Novel Strategies for Plant-Derived Anticancer Agents

Natural Products/Bioactive Compounds as a Source of Anticancer Drugs

Cancer is one of the major deadly diseases globally. The alarming rise in the mortality rate due to this disease attracks attention towards discovering potent anticancer agents to overcome its mortality rate. The discovery of novel and effective anticancer agents from natural sources has been the main point of interest in pharmaceutical research because of attractive natural therapeutic agents with an immense chemical diversity in species of animals, plants, and microorganisms. More than 60% of contemporary anticancer drugs, in one form or another, have originated from natural sources. Plants and microbial species are chosen based on their composition, ecology, phytochemical, and ethnopharmacological properties. Plants and their derivatives have played a significant role in producing effective anticancer agents. Some plant derivatives include vincristine, vinblastine, irinotecan, topotecan, etoposide, podophyllotoxin, and paclitaxel. Based on their particular activity, a number of other plant-derived bioactive compounds are in the clinical development phase against cancer, such as gimatecan, elomotecan, etc. Additionally, the conjugation of natural compounds with anti-cancerous drugs, or some polymeric carriers particularly targeted to epitopes on the site of interest to tumors, can generate effective targeted treatment therapies. Cognizance from such pharmaceutical research studies would yield alternative drug development strategies through natural sources which could be economical, more reliable, and safe to use.

Approaches to Automating the Dereplication of Bioactive Natural Products—The Key Step in High Throughput Screening of Bioactive Materials From Natural Sources

The rapid identification of the bioactive component(s) of natural product mixtures in high throughput screening programs has become a critical factor to ensure that this source of diverse chemotypes can compete effectively with chemical compound libraries and combinatorial synthetic efforts. The effective use of automated procedures and databases in the isolation, identification and biological profiling of bioactive compounds will be described. In addition, the potential of new technologies to enhance this process will be discussed as well as the possible reintroduction of TLC as a parallel dereplication method.

Selection methodology with scoring system: application to Mexican plants producing podophyllotoxin related lignans

As most anticancer drugs are derived from natural sources, the screening of local medicinal flora should be considered a primary step in the search for new sources for antineoplastic agents. In Mexico, more than 6000 medicinal plant species are used for the treatment of various diseases, including cancer. A multifactorial plant selection method, employing various criteria was designed and applied in order to select alternative sources of podophyllotoxin lignan analogues. For each criterion (chemotaxonomy, traditional medical uses and published scientific data), an arbitrary score system was ascribed to the species and the sum of these enabled us to compare potential candidates. The resulting selected plants were tested for cytotoxic activity and the compounds responsible for this activity were evaluated by liquid chromatography-mass spectroscopy (LC-MS). Around 50 species from the Mexican flora were initially considered. From these, six species were selected by referring to the results from the scoring system and these were then collected. Three extracts were evaluated as being highly cytotoxic against three different cancer cell lines. Finally, podophyllotoxin-like lignans could be identified by observing the fragmentation pattern on mass spectra, obtained from the LC-MS in two species: Linum scabrellum and Hyptis suaveolens.

Drug discovery from medicinal plants

Current research in drug discovery from medicinal plants involves a multifaceted approach combining botanical, phytochemical, biological, and molecular techniques. Medicinal plant drug discovery continues to provide new and important leads against various pharmacological targets including cancer, HIV/AIDS, Alzheimer's, malaria, and pain. Several natural product drugs of plant origin have either recently been introduced to the United States market, including arteether, galantamine, nitisinone, and tiotropium, or are currently involved in late-phase clinical trials. As part of our National Cooperative Drug Discovery Group (NCDDG) research project, numerous compounds from tropical rainforest plant species with potential anticancer activity have been identified. Our group has also isolated several compounds, mainly from edible plant species or plants used as dietary supplements, that may act as chemopreventive agents. Although drug discovery from medicinal plants continues to provide an important source of new drug leads, numerous challenges are encountered including the procurement of plant materials, the selection and implementation of appropriate high-throughput screening bioassays, and the scale-up of active compounds.

Biodiversity and drug discovery--a symbiotic relationship

The profound developments in natural products drug discovery in the past few years are discussed, and the importance of a global approach to biodiversity and drug discovery involving natural products for the early part of the 21st century is presented.

Cytotoxic natural products from thai plants: a recent study

Natural products will continue to be the most prolific source of bioactive compounds. Natural products exhibiting antitumor activity continue to be the subject of extensive research aimed at the development of drugs for the treatment of different human tumors. It is generally accepted that natural products offer a diversity and complexity of structure unmatched by even the most active imaginations of synthetic organic chemists. This paper reviews the research of selected Thai plants for the discovery of therapeutic agents. Attention will be focused on our recent research on Thai plants that possess cytotoxic properties. Synthetic modification and reaction of some of these compounds aimed at enhancing their potency will also be presented.

Rapid analysis of antibiotic-containing mixtures from fermentation broths by using liquid chromatography-electrospray ionization-mass spectrometry and matrix-assisted laser desorption ionization-time-of-flight-mass spectrometry

A crucial step in the isolation of antibiotic substances is establishing whether or not the isolated material represents a new chemical entity. Because of the importance of molecular weight to this process-known as dereplication-mass spectrometry has traditionally played an active role. In this communication a strategy for utilizing liquid chromatography-mass spectrometry (LC/MS) for novelty assessment is described. Crude extracts (20-50 µg) are chromatographed by conventional bore high-performance liquid chromatography (1 mL/min) after which a postcolumn split to divert roughly one-tenth of the sample to the mass spectrometer for molecular weight determination by electrospray ionization (ESI) mass spectrometry. The majority of the effluent is sent to a UV detector and ultimately collected as 1-min fractions for biological testing. As a secondary confirmation of molecular weight, an aliquot of each fraction (< 5%) is taken for analysis by matrix-assisted laser desorption ionization (MALDI). The improved efficiency of this approach over more traditional schemes utilizing off-line fraction collection and conventional ionization methods can be explained by several factors. First, the superior sensitivity of ESI and MALDI means that less material is required for successful analysis. Second, on-line LC/MS optimizes the efficiency of sample transfer and saves both time and labor. Furthermore, the concentration dependence of ESI allows a majority of the material injected for LC/MS to be recovered for biological testing without compromising the signal available for molecular weight determination. As a validation of the above method, crude extracts containing two well-characterized antibiotics-teicoplanin and phenelfamycin-were examined. Results from these analyses are presented along with data from the analysis of a potent unknown antifungal sample.