RPR112378 and RPR115781: Two Representatives of a New Family of Microtubule Assembly Inhibitors
- Cécile Combeau,
- Jean Provost,
- Frédérique Lancelin,
- Yann Tournoux,
- François Prod'homme,
- Frédéric Herman,
- François Lavelle,
- Jean Leboul and
- Marc Vuilhorgne
Abstract
A screening program aimed at the discovery of new antimicrotubule agents yielded RPR112378 and RPR115781, two natural compounds extracted from the Indian plant Ottelia alismoides. We report their isolation, structural determination, and mechanisms of action. RPR112378 is an efficient inhibitor of tubulin polymerization (IC50 = 1.2 μM) and is able to disassemble preformed microtubules. Regarding tubulin activity, RPR115781 is 5-fold less active than RPR112378. Tubulin-RPR112378 complexes, when isolated by gel filtration, were able to block further tubulin addition to growing microtubules, a mechanism that accounts for the substoichiometric effect of the drug. RPR112378 was found to prevent colchicine binding but not vinblastine binding to tubulin. Although colchicine binding is known to induce an increase of tubulin GTPase activity, no such increase was observed with RPR112378. We show that RPR112378 is a highly cytotoxic compound and that RPR115781 is 10,000-fold less active as an inhibitor of KB cell growth. Part of the cytotoxicity of RPR112378 is probably caused by a reaction of addition with sulfhydryl groups, an observation that has not been made with RPR115781. In conclusion, these molecules represent a new class of inhibitors of microtubule assembly with potential therapeutic value.
Footnotes
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Send reprint requests to: Dr. C. Combeau, Department of Oncology, Rhône-Poulenc Rorer S.A., Centre de Recherche de Vitry-Alfortville, 13 quai Jules Guesde, 94403 Vitry-Sur-Seine Cedex, France. E.mail: cecile.combeau{at}rp-rorer.fr
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This work was presented at the 37th American Association for Cancer Research meeting, April 20–24, 1996, Washington DC [Combeau C, Lancelin F, Provost J, Commerçon A, Riou J-F and Lavelle F (1996) Mechanism of action of RPR 112378, a new inhibitor of tubulin polymerization. Proc Am Assoc Cancer Res 37: abstr. 3006].
- Abbreviations:
- TLC
- thin-layer chromatography
- MES
- 2-(N-morpholino)ethanesulfonic acid
- IR
- infrared
- amu
- atomic mass units
- nOe
- nuclear Overhauser exchange
- HPLC
- high-performance liquid chromatography
- RB
- reassembly buffer
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- Received March 26, 1999.
- Accepted December 9, 1999.
- The American Society for Pharmacology and Experimental Therapeutics
