Effect of retinoic acid on the growth and morphology of a prostatic adenocarcinoma cell line cloned for the retinoid inducibility of alkaline phosphatase.

Cells derived from the G-subline of the Dunning R-3327 rat prostatic adenocarcinoma were selected on the basis of their inducibility for alkaline phosphatase (AP) activity by retinoic acid. A p-nitrophenylphosphate-agarose overlay procedure was used to identify AP-inducible clones. The frequency of AP-inducible cells in one rapidly growing tumorigenic clone, designated 9-1C, has remained at 100% during at least 4 months of continuous culture. In culture, 9-1C cells had a mean population-doubling time in log phase of 14 hr. Retinoic acid (10 microM) did not significantly affect the rate of growth in log phase. It did, however, cause the cultures to saturate at a cell density which was 40% lower than that of control cultures. This effect on saturation density was reversible within 24 hr after removing retinoic acid from the medium. Retinoic acid-treated cells occupied greater areas on the culture dish surface, and the cross-sectional area of these cells, measured on dispersed cells by light-scatter flow cytometry, was 35 to 40% greater than that of control cells. The inducibility of 9-1C cells for AP activity decreased as the culture density increased. Cells of the 9-1C clone produced tumors when injected into male and female Fischer X Copenhagen F1 rats. No histological differences were detected between tumors grown in male and female rats. Although the tumors were poorly differentiated, primitive acinar-like structures were observed. Cells staining uniformly positive for AP activity were distributed randomly throughout the tumors. In the acinar-like structures, AP activity was localized only on the apical surfaces of the cells lining the lumens. This was also the site of enzyme activity in acini of the lateral component of the dorsolateral prostate, the source of the original R-3327 tumor. In the lateral prostatic component, AP activity was also found in the basal region of the acini, and the secretory material filling the lumens was strongly positive for the enzyme. These two regions of the tumor acini were negative for AP activity. With the exception of activity in capillaries at the basal surface, the acini of the dorsal component of the dorsolateral prostate were devoid of AP activity.