Multiple mechanisms of action of the benzamides and nicotinamides as sensitizers of radiotherapy: opportunities for drug design

Synthesis and in vitro biological evaluation of novel diaminothiophene scaffolds as antitumor and anti-influenza virus agents. Part 2

Herein, we report the synthesis and biological evaluation of a novel series of diethyl 2,5-diaminothiophene-3,4-dicarboxylate (DDTD) derivatives as antitumor and anti-influenza virus agents.

Novel synthesis of nicotinamide derivatives of cytotoxic properties

A variety of 2-substituted-4,6-diaryl-3-pyridinecarboxamides 5 were synthesized through aromatic nucleophilic substitution reaction of secondary amines with 2-bromo analogues 4. The latter were obtained via bromination of 2-cyano-3,5-diaryl-5-oxo-N-substituted pentamides 3 in glacial acetic acid. Moreover, pentamide derivatives 3 were prepared through base-catalyzed Michael addition of cyanacetanilides 2 with 1,3-diaryl-2-propen-1-ones 1. Otherwise, reaction of 2-bromo-3-pyridinecarboxamides 4 with primary aromatic amines in refluxing pyridine afforded the corresponding 2-(arylamino)-3-pyridinecarboxamides 6 besides the unexpected 2-unsubstituted amino analogues 7. Antitumor properties of the synthesized pyridinecarboxamides utilizing 59 different human tumor cell lines, representing leukemia, melanoma, and cancers of the lung, colon, brain, ovary, breast, prostate as well as kidney, were screened. Many of the tested compounds show considerable in vitro antitumor properties especially 5c and 7a, which reveal moderate activities against most of the used human tumor cell lines. It has also been achieved that, all the tested nicotinamide derivatives reveal promising antitumor properties against MDA-MB-231/ATCC (breast cancer).

Gene knockout or pharmacological inhibition of poly(ADP-ribose) polymerase-1 prevents lung inflammation in a murine model of asthma

Airway inflammation is a central feature of asthma and chronic obstructive pulmonary disease. Reactive oxygen species (ROS) contribute to inflammation by damaging DNA, which, in turn, results in the activation of poly(ADP-ribose) polymerase-1 (PARP-1) and depletion of its substrate, nicotinamide adenine dinucleotide. Here we show that prevention of PARP-1 activation protects against both ROS-induced airway epithelial cell injury in vitro and airway inflammation in vivo. H(2)O(2) induced the generation of ROS, PARP-1 activation and concomitant nicotinamide adenine dinucleotide depletion, and release of lactate dehydrogenase in A549 human airway epithelial cells. These effects were blocked by the PARP-1 inhibitor 3-aminobenzamide (3-AB). Furthermore, 3-AB inhibited both activation of the proinflammatory transcription factor nuclear factor-kappaB and expression of the interleukin-8 gene induced by H(2)O(2) in these cells. In a murine model of allergen-induced asthma, 3-AB prevented airway inflammation elicited by ovalbumin. Moreover, PARP-1 knockout mice were resistant to such ovalbumin-induced inflammation. These protective effects were associated with an inhibition of expression of the inducible nitric oxide synthase. These results implicate PARP-1 activation in airway inflammation, and suggest this enzyme as a potential target for the development of new therapeutic strategies in the treatment of asthma as well as other respiratory disorders such as chronic obstructive pulmonary disease.

Mechanism of action for N-substituted benzamide-induced apoptosis

We have analysed the mechanism of action for induction of apoptosis by N-substituted benzamides using declopramide as a lead compound. We show here that declopramide at doses above 250 microM in the mouse 70Z/3 pre-B cell line or in the human promyeolocytic cancer cell line HL60 induced cytochrome c release into the cytosol and caspase-9 activation. The broad spectrum caspase inhibitor zVADfmk and caspase-9 inhibitor zLEDHfmk inhibited apoptosis and improved cell viability when administrated to cells 1 h before exposure to declopramide, whereas the caspase-8 inhibitor zIEDHfmk had less effect. Also, the over expression of Bcl-2 by transfection in 70Z/3 cells inhibited declopramide-induced apoptosis. Prior to the induction of apoptosis, a G(2)/M cell cycle block was induced by declopramide. The cell cycle block was also observed in the presence of broad spectrum caspase inhibitor zVADfmk and in a transfectant expressing high levels of Bcl-2. Furthermore, while p53 was induced in 70Z/3 cells by declopramide, neither the apoptotic mechanism nor the G(2)/M cell cycle block were dependent on p53 activation since both effects were also seen in p53 deficient HL60 cells after addition of declopramide.

N-substituted benzamides inhibit nuclear factor-kappaB and nuclear factor of activated T cells activity while inducing activator protein 1 activity in T lymphocytes

N-substituted benzamides are compounds that have recently been reported to inhibit nuclear factor-kappaB (NF-kappaB) activity and induce apoptosis in a pre-B cell line. In this study, we focused on the effects of N-substituted benzamides on transcriptional regulation in Jurkat T cells. We used a model system where the cells can be stimulated either through TCR/CD28 or by treatment of the cells with PMA and ionomycin to induce transcription factors typical for T lymphocyte activation. Treatment of the Jurkat cells with procainamide did not influence the transcription factor profile of stimulated cells, while treatment with a derivative having an acetyl group in position 4 of the aromatic ring inhibited NF-kappaB and nuclear factor of activated T cells (NFAT) activity. Declopramide, which contains a chloride in position 3 of the aromatic ring, was inactive in this system, whereas also the acetylated derivative of this compound inhibited NF-kappaB and NFAT activity. In contrast, the transcriptional activity and nuclear expression of activator protein 1 induced by TCR/CD28 stimulation or PMA and ionomycin treatment was enhanced by the acetylated variants of the N-substituted benzamides. Finally, we investigated the effect of N-substituted benzamides on intact promoters for two genes central in immune regulation; the CD40 ligand (CD40L) and IL-2 promoters. The transcriptional activity of the CD40L promoter as well as surface expression of the CD40L induced by signaling through TCR/CD28 was inhibited by addition of acetylated N-substituted benzamides, while the transcriptional activity of the IL-2 promoter was enhanced. Taken together, these data indicate that derivatives of N-substituted benzamides are potential drug candidates for quantitative as well as qualitative modulation of immune functions.

N-substituted benzamides inhibit NFkappaB activation and induce apoptosis by separate mechanisms

Benzamides have been in clinical use for many years in treatment against various disorders. A recent application is that as a sensitizer for radio- or chemotherapies. We have here analysed the mechanism of action of N-substituted benzamides using an in vitro system. We found that while procainamide was biologically inert in our system, the addition of a chloride in the 3' position of the benzamide ring created a compound (declopramide) that induced rapid apoptosis. Furthermore, declopramide also inhibited NFkappaB activation by inhibition of IkappaBbeta breakdown. An acetylated variant of declopramide, N-acetyl declopramide, showed no effect with regard to rapid apoptosis induction but was a potent inhibitor of NFkappaB activation. In fact, the addition of an acetyl group to procainamide in the 4' position was sufficient to convert this biologically inactive substance to a potent inhibitor of NFkappaB activation. These findings suggest two potential mechanisms, induction of early apoptosis and inhibition of NFkappaB mediated salvage from apoptosis, for the biological effect of N-substituted benzamides as radio- and chemo-sensitizers. In addition it suggests that N-substituted benzamides are potential candidates for the development of anti-inflammatory compounds using NFkappaB as a drug target.