The effect of monensin and chloroquine on the endocytosis and toxicity of chimeric toxins |
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Authors: | R Ippoliti P Ginobbi E Lendaro I D'Agostino D Ombres P A Benedetti M Brunori G Citro |
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Institution: | (1) Istituto Pasteur-Fondazione Cenci Bolognetti, Department of Biochemical Sciences ‘A. Rossi-Fanelli’, University of Rome ‘La Sapienza’, P. le Aldo Moro 5, I-00185 Rome (Italy), Fax +39 6 4440062, e-mail: ippoliti@axrma.uniroma1.it, IT;(2) Experimental Chemotherapy Laboratory, Regina Elena Cancer Institute, Rome (Italy), IT;(3) CNR Biophysics Institute, Pisa (Italy), IT |
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Abstract: | The toxicity of two conjugates containing ribosome-inactivating proteins (RIPs, i.e. saporin and ricin-A chain x-linked to
transferrin) has been measured on a prostatic cancer line (PC3) naturally overexpressing the transferrin receptor, in the
presence of monensin and chloroquine. This paper investigates whether the increased toxicity of Tf-RIPs induced by monensin
and chloroquine may be due to alterations of the normal endocytotic pathway of the complexes mediated by the transferrin receptor.
Monensin, besides inducing alkalinization of normally acid intracellular compartments, causes an accumulation of the receptor-bound
Tf-RIP in a perinuclear region contiguous to the cisternae of the trans-Golgi network. Chloroquine, though increasing the
intracellular pH, seems not to modify the endocytotic pathway of these chimeric molecules. We believe that the enhanced toxicity
of the Tf-RIPs may be related to intracellular alkalinization (i.e. endosomal or lysosomal pH) rather than to the effects
on the recycling of transferrin receptor-bound toxins. We conclude that the efficacy of chimeric toxins may be modulated not
only by the carrier used for their engineering but also by addition of drugs able to influence the stability and activation
of the toxins inside the cell.
Received 22 December 1997; received after revision 30 March 1998; accepted 15 May 1998 |
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Keywords: | , Ricin, transferrin, monensin, chloroquine, endocytosis, chimeras, cancer, |
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