CAMPTOTHECIN INDUCES DIFFERENTIATION, TISSUE TRANSGLUTAMINASE AND APOPTOSIS IN CULTURED KERATINOCYTES

Cultured normal human adult keratinocytes were exposed to (S)-(+)- cam ptothecin over the concentration range 10(-5) to 10(-10) M. The dose-d ependent inhibition of growth was recorded using cell counting. The in duction of terminal differentiation was demonstrated by the relative i ncrease in squamous and cornified cells, and the concomitant decrease in small, proliferative cells, with an overall decrease in total cell numbers on going from 10(-10) to 10(-6) M concentration of the drug. T he induction of apoptosis was studied by assay of two types of transgl utaminase, ''tissue'' and ''keratinocyte'', and by assay of histone-li nked mono- and oligonucleosomes. Induction of apoptosis was accompanie d with increase in ''tissue'' transglutaminase and in the amount of nu cleosomes, the latter being indicative of endonuclease activity. This activity was sharply increased at a camptothecin concentration of 10(- 5) M, and may have been facilitated by ''tissue'' transglutaminase at lower concentrations. The data suggest that camptothecin restricts ker atinocyte growth by several mechanisms including apoptosis and emphasi ze its possible use in topical therapy for psoriasis.