Send Orders of Reprints at reprints@benthamscience.org 996 Medicinal Chemistry, 2012, 8, 996-1002 1875-6638/12 $58.00+.00 © 2012 Bentham Science Publishers Transient Injury-Dependent Up-Regulation of CD105 and its Specific Targeting with an Anti-Vascular Anti-Mouse Endoglin-Nigrin b Immuno- toxin Raquel Muñoz 1 , Yolanda Arias 1 , José Miguel Ferreras 1 , Pilar Jiménez 2 , Maria Ángeles Rojo 1 , Carmelo Bernabéu 3 , Damián Córdoba-Díaz 4 and Tomás Girbés 2 * 1 Departamento de Bioquímica y Biología Molecular, Facultad de Ciencias, Universidad de Valladolid, 47005 Vallado- lid, Spain 2 Nutrición y Bromatología-Facultad de Medicina and Centro de Investigación en Nutrición, Alimentación y Dietética (CINAD), Universidad de Valladolid, 47005 Valladolid, Spain 3 Centro de Investigaciones Biológicas, Consejo Superior de Investigaciones Científicas (CSIC) and Centro de Investi- gación Biomédica en Red de Enfermedades Raras (CIBERER), E-28040 Madrid, Spain 4 Departamento de Farmacia y Tecnología Farmacéutica, Facultad de Farmacia, Universidad Complutense de Madrid, E-28040 Madrid, Spain Abstract: Endoglin (CD105), a cell-surface co-receptor for transforming growth factor-beta (TGF-) superfamily mem- bers, is over-expressed in tumor neovasculature and can be targeted with anti-endoglin antibodies, thus becoming an im- portant tool for anti-tumoral therapy. Injury of the mouse tail induced the transient expression of endoglin, this peaking at three days after injury and disappearing six days later. An immunotoxin containing the anti-mouse endoglin rat mono- clonal antibody MJ7/18 and the non-toxic ribosome-inactivating protein nigrin b (Ngb) was found to be very active in tar- geting mouse endoglin in the L929 fibroblast cell line (IC 50 of 4 x 10 -11 M). At that concentration, the immunotoxin lacked unspecific activity. Upon induction of endoglin after injury, the MJ7-Ngb immunotoxin strongly attacked and de- ranged the injured tail, inducing tissue damage. Such effects were dependent on the age of the animals and were evident in six-week-old mice, but not in eight-month-old mice. Our results indicate that endoglin is up-regulated in newly formed vessels upon injury and can be targeted by the MJ7-Ngb immunotoxin; thus, it could be a useful tool for tumor ablation research. Keywords: Anti-endoglin Antibody, Anti-tumor Therapy, CD105, CD105 Ablation, Endoglin, Nigrin b. INTRODUCTION Tumor mass development is characterized by the re- quirement of a blood supply through a new vascular network whose induction depends on factors released by tumor cells [1]. Targeting the tumor vascular supply rather than cancer cells is widely recognized for its therapeutic potential [2, 3]. The rationale of this is based on the fact that one blood ves- sel supports thousands of cancer cells, such that the destruc- tion of a few vessels would block the supply of oxygen and nutrients to the cancer cells which trigger apoptosis and therefore the destruction of a large amount of tumor [4]. This enables a reduction in the concentration of the anti-cancer drug required and hence the potential harmful effects of such drugs usually appear at high concentrations. One treatment used to target tumor neovasculature is the anti-angiogenic approach, which is currently carried out with angiogenesis inhibitors [5, 6]. Such inhibitors alter the for- *Address correspondence to this author at the Nutrición y Bromatología, Facultad de Medicina, Universidad de Valladolid, E-47005 Valladolid, Spain; Tel: +34 983 423082; Fax: +34 983 423082; E-mail: girbes@bio.uva.es mation of new capillary vessels (neovasculature), without interfering with pre-existing vessels. The inhibition of the growth of tumor neovasculature promotes a reduction in the supply of oxygen and nutrients to tumor cells, inducing growth delay/dormancy and a slow tumor regression, though it cannot completely destroy cancer cells that remain quies- cent [5, 7, 8]. This approach to tumor therapy seems to cir- cumvent the problem of acquired resistance to chemotherapy drugs that act on tumor cells [9]. Nevertheless, tumors may become resistant to antiangiogenic therapy [10, 11]. Another advantage of this therapy is to avoid the problem of the low access of tumor cells to drugs [4]. Antiangiogenic therapy with angiogenesis inhibitors is a somewhat slow process since what is affected is the growth of new vessels. A con- siderable body of preclinical evidence indicates that combin- ing antiangiogenic agents with conventional cytotoxic agents or radiation therapy results in additive or even synergistic anti-tumor effects [12]. Another approach to tumor therapy is vascular targeting with immunotoxins and radio-antibodies against markers of tumor neovasculature [13-16]. Since what is pursued is the destruction of neovasculature, therapy with immunotoxins