the methods of the present invention can be used for preventing , stabilizing or causing the regression of vls . the vascular leak syndrome being treated can be caused in various ways . for example , vls can be caused by bacterial infections , nitric oxide , viral infections and infections with helminthic parasites . it is preferred that the vls result from administration of biological molecules , such as interferons ( e . g ., gamma interferon ), cytokines and immunotoxins . for purposes of this application , a cytokine is defined as a protein factor than can cause proliferation and differentiation of blood cells . examples of cytokines which induce vls include interleukin - 2 ( il - 2 ), tumor necrosis factor alpha ( tnf - α ), and granulocyte - macrophage colony stimulating factor ( gmcsf ). for purposes of this application , an immunotoxin is defined as a chimeric molecule in which cell - binding ligands ( or antibodies ) are coupled to toxins , thus redirecting the cell - killing activity of the toxin to the receptor targeted by the cell binding moiety . examples of immunotoxins include those prepared with blocked ricin , ricin a chain ( in native and deglycosylated forms ), pe40 and saporin see ., grossbard , m . l . et al ., blood 79 , 576 - 585 ( 1992 ); grossbard , m . l . et al ., j . clin . oncol . 11 , 726 - 737 ( 1993 ); weiner , l . m . et al ., cancer res . 49 , 4062 - 4067 ( 1989 ); vitetta , e . s . et al ., cancer res . 51 , 4052 - 4058 ( 1991 ); lemaistre , c . f . et al ., blood 78 , 1173 - 1182 ( 1991 ); byers , v . s . et al ., blood 75 , 1426 - 1432 ( 1990 ); byers , v . s . et al ., cancer res . 49 , 6153 - 6160 ( 1989 ); spitler , l . e . et al ., cancer res . 47 , 1717 - 1723 ( 1987 ); amlot , p . l . et al ., blood 82 , 2624 - 2633 ( 1993 ); falini , b . et al ., lancet 339 , 1195 - 1196 ( 1992 )!. specific immunotoxins include anti - thy 1 . 2 - ricin a chain vallera , d . a . et al ., blood 77 , 182 - 194 ( 1991 )!, anti - gd3 antibody r24 bajorin , d . f . et al ., melanoma res . 2 , 355 - 362 ( 1992 )!, and br96 sfv - pe40 friedman , p . n . et al ., j . immunol . 150 , 3054 - 3061 ( 1993 ); siegall , c . b . et al ., j . immunol . 152 , 2377 - 2384 ( 1994 )!. in accordance with the present invention , various materials can be used in treating vls . suitable materials include 15 - deoxyspergualin ( dsg ) and related compounds . in particular , compounds of the following formula a : ## str1 ## wherein y is an alkylene group having an even number of from 4 to 10 carbons , preferably 6 or 8 carbons , or a meta or para mono - or dialkylenephenyl radical substituent group having in total 2 to 5 carbons in the alkylene residue ( s ), preferably 2 to 4 carbons , and x is an alkylene or aphahydroxyalkylene radical having 1 to 5 carbons , preferably 1 to 2 carbons , or an amino acid residue , especially gly , l - his , l - and d - ser , γ - aba and dl - haba , may be used . 15 - deoxyspergualin and a process for its preparation is described in u . s . pat . no . 4 , 525 , 299 to umezawa et al ., while u . s . pat . no . 4 , 851 , 446 to umezawa , deceased , et al ., describes an immunosuppressing method comprising the administration of 15 - deoxyspergualin and related compounds . the no . &# 39 ; 299 and no . &# 39 ; 466 umezawa patents are each incorporated herein by reference thereto . illustrative compounds of the structure ( i ) include those in which y is ( ch 2 ) 6 and x is choh , y is ( ch 2 ) 6 and x is gly , y is ( ch 2 ) 6 and x is l - ala , y is ( ch 2 ) 6 and x is l - leu , y is ( ch 2 ) 6 and x is l - phe , y is ( ch 2 ) 6 and x is l - asp , y is ( ch 2 ) 6 and x is l - gln , y is ( ch 2 ) 6 and x is l - pro , y is ( ch 2 ) 6 and x is l - his , y is ( ch 2 ) 6 and x is l - arg , y is ( ch 2 ) 6 and x is l - ser , y is ( ch 2 ) 6 and x is d - ser , y is ( ch 2 ) 6 and x is l - thr , y is ( ch 2 ) 6 and x is β - ala , y is ( ch 2 ) 6 and x is γ - aba , y is ( ch 2 ) 6 and x is dl - haba , y is pc 6 h 4 ( ch 2 ) 3 and x is gly , y is pc 6 h 4 ( ch 2 ) 3 and x is l - ser , y is p ( ch 2 ) 3 c 6 h 4 and x is gly , y is p ( ch 2 ) 3 c 6 h 4 and x is ser , y is pch 2 c 6 h 4 ( ch 2 ) 2 and x is ser , y is mch 2 c 6 h 4 ( ch 2 ) 2 and x is ser , y is pc 6 h 4 ( ch 2 ) 4 and x is ser , y is pc 6 h 4 ( ch 2 ) 5 and x is ser . the deoxyspergualin compounds set forth above are typically used in the form of a pharmaceutically acceptable salt , for example , chloride and hydrochloride salts , especially the tri - hydrochloride salt . 