In vitro cytotoxic activity of Thai medicinal plants used traditionally to treat cancer

The SRB assay was used to test cytotoxicity against three human cancer cell lines and one normal cell line of 11 Thai medicinal plant species used by traditional doctors in treating cancer patients. The extraction procedures used were similar to those practised by Thai traditional doctors (ethanolic and water extracts). Extracts were tested against the human large cell lung carcinoma cell line COR-L23, the human breast adenocarcinoma cell line MCF-7 and human colon adenocarcinoma cell line LS-174T and normal human keratinocytes SVK-14. The results showed that three plants; Dioscorea membranacea Pierre ex Prain & Burkill, Dioscorea birmanica Prain & Burkill (Dioscoreaceae) and Siphonodon celastrineus Griff. (Celastraceae), exhibited high cytotoxic activity showing a certain degree of selectivity against the different cell types.

High-throughput screening for the identification of small-molecule inhibitors of retinoblastoma protein phosphorylation in cells

The tumor suppressor protein, pRb, regulates progression through the G1 phase of the cell cycle by its ability to bind to and regulate the activity of a variety of transcription factors. This function of pRb is disabled through its phosphorylation by the cyclin-dependent kinase (CDK) family of serine/threonine kinases. In many human cancers, genetic alteration such as loss of CDK inhibitor function and deregulated G1 cyclin expression leads to inappropriate phosphorylation and hence inactivation of this tumor suppressor. Identification of cell-permeable small molecules that block pRb phosphorylation in these tumors could therefore lead to development of an effective anticancer treatment. As a result, we have developed a high-throughput assay to detect changes in the level of pRb phosphorylation in cells. Signal detection is by a time-resolved fluorescence-based cellular immunosorbant assay on a fixed monolayer of cells. This comprises a mouse monoclonal antibody that recognizes the phosphorylated form of serine 608 on pRb, a known site of CDK phosphorylation, and a Europium-labeled secondary antibody for signal detection. The assay is reproducible and amenable to automation and has been used to screen 2000 compounds in a search for cell-permeable small molecules that will block pRb phosphorylation.

Design and synthesis of novel pyrrolobenzodiazepine (PBD) prodrugs for ADEPT and GDEPT

Three N10-(4-nitrobenzyl)carbamate-protected PBD prodrugs (9a, 9b and 15) have been synthesized and evaluated for potential use in nitroreductase-based ADEPT and GDEPT therapies. An approximately 100-fold activation was observed for the DC-81 prodrug 9a.

Cytotoxic activity of indole alkaloids from Alstonia macrophylla

Thirteen indole alkaloids isolated from the root bark of Alstonia macrophylla and a semisynthetic bisindole O-acetylmacralstonine have been assessed for cytotoxic activity against two human lung cancer cell lines, MOR-P (adenocarcinoma) and COR-L23 (large cell carcinoma), using the SRB assay. Pronounced cytotoxic activity was exhibited by the bisindoles on both cell lines. This suggests that, in comparison with the corresponding monomeric indoles, at least part of both the ring systems present in the bisindoles is essential for cytotoxic activity. The potent alkaloids were further tested against a human normal cell line (breast fibroblasts) and other human cancer cell lines including StMI1 1a (melanoma), Caki-2 (renal cell carcinoma), MCF7 (breast adenocarcinoma), and LS174T (colon adenocarcinoma). The bisindoles O-acetylmacralstonine, villalstonine and macrocarpamine were found to possess pronounced activity against cancer cell lines with IC50 values in the range of 2-10 microM, with no discernible cell-type selectivity. However, O-acetylmacralstonine displayed discernibly less toxicity against the normal breast fibroblasts.

Activity of extracts and alkaloids of thai Alstonia species against human lung cancer cell lines

Methanol extracts of root barks of Alstonia macrophylla, A. glaucescens, and A. scholaris, collected from Thailand, have been assessed for cytotoxic activity against two human lung cancer cell lines, MOR-P (adenocarcinoma) and COR-L23 (large cell carcinoma), using the SRB assay. Significant cytotoxic activity was exhibited by the extract of A. macrophylla on both cell lines. Activity-directed fractionation led to the isolation of a novel indole alkaloid, O-methylmacralstonine, from the most active fraction of A. macrophylla along with four known alkaloids, talcarpine, villalstonine, pleiocarpamine, and macralstonine. Structure elucidation of the novel alkaloid was based on spectroscopic methods, especially 2D-NMR. The bisindole villalstonine was found to possess pronounced activity on both cell lines with an IC50 value less than 5 muM, but was about 10(3) times less potent than vinblastine sulphate. The monomeric alkaloid, talcarpine, was found to be inactive. Pleiocarpamine, O-methylmacralstonine and macralstonine were all considerably less active than villalstonine.