Functional Analysis of the ATM-p53-p21 Pathway in the LRF CLL4 Trial: Blockade at the Level of p21 Is Associated with Short Response Duration

Abstract

Purpose: This study sought to establish whether functional analysis of the ATM-p53-p21 pathway adds to the information provided by currently available prognostic factors in patients with chronic lymphocytic leukemia (CLL) requiring frontline chemotherapy.Experimental Design: Cryopreserved blood mononuclear cells from 278 patients entering the LRF CLL4 trial comparing chlorambucil, fludarabine, and fludarabine plus cyclophosphamide were analyzed for ATM-p53-p21 pathway defects using an ex vivo functional assay that uses ionizing radiation to activate ATM and flow cytometry to measure upregulation of p53 and p21 proteins. Clinical endpoints were compared between groups of patients defined by their pathway status.Results: ATM-p53-p21 pathway defects of four different types (A, B, C, and D) were identified in 194 of 278 (70%) samples. The type A defect (high constitutive p53 expression combined with impaired p21 upregulation) and the type C defect (impaired p21 upregulation despite an intact p53 response) were each associated with short progression-free survival. The type A defect was associated with chemoresistance, whereas the type C defect was associated with early relapse. As expected, the type A defect was strongly associated with TP53 deletion/mutation. In contrast, the type C defect was not associated with any of the other prognostic factors examined, including TP53/ATM deletion, TP53 mutation, and IGHV mutational status. Detection of the type C defect added to the prognostic information provided by TP53/ATM deletion, TP53 mutation, and IGHV status.Conclusion: Our findings implicate blockade of the ATM-p53-p21 pathway at the level of p21 as a hitherto unrecognized determinant of early disease recurrence following successful cytoreduction. Clin Cancer Res; 18(15); 4191-200. Ó2012 AACR.

ATM mutations uniformly lead to ATM dysfunction in chronic lymphocytic leukemia: application of functional test using doxorubicin

“…The defects in ATM-p53-p21 pathway integrating response to DNA damage have shown independent prognostic value in CLL, 38 and effective functional testing of this pathway is, therefore, desirable. Initially, two basic defect types after IR exposure were defined as "type A", which associates with TP53 mutation, and "type B" connected with ATM mutation.…”

“…Initially, two basic defect types after IR exposure were defined as "type A", which associates with TP53 mutation, and "type B" connected with ATM mutation. 25 Later, "type C" that was correlated with polymorphism in p21 gene 39 and "type D", having unclear association with any gene defect 38 were described. The functional test based on IR may not, however, be convenient for all laboratories, and use of radiomimetic drugs seems to be a reasonable alternative approach.…”

ATM Mutations in Cancer: Therapeutic Implications

“…As referenced above, heterozygous germ-line ATM mutations appear to impart some vulnerability to chemotherapy and radiotherapy toxicity. To this end, many groups have designed assays to measure ATM protein function (36,54,63,64).…”

Assessment of TP53 functionality in chronic lymphocytic leukaemia by different assays; an ERIC‐wide approach

“…P-value <0Á05 was considered statistically significant. (Lin et al, 2012). (D) Results of the FACS-based assay are shown in a color format using MultiExperiment Viewer.…”

“…(D) Results of the FACS-based assay are shown in a color format using MultiExperiment Viewer. Values lower than the previously established cut-off (Lin et al, 2012) for given parameters were assigned green. Values higher than previously established cut-off were assigned red.…”