Abstract: Disclosed is a method of selectively inhibiting growth of non-target cells in a mixed population of target and non-target cells, the method comprising the steps of: (a) contacting the mixed population with a selective agent which comprises a carrier moiety linked by a scissile linkage to a toxic moiety; wherein the selective agent is able to enter non-target cells in which the scissile linkage is cleaved, releasing the toxic moiety to exert a toxic effect on the non-target cells causing inhibition of the growth of the non-target cells, whereas the selective agent is unable to enter target cells and/or the scissile linkage is not cleaved in target cells and/or toxic moiety, if released from the selective agent, does not exert a toxic effect on the target cell; and (b) culturing the cells in conditions which allow for growth of non-inhibited cells.