Abstract
Alkyllysophospholipids (ALP) which are 1-O-alkyl analogs of the cell membrane component 1-acyl-sn-glycero-3-phosphocholine (1-acyl-GPC) represent a family of new antitumor drugs. Susceptibility of cells to ALP is correlated to a selective inhibition of fatty acid incorporation into 1,2-diacyl-sn-glycero-3-phosphocholine in intact cells. This report examines oleoyl-CoA-1-acyl-GPC acyl-transferase activities in cell-free systems of ALP-sensitive methylcholanthrene-induced fibrosarcoma cells (MethA cells) and ALP-resistant bone marrow-derived murine macrophages (BMM phi). The specific activities for the oleoyl-CoA-1-acyl-GPC acyltransferases were 1.05 +/- 0.06 nmol X mg-1 X min-1 and 2.98 +/- 0.27 nmol X mg-1 X min-1, respectively. The kinetic parameters for 1-palmitoyl-GPC were Km = 16.6 microM, Vmax = 4.3 nmol X mg-1 X min-1 (BMM phi) and Km = 7.6 microM, Vmax = 2.0 nmol X mg-1 X min-1 (MethA cells). In the presence of 1-O-octadecyl-2-O-methyl racemic glycero-3-phosphocholine (ET-18-OCH3), one of the most potent cytotoxic ALP, the acyltransferase was dose dependently inhibited in MethA cells with a 50% inhibition concentration at 40 micrograms/ml. The BMM phi-acyltransferase was not affected up to 80 micrograms of ET-18-OCH3/ml. The kinetic parameters (Km' = 15.4 microM, Vmax' = 2.2 nmol X mg-1 X min-1) suggest that ET-18-OCH3 is a competitive inhibitor in MethA cells. Inhibitor constants for ET-18-OCH3, calculated from Dixon plots, were found to be 423 microM (BMM phi) and 13 microM (MethA cells) indicating a 33-fold larger affinity of ET-18-OCH3 to the MethA cells than to the BMM phi acyltransferase. From these data we assume that the inhibition of oleic acid incorporation into cellular phosphocholine during the antineoplastic action of ALP may be due to different affinities of the inhibitor to the 1-acyl-GPC acyltransferases in different cell types.
Highlights
From the $Max-Planck-lnstitut fur Immunbiologie, 7800 Freiburg andBoehringer Mannheim GmbH, 6800 Mannheim, Federal Republic of Germany and the BMedizinische Universitatsklinik, 7800 Freiburg, Federal Republieof Germany
Susceptibility of cells cycle (Lands pathway [12]), which is responsible for the to ALP is correlated to a selective inhibition of fatty specific nonrandom fatty acid distribution in phosphocholine pstarihcatTiiondvhcsehiifsneomcrlriaoeensrtpeephooyirnarltcachtietinioxovtlanaiatmcniitentichsnteoreleilsnsn1o.e,lc-e2ieo-nlyddlli-u-faCcrceeoysedAly-s-fst1iebn-m-arocgsylsoayl-frcGceAorPLmoC-Pa3-a-sccepeynhllol--ss-bGs(EpoPelCiCcci’3ep).s1awo.t1hfh.w4idc)aihfyofeinsirseg1nle,t-n2ac-ecedrylailltsae-c(dsy1nlb3--y)gs.lnTtyh-hcgeeelaryicocnt-eti3ero-ronmp-h3oeo-fdsppiphahhotoosecpsiphhnohotclohhiliions(plela-imsan(ec1eeyt,A2al,-(MethA cells) and ALP-resistantbone marrow-derived diacyl-GPC) and which serves as fatty acyl acceptor in the murine macrophages (BMM4)
The in vitro [15,16] andin vivo [17].This effect has been explained by a direct selective antineoplastic action onto malignant cells and by the generation of tumoricidal macrophages [14].These ether phospholipids have already been applied in phase I studies in humancancer therapy [18,19]
Summary
DIFFERENTAFFINITIES TO LYSOPHOSPHOCHOLINE ACYLTRANSFERASES IN SENSITIVE AND RESISTANT CELLS*. An adequate percentage of unsaturated fatty acids in phospholipids of cellular membranes is necessary to maintain the structural andfunctional properties of the membrane, including fluidity ( l ) , agglutinability [2], responses to mitogenic stimuli [3],endocytosis [4], transportof metabolites [5], and drugs [6], enzymatic activities [7] and susceptibility to humoral and cellular immune attack [8,9,10] Reduction of this resting lymphocytes; despite this, they are progressively destroyed by ET-18-OCH8while normal lymphocytes are unaffected [25]. Small background activities due to a transfer of endogenous acyl groups to 1-palmitoyl-GPC were obtained by incubation of enzyme protein in the absence of exogenous oleoyl-CoA. Susceptibility of tumor targets was correlated to a selective inhibition of oleic acid incorporation into 1,2-diacyl-GPC These changes in fatty acid incorporation in thepresence of ET-18-OCH3 preceded cellular destruction for about 6 h, indicating that thedisturbances of the phospholipid metabo-. Lism may not be a simple consequence of cell death
Sign-in/Register to view highlights & summary 
Published Version
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call