Antibody-targeted duotoxins combining Pseudomonas exotoxin and mertansine (DM1) for the treatment of B-cell malignancies

• Applicant: Dr. Fabian Müller
• Subject Area: Hematology, Oncology
• Term: from 2018 to 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 401223203

Immunotoxins are fusion proteins of an antibody fragment and the Pseudomonas exotoxin. CD22-targeted immunotoxins have a high clinical activity against hairy cell leukemia but are substantially less active in patients with other CD22-expressing malignancies. We recently demonstrated that the cytotoxic activity of immunotoxins depends on the time that cells are exposed; thus, their efficacy in vivo increases substantially when the clinically used bolus dose is exchanged for continuous administration. Paclitaxel, which by itself has very little in vivo efficacy against lymphoma, enhances the anti-lymphoma activity of bolus doses of immunotoxins two-fold and continuously administered immunotoxin up to 100-fold. Based on these results we newly developed the CD22-targeted “Duotoxin” LMIT-2-DM1 which combines Pseudomonas exotoxin (PE) and the paclitaxel-like small molecule DM1 on one antibody fragment. LMIT-2-DM1 has improved activity against selected cell lines in vitro. In vivo, bolus doses of LMIT-2-DM1 are more efficacious than the immunotoxin or the DM1-only control. The efficacy of continuous infusion of LMIT-2-DM1 has not been tested yet.Supported by this proposal we aim to produce an up-scaled LMIT-2-DM1 to test the efficacy of continuous infusion by intraperitoneally implanted osmotic pumps. Furthermore, the in vitro cell death mechanism of duotoxins will be biochemically established and the duotoxins will be tested in additional xenograft models using lymphoma cell lines and primary ALL blasts from patients. Currently, the mechanism by which paclitaxel enhances immunotoxins in vivo is not understood. Because duotoxins simultaneously deliver both drugs to the target cells, RNA deep sequencing based approaches on sorted cells from the murine bone marrow are applied to clarify the mechanism behind the exceptional in vivo-specific drug synergy.The CD22-targeted duotoxins delivering two highly synergistic drugs directly to the cancer cells while healthy tissue is spared may become a powerful treatment option for patients with relapsed/refractory B-cell malignancies.

• DFG Programme: Research Grants