Synthesis and in vitro cytotoxicity of hexacyclic camptothecin analogues

A derivative of the natural compound kakuol affects DNA relaxation of topoisomerase IB inhibiting the cleavage reaction

Topoisomerases IB are anticancer and antimicrobial targets whose inhibition by several natural and synthetic compounds has been documented over the last three decades. Here we show that kakuol, a natural compound isolated from the rhizomes of Asarum sieboldii, and a derivative analogue are able to inhibit the DNA relaxation mediated by the human enzyme. The analogue is the most efficient one and the inhibitory effect is enhanced upon pre-incubation with the enzyme. Analysis of the different steps of the catalytic cycle indicates that the inhibition occurs at the cleavage level and does not prevent DNA binding. Molecular docking shows that the compound preferentially binds near the active site at the bottom of the catalytic residue Tyr723, providing an atomistic explanation for its inhibitory activity.

The use of endophytes to obtain bioactive compounds and their application in biotransformation process

Endophytes are microorganisms that reside asymptomatically in the tissues of higher plants and are a promising source of novel organic natural metabolites exhibiting a variety of biological activities. The laboratory of Bioaromas (Unicamp, Brazil) develops research in biotransformation processes and functional evaluation of natural products. With the intent to provide subsidies for studies on endophytic microbes related to areas cited before, this paper focuses particularly on the role of endophytes on the production of anticancer, antimicrobial, and antioxidant compounds and includes examples that illustrate their potential for human use. It also describes biotransformation as an auspicious method to obtain novel bioactive compounds from microbes. Biotransformation allows the production of regio- and stereoselective compounds under mild conditions that can be labeled as "natural," as discussed in this paper.

Camptothecin and its analogues: a review on their chemotherapeutic potential

Topoisomerase I (Topo-I) is a major target for anticancer drug discovery and design. As a result, Topo-I inhibitors constitute an important class of the current anticancer drugs. To date, all of the Topo-I inhibitors that have been clinically evaluated are analogues of camptothecin (CPT), an extract of the Chinese tree Camptotheca acuminata. CPT has shown significant antitumor activity to lung, ovarian, breast, pancreas and stomach cancers. In this article the, phytochemical aspect, and various structural modifications are comprehensively reviewed as in rings A, B, C, D and E. Biological activity of camptothecin, other than anticancer, reported till the year 2003 has also been discussed.

Camptothecins

Camptothecin analogues and derivatives appear to exert their antitumour activity by binding to topoisomerase I and have shown significant activity against a broad range of tumours. In general, camptothecins are not substrates for either the multidrug-resistance P-glycoprotein or the multidrug-resistance-associated protein (MRP). Because of manageable toxicity and encouraging activity against solid tumours, camptothecins offer promise in the clinical management of human tumours. This review illustrates the proposed mechanism(s) of action of camptothecins and presents a concise overview of current camptothecin therapy, including irinotecan and topotecan, and novel analogues undergoing clinical trails, such as exatecan (DX-8951f), IDEC-132 (9-aminocamptothecin), rubitecan (9-nitrocamptothecin), lurtotecan (GI-147211C), and the recently developed homocamptothecins diflomotecan (BN-80915) and BN-80927.