it is appreciated that the detailed description that follows is intended only to illustrate certain preferred embodiments of the present invention . it is in no way intended to limit the scope of the invention , as set out in the claims . the present invention describes use of jasmonates to prevent proliferation and induce death of malignant cells . particularly preferred jasmonates include jasmonic acid [(−)- ja and / or (+)- 7 - iso - ja ], methyl jasmonate , jasmone , and 9 , 10 - dihydro - jasmonic acid and its lower alkyl ester . other preferred jasmonates include 4 , 5 - didehydro - 7 - iso - ja , 3 , 7 - didehydro - ja , cucurbic acid ( ca ), 6 - epi - ca , 6 - epi - ca - lactone , 12 - hydroxy - ja , 12 - hydroxy - ja - lactone , 11 - hydroxy - ja , 8 - hydroxy - ja , homo - ja , dihomo - ja , 11 - hydroxy - dihomo - ja , 8 - hydroxy - dihomo - ja , tuberonic acid ( ta ), ta - o - β - glucopyranoside , ca - o - β - glucopyranoside , amino acid conjugates of ja , as well as the corresponding lower alkyl esters of each of these acids . the applicants have proven below , that two jasmonates , methyl jasmonate and jasmonic acid , have a positive therapeutic effect on malignant cells , yet do not harm normal cells such as normal circulatory lymphocytes . the following examples demonstrate that jasmonates are cytotoxic to four different types of malignant cells in culture , in doses that would be considered safe and attainable in mammals , and do not inhibit growth of healthy lymphocytes . the applicants have additionally proven , in example 5 , that jasmonates are effective in prolonging the lifetime of mice injected with lymphoma cells , resulting in a survival rate that is significantly higher than that of untreated mice ( 2 . 25 times the number of survivors than in the untreated group ). plant stress hormones are cytotoxic for four human transformed cell lines four transformed cell lines of different histological lineages were exposed to one of three plant stress hormones . the cell lines chosen represent four types of cancer of widespread clinical importance . molt - 4 is a human t lymphoblastic leukemia cell line , sk - 28 are human melanoma cells . lncap is an androgen - responsive human prostate adenocarcinoma cell line , and mcf7 is a human breast carcinoma cell line . all cell lines were purchased from atcc ( rockville , md .). all reagents were purchased from sigma chemicals ( st . louis , mo .) unless otherwise stated . ja and mj were dissolved in ethanol . all cell cultures were performed in rpmi - 1640 with 10 % fetal calf serum ( biological industries , beit - haemek , israel ), and cells ( except for molt - 4 and lymphocytes from the peripheral blood ) were allowed to adhere prior to every treatment mentioned below . lncap , mcf7 and sk - 28 cells ( at 4 × 10 3 / well ) and molt - 4 cells ( at 1 . 5 × 10 4 / well ) were seeded in 96 - well plates and allowed to adhere overnight . plant stress hormone at increasing concentrations was added as indicated below , and toxicity was measured after 24 hours using the celltiter 96 aqueous non - radioactive cell proliferation assay ( promega , madison , wis . ); an assay in which viable cells produce a colored product ( for details on the protocol of this assay , see below ). this assay is quantitative , as the amount of color produced is read using an elisa reader . the highest non - toxic pharmacological concentration used in humans , of the nonsteroidal anti - inflammatory drug sa , is approximately 3 mm ( katzung , lange medical book , stamford , 1998 ). in order to compare the additional plant stress hormones ja oasmonic acid ) and mj ( methyl jasmonate ) with sa , the same range of concentrations ( 0 . 5 - 3 mm ) was chosen . these compounds at the aforementioned concentrations are not toxic for mice . each cell line was incubated with each of these hormones at a concentration ranging from 0 . 5 - 3 mm for 24 hours , after which cytotoxicity was measured . the statistical significance of the results was determined ( where appropriate ) by two - tailed student &# 39 ; s t - test , n = 3 . results are presented as means ± standard deviation . in reference to fig1 the cytotoxicity of each one of three plant hormones is plotted as a measure of its concentration . referring to fig1 a , all cell lines responded in a dose - dependent fashion to sa . cytotoxicity of sa was significant , p & lt ; 0 . 05 , in molt - 4 lymphoblastic leukemia cells , sk28 melanoma cells and mcf7 breast carcinoma cells at all concentrations , and in lncap human prostate adenocarcinoma cells , from 1 mm and higher . sa was shown here to inhibit cell proliferation of different cancer cells from 20 to 40 %, depending on the cell line . this finding is in agreement with similar reported observations , where sa inhibited growth of breast cancer cell lines , rat hepatoma and human fibroblasts cultures ( sotiriou et al ., anticancer res ., 19 , 2997 - 3006 1999 ; hial et al ., j . pharmacol . exp . ther ., 202 , 446 - 454 1977 ). a possible interpretation of this data is that sa causes stress in cancer cells , resulting in suppression of proliferation in those cells . ja and mj were studied in comparison to sa in order to determine whether the effects of sa on cancer cells are common to plant stress hormones , and whether jasmonates would be deemed more effective than salicylic acid at targeting and inhibiting the growth of malignant cells . referring to fig1 b , the responsiveness to ja was dose - dependent . the cytotoxicity of ja was significant , p & lt ; 0 . 