TOXINS TARGETED TO THE CELL MEMBRANE--DISRUPTION OF SIGNAL TRANSDUCTION

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This project seeks to develop targeted agents which disrupt cellular signal transduction, in addition to or instead of inhibition of protein synthesis. Work from LBC had previously shown that cholera toxin (CT) can inhibit the growth of certain carcinoma cell lines. Therefore efforts during the past year have focused on first, creating novel means of delivering CT-A chain to the surface of malignant cells, and second, defining novel targets in clinically relevant circumstances at which CT might be directed. We have constructed artificial genes in which the CT-A chain nucleotide sequence is fused in frame with a segment of diphtheria toxin (DT) sequence important for membrane translocation, and this segment is in turn also in frame with sequences encoding, in separate constructs, IL-2 and EGF. Such constructs could target neoplasms bearing receptors for these growth factors. We are now attempting to express these constructs in a way that will allow retention of enzymatic activity by CT. We have also defined in a series of leukemic specimens from patients with cutaneous T-cell lymphoma (CTCL) that IL-7 is an important co-stimulatory growth factor with IL-2, that IL-7 receptor and IL-7 ligand m-RNA are expressed in a fraction of patient-derived specimens, and that IL-7 stimulation leads to up regulation of both IL-7 and IL-2 receptors. We have completed a clinical trial which demonstrated clinical activity of DAB486 IL-2, a chimeric diphtheria toxin-IL2 fusion protein in CTCL. Collectively these studies point to the importance of the IL-7 and IL-2 receptor systems in CTCL as important targets for therapeutic agents which can disrupt intracellular signalling. We are also continuing ongoing studies of anti DC19 and anti CD22 antibodies as means of analogously disrupting signals in B-cells, and of anti-DC19 and anti-CD22 directed immunotoxins in patients with B-cell lymphoma.