Antiproliferative properties of flavone acetic acid (NSC 347512) (LM 975), a new anticancer agent

Identification of New Flavone-8-Acetic Acid Metabolites Using Mouse Microsomes and Comparison with Human Microsomes

Flavone-8-acetic acid (FAA) is a potent anticancer agent in mouse but has not shown activity in humans. Because FAA metabolism could play a role in this interspecies difference, our aim was to identify the metabolites formed in vitro using mouse microsomes compared with those in human microsomes. Mouse microsomes produced six metabolites as detected by reversed-phase high-performance liquid chromatography-mass spectrometry (MS). Three metabolites were identified as the 3'-, 4'-, or 6-hydroxy-FAA, by comparison with retention times and UV and MS spectra of standards. Two metabolites presented a molecular weight of 296 (FAA = 280) indicating the presence of one oxygen but did not correspond to any monohydroxylated FAA derivative. These two metabolites were identified as epoxides because they were sensitive to epoxide hydrolase. The position of the oxygen was determined by the formation of the corresponding phenols under soft acidic conditions: one epoxide yielded the 3'- and 4'-hydroxy-FAA, thus corresponding to the 3',4'-epoxy-FAA, whereas the other epoxide yielded 5- and 6-hydroxy-FAA, thus identifying the 5,6-epoxy-FAA. The last metabolite was assigned to the 3',4'-dihydrodiol-FAA because of its molecular weight (314) and sulfuric acid dehydration that indicated that the 3'- and 4'-positions were involved. Compared with mouse microsomes, human microsomes (2 pools and 15 individual microsomes) were unable to metabolize FAA to a significant extent. In conclusion, we have identified six new FAA metabolites formed by mouse microsomes, whereas human microsomes could not metabolize this flavonoid to a significant extent. The biological importance of the new metabolites identified herein remains to be evaluated.

Characterization of monohydroxylated derivatives of the anticancer agent flavone-8-acetic acid by liquid chromatography with on-line UV and mass spectrometry

The experimental anticancer agent flavone-8-acetic acid (FAA) is metabolized into several monohydroxylated derivatives using mouse microsomes. Because these metabolites could be involved in the biological effects of FAA, the aim of this study was to characterize all its possible monohydroxylated derivatives. To do so, we have developed a methodology using reversed-phase high-performance liquid chromatography (RP-HPLC) coupled with ultraviolet (UV) detection and mass spectrometry (MS) to analyze and identify FAA derivatives hydroxylated at the 2', 3', 4', 3, 5, 6, or 7 position. In RP-HPLC, 4'-, 3'-, 2'-, 6-, and 7-OH-FAA eluted before FAA, whereas 3- and 5-OH-FAA eluted after FAA. UV spectra showed a bathochromic shift of band I for all derivatives and of band II for 5- and 6-OH-FAA. In addition, the position of the OH group could be determined by the presence of certain product ions in MS. Ions at m/z 133 and 151 were specific for 2'-, 3'-, 4'-, and 3-OH-FAA, whereas the ion at m/z 177 was specific for 3-OH-FAA only. The ions m/z 133, 151 and 167 were specific for 2'-OH-FAA. Ions at m/z 149 were specific for the presence of the OH group on cycle A only (i.e., 5-, 6- or 7-OH-FAA). The presence of both product ions m/z 149 and 179 were specific for 7-OH-FAA. Finally, ions at m/z 149 and several product ions of even m/z values were specific for 5-OH-FAA. In conclusion, the methodology described can be used to identify all possible monohydroxylated FAA derivatives.

Synthesis and biological study of a flavone acetic acid analogue containing an azido reporting group designed as a multifunctional binding site probe

Flavone-8-acetic acid (FAA) is a potent immunomodulatory small molecule that is uniquely characterized as being active on mouse but not human cells. Although FAA is a potent inducer of murine cytokine, chemokine and interferon gene expression, its mode of action remains unknown. In this report, we describe the synthesis of a new flavone acetic acid (FAA) analogue, (2-[2-(4-azidophenyl)-4-oxochromen-8-yl-]acetic acid (compound 2). We demonstrate that compound 2 is equally active as the parent FAA in inducing chemokine gene expression and that the azide functional group is capable of reacting with a reporter molecule, such as the FLAG peptide-phosphine, under mild conditions. This reaction will be useful for detecting the drug-bound protein active complex utilizing an anti-FLAG antibody.