05 , in molt - 4 cells from 1 mm and higher , in lncap and sk28 cells from 2 mm and higher , and in mcf7 cells at 3 mm . the order of sensitivity to ja was molt - 4 & gt ; sk - 28 & gt ; lncap & gt ; mcf7 . referring to fig1 c , cytotoxicity of mj was significant , p & lt ; 0 . 01 , in molt - 4 cells at all concentrations and in mcf7 cells at 3 mm ; and at p & lt ; 0 . 05 in lncap and sk28 cells from 2 mm and higher . the results presented here show that mj caused the highest level of cytotoxicity . for instance , 0 . 5 mm of mj induced 87 . 52 % cytotoxicity in molt - 4 cells . the other cell lines responded to mj in a dose - dependent way . the order of sensitivity was molt - 4 & gt ; lncap & gt ; sk28 & gt ; mcf7 . appropriate controls established that ethanol ( in which ja and mj were dissolved ) by itself did not induce any cytotoxicity . example 1 demonstrates that while cancer cells from various origins responded to plant stress hormones , their response was differential . among the cell lines examined , molt - 4 responded strongly to ja ( 90 % cytotoxicity at 3 mm ) and mj ( 90 % cytotoxicity at 0 . 5 mm ). inhibition of cell proliferation was determined by the celltiter 96 aqueous non - radioactive cell proliferation assay ( promega , madison , wis . ): upon completion of a given experiment , mts ( a tetrazolium compound ) at 333 μg / ml + phenazine methosulfate ( at 25 μm ) was added to each well of the 96 - well plate for 1 hour at 37 ° c . this allowed for development of a color reaction in which dehydrogenases reduce the mts in metabolically active cells . since the cells were not washed before the addition of mts , there were no potentially loosely adherent or non - adherent cells that could have been problematic . soluble mts formazan product was measured at a wavelength of 490 nm using a ceres 900 hdi elisa reader ( bio - tek instruments , inc , highland park , vt .). optical density is directly proportional to the number of living cells in culture . cytotoxicity (%) was calculated in the following way : [( od of control cells − od of drug - treated cells )/ od of control cells ]× 100 . since the same number of cells was aliquoted into each well initially , decreased optical density as measured in wells containing treated cells ( above ) reflects cellular death and / or decrease in the rate of proliferation . to distinguish between these two possibilities we employed an additional cytotoxicity assay which detects cell death by lack of trypan blue exclusion . cells were incubated with 0 . 1 % trypan blue for 2 - 5 minutes and the percentage of dead cells ( those , which did not exclude the dye ) was determined microscopically . referring to table 1 , among the plant hormones tested , mj induced death most effectively in every cell line . mj is more effective in killing human transformed cell lines than its non - methylated form ja ( fig1 b , 1 c and table 1 ). sa suppressed proliferation in all cell lines , while ja induced death in lymphoblastic leukemia cells and suppression of proliferation in the other cells . in terms of relative susceptibility , molt - 4 cells are followed by sk28 , lncap and mcf7 cells , in that order . differential susceptibility of the different cell lines to the plant stress hormones suggests a specificity of the influence of those compounds on the cells . it is important to note the difference between sa and jasmonates in their influence on cancer cell lines . sa causes inhibition of cell proliferation in the tested cell lines , ja causes cell death in molt - 4 cells and inhibition of cell proliferation in sk28 , lncap and mcf7 cells , whereas mj causes death in all cell lines . these differences could be explained by different structures of plant stress hormones and / or by difference in biochemical events that those compounds induce in the cells . elevated levels of caspase - 3 are a specific marker of the apoptosis process ( porter and janicke , cell death differ ., 6 , 99 - 104 , 1999 ). in order to definitively determine that the cause of cell death was apoptosis , the level of caspase - 3 activity was measured in cells after treatment with ja and mj . molt - 4 cells were incubated with ja and mj for 2 , 4 and 14 hours , and levels of activity of the apoptosis - mediating protease , caspase - 3 , were determined using the caspase - 3 ( cpp32 ) protease assay kit ( pharmingen , san diego , calif .) as suggested by the manufacturer . briefly , 2 × 10 6 cells were lysed and resuspended in 100 μl of reaction buffer containing a fluorogenic caspase - 3 ( cpp32 ) substrate ac - devd - amc . reactions were incubated at 37 ° c . for 2 hours and samples were assayed at excitation wavelength of 360 nm and emission wavelength of 460 nm , in the fl600 microplate fluorescence reader ( bio - tek instruments , winooski , vt ., usa ). referring to fig2 dose - dependent elevation of caspase - 3 activity was observed : as can be seen in fig2 ja and mj increased caspase - 3 activity significantly , p & lt ; 0 . 