Isolation of apoptosis- and differentiation-inducing substances toward human promyelocytic leukemia HL-60 cells from leaves of Juniperus taxifolia.

A chloroform extract of the leaves of Juniperas taxifolia exhibited a marked antiproliferative effect on human promyelocytic leukemia HL-60 cells at a concentration of 2.5 microg/ml. Deoxypodophyllotoxin (4) was identified in the extract as an outstanding antiproliferative compound, and five diterpenes (1-3, 5, and 6) were isolated as known compounds with weak or no cytotoxicity. These compounds were examined for their respective apoptosis- and differentiation-inducing activities toward HL-60 cells by DNA fragmentation and NBT-reducing assays, respectively. Among them, 7alpha-hydroxysandaracopimaric acid (6) was found to have a potent differentiation-inducing activity in a dose-dependent manner at 0.125-2 microg/ml (0.39-6.29 microM), together with apoptosis-inducing activity at concentrations of more than 2.5 microg/ml (7.86 microM). Deoxypodophyllotoxin (4) that exerted cytotoxic and apoptosis-inducing activities at 2 ng/ml (5 nM) did not induce differentiation at the same concentration, and the other diterpenes (1-3 and 5) showed no effect on cell differentiation, even at 5 microg/ml. It was thus demonstrated for the first time that 7alpha-hydroxysandaracopimaric acid was an effective differentiation-inducing compound toward HL-60 cells.