Synthesis and antitumor activity of new derivatives of xanthen-9-one-4-acetic acid

Xanthen-9-one-4-acetic acid (XAA) analogues in which the substituents in positions 5 and 6 are included in cyclic structures are described. Direct in vitro toxicity of the synthesized compounds against four tumor cell lines was evaluated, and their ability to stimulate mouse peritoneal macrophages and human monocytes in culture to become tumoricidal (indirect toxicity) was also studied. Despite low direct toxicity, almost all the compounds proved to be able to significantly enhance the lytic properties of both murine macrophages and human monocytes as well as the parent compound XAA and its most active derivative DMXAA taken as reference. In particular, compounds 4a, 5a, 7a, 13a,b, and 16a,b showed higher activity than the lead compound on human monocytes, compound 7a being 2.5 times more active than DMXAA, which is the most potent compound synthesized so far. Moreover, compounds 4a, 5a, 7a, 13a, 16a, and 16b proved to be able to induce TNF production in human immune cells.

Synthesis and biological activity of some rigid analogues of flavone-8-acetic acid

Some rigid analogues of flavone-8-acetic acid are described. Direct in vitro toxicity of the synthesised compounds was evaluated towards four tumoral cell lines and the ability of these compounds to stimulate mouse peritoneal macrophages in culture to become tumoricidal (indirect toxicity) was also studied. All compounds were able to induce direct cytotoxicity only at very high concentrations but showed a remarkable indirect activity. In particular compound 4d was able to significantly increase macrophage lytic properties and has been selected for further investigations.

The in vivo interaction between flavone acetic acid and hyperthermia

The in vivo interaction between flavone acetic acid (FAA) and hyperthermia was studied in a C3H mammary carcinoma grown in the feet of female CDF1 mice and in normal foot skin. FAA was intraperitoneally injected prior to local tissue heating in restrained non-anaesthetized animals. Alone, FAA at doses of 100 mg/kg and above, inhibited tumour growth in a dose-dependent fashion. FAA also enhanced the tumour response to heat, the effect being dependent on both the time interval between the two modalities and the FAA dose, the greatest effect occurring when FAA doses of > or = 150 mg/kg preceeded heat by 3-48 h. These effects of FAA correlated with the drug's ability to decrease tumour blood perfusion measured using the RbCl extraction procedure. Injecting 150 mg/kg FAA 3 h before heating (42.7 degrees C) resulted in a 2.2-fold increase in tumour heat damage, but had little effect on the response of normal foot skin in non-tumour-bearing mice. However, this treatment gave a 2.0-fold increase in normal tissue damage when the skin experiments were repeated in tumour-bearing animals. These effects in skin occurred in the absence of any blood perfusion changes, but appeared to be associated with FAA-induced TNF-alpha production.

Preclinical in vitro and in vivo activity of 5,6-dimethylxanthenone-4-acetic acid

5,6-Dimethylxanthenone-4-acetic acid (5,6-MeXAA) is a fused tricyclic analogue of flavone acetic acid (FAA) which was developed in an attempt to improve on the activity of FAA. Previous studies have shown 5,6-MeXAA to be curative in 80% of mice bearing colon 38 tumours and 12 times more dose potent than FAA. This investigation has demonstrated that a murine colon tumour cell line (MAC15A) is approximately 60 times more sensitive to 5,6-MeXAA than to FAA, although these differences were not seen in three human cell lines tested. 5,6-MeXAA caused significant blood flow shutdown and haemorrhagic necrosis in subcutaneous MAC15A tumours in syngeneic and nude hosts, but measurable changes in tumour volume were seen only in syngeneic hosts. 5,6-MeXAA was inactive against intraperitoneal MAC15A but produced significant anti-tumour effects against the same cell line inoculated via an intravenous route. FAA has been shown previously to be inactive in this model. Interestingly, the effects against lung colonies were not accompanied by obvious necrotic changes, suggesting that they may be the result of increased direct cytotoxicity rather than an indirect host mechanism. Further studies to investigate the effects against systemic tumour deposits are under way.

Combined treatments of heat, radiation, or cytokines with flavone acetic acid on the growth of cultured endothelial cells

