Inhibition of growth factor-dependent inositol phosphate Ca2+ signaling by antitumor ether lipid analogues.
Cytotoxic ether lipid analogues have been studied for their ability to inhibit growth factor-dependent [Ca2+]i signaling in Swiss 3T3 fibroblasts. 1-Octadecyl-2-methyl-rac-glycero-3-phosphocholine (ET-18-OCH3) inhibited 45Ca2+ uptake and inositol(1,4,5)trisphosphate-induced 45Ca2+ release in saponin permeabilized cells with concentration producing 50% inhibition values of 55 and 360 microM, respectively. When cells were exposed to ET-18-OCH3 for 18 h before permeabilization there was selective inhibition of inositol(1,4,5)trisphosphate-induced 45Ca2+ release with a concentration producing 50% inhibition value of 20 microM, but no effect on 45Ca2+ uptake, or on 45Ca2+ release by arachidonic acid. The concentration of ET-18-OCH3 with continuous exposure to inhibit cell growth 50% was 19 microM. The ether lipid analogues 1-hexadecylthio-2-ethyl-rac-glycero-3- phosphocholine and 1-S-octadecyl-2-O-methylthiopropyl-3-N,N-dimethyl-gamma-hydroxy pro pyl ammonium iodide had effects similar to those of ET-18-OCH3 but the noncytotoxic analogue 1-alkyl-2-hydroxy-sn-glycero-3- phosphocholine was without effect. Exposure of cells to 10 microM ET-18-OCH3 produced 81% inhibition of platelet-derived growth factor-stimulated inositol phosphate formation and 66% inhibition of fluoroaluminate anion-stimulated inositol phosphate formation. Addition of ET-18-OCH3 to cells in medium with 10% fetal calf serum gave a transient increase in [Ca2+]i without causing an increase in resting [Ca2+]i, while the addition of ET-18-OCH3 to cells in medium without serum gave a sustained increase in resting [Ca2+]i. Cells exposed to 5 microM ET-18-OCH3 for 18 h showed no increase in resting [Ca2+]i but there was 95% inhibition of the [Ca2+]i response to platelet-derived growth factor, 63% inhibition of the response to bradykinin, and 55% inhibition of the response to vasopressin. The block by ether lipid analogues of inositol phosphate-mediated [Ca2+]i signaling suggests a mechanism for preventing the action of growth factors that could contribute to the inhibition of cell proliferation by the agents.
Seewald
M J
MJ
Department of Pharmacology, Mayo Clinic and Foundation, Rochester, Minnesota 55905.
Olsen
R A
RA
Sehgal
I
I
Melder
D C
DC
Modest
E J
EJ
Powis
G
G
D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology*; D001693:Biological Transport, Active / Q000187:drug effects; D001920:Bradykinin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism / Q000502:physiology*; D002478:Cells, Cultured; D006133:Growth Substances / Q000494:pharmacology*; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism*; D007700:Kinetics; D051379:Mice; D010742:Phospholipid Ethers / Q000494:pharmacology*; D010982:Platelet-Derived Growth Factor / Q000494:pharmacology; D015398:Signal Transduction / Q000187:drug effects*; D013329:Structure-Activity Relationship; D014667:Vasopressins / Q000494:pharmacology
D000970:Antineoplastic Agents; D006133:Growth Substances; D010742:Phospholipid Ethers; D010982:Platelet-Derived Growth Factor; D014667:Vasopressins; D015544:Inositol 1,4,5-Trisphosphate; D001920:Bradykinin; D002118:Calcium