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Chronic lymphocytic leukemia (CLL) cells depend on microenvironmental non-malignant cells for survival. We compared the transcriptomes of primary CLL cells cocultured or not with protective bone marrow stromal cells (BMSCs) and found that oxidative phosphorylation, mitochondrial function, and hypoxic signaling undergo most significant dysregulation in non-protected CLL cells, with the changes peaking at 6-8 h, directly before induction of apoptosis. A subset of CLL patients displayed a gene expression signature resembling that of cocultured CLL cells and had significantly worse progression-free and overall survival. To identify drugs blocking BMSC-mediated support, we compared the relevant transcriptomic changes to the Connectivity Map database. Correlation was found with the transcriptomic signatures of the cardiac glycoside ouabain and of the ipecac alkaloids emetine and cephaeline. These compounds were highly active against protected primary CLL cells (relative IC 50 's 287, 190, and 35 nM, respectively) and acted by repressing HIF-1α and disturbing intracellular redox homeostasis. We tested emetine in a murine model of CLL and observed decreased CLL cells in peripheral blood, spleen, and bone marrow, recovery of hematological parameters and doubling of median survival (31.5 vs. 15 days, P = 0.0001). Pathways regulating redox homeostasis are thus therapeutically targetable mediators of microenvironmental support in CLL cells.

Differential expression of molecules in chronic lymphocytic leukemia (CLL) may define prognostic markers and suitable targets for immunotherapy. Expression of the tumor-associated antigen (TAA) RHAMM (receptor for hyaluronic acid-mediated motility) as well as RHAMM splicing variants was assessed in series of 72 CLL patients. Quantitative reverse transcriptase PCR showed higher RHAMM expression in high-risk CLL patients, as well as in the advanced stages of the disease. CLL cases with a higher RHAMM expression showed a significantly shorter median treatment-free survival. Among patients with mutated immunoglobulin heavy chain genes, an analysis of RHAMM expression enabled to distinguish subgroup of patients with favorable prognosis. In lymph nodes, RHAMM staining correlated with a higher Ki-67 index and CD40L expression. Functionally, stimulation with CD40L enhanced RHAMM expression in CLL. We further characterized RHAMM-specific CD8(+) T cells in patients with CLL, as the expression of TAAs might influence the clinical outcome by the means of immune reactions. The cytotoxic potential of RHAMM-specific T cells was shown against target cells bearing RHAMM-derived epitope as well as against CLL cells expressing RHAMM. In conclusion, RHAMM expression appears to be of prognostic value, as well as may reflect the proliferative capacity of CLL cells, and might therefore represent interesting target for immunotherapy.