Antitrypanosomal Activities of Tryptanthrins

Abstract

New drugs and molecular targets are needed against Trypanosoma brucei, the protozoan that causes African sleeping sickness. Tryptanthrin (indolo[2,1-b]quinazoline-6,12-dione), a traditional antifungal agent, and 11 analogs were tested against T. brucei in vitro. The greatest activity was conferred by electron-withdrawing groups in the 8 position of the tryptanthrin ring system; the most potent compound had a 50% effective concentration of 0.40 M.Members of the Trypanosoma brucei species are flagellated protozoa that are transmitted by tsetse flies. They cause sleeping sickness in humans and a related disease in cattle. The characteristic meningoencephalitis of African sleeping sickness is fatal if it is not treated, and currently available drugs are limited by toxicity and growing parasite resistance (7,9,12). Unfortunately, in recent years there has been a dramatic and devastating resurgence of sleeping sickness (14). The need for safe and effective new antitrypanosomal agents is pressing.Tryptanthrin (indolo[2,1-b]quinazoline-6,12-dione; in Fig. 1, X is H in tryptanthrin) is a weakly basic alkaloid found in a number of plant species (11). This alkaloid is unusual in that its synthesis was described a half century before it was discovered as a natural product (6). Tryptanthrin is the active principal of a traditional Japanese herbal remedy for fungal infections (8). Subsequent studies extended the spectrum of antimicrobial activity to include bacteria (10, 11), particularly Mycobacterium tuberculosis (1). The activity of tryptanthrin against this intracellular organism prompted us to evaluate tryptanthrin and a series of derivatives of tryptanthrin against intracellular parasites, including Plasmodium falciparum, which causes malaria (13). In this report we describe the activities of a series of substituted tryptanthrins and 4-azatryptanthrins (Fig. 1) against Trypanosoma brucei, an extracellular protozoan parasite.Tryptanthrins. Tryptanthrin compounds were synthesized as described by Baker and Mitscher (1) and were characterized by their infrared and mass spectra. Stock solutions were prepared in dimethyl sulfoxide (99.8%; 27,685-5; Aldrich) and were then serially diluted into culture medium.Assay. Bloodstream-form T. brucei (MiTat 1.2, strain 427) organisms were grown axenically (5) at 37°C in HEPES-buffered Iscove's modified Dulbecco's medium that did not contain phenol red but that was supplemented with glutamate, hypoxanthine, cysteine, thymidine, sodium pyruvate, mercaptoethanol, bathocuproinedisulfonate, 10% Serum Plus, and 10% heat-inactivated fetal bovine serum, as described previously (2). Ten concentrations of each tryptanthrin were assayed in quadruplicate. Exponentially growing cells were incubated in 96-well plates (Falcon no. 3072 plates; Becton Dickinson) with or without test compound for 20 h and were then lysed and incubated for 3 to 6 h with p-nitrophenol phosphate. The acid phosphatase activity was determined, and 50% effective concentrations (EC 50 s) were obtained from curves fit to the da...

Natural Products Active Against African Trypanosomes: A Step Towards New Drugs

“…40 Tryptanthrin 44 (indolo [2,1-b]quinazoline-6,12-dione) is unusual in that its synthesis was described 50 years before it was discovered in a number of plant species. Scovill et al 41 The unsubstituted compounds were weakly active (IC 50 = 23 and 40 µM for 44 and 45 respectively). The antitrypanosomal activity was markedly improved by the presence of an electron-withdrawing group (halogen or nitro) at position 8 of the (aza)tryptanthrin ring system: the most active analog of the series, 4-aza-8-bromotryptanthrin 46, was up to 100 times more active than the unsubstituted parent compound 45 (IC 50 = 0.4 µM).…”

“…The antitrypanosomal activity was markedly improved by the presence of an electron-withdrawing group (halogen or nitro) at position 8 of the (aza)tryptanthrin ring system: the most active analog of the series, 4-aza-8-bromotryptanthrin 46, was up to 100 times more active than the unsubstituted parent compound 45 (IC 50 = 0.4 µM). 41 Camptothecin 47, a pentacyclic alkaloid from Camptotheca acuminata (Nyssaceae), is a well known antitumor agent and a specific inhibitor of human DNA topoisomerase I. Bodley et al have shown that 47 also inhibits the nuclear and mitochondrial topoisomerase I of T. b. brucei thus blocking DNA replication and inducing the death of bloodstream trypomastigotes (IC 50 = 1.6 µM). 42 In a study of a series of camptothecin analogs, the 9-substituted-10,11-methylenedioxy derivatives were significantly more active on T. b. brucei bloodstream trypomastigotes than the parent compound and retained as intracellular target the parasites' topoisomerase I.…”

Synthesis of some new mono, bis-indolo[1, 2-c]quinazolines: evaluation of their antimicrobial studies

“…30 The formation of intermediate azomethines (1)(2)(3)(4)(5)(6)(7)(8)(9)(10) disappearance of peaks at 1680-1695 cm -1 for -CHO and 3380-3440 cm -1 for -NH 2 of starting materials and at the same time appearance of band at 1610-1635 cm -1 which is characteristic for -CH=N group. 31 The formation of title compounds (11)(12)(13)(14)(15)(16)(17)(18)(19)(20) were confirmed by the disappearance of the absorption maxima at 3330-3400 cm -1 , which are ascribed to the vibrations of NH group of the indole ring; at the same time the appearance of a new maximum at 1360-1380 cm -1 , which is characteristic for indolo [1,2-c] quinazoline ring with a tertiary nitrogen atom, appears. 32 The exhibited chemical shifts obtained from 1 H NMR spectra of compounds 1-20 supported the proposed structures of the compounds.…”

“…Screening results are summarized in Table 1. The antimicrobial screening revealed that some of the compounds (15)(16)(17)(18)(19)(20) showed high activity against all bacterial and fungal strains. In particular, bis-indolo [1,2-c] quinazolines (19 and 20) showed excellent activity against all tested strains.…”

“…Fused cyclic indole derivatives, such as indolocarbazoles, 16,17 indolo[2,3-b] quinolines, 18,19 indolo[l,2-c] quinazolines, 20,21 bis-indoles 22,23 and many others, have also interesting pharmacological properties. Moreover, indoles and their cyclic derivatives constitute an important class of compounds for new drug development in order to discover an effective compound against multi-drug-resistant microbial infections.…”