DIFFERENTIAL INDUCTION OF APOPTOSIS BY ALL-TRANS-RETINOIC ACID AND N-(4-HYDROXYPHENYL)RETINAMIDE IN HUMAN HEAD AND NECK SQUAMOUS-CELL CARCINOMA CELL-LINES

Retinoids have been shown to act as cytostatic agents against a variet y of tumor cell types, including squamous carcinoma cells, Recently it was reported that certain retinoids fan induce apoptosis as well, Bec ause we are investigating the potential of retinoids in chemopreventio n and therapy for head and neck premalignant and malignant lesions, we compared the effects of all-trans-retinoic acid (ATRA) and N-(4-hydro xyphenyl)retinamide (4HPR) on seven human head and neck squamous cell carcinoma cell lines (17A, 17B, 22A, 22B, 38, SqCC/Y1, and 1483), Six of the seven cell lines showed dramatic morphological changes after tr eatment with 10 mu M 4HPR, whereas no such changes were induced by 10 mu M ATRA, To determine whether these retinoids can induce apoptosis, we analyzed both detached and attached cells after 2, 5, and 7 days of treatment for evidence of DNA fragmentation by DNA electrophoresis on agarose gels, In five of the seven cell lines, a DNA ladder was obser ved after treatment with 10 mu M 4HPR for 5 or 7 days, whereas treatme nt with ATRA resulted in a less pronounced effect, In 17B cells, a cle ar DNA ladder was observed as early as 2 days after treatment with 4HP R; however, neither ATRA nor 9-cis-retinoic acid was as effective, In addition, morphological changes associated with apoptotic cell death, such as chromatin condensation and nuclear segmentation, were observed by propidium iodide staining and by electron microscopic analysis aft er 4HPR treatment, These results demonstrate that 4HPR causes apoptosi s in several head and neck squamous cell carcinoma cell lines and that it is more potent in this effect than ATRA.