The antileukemic efficacy of an immunotoxin composed of a monoclonal anti-Thy-1 antibody disulfide linked to the ribosome-inactivating protein gelonin

Abstract

We prepared an immunoconjugate consisting of a monoclonal antibody recognizing the Thy-1 antigen and the ribosome-inactivating protein gelonin linked by a disulfide bond. This immunotoxin preparation was judged to contain less than 5% free antibody or gelonin. It was highly toxic in vitro in an antigen-specific fashion to the Thy-1 expressing RADA leukemia of A/J mice. The IC50 of this preparation on RADA in vitro was 10(-12) M, while the IC50 on the Thy-1 negative S1509a fibrosarcoma of A/J mice was 10(-7) M. The toxicity of this immunoconjugate was also measured in a direct proliferation and it was found that a 4-h exposure and a 24-h exposure of RADA cells to a 1 nM concentration of immunotoxin killed 90% and 99.9% of cells, respectively. Furthermore, efficacy in vitro was not due to the intrinsic susceptibility of RADA cells to tis type of immunotoxin, as one prepared with gelonin and an antibody recognizing the TLa determinant on this leukemia had no efficacy in vitro. Clearance of the anti-Thy-1-gelonin immunoconjugate from the circulation of A/J mice after i.v. injection was rapid, especially during the first 8 h after injection, possibly because of binding to Thy-1 expressing tissue. Delivery of immunoconjugate to ascitic tumor in vivo was substantially better if the immunoconjugate was given by i.p. injection, rather than by the i.v. route. When given either i.v. or i.p. at the time of i.p. tumor inoculation in vivo, the anti-Thy-1-gelonin immunotoxin showed potency in an antigen-specific fashion; while this immunoconjugate prolonged survival and frequently cured RADA-inoculated mice, neither anti-Thy-1 antibody, gelonin, a combination of the two, nor immunotoxin of irrelevant specificity had any significant effect on survival. Anti-Thy-1-gelonin also had no effect on survival of A/J mice inoculated i.p. with S1509a. Furthermore, it was determined that a single i.p. dose of anti-Thy-1-gelonin killed 90% to 99% cells in vivo, and that the immunoconjugate was about as effective in this model as either adriamycin or cytoxan.

In vivo cytotoxic efficacy of immunotoxins prepared from anti-CD5 antibody linked to ricin A-chain

“…The model chosen consisted of a BALB/c nude mouse bearing a wide xenograft composed of 900x 106 human leukemic cells, in order to mimic the clinical situations [18]. This contrasts with previous experiments for quantitative analysis of immunotoxin cytotoxic efficacy where the tumour burden represented fewer than 107 cells [26,24,10].…”

Anti-Endosialin Antibody–Drug Conjugate: Potential in Sarcoma and Other Malignancies

“…The requirements for a cell surface molecule to be suitable as an antibody-drug conjugate (ADC) target are well established (23)(24)(25)(26)(27)(28)(29)(30). The optimal ADC has antigen recognition that is not different from the unconjugated antibody.…”

Potentiation of Antiproliferative Effects of Monoclonal Antibody Lym-1 and Immunoconjugate Lym-1-gelonin on Human Burkittʼs Lymphoma Cells with γ-Interferon and Tumor Necrosis Factor

“…In the evaluation of such immunoconjugates, it is critical to remove the unconjugated mAbs because they may have antiproliferative activity of their own. Gelonin immunoconjugates have been synthesized using antimelanoma (17), anti-epidermal growth factor (EGF) receptor (18), and anti-Thy-1 (19) mAbs. This study describes the synthesis and activity of a gelonin immunoconjugate using mAb Lym-1, which reacts with most B-cell lymphomas and B-cell chronic lymphocytic leukemia.…”