Heterogeneous responses of human colon carcinomas to hexamethylene bisacetamide

Primary cultures of resected human colon carcinoma were used to study differentiation agents directly on the biologically relevant cancer cells rather than on highly selected established cell lines. To achieve primary cultures which remained viable and replicating for several days, carcinomas were partly digested to epithelial organoids, which were selectively plated with high efficiency on collagen I-bovine serum albumin films in specially formulated serum-free medium. A monoclonal antibody, 29-15, was identified which binds to a cell surface epitope expressed on 16 of 21 invasive colon carcinomas of the Dukes' B2, C, or D histopathology classes, but not expressed on any of 11 noninvasive benign tumors (adenomas) at identical antibody titer. Noncytotoxic concentrations of the differentiation agent, hexamethylene bisacetamide (HMBA), induced the loss of the 29-15 epitope from HT29 colon carcinoma cells. HMBA also induced HT29 cells to lose the capacity for anchorage-independent growth with a similar dose-response curve and time course to the loss of 29-15 epitope. Twelve primary cultured human colon carcinomas exhibited differential responses when exposed to 1 to 7 mM HMBA for 7 days. Four moderately to well-differentiated carcinomas lost expression of the 29-15 epitope at each HMBA concentration. The tumor growth fraction was decreased in each tumor, with a mean decrease of 76% at 5 mM HMBA. A dose-dependent induction of nonproliferating tumor colonies, lacking [3H]thymidine labeling, occurred in three of the four carcinomas. In six other tumors, including those at less differentiated stages, HMBA induced the opposite effect: a two- to threefold increase in the tumor growth fraction at the optimal value of 5 mM HMBA, an increase in mean colony size, and no loss of the 29-15 malignancy epitope. No effects were observed in the two other carcinomas tested. Thus HMBA was able to induce growth arrest and loss of the malignancy epitope 29-15 in those carcinomas already at an advanced stage of differentiation, and to exert a growth stimulating effect on those carcinomas apparently at more immature stages.