The antitumour effects of flavone acetic acid (FAA) against a broad spectrum of established experimental tumours has been demonstrated. Damage to the vasculature, which rapidly disrupts blood flow and induces haemorrhagic necrosis, is believed to be a major mechanism contributing to the observed antitumour effects. Despite these established observations, FAA has shown little effect against human tumours. However, other applications of FAA, for examples, for an extended period of treatments or in combination with other antitumour modalities, have not been sufficiently explored. In order to test the direct effects of FAA on vasculature, endothelial cells isolated from human umbilical vein (HUVEC) and bovine pulmonary artery (CPAEC) were used in this study. FAA at the concentrations of 50 to 200 micrograms/ml causes reduction in cell number (from 20 to > 30% of the cells) of HUVEC as measured by MTT assay after 1, 3, and 5 h of treatment at 37 degrees C. FAA did not produce significant effects on similarly treated human squamous cell carcinoma, cell line UM-SCC-2. After 1 h treatment of FAA at 300 micrograms/ml, a large number of HUVECs failed to react with an actin stain, NBD-phallacidin. The growth of HUVECs and CPAEC in the presence of FAA for 1-3 days was progressively reduced. The number of HUVEC treated for 3 days at the concentrations of 100, 200, and 300 micrograms/ml were reduced by 75-86% in comparison with the control culture. The experiments with CPAEC showed similar results. The inhibition of the growth of endothelial cells by FAA was enhanced when it combines with tumour necrosis factor-alpha but not with interleukin-1, interferon-gamma, heat, or radiation. We observed that FAA can initiate both immediate effects and growth inhibition on cultured endothelial cells. These results support the notion that FAA rapidly induces vasculature damage. Furthermore, cytokines such as tumour necrosis factor-alpha can enhance the toxicity of FAA on endothelial cells.

Tumour necrosis factor-alpha plasma levels after flavone acetic acid administration in man and mouse

Flavone acetic acid (FAA) is a synthetic flavonoid with a remarkable spectrum of anticancer activities in mouse tumours, but with no anticancer activity in humans. The mechanism of action of this drug is complex and involves a tumour vasculature action similar to the effects of tumour necrosis factor (TNF). To assess directly the role of TNF in FAA mechanism of action, this cytokine was assayed in both mouse and human plasma after intravenous administration of the drug. In mouse, a species particularly sensitive to FAA antitumour action, FAA plasma concentrations reached 268 micrograms/ml at 0.5 h and remained high (165 micrograms/ml) at 6 h following the intravenous administration of an anticancer efficacious dose (540 mg/m2). After FAA administration in mouse, TNF activity (L929 mouse cell bioassay) increased to 300 pg/ml TNF-alpha-equivalent at 2 h, reached a maximum concentration of 600 pg/ml at 4 h, and declined thereafter to 220 pg/ml at 6 h. TNF activity in mouse plasma was completely abrogated in the presence of mouse TNF-alpha antibodies. FAA added directly to blank mouse plasma did not show TNF activity. In patients receiving the drug as a 6-h intravenous infusion at doses ranging from 3.6 to 8.1 g/m2, FAA plasma levels ranged from 58 to 449 micrograms/ml at the end of infusion. Human TNF-alpha levels assayed with an immunoradiometric assay were either not detectable or very low (< 25 pg/ml) before FAA administration. At completion of the FAA infusion, TNF-alpha remained near background levels in 20 of the 21 courses. A slight increase in plasma TNF-alpha was observed in 1 patient at the 8.1 g/m2 dose level of FAA, from 13 pg/ml before intravenous infusion, to 70 pg/ml at completion of intravenous infusion. Taken together, these data demonstrate a marked interspecies difference with regard to TNF-alpha secretion after FAA treatment, as this cytokine is produced in mice, whereas it is not significantly secreted in pretreated patients. Although the low TNF-alpha levels achieved in mice probably do not explain all of FAA antitumour activity in that species, the observed interspecies difference in TNF-alpha secretion after FAA administration could partly explain the marked difference in FAA antitumour activity observed between mice and humans.

A phase I and pharmacokinetic study of 12-h infusion of flavone acetic acid

This phase I study investigated flavone acetic acid (FAA) given as a 12-h intravenous infusion every 3 weeks in the absence of urinary alkalinisation. Cohorts of three patients were treated at doses of 7, 10 and 13 g/m2. One subject had colon cancer; 5, renal cancer; and 3, lung cancer. The Eastern Cooperative Oncology Group (ECOG) performance status was 0 in four patients, 1 in two subjects and 2 in three cases. The maximum tolerated dose was 13 g/m2. The dose-limiting toxicities were WHO grade 3 hypotension and grade 3 diarrhoea. Other toxicities included lethargy and dizziness, nausea, temperature fluctuation, myalgia and dry mouth, but no significant myelosuppression was encountered. One patient receiving 10 g/m2 for renal cancer showed a partial response that lasted for 3 months and included the resolution of pulmonary and cutaneous metastases. The pharmacokinetics showed large interpatient variability. At 12-16 h post-infusion, the plasma elimination profile entered a plateau phase, with frequent increases in concentration suggesting enterohepatic recycling. Neither peak FAA levels nor AUC values were dose-dependent at the doses studied. Peak plasma levels were 101-402 micrograms/ml and AUC (0-48 h) values were 75-470 mg ml-1 min. Plasma protein binding varied with total concentration. Two metabolites were detected in the plasma, and both also underwent apparent enterohepatic recycling. Repeat dosing resulted in decreases of up to 48% in peak levels and AUC values for FAA in three of six patients. Of the total FAA dose, 39%-77% was excreted in the urine as FAA or metabolites within 2 days. The dose recommended for further phase II studies is 10 g/m2.

