Plasma disposition, metabolism and excretion of the experimental antitumour agent 5,6-dimethylxanthenone-4-acetic acid in the mouse, rat and rabbit

5,6-Dimethylxanthenone-4-acetic acid (DMXAA), an experimental antitumour agent currently undergoing phase I clinical trial, has a maximum tolerated dose (MTD) in male BDF1 mice of 99 micromol/kg. We have found the male Sprague-Dawley rat and the New Zealand White rabbit to have greater tolerance to DMXAA, with MTDs being 990 and 330 micromol/kg, respectively. To investigate the causes of this difference, we measured plasma and urine DMXAA concentrations by high-performance liquid chromatography (HPLC) after single i.v. bolus injections of 99 and 990 micromol/kg in the rat and following a bolus dose of 99 micromol/kg and a 10-min infusion of 330 micromol/kg in the rabbit. Following administration of DMXAA at the MTD in the mouse, rat and rabbit the maximal concentrations were 600, 2,200 and 1,708 microM, respectively, whereas areas under the concentration-time curves were 2,400, 19,000 and 2,400 microMh, respectively, for unchanged DMXAA. Data obtained for mice and rabbits were satisfactorily fitted to a two-compartment model with Michaelis-Menten kinetics. DMXAA was highly bound to plasma proteins, with the highest degree of binding being found in the rabbit. A small proportion of the total dose (7.8%, 0.6% and 12.4%, respectively) was excreted unchanged in urine over 24 h. This proportion increased (to 11.6%, 3.5% and 72.4%, respectively) following alkaline hydrolysis, suggesting the presence of glucuronide metabolites. Examination of rat and mouse urine by HPLC revealed the presence of two metabolites, which were characterized by mass spectrometry and nuclear magnetic resonance to be the acyl glucuronide of DMXAA and 6-(hydroxymethyl)-5-methylxanthenone-4-acetic acid. Thus, both mice and rats metabolise DMXAA by similar pathways. The results demonstrate considerable interspecies variations in tolerance to DMXAA that cannot be explained by differences in pharmacokinetics.

Sequence-specific interactions of minor groove binders with restriction fragments of cDNAs for H tau 40 protein and MAP kinase 2. A qualitative and quantitative footprinting study

A series of DNA minor groove binders comprising netropsin, distamycin, the bisquaternary ammonium heterocycles SN 6999 and SN 6570, cis-diammine platinum(II)-bridged bis-netropsin, cis-diammine platinum(II)-bridged bis-distamycin and bis-glycine-linked bis-distamycin were investigated for sequence-specific interactions. The oligonucleotides used were the 154 base pair HindIII-RsaI restriction fragment of cDNA of h tau 40 protein and the 113 base pair NcoI-PvuII restriction fragment of cDNA of MAP kinase 2. Both proteins are believed to be involved in the pathology of Alzheimer's disease. For all these ligands, binding sites were localised at positions 1134-1139 (5'AATCTT3'), 1152-1156 (5'ATATT3') and 1178-1194 (5'TTTCAATCTTTTTATTT3') for the former and 720-726 (5'TATTCTT3'), 751-771 (5'AATTGTATAATAAATTTAAAA3') and 781-785 (5'TATTT3') for the latter. The AT-preference of ligand binding was obvious and footprint titration experiments were applied to estimate binding constants (Ka) for each individual binding site mentioned above. The binding strength decreases in the order netropsin > distamycin > SN 6999 approximately SN 6570>platinum-bridged netropsin or distamycin approximately bis-glycine-bridged distamycin and was found independently of the binding sites examined. GC-base pairs interspersed in short AT-tracts reduced the Ka-values by as much as two orders of magnitudes. The dependence of extended bidentate as well as of monodentate binding of netropsin and distamycin derivatives on the length of AT-stretches has been discussed.

