A series of 70 triazine derivatives have been synthesized and tested for their capacity to modulate multidrug resistance (MDR) in DC-3F/AD and KB-A1 tumor cells in vitro, in comparison with verapamil (VRP), a calcium channel antagonist currently used in therapy as an antihypertensive drug, which also shows MDR modulating activity. Among the 12 selected compounds, 16 (S9788) showed high MDR reversing properties in vitro (300- and 6-fold VRP at 5 microM in DC-3F/AD and KB-A1 cells, respectively) and induced a strong accumulation of adriamycin. The relationship between the increase of ADR accumulation and the fold reversal induced by these compounds and their lack of effects on the sensitive DC-3F cells suggest that they act mainly by inhibiting the P-glycoprotein (Pgp) catalyzed efflux of cytotoxic agents, as already described for a majority of MDR modulators. In vivo, in association with the antitumor drug vincristine (0.25 mg/kg), 16 (100 mg/kg) increased the T/C by 39% in mice bearing the resistant tumor cell line P388/VCR. According to these interesting properties, 16 was selected for a clinical development because it was more bioavailable than 34, even though it was less active.

A new series of imidazolyl nitrones spin traps has been synthesized and evaluated pharmacologically. The salient structural feature of these molecules is the presence of an imidazole moiety substituted by aromatic or heteroaromatic cycles. This connectivity imparts to the nitrone superior neuroprotective properties in vivo and in parallel reduced side effects and toxicity. Thus compound 6a (a 2-phenylimidazolyl nitrone) administered intraperitoneally protects (80%) mice from lethality induced by an intracerebroventricular administration of tert-butyl hydroperoxide (t-BHP) an oxidant capable of inducing neurodegenerative processes. Administration of the archetypal nitrone phenyl-tert-butyl nitrone (PBN) at an equimolar dose also affords some protection (60%) in this test. However, this activity is accompanied by hypothermia, whereas no such effect is apparent for 6a. Moreover, previously prepared nonsubstituted or alkyl-substituted imidazolyl nitrones were shown to be extremely toxic to rats in contrast to the compounds prepared in this study. The observed activities in vivo correlate well with the calculated partition coefficients (ClogP) and HOMO energy level.

S 9788 is a novel triazinoaminopiperidine derivative which does not belong to any of the classes of compounds known to reverse multidrug resistance (MDR). S 9788 was far more potent than verapamil (VRP) in reversing resistance to adriamycin (ADR) in the ADR-selected murine leukaemia cell lines P388/ADR-1 and P388/ADR-10, and the human chronic myelogenous leukaemia K562/R. Fold reversion with S 9788 (5 microM) was, respectively, 3.5, 5.4 and 11.3 times greater than that with VRP (5 microM). S 9788 was also a more potent reversant of ADR resistance in the intrinsically resistant human colon adenocarcinoma COLO 320DM (2.3 fold), and of vincristine (VCR) resistance in the human MDR1 gene-transfected squamous lung carcinoma line S1/tMDR1 (5.6 fold). The activity of S 9788 depended on both the MDR cell line and the cytotoxic agent. S 9788 (50-100 mg/kg/d) administered IP once a day on days 1-4 resulted in a dose-dependent increase in the chemotherapeutic effect of VCR (0.25 mg/kg/d) in P388/VCR - bearing mice and ADR (4 mg/kg/d) in P388/ADR - bearing mice. Increases in antitumor activity were (% T/C) of +20-34% in the P388/ADR model and + 50-78% in the P388/VCR model with respect to cytotoxic agent treatment alone. S 9788 appeared to be devoid of toxicity at its effective doses. The mechanism of action of S 9788 is unknown but S 9788 (0.5-10 microM) induced a dose-dependent increase in ADR accumulation in KB-Al cells and compared to verapamil its effect was twice as active and approximately seven times more potent. We conclude that S 9788 is a novel agent capable of reversing MDR in vitro and in vivo, and whose pharmacological profile warrants its selection as a candidate drug for eventual assessment in the clinic.

A series of 36 purine and purine analog derivatives have been synthesized and tested for their ability to modulate multidrug resistance in vitro (P388/VCR-20 and KB-A1 cells) and in vivo (P388/VCR leukemia). Compounds were compared to S9788, a triazine derivative which has already shown some activity during phase 1 clinical trials and also a limiting cardiovascular side effect possibly linked to its calcium channel affinity. The fact that active compounds increase adriamycin accumulation in the resistant KB-A1 cells, and not in the sensitive KB-3-1 cells, suggests they act predominantly by inhibiting the P-glycoprotein-catalyzed efflux of cytotoxic agents. No direct relation was found between the affinity for the phenylalkylamine binding site of the calcium channel and in vitro sensitization of resistant cells. In vivo, when administered po in association with vincristine (0.25 mg/kg), five compounds (3, 4, 9, 25, and 26), of very differing calcium channel affinities (Ki from 5 to 560 nM), fully restored (T/V > or = 1.4) the sensitivity of P388/VCR leukemia to vincristine.

S 9788, a new triazinoaminopiperidine derivative, was found to be a potent reversant of vincristine resistance in the in vivo murine leukemic P388/VCR model. In two treatment regimens (Q4D days 1, 5 and 9 and QD days 1-9), S 9788 enhanced the antitumor activity of vincristine in a dose-dependent manner, resulting in a complete circumvention of drug resistance for well-tolerated doses of S 9788. S 9788 was also effective in enhancing therapeutic effects of vincristine in the treatment of sensitive P388-bearing mice. These results strongly suggest that S 9788 may be a potential candidate for circumvention of multidrug resistance (MDR) in clinical practice.