Cell surface antigens in a rat colon cancer model: correlation with inhibition of tumor growth

Chemically induced bowel tumors in Wistar/Furth (W/F) rats possess surface antigens analogous to those demonstrated in humans with colon carcinoma. To determine if these in vitro tumors markers have any in vivo significance, tumor isograft challenge experiments were performed. Groups of animals received three immunizing doses of 10(7) cells from chemically induced colon carcinomas NG-W1, DMH-W49, or DMH-W9 or small-bowel adenocarcinoma DMH-W7. Control rats were immunized with a noncross-reacting, virally induced mammary fibroadenoma A9-W1. Six weeks after immunization, all animals were challenged with 1 X 10(5) or 3 X 10(4) colon carcinoma NG-W1 cells. None of the NG-W1-immunized animals developed tumors after either NG-W1 challenge dose. In contrast to this strong protection by "private" tumor rejection antigen (TRA), protection by common or "tissue type specific" antigens was evident only if tumor volumes were measured. Twenty-two days after low-dose NG-W1 challenge, mean tumor volume (m) in animals immunized with colon tumor DMH-W9 (m=0.25 cu cm) and DMH-W49 (m=0.17 cu cm) were less (p less than 0.05) than in animals untreated (m=1.0 cu cm) or immunized with mammary fibroadenoma A9-W1 (m=0.9 cu cm). Embryonic antigens also may function as weak TRAs. NG-W1 challenge tumor volumes in fetal-gut-immunized (m=0.9 cu cm) and whole embryo-immunized animals (m=0.9 cu cm) were less (p less than 0.05) than in fetal-kidney-immunized (m=2.5 cu cm) or adult-colon-immunized animals (m=1.8 cu cm). Low-dose NG-W1 challenge tumor volumes were less (p less than 0.01) in multiparous females (m=0.3 cu cm) than in either untreated (m=1.2 cu cm) or age-matched virgins (m=1.4 cu cm). In vitro tumor markers in this model may serve an important function in vivo as TRAs.