Flavone acetic acid induced changes in human endothelial permeability: potentiation by tumour-conditioned medium

Flavone acetic acid (FAA) causes significant regression of larger established tumours in murine in vivo systems. This in vivo effect of FAA has been shown to include a vascular component. In an effort to elucidate the mechanism of action of FAA, we have studied the effects of FAA on the permeability of human endothelium in vitro. Monolayers of human umbilical vein endothelial cells (HUVEC) grown on polycarbonate filters were incubated in 1 mg/ml FAA for 120 min at 37 degrees C. During the first 60 min, there was a 6-8-fold increase in permeability; this was followed by a return to control levels even in the continued presence of FAA. In contrast, in the presence of tumour conditioned medium, FAA caused a rapid 6-fold increase in permeability which did not subsequently return to control levels. The permeability changes which occurred under the latter conditions were accompanied by a rapid contraction of the cytoskeleton. The permeability of monolayers of human melanoma cells was unaffected by FAA.

In vitro methods for screening agents with an indirect mechanism of antitumour activity: xanthenone analogues of flavone acetic acid

Xanthenone-4-acetic acid (XAA) resembles flavone acetic acid (FAA) in its effects on solid tumours in mice. The activity of methyl-substituted XAA derivatives in vitro was determined using 18 h 51Cr-release assays, continuous exposure growth inhibition assays and stimulation of tumouricidal activity of cultured murine resident peritoneal macrophages. The macrophage assay identified the high biological activity and dose potency of 5-MeXAA in vivo, and was the most accurate in vitro predictor of the ability of congeners to induce either haemorrhagic necrosis of subcutaneous Lewis lung and colon 38 tumours or splenic natural killer activity. In vitro immune stimulation may be more appropriate than direct cytotoxicity for screening compounds with indirect mechanisms of antitumour activity.

The effect of therapy on tumour vascular function

It has been established that malignant tissue as a consequence of abnormal morphogenesis has a structurally abnormal blood supply. These structural and as a consequence functional differences between normal and neoplastic vasculature provide a basis for selective modulation of tumour vascular function. Agents have been identified which can induce both irreversible and reversible effects on tumour blood flow. Hyperthermia, photodynamic therapy, tumour necrosis factor and flavone acetic acid are known to elicit most of their anti-tumour effect via irreversible changes in tumour vascular function. In addition to the extensive tumour cell kill and thus therapeutic potential provided by such chronic modulation of blood flow, acute transient changes in macroregional and microregional tumour blood flow could also play an important role if used appropriately with conventional therapies. The use of this latter type of modulation is discussed with reference to known examples of such 'vasoactive' compounds. It is also emphasized that blood flow changes induced in tumour tissue can be a 'double-edged sword' with detrimental consequences for therapeutic outcome if inappropriate changes are induced, for example, reductions in flow at the time of conventional radiotherapy or chemotherapy by agents not considered to be 'vasoactive'. To emphasize this point examples of blood flow modulation by pimonidazole and cis-platinum, agents that are used in conjunction with radiotherapy, are described.

Natural killer (NK) and lymphokine activated killer (LAK) cell activity in patients (PTS) treated with flavone acetic acid (FAA)

Natural killer (NK) cell activity was measured in nine patients with different solid tumors treated with flavone acetic acid (FAA). In three of them, NK cell activity was significantly increased, in two instances even after repeated courses of treatment. A significant increase in lymphokine activated killer (LAK) cell activity was also observed in three of four patients after in vivo treatment with FAA and in vitro incubation of lymphocytes with recombinant Interleukin-2. We observed some inter-individual variability in drug clearance, but no apparent correlation between drug plasma levels (neither peak nor AUC values) and the effects on NK and LAK activity.

