Bioprospecting for Podophyllotoxin*

Podophyllotoxin is a natural lignan that is currently being used as a precursor to semi-synthetic anticancer drugs etoposide, teniposide, and etopophos. These compounds have been used for the treatment of lung and testicular cancers as well as certain leukemias (Stahelin and Wartburg 1991; Imbert 1998). The patent for the use of etoposide in such therapies expired in 1995 and since then, etoposide has been tested in 167 clinical trials for the use as new investigative cancer treatments or as positive control (Ekstrom et al. 1998; Holm et al. 1998; Ajani et al. 1999). In addition, podophyllotoxin is also the precursor to a new derivative CPH 82 that is being tested for rheumatoid arthritis in Europe and other derivatives for the treatment of psoriasis and malaria (Leander and Rosen 1988; Lerndal and Svensson 2000). Podophyllotoxin preparations are also on the market for dermatological use to treat genital warts (Beutner 1996) and recently, immunestimulatory activities of podophyllotoxin have been reported (Pugh et al. 2001). Total synthesis of podophyllotoxin is an expensive process and availability of the compound from natural resources is an important issue for pharmaceutical companies that manufacture these drugs (Canel et al. 2000b). Currently, the commercial source of podophyllotoxin is the rhizomes and roots of Podophyllum emodi Wall., Berberidaceae (syn. P. hexandrum Royle), an endangered species from the Himalayas (Foster 1993). Recent findings concluded that the leaf blades of the North American mayapple (P. peltatum L.) may serve as an alternative source of podophyllotoxin production, since leaves are renewable organs that store lignans as glucopyranosides (Canel et al. 2001; Moraes et al. 2001). Using the new buffer extraction procedure reported by Canel et al. (2000a), podophyllotoxin can be obtained by conversion of podophyllotoxin 4-O-β-Dglucopyranoside into the aglycone. This extraction procedure of P. peltatum leaves yields podophyllotoxin (40.0 mg·g on a dry weight basis) in amounts similar to the ethanol extraction of P. emodi rhizomes and roots (Jackson and Dewick 1984; Canel et al. 2001). After the publication of these findings, there has been an increasing interest in domestication and cultivation of P. peltatum for podophyllotoxin production; however there remains a need for identification and confirmation of the most economical isolated yielding source. Our objective was to quantify podophyllotoxin in other genera and to evaluate their potential production based on yields and abundance. These other genera were Linum, Juniperus, Hyptis, Teucrium, Nepeta, Dysosma, Jeffersonia, Thymus, and Thuja (Kupchan et al. 1965; San Feliciano et al. 1989a,b; Broomhead and Dewick, 1990a,b; Yu et al. 1991; Kuhnt et al. 1994; Konuklugil 1996a,b; Muranaka et al. 1998). In addition, extractions with buffer and other solvents were compared using two abundant US species as sources.