CHANGES IN GROWTH, PO(2) AND PH AFTER EXPOSURE TO OXAMATE - STUDIES OF 2 HUMAN TUMOR-CELL LINES GROWING AS MULTICELLULAR SPHEROIDS

The basic metabolism and pO(2) and pH gradients in spheroids were char acterized and, in some cases, changed by the addition of the pyruvate analogue oxamate. Two human tumour spheroid types, colon adenocarcinom a HT29 and malignant glioma U118MG, were applied as models. Microelect rode measurements in HT29 spheroids showed steep pO(2) gradients with large differences between surface and center, Delta pO(2), and low cen tral pO(2) values. The HT29 spheroids had rather flat pH gradients. Th e U118MG spheroids had less steep pO(2) gradients but steeper pH gradi ents. Determinations of 1-C-14 and 2-C-14 pyruvate oxidation rates, fo r characterization of the oxidative glucose breakdown as well as of la ctate dehydrogenase kinetics, showed consistent results with the micro electrode measurements in that there was high oxidative metabolism in the HT29 spheroids whereas the U118MG spheroids relied more on glycoly sis. Western blot investigations of the LDH isoenzyme composition show ed different isoenzyme patterns in the two spheroid types with a lack of LDH1 in U118MG spheroids. Addition of 40 mM of oxamate gave decreas ed 1-C-14- and 2-C-14-pyruvate oxidation rates in the HT29 cells and i nhibition of LDH activity in the U118MG cells. Oxamate increased the c entral pO(2) values in HT29 spheroids and the central pH values in U11 8MG spheroids. One example of experimental therapy was applied and oxa mate acted as a radiation sensitizer in the U118MG system and as a rad ioprotective substance in the HT29 system. This has to be analysed in more detail.