Microenvironmental Stromal Cells Rescue CLL Cells from Apoptosis Via Hypoxia That Can be Targeted Therapeutically

• Published in: Blood 2015-12, Vol.126 (23), p.4140-4140
• Main Authors: Idler, Irina, Yosifov, Deyan, Bhattacharya, Nupur, Reichenzeller, Michaela, Meyer-Pannwitt, Viola, Ezerina, Daria, Scheffold, Annika, Kugler, Sabrina, Dick, Tobias, Dohner, Hartmut, Stilgenbauer, Stephan, Mertens, Daniel
• Format: Article
• Language: English
• ISSN: 0006-4971; 1528-0020
• DOI: 10.1182/blood.V126.23.4140.4140

Microenvironmental support protects malignant cells from apoptosis and from the effects of therapy. We hypothesized that in chronic lymphocytic leukemia (CLL) cells, the non-malignant bystander cells induce a transcriptional signature that prevents apoptosis. We aimed to use this transcriptional signature to identify compounds that target this protective microenvironmental effect. If these compounds are effective against protected CLL cells, we assume that understanding the underlying molecular pathways will open novel therapeutic options for therapy-resistant CLL. In primary CD19+ CLL cells cultured without support after isolation from peripheral blood, apoptosis can already be detected after 8 hrs. These cells can however be rescued by coculture with either human or murine bone-marrow derived stromal cell lines HS-5 and M210B4. In order to identify clinically relevant substances that counteract this pro-survival microenvironmental support, we determined the transcriptional signature that is induced in primary CLL cells by protective feeder cells at 8 timepoints before apoptosis could be detected and compared it to the connectivity map database of transcriptomes induced by 1300 compounds (cMAP). We identified 7 compounds with a transcriptome signature that is negatively correlated to the protective signature induced in CLL cells by in-vitro coculture. Of note, 5 of these substances were more potent than fludararabine to induce apoptosis in protected primary CLL cells. In contrast, none of the 10 control compounds with non-correlated signatures had an effect after 48h of coculture. Most potent were the isoquinoline alkaloids emetine and cephaeline and the cardiac glycoside ouabain that displayed IC50s of 34nM, 190nM and 287nM, while a concentration of 5.1µM of fludarabine was required for comparable induction of apoptosis. To test the efficacy of emetine against CLL in vivo, TCL1-induced murine CLL-like tumors were transplanted into immunocompetent syngeneic mice and treated with 3 high doses of emetine (24mg/kg) after CD5+CD19+ CLL cells reached 40% of leukocytes (CD45+ cells). Treated animals displayed a significant reduction in body weight compared to untreated (26.0g vs 29.1g, p