Camptothecin analog (CPT-11)-sensitive human pancreatic tumor cell line QGP-1N shows resistance to SN-38, an active metabolite of CPT-11

Sachi Takeda, Takao Shimazoe, Hiroshi Kuga, Keiki Sato, Akira Kono

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In the course of our study to determine the cross-sensitivity between CPT-11 and its active metabolite, SN-38, we found a SN-38-resistant human pancreatic tumor cell line, QGP-1N, which shows sensitivity to CPT-11. The IC50 of SN-38 was 152 times greater for QGP-1N than for SUIT-2, also a human pancreatic tumor cell line, whose IC50 of CPT-11 was similar to that for QGP-1N. The uptakes of CPT-11 and SN-38 and the intracellular conversion of CPT-11 to SN-38 could not explain the difference in sensitivity. DNA synthesis of QGP-1N cells was inhibited by CPT-11 which did not affect that of SUIT-2, while SN-38 Inhibited the DNA synthesis of SUIT-2 at lower concentrations than that of QGP-1N. The inhibition test of topoisomerase I catalytic activity by CPT-11 or SN-38 revealed no difference in the biochemical properties of the topoisomerase I enzymes to the compounds between these two cell lines.These results indicate that CPT-11 should have its own inhibitory effect on DNA synthesis through a yet unknown mechanism in QGP-1N cells, although SN-38 plays an essential role in the antitumor activity of CPT-11 in SUIT-2 cells. In some cases, the antitumor effect of CPT-11 might be consequent not only on SN-38 but also on CPT-11 itself.

Original languageEnglish
Pages (from-to)70-77
Number of pages8
JournalBiochemical and Biophysical Research Communications
Issue number1
Publication statusPublished - Oct 15 1992
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Biophysics
  • Biochemistry
  • Molecular Biology
  • Cell Biology


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