As part of a program to identify novel mechanisms of resistance to topoisomerase I (topo I) inhibitors, the cellular pharmacology of 7-ethyl-10-hydroxycamptothecin (SN-38), the active metabolite of clinically used irinotecan (CPT-11) and NU/ICRF 505, an anthraquinone-tyrosine conjugate, has been investigated in two human colorectal cancer (CRC) cell lines. Two novel metabolites of NU/ICRF 505 (M1 and M2) and a single metabolite of SN-38 (M1) were detected by high performance liquid chromatography in the culture medium of HT29 cells but were absent in HCT116 cells. Identities of all three metabolites were established by a combination of biochemical and physicochemical techniques. M1 of SN-38 was the C10-(beta)-glucuronide of the parent lactone while M1 of NU/ICRF 505 was the C4-O-glucuronide and M2 the tyrosine-O-glucuronide, both of the parent compound. Drug transport studies revealed that by 24hr HT29 cells had effectively cleared 82.5% of NU/ICRF 505 (10 microM) into the culture medium as the two glucuronides. In contrast, intracellular concentrations of NU/ICRF 505 were maintained in HCT116 cells in the absence of glucuronidation at a level 550 times greater than in HT29 cells. HT29 cells cleared 40.9% of SN-38 (1 microM) as the glucuronide to the culture medium, while the parent drug was maintained at a level 2-fold greater in HCT116 cells. Enhanced drug clearance due to glucuronidation may contribute to intrinsic drug resistance of human CRC.

Download full-text PDF

Source
http://dx.doi.org/10.1016/s0006-2952(01)00812-7DOI Listing

Publication Analysis

Top Keywords

nu/icrf 505
20
ht29 cells
16
culture medium
12
hct116 cells
12
cells
8
nu/icrf
5
0
5
enhanced clearance
4
clearance topoisomerase
4
topoisomerase inhibitors
4

Similar Publications

Background: Glucuronidation represents a novel mechanism of intrinsic drug resistance in colon cancer cells. To safely reverse this mechanism in vivo, it is essential to identify which isoforms of UDP-glucuronosyltransferases are responsible for catalysing this drug metabolism in tumour tissue.

Materials And Methods: LC-MS was applied to measure rates of glucuronidation of two anticancer compounds (SN-38 and NU/ICRF 505) by patient colon cancer biopsies and paired normal colon.

View Article and Find Full Text PDF
Article Synopsis
  • Colon cancer is resistant to chemotherapy due to mechanisms like glucuronidation, which involves the enzyme UDP-glucuronosyltransferases (UGTs).
  • Research identified UGT1A9 as the key enzyme in glucuronidating two topoisomerase I inhibitors, enhancing drug resistance in colon cancer cells.
  • Inhibiting this glucuronidation can significantly increase drug effectiveness, suggesting that dietary substances and certain medications could potentially alter drug resistance in colon cancer.
View Article and Find Full Text PDF

We have recently shown that drug conjugation catalysed by UDP-glucuronosyltransferases (UGTs) functions as an intrinsic mechanism of resistance to the topoisomerase I inhibitors 7-ethyl-10-hydroxycamptothecin and NU/ICRF 505 in human colon cancer cells and now report on the role of drug transport in this mechanism. The ability of transport proteins to recognise NU/ICRF 505 as a substrate was evaluated in model systems either transfected with breast cancer-resistance protein 1 (Bcrp1), multidrug-resistance protein 2 (Mrp2) or Mrp3, or overexpressing MRP1 or P-170 glycoprotein. Results from chemosensitivity assays suggested that NU/ICRF 505 was not a substrate for any of the above proteins.

View Article and Find Full Text PDF

As part of a program to identify novel mechanisms of resistance to topoisomerase I (topo I) inhibitors, the cellular pharmacology of 7-ethyl-10-hydroxycamptothecin (SN-38), the active metabolite of clinically used irinotecan (CPT-11) and NU/ICRF 505, an anthraquinone-tyrosine conjugate, has been investigated in two human colorectal cancer (CRC) cell lines. Two novel metabolites of NU/ICRF 505 (M1 and M2) and a single metabolite of SN-38 (M1) were detected by high performance liquid chromatography in the culture medium of HT29 cells but were absent in HCT116 cells. Identities of all three metabolites were established by a combination of biochemical and physicochemical techniques.

View Article and Find Full Text PDF

The effect of the novel topoisomerase I inhibitor NU/ICRF 505 (20 microM, approximate IC50 concentration) on the cell cycle was studied by flow cytometry in four Chinese hamster ovary (CHO) cell lines. Postdrug treated cells were incubated with optimal concentrations of cytochalasin B to prevent re-entry of daughter cells into the cell cycle. NU/ICRF 505 had no significant effect on cell cycle distribution in the parent cell line (CHO-K1) and two mutants hypersensitive to topo II inhibitors (ADR-1, ADR-3), all of which express similar levels of topo I protein.

View Article and Find Full Text PDF

Want AI Summaries of new PubMed Abstracts delivered to your In-box?

Enter search terms and have AI summaries delivered each week - change queries or unsubscribe any time!