the invention relates to an isolated factor , designate ocaf , that activates ovarian cancer cells , by stimulating the release of intracellular calcium . the term &# 34 ; isolated &# 34 ; is used herein with reference to a factor that is substantially free from proteins and peptides , i . e . is free from proteins and peptides detectable by protein staining techniques . the activating property of the factor with respect to ovarian cancer cells is revealed using the fluorescence scanning technique and the incubation protocol reported by mills et al , supra , which is incorporated herein by reference . briefly , established ovarian cancer cells , of the line designated hey , are preincubated with the fluorescing calcium chelator indo - 1 ; after addition of the factor , the cells are scanned using a spectrophotometer to measure chelated calcium and thus indirectly measure the increased concentration of intracellular calcium . the various identifying characteristics of the ovarian cancer ascites factor of the present invention were revealed upon examination of a preparation obtained from ascites fluid that was taken from ovarian cancer patients . the preparation was obtained in the manner described in example 1 herein . briefly , this entailed a first methanol / chloroform extraction of fresh human ovarian cancer ascites fluid according to the method described by bligh and dyer in can . j . biochem . physiol ., 1959 , 37 : 911 . the ocaf activity was recovered in the aqueous / methanol phase , which was re - extracted with acidified chloroform and methanol according to the method described by schact in methods enzymol ., 1981 , 72 : 626 . the factor - containing chloroform phase was then fractionated on silica gel , and the isolated ocaf was eluted using methanol . the factor resulting from this extraction was subjected to various analytical techniques , and its ovarian cancer activating properties were compared with other known activating and growth factors , using the hey - based fluorescence scanning assay . as is revealed in the examples which follow , ocaf is probably lipid in nature , and may be a unique form of phosholipid . in its extracted form , ocaf may be exploited in screening assays designed to identify compound ( s ) that inhibit ocaf - mediated activation of ovarian cancer cells . such an assay entails incubating an ovarian cancer cell line , such as the hey cell line , in the presence of ocaf and a compound the inhibiting properties of which are to be determined . inhibition by the compound will be revealed by elimination of or a reduction in the intracellular release of calcium within the ovarian cancer cell line , relative to a control experiment in which only ocaf is present . inhibitors of ocaf may be in the form of antibodies , raised by immunizing rabbits , for instance , with ocaf and then recovering the antibodies so formed according to well established procedures . when conjugated to a reporter such as an enzyme , e . g . urease , peroxidase and the like , such antibodies can also be exploited to determine the presence of ocaf in biological samples , as a way of diagnosing ovarian cancer . freshly obtained ascites was centrifuged to remove cells . 25 ml of methanol and 12 . 5 ml of chloroform were added to 10 ml of ascites . after thorough mixing of their contents , the mixture was centrifuged ( 1000 g , 10 min ). the supernatant was removed to a new tube and the precipitate was re - extracted with 12 . 5 ml of chloroform . the combined supernatant was washed with 12 . 5 ml of 0 . 88 % kcl in h 2 o and separated into two layers by centrafugation . the precipitate , which contained more than 99 % protein ( determined by the bio - rad protein assay ), had no ocaf activity and was discarded . the lower chloroform phase , which contained mostly neutral lipids ( revealed by tlc analysis ), had no ocaf activity . the upper aqueous / methanol layer contained ocaf activity (˜ 90 % activity from crude ascites ). the methanol and most of the h 2 o in this phase was removed by a rotary evaporator at 50 ° c . the resulting material was brought up to 1 ml by h 2 o and 3 ml of chloroform / methanol ( 1 : 2 ) was added and mixed . then , 1 ml of 2 . 