Heat-Shock Protein Signature Is Associated with Refractory Chronic Lymphocytic Leukemia Cells From Different In Vivo Microenvironments,

Abstract 3866

Chronic Lymphocytic Leukemia (CLL) is a monoclonal B-cell disorder with accumulation of leukemic cells in peripheral blood, bone marrow and lymphoid organs. It presents with a heterogeneous clinical course. Many patients survive long periods of time without any need for treatment, whereas other patients show resistance to treatment or relapse soon after administration of therapy. Although some prognostic markers such as mutational status of immunoglobulin variable heavy chain, chromosomal abnormalities, CD38 levels, or ZAP-70 expression may help predict at initial diagnosis which patients will have more aggressive disease, the exact factors that can determine chances of remission in CLL are still not clear, making treatment challenging. Furthermore, CLL remains an incurable disease, necessitating a way for controlling its progression. Identifying novel molecular signatures associated with refractory CLL disease may help devise targeted treatment strategies and thus may prolong survival times and prevent the progression of CLL in relapsed patients. Considering this, we performed gene expression profiling (GEP) on peripheral blood (PB), bone marrow (BM) and lymph node (LN) samples collected at the time of diagnosis. We divided CLL samples into 3 groups based on their response to treatment; i) Stable CLL group: asymptomatic patients requiring no treatment, ii) Treated but stable CLL group: patients required treatment but had stable disease for at least one year after the end of the treatment cycle, and iii) Relapsed CLL: patients who relapsed within a year of end of the treatment cycle. Significance analysis of microarray (SAM) revealed that the heat-shock protein (HSP) signature (HSJ2, HSP70, HSP90, HSP60, HSP10, HSP 105, HSP40, HSP27, HSPA2, HSJ1, HSF4, HSPCA), BCR signaling pathway (JUN, NFATC4, NFKBIE, PPP3CB, TRAF3, CD81, CCT4), activation markers (CD81, CD83) and MMPs (MMP3, MMP9) were overexpressed in relapsed PB-CLL (n=3) compared to stable PB-CLL (n=6) and treated but stable PB-CLL (n=10). Overexpression of heat-shock protein signature genes were further observed in additional relapsed PB-CLL (n=6) group compared to other two PB-CLL (n=22) group. Interestingly, the HSP signature was consistently overexpressed in relapsed BM-CLL (n=6) and LN-CLL (n=12) compared to stable and treated but stable BM-CLL (n=11) and LN-CLL (n=3) groups. HSPs are considered chaperones of tumorigenesis and known to enhance survival, migration, and proliferation of tumor cells which may contribute to relapse in patients. Furthermore, the HSPs genes (HSP90 and HSP70) were significantly overexpressed in LN-CLL as compared to PB-CLL which implies important role of the microenviroment in rendering CLL refractory. To investigate the link between the expression of the individual genes with the aggressiveness of the disease, Kaplan-Meier log-rank tests were performed. We found that the higher expression of HSP90A, HSP90B, HSJ, and MMP9 were significantly (p<0.05) associated with shorter time to treatment. In summary, our study suggests that HSP genes are overexpressed in refractory CLL patients and thus are promising targets to improve clinical outcome.