15 - deoxyspergualin ( dsg ) has the structure ( i ) wherein y is ( ch 2 ) 6 and x is choh . the clinically therapeutic dose of dsg and related compounds is from about 0 . 1 to about 40 mg / day / kg of patient body weight , and may be administered in single or divided doses in a systemic dosage form as described below for a period sufficient to prevent vls . the peak plasma concentration obtained from such dose is from about 0 . 1 to about 20 μg / ml . patients achieve a c max of approximately 10 μg / ml of dsg at 4 mg / kg by 3 hour i . v . infusion . because of the relatively rapid clearance of dsg from plasma , this level drops quite rapidly . thus , six hours following intravenous injection , the plasma concentration ranges from about 20 to 200 ng / ml . a delivery schedule resulting in a steady state plasma concentration of 10 to 200 ng / ml should therefore be effective for preventing vls . the present invention can also be practiced using dsg and related compounds as a racemic mixture , as well as the (+) and (-) isomers of dsg . other suitable materials include phospholipase a 2 ( pla 2 ) inhibitors . in particular , compounds which may be used are of the following formula b : ## str2 ## wherein r = substituted or unsubstituted alkyl , arylalkyl , alkenyl or arylalkenyl groups having 6 or more carbon atoms ; and x and y are different and each is of the form ## str3 ## wherein r &# 39 ; and r &# 34 ; are independently h or alkyl of c 1 - 6 . these compounds , their geometric isomers and their pharmaceutical salts may be used in preventing vascular leak syndrome . the preparation and administration of the compounds of formula b are described in u . s . pat . no . 5 , 141 , 959 , in u . s . patent application ser . no . 079 , 072 , filed on jun . 16 , 1993 , abandoned , and in u . s . pat . no . 5 , 436 , 369 , which are incorporated herein by reference . particularly preferred are the compounds 11 - cis , 13 - cis - 12 ( 3 - carboxyphenyl ) retinoic acid , having the formula : ## str4 ## and ( 2z ), ( 4z )- 3 - methyl - 4 -( 3 - carboxyphenyl )- 5 - 1 , 2 , 3 , 4 - tetrahydro - 1 , 1 , 4 , 4 - tetramethyl - 6 - anthracenyl !- 2 - 4 - pentadienoic acid , having the formula ## str5 ## additional suitable materials include corticosteroids such as dexamethasone , cortisone , hydrocortisone , prednisone , prednisolone , triamcinolone , methylprednisolone , betamethasone , flunisolide and beclomethasone dipropionate , and non - steroidal anti - inflammatory agents such as indomethacin , piroxicam , meclofenamate , naproxen , ibuprofen and aspirin . it is particularly preferred that the agent used to prevent vls not affect the therapeutic activity of the agent causing vls . for example , in the case of br96 sfv - pe40 , it is preferred that its anti - tumor activity not be abolished by the agent used to treat vls . in carrying out the methods of the present invention , the agent used to treat vls may be administered to various mammalian species , such as monkeys , dogs , cats , rats , humans , etc ., in need of such treatment . the agent used to treat vls may be administered systemically , such as orally or parenternally and may be administered intravenously , subcutaneously and intraperitoneally . the agent used to treat vls may be incorporated in a conventional dosage form , such as tablet , capsule , elixir or injectable . the above dosage forms will also include the necessary carrier material , exipient , lubricant , buffer , antibacterial , bulking agent ( such as mannitol ), anti - oxidants ( ascorbic acid or sodium bisulfite ) or the like . oral dosage forms are preferred , although parenternal forms are quite satisfactory as well . with regard to such systemic or local formulations , single or divided doses of from about 1 to 100 mg / kg , from 1 to 3 times daily , may be administered in systemic dosage forms as described above for a period sufficient to prevent vls . the exact route of administration , dosage form , mount to be administered and method of administration will vary depending on the agent employed and may readily be determined by one of ordinary skill in the art . the following examples are further illustrative of the present invention . these examples are not intended to limit the scope of the present invention , and provide further understanding of the invention . the single - chain immunotoxin fusion protein br96 sfv - pe40 was expressed in e . coli and purified as previously described siegall , c . b ., et al ., j . immunol 152 , 2377 - 2384 ( 1994 )!. diphenhydramine - hydrochloride was purchased from elkins - sinn ( cherry hill , n . j .). cyclosporine a ( csa ) was purchased from sandoz ( basel , switzerland ). 