4n hcl and 1 ml chloroform were added . after thorough mixing , the mixture was centrifuged ( about 1000 g for 10 min ) and the lower layer was transferred into new tubes . the interface and upper phase were extracted once more with 2 ml of chloroform . the combined lower phases were washed with 4 ml of methanol - 1nhcl , 1 : 1 ( v / v ). the upper phase , found to contain no ocaf activity , was discarded after centrifugation . the lower layer was collected , and found to possess ocaf activity (& gt ; 80 % recovery from crude ascites ). ocaf in this acidified chloroform was passed on a sep - pak silica cartridge (˜ 10 ml / cartridge ), which was washed with 20 ml of chloroform , 20 of acetone and then 20 ml of chloroform / methanol ( 50 : 50 , v / v ). the ocaf activity was eluted with 50 ml of methanol with overall recovery & gt ; 70 %. this ocaf preparation is free of protein and amino acid , as assessed by silver - stained sds page and tlc analysis by staining with ninhydrin . tlc analysis also indicated that ocaf is substantially free of neutral lipids . the activating properties of ocaf and various comparison compounds were investigated by determining increases in the intracellular calcium concentration within hey cells . for this purpose , hey cells ( a human ovarian cancer cell line obtained from toronto general hospital ) having the properties described by buick et al , cancer research , 1985 , 45 : 3668 ) were cultured in complete medium ( rpmi 1640 ( gibco , grand island , n . y .) substituted with 5 % ( v / v ) fcs ( flow laboratory , maclean , va ), 2 mm glutamine ( gibco ) and 1 × 10 5 m mercaptoethanol . cells were split weekly and were cultured in rpmi 1640 without fcs for at least 20 hours prior to use . cells were harvested in pbs , 2 mm edta . measurements of intracellular calcium were obtained as described by mills et al , supra , using indo - 1 - am as the ca ++ chelator and fluorescence indicator . hey cells were loaded with indo - i am , washed and incubated at 37 ° c . for at least 30 min . different compounds were added to the cells at concentrations as indicated and fluorescence changes were measured by a hitachi 4000 spectrophotometer at 37 ° c . ascites was used as a positive control to show that the cells were responsive . in all cases , assays were performed in a calcium free buffer ( 140 mm nacl , 1 mm kcl , 1 mm mgcl 2 , 10 mm glucose , and 20 mm hepes , ph 7 . 23 ) and 1 mm egta was added followed by the test samples . to confirm that various known growth factors were not responsible for ocaf activity , the factors identified in table 1 were evaluated in the hey - based assay at the noted concentrations . table i______________________________________peptide growth factorstested in [ ca . sup .++ ]. sub . i assay assaycompound concentration ( ca . sup .++) ______________________________________tgf - α 0 . 01 ng - 1 μg / ml - tgf - β 100 ng / ml - egf 0 . 01 ng - 1 μg / ml - acidic fgf 0 . 01 ng - 1 μg / ml - basic fgf 0 . 01 ng - 1 μg / ml - pdgf 5 ng / ml - igf - i 0 . 01 ng - 1 μg / ml - igf - ii 0 . 01 ng - 1 μg / ml - il - 1 1 , 000 half - max . units / ml - il - 2 0 . 01 ng - 1 μg / ml - il - 8 0 . 01 ng - 1 μg / ml - tnf - α 100 ng / ml - insulin 10 . sup .- 6 m - lif * 0 . 01 - 1 μg / ml - thrombin 0 . 1 - 10 unit / ml + fibrinogen 2 - 200 μg / ml - vasopressin 100 ng / ml - angiotesin 100 ng / ml - α - & amp ; β - interferons 10 , 000 units / ml - bombesin 10 nm - 1 μm - bradykinin 10 nm - 1 μm - pha ** 30 μg / ml - ______________________________________ * lif : leukaemia inhibitory factor ** pha : mitogenic lectin phytohemagglutinin of the more than 20 different peptide growth factors tested , only thrombin stimulated a transient [ ca ++ ] i increase in hey cells . however , thrombin did not interfere with the ocaf - activated calcium signal , although some attenuation did occur ( fig1 a and 1b ). furthermore , antithrombin was found to block thrombin activity , but not ocaf activity . still further evidence that ocaf is not a protein was obtained from protease digestion studies . it was found that ocaf activity was not abolished after treatment with