ABSTRACT
Natural products are a rich source of bioactive compounds, and numerous natural compounds have found application in cancer chemotherapy. However, unfavorable physicochemical properties often prevent the use of the original natural product as a drug. A prominent example is camptothecin from the Chinese tree Camptotheca acuminata, which shows extraordinary cytotoxic activity based on a specific molecular mode of action (inhibition of human topoisomerase I). Due to its extremely poor solubility, the original natural product cannot be used as a drug. The marketed drug topotecan was developed from this lead structure by semi-synthesis utilizing a Mannich aminomethylation as the crucial step. In this review, the long-distance run leading to this drug and further perspectives are summarized.
Subject(s)
Antineoplastic Agents, Phytogenic/pharmacology , Biological Products/pharmacology , Camptotheca/chemistry , Neoplasms/drug therapy , Topoisomerase I Inhibitors/pharmacology , Topotecan/pharmacology , Animals , Antineoplastic Agents, Phytogenic/chemistry , Antineoplastic Agents, Phytogenic/isolation & purification , Biological Products/chemistry , Biological Products/isolation & purification , Cell Proliferation/drug effects , DNA Topoisomerases, Type I/metabolism , Humans , Molecular Structure , Neoplasms/pathology , Topoisomerase I Inhibitors/chemistry , Topoisomerase I Inhibitors/isolation & purification , Topotecan/chemistry , Topotecan/isolation & purificationABSTRACT
A sensitive and selective reversed-phase high-performance liquid chromatographic (HPLC) assay has been developed and validated for quantification of total topotecan in human and mouse plasma and in mouse tissue samples. Isocratic separation was achieved on a Zorbax SB-C(18) column and topotecan was monitored fluorimetrically. Two ranges of calibrations curves were used to determine lower levels of topotecan more accurately. Acceptable accuracy and precision was achieved for all matrices. Topotecan was stable upon repeated freeze-thawing for three cycles or storage for 24 h at ambient temperatures in spiked plasma samples and tissue homogenates, except in heart homogenates. In an additional validation experiment in which (14)C-labeled topotecan was administered to mice, the levels of unchanged topotecan were about 80-90% of the total radioactivity in tissue homogenates collected 10 min after drug administration and virtually similar as in plasma samples. However, results in tissue homogenates obtained 4 h post-drug administration indicated substantial metabolism of topotecan. This assay is suitable for studying the pharmacokinetics and tissue distribution of topotecan in mice. Our results demonstrate the importance of including all tissues of interest for pharmacokinetic studies in the validation procedure.
