Preclinical Testing Of a Novel Axl-Kinase Inhibitor In Chronic Lymphocytic Leukemia

• Published in: Blood 2013-11, Vol.122 (21), p.2879-2879
• Main Authors: Göbel, Maria, Möllmann, Michael, Görgens, André, Dührsen, Ulrich, Göthert, Joachim Rudolf, Giebel, Bernd, Schultz-Fademrecht, Carsten, Unger, Anke, Klebl, Bert, Choidas, Axel, Dürig, Jan
• Format: Article
• Language: English
• ISSN: 0006-4971; 1528-0020
• DOI: 10.1182/blood.V122.21.2879.2879

The receptor tyrosine kinase Axl belongs to the TAM (Tyro-3, Axl and Mer) family and is involved in the progression of several human malignancies including chronic lymphocytic leukemia (CLL), where it is has been found to be overexpressed in comparison to normal B-cells. An increasing body of evidence suggests that Axl acts as an oncogene which increases the survival, proliferation, metastatic potential and chemotherapy resistance of tumor cells. Hence, it has been recently identified as a potential therapeutic target in a wide range of tumor entities with deregulated Axl expression including prostate cancer, glioma, lung cancer and CLL. Here, we investigated two different Axl inhibitors for their ability to inhibit the migratory capacity and survival of leukemic cells in preclinical CLL models. In vitro studies: We measured soluble Axl plasma concentrations by enzyme-linked immunosorbent assay (ELISA) in 71 CLL patients and 24 healthy donors. Soluble Axl levels were not significantly higher in CLL patients compared to healthy donors (p=0. 11). However, in CLL patients high sAxl plasma concentrations were differentially expressed with some patients exhibiting normal and others elevated plasma concentrations. The latter showed an association with shorter time to first treatment (p=0.0005) and several poor prognostic markers (e.g. CD38, FISH cytogentics, Binet stage). Freshly isolated PBMC (>90% CD5+CD19+) from CLL patients were incubated in serum free medium for 48h containing concentrations series of 2 different Axl inhibitors: BMS777607, a previously published inhibitor of the MET kinase family, and LDC2636, a novel inhibitor of the TAM receptor tyrosine kinase (RTK) family with high affinity to Axl. Viability of CLL cells was assessed by trypan blue staining and flow cytometry employing annexin V staining. Cellular polarization was analyzed by time-lapse microscopy. We detected cytotoxic effects in a patient-dependent manner that were more prevalent in LDC2636 as compared to BMS777607 treated cells (IC50= 0.21 µM vs. 2.88 µM, p