Concentration dependence of 8Cl-cAMP- and 8Cl-AD–mediated growth inhibition in MM.1S and MM.1R cells. Cells are treated with the indicated concentration of drug for 5 days and then cell number is assayed and presented as described in Materials and Methods. MM.1S treated with 8Cl-cAMP (•); MM.1S treated with 8Cl-AD (○); MM.1R treated with 8Cl-cAMP (▪); MM.1R treated with 8Cl-AD (□).