5,7-Disubstituted analogues of the mixed topoisomerase I/II poison N-[2-(dimethylamino)ethyl]acridine-4-carboxamide (DACA): DNA binding and patterns of cytotoxicity

DACA is a DNA-intercalating agent and dual topoisomerase (topo) I/II inhibitor currently in clinical trial as an anticancer drug. Substitutions in the acridine ring of DACA have significant effects on biological activity, with 5-substituted analogues being more potent but relatively less active against cell lines that underexpress topo II, and the converse for 7-substituted analogues. A small series of 5,7-disubstituted analogues was therefore prepared and evaluated. The compounds were prepared by CDI-assisted coupling of the appropriate acridine acids. When these contained no or only one halogen atom, they could be prepared by Al/Hg amalgam reduction of the corresponding acridine acids. However, this method could not be used to prepare dihalogen-substituted acridine acids due to substantial dehalogenation, and these intermediates were synthesized via cyclization of the appropriate aldehydes to give the acridines directly. These compounds showed enhanced DNA binding compared with the parent DACA, indicating that the known favourable influence of 5-substituents on DNA binding is retained. Cell line studies showed that the 5,7-disubstituted compounds retained both the broad-spectrum effectiveness of the 7-monosubstituted analogues and the higher cytotoxic potency of the 5-monosubstituted analogues. The 7-chloro-5-methyl and 5-chloro-7-methyl analogues showed comparable in vivo antitumour activity to DACA in the subcutaneous colon 38 model, but were substantially more potent (optimal doses of 60 mg/kg compared with 200 mg/kg for DACA).

Stimulation of tumors to synthesize tumor necrosis factor-alpha in situ using 5,6-dimethylxanthenone-4-acetic acid: a novel approach to cancer therapy

The selective induction of tumor vascular collapse represents an exciting approach to cancer treatment. However, clinical evaluation of tumor necrosis factor-alpha (TNF), an agent that accomplishes this goal, has been limited by systemic toxicity, and clinical approaches using bacterial components to induce TNF production have also been disappointing. Our laboratory has developed synthetic low molecular weight inducers of TNF, including 5,6-dimethylxanthenone-4-acetic acid (DMXAA), as an alternative strategy. DMXAA induces rapid vascular collapse in transplantable murine tumors and induces TNF synthesis in vitro in both murine and human systems. We show here that the extent of DMXAA-induced TNF synthesis is greater in tumors than that in the spleen, liver, or serum. As shown by in situ hybridization studies of the murine Colon 38 tumor, DMXAA induced tumor as well as host cells to express TNF mRNA. The distribution of cells containing TNF mRNA in tumor tissues after DMXAA administration contrasted significantly with that obtained after lipopolysaccharide (LPS) treatment, although splenic and hepatic tissues showed a similar distribution of TNF mRNA-positive cells. In the Colon 38 tumor, the action of LPS was limited to host cells in the periphery of the vessels. DMXAA treatment induced 7-fold higher peak TNF levels in tumor than in serum. In contrast, LPS treatment induced 9-fold higher TNF levels in serum than in tumor. DMXAA induced 35-fold higher TNF activity in the Colon 38 tissue than did LPS. One ovarian, one squamous, and three melanoma human tumor xenografts implanted in athymic nude mice expressed TNF mRNA of human and murine origin in response to DMXAA, confirming that DMXAA can activate both host and tumor cells. The use of low molecular weight agents to induce TNF synthesis in situ in the tumor represents a novel approach to TNF-mediated therapy of cancers.

Suppression of serum tumour necrosis factor-alpha by thalidomide does not lead to reversal of tumour vascular collapse and anti-tumour activity of 5,6-dimethylxanthenone-4-acetic acid

The antitumour agent 5,6-dimethylxanthenone-4-acetic acid (DMXAA), developed in this laboratory as a potent analogue of flavone acetic acid (FAA), has a novel antitumour action involving both immune and vascular components. DMXAA induces the synthesis of tumour necrossi factor-alpha (TNF) and it has been hypothesised that this mediates its selective reduction of tumour blood flow and consequent induction of tumour necrosis. Unexpectedly, the drug thalidomide, while reducing the serum TNF response to DMXAA, potentiates its antitumour effect. We have investigated this in the MDAH-MCa-4 mammary carcinoma model, comparing it to previous data with the Colon 38 adenocarcinoma. We have related DMXAA-induced blood flow changes in the MCa-4 tumour to tumour growth delay, serum TNF and extractable TNF from tumour tissue. We have also compared the effect of thalidomide (387 mumol/kg) on DMXAA (80 mumol/kg) with that of a monoclonal anti-TNF antibody (50 micrograms/mouse). We find that tumour blood flow reduction is strongly correlated with tumour growth delay. Coadministration of anti-TNF antibody abolishes serum TNF levels and slightly reduces the antitumour effects of DMXAA. While tumour growth delay is not correlated with serum induced TNF levels, it is related to tumour TNF levels. We conclude that while the data are consistent with TNF being the principal mediator of the action of DMXAA, serum TNF levels do not reflect the antitumour response.