15 - deoxyspergualin ( dsg ) was obtained from nippon kayaku ( tokyo , japan ). dexamethasone ( dex ) was purchased from anpro pharmaceuticals ( arcadia , calif .). six to eight week old female wistar furth and rowett , nu / nu ( athymic ) rats ( harlan sprague dawley , indianapolis , ind .) were intravenously injected with various amounts of br96 sfv - pe40 ( 0 . 25 - 4 mg / kg ). after 24 hours , they were euthanized by exposure to co 2 , and the tissues analyzed using gross and microscopic techniques . cardiac blood was collected from comatose animals and placed either in serum collection tubes for blood chemistry analysis or edta tubes for complete blood count ( cbc ). hydrothorax fluid was collected from separate animals by placing the carcass in dorsal recumbancy , carefully removing the ventral chest wall and aspirating fluid using a 5 cc syringe and 21 g needle . trachea , lungs and heart were removed as a unit and the lungs were gently inflated with approximately 2 cc of fixative solution delivered via the trachea . these organs , as well as the chest wall , diaphragm , liver , kidney , and spleen were fixed for at least 48 hours in 10 % neutral buffered formalin . fixed tissues were processed for paraffin embedding , sectioned at 6 m and stained with hematoxylin and eosin for histologic evaluation . treatment of rats carrying h3396 tumor xeno grafts . h3396 tumor xeno grafts were established in athymic rats as previously described siegall , c . b ., et al ., j . immunol . 152 , 2377 - 2384 ( 1994 )!. groups ( n = 6 ) were either left untreated , iv . injected with a single dose of br96 sfv - pe40 ( 0 . 5 mg / kg ), pretreated with three i . p . administrations of dex ( 1 mg / kg ) at 50 , 26 , and 2 hours prior to immunotoxin administration ( 0 . 5 mg / kg br96 sfv - pe40 ), or pretreated with three i . p . injections of dsg ( 10 mg / kg ) and immunotoxin as above . wistar furth immunocompetent rats were intravenously administered with a single dose of br96 sfv - pe40 ( 0 . 25 to 4 . 0 mg / kg ). necropsy was performed 24 hours following immunotoxin administration . the appearance of large amounts of clear fluid in the thoracic cavity ( hydrothorax ) was found to be dose dependent with doses of 2 . 0 mg / kg or greater resulting in fluid accumulations of & gt ; 5 cc ( table 1 ). at 1 mg / kg , there was either small or no fluid accumulation and below 1 mg / kg , no fluid was detected . acute toxicity was clinically apparent in rats treated at 2 - 4 mg / kg . rats treated with 4 mg / kg br96 sfv - pe40 ( and not euthanized earlier ) died within 72 hours . the cause of death in these rats was determined to be asphyxiation and other complications as a result of fluid accumulation in the lungs and thoracic cavity occurring within 48 - 72 hours after administration of br96 sfv - pe40 . comparatively , doses of 0 . 25 and 0 . 5 mg / kg were previously used to promote tumor regressions without toxicity in xenografted rats siegall , c . b ., et al ., j . immunol . 152 , 2377 - 2384 ( 1994 )!. associated with an increase in thoracic fluid accumulation , there was a slight increase in hematocrit at 2 mg / kg and a dramatic increase at 3 and 4 mg / kg . there was also an opposing effect on serum albumin as decreased levels were found at 2 mg / kg or higher br96 sfv - pe40 doses ( table 1 ). hematocrit and serum albumin levels in the normal range were observed with br96 sfv - pe40 doses of less than 2 mg / kg . additionally , an increase in body weight ( up to 10 %) was associated with the onset of the hydrothorax in rats administered with br96 sfv - pe40 at 1 . 