The long term goal of this application is to develop immunotoxins for treating refractory Hodgkin's disease. Despite major advances in combination chemotherapy, about 30 percent of patients still die from their disease. In the previous period of support, the applicant developed immunotoxins that are specific for the Reed-Sternberg cell-associated antigens, CD25, CD30 and IRac. These immunotoxins had marked anti-tumor activity in mice bearing L540 human Hodgkin tumors, provided tumors were small or disseminated. The most potent immunotoxin, RFT5gamma1.dgA, entered Phase I/II clinical trials in refractory Hodgkin's disease patients, with promising results. In this application, the goal is to develop additional reagents for treating large solid tumors, which are usually present in refractory Hodgkin's patients. Immunotoxins will be synthesized that destroy the blood vessels of the tumor, thereby killing the tumor cells indirectly by starving them of nutrients and oxygen. The key advantage of this approach is that the endothelial cells which line the blood vessels of solid tumors are freely accessible to immunotoxins in the blood, whereas the majority of tumor cells are inaccessible. As the applicant has recently shown, immunotoxins directed against tumor endothelial cells can produce dramatic regressions in mice bearing large solid tumors and can be curative if combined with anti-tumor cell immunotoxins. The immunotoxins for targeting the vasculature of Hodgkin tumors will recognize E-selectin or vascular cell adhesion molecule-1 (VCAM-01) which are induced on tumor endothelial cells by cytokines (IL-1, TNF- alpha, lymphotoxin) secreted by Reed-Sternberg cells. E-selectin and VCAM-1 are largely absent from the vasculature of normal tissues and so, operationally, provide a specific marker of tumor endothelial cells in Hodgkin's disease patients. A model will be set up to test this approach by growing L540 Hodgkin tumors subcutaneously or as disseminated tumors in SCID mice. Preliminary experiments have established that murine E-selectin and VCAM-1 are induced on the tumor endothelial cells and are virtually absent elsewhere. Anti-murine E-selectin and VCAM-1 monoclonal antibodies will be tested for their ability to localize to L540 tumors. Immunotoxins constructed from these antibodies will be tested for anti-tumor activity, alone and in combination with immunotoxins directed against Reed-Sternberg cell-associated antigens. These studies will pave the way for clinical trials in which anti-human E-selectin and VACM-1 immunotoxins are used in conjunction with RF5gammal.dgA to treat patients with refractory Hodgkin's disease.
Showing the most recent 10 out of 20 publications