Mutagenic properties of topoisomerase-targeted drugs

Topoisomerases maintain DNA structure by relieving torsional stress occurring in DNA during transcription, replication and cell division. Topoisomerases are of two main types, causing transient breaks in one (type I) or both (type II) and strands of DNA, and a number of clinical anticancer drugs are thought to act by inhibiting religation of these transient breaks. Topoisomerase II appears to have a close association with the SMC (stable maintenance of chromosomes) family of proteins involved in organisation of the chromatin in a series of loops on the proteinaceous chromosomal scaffold. Inhibition of topoisomerase II function can result in deletions of such loops, probably mediated by reciprocal exchange of topoisomerase subunits. Disruption of topoisomerase I and/or II function during DNA replication results in smaller DNA deletions and other mutations, probably arising from non-homologous recombination. Inhibition of topoisomerase II action during mitosis and meiosis can cause incomplete separation of chromatids and chromosomes, with the consequent production of genomic mutations. Topoisomerase-mediated mutagenicity is important because it can lead not only to drug resistance but also to drug-induced secondary cancers. Mutagenicity of topoisomerase-directed agents has been underestimated in the past, since these drugs are not usually capable of reacting covalently with DNA and usually have low mutagenicity in microbial assays.

Interaction of thalidomide, phthalimide analogues of thalidomide and pentoxifylline with the anti-tumour agent 5,6-dimethylxanthenone-4-acetic acid: concomitant reduction of serum tumour necrosis factor-alpha and enhancement of anti-tumour activity

DMXAA (5,6-dimethylxanthenone-4-acetic acid), a novel anti-tumour agent currently undergoing clinical evaluation, appears to mediate its anti-tumour effects through immune modulation and the production of the cytokine tumour necrosis factor-alpha (TNF). Our previous studies have shown that thalidomide, a potent inhibitor of TNF biosynthesis that has numerous biological effects, including inhibition of tumour angiogenesis, unexpectedly augments the anti-tumour response in mice to DMXAA. We show here that thalidomide (100 mg kg(-1)) has no effect when administered with inactive doses of DMXAA, and that it must be given simultaneously with an active dose of DMXAA to have its maximum potentiating effect on the growth of the murine Colon 38 adenocarcinoma. To address the issue of whether inhibition of serum TNF production is important for potentiation of anti-tumour activity, we have tested three potent analogues of thalidomide. All three analogues, when co-administered with DMXAA to mice at doses lower than those used with thalidomide, inhibited TNF production and were effective in potentiating the anti-tumour activity of DMXAA against transplanted Colon 38 tumours. One of the analogues, N-phenethyltetrafluorophthalimide, was 1000-fold more potent than thalidomide and at a dose of 0.1 mg kg(-1) in combination with DMXAA (30 mg kg(-1)) cured 100% of mice, compared with 67% for the group treated with DMXAA alone. We also tested pentoxifylline and found it to suppress TNF production in response to DMXAA and to potentiate the anti-tumour effect of DMXAA. The results are compatible with the hypothesis that pharmacological reduction of serum TNF levels might benefit the anti-tumour effects of DMXAA and suggest new strategies for therapy using this agent.

Enhancement of the anti-tumour effects of the antivascular agent 5,6-dimethylxanthenone-4-acetic acid (DMXAA) by combination with 5-hydroxytryptamine and bioreductive drugs