5 mg / kg ( maximum tolerated dose ) within 7 days of administration ( data not shown ). histopathology was performed on rats sacrificed 24 hours after treatment with 2 mg / kg br96 sfv - pe40 to assess tissue damage to major organs . diffuse hepatocellular degeneration or less frequent , mild liver necrosis was occasionally observed . however , major histologic lesions were confined to the lungs of rats treated with immunotoxin . the principle histologic lesion was characterized by the accumulation of light pink fluid in the peribronchovascular space consistent with edema fluid ( fig1 a and b ). the edema fluid filled lymphatics and dissected and expanded adjacent connective tissues . alveolar walls were normal to very slightly thickened and there was scant to moderate pleural mesothelial cell hypertrophy . it was common for fluid accumulated in perivascular spaces to contain small numbers of mixed , but primarily mononuclear , inflammatory cells ( fig1 c ). in fewer than 25 % of cases , lesions were slightly to moderately more severe with alveolar walls being prominently thickened and adjacent airspaces containing increased numbers of macrophages along with fewer polymorphonuclear leukocytes , lymphocytes , and erythrocytes ( fig1 d ). the hydrothorax found in rats following administration of 2 - 4 mg / kg br96 sfv - pe40 was not seen in immunocompetent mice ( table 2 ). serum albumin was constant and only a slight increase in hematocrit was observed at 2 - 4 mg / kg immunotoxin , doses that are lethal to mice . severe hepatic lesions were found to be the dose - limiting toxicity in mice . thus rats , but not mice , can serve as a model for br96 sfv - pe40 induced vls . assessment of prophylactic drug treatment on rats prior to immunotoxin therapy utilizing this immunotoxin - induced rat vls model , experiments were initiated to evaluate the effect of several anti - inflammatory and immunosuppressant drugs for ability to block hydrothorax . the drugs that were chosen were diphenhydramine ( anti - histamine ), csa ( immunosuppressant ), dsg ( immunosuppressant ), and dex ( anti - inflammatory / immunosuppressant ). rats were treated either with diphenhydramine , 25 and 2 hours prior to immunotoxin administration , or csa , dsg , or dex , at 50 , 26 , and 2 hours prior to administration of br96 sfv - pe40 ( 2 mg / kg ). dex pretreatment effectively blocked br96 sfv - pe40 - induced vls in rats , with no detectable fluid accumulation in the thoracic cavity ( table 1 ). a variable though reproducible reduction in br96 sfv - pe40 - induced hydrothorax ( 0 . 5 - 5 cc ) was observed in dsg pre - treated rats , while neither csa nor diphenhydramine were effective at blocking vls ( table 1 ). these results show that dex is a potent inhibitor of immunotoxin - induced vls and dsg has a variable inhibitory effect on vls . since vls is the dose limiting toxicity in br96 sfv - pe40 treated rats , we evaluated the ability of these drugs to prevent immunotoxin - induced death . rats were pretreated as described above , followed by administration of a lethal dose of br96 sfv - pe40 , 2 mg / kg , and were observed for survival until death or through day 10 , post immunotoxin treatment . all rats treated with 2 mg / kg br96 sfv - pe40 and no prophylaxis succumbed within 72 hours . all dex pretreated rats survived the otherwise lethal dose of immunotoxin ( table 3 ). no evidence of hydrothorax or other gross lesions were detected at necropsy . neither csa nor diphenhydramine prophylaxis resulted in prolongation of survival . injection of rats with dex either at the same time or 24 hours following br96 sfv - pe40 administration was unable to prevent hydrothorax or prolong survival . thus , exposure to dex , prior to immunotoxin administration , is necessary for the prevention of hydrothorax . effects of br96 sfv - pe40 and vls - blocking drugs on blood chemistry and cbc in rats vls induced by immunotoxins has been shown to be associated with hematologic changes . since dex , and to a lesser extent dsg , were found to block vls in br96 sfv - pe40 treated rats , we investigated the effects of these drug combinations on immunotoxin - induced changes in rat blood chemistry and cbc . br96 sfv - pe40 ( 2 mg / kg ) administration caused an increase in polymorphonuclear cells and hematocrit in peripheral blood , while decreasing the monocyte count ( table 4 ). total white blood cell counts were within normal limits . pre - treatment with dex , followed by br96 sfv - pe40 resulted in a leukocytosis and neutrophilia along with a rise in hematocrit , both predictable side - effects of dex duncan . j . r . and prasse , k . w ., veterinary laboratory medicine , 2nd ed ., iowa state univ . press , ames , iowa , 124 - 126 ( 1986 ); haynes , r . c . and murad , f ., the pharmacological basis of therapeutics , 7th ed ., ( macmillan pub . co ., n . y ., 1459 - 1489 ( 1985 )!. as expected , the lymphocyte count was depressed in these rats . dsg pre - treatment had a minor suppressive effect on all immunotoxin - induced hematologic changes , and ameliorated the elevated hematocrit induced by br96 sfv - pe40 ( table 4 ). however , dsg caused a pronounced decrease in monocytes consistent with the general myelosuppression effect of dsg that had been previously reported nemoto , k . et al ., jpn . j . cancer res . 