Anti-tumour activity of flavone acetic acid (NSC 347512) in mice--influence of immune status

Flavone acetic acid (FAA) is a synthetic flavonoid with dramatic pre-clinical anti-tumour activity involving a vascular component in its mechanism but no clinical effects have been seen to date. As FAA also has immunomodulatory activity, immunological factors might explain differences in activity between mouse and man. This study examines the influence of host immune status on the anti-tumour activity of FAA. Two human colon tumour xenografts (COBA, HT-29) fail to respond to FAA in nude mice. The lack of activity of FAA against HT-29 xenografts cannot be explained on the basis of limited drug bioavailability as achievable plasma, and tumour levels of FAA are similar to those seen in sensitive murine colon tumours. The immune status of the host also influences the activity of FAA against two transplantable tumours of the mouse colon. Both these tumours are highly responsive to FAA in their normal NMRI hosts, but neither tumours exhibited significant growth delay in thymectomised NMRI or nude hosts. Histological examination of treated tumours revealed significant areas of haemorrhagic necrosis in all three hosts. These data suggest a clear immunological component in the mechanism of action of FAA which is separate from the previously described haemorrhagic necrosis.

Flavone acetic acid suppresses human peripheral blood lymphocyte and human colonic lamina propria lymphocyte DNA synthesis

Flavone 8-acetic acid (FAA) is a new experimental antitumor drug with activity against various murine and human solid tumors in vitro and in vivo. We previously demonstrated that FAA suppressed the growth of a human colon cancer cell line (HCT-116). In this study we investigated the effect of FAA on human peripheral blood (PBL) and human colonic lamina propria lymphocyte (LPL) DNA synthesis. Our results show that FAA inhibited DNA synthesis in PBL and LPL in a dose-dependent fashion. In addition, FAA inhibited the activity of the intracellular enzyme, ornithine decarboxylase (ODC), in stimulated PBL and LPL. FAA did not inhibit phorbol ester (PDB) and calcium ionophor(ionomycin)-stimulated LPL DNA synthesis. These results suggest that FAA alters DNA synthesis of human peripheral and colonic mucosal lymphocytes. We postulate that FAA may affect the human peripheral and mucosal immune system.

Interaction between flavone acetic acid (LM-975, NSC 349512) and radiation in Glasgow's osteogenic sarcoma in vivo

Flavone acetic acid (FAA) is a new anticancer agent in Phase II trials in Europe. In preclinical testing FAA showed broad activity against murine solid tumors and minimal activity against murine leukemias. Our interest in studying the combination of FAA and radiation was based on two of its biological effects which might modify radiation damage. First, FAA depletes ATP and inhibits macromolecular synthesis which are needed to repair radiation-induced DNA strand breaks; and second, inhibition of tumor blood flow by FAA could lead to radiobiological hypoxia. Various schedules of FAA (170 mg/kg I.V.) (n = 9, SF = 0.44) and radiation (10 Gy) (n = 9, SF = 0.37) were investigated against s.c. implanted Glasgow osteogenic sarcoma. In the same model we studied both the kinetics of ATP depletion by 31P-Nuclear Magnetic Resonance Spectroscopy and the repair of radiation induced single and double strand breaks by alkaline elution. The combined response was not significantly different from log-additive when radiation was given 24, 5 or 1 hr before FAA. When FAA was given immediately before radiation an increase in tumor response, significantly different from log-additive (p = 0.03) was observed. This enhancement disappeared when radiation was delayed for between 1 and 48 hr after FAA. While decreased ATP levels and increased response to radiation occurred within minutes after FAA administration, no effect of FAA at either 180 or 200 mg/kg was observed on the repair of radiation induced single or double strand breaks (10 and 50 Gy, respectively; 5 hr after FAA) in spite of significant ATP depletion in the tumors.

Flavone acetic acid distribution in human malignant tumors

The pharmacokinetics of flavone acetic acid (FAA) after a dose of 4.8 mg/m2 given i.v. over 1 h was investigated in 13 patients with different solid tumors. The mean volume of distribution and clearance were 52 +/- 4 l/m2 and 2.6 +/- 0.2 l/h x m2, respectively. A tumor or metastasis biopsy was obtained from six patients 2 h after the end of infusion. Tumor FAA levels ranged from 39.6 to 148.8 micrograms/g and were similar to those obtained after a therapeutic i.v. dose of 200 mg/kg FAA in animals bearing Pan/03 tumor, which is very sensitive to the drug. Although FAA tumor concentration could be detected only during one interval and we therefore cannot draw a definitive conclusion, differences in the agent's antitumor activity in mice and patients (i.e. very active in the former and inactive in the latter) are apparently not due to discrepancies in drug distribution and pharmacokinetics.

