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.
OBJECTIVE
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.


METHODS
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.


CONCLUSIONS
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.
Department of Molecular and Clinical Cancer Medicine, University of Liverpool, Liverpool, United Kingdom.
Ke
K
Lin
Janet
J
Adamson
Gillian G
GG
Johnson
Anthony
A
Carter
Melanie
M
Oates
Rachel
R
Wade
Sue
S
Richards
David
D
Gonzalez
Estella
E
Matutes
Claire
C
Dearden
David G
DG
Oscier
Daniel
D
Catovsky
Andrew R
AR
Pettitt
D000368:Aged; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000627:therapeutic use; D064007:Ataxia Telangiectasia Mutated Proteins; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism*; D002699:Chlorambucil / Q000008:administration & dosage; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000235:genetics / Q000378:metabolism*; D003520:Cyclophosphamide / Q000008:administration & dosage; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D005260:Female; D005434:Flow Cytometry; D006801:Humans; D015451:Leukemia, Lymphocytic, Chronic, B-Cell / Q000097:blood / Q000188:drug therapy; D007963:Leukocytes, Mononuclear / Q000187:drug effects / Q000378:metabolism; D008297:Male; D008875:Middle Aged; D009154:Mutation; D011379:Prognosis; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D016032:Randomized Controlled Trials as Topic; D015398:Signal Transduction / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D016019:Survival Analysis; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism*; D025521:Tumor Suppressor Proteins / Q000235:genetics / Q000378:metabolism*; D014740:Vidarabine / Q000008:administration & dosage / Q000031:analogs & derivatives
C493956:CDKN1A protein, human; D018797:Cell Cycle Proteins; D050759:Cyclin-Dependent Kinase Inhibitor p21; D004268:DNA-Binding Proteins; D016159:Tumor Suppressor Protein p53; D025521:Tumor Suppressor Proteins; D002699:Chlorambucil; D003520:Cyclophosphamide; C576324:ATM protein, human; D064007:Ataxia Telangiectasia Mutated Proteins; D017346:Protein Serine-Threonine Kinases; D014740:Vidarabine; C024352:fludarabine