The role of topoisomerases and RNA transcription in the action of the antitumour benzonaphthyridine derivative SN 28049

PURPOSE

SN 28049 (N-[2-(dimethylamino)ethyl]-2,6-dimethyl-1-oxo-1,2-dihydrobenzo[b]-1,6-naphthyridine-4-carboxamide) is a DNA intercalating drug that binds selectively to GC-rich DNA and shows curative activity against the Colon 38 adenocarcinoma in mice. We wished to investigate the roles of topoisomerase (topo) I, topo II and RNA transcription in the action of SN 28049.

METHODS

We used clonogenic assays to study the cytotoxicity of SN 28049; RNA interference and enzyme assays to examine the role of topo I in SN 28049 action; 3H uridine incorporation and reporter assays to study its effects on transcription; and RT-PCR to examine its ability to reduce endogenous h-TERT expression.

RESULTS

In clonogenic assays, SN 28049 showed a biphasic cytotoxic dose response curve in H460 cells typical of acridine derivatives such as N-[2-(dimethylamino)ethyl]acridine-4-carboxamide (DACA) although it was approximately 16-fold more potent. Down-regulation of topo IIalpha in HTETOP cells reduced the cytotoxicity of SN 28049, establishing its action as a topo IIalpha poison. Surprisingly, down-regulation of topo I in H460 cells by RNA interference sensitised them to the actions of SN 28049 and other topo II poisons. SN 28049 also inhibited topo I-mediated relaxation of supercoiled plasmid DNA. SN 28049 was also an inhibitor of transcription in HEK293 cells and was more potent at reducing luciferase expression from a GC-rich SP-1 binding promoter than from a non-GC-rich AP-1 binding promoter. The drug also reduced luciferase reporter gene expression driven by the SP-1-binding survivin promoter as well as reducing endogenous h-TERT expression in HEK293 cells whose promoter also contains SP-1 binding sites.

CONCLUSION

We conclude that SN 28049 has a complex action that may involve poisoning of topo IIalpha, suppression of topo I and inhibition of gene transcription from promoters with SP-1 sites. These actions may contribute to the promising experimental solid tumour anticancer activity of SN 28049.

Synthesis, biological evaluation and molecular modelling of sulfonohydrazides as selective PI3K p110alpha inhibitors

A series of 2-methyl-5-nitrobenzenesulfonohydrazides were prepared and evaluated as inhibitors of PI3K. An isoquinoline derivative shows good selectivity for the p110alpha isoform over p110beta and p110delta, and also demonstrates good in vitro activity in a cell proliferation assay. Molecular modelling provides a rationalisation for the observed SAR.

Consequences of increased vascular permeability induced by treatment of mice with 5,6-dimethylxanthenone-4-acetic acid (DMXAA) and thalidomide

PURPOSE

5,6-Dimethylxanthenone-4-acetic acid (DMXAA) (AS1404), a small-molecule vascular disrupting agent currently in clinical trial, increases vascular permeability and decreases blood flow in both murine and human tumours. DMXAA induces tumour necrosis factor (TNF) in mice and the effects on vascular permeability are hypothesised to result from both direct (DMXAA) and indirect (TNF) effects. Skin temperature decreases in mice treated with high doses of DMXAA, raising the question of whether host toxicity is mediated by the induction of increased vascular permeability in normal tissue. Thalidomide is an anti-inflammatory agent that potentiates the anti-tumour activity of DMXAA but decreases induction of TNF in plasma. We wished to determine how it potentiated the effects of DMXAA.

METHODS

Vascular permeability was measured in Colon 38 tumour and liver tissue by uptake of Evans Blue dye. Blood haematocrit and body temperature were also measured.

RESULTS

Tumour vascular permeability was increased following administration of DMXAA (25 mg/kg i.p.), minimally affected following thalidomide (100 mg/kg i.p.) but strongly increased following co-administration of both drugs. In contrast, dye uptake into liver tissue was decreased following administration of DMXAA, thalidomide or both drugs. Administration of DMXAA at a potentially toxic dose (35 mg/kg i.p. or 50 mg/kg orally) was found to decrease body temperature and to increase the blood haematocrit, while administration of thalidomide alone (100 mg/kg i.p.) had no effect. Co-administration of thalidomide potentiated the effects of DMXAA on both body temperature and haematocrit but surprisingly did not increase toxicity.

