Survival curves for U937 cells transfected with empty vector (neo) or S3a in the sense orientation, exposed to ara-C (top panels) or DNR (bottom panels) with or without previous exposure to ATRA (10⁻⁷ mol/L) before drug.

For the parental cells, there was no significant change in D10 (A) or the cells became more resistant (C). For 1302 cells, D10 values were decreased significantly after ATRA for cells exposed to ara-C (B) or DNR (D). S3a transfectants in the sense orientation showed sensitization to ara-C and DNR, whereas controls showed no effect of ATRA. Curves for transfectants in the antisense orientation were similar to those for controls and are not shown.