83 , 789 - 793 ( 1992 )!. the effects of various treatments on blood chemistry was also compared at 2 mg / kg br96 sfv - pe40 . br96 sfv - pe40 induced a mild increase in the liver enzymes serum glutamic - pyruvic transaminase ( sgpt ) and serum glutamic - oxaloacetic transaminase ( sgot ) by 6 and 3 - fold , respectively , as well as a decrease in both albumin and total protein ( table 4 ). rats pre - treated with dex followed by br96 sfv - pe40 were found to have extremely elevated sgpt and sgot levels ( 36 - 50 fold ) as well as slightly elevated albumin and total protein levels , all of which are secondary to dex treatment . rats treated with dex only had slightly elevated transaminases ( 71 and 153 , for sgpt and sgot , respectively ). thus , dex appears to exacerbate the hepatotoxicity of br96 sfv - pe40 by increasing the transaminase levels . the effects of dex pretreatment on rats receiving 2 mg / kg br96 sfv - pe40 was evaluated histologically 24 hours after immunotoxin administration . animals pretreated with dex had only slight vascular edema or were indistinguishable from the control animals receiving no immunotoxin , whereas unprotected rats exhibited marked accumulation of fluid in the perivascular and surrounding parenchymal spaces ( fig2 ). thus , pretreatment of rats receiving 2 mg / kg br96 sfv - pe40 and 1 mg / kg dex blocks both gross and microscopic evidence of pulmonary edema . dex or dsg does not abrogate the antitumor activity of br96 - immunotoxin on tumor xenografts in rats dex and dsg are both immunomodulating agents . having determined that dex and to a lesser extent dsg , inhibits vls in br96 sfv - pe40 ( 2 mg / kg ) treated rats , we next evaluated whether or not they would interfere with immunotoxin activity against tumors in vivo . the antitumor activity of br96 sfv - pe40 has previously been measured against h3396 human breast carcinoma xenografts in rats siegall , c . b . et al ., j . immunol . 152 , 2377 - 2384 ( 1994 )!. since the rats used in the antitumor study were athymic , we also tested the ability of athymic rats to develop dose - dependent hydrothorax . the same accumulation of thoracic fluid was found in the athymic rats as was found in the immunocompetent rats . using the h3396 model , rats were pretreated with either dex or dsg , followed by a single suboptimal intravenous dose of br96 sfv - pe40 ( 0 . 5 mg / kg ). regressions of the h3396 tumor xenografts were observed in the immunotoxin treated animals , with or without dex or dsg pre - treatment ( fig3 ). in the dex pre - treated group , there was a slight reduction in the regression of the tumor xenograft in comparison with tumors in both the dsg or non - pretreated groups . thus , pre - treatment of rats with the immunomodulatory agents dex or dsg does not block br96 sfv - pe40 from regressing implanted tumor xenografts . immunotoxin therapy is a promising approach for the treatment of cancer grossbard , m . l . and nadler , l . m ., important advances in oncology , ( j . p . lippincott co ., philadelphia , pa . ), 111 - 135 ( 1992 ); pasten , i . et al ., annu . rev . biochem . 61 , 331 - 354 ( 1992 )!. however , dose - limiting side - effects have prevented the use of sufficient amounts needed for the best therapeutic response . vls has been the most limiting of these side - effects vitetta , e . s . et al ., cancer res . 51 , 4052 - 4058 ( 1991 ); vitetta , e . s . et al ., trends pharm . sci . 14 , 148 - 154 ( 1993 )!. for immunotoxins to become effective drugs for the treatment of human cancer , prevention of immunotoxin - induced vls is necessary . studies in non - human primates suggest that these models may be poor predictors of vls toxicity in humans , as evidenced by the lack of vls in monkeys and presence of vls in humans treated with b3 - lyspe40 immunoconjugates pai , l . h . et al ., cancer res . 52 , 3189 - 3193 ( 1992 ); skolnick , a . a ., jama 270 , 2280 ( 1993 )!. no immunocompetent animal model of immunotoxin - induced vls has been described to date . administration of ricin a chain - immunotoxins was reported to be unable to induce vls in immunocompetent mice , rats , or guinea pigs soler - rodrigues , a . m . et al ., exp . cell . res . 