CONCLUSIONS

The results are consistent with the hypothesis that the host toxicity of high-dose DMXAA is mediated by effects on host vasculature. Co-administration of thalidomide increases the effective dose of DMXAA by reducing clearance but also, by inhibiting production of circulating TNF, reduces the host toxicity of DMXAA.

Evidence for the involvement of p38 MAP kinase in the action of the vascular disrupting agent 5,6-dimethylxanthenone-4-acetic acid (DMXAA)

AIMS

DMXAA (AS1404), a small-molecule vascular disrupting agent that has now completed Phase II clinical trial, induces endothelial cell apoptosis, increased vascular permeability and decreased tumour blood flow in vivo. Its action is incompletely understood and we wished to develop an in vitro system to study its effects.

METHODS

Human tumour cell lines developed from aggressive tumours were grown on Matrigel to simulate a tumour microenvironment. Cells were analysed by light microscopy and by gene expression profiling.

RESULTS

Several cell lines formed networks when grown on Matrigel and the NZM7 melanoma cell line was chosen for further study. Addition of DMXAA at a clinically achievable concentration (30 microg/mL) prevented network formation, but co-addition of SB203580 (10 microM), a selective inhibitor of p38 MAP kinase, reversed the effect of DMXAA and restored network formation. Analysis of expression genes for endothelial and related functions showed that cells growing on Matrigel expressed a pattern similar to that of NZM7 cells growing as xenografts in vivo but different from that of cells grown on standard tissue culture plates. Addition of DMXAA resulted in the inhibition of expression of several genes including the transcriptional activator Ets1 and matrix metalloproteinase-2 (MMP2), but co-addition of SB203580 did not reverse these effects of DMXAA on gene expression.

CONCLUSION

The results suggest that p38 MAP kinase plays an important role in the action of DMXAA and that growth of tumour cells on Matrigel provides a promising model for further studies on the action of this drug.

NF-kappaB-independent induction of endothelial cell apoptosis by the vascular disrupting agent DMXAA

BACKGROUND

DMXAA (5,6-dimethylxanthenone-4-acetic acid; AS1404), a vascular disrupting agent currently in clinical trials, induces tumour endothelial cell apoptosis in vivo in mice and in cancer patients. DMXAA activates NF-kappaB in many different cell types. In this study, whether DMXAA-induced endothelial cell apoptosis was NF-kappaB dependent was determined.

MATERIALS AND METHODS

HUVEC endothelial and T24 endothelial-like cells were treated with DMXAA and apoptosis was measured by terminal deoxynucleotidyl transferase biotin-dUTP nick end labelling (TUNEL). NF-kappaB activation was measured by electrophoretic mobility shift assays (EMSA). T24 cells were transfected with IkappaBalphaM, a mutant form of the IkappaBalpha gene which cannot be phosphorylated and degraded, hence preventing NF-kappaB expression.

RESULTS

No NF-kappaB up-regulation was detected in apoptotic HUVEC treated with DMXAA. The IkappaBalphaM-transfected T24 cells showed similar apoptotic responses to those of parental cells.

CONCLUSION

The DMXAA-induced apoptosis is neither mediated by, nor inhibited by, the expression of the NF-kappaB pathway.

5,6-Dimethylxanthenone-4-acetic acid in the treatment of refractory tumors: a phase I safety study of a vascular disrupting agent