The tumour blood flow inhibitor 5,6-dimethylxanthenone-4-acetic acid (DMXAA) causes dramatic haemorrhagic necrosis in murine tumours, but activity is seen only at doses close to the toxic limit. This study investigates two approaches for increasing the therapeutic ratio of DMXAA. The first approach combines DMXAA with a second tumour blood flow inhibitor, 5-hydroxytryptamine (5-HT). Co-administration of 5-HT (700 micromol kg(-1)) to C3H mice caused marked enhancement of DMXAA effects against MDAH-MCa-4 tumours, with dose-modifying factors (DMFs) of >3 for blood flow inhibition (at 4 h), 2.3 for necrosis (at 12 h) and 2.0 for growth delay, without compromising the maximum tolerated dose of DMXAA (90 micromol kg(-1)). The data are consistent with ischaemic injury to the tumour being the major mechanism of anti-tumour activity. The second approach combines DMXAA (+/- 5-HT) with hypoxia-selective bioreductive drugs. Anti-tumour activity of all three bioreductive drugs tested (tirapazamine, CI-1010, SN 23816) was strongly potentiated by DMXAA, suggesting that there is a population of reversibly hypoxic tumour cells after DMXAA treatment. Co-administration of 5-HT further potentiated anti-tumour activity, but also increased host toxicity of tirapazamine and CI-1010 so that little therapeutic benefit was achieved. In contrast, the host toxicity of the dinitrobenzamide mustard SN 23816 was only slightly increased by DMXAA/5-HT, whereas the tumour growth delay at the maximum tolerated dose of SN 23816 was increased from 3.5 to 26.5 days. This study demonstrates that 5-HT and/or bioreductive drugs can improve the therapeutic activity of DMXAA in mice, and that with SN 23816 both approaches can be used together to provide considerably enhanced anti-tumour activity.

Antitumour activity of the novel immune modulator 5,6-dimethylxanthenone-4-acetic acid (DMXAA) in mice lacking the interferon-gamma receptor

5,6-Dimethylxanthenone-4-acetic acid (DMXAA), a novel antitumour agent currently undergoing clinical evaluation, appears to mediate its antitumour effects through immune modulation and the production of cytokines. We used mice with a targeted disruption of the interferon-gamma (IFN-gamma) receptor gene as a model to evaluate the role of the host response to IFN-gamma in the antitumour action of DMXAA on colon 38 tumours. A feature of the results was that while DMXAA treatment induced both IFN-gamma and tumour necrosis factor (TNF) in serum, the increase was > 20-fold higher in IFN-gamma R0/0 mice than in wild-type mice. In contrast, mRNA levels for IFN-gamma and TNF were similar in the two mouse strains, suggesting that the concentrations of these cytokines were controlled by a post-transcriptional mechanism. Serum nitrate levels, used as a measure of nitric oxide production, were increased by DMXAA, but to a similar extent in both strains of mice. Complete regressions of colon 38 tumours were obtained in response to DMXAA in the knockout mice, although the dose required for 100% cure was higher and the reduction in tumour volume occurred more slowly than in the wild-type counterparts. The results demonstrate that the host response to IFN-gamma is not essential for an anti-tumour response. Similar results were obtained in mice that were immunosuppressed by treatment with cyclosporin A before treatment with DMXAA. The results are consistent with the concept that the antitumour activity of DMXAA involves complex immunomodulation, probably with significant redundancy in contributing cytokines.

Inhibition of growth of primary human tumour cell cultures by a 4-anilinoquinazoline inhibitor of the epidermal growth factor receptor family of tyrosine kinases

The epidermal growth factor receptor (EGFR) is thought to mediate the action of the mitogens EGF and tumour growth factor-alpha (TGF-alpha) in a variety of cancers, including those of the lung, breast and ovary. A number of new selective inhibitors of EGFR tyrosine kinase have now been developed as potential new antitumour agents. We used a potent inhibitor of this tyrosine kinase, 6-amino-4-[(3-bromophenyl)amino]-7-(methylamino)quinazoline (SN 25531; PD 156273), to determine the responses of primary cultures derived from patients with cancer of the lung, ovary, breast, cervix and endometrium. Cells were cultured in 96-well plates and proliferation assessed by incorporation of 3H-thymidine. Measured growth inhibitory concentrations IC50 values) varied from 1 nM to 14 microM with a 1000-fold differential between sensitive and resistant cultures. Results were compared with rates of proliferation, estimated using a paclitaxel-based method. We also measured the IC50 values for the tyrosine kinase inhibitor using a number of established human cell lines, and compared them with EGFR content using fluorescent antibody staining and flow cytometry. The presence of EGFR was found to be necessary, but not sufficient, for in vitro response. Only a small number of cell lines (3 of 7 for lung, 1 of 7 for ovarian, 2 of 3 squamous cell and 0 of 12 for melanoma) were sensitive to the tyrosine kinase inhibitor. In contrast, 40 of the 50 primary cultures (including 14 of 15 lung cancer samples and 14 of 19 ovarian cancer samples) were sensitive.

