The novel sequence-specific DNA cross-linking agent SJG-136 (NSC 694501) has potent and selective in vitro cytotoxicity in human B-cell chronic lymphocytic leukemia cells with evidence of a p53-independent mechanism of cell kill.
SJG-136 (NSC 694501) is a novel DNA cross-linking agent that binds in a sequence-selective manner in the minor groove of the DNA helix. It is structurally novel compared with other clinically used DNA cross-linking agents and has exhibited a unique multilog differential pattern of activity in the NCI 60-cell line screen (i.e., is COMPARE negative to other cross-linking agents). Given this profile, we undertook a preclinical evaluation of SJG-136 in primary tumor cells derived from 34 B-cell chronic lymphocytic leukemia (B-CLL) patients. SJG-136 induced apoptosis in all of the B-CLL samples tested with a mean LD50 value (the concentration of drug required to kill 50% of the cells) of 9.06 nmol/L. Its cytotoxicity was undiminished in B-CLL cells derived from patients treated previously, those with unmutated VH genes, and those with p53 mutations (P=0.17; P=0.63; P=0.42, respectively). SJG-136-induced apoptosis was associated with the activation of caspase-3 that could be partially abrogated by the caspase-9 inhibitor Z-LEHD-FMK. Furthermore, SJG-136 did not trigger the phosphorylation of p53 or the up-regulation of GADD45 expression in B-CLL cells whereas the cross-linking agent chlorambucil elicited both of these effects. This suggests that SJG-136 cross-linking adducts are not subject to p53-mediated DNA excision repair mechanisms in B-CLL cells. Taken together, these data demonstrate a novel mechanism of action for SJG-136 that appears to circumvent the effects of poor prognostic markers. This unique cytotoxicity profile warrants further investigation and supports the evaluation of this agent in Phase I clinical trials for patients with B-CLL.
Pepper
Christopher J
CJ
Department of Haematology, University of Wales College of Medicine, Cardiff, United Kingdom. peppercj@cf.ac.uk
Hambly
Rachel M
RM
Fegan
Christopher D
CD
Delavault
Patrick
P
Thurston
David E
DE
D017209:Apoptosis / Q000187:drug effects; D001402:B-Lymphocytes / Q000166:cytology / Q000187:drug effects / Q000473:pathology; D001569:Benzodiazepines / Q000494:pharmacology; D001570:Benzodiazepinones / Q000494:pharmacology*; D016022:Case-Control Studies; D053148:Caspase 3; D020169:Caspases / Q000378:metabolism; D003432:Cross-Linking Reagents / Q000494:pharmacology*; D004249:DNA Damage; D004260:DNA Repair; D004789:Enzyme Activation; D006801:Humans; D020014:K562 Cells; D015451:Leukemia, Lymphocytic, Chronic, B-Cell / Q000097:blood / Q000188:drug therapy* / Q000235:genetics / Q000473:pathology; D011758:Pyrroles / Q000494:pharmacology*; D013601:T-Lymphocytes / Q000166:cytology / Q000187:drug effects / Q000473:pathology; D014407:Tumor Cells, Cultured; D016159:Tumor Suppressor Protein p53 / Q000502:physiology*; D014740:Vidarabine / Q000031:analogs & derivatives* / Q000494:pharmacology
C423343:1,1'-((propane-1,3-diyl)dioxy)bis(7-methoxy-2-methylidene-1,2,3,10,11,11a-hexahydro-5H-pyrrolo(2,1-c)(1,4)benzodiazepin-5,11-dione); D001570:Benzodiazepinones; D003432:Cross-Linking Reagents; D011758:Pyrroles; D016159:Tumor Suppressor Protein p53; D001569:Benzodiazepines; C505407:CASP3 protein, human; D053148:Caspase 3; D020169:Caspases; D014740:Vidarabine; C024352:fludarabine