Figure 6.

Retinoic acid inhibits tumor formation and the symptoms of Cushing syndrome. AtT-20 cells were treated with vehicle (a) or 10 nM retinoic acid (b) for 3 hours and then injected into nude mice. (a and b) Representative examples of the mice after 5 weeks (n = 10 in each treatment). Notice the 12-mm-diameter tumor developed by vehicle-treated cells (a). Thinning of the skin was consistently observed in mice with tumors (a). (c–j) Mice with tumors were injected intraperitoneally with 10 mg/kg retinoic acid or vehicle (n = 5 in each experiment) every 4 days for 3 weeks. At the end of the treatment the tumors (c and d) (arrows indicate areas of necrosis), adrenal glands (e–g), and skin samples (h–j) were shock-frozen and analyzed by hematoxylin-eosin staining. Adrenals (e) and skin (h) from vehicle-treated mice without tumors. Tumor (c), adrenals (f), and skin (i) from vehicle-treated mice with tumors. Tumor (d), adrenals (g), and skin (j) from retinoic acid–treated mice with tumors. These results are representative of two independent experiments.