Survey Tumor therapeutics by design: targeting and activation of death receptors Harald Wajant a , Jeannette Gerspach b , Klaus Pfizenmaier b, * a Department of Internal Molecular Medicine, Medical Polyclinic, University of Wuerzburg, Germany b Institute of Cell Biology and Immunology, University of Stuttgart, Allmandring 31, 70569 Stuttgart, Germany Abstract Due to their strong apoptosis-inducing capacity, the death receptor ligands CD95L, TNF and TRAIL have been widely viewed as potential cancer therapeutics. While clinical data with CD95L and TRAIL are not yet available, TNF is a registered drug, albeit only for loco-regional application in a limited number of indications. The TNF experience has told us that specific delivery and restricted action is a major challenge in the development of multifunctional, pleiotropically acting cytokines into effective cancer therapeutics. Thus, gene-therapeutic approaches and new cytokine variants have been designed over the last 10 years with the aim of increasing anti-tumoral activity and reducing systemic side effects. Here, we present our current view of the therapeutic potential of the death receptor ligands TNF, CD95L and TRAIL and of the progress made towards improving their efficacy by tumor targeting, use of gene therapy and genetic engineering. Results generated with newly designed fusion proteins suggest that enhanced tumor-directed activity and prevention of undesirable actions of death receptor ligands is possible, thereby opening up a useful therapeutic window for all of the death receptor ligands, including CD95L. # 2004 Published by Elsevier Ltd. Keywords: Tumor targeting; FasL; TNF; TRAIL; Antibody fusion protein; Gene therapy Contents 1. Introduction ................................................................................ 56 2. Death inducing ligands and their receptors ........................................................... 56 3. CD95L and TRAIL in tumor surveillance and as mediators of drug-induced cancer cell apoptosis .................... 58 4. CD95 activation as therapeutic principle ............................................................. 59 4.1. Cell surface targeting-dependent activation of CD95L fusion proteins.................................... 59 4.2. Transmembrane CD95L-based gene therapy ..................................................... 61 4.3. CD95-specifc antibodies with tissue-restricted agonistic properties ...................................... 61 5. TRAIL in tumor therapy ........................................................................ 61 5.1. Transmembrane TRAIL and differently aggregated preparations of soluble TRAIL exert different bioactivities ....... 61 5.2. TRAIL fusion proteins showed enhanced activity after cell surface immobilization .......................... 63 5.3. Transmembrane TRAIL-based gene therapy ..................................................... 64 5.4. TRAILR1- and TRAILR2-specifc antibodies ..................................................... 64 6. TNF in tumor therapy ......................................................................... 64 6.1. TNF in isolated limb perfusion .............................................................. 64 6.2. TNF fusion proteins in tumor therapy .......................................................... 65 www.elsevier.com/locate/cytogfr Cytokine & Growth Factor Reviews 16 (2005) 55–76 * Corresponding author. Tel.: +49 711 685 6986; fax: +49 711 685 7484. E-mail address: klaus.pfizenmaier@izi.uni-stuttgart.de (K. Pfizenmaier). 1359-6101/$ – see front matter # 2004 Published by Elsevier Ltd. doi:10.1016/j.cytogfr.2004.12.001