Enhancement of tumorigenic potential in virgin mice of a pregnancy-dependent mouse mammary tumor (TPDMT-4) by enzymatic cell dissociation

Abstract

The transplantable pregnancy-dependent mouse mammary tumor line TPDMT-4 behaves like a preneoplastic lesion in virgin mice when implanted with tissue pieces. This study was conducted to elucidate whether enzymatic cell dissociation enhances the tumorigenic potential as in hyperplastic mammary nodules. When tissue pieces were implanted in virgin mice, there was an increase in tumor incidence from 0% at generation 14 (F14) to 40% at 38 (F38) during the 6-month observation; early (F8), middle (F16-18) and late (F39-40) transplant generation (ETG, MTG and LTG respectively) tumors were dissociated with collagenase and hyaluronidase. DDD strain females receiving an injection of 10(5) dissociated cells into the fat pad were observed as virgin or ovariectomized. ETG cells formed palpable tumors in 18 (43%) and 21 (50%) of 28 virgins at latent periods of 133 +/- 11 (mean +/- SE) and 142 +/- 10 days for 6 and 8 months respectively. MTG and LTG cells did so in 24 (60%) of 40 and 25 (89%) of 28 virgins at 77 +/- 5 and 68 +/- 5 days respectively for 6 months. In ovariectomized mice, however, no palpable tumors developed from any of these cells. Most ETG and MTG cell-derived tumors repeated palpable growth and total regression one or more times, and subsequently disappeared or grew slowly, whereas almost all LTG tumors grew progressively from the onset. MTG cells infiltrated into the fat pad more extensively than ETG and LTG cells: MTG cells occupied almost the whole fat pad at 6 weeks, whereas the outgrowths of the other cells were confined to one-eight of the fat pad. Southern blot analyses demonstrated the absence of certain extra MMTV DNA fragments in MTG tumors, although the distinct behaviors of MTG cells could not be ascribed to it alone. The results suggest that enzymatic cell dissociation may enhance tumorigenesis by hormone-dependent mammary tumor cells at lower hormone levels.