Major changes in chromatin condensation suggest the presence of an apoptotic pathway in plant cells

A large decrease in fluorescence intensity of propidium iodide (PI)-stained nuclei is observed during senescence of plant cells. The phenomenon reflects a decrease in accessibility of DNA to this fluorochrome and is a consequence of chromatin condensation. This decrease is substantially greater than usually found in animal nuclei whose chromatin undergoes condensation, e.g., during differentiation or quiescence. Chromatin condensation was confirmed by analyses of (i) DNA accessibility to DNase I, (ii) histone disassociation induced by HCl, (iii) saturation of binding sites by the PI fluorochrome (iv), and (v) visual inspection by fluorescence and confocal microscopy. The extent of changes revealed by these assays was used to map progressive changes in chromatin condensation which allowed us to identify different stages in an apoptosis-like pathway in plants. The initial step of chromatin condensation which occurred prior to endonucleolytic DNA degradation was detected by fluorescence and confocal microscopy and confirmed by a variety of assays employing flow cytometry. The initial chromatin condensation appears to be a reversible step in the early stage of apoptosis. The loss of reversibility of chromatin condensation observed subsequently may be a critical point in the cascade of apoptotic events, leading to further irreversible changes during apoptosis in plants.

Sequence specific modulation of DNA restriction enzyme cleavage by minor groove binders

The inhibition of restriction endonuclease cleavage by a series of bisquaternary ammonium derivatives (BQA-derivatives) which bind to the minor groove of DNA has been studied. The derivatives considered included six sequence-selective binders (SN 6570, SN 6999, SN 6050, SN 6132, SN 6131 and SN 18071) and four non-specific binders (SN 6113, SN 5754, SN 6324 and SN 4094) and can be distinguished by their activity on restriction endonucleases. Digestion experiments with pUC19 DNA were monitored electrophoretically using the transition of the covalently closed circular (ccc) DNA into the linear double stranded (lds) one. Only the sequence-specific binders inhibit the cleavage activity of restriction endonucleases EcoRI, SspI and DraI with four and six dAdT-base pairs within their restriction sites, while the activity of SalI and BamHI with less than four dAdT-sequences was unaffected. In contrast, the non-specific binding ligands were incapable of suppressing enzyme digestion. The inhibition of the restriction endonuclease PvuII indicates that ligand binding in close vicinity to the cleavage sites is also involved in the enzyme inhibition. The dAdT-content in proximity to the palindromic sequences of three DraI cutting sites in pUC19 DNA explains why the derivative SN 6053 protects these sequences in different manners. Gel shift experiments indicated that BQA-derivatives inhibit the DNA-enzyme complex formation if the ligand was added to the DNA before the enzyme. In contrast, complex formation between DNA and enzyme remained unchanged when the enzyme was added first.

Differential actions of aclarubicin and doxorubicin: the role of topoisomerase I

Aclarubicin and doxorubicin are DNA binding anthracycline antibiotics of related chemical structure but differing cytotoxic action. Although doxorubicin mediates its cytotoxicity by poisoning the enzyme topoisomerase II, aclarubicin has been hypothesized to inhibit the catalytic action of topoisomerase II. We show here that aclarubicin, in contrast to doxorubicin, is highly effective in inhibiting the action of topoisomerase I. Aclarubicin not only inhibits this enzyme in a cell-free assay but also markedly inhibits DNA-protein cross-linking in H460 human lung adenocarcinoma cells as measured by the K(+)-SDS precipitation technique. It also displaces topoisomerase I from DNA as measured by Western blotting. Aclarubicin reverses the cytotoxicity of both amsacrine and camptothecin in clonogenic survival assays, consistent with the hypothesis that it is a dual topoisomerase I/II inhibitor. We suggest that the self-inhibition of topoisomerase I in short-term assays may mask the underlying activity of aclarubicin as a topoisomerase I poison. In short-term (1-H) drug exposure assays, aclarubicin kills both exponential and plateau phase cells by a non-cell cycle-selective mechanism apparently not involving G2 phase arrest. This may be a consequence of simultaneous inhibition of topoisomerases I and II.

