Molecular Heterogeneity as a Basis for Rational Therapeutics in Chronic Lymphocytic Leukemia.

Abstract 2348

Poster Board II-325

Chronic lymphocytic leukemia (CLL), the most frequent form of adult leukemia in Western countries, is characterized by a highly variable clinical course. Data from our group have shown that the gene expression profile can be used to classify CLL patients into different risk groups, according to a biology-based predictive model that includes genes from essential survival pathways, such as the B cell receptor (BCR) and NF-κB pathways. We propose that this molecular heterogeneity may be associated with variable sensitivity to drugs affecting these survival pathways. Using the Connectivity Map bioinformatic tool, we identified several drugs that may indirectly regulate BCR signaling. We decided to explore one inhibitor of calmodulin (Calmidazolium) further. Based on previously available information about specific signaling cascades, we also selected a PIM kinase inhibitor (C6) and a small molecule inhibitor (SMI) of the BCL2 family (TW-37), which targets Bcl-2, Bcl-XL, and, unlike most SMIs, Mcl-1. An automated drug dispensation protocol coupled to a cell viability assay was set up to test these compounds in primary CLL samples. EC50s were calculated at 72 hours of treatment for each sample and drug. EC50s were in the low μM range for Calmidazolium (0.9-6.8 μM) and C6 (1.5-6.5 μM) and in the nM range for TW-37 (90-740 nM). Patients were stratified using IgVH, SHM, ZAP70, PIM1, PIM2, MCL1 expression, and BCR signature expression as markers. Pharmacodynamic markers such as p-AKT were chosen. Associations of EC50s with SHM and ZAP70 clinical parameters were examined. Strikingly, unmutated cases (4/13), characterized by a worse prognosis, were associated with greater sensitivity (i.e., lower values of EC50) to TW-37 (p = 0.017). Interestingly, ZAP70-positive cases (4/10) also showed a tendency towards greater sensitivity to the TW-37 treatment (p = 0.079). However, variability in the response to Calmidazolium and C6 was not statistically significant, given the small size of the series (11 and 5 samples, respectively). In summary, we show that samples from patients with a poor prognosis (unmutated IgHV and ZAP70-positive) are more sensitive to the BCL2 family SMI, supporting the hypothesis that molecular heterogeneity in CLL is associated with variable drug response.