Inhibition of the intrinsic apoptosis pathway downstream of caspase-9 activation causes chemotherapy resistance in diffuse large B-cell lymphoma.
OBJECTIVE
Inhibition of the apoptosis cascade is an important cause of therapy resistance in diffuse large B-cell lymphomas (DLBCL). In this study, we investigated possible mechanisms and expression levels of apoptosis-related genes in the apoptosis pathway that may be responsible for differences in chemotherapy sensitivity between DLBCL patients.


METHODS
Twenty-eight DLBCL patient samples were investigated for their expression levels of apoptosis-related genes using reverse transcription-multiplex ligation-dependent probe amplification analysis. Functional analysis of the intrinsic, caspase-9-mediated pathway was done using fluorescence-activated cell sorting analysis, Western blot analysis, and immunohistochemistry.


RESULTS
Two DLBCL groups were identified: one with low expression levels of both proapoptotic and antiapoptotic genes and one group with high expression levels of these genes. DLBCL with high expression levels of proapoptotic and antiapoptotic genes frequently seemed to be refractory to clinical chemotherapy. Functional analysis in these latter DLBCL samples and DLBCL cell lines with comparable expression profiles revealed high levels of spontaneous caspase-9 activity without induction of apoptosis, indicating disruption of the apoptosis pathway downstream of caspase-9 activation. This disruption of the apoptosis pathway could be restored using a small-molecule XIAP antagonist.


CONCLUSIONS
We conclude that the intrinsic, caspase-9-mediated apoptosis pathway is constitutively activated in part of chemotherapy-refractory DLBCL with concomitant downstream inhibition of the convergence apoptosis pathway and that inhibition of XIAP might be an alternative therapy for chemotherapy-refractory DLBCL.
Department of Clinical Pathology, VU University Medical Center, Amsterdam, the Netherlands.
Saskia A G M
SA
Cillessen
Corine J
CJ
Hess
Erik
E
Hooijberg
Kitty C M
KC
Castricum
Pim
P
Kortman
Fedor
F
Denkers
Wim
W
Vos
Mark A
MA
van de Wiel
Gerrit J
GJ
Schuurhuis
Gert J
GJ
Ossenkoppele
Chris J L M
CJ
Meijer
Joost J
JJ
Oudejans
D000814:Aniline Compounds / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology*; D051017:Apoptosis Regulatory Proteins / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism; D053148:Caspase 3 / Q000378:metabolism; D053453:Caspase 9 / Q000378:metabolism*; D061945:Caspase Inhibitors; D045744:Cell Line, Tumor; D019008:Drug Resistance, Neoplasm; D004789:Enzyme Activation / Q000187:drug effects; D005047:Etoposide / Q000494:pharmacology; D015870:Gene Expression; D006801:Humans; D016403:Lymphoma, Large B-Cell, Diffuse / Q000188:drug therapy* / Q000235:genetics / Q000378:metabolism*; D010671:Phenylurea Compounds / Q000494:pharmacology; D051636:X-Linked Inhibitor of Apoptosis Protein / Q000037:antagonists & inhibitors* / Q000378:metabolism
D000814:Aniline Compounds; D051017:Apoptosis Regulatory Proteins; D061945:Caspase Inhibitors; C500895:N-(6-((anilinocarbonyl)amino)-5-((anilinocarbonyl)((1-(4-cyclohexylbutyl)pyrrolidin-2-yl)methyl)amino)hexyl)-N-methyl-N'-phenylurea; D010671:Phenylurea Compounds; D051636:X-Linked Inhibitor of Apoptosis Protein; C496866:XIAP protein, human; D005047:Etoposide; D053148:Caspase 3; D053453:Caspase 9