This phase I safety study aimed to identify the optimal dose of the vascular disrupting agent 5,6-dimethylxanthenone-4-acetic acid (DMXAA) for combination studies. Using a crossover design, 15 patients with refractory tumors were allocated randomly to receive six sequential doses of DMXAA (300, 600, 1,200, 1,800, 2,400, and 3,000 mg m(-2)), each given once-weekly as a 20-minute i.v. infusion. The drug was generally well tolerated. Transient, moderate increases in the heart rate-corrected cardiac QT interval occurred at the two highest doses. DMXAA produced transient dose-dependent increases in blood pressure. Transient, dose-related visual disturbances occurred at the two highest doses. No significant changes in K(trans) and k(ep) were observed but V(e), a secondary dynamic contrast-enhanced magnetic resonance imaging variable, increased significantly after giving DMXAA. At 1,200 mg m(-2), the Cmax and the area under the concentration-time curve over 24 hours for total and free DMXAA plasma concentrations were 315 +/- 25.8 microg/mL, 29 +/- 6.4 microg/mL x d, 8.0 +/- 1.77 microg/mL, and 0.43 +/- 0.07 microg/mL x d, respectively. Plasma levels of the vascular damage biomarker 5-hydroxyindoleacetic acid increased in the 4 hours after treatment in a dose-dependent fashion up to 1,200 mg m(-2), with a plateau thereafter. Doses in the range of 1,200 mg m(-2) have been selected for further studies (phase II combination studies with taxanes and platins are under way) because this dose produced no significant effect on heart rate-corrected cardiac QT interval, produced near maximum levels of 5-hydroxyindoleacetic acid, achieved DMXAA plasma concentrations within the preclinical therapeutic range, and was well tolerated.

Pharmacokinetics of 5,6-dimethylxanthenone-4-acetic acid (AS1404), a novel vascular disrupting agent, in phase I clinical trial

PURPOSE

5,6-Dimethylxanthenone-4-acetic acid (DMXAA) (AS1404) is a novel antitumour agent that selectively disrupts tumour vasculature and induces cytokines. The purpose of this study was to determine the pharmacokinetics (PK) of DMXAA in cancer patients enrolled in a phase I clinical trial.

METHODS

DMXAA was administered as a 20-min i.v. infusion every 3 weeks and doses were escalated in cohorts of patients according to a predefined schema. PK samples were taken over the first 24 h of at least the first cycle.

RESULTS

DMXAA was administered to 63 patients at 19 dose levels from 6 to 4,900 mg m(-2), and 3,700 mg m(-2) was established as the maximum tolerated dose. The PK observed over the dose range showed a non-linear fall in clearance from 16.1 to 1.42 l h(-1) m(-2) and resultant increase in the area under the concentration-time curve (AUC) from 1.29 to 12,400 microM h. In contrast, the increase in peak plasma concentrations from 2.17 to 1,910 microM approximated linearity. DMXAA was highly protein-bound to albumin (>99%) until saturation occurred at higher doses, leading to a rapid increase in the free fraction (up to 20%) and greater concentrations of DMXAA bound to non-albumin proteins. However, the main determinant of the non-linearity of the PK appeared to be sequential saturation of elimination mechanisms, which include hydroxylation, glucuronidation and perhaps hepatic transport proteins. This resulted in an exaggerated non-linear increase in free DMXAA plasma concentrations and AUC compared to total drug.

CONCLUSIONS

The PK of DMXAA are well-defined, with a consistent degree of non-linearity across a very large dose range.

Association of mutant TP53 with alternative lengthening of telomeres and favorable prognosis in glioma

The molecular basis for alternative lengthening of telomeres (ALT), a prognostic marker for glioma patients, remains unknown. We examined TP53 status in relation to telomere maintenance mechanism (TMM) in 108 patients with glioblastoma multiforme and two patients with anaplastic astrocytoma from New Zealand and United Kingdom. Tumor samples were analyzed with respect to telomerase activity, telomere length, and ALT-associated promyelocytic leukemia nuclear bodies to determine their TMM. TP53 mutation was analyzed by direct sequencing of coding exons 2 to 11. We found an association between TP53 mutation and ALT mechanism and between wild-type TP53 and telomerase and absence of a known TMM (P < 0.0001). We suggest that TP53 deficiency plays a permissive role in the activation of ALT.

Antitumour action of 5,6-dimethylxanthenone-4-acetic acid in rats bearing chemically induced primary mammary tumours

PURPOSE

To evaluate the antitumour activity of 5,6-dimethylxanthenone-4-acetic acid (DMXAA), a vascular disrupting agent currently under phase II clinical trials in combination with cancer chemotherapy, in rats bearing chemically induced primary mammary tumours.

METHODS

Tumours were induced in female Wistar rats by injection of N-nitroso-N-methylurea at 100 mg/kg subcutaneously. A clinically relevant single dose of DMXAA (1,800 mg/m(2)) was given to animals when tumours were measurable. Tumour volume, extent of necrosis and cytokine profiles were measured.

