Early changes accompanying development of adriamycin resistance in spheroids of a mouse mammary carcinoma line.

The early changes accompanying development of ADR resistance were studied in a mouse mammary adenocarcinoma cell line sensitive to ADR (S). Resistant cells (R) were derived from S by five separate exposures to 1 microgram/ml ADR for 1 hr. The R cells had a 3-fold increased resistance to ADR, a higher proportion of larger cells, higher numbers of chromosomes per cell and higher incidence of minute chromosomes. R spheroids had a higher degree of differentiation. They were more compact, had increased numbers of gap-junctions, and altered membranes. An inversion in the X chromosome in S cells was corrected in the R cells.