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

Abstract

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.

SG2285, a Novel C2-Aryl-Substituted Pyrrolobenzodiazepine Dimer Prodrug That Cross-links DNA and Exerts Highly Potent Antitumor Activity

“…Potent in vitro activity was also confirmed in primary B-CLL samples with an LD 50 value more than 2 logs lower than fludarabine, the current treatment choice for this condition, and lower than SJG-136 (30). Importantly, SG2285 exhibited significant differential apoptotic activity (by the intrinsic apoptotic pathway) between normal B and T lymphocytes, and B-CLL cells.…”

The sesquiterpene lactone parthenolide induces selective apoptosis of B-chronic lymphocytic leukemia cells in vitro

“…8 Recent studies have therefore focused on drugs that induce CLL cell killing via direct interaction with novel cellular targets involved in apoptosis regulation. [9][10][11][12] There has also been considerable interest in natural products active against CLL cells, including the green tea polyphenol epigallocatechin-3-gallate 13 and the bacterial metabolite prodigiosin. 14 The sesquiterpene lactone parthenolide (PTL) has been widely used in traditional medicine for the treatment of migraines and inflammation.…”

Direct liquid chromatography determination of the reactive imine SJG-136 (NSC 694501)

“…SJG-136 (NSC 694501); 8,8 -[[(propane-1,3-diyl)dioxy]-bis[(11aS)-7-methoxy-2-methylidene-1,2,3,11a-tetrahydro-5H-pyrrolo [2,1-c] [1,4]benzodiazepin-5-one]) is a novel sequence-selective DNA-interactive minor-groove interstrand cross-linking agent that has shown significant activity in both in vitro and in vivo models [1][2][3][4][5][6][7]. It binds in the minor groove of DNA, predominantly at Purine-GATC-Pyrimidine sequences, cross-linking the two guanine residues on opposite strands via covalent aminal bonds between the N2-positions of the guanine residues and the C11/C11 -positions (CH N) of SJG-136 molecules [1,2].…”