Wortmannin, a phosphoinositide 3-kinase inhibitor, selectively enhances cytotoxicity of receptor-directed-toxin chimeras in vitro and in vivo

Anticancer Res. May-Jun 1999;19(3A):1705-13.


Background: Generalized resistance of some neoplastic cell lines to treatment with ligand-toxin chimeras has been attributed to an increased rate of lysosomal uptake and degradation following endocytosis of the chimera-receptor complex. Because phosphoinositide 3-kinase (Pl 3-kinase) activity is known to play a role in intracellular trafficking, particularly from endosomes to lysosomes, we hypothesized that co-exposing cells to the Pl 3-kinase inhibitor, wortmannin, might enhance cytotoxicity of ligand-toxin chimeras.

Methods: In vitro, cytotoxicity of five receptor directed-toxin chimeras (bFGF-SAP, bFGF-PE, aFGF-PE, HBEGF-SAP, bFGF-gelonin) and an immunotoxin (11A8-SAP) was examined in the presence or absence of this Pl 3-kinase inhibitor against a panel of human neoplastic cell lines: SK-MEL-5 (melanoma), PA-1 (ovarian teratocarcinoma), DU145 (prostatic carcinoma) and MCF-7 (breast carcinoma). In vivo, antitumor activity of a treatment regimen combining wortmannin (1 or 2 mg/kg i.p.) and bFGF-SAP (10 micrograms/kg i.v.) once a week for 4 weeks was evaluated compared to administration of each agent alone in C3H/HeN mice implanted with the FSallC murine fibrosarcoma.

Results: At concentrations greater than the reported Ki for Pl 3-kinase inhibition (1-10 microM), wortmannin enhanced cytotoxicity when combined with saporin or gelonin chimeras, but produced subadditive cytotoxicity when combined with Pseudomonas exotoxin chimeras. When low nanomolar concentrations selective for Pl 3-kinase inhibition (5-100 nM) were examined for effects on one receptor directed-toxin chimera, wortmannin dramatically enhanced bFGF-SAP cytotoxicity in three of the four cell lines. A different Pl 3-kinase inhibitor, LY294002 (Ki approximately 1 microM), however, failed to potentiate bFGF-SAP. When administered to mice, wortmannin combined with bFGF-SAP resulted in a significant decrease in tumor volumes compared to vehicle-treated controls that was not observed in mice treated with either agent alone.

Conclusions: Taken together, these results suggest that although wortmannin increases the cytotoxic efficacy of some receptor-directed chimeras, potentiation may occur through an alternative pathway not involving Pl 3-kinase inhibition.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Adenocarcinoma / pathology
  • Androstadienes / pharmacology*
  • Androstadienes / therapeutic use
  • Animals
  • Antineoplastic Agents / pharmacology*
  • Antineoplastic Agents / therapeutic use
  • Cell Division / drug effects
  • Drug Screening Assays, Antitumor
  • Drug Synergism
  • Enzyme Inhibitors / pharmacology*
  • Enzyme Inhibitors / therapeutic use
  • Fibroblast Growth Factor 2 / pharmacology*
  • Fibroblast Growth Factor 2 / therapeutic use
  • Fibrosarcoma / pathology
  • Humans
  • Male
  • Melanoma / pathology
  • Mice
  • Mice, Inbred C3H
  • Neoplasm Proteins / drug effects*
  • Neoplasm Transplantation
  • Phosphoinositide-3 Kinase Inhibitors*
  • Plant Proteins / pharmacology*
  • Plant Proteins / therapeutic use
  • Receptors, Fibroblast Growth Factor / drug effects*
  • Recombinant Fusion Proteins / pharmacology
  • Recombinant Fusion Proteins / therapeutic use
  • Ribosome Inactivating Proteins, Type 1
  • Saporins
  • Sarcoma, Experimental / pathology
  • Teratocarcinoma / pathology
  • Toxins, Biological / pharmacology*
  • Toxins, Biological / therapeutic use
  • Tumor Cells, Cultured
  • Wortmannin


  • Androstadienes
  • Antineoplastic Agents
  • Enzyme Inhibitors
  • Neoplasm Proteins
  • Phosphoinositide-3 Kinase Inhibitors
  • Plant Proteins
  • Receptors, Fibroblast Growth Factor
  • Recombinant Fusion Proteins
  • Ribosome Inactivating Proteins, Type 1
  • Toxins, Biological
  • basic fibroblast growth factor-saporin mitotoxin, recombinant
  • Fibroblast Growth Factor 2
  • Saporins
  • Wortmannin