RESULTS

Compared with the control group, DMXAA treatment significantly delayed tumour doubling time and extended the time from treatment to euthanasia. Four of five DMXAA-treated animals showed necrosis involving 3.7-41.2% of the area of the tumour section at 24 h compared with none of four control animals (P < 0.028, Chi-square test). Intratumoural levels of TNFalpha, IL-6, VEGF and IL-1alpha were increased 4 h after DMXAA treatment.

CONCLUSIONS

This study shows for the first time that DMXAA has significant in vivo antitumour activity against non-transplanted autochthonous tumours and in a host species other than the mouse.

Inhibition of DMXAA-induced tumor necrosis factor production in murine splenocyte cultures by NF-kappaB inhibitors

The induction of cytokine synthesis within tumor tissue is a key component of the antivascular action of 5,6-dimethylxanthenone-4-acetic acid (DMXAA) in murine tumors. We previously showed that DMXAA alone induced only low amounts of tumor necrosis factor (TNF) in cultured spleen cells, but the addition of suboptimal concentrations of lipopolysaccharide (LPS) provided a costimulatory signal that resulted in 6-10-fold increase in secreted TNF. In this study we investigated the molecular pathway involved, and showed that the addition of NF-kappaB inhibitors salicylate and parthenolide reduced the levels of TNF secreted into the culture supernatants induced with DMXAA (10 microg/ml) alone or in combination with LPS (10 microg/ml). Results from gene arrays, confirmed with RT-PCR, showed that the TNF gene was not upregulated with DMXAA alone, and was only slightly increased above the level of significance when LPS was added simultaneously. This contrasted with secreted TNF protein levels, which increased 5- and 48-fold, respectively, above that in untreated cultures with DMXAA alone or in combination with LPS. In addition to TNF, protein arrays showed IL-6, IL-10, MIP-1alpha, MIP-2, and RANTES were also secreted following treatment with 10 microg/ml DMXAA alone, and IL-4, IFN-gamma, MCP-5, and TIMP-1 were additionally induced using a higher dose of 300 microg/ml DMXAA. The drug is currently showing promise in phase II combination trials, and these studies suggest that DMXAA-induced TNF production in the splenocyte cultures was not due to increased expression of the TNF gene, but through effects on NF-kappaB-dependent posttranscriptional regulation.

Do negative feedback oscillations drive variations in the length of the tumor cell division cycle?

The cell cycle length of individual cells within a tumor cell population is known to vary, mainly as a consequence of differences in the length of G1 phase. A number of observations suggest that the distribution of G1 phase transit times is well described by models where the transition from G1 to S phase is governed by a probability mechanism. However, entry into S phase as a consequence of progressive accumulation of cyclin E with time, to the point where cyclin-dependent kinase-2 (cdk2) is activated, does not provide a basis for a probability mechanism. We suggest that oscillation of the activity of the E2F-1 transcription factor during G1 phase could provide a mechanism that explains the kinetic behavior of G1 phase cells. A negative feedback loop controlling oscillation is possible because activation of cdk2, following activation by cyclin E, phosphorylates the E2F-1 transcription factor, marking it for ubiquitination by the Skp2-cullin-F-box complex and subsequent proteolytic removal. The activity of several cellular transcription factors, including p53 and NF-kappaB, has been shown to oscillate by negative feedback loops leading to ubiquitination and subsequent proteolytic degradation. The oscillatory mechanisms for p53 and NF-kappaB suggest that transitions from the cell cycle to apoptosis are also governed by probability functions.

A comparison of the ability of DMXAA and xanthenone analogues to activate NF-kappaB in murine and human cell lines

