dpm/Mg DNA (n = 3) after perfusion for 3 h. Cells, plasma, and plasma subfractions from hyperlipemic blood were reconstituted to whole blood using plasma, cells, and whole blood, re spectively, from fed rats and the mixtures were perfused into tumors growing in fed adult rats. Mixtures containing hyperlipemic plasma, lipid extracts (ethanol:acetone, 1:1) of hyperlipemic plasma, or albumin from hyperlipemic plasma increased tumor |3H]thymidine incorporation. Free fatty acid concentrations were increased about five times in hyperlipemic plasma and perfusion of tumors with normolipemic blood containing added linoleic and arachidonic acids increased [3IIJthymidinc incorpora tion. Blood mixtures containing palmitic, stearic, and oleic acids were inactive. We conclude that linoleic and arachidonic acids are rate limiting for ('I I|th>nudine incorporation in tumors growing in young and adult