the following proteases , all of which were separately incubated with ocaf at 37 ° c . for 3 - 5 hours : bromelain , carboxypeptidase y , peptidase , pepsin , papain , protease types xxv ( pronase e ), xvii - b ( v8 ), xiii and xiv ( pronase e ), proteinase k , thermolysin , and trypsin . further characterization of ocaf also demonstrated that it is resistant to extremely harsh treatment including boiling in water for fifteen minutes , extremes of ph and detergent treatment . furthermore , it is soluble in 80 % acetone and 100 % meoh , suggesting that it could be a lipid . more than 20 known lipid growth factors / mediators were then tested , and the results are presented in table ii . table ii__________________________________________________________________________organic compounds tested in [ ca . sup .++ ]. sub . i assaycompound concentration assay ( ca . sup .++) __________________________________________________________________________arachidonic acid 12 , 24 , 60 , 120 , 480 μm - oleic acid 1 , 12 , 120 μm - diacylglycerol 1 , 12 , 20 , 200 μm - phosphatidic acid 12 , 60 μm - phosphatidylcholine 12 , 30 , 75 , 300 μm - phosphatidylethanolamine 12 , 30 , 80 μm - phosphatidylserine 12 , 30 , 80 μm -** lpa 1 , 12 μm + lpc 12 , 60 μm - lpe 1 , 12 , 20 μm - lpg 1 , 12 , 20 , 50 μm - lpi 1 , 12 , 20 , 50 μm -** lps 1 , 12 μm + sphingosine 1 , 12 , 20 , 50 μm -** spc 1 , 12 , 20 μm + sphinogomyelin 1 , 12 , 20 μm - osm 2 , 10 , 20 μm - ceramide 1 , 12 , 20 μm - paf 10 . sup .- 11 to 10 . sup .- 5 m - tpa 10 . sup .- 10 to 10 . sup .- 6 m - carbachol 0 . 2 , 1 . 2 , 2 . 4 mm - __________________________________________________________________________ lpa : lysophosphatidic acid ( oleoyl , palmitoyl or stearoyl ) lpc : lα - lysophosphatidylcholine ( oleoyl or palmitoyl ) lpe : lysophosphatidylethanolamine ( oleoyl ) lpg : lysophosphatidylglycerol lpi : lysophosphatidylinositol lps : lysophosphatidylserine spc : sphingosylphosphorylcholine osm : noleoyl - d - sphingomyelin paf : platelet activating factor tpa : 12o - tetradecanoylphorbol - 13 - acetate it will be seen from table ii that lpa ( oleoyl , palmitoyl and stearoyl ), lps and spc were found to stimulate [ ca ++ ] i release in hey cells . furthermore , they all cross inhibit ocaf and each other in the assay and fig2 and 3 show typical interactions . enzymatic digestions of ocaf and other lipids were carried out to determine whether ocaf is phospholipid in nature , and whether other phospholipids might possess ocaf activity . phospholipase digestions were carried out in 10 mm hepes , ph 7 . 4 , with either 100 mm nacl or 4 mm cacl 2 at 37 ° c . for 3 h . the reactions were stopped by freezing at - 20 ° c . no further extraction was done and the mixtures were assayed for calcium release activity as described above . the enzymes used were also incubated in the absence of substrate under the same conditions , and no calcium release was observed . the results are shown in table iii . table iii______________________________________ [ ca . sup .++]. sub . i release after enzymatic digestionssample control pl - b pl - d lipoxidase______________________________________ocaf ++ - - - lpa ++ - ++ ++ lpc - - ++ - lps ++ - ++ - spc ++ ++ - ++ thrombin ++ ++ ++ ++ ______________________________________ lpa : lysophosphatidic acid ( oleoyl , palmitoyl or stearoyl ) lpc : lysophosphatidylglycerol lps : lysophosphatidylserine spc : sphingosylphosphorylcholine pl - b : phospholipase b ( vibrio species ) pl - d : phospholipase d , type vi ( streptomyces chromofuscus ) lipoxidase : lipoxidase ( soybean ) the digestion profile of ocaf does not correspond to those observed for other phospholipids , but imply structural similarity . judging from its sensitivity to phospholipase b and d , ocaf is likely a phospholipid other than lpa , lps and spc .
herein described is an ovarian cancer activating factor that has been isolated from ovarian cancer ascites fluid . the factor may be utilized in its isolated form in a screening program aimed at identifying inhibitors of factor - mediated ovarian cancer activation , or as a growth supplement useful for culturing ovarian and other cancer cell lines .