When treated with phorbol tumor promoters, HL-60 cells undergo termina
l differentiation evidenced by a transition from a non-phagocytic susp
ension culture to an attached fibroblast-like culture with high phagoc
ytic activity. internalization of fluorescent particles by cells exhib
iting the phagocytic positive phenotype (phag(+)) provides a sensitive
indication of promoter-induced differentiation, and the resulting flu
orescent cells can be quantitatively analyzed by flow cytometry. The c
urrent study was initiated to further test the predictive power of a n
ow cytometry based HL-60 differentiation assay in the detection of age
nts associated with tumor promotion. Specifically, experiments were de
signed to assess the sensitivity of the test system to co-promoters wh
ich enhance promoter activity in vivo. Prostaglandin E(2) (PGE(2)) was
chosen as a model co-promoter since it has been shown to potentiate p
horbol ester (i.e. 12-O-tetradecanoyl phorbol-13-acetate; TPA) induced
biological effects in vivo. Results detailed in the current report in
dicate that PGE(2) enhances TPA-induced differentiation of HL-60 cells
in a dose-dependent manner. As with in vivo co-promotion experiments,
PGE(2) exhibited a maximum potentiating effect when administered prio
r to TPA. These data indicate that HL-60 cells are not only sensitive
to phorbol promoters, but also to the co-promoter PGE(2). These experi
ments support the hypothesis that a flow cytometry based HL-60 assay m
ay prove useful for studying chemical agents or intrinsic cellular fac
tors that are involved in the tumor promotion phase of carcinogenesis.