Factors influencing the cellular accumulation of SN-38 and camptothecin

Cancer Chemother Pharmacol. 2002 Mar;49(3):194-200. doi: 10.1007/s00280-001-0393-3. Epub 2002 Jan 22.

Abstract

Purpose: The influence of biophysical factors (drug metabolism, transport proteins, and chemical stability) on the cellular accumulation of camptothecin (CPT) and SN-38 was examined.

Methods: Drug transporter RNA transcript levels were measured by real-time reverse transcriptase polymerase chain reaction (RT-PCR). Intracellular drug accumulation, metabolism, and drug stability studies were all performed by HPLC.

Results: A panel of three human cell lines exhibiting different drug resistant phenotypes was investigated. HT29 colon cells glucuronidated SN-38 but did not express P-gp or MRP1 or 2. HCT116 colon cells expressed P-gp and MRP2 but did not catalyse conjugation. A2780 ovarian cells neither catalysed drug metabolism nor contained these drug transporters. In all lines, SN-38 lactone was rapidly taken up achieving peak concentrations at the earliest time point studied (5 min, 3.3-4.1 ng/10(6) cells). Subsequently, a fall in intracellular lactone concentration occurred, stabilising after 4 h at 0.48-1.18 ng/10(6) cells. No significant differences in intracellular levels of lactone were observed between the three cell lines with one exception: a twofold increase in HCT116 cells at 24 h. Stability studies in culture medium revealed that SN-38 lactone concentrations disappeared at the same rate regardless of whether cells were present, initially falling to reach equilibrium with the hydroxy acid by 4 h. Indeed, changes in intracellular lactone concentrations followed closely chemical stability profiles in media. Similar patterns of cellular retention and chemical degradation were observed with CPT.

Conclusion: The major determinant of drug accumulation in three diverse cell line phenotypes was lactone chemical stability in culture medium.

MeSH terms

  • Adenocarcinoma
  • Biological Transport
  • Camptothecin / analogs & derivatives
  • Camptothecin / pharmacokinetics*
  • Colonic Neoplasms
  • Drug Resistance, Multiple
  • Enzyme Inhibitors / pharmacokinetics
  • Female
  • Genes, MDR
  • Humans
  • Irinotecan
  • Kinetics
  • Membrane Transport Proteins*
  • Multidrug Resistance-Associated Proteins / genetics
  • Ovarian Neoplasms
  • Reverse Transcriptase Polymerase Chain Reaction
  • Time Factors
  • Topoisomerase I Inhibitors*
  • Tumor Cells, Cultured

Substances

  • Enzyme Inhibitors
  • Membrane Transport Proteins
  • Multidrug Resistance-Associated Proteins
  • Topoisomerase I Inhibitors
  • multidrug resistance-associated protein 2
  • Irinotecan
  • Camptothecin
  • multidrug resistance-associated protein 1