Screening for Cytotoxic Compounds in Poor-prognostic Chronic Lymphocytic Leukemia

Background/Aim: For chronic lymphocytic leukemia (CLL) patients with poor-prognostic genomic aberrations the therapeutic options are limited. We used the Spectrum Collection library to identify compounds with anti-leukemia activity in high-risk CLL. Materials and Methods: We identified substances with equal high cytotoxic activity in vitro in samples from poor-prognostic CLL (11q-/17p-, n=3) as compared to those from favourable-prognostic CLL (13q-, n=3). Cell survival was measured by fluorometric microculture cytotoxicity assay. Results: Out of 2,000 compounds, 65 had a similar effect in both prognostic groups. Fifteen compounds were selected for dose-response experiments in 16 additional CLL samples. Of these compounds, 12 continued to have similar cytotoxicity between prognostic subgroups. Additional experiments demonstrated that in CLL cells with 11q or 17p deletion, 5- azacytidine induced apoptosis in a dose-dependent manner and lipoprotein lipase expression was reduced following orlistat treatment. Conclusion: Using primary cultures of cells from high-risk CLL patients for compound screening is a feasible approach and that 5-azacytidine and orlistat exemplify substances that exhibit cytotoxicity in poor-risk CLL. Among a number of biological parameters that have emerged as independent prognostic markers in chronic lymphocytic leukemia (CLL), of particular importance are cytogenetic aberrations (1) and the mutational status of the immunoglobulin heavy variable (IGHV) genes (2, 3). Today, the marker portending the most adverse prognosis in CLL is deletion of chromosome 17p, covering the TP53 gene, a key regulator of cell death following DNA damage (4). This deletion is found in approximately 5-10% of patients with CLL (1, 5, 6) and the median overall survival for patients within this group is approximately 2.5-4 years (1, 7, 8). CLL patients with 17p deletion usually have disease resistant to alkylating agents (9) and fludarabine (10); however, therapy with drugs such as steroids (11), lenalidomide (12) or alemtuzumab (13) may have an effect. Furthermore, deletion of 11q, found in 12-18% of patients with CLL (1, 5, 6) is also considered a marker of inferior prognosis and is associated with a lower response rate to purine analogs (14) and refractoriness to DNA-damaging chemotherapy (15). There is still a need for new anticancer agents that are active in the poor-prognostic CLL subgroups resistant to conventional therapy.