Enhancement of 5-Fluorouracil Sensitivity by an rTS Signaling Mimic in H630 Colon Cancer Cells

Abstract

The rTSB protein has been hypothesized to synthesize signaling molecules that can down-regulate thymidylate synthase. These molecules share biological and chemical properties with acyl-homoserine lactones (AHL), suggesting some AHLs might act as rTS signaling mimics and downregulate thymidylate synthase. We have determined that the AHL, 3-oxododecanoyl homoserine lactone (3-oxo-C12-(L)-HSL) can down-regulate thymidylate synthase protein at 10 Mmol/L and reduce H630 (human colorectal cancer) growth by 50% at 23 Mmol/L (IC 50 ) in cell culture. At its IC 50 concentration, 3-oxo-C12-(L)-HSL reduces the apparent IC 50 of 5-fluorouracil (5-FU) from 1 Mmol/L to 80 nmol/L (12-fold) in a colony formation assay. 3-Oxo-C12-(L)-HSL enhances the activity of 5-fluorodeoxyuridine, tomudex, and taxol but not the activity of 5-fluorouridine, methotrexate or Adriamycin. The unexpected interaction with taxol probably results from effects of the AHL on tubulin expression. Differences in taxol sensitivity, tubulin, and cellular morphology between H630 and the thymidylate synthase and rTSB-overproducing, 5-FUresistant H630-1 cell line as determined by colony formation assays, Western analysis of one-dimensional and two-dimensional gels, and photomicroscopy confirm that cytoskeletal changes are induced by the AHL or by rTS signaling. Isozyme differences in thymidylate synthase and rTSB also exist in the two cell lines. Phosphorylation of rTSB amino acid S121 is shown to occur and is decreased at least 10-fold in the drug-resistant cells. The data presented provide support for further investigations of rTS signaling mimics as enhancers to thymidylate synthase-directed chemotherapy, evidence that the phosphorylation state of rTSB may be a marker for 5-FU resistance and a previously unrealized relationship between rTS signaling and the cytoskeleton. (Cancer Res 2005; 65(13): 5917-24)

Quorum sensing and social networking in the microbial world

“…The structure of this signal molecule is currently unknown but the rTSb products are known to be metabolites of methionine biosynthesis formed directly from S-adenosylmethionine (and an uncharacterized substrate), which might indicate that this signal shares structural similarity with AHLs (Dolnick et al 2003). The possible structural relationship between AHLs and the rTS signal prompted Dolnick et al (2005) to test a range of AHLs for the ability to reduce TS protein levels. Western blot analysis showed that TS expression was reduced considerably in the presence of physiologically relevant concentrations of 3-oxo-C12-HSL, which also reduced the growth of human colorectal cancer cells (H630) by 50 per cent.…”

In vitro and in vivo evaluation of anticancer actions of natural and synthetic vitamin E forms

“…Effects of vitamin E compounds on colony formation of human breast cancer cells and 66cl-4-GFP cells were determined as described previously with the following modifications [23]. Vitamin E compounds were dissolved in DMSO at 200 mM, then further diluted in ethanol to achieve 40 mM stock solutions.…”

Novel Acridine-Based <i>N</i>-Acyl-homoserine Lactone Analogs Induce Endoreduplication in the Human Oral Squamous Carcinoma Cell Line SAS

“…In general, long acyl chains (C12) are considered important to the stability of AHL liquids, and are also important for AHL activity. 15,21,22) However, we found that the cytotoxic activity of AHL analogs was independent of acyl chain length (Fig. 1B).…”