05 , at all concentrations and times . referring to fig2 a , incubation with ja for 2 hours didn &# 39 ; t induce an elevation in the level of caspase - 3 . referring to fig2 b , after 14 hours of exposure to mj , the extent of death at 1 mm and above was such that caspase - 3 activity could not be determined . these results suggested that ja and mj induced apoptotic death in molt - 4 cells . to confirm this fact , molt - 4 cells were treated with ja ( 2 mm ) and mj ( 0 . 5 mm ) for 14 hours , and analyzed by fluorescence microscopy in order to detect essential morphological characteristics of apoptosis such as condensation and fragmentation of chromatin . referring to fig3 fluorescence microscopy pictures are shown depicting changes in cellular morphology within the nuclei of molt - 4 cells , after treatment with plant stress hormones ja or mj . 5 × 10 5 cells / sample were harvested , then fixated by addition of a solution of phosphate - buffered saline ( pbs ) containing [ 3 % paraformaldehyde and 0 . 1 % triton x - 100 ], for one hour . cells were stained for 10 minutes with dapi ( 1 μg / ml ). nuclei were analyzed by fluorescence microscopy , ( using a fluorescence microscope model . a × 70 trf , made by olympus optical , japan ) at a magnification of 1 : 400 . characteristic apoptotic nuclei are marked with arrows . referring to fig3 b , molt - 4 cells were treated with ja at 2 mm for 14 hours . treatment with ja induced condensation and fragmentation of chromatin . referring to fig3 c , molt - 4 cells were treated with mj at 0 . 5 mm for 14 hours . treatment with mj completely destroyed nuclear morphology in almost all cells . these results confirm that ja and mj caused apoptotic death in molt - 4 cells , based on the rise in caspase - 3 activity , which is one of the features of apoptosis , and on characteristic morphological changes . sa was reported to induce apoptosis and activation of caspases in myeloid leukemia cell lines and in b - cell chronic lymphocytic leukemia cells . there is also evidence that sa enhances apoptosis and causes apoptosis in fs - 4 cells via p38 ( schwenger et al ., proc . natl . acad . sci . usa , 4 , 2869 - 2873 , 1997 ). in those studies different cell lines undergo apoptosis on incubation with concentrations of salicylates higher than those achieved in plasma of patients treated for inflammatory disorders . in the present invention , concentrations of salicylates were used , that are comparable to those achieved in the plasma . this can explain the difference between studies where sa induced apoptosis , and our results . the results shown above prove that plant stress hormones possess the ability to adversely affect cancer cells . the effect of these plant products was tested on normal cells , to determine if jasmonates have an adverse cytotoxic effect on non - cancerous cells as well . normal lymphocytes were separated from peripheral blood , as follows : mononuclear cells ( mnc ) from venous blood of healthy donors were collected by ficoll - hypaque ( phamacia fine chemicals , uppsala , sweden ) density gradient centrifugation . the resultant mononuclear cell preparation was allowed to adhere to plastic dishes to remove contaminant macrophages . the non - adherent peripheral blood lymphocytes were selected for use . prior to treatment with ja and mj , normal lymphocytes were stimulated by tpa ( 5 ng / ml ) and pha ( 0 . 8 μg / ml ) for 48 hours , to cause the lymphocytes to proliferate ( and so , be comparable to the immortal malignant cells ). normal lymphocytes and molt - 4 cells were seeded ( at 1 . 5 × 10 4 / well ) in 96 - well plates . jasmonates or salicylic acid were added at a concentration of 1 mm or 3 mm , and cells were incubated for 24 hours . optical density representing viable cells was determined by the celltiter 96 aqueous non - radioactive cell proliferation assay . each plant stress hormone induced significant cytotoxicity in molt - 4 cells , p & lt ; 0 . 