Cellular responses to methyl-N-[4-9-acridinylamino)-2-methoxyphenyl] carbamate hydrochloride, an analogue of amsacrine active against non-proliferating cells

The acridine derivative m-AMCA (methyl-N-[4-(9-acridinylamino)-2-methoxyphenyl]carbamate hydrochloride), a carbamate analogue of the topoisomerase II poison amsacrine, is distinguished by its high cytotoxicity against non-cycling tumour cells. We compared the response of cultured Lewis lung carcinoma cells to m-AMCA, amsacrine and the topoisomerase I poison camptothecin. The DNA polymerase inhibitor aphidicolin reversed the cytotoxicity of camptothecin fully, that of amsacrine partially, and that of m-AMCA minimally. The ability of m-AMCA to induce the enzyme poly(ADP-ribose)polymerase (PARP) was markedly lower than that of camptothecin or amsacrine. Cell cycle responses to m-AMCA and amsacrine were similar, with slowing of progress through S-phase and arrest in G2-phase. These cell cycle changes were also observed when plateau phase cultures were exposed to drug for 1 h, washed free of drug and cultured in fresh medium, with m-AMCA having a more pronounced effect than amsacrine and camptothecin having no effect. We also examined the role of p53 protein in the response using cultured human H460 cells. Both m-AMCA and amsacrine induced p53 protein expression in proliferating but not in non-proliferating H460 cells, and induced p21WAF1 regardless of proliferation status. Both induced G1-phase cell cycle arrest. It is suggested that two cytotoxicity mechanisms can be distinguished using these drugs. The first is specific for S-phase cells, is reversed by aphidicolin and induces PARP activity. The second is cell cycle non-specific, does not induce PARP and is unaffected by aphidicolin. Camptothecin activates only the first, m-AMCA primarily the second and amsacrine activates both.

Synthesis and antitumor properties of N-[2-(dimethylamino)ethyl]carboxamide derivatives of fused tetracyclic quinolines and quinoxalines: a new class of putative topoisomerase inhibitors

A series of tetracyclic quinoline- and quinoxalinecarboxamides were prepared, and their cytotoxicities were evaluated in a series of murine human tumor cell lines. Most of the quinoline derivatives were prepared by an adaptation of the Pfitzinger synthesis, followed by thermal decarboxylation and coupling with N,N-dimethylethylenediamine via a mixed anhydride method using isobutyl chloroformate. The quinoline analogues showed cytotoxicities broadly similar to those of the known tricyclic acridine-4-carboxamide mixed topoI/II inhibitor DACA, with thieno and indeno analogues being the most active. They showed little decrease in potencies against the Jurkat human leukemia topo II-resistant lines JLA and JLC, suggesting their cytotoxicity does not result primarily from inhibition of topo II. The quinoxaline analogues had more varied IC50 values, being on average less cytotoxic than the quinoline derivatives, but appeared to have a similar mode of action. Overall, this new class of compounds appear to be mixed topo I/II inhibitors, up to 3-fold more cytotoxic than DACA in the human leukemia cell lines studied, with in vivo activity in colon 38 comparable to that of DACA and doxorubicin.

Structure-activity relationships for acridine-substituted analogues of the mixed topoisomerase I/II inhibitor N-[2-(dimethylamino)ethyl]acridine-4-carboxamide

The mixed topoisomerase I/II inhibitor N-[2-(dimethylamino)ethyl]acridine-4-carboxamide (DACA) is currently in clinical trial as an anticancer drug. A series of acridine-substituted analogues were prepared, using a new synthetic route to substituted acridine-4-carboxylic acids (conversion of substituted diphenylamine diacid monoesters to the corresponding aldehydes and mild acid-catalyzed ring closure to form the acridines directly). The analogues were evaluated in a panel of cell lines which included wild-type (JLC) and mutant (JLA and JLD) forms of the human Jurkat leukemia line. The latter mutant lines are resistant to topoisomerase II targeted agents due to lower levels of the enzyme. Structure-activity studies suggest that the electronic properties of the substituents do not markedly affect cytotoxicity, but steric bulk is important, with larger groups leading to loss of activity. The compounds fell broadly into two categories. The majority had cytotoxicities similar to (or lower than) that of DACA itself and were equitoxic in all the Jurkat lines, suggesting a relatively greater effect on topoisomerase I compared with topoisomerase II. Most of the 5-substituted derivatives and the 7-Ph compound were more cytotoxic than DACA, but were less effective against JLA and JLD cell lines than in the wild-type JLC, suggesting a mode of cytotoxicity largely mediated by effects on topoisomerase II. Both DACA and selected acridine-substituted analogues were active in the relatively refractory subcutaneous colon 38 tumor model in vivo.