Flavone acetic acid antitumour activity against a mouse pancreatic adenocarcinoma is mediated by natural killer cells

Flavone acetic acid (FAA) is one of the most active antitumour agents against mouse solid tumours. A number of reports favour the hypothesis that FAA could behave as a biological response modifier; in fact FAA stimulates natural killer (NK) cells, induces secretion of type I interferon and synergizes with interleukin-2 to increase NK/lymphokine-activated killer (LAK) activity in vivo. However, there is no conclusive evidence that the antitumour activity of FAA is mediated via the modulation of NK/LAK cells. The present study was designed to evaluate whether the reported activation of NK cells is instrumental in FAA antitumour activity. FAA (180 mg/kg, i.v. on days 3, 7 and 11 after tumour implant) was significantly effective in inhibiting the subcutaneous growth of the pancreatic adenocarcinoma PAN/03 in C57/Bl mice. After 132 days the number of tumour-free survivors was 36%, whereas in the control group receiving no treatment, or in the group of mice treated with 10 micrograms/mouse of alpha-asialo-GM1 the value was only 0 or 6.7%, respectively. The combination of FAA and alpha-asialo-GM1 resulted in only 6% tumour-free mice. In parallel experiments, splenocytes and peritoneal cells from C57/B1 mice were tested in a standard cytotoxicity NK assay. While animals treated with FAA showed a significant increase in NK activity, those injected with alpha-asialo-GM1 had very low levels, and the combined treatment of FAA and alpha-asialo-GM1 resulted in a lower or similar NK activity compared to that in untreated mice. The fact that the abrogation of the NK-stimulating effect of FAA is accompanied by a lack of anti-tumour activity indicates that, at least in this experimental model, FAA is likely to act via an immunomodulatory mechanism.

Flavone acetic acid and plasma protein binding

Both the capacity of healthy human, cancer patient, and mouse plasma proteins to bind flavone acetic acid (FAA) and the qualitative differences in the plasma protein-binding site were studied. The binding capacity of plasma proteins for FAA was saturated within the therapeutic range in both species. The binding of FAA to plasma protein was significantly greater in both healthy human and cancer patient plasma than in mouse plasma. Plasma from patients with cancer bound on the average less FAA than did healthy patient plasma. The concentration of albumin in the plasma varied between healthy humans, cancer patients, and mice, being 5.3 +/- 0.7, 4.7 +/- 0.8, and 3.9 +/- 0.3 g/100 ml, respectively. The protein binding of FAA was found to be dependent on the plasma albumin concentration, but albumin concentration alone was not adequate for the accurate prediction of the percentage of FAA protein bound. Scatchard plots indicated that healthy human plasma had a greater number of high-affinity binding sites than did mouse plasma. FAA binds at the indolebenzodiazepine binding area on albumin and can be displaced from this site by salicylic acid and clofibric acid, but only at supratherapeutic concentrations. Our results indicate that alterations in plasma albumin could contribute to a variable effect with FAA. Therefore, the influence of serum albumin concentration and the nonlinearity of FAA protein binding should be considered in assessment of the appropriateness of a dose schedule for FAA.

Flavone acetic acid induces a coagulopathy in mice

The effects of flavone acetic acid (FAA) on the coagulation properties of plasma from tumour-bearing and non-tumour-bearing mice have been investigated. The study was carried out primarily on CBA mice and the CaNT tumour, although substantiating data are included for two other tumours grown in the WH strain. FAA was injected at a range of single doses up to a maximum of 300 mg kg-1, and clotting properties of the plasma were measured in vitro at various times after FAA administration. Platelet numbers and the concentration of fibrin degradation products (FDP) in the plasma were also determined. Following a dose of 300 mg kg-1, the clotting times were significantly reduced at 15-30 min in both tumour-bearing and non-tumour-bearing mice of both strains. Detailed studies on coagulation in the CBA strain (+/- CaNT tumour) indicate that in tumour-bearing animals the initial decrease in clotting time is followed 4-6 h later by an increase in clotting time, thrombin time and FDP levels. Platelet counts of tumour-bearing mice also decreased significantly over this period. Similar experiments in non-tumour-bearing mice did not show these late effects. All the data from the coagulation tests on mice with CaNT tumours are consistent with the hypothesis that intravascular coagulation occurs following treatment with FAA, and that vascular occlusion in tumours, as a results of FAA-induced coagulopathy, may contribute to tumour regression.

Vascular collapse after flavone acetic acid: a possible mechanism of its anti-tumour action

Flavone acetic acid (FAA, LM 975) causes regression and growth retardation in several solid murine tumours. The mechanism of action is unknown, although various lines of evidence suggest an indirect cytotoxic effect. We have carried out preliminary studies on the effect of FAA on relative blood flow in six experimental murine tumours using 86RbCl extraction. We have also measured growth delay after treatment with the same dose of FAA (200 mg/kg). The data show that the drug induces a drop in tumour perfusion within 6 h of treatment in all of the tumours, and that this can be correlated with the growth delay measured. We conclude that vascular collapse may be an important component of the action of this drug, and that further investigation of this phenomenon is warranted.