05 , while non of the hormones induced any significant cytotoxicity in normal lymphocytes . referring to fig4 normal blood lymphocytes ( represented by solid bars ) were practically not influenced by plant stress hormones , contrary to the molt - 4 transformed lymphoblastic leukemia cells ( represented by open bars ). fig4 a shows treatment with sa at concentrations of 1 mm and 3 mm . fig4 b shows treatment with ja at concentrations of 1 mm and 3 mm , and fig4 c shows treatment with mj at concentrations of 1 mm and 3 mm . refer to table 1 as well , which illustrates the selectivity of jasmonates for malignant cells versus healthy cells . in this example , the influence of plant stress hormones on transformed lymphocytes ( molt - 4 cells ) was compared , versus their influence on normal lymphocytes extracted from peripheral blood . normal lymphocytes ( that had been stimulated by tpa / pha to induce proliferation ), were not influenced by sa and jasmonates , contrary to transformed lymphocytes . this data supports the potential use of plant stress hormones as selective anti - cancer agents . syngeneic lymphoma cells were injected into a test group and a control group of mice ( strain c57bl ). the injections were administered either sub - cutaneously , or intra - peritoneally . methyl jasmonate was administered orally , by injection directly into the resultant tumor or into the peritoneum , and the effect on tumor progression and on the rate of survival , were analyzed . 400 , 000 el - 4 lymphoma cells were injected intra - peritoneally into 20 test mice , or 19 control mice , of the c57bl strain . preliminary experiments had shown that methyl jasmonate at a dosage of 236 - 472 mg / kg . body weight was appropriate for prevention of tumoral growth . therefore , methyl jasmonate was dissolved in a lipid carrier ( 0 . 4 % lipofundin , manufactured by b . brown , melsunger , germany ) and administered orally at a dosage of 236 mg / kg body weight . administration was daily , via the drinking water , beginning with the day of injection of the lymphoma cells . 19 control mice received the lipid carrier only ( 0 . 4 % lipofundin ), with no methyl jasmonate dissolved within . the survival time of each group of mice was measured ( in days ), and analyzed . referring to fig5 a kaplan & amp ; meier survivorship function graph is shown , illustrating the cumulative percentage of survival in each group , as the experiment progressed . survival rates were significantly higher for the treated group ( represented by crosses , and by the letter “ t ”), versus the control group ( represented by circles , and by the letter “ c ”); as can be seen , for example , in the plateau of 50 % survival reached by the treated group on the 33 rd day , as opposed to the plateau of 20 % survival reached by the control group . the significance of these results was analyzed statistically , using two highly stringent statistical means of analysis , the log - rank test and the cox - mantel test . each of these tests weighs numerically the importance of a death within one of the two groups of mice , on a given day , compared to the number of surviving mice in the whole . the significance of the results was deemed to be high , p = 0 . 01492 for the log - rank test , and p = 0 . 00953 for the cox - mantel test ( wherein a result is considered significant if p & lt ; 0 . 05 ). in conclusion , examples 1 - 5 elucidate the effect of the structurally - diverse plant stress hormones , jasmonates and salicylate , on cell proliferation and viability in several diverse cancer cell lines . there were four major findings . firstly , all the stress hormones investigated share the ability to adversely affect proliferation of cancer cells . jasmonic acid ( ja ) induced death in lymphoblastic leukemia cells and caused suppression of cell proliferation in the other human cancer cells mentioned above . methyl jasmonate ( mj ) induced death in each of the cell lines . the plant hormones acted dose - dependently in the following order of sensitivity : lymphoblastic leukemia & gt ; prostate cancer & gt ; melanoma & gt ; breast cancer . secondly , death caused by jasmonates in molt - 4 cells was determined as apoptotic , similar to the mechanism most chemotherapeutic drugs employ at the cellular level . thirdly , jasmonates do not cause damage to normal lymphocytes . fourthly , jasmonates are effective not only in vitro , but also in an animal model of lymphoma , significantly increasing the survival rate ( by 2 . 25 times ), using a dosage deemed safe in mice . these findings suggest that plant stress hormones may be used as a novel class of anti - cancer drugs .
a pharmaceutical composition useful for the treatment of cancer in mamnmals , comprising as the active ingredient a therapeutically effective amount of a jasmonate of the formula : wherein : n is 0 , 1 , or 2 ; r 1 is oh , alkoxy , o - glucosyl , or imino ; r 2 is oh , o , alkoxy or o - glucosyl ; r 3 , r 4 and r 5 are h , oh , alkoxy or o - glucosyl ; and / or wherein r 1 and r 2 , or r 1 and r 4 together form a lactone ; and further wherein the bonds between c 3 : c 7 , c 4 : c 5 , and c 9 : c 10 may be double or single bonds ; or a derivative of said formula ; the derivative having at least one of the following : a lower acyl side chain at c 3 ; a keto or hydroxy moiety at the c 6 carbon ; or an n - pentenyl or n - pentyl side chain at c 7 . these jasmonates are useful in treating a wide variety of malignancies .