Um panorama atual da química e da farmacologia de naftoquinonas, com ênfase na beta-lapachona e derivados

Naphthoquinones have been extensively studied due to their activity as topoisomerase inhibitors. These enzymes are critical to DNA replication in cells. In addition, naphthoquinones have been shown to induce what are known as "reactive oxygen species" that can cause damage to cells. beta-Lapachone is a very important pyranaphthoquinone obtained from the heartwood of the lapacho tree, Tabebuia avellanedae Lorentz ex. Griseb. (Bignoniaceae), and other Tabebuia trees native to Central and South America and chemically from lapachol. beta-Lapachone has a diversity of useful biological activities against various cancer cell lines such as human ovarian and prostate tumors and, at lower doses is a radiosensitizer of several human cancer cell lines. It gives rise to a variety of effects in vitro including the inhibition or activation of topoisomerase I an II in a distinct manner from that of other topoisomerase inhibitors. This review intend to discuss some details of the mechanisms of quinone-induced cell damage and death, and we also summarize results of the literature indicating that b-Lapachone may take part in quinone-elicited apoptosis despite the fact that its mechanism of action in vivo and its targets are still unknown.

Toxicity to sea urchin egg development of the quinone fraction obtained from Auxemma oncocalyx

Auxemma oncocalyx Taub. belongs to the Boraginaceae family and is native to the Brazilian northeast where it is known as "pau-branco". We investigated the ability of the water soluble fraction isolated from the heartwood of A. oncocalyx to inhibit sea urchin egg development. This fraction contains about 80% oncocalyxone A (quinone fraction), a compound known to possess strong cytotoxic and antitumor activities. In fact, the quinone fraction inhibited cleavage in a dose-dependent manner [IC50 of 18.4 (12.4-27.2) µg/ml, N = 6], and destroyed the embryos in the blastula stage [IC50 of 16.2 (13.7-19.2) µg/ml, N = 6]. We suggest that this activity is due to the presence of oncocalyxone A. In fact, these quinones present in A. oncocalyx extract have strong toxicity related to their antimitotic activity.