Paclitaxel-2′-ethylcarbonate prodrug can circumvent P-glycoprotein-mediated cellular efflux to increase drug cytotoxicity

Tadatoshi Tanino, Akihiro Nawa, Eisaku Kondo, Fumitaka Kikkawa, Tohru Daikoku, Tatsuya Tsurumi, Chenhong Luo, Yukihiro Nishiyama, Yuki Takayanagi, Katuhiko Nishimori, Seiji Ichida, Tetsuyuki Wada, Yasuyoshi Miki, Masahiro Iwaki

Research output: Contribution to journalArticlepeer-review

21 Citations (Scopus)


Purpose. The aim of the study was to investigate whether 2′-ethylcarbonate-linked paclitaxel (TAX-2′-Et) circumvents P-glycoprotein (P-gp)-mediated cellular efflux and cytotoxicity enhanced by TAX-2′-Et activation within human culture cells transfected with a rabbit liver carboxylesterase (Ra-CES) cDNA. Materials and Methods. TAX-2′-Et transport was characterized in a human colon carcinoma cell line (Caco-2) and paclitaxel (TAX)-resistant ovarian carcinoma cells (SKOV3/TAX60). Expression of P-gp, multidrug resistance protein (MRP) 2 and Ra-CES was detected by Western blotting. Cytotoxicity against Ra-CES-expressing cells and cellular amount of TAX produced were determined by MTT assay and using HPLC, respectively. Results. Unlike rhodamine123 and TAX, TAX-2′-Et did not exhibit polarized transport in the Caco-2 cells in the absence or presence of verapamil. P-gp levels were expressed much higher in the SKOV3/TAX60 cells than in the Caco-2 cells. MRP2 protein was not detectable in the SKOV3/TAX60 cells. Uptake by the SKOV3/TAX60 cells was similar in quantity to the amount internalized by P-gp-negative SKOV3 cells. In the SKOV3/TAX60 cells, cellular uptake of TAX-2′-Et was not altered regardless of the absence or presence of verapamil. The cytotoxicity to the untransfected SKOV3 cells induced by TAX-2′-Et was significantly lower than that induced by TAX. In the Ra-CES-expressing SKOV3 line, the EC50 value of TAX (10.6 nM) was approximately four-fold higher than that of TAX-2′-Et (2.5 nM). Transfection of Ra-CES into another TAX-resistant ovarian carcinoma cells (KOC-7c) conferred a high level of TAX-2′-Et cytotoxicity via prodrug activation. The intracellular levels of TAX produced from TAX-2′-Et in the Ra-CES-positive KOC-7c cells significantly increased compared with the levels seen in exposure of the untransfected KOC-7c cells to TAX. Conclusions. TAX-2′-Et can circumvent P-gp-associated cellular efflux of TAX. TAX-2′-Et is converted into TAX by the Ra-CES, supporting its potential use as a theoretical GDEPT strategy for cancer cells expressing high levels of P-gp. The TAX-2′-Et prodrug efficiently increased the amount of intracellular TAX, which mediates tumor cell death.

Original languageEnglish
Pages (from-to)555-565
Number of pages11
JournalPharmaceutical research
Issue number3
Publication statusPublished - 2007 Mar
Externally publishedYes


  • Carboxylesterase-prodrug
  • Gene-directed enzyme prodrug therapy
  • Growth inhibition
  • P-glycoprotein
  • Paclitaxel

ASJC Scopus subject areas

  • Biotechnology
  • Molecular Medicine
  • Pharmacology
  • Pharmaceutical Science
  • Organic Chemistry
  • Pharmacology (medical)


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