206 , 227 - 234 ( 1993 )!. however , it has been reported that irradiated mice displayed vls symptoms following administration of the pan t - cell immunotoxin anti - thy 1 . 2 - ricin a chain vallera , d . a . et al ., blood 77 , 182 - 194 ( 1991 )!. in vitro experimentation to investigate vls has been performed because of the lack of an adequate in vivo model . it has been demonstrated that ricin a chain could be directly cytotoxic to endothelial cells soler - rodrigues , a . m . et al ., exp . cell . res . 206 , 227 - 234 ( 1993 )!. however , it is not clear whether or not in vivo toxicity to endothelial cells is , in fact , the cause of immunotoxin - induced vls . we have focused on establishing an animal model that approximates vls as seen in human clinical trials utilizing targeted immunotoxins . rats administered with the single - chain immunotoxin br96 sfv - pe40 responded with a dose - dependent vls similar to that seen in humans . the vls response was seen as an accumulation of thoracic fluid and pulmonary edema with a concomitant increase in hematocrit and body weight as well as a decrease in serum albumin levels ( table 1 ). the rats died within 48 - 72 hours after administration of br96 sfv - pe40 as a result of fluid accumulation in the lungs and thoracic cavity . in contrast , there were no vls symptoms in mice administered with br96 sfv - pe40 at doses up to 4 mg / kg , in which mice died due to hepatic toxicity ( table 2 ). preliminary studies indicate that dogs do not respond to br96 sfv - pe40 with any vls - like symptoms at doses at least 6 - times higher ( on a mg / m 2 basis ) than that causing a vls response in a rat ( data not shown ). additionally , there were no apparent vls symptoms in monkeys following administration of immunotoxins prepared with both ricin a chain and pe40 vitetta , e . s . et al ., cancer res . 51 , 4052 - 4058 ( 1991 ); pai , l . h . et al ., cancer res . 52 , 3189 - 3193 ( 1992 )!. thus , rats represent the only species described so far to naturally respond to an immunotoxin like that seen in humans . to accurately evaluate the toxicity of immunotoxins , standard screening of more than two species ( often done with mouse and monkey ) may be necessary . while rats provide a useful model for br96 sfv - pe40 - induced toxicity because they respond with a dose - limiting vls , they may not be the optimal species for other immunotoxins with different specificities or with different toxins . therefore , continued experimentation in evaluating the toxicity of other immunotoxins in the rat model , specifically focusing oh vls symptoms , has been initiated . having a model for le . sup . γ - immunotoxin - induced vls , we set out to search for inhibitors of vls that could be combined with the immunotoxin without masking its antitumor activity . of the drugs tested , dex totally blocked , and dsg variably inhibited immunotoxin - induced vls ( table 3 ). additionally , dex prevented death in rats treated with an otherwise lethal dose ( 2 mg / kg ) of br96 sfv - pe40 ( table 3 ), while dsg did not . however , dex was unable to prolong survival in rats treated with 4 mg / kg br96 sfv - pe40 ( data not shown ). the mechanism whereby dex suppresses vls in this model system is unclear . glucocorticoids are capable of exerting a multiplicity of antiinflammatory and immunosuppressive effects including blockade of arachidonate metabolism , suppression of lymphocyte and macrophage functions with marked lympholysis in rodents , down - regulation of several pro - inflammatory cytokines , and stabilization of mast cells among others haynes , r . c . and murad , f ., the pharmacological basis of therapeutics , ( macmillan pub . co ., n . y . ), 1459 - 1489 ( 1985 ); boumpas , d . t . et al ., clin . exp . rheum . 