ABSTRACTlabile group of amino acids to a diphtheria toxin (DT) payload that has been truncated at its receptor binding region. 20 Since IL-3, the natural ligand for IL-3R, binds with very high specificity and avidity, 21 SL-401 is able to transport DT efficiently and preferentially to cells that overexpress IL-3R, leading to internalization followed by receptor-mediated endocytosis and localization of SL-401 to early endosomes. After cleavage of the SL-401 DT constituent in the acidic medium of endosomes, DT translocates into the cytosol and binds to ADP-ribosylated elongation factor 2, leading to blockade of protein synthesis and cell death. 22 Given the ubiquitous and high expression of IL-3R by BPDCN and the lack of therapies available to treat BPDCN, SL-401 is a potential therapeutic for BPDCN. The present study evaluated the cytotoxicity of SL-401 against patient-derived BPDCN cell lines (CAL-1 and GEN2.2) and primary BPDCN cells isolated directly from 12 patients. The investigations were performed in vitro, as well as in vivo in a murine model of BPDCN. The aim of the study was to provide further support for the use of SL-401 in patients suffering from BPDCN.
Methods
Patients' cells and cell linesPeripheral blood or bone marrow cells were obtained for diagnostic purposes from 12 BPDCN patients (Table 1) from our national network that collects data and cells from cases diagnosed in France since (authorization number #DC-2008. BPDCN was diagnosed from the results of histopathology and immunostaining of cutaneous lesions, blood or bone marrow. 2,8 Two established cell lines derived from BPDCN patients were used (GEN 2.2, patent #0215927, Dr. Plumas, EFS Rhone-Alpes, Grenoble, France and CAL-1, Dr. Maeda, Nagasaki University, Japan) as well as TF/H-Ras (Prof. Frankel) and CD123 neg (MFI<800) Daudi cell lines (ACC78, DSMZ Braunschweig, Germany) as positive and negative controls, respectively. Other lymphoid and myeloid leukemic cells used to compare sensitivity to SL-401 are described in the Online Supplementary Appendix.
Drug and cultureThe SL-401 drug (Stemline Therapeutics, New York, NY, USA) was stored at -80°C and tested at eight concentrations ranging from 365 pM to 0.08 fM (21 ng/mL to 0.4 ng/mL) in order to cover (including myeloperoxidase, CD13, CD33, CD117, CD15, CD65, CD14, CD64); T : T lymphoid markers (including membrane CD3, intracytoplasmic CD3, CD7, CD5, CD2, CD8)
Cytotoxicity evaluation by flow cytometryFlow cytometry was performed using a CANTO II cytometer (BD Biosciences, San Jose, CA, USA) and DIVA 6.2 software (BD Biosciences). The cytotoxic effects of SL-401 and the various drugs were evaluated using annexin-V and 7-amino actinomycin D (AV/7AAD) and a panel of different monoclonal antibodies to gate the blastic population described in the Online Supplementary Appendix. In the mouse model, anti-mouse and anti-human CD45 plus anti-human CD123, CD4, CD56, CD304 were used to identify BPDCN human cells (Online Supplementary Appendix). A defined number of calibrated 3-mm latex beads (Flowco...
