Despite more and more specific antibodies having been developed successfully for treatment of cancer, there still is a need for increasing their anti-tumor efficacy. The discovery of a highly potent, yet targeted therapy may be achieved by coupling a highly potent toxin to an antibody with high affinity and specificity for a tumor cell -associated target. Crucial is the linker, by which the toxin is coupled to the specific antibody. Is the coupling between antibody and toxin too ´loose´, the systemic release of the toxin will cause side effects and damage healthy organs and tissues. Is the binding too ´strong´, this may result in inefficacy against the tumor. Heidelberg Pharma is currently exploring a number of linker and toxin technologies for building the optimum antibody-drug candidate.