NBTI inhibits 8Cl-cAMP and 8Cl-AD activity. MM.1S cells are treated with 8Cl-cAMP for 5 days at the indicated concentrations in the presence (light bars) or absence (dark bars) of 50 μmol/L NBTI. MM.1S cells treated with 3 μmol/L 8Cl-AD are also included. Cell number is assayed and presented as described in Materials and Methods.