9 , 413 - 423 ( 1991 )!. the absence of any modulating effects following csa pre - treatment and the presence of an effect in athymic rats suggest that in this model , vls is not mediated by classic t - cell responses . the variable regulation of vls associated with dsg pre - treatment , along with the potent effect of dex suggests that the targets influenced by these immunosuppressive drugs may be critical to the pathogenesis of vls in rats . while vls is the dose - limiting toxicity of many immunotoxins , it remained to be determined whether the same properties that mediate vls are also responsible for tumor reduction . to address this issue , the effects of dex or dsg prophylaxis on immunotoxin anti - tumor activity was studied in athymic rats carrying established h3396 human breast carcinomas . it was found that tumor xenografts in rats pretreated with either drug underwent regression similarly as compared to xenografts in rats treated with br96 sfv - pe40 alone ( fig3 ), although xenografts in rats that received prophylactic dex were regressed slightly less compared to xenografts in non - pretreated rats or those pretreated with dsg . one explanation for the slight reduction in antitumor activity is that dex has been shown to decrease the delivery of a carcinoma reactive monoclonal antibody to tumor xenografts in athymic rats neuwelt , e . a . et al ., neurosurgery 33 , 478 - 484 ( 1993 )!. thus , in our study , the immunotoxin may have been slightly retarded from leaving the vasculature in dex treated animals . however , since we specifically used a suboptimal treatment of immunotoxin and could only detect a slight difference between dex pre - treated and control groups , while the same level of dex completely prevented all signs of vls , it suggests that at least in the rat model , antitumor activity and vls occur by separate mechanisms . dsg is currently undergoing clinical evaluation for suppression of hama in cancer patients treated with an antibody or antibody - based imaging agent . preliminary results from these studies suggest that dsg is effective at blocking hama . these results combined with our results showing dsg inhibits vls in rats without abolishing antitumor effects of br96 sfv - pe40 , support the further investigation of dsg in the clinic for combination therapy with immunotoxins . il - 2 has also been found to cause vls in humans rosenstein , m . et . al ., immunology 137 , 1735 - 1742 ( 1986 ); rosenberg , s . a . et al ., n . engl . j . med . 316 , 889 - 897 ( 1987 )!. corticosteroids have been shown to reduce il - 2 mediated side effects vetto , j . et al ., j . clin . oncol . 5 , 496 - 503 ( 1987 ); mier , j . w . et al ., blood 76 , 1933 - 1940 ( 1990 )!. however , corticosteroids also reduce the antitumor effect of il - 2 in mouse models of cancer since they are immunosuppressive and inhibit adoptive immunotherapy papa , m . z . et al ., cancer res . 46 , 5618 - 5623 ( 1986 )!. corticosteroids have been administered either concurrently or subsequent to use of anti - cd22 - ricin a chain immunotoxin conjugates in humans , based on the ability of corticosteroids to inhibit il - 2 induced vls vitetta , e . s . et al ., cancer res . 51 , 4052 - 4058 ( 1991 ); amlot , p . l . et al ., blood 82 , 2624 - 2633 ( 1993 )!. these limited studies were unable to correlate the grade of toxicity in groups of patients that received corticosteroids in combination with immunotoxin , nor were they able to determine whether corticosteroids masked the ability of immunotoxins to regress tumors . pentoxifylline , a synthetic xanthine , has been shown to inhibit il - 2 induced vls in rats edwards , m . j . et al ., surgery 110 , 199 - 204 ( 1991 ); edwards , m . j . et al ., j . clin . invest . 90 , 637 - 641 ( 1992 )!, and guinea pigs ishizaka , a . et al ., j . appl . physiol . 67 , 2432 - 2437 ( 1989 )!, and tumor necrosis factor - alpha ( tnf - α ) induced vls in guinea pigs lilly , c . et al ., am . rev . respir . dis . 139 : 1361 - 1368 ( 1989 )!. our data suggests that prophylactic treatment may be the key to blocking vls induced by immunotoxin therapy . additional drugs were screened for their ability to prevent br96 sfv - pe40 - mediated vls in rats ( table 5 ). prophylactic administration of indomethacin , a non - steroidal anti - inflammatory drug ( nsaid ), prevented hydrothorax in rats treated with 2 mg / kg br96 sfv - pe40 . however , the dose range of indomethacin that was effective in preventing vls ( 15 - 30 mg / kg ) was higher than usually used clinically . at 5 mg / kg , indomethacin was unable to prevent br96 sfv - pe40 - mediated vls . piroxicam , also an nsaid , was found to prevent vls in the same model system when administered prophylactically either i . p . or orally with a dose of 20 mg / kg . the pla 2 inhibitor 11 - cis , 13 - cis - 12 ( 3 - carboxyphenyl ) retinoic acid was also found to prevent vls in rates following