Studies on the metabolism of the novel antitumor agent [N-methyl-11C]N-[2-(dimethylamino)ethyl]acridine-4-carboxamide in rats and humans prior to phase I clinical trials

This study reports on the biodistribution and metabolism of the 11C-labeled novel antitumor agent N-[2-(dimethylamino)ethyl]acridine-4-carboxamide (DACA) (also known as NSC 601316) in rats (plasma and tissues) and humans (plasma). Information on plasma metabolites was uniquely obtained in humans prior to Phase I clinical trial following i.v. injection of [11C]DACA at tracer dose. DACA was labeled in the N-methyl position using no-carrier-added [11C]iodomethane. Rapid high-performance liquid chromatography methods were developed for metabolite analysis of [11C]DACA. The metabolism of [11C]DACA was investigated in patients by plasma sampling. The biodistribution and metabolism of [11C]DACA was investigated in rats by plasma sampling, sacrifice experiments with tissue analyses, and imaging using positron emission tomography scanning. Analysis of human plasma demonstrated rapid and extensive metabolism of [11C]DACA. The levels of [11C]DACA changed from 77 +/- 8% (SD) at 5 min to 25 +/- 5% at 45 min postinjection. Seven radioactive metabolites were observed in human plasma, and one was identified as [11C]DACA-N-oxide. Rapid clearance of 11C radioactivity from rat blood, plasma, and major organs was observed. The half-life of 11C radioactivity clearance in rat blood between 15 and 90 min was calculated to be 3.2 h; the levels of [11C]DACA in rat plasma decreased from 69 +/- 3% (SD) at 2 min to 29 +/- 1.5% at 25 min. The number of radioactive metabolites in rat plasma was the same as in human plasma except that the proportions differed. Again, one metabolite was identified as the [11C]DACA-N-oxide. Analysis of rat tissues showed rapid and extensive metabolism in tissues, particularly liver and kidney; however, [11C]DACA (i.e., the parent compound) was the major radioactive component in the lung, heart, and brain over 40 min. Positron emission tomography scanning using [11C]DACA in the rat showed little retention of 11C radioactivity in major organs with rapid excretion via gut and kidney. The rat data were consistent with animal (mouse and rat) preclinical data obtained with preexisting techniques with longer-lived isotopes. Labeling of potential anticancer drugs with positron-emitting radionuclides and performing in vivo preclinical evaluation at tracer doses in animals and humans prior to Phase I clinical trials provides unique information that could speed up the assessment of the drug and could potentially assist drug development programs. In this example, there was no unexpected interspecies difference in metabolism of DACA that would have alerted us to make a change in the planned Phase I study.

Aniline mustard analogues of the DNA-intercalating agent amsacrine: DNA interaction and biological activity

Two series of analogues of the clinical antileukemic drug and DNA-intercalating ligand amsacrine have been prepared, containing aniline mustard sidechains of varying reactivity, linked either at the 4-position of the intercalating acridine chromophore (type A) or at the 1'-position of the 9-anilino group (type B). DNase I footprinting assays showed that compounds of type B had stronger reversible binding to DNA than did compounds of type A. Compounds of each type showed similar patterns of alkylation-induced cleavage of DNA, and alkylate at the N7 of guanines in runs of guanines (similar to the pattern for untargeted mustards) as well as some adenines. Both classes of compounds crosslinked DNA, although those bearing relatively inactive mustards did so only at high drug/base pair ratios. However, while the patterns of DNA alkylation were broadly similar, the compounds were considerably more cytotoxic than analogous untargeted mustards. Comparison of their cytotoxicities in wild-type and DNA repair-deficient lines indicated this toxicity was due to DNA crosslinks (except for the least reactive SO2-linked mustards). The 4-linked analogues showed slightly higher in vivo antileukemic activity than the corresponding 1'-linked analogues.

Carbon-11 labelling of the antitumour agent N-[2-(dimethylamino)ethyl]acridine-4-carboxamide (DACA) and determination of plasma metabolites in man

The potential anti-cancer agent N-[2-(dimethylamino)ethyl] acridine-4-carboxamide, DACA has been labelled with carbon-11. N-[2-11C-methyl]DACA was produced in 73% radiochemical yield from [11C]iodomethane in 40 min from EOB. The average radiochemical yield was 3.2 GBq with specific radioactivity of 41.5 GBq mumol-1 at EOS, corresponding to 24 micrograms of stable DACA. The position of labelling was confirmed by co-labelling with [11/13C]iodomethane. PET studies in patients have been performed prior to Phase I trial of DACA and during Phase I trial of DACA. Analysis of serial plasma samples showed that the metabolism of N-[2-11C-methyl]DACA is rapid and extensive in patient plasma.

