The antiproliferative agent MLN944 preferentially inhibits transcription

Abstract

MLN944 is a novel compound currently being codeveloped by Millennium Pharmaceuticals and Xenova Ltd. as a cancer therapeutic and is in a phase I clinical trial for solid tumors. Although MLN944 was originally proposed to function as a topoisomerase I and II inhibitor, more recent data has shown that it is a DNA-intercalating agent that does not inhibit the catalytic activity of topoisomerase I or II. We show here that MLN944 inhibits incorporation of radiolabeled precursors into RNA preferentially over incorporation into DNA and protein in HCT116 and H460 cells. To determine if MLN944 inhibits transcription, a human RNA polymerase II in vitro transcription system was used. MLN944 inhibited initiation when added before or after the formation of preinitiation complexes and inhibited elongation at higher concentrations. The preferential inhibition of initiation differentiates MLN944 from actinomycin D, which more strongly inhibits elongation. Transcription of all RNA polymerases was inhibited in nuclei isolated from HeLa cells treated with low concentrations of MLN944. Our data are consistent with transcription as the target of the potent cytotoxic effects of MLN944. [Mol Cancer Ther 2005;4(8):1260 -7]

XR5944: A potent inhibitor of estrogen receptors

“…1A) is a bis-phenazine in phase I clinical trials (9). It originated from a rational drug design program aimed at developing potential topoisomerase inhibitors (10).…”

“…The parent compounds of XR5944, phenazinecarboxamides, as well as closely related acridinecarboxamides, are both dual DNA topoisomerase I/II inhibitors (11 -13). Although initial reports showed that XR5944 could bind strongly to DNA and that it may interfere with the normal function of topoisomerase I and II in vitro (14), recent studies have indicated that the primary mechanism of XR5944 action is independent of topoisomerases and, furthermore, that it is related with transcription inhibition (9,15). XR5944 has shown exceptional activity against human and murine tumor models both in vitro and in vivo and was significantly more potent than well-known topoisomerase inhibitors such as doxorubicin, topotecan, and TAS-103 (14).…”

Considerations for Treatment Development in Rhabdomyosarcoma: In Vitro Assessment of Novel DNA Binding Drugs

“…Within this class, the clinical candidate MLN944/XR5944 bisintercalates with its linker in the DNA major groove making hydrogen bonding interactions to guanines in a sequence specific manner. This compound possesses a unique mechanism of action, including the inhibition of transcription factor binding to DNA, which ultimately leads to the inhibition of transcription (Byers et al, 2005). The bis(phenazine-1-carboxamides) studied are of two structural types: SN26356 (MLN944/XR5944) and SN26700 are 9-methylphenazines joined via a dicationic -(CH2)2NH(CH2)NH(CH2)2-linker, and differ in that SN26700 has the amines substituted with a methyl group ( Figure 1B).…”

“…This generalized resistance to the bisacridines also extends to the bis(phenazinecarboxamide) dimers, with one important exception. These compounds were designed as bisintercalating topoisomerase I and II poisons (Spicer et al, 2000), but their actual mechanism of action is complex and appears to involve both transcription inhibition, along with topoisomerase I poisoning (Byers et al, 2005). The three compounds studied here are potently cytotoxic in mouse leukemia P388, mouse Lewis lung and Jurkat human leukemia cells (Gamage et al, 2001).…”

First-into-man phase I and pharmacokinetic study of XR5944.14, a novel agent with a unique mechanism of action

“…Initially, it was thought to interfere with the normal function of topoisomerase I and II (Stewart et al, 2001). Recent studies, however, have indicated that the agent intercalates into DNA and inhibits transcription, but has no effect on the catalytic activity of either topoisomerase I or II (Dai et al, 2004;Byers et al, 2005). XR5944.14 induces a G(1) and G(2) cell cycle arrest (Sappal et al, 2004).…”