Influence of site on the chemosensitivity of transplantable murine colon tumours to flavone acetic acid (LM975, NSC 347512)

A number of experimental studies have demonstrated significant responses of s.c. solid tumours to flavone acetic acid (FAA). Clinical studies to date have been disappointing, with no objective responses being seen. The present study demonstrated that the tumour site is important for the anti-tumour action of FAA against two transplantable adenocarcinoma lines (MAC) in NMRI mice. Responses were achievable only when the tumours were implanted s.c. Ascitic or systemic tumours did not respond to FAA. Experimentally achievable plasma levels of FAA were not sufficient to induce significant cell kills in either MAC 15A or MAC 26 cell lines in vitro. A poor correlation exists between in vitro and in vivo responses, as the clonogenic assay could not predict the response of the solid MAC tumours grown s.c. The in vitro data indicated that the length of exposure to FAA was important, with long exposure times being necessary for cytotoxicity to develop, in these tumour cell lines. These studies imply that more than one mechanism is involved, and it is likely that the activity of FAA against s.c. tumours relies at least in part on a specific biological feature of tumours in this site. However, it may still be possible to achieve systemic tumour cell kill in vivo by increasing drug-exposure times.

Effect of flavone acetic acid (NSC 347,512) on splenic cytotoxic effector cells and their role in tumour necrosis

Flavone acetic acid (FAA), an antitumour agent currently undergoing clinical trial, has immune-modulatory effects on various cytotoxic cells in mice. Natural killer (NK) cell activity in the spleen was augmented 4 h after FAA treatment, and when spleen cells were cultured with interleukin-2 to induce the production of lymphokine-activated-killer (LAK) cells, higher levels of LAK cell activity were generated by spleen cells from FAA-treated animals than by spleen cells from untreated, control mice. The response to FAA by spleen cells from mice bearing the Colon 38 tumour was compared to that of non-tumour bearers. Activity against NK-sensitive YAC-1 tumour targets was augmented to a similar degree, and no activity against NK-resistant P815 targets was detected. FAA was shown to induce haemorrhagic necrosis in the P815 tumour grown as a subcutaneous solid tumour. Furthermore, haemorrhagic necrosis was induced by FAA on Colon 38 tumours growing in mice which had been depleted of NK activity by treatment with anti-asialo GM-1 antibody. Thus, although NK activity could be involved in the long-term host response to the tumour, it does not appear to be a major determinant of FAA-induced haemorrhagic tumour necrosis.

Flavone acetic acid (LM-975; NSC-347512) activation to cytotoxic species in vivo and in vitro

Flavone acetic acid (FAA; LM 975; NSC 347512) is a new anticancer agent with unprecedented, broad antitumor activity in murine models. Although FAA is very effective in vivo against solid tumors, including colon 38 adenocarcinoma, it was not cytotoxic in vitro against colon 38 cells and human colon adenocarcinoma cells HCT116 at pharmacologically achievable concentrations and exposure times. For example, a concentration of 300 micrograms/ml for a 10-day exposure time was required to obtain less than 1 log cell kill. After the administration of an effective FAA dose (180 mg/kg, i.v.) to mice, plasma cytotoxicity against HCT116 cells attained a 2 log cell kill between 0.5 and 2 h, which decreased to 1 log cell kill at 4 h. No cytotoxicity was observed 6, 12 or 21 h after drug administration. The controls used comprised mouse plasma containing FAA concentrations similar to those assayed in the above plasma samples from in-vivo-dosed mice. These spiked plasma were not cytotoxic, indicating that other cytotoxic species, formed in vivo, were responsible for the increased cytotoxicity. Mouse hepatocytes co-cultured with HCT116 cells increased FAA cytotoxicity to 1 log cell kill at 30-100 micrograms/ml. The addition of phenobarbital-induced mouse liver supernatant S-9000xg also markedly increased FAA cytotoxicity to a 2 log cell kill at 300 micrograms/ml. We conclude that FAA can be activated both in vivo and in vitro to cytotoxic species that are more active than the parent compound.

