Factors influencing the cellular accumulation of SN-38 and camptothecin

Jeffrey Cummings, Gary Boyd, Janet S. Macpherson, Helga Wolf, Gillian Smith, John F. Smyth, Duncan I. Jodrell

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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/106 cells). Subsequently, a fall in intracellular lactone concentration occurred, stabilising after 4 h at 0.48–1.18 ng/106 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.
Original languageEnglish
Pages (from-to)194-200
Number of pages7
JournalCancer Chemotherapy and Pharmacology
Volume49
Issue number3
DOIs
Publication statusPublished - 2002
Externally publishedYes

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Cummings, J., Boyd, G., Macpherson, J. S., Wolf, H., Smith, G., Smyth, J. F., & Jodrell, D. I. (2002). Factors influencing the cellular accumulation of SN-38 and camptothecin. Cancer Chemotherapy and Pharmacology, 49(3), 194-200. https://doi.org/10.1007/s00280-001-0393-3