administration of br96 sfv - pe40 . with prophylactic administration ( i . p .) of 11 - cis , 13 - cis - 12 ( 3 - carboxyphenyl ) retinoic acid , vls was reduced by 50 % ( 30 mg / kg ) or completely blocked ( 100 mg / kg ). indomethacin , as well as other nsaids , act by blocking the enzyme cyclooxygenase , thus preventing the generation of prostaglandin endoperoxides ( from which prostaglandins and thromboxanes are metabolized ) from arachidonic acid . the pla 2 inhibitor 11 - cis , 13 - cis - 12 ( 3 - carboxyphenyl ) retinoic acid blocks the generation of arachidonic acid from membrane phospholipids . these date are suggestive of a major role for prostanoids and specifically prostaglandins in the advent of br96 sfv - pe40 mediated vls . table 1______________________________________identification of an immunotoxin - mediated , dose - dependenthydrothorax condition in ratsit dose , hydrothorax hematocrit albuminmg / kg ( mg / m . sup . 2 ) ( cc ) (%) g / dl ) ______________________________________0 0 38 . 9 3 . 60 . 25 ( 1 . 475 ) 0 39 . 9 3 . 80 . 5 ( 2 . 95 ) 0 39 . 7 3 . 51 . 0 ( 5 . 9 ) 0 - 3 * 39 . 5 3 . 22 . 0 ( 11 . 8 ) & gt ; 5 42 . 9 2 . 63 . 0 ( 17 . 7 ) & gt ; 5 56 . 1 2 . 54 . 0 ( 23 . 6 ) & gt ; 5 55 . 5 2 . 6______________________________________ br96 sfvpe40 was intravenously administered in a volume of 0 . 2 ml in pbs . fluid accumulation into the thoracic cavity was collected 24 hours after administration of it ( 2 - 4 animals were treated at each dose ). five cc of hydrothorax fluid indicates a range between 5 - 8 cc . * 2 / 3 rat had no fluid and 1 / 3 had 3 cc hydrothorax fluid . table 2______________________________________lack of hydrothorax in miceit dose , mg / kg ( mg / m . sup . 2 ) hydrothorax ( cc ) hematocrit (%) albumin ( g / dl ) ______________________________________0 0 36 . 4 3 . 152 . 0 ( 6 . 0 ) 0 42 . 8 3 . 34 . 0 ( 12 . 0 ) 0 46 . 0 3 . 3______________________________________ br96 sfvpe40 was administered and fluid accumulation measure as in legend for table 1 . table 3______________________________________prevention of vlsit dose hydrothorax ( cc ) survival at 10 d ( mg / kg ) pretreatment ( 24 h ) (# alive /# total ) ______________________________________2 dexamethasone 0 10 / 102 deoxyspergualin 0 . 5 - 5 . 0 0 / 52 cyclosporine a & gt ; 5 0 / 32 none & gt ; 5 0 / 102 diphenylhydramine & gt ; 5 0 / 3______________________________________ br96 sfvpe40 was administered intravenously in 0 . 2 ml pbs either alone or two hours following the last pretreatment dose of dexamethasone ( 1 mg / kg , q1dx3 , intraperitoneal ); deoxyspergualin ( 10 mg / kg , q1dx3 , intraperitoneal ); cyclosporine a ( 100 mg / kg , q1dx3 , subcutaneous ), diphenylhydramine ( 1 mg / kg , q1 dx2 , intraperitoneal ). it = immunotoxin ( br96 sfvpe40 ). table 4______________________________________cbc and chemistry screen chartcell it dexamethasone + deoxyspergualin + type untreated only it it______________________________________wbc 13 . 0 13 . 8 16 . 9 9 . 2poly 1593 5032 13130 328lymph 8217 7322 2584 5587mono 659 395 486 230hemato . 36 . 8 48 . 6 53 . 1 38 . 9chemistry screensgpt 56 301 5790 113sgot 99 299 3641 131albumin 3 . 6 2 . 8 4 . 5 3 . 2tot . prot 6 . 7 5 . 0 7 . 1 6 . 3______________________________________ data ( average of 2 - 4 rats ) are taken 24 hours postit administration ( 2 mg / kg ). wbc count in thousands / mm . sup . 3 ; polymorphonuclear cells , lymphocytes and monocytes are in absolute numbers ; hematocrit is in %, sgpt and sgot are in iu / l , albumin and total protein are in g / dl . table 5______________________________________vls inhibitor study hydrothorax # rats pretreatment treatment ( cc ) ______________________________________4 indomethacin ; 30 mg / kg , sc br96 sfv - pe40 , 0 2 mg / kg , iv2 indomethacin ; 15 mg / kg , sc same 02 indomethacin ; 5 mg / kg , sc same & gt ; 52 11 - cis , 13 - cis - 12 ( 3 - same 2 . 5 carboxyphenyl ) retinoic acid ; 30 mg / kg , ip2 11 - cis , 13 - cis - 12 ( 3 - same 0 carboxyphenyl ) retinoic acid ; 100 mg / kg , ip______________________________________
a novel method for preventing , stabilizing or causing regression of vascular leak syndrome is disclosed . the method comprises administering to a patient in need thereof a compound selected from the group consisting of a corticosteroid , a non - steroidal anti - inflammatory agent , 15 - deoxyspergualin and related compounds , and phospholipase a 2 inhibitors .