Wortmannin, a phosphoinositide 3-kinase inhibitor, selectively enhances cytotoxicity of receptor-directed-toxin chimeras in vitro and in vivo.
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.
Davol
P A
PA
Department of Medicine, Roger Williams Medical Center, Providence, Rhode Island 02908, USA.
Bizuneh
A
A
Frackelton
A R
AR
D000230:Adenocarcinoma / Q000473:pathology; D000730:Androstadienes / Q000494:pharmacology* / Q000627:therapeutic use; D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology* / Q000627:therapeutic use; D002455:Cell Division / Q000187:drug effects; D004354:Drug Screening Assays, Antitumor; D004357:Drug Synergism; D004791:Enzyme Inhibitors / Q000494:pharmacology* / Q000627:therapeutic use; D016222:Fibroblast Growth Factor 2 / Q000494:pharmacology* / Q000627:therapeutic use; D005354:Fibrosarcoma / Q000473:pathology; D006801:Humans; D008297:Male; D008545:Melanoma / Q000473:pathology; D051379:Mice; D008809:Mice, Inbred C3H; D009363:Neoplasm Proteins / Q000187:drug effects*; D009368:Neoplasm Transplantation; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010940:Plant Proteins / Q000494:pharmacology* / Q000627:therapeutic use; D017468:Receptors, Fibroblast Growth Factor / Q000187:drug effects*; D011993:Recombinant Fusion Proteins / Q000494:pharmacology / Q000627:therapeutic use; D054789:Ribosome Inactivating Proteins, Type 1; D000076985:Saporins; D012513:Sarcoma, Experimental / Q000473:pathology; D018243:Teratocarcinoma / Q000473:pathology; D014118:Toxins, Biological / Q000494:pharmacology* / Q000627:therapeutic use; D014407:Tumor Cells, Cultured; D000077191:Wortmannin
D000730:Androstadienes; D000970:Antineoplastic Agents; D004791:Enzyme Inhibitors; D009363:Neoplasm Proteins; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010940:Plant Proteins; D017468:Receptors, Fibroblast Growth Factor; D011993:Recombinant Fusion Proteins; D054789:Ribosome Inactivating Proteins, Type 1; D014118:Toxins, Biological; C078442:basic fibroblast growth factor-saporin mitotoxin, recombinant; D016222:Fibroblast Growth Factor 2; D000076985:Saporins; D000077191:Wortmannin