Flavone 8-acetic acid: our current understanding of its mechanism of action in solid tumours

Flavone 8-acetic acid (FAA) represents a novel chemical structure undergoing clinical trials as an anticancer drug. Its unusual properties tend to distinguish it from a conventional cytotoxic compound, particularly in the response of solid murine tumours; as a consequence, novel mechanisms of action are currently under investigation. In this review we summarised these mechanisms into one of the three categories (a) direct cytotoxicity, (b) biologic response modifier and (c) pharmacologic effector and considered the evidence for and against each. FAA is cytotoxic to tumour cells in vitro, but only at high concentrations and after long exposures. In vivo it is considerably more cytotoxic to the same cells, and it is unlikely that direct cytotoxicity alone can account for this difference. FAA stimulates NK cell activity, induces interferon alpha and synergises with interleukin 2 in the treatment of murine renal cancer. However, a definite link between immunomodulation and antitumour activity has still to be confirmed. Perhaps FAA's most unusual property is its ability to reduce tumour blood flow dramatically, which may provide the appropriate conditions for reactive chemistry to occur. Finally, a combination of the above mechanisms probably work together in producing the drug's unique spectrum of antitumour activity.

Unique chemosensitivity of MAC 16 tumours to flavone acetic acid (LM975, NSC 347512)

MAC 16 is one of a series of mouse colon tumours originally induced by dimethylhydrazine. It is a relatively slow growing subcutaneous adenocarcinoma which becomes necrotic as it grows and causes severe body wasting in the host. This study has indicated that the tumour is resistant to a large number of standard anti-cancer drugs but is highly responsive to the investigational agent flavone acetic acid (FAA). The levels of FAA achieved in tumours are lower than those necessary for activity in vitro suggesting its mechanism of action in vivo is not direct cytotoxicity. Responding tumours demonstrate massive tissue necrosis and those which are not cured have viable tumour cells associated with tumour blood vessels. The anti-tumour effects are accompanied by control of the host's cancer cachexia. The unique chemosensitivity of MAC 16 to FAA suggests that this agent has a novel mechanism which may be dependent upon specific biological characteristics of tumours.

Enhancement of in vitro cytotoxicity of mouse peritoneal exudate cells by flavone acetic acid (NSC 347512)

Flavone acetic acid (FAA), an antitumour agent currently undergoing clinical trials, was found to augment the tumoricidal activity of peritoneal exudate (PE) cells in vitro. Lysis of tumour targets was measured using a standard 18 h 51Cr release assay for activated macrophages. Lytic activity increased with increasing concentrations of FAA up to 100 micrograms/ml before reaching a plateau. At 80 micrograms/ml FAA, 3-fold fewer PE cells were necessary to obtain the same level of activity as in control cultures without FAA. The lytic activity was mediated by Thy-1 negative and glass-adherent cells in the PE population, and was inhibited by dexamethasone. The activity of PE cells against several different tumour targets (P815 mastocytoma, YAC-1 lymphoma, P388 lymphoma, and a Lewis lung carcinoma cell line) were all enhanced by FAA. The results show that FAA can enhance the lytic potential of peritoneal macrophages in vitro to kill a range of tumour cells.

Response of chemically induced primary colon tumours of the mouse to flavone acetic acid (NSC 347 512)

Flavone acetic acid (FAA) is a compound with proven activity against various transplantable colon cancers in mice. In this study it was evaluated against primary colon tumours, chemically induced by methylazoxymethanol in outbred CF1 mice. FAA was given i.v. at doses of 70 or 100 or 150 mg kg-1 every 7 days for 6 weeks. Only 4 out of 60 FAA treated mice died of toxicity. FAA reduced tumour number and tumour burden compared to control mice (P less than 0.05 at least), with no apparent dose-response relationship. Antitumour activity of FAA was comparable to that of 5-fluorouracil (5-FU) used as standard. Moreover, FAA was more effective that 5-FU against large tumours. FAA levels in plasma and different tissues (including colonic neoplastic lesions) after a single i.v. dose of 150 mg kg-1 were investigated. Tumour FAA levels appear insufficient to be responsible for the antitumour activity based only on a direct FAA cytotoxic effect. The results confirm clinical interest in FAA and suggest that mechanisms other than direct cytotoxicity may be involved in its activity.

Response to flavone acetic acid (NSC 347512) of primary and metastatic human colorectal carcinoma xenografts

The antitumour activity of flavone acetic acid (FAA) was evaluated against two human colorectal carcinoma (HCC) lines, HCC-P2988 and HCC-M1410, transplanted into nude mice. On repeated i.v. injection of 200 mg kg-1 every 4 days FAA was moderately active against the s.c. growing HCC-P2988. HCC-M1410 transplanted s.c. was almost unresponsive in the same experimental conditions. In contrast, FAA (200 mg kg-1 i.v. every 4 days, repeated three times) significantly reduced liver tumour colonies produced by the HCC-M1410 cells injected intrasplenically into nude mice. These findings suggest that FAA has potential activity against human colorectal carcinoma, particularly against liver metastases.