Tetramethylpiperidine-substitution increases the antitumor activity of the riminophenazines for an acquired multidrug-resistant cell line.

The multidrug resistance (MDR)-neutralizing and cytotoxic properties of five tetramethylpiperidine (TMP)-substituted phenazines were compared with those of their corresponding isopropyl-substituted analogues using a P-glycoprotein (P-gp)-expressing small cell lung cancer cell line (H69/LX4). All of the TMP-substituted phenazines tested outperformed their isopropyl analogues with respect to both cytotoxic and chemosensitizing properties, indicating the importance of TMP-substitution when designing novel riminophenazines with increased activity against MDR cancer cell lines. Of the TMP-substituted phenazines tested, B4112, chlorinated at position 3 of the phenyl- and anilino-rings, had the most potent anti-cancer activity in vitro, making this agent a potential candidate for evaluation in experimental and clinical oncology.