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N-Substituted 4-Aminobenzamides (Procainamide Analogs): An Assessment of Multiple Cellular Effects Concerning Ion Trapping

Centre de Recherche en Rhumatologie et Immunologie (G.M., F.M.) and Biotechnology and Bioengineering Unit, Hôpital St-François d'Assise (E.M., R.C.-G.), Centre Hospitalier Universitaire de Québec, Québec, Québec, Canada

Procainamide and related triethylamine-substituted 4-aminobenzamides, such as metoclopramide and declopramide, exert cellular effects potentially exploitable in oncology at millimolar concentrations (DNA demethylation, nuclear factor-B inhibition, apoptosis) and display anti-inflammatory properties. However, these drugs induce massive cell vacuolization at similar concentrations, a response initiated by vacuolar (V-) ATPase-dependent ion trapping into and osmotic swelling of acidic organelles. We have examined whether this overlooked response might be related to the effects on cell proliferation and viability using cultured vascular smooth muscle cells and tumor-derived cell lines (Morris 7777 hepatoma, HT-1080 fibrosarcoma). Giant vacuole formation, of confirmed trans-Golgi origin (labeled with C5-ceramide, p230, golgin-97), is a cellular response to all tested amines in the series (2.5 mM), including triethylamine. These drugs and the V-ATPase inhibitor bafilomycin A1 inhibited smooth muscle cell proliferation, suggesting that acidification of a cellular compartment is essential to cell division. The cytotoxicity was maximal with metoclopramide, and this effect was minimally influenced by bafilomycin A1; furthermore, metoclopramide (2.5 mM) induced apoptosis in tumor cells as judged by poly(ADP-ribose)polymerase (PARP) cleavage. Triethylamine and procainamide exhibit a low level of cytotoxicity variably reduced by bafilomycin cotreatment. In Morris cells, the secretion of -fetoprotein is inhibited by amines, consistent with the impairment of the secretory pathway. The most highly substituted 4-aminobenzamides are significant NF-B inhibitors in smooth muscle cells. Although some effects of 4-aminobenzamides are independent of V-ATPase-driven ion trapping (inhibition of NF-B nuclear translocation, agent-specific cytotoxicity, PARP cleavage), other effects are dependent on this phenomenon (vacuolization, a component of the cytotoxicity, inhibition of secretion).

Address correspondence to: Dr. François Marceau, Centre Hospitalier Universitaire de Québec, Centre de Recherche en Rhumatologie et Immunologie, 2705 Laurier Blvd., Québec, QC, Canada G1V 4G2. E-mail: francois.marceau{at}crchul.ulaval.ca