Netrin-1 has been shown to be up-regulated in a fraction of human cancers as a mechanism to allow these tumors to escape the pro-apoptotic activity of some of its main dependence receptors, the UNC5 homologs (UNC5H). Here we identify the V-2 domain of netrin-1 to be important for its interaction with the Ig1/Ig2 domains of UNC5H2. We generate a humanized anti-netrin-1 antibody that disrupts the interaction between netrin-1 and UNC5H2 and triggers death of netrin-1-expressing tumor cells in vitro. We also present evidence that combining the anti-netrin-1 antibody with epidrugs such as decitabine could be effective in treating tumors showing no or modest netrin-1 expression. These results support that this antibody is a promising drug candidate.

Netrins were first identified as neural guidance molecules, acting through receptors that are members of the DCC and UNC-5 family. All netrins share structural homology to the laminin N-terminal domains and the laminin epidermal growth factor-like domains of laminin short arms. Laminins use these domains to self-assemble into complex networks. Here we demonstrate that netrin-4 is a component of basement membranes and is integrated into the laminin polymer via interactions with the laminin ␥1 and ␥3 short arms. The binding is mediated through the laminin N-terminal domain of netrin-4. In contrast to netrin-4, other members of the netrin family do not bind to these laminin short arms. Moreover, a truncated form of netrin-4 completely inhibits laminin-111 self-assembly in vitro, and full-length netrin-4 can partially disrupt laminin self-interactions. When added to explant cultures, netrin-4 retards salivary gland branching morphogenesis.Netrins were first isolated as long range guidance cues, acting in early embryogenesis by regulating the migration of neurons and the axonal growth cone (1). These proteins showed either chemoattractive or chemorepulsive effects upon distinct sets of cells, hence cells expressing netrin-1 can mimic the ability of the floor plate to repel the growth cones of trochlear motor neurons in vitro, while attracting the axons of spinal commissural neurons (2-4). Consequently, netrin-1 is considered a bifunctional guidance cue. This activity has been shown to relate to expression levels of specific receptors from either the DCC or UNC-5 families (5-9).

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Abstract.-DNA isolated from skin epitheliomas containing papovavirus induced lymphomas within four to eight weeks in 40 to 50 per cent of newborn Syrian hamsters injected. This DNA effect was eliminated by DNase but not by RNase and was not induced by DNA preparations of transplanted epitheliomas or the induced lymphomas. Lymphomas were similarly induced by cellfree filtrates from certain human tumors such as gastric carcinomas and ovarian tumors. Little or no lymphoma effects were observed following injections with filtrates derived from normal human or animal tissues or human blood. The lymphomas induced by DNA and human tumors were transmissible by cell-free filtrates to newborn Syrian hamsters; however, successful serial passage, like the primary lymphomas induced by the DNA preparations, depended upon the use of a newborn hamster from a special breeding colony of hamsters.Introduction.-In previous publications, we reported both the spontaneous incidence of multiple skin epitheliomas (papillomas) containing large numbers of papovaviruses in Syrian hamsters1 and an associated induction of leukemias, predominantly lymphomas.2 The latter originated in almost every case in the liver of Syrian hamsters which as newborns had been treated with cell-free filtrates from the hamster skin tumors. The hamster lymphomas, which were separately transmissible by cell-free extract, contained a virus with the morphology of the C-type murine leukemia virus; interestingly, the papovavirus present in skin tumors could not be detected in the lymphomas by electron microscopic examination. Herewith, we report additional results concerning especially the induction of hamster lymphomas by DNA from spontaneous skin epitheliomas containing papovavirus. In addition, experiments are briefly described in which the lymphomas also appeared in significant numbers after subcutaneous inoculation of hamsters with filtrates derived from certain human tumors.Materials and Methods.-DNA was isolated from tissues of primary skin epitheliomas containing papovavirus. The tissue was either freshly excised or frozen at -80'C. The

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