A carbamate analogue of amsacrine with activity against non-cycling cells stimulates topoisomerase II cleavage at DNA sites distinct from those of amsacrine

AMCA (methyl N-[4-(9-acridinylamino)-2-methoxyphenyl]carbamate hydrochloride), an amsacrine analogue containing a methylcarbamate rather than a methylsulphonamide side chain, contrasts with amsacrine, doxorubicin and etoposide in its relatively high cytotoxicity against non-cycling tumour cells. AMCA bound DNA more tightly than amsacrine, but the DNA base selectivity of binding, as measured by ethidium displacement from poly[dA-dT].[dA-dT] and poly[dG-dC].[dG-dC], was unchanged. AMCA-induced topoisomerase cleavage sites on pBR322, C-MYC and SV40 DNA were investigated using agarose or sequencing gels. DNA fragments were end-labelled, incubated with purified topoisomerase II from different mammalian sources and analysed after treatment with sodium dodecylsulphate/proteinase K. AMCA stimulated the cleavage activity of topoisomerase II, but the DNA sequence selectivity of cleavage was different from that of amsacrine and other topoisomerase inhibitors. It was similar to that of the methoxy derivative of AMCA, indicating that the changed specificity resulted from the carbamate group rather than from the methoxy group. The pattern of DNA cleavage induced by AMCA was similar for topoisomerase II alpha and II beta.

Preclinical prediction of factors influencing the elimination of 5,6-dimethylxanthenone-4-acetic acid, a new anticancer drug

The glucuronidation of 5,6-dimethylxanthenone-4-acetic acid (DMXAA), a newly developed anticancer drug, was investigated in vitro to determine factors likely to affect the elimination of this compound in patients. Human liver microsomal DMXAA glucuronidation followed Michaelis-Menten kinetics, with a mean apparent Km of approximately 100 microM. Two cDNA-expressed UGT isoforms, UGT1*02 and UGT2B7, had the capacity to glucuronidate DMXAA, although comparative kinetic and inhibitor studies were more consistent with a greater contribution of UGT2B7 to the human hepatic reaction. Microsomal DMXAA glucuronide formation was screened for inhibition by drugs known to be eliminated by glucuronidation. Of the drugs screened, significant inhibition was observed with diclofenac, epirubicin, indomethacin, R,S-ketoprofen, lorazepam, S-naproxen, oxazepam, and temazepam; apparent Ki values ranged from 9.5-318 microM. These values are substantially above unbound concentrations of the individual drugs achieved in vivo. DMXAA glucuronide was found to be unstable at physiological pH values, and the rate of degradation was marginally increased in the presence of albumin. Taken together, these data indicate that the kinetics of DMXAA glucuronidation in vivo are likely to be linear and unaffected by the coadministration of most glucuronidated drugs, but plasma DMXAA clearance may be decreased in patients with renal dysfunction. This study illustrates the utility of in vitro techniques for the prediction of potential drug interactions and other dispositional characteristics of newly developed anticancer drugs before their administration to patients.

In vivo effects of chlorophyllin on the antitumour agent cyclophosphamide

Cyclophosphamide (CP) is a potent antitumour agent used against many forms of cancer and against certain other diseases. Chlorophyllin (CHL), which is obtained by hydrolysis of chlorophyll to remove phytyl alcohol, is an efficient antimutagenic agent and has been used as a dietary supplement or to diminish the intensity of the discomforting side effects of CP therapy. We undertook to determine the antimutagenic effectiveness of CHL against CP in a mouse model and to determine whether the antitumour efficacy of CP was compromised in vivo by CHL treatment. Experiments utilised CHL administered either in drinking water (1%) for 2 days before treatment, or by gavage (200 mg/kg) 2 hr before treatment with CP (220 mg/kg). Urinary mutagenicity following CP treatment, as determined by the Salmonella/microsome assay, was decreased by both regimes of CHL co-treatment. Similarly, the increase in micronuclei in bone marrow polychromatic erythrocytes in response to CP was reduced by concomitant CHL treatment. In contrast, antitumour efficacy, as determined by growth delay of Colon 38 adenocarcinomas, was not diminished by CHL treatment. We conclude that CHL may have beneficial effects when used in combination with CP therapy.