Cytochemical Effects of 5-Fluorouracil on Sensitive and Resistant Ehrlich Ascites Tumor Cells*

5-Fluorourac i I was d e v e l o p e d b y H e i d e l b e r g e r , D u s c h i n s k y , a n d associa tes (10, 14). I t was s h o w n by H e i d e l b e r g e r et ol. t h a t 5f luorourac i l (5 -FU) inh ib i t s t he g r o w t h of t r a n s p l a n t e d t u m o r s in r a t s a n d mice (14). I n cl inical t r ials , r egress ion of s o m e h u m a n cancer s a f t e r t r e a t m e n t w i t h 5 F U has b e e n r e p o r t e d (7). One of t h e b iochemica l effects of th i s series of f l uo r ina t ed p y r i m i d i n e s was t h e inh ib i t i on of d e o x y r i b o n u c l e i c ac id ( D N A ) syn thes i s b y b lock ing t h e f o r m a t i o n of t h e m e t h y l g r o u p of t h y m i n e (1, 4, 8, 14, 15). Quantitative histochemical studies of tumor cells treated with 5-FU were made to a t tempt a correlation of histochemical results with biochemical findings and to study the morphology of these tumor cells after such treatment. Preliminary findings were reported earlier (23).