This invention relates to an agent, a composition and a product comprising at least one apoptosis-inducing substance, and at least one substance which inhibits expression and/or activity of an apoptosis-inhibiting substance; a method for inducing apoptosis or for treating a proliferative disease using one or more of them; a nucleic acid construct comprising a nucleic acid molecule encoding a protein to be expressed and a nucleic acid molecule which inhibits expression of an undesired protein; and a method for expressing a desired protein in a cell while inhibiting the expression of an undesired protein.