Identification Of Therapeutic Targets For Chronic Lymphocytic Leukemia In The Relapsed And Refractory Setting

Abstract Cancer patients with relapsed or refractory disease often require repeated sequential therapies. This approach may induce resistance to conventional chemotherapy and may drive selection for cancer cells that rely on pro-survival signals. Such changes in the molecular constitution of the cancer at the time of each treatment have implications in the drive to personalize cancer therapy. We investigated this phenomenon in Chronic Lymphocytic Leukemia (CLL), a common incurable leukemia that often requires multiple therapeutic regimens over time. Using stored purified CLL cells and serum from a cohort of patients followed at the Duke University and Durham VA Medical Centers, we identified twenty pairs of samples collected from patients prior to and after therapy, and eight pairs of samples collected from patients where no therapy was administered. There were no significant differences in time between paired sample collection or prognostic factors such as Rai stage, cytogenetic aberrations, or IgVH mutational, CD38 or ZAP70 status between these two groups of patients. In the group of sample pairs collected before therapy and upon progression, there was a lower white blood cell count in the second sample (p = 0.04, Wilcoxon signed rank), but no significant change in percentage of cells expressing CD38 or ZAP70 by flow cytometry. The therapies given to patients included alkylating agents alone (14/20), R-CHOP (1/20), Fludarabine-containing regimens (4/20), and single agent-Rituximab (1/20). We profiled gene expression of malignant lymphocytes using Affymetrix U133 Plus 2.0 GeneChips and measured serum levels of circulating cytokines and cytokine receptors from these paired samples in order to identify consistent changes that occurred with therapy. Using supervised analyses of the genomic data, we identified 207 gene probes that were differentially expressed in the twenty pairs of samples where treatment was given. Importantly, these gene probes were not altered in the pairs of samples where no therapy was administered. We next analyzed genomic pathways using gene ontology, Gene Set Enrichment Analysis, and genomic signatures of oncogenic deregulation. We found that after therapy, there is upregulation of genes involved in cellular and nucleic acid metabolism, cell interaction, and signal transduction, with the phosphoinositol 3-kinase and beta-catenin pathways specifically affected. In addition, upregulation of the myc pathway prior to therapy was associated with a shorter duration of response to therapy. Upon studying serum cytokine and cytokine receptor levels in these patients, we found significantly different levels of EGF, EGFR, G-CSF, and RAGE before therapy compared to those on progression of disease. Higher levels of pre-treatment serum cytokines such as GM-CSF and IL-6 were associated with shorter durations of response to therapy. The results of these experiments demonstrate that there are consistent intra- and extra-cellular signals in CLL that are altered after heterogeneous therapies. These signals could be responsible for maintaining leukemic cells despite therapy, and thus are potential targets for future therapies, specifically in the relapsed and refractory patient.