DMXAA (5,6-dimethylxanthenone-4-acetic acid), the most potent of a series of xanthenone (XAA) analogues developed in this laboratory, is currently undergoing combination clinical trials as an antivascular agent for cancer treatment. XAAs have a complex mode of action, and in vitro assays that are predictive of in vivo antitumor activity have been difficult to develop. In this study, we have utilized a series including XAA, DMXAA, and mono-substituted XAA derivatives to determine firstly whether in vitro NF-kappaB activation of mouse cell lines predicts for the in vivo antitumor potential of this class of agents, and secondly whether the relative activity of these analogues is similar in murine and human cell lines. Electromobility shift assays were used to measure NF-kappaB activation in murine HECPP endothelial and 70Z/3 pre-B cells, and in human HPLNEC.B3 endothelial and Raji B-lymphoma cells. A significant correlation was obtained between NF-kappaB activation in HECPP cells by a series of XAA analogues at 100 microg/ml (r = 0.78, p = 0.008) and at 300 microg/ml (r = 0.75, p = 0.01) and the amount of hemorrhagic necrosis induced in Colon 38 tumors. Different structure-activity relationships were observed in human and murine cell lines. 8-MeXAA, which was inactive in HECPP and 70Z/3 murine cell lines, showed similar NF-kappaB activation to DMXAA in human HPLNEC.B3 cells and Raji B-lymphoma cells. These results suggest that the receptor protein(s) in human cells that mediate the human response may have a lower stringency to that for murine cells. We also noted differences in the dose-response relationships for NF-kappaB activation between lymphoid and endothelial lines that were species independent. With increasing concentrations of DMXAA, NF-kappaB activation in both murine and human lymphoid lines showed a reproducible fluctuation, while in endothelial lines, the intensity of NF-kappaB activation was relatively constant above a threshold concentration. The results demonstrate interspecies differences in the NF-kappaB response to XAA analogues, and may also reflect the complex nature of NF-kappaB regulation.

Phenazine-1-carboxamides: Structure–cytotoxicity relationships for 9-substituents and changes in the H-bonding pattern of the cationic side chain

A series of phenazine-1-carboxamides were prepared, including variations in both chromophore substituents and the nature of the cationic side chain. The novel side-chain analogues were prepared from the corresponding phenazine-1-carboxylic acids via Schmidt conversion to the 1-amines and from the corresponding 1-halides. Structure-cytotoxicity relationships for these compounds in a panel of tumor cell lines showed that there is very limited scope for variation of the structure of the 1-carboxamide side chain, consistent with the recent structural model of how tricyclic carboxamides bind to DNA. There was generally little difference in IC(50)s between parent and P-glycoprotein expressing cell lines, suggesting that most of the compounds are not affected by the presence of this efflux pump.

Transport of the investigational anti-cancer drug 5,6-dimethylxanthenone-4-acetic acid and its acyl glucuronide by human intestinal Caco-2 cells

5,6-Dimethylxanthenone-4-acetic acid (DMXAA), a potent cytokine inducer, exhibited marked antitumor activity when given as multiple oral doses in mice. The aim of this study was to examine the transport of DMXAA and its acyl glucuronide (DMXAA-G) using the human Caco-2 cells. DMXAA was minimally metabolized by Caco-2 cells and both DMXAA and DMXAA-G were taken up to a minor extent by the cells. The permeability coefficient (Papp) values of DMXAA over 10-500 microM were 4x10(-5) cm/s to 4.3x10(-5) cm/s for both apical (AP) to basolateral (BL) and BL-AP transport, while the Papp values for the BL to AP flux of DMXAA-G were significantly greater than those for the AP to BL flux, with Rnet values of 4.5-17.6 over 50-200 microM. The BL to AP active efflux of DMXAA-G followed Michaelis-Menten kinetics, with a Km of 83.5+/-5.5 microM, and Vmax of 0.022+/-0.001 nmol/min. The flux of DMXAA-G was energy and Na+-dependent and MK-571 significantly (P<0.05) inhibited its BL to AP flux, with an estimated Ki of 130 microM. These data indicate that the transport of DMXAA across Caco-2 monolayers was through a passive process, whereas the transport of DMXAA-G was mediated by MRP1/2.

Modelling the flow of cytometric data obtained from unperturbed human tumour cell lines: parameter fitting and comparison

In this paper we firstly present three alternative formulations of a mathematical model for human tumour cell lines unperturbed by cancer therapy. The model counts the number density of cells in each phase of the cell cycle over time where cells are differentiated by their DNA content. Data are available from the Auckland Cancer Society Research Centre, Auckland, New Zealand, in the form of DNA histograms or profiles from 11 different human tumour cell lines (i.e. in vitro) unperturbed by cancer therapy. We then apply one (computationally fast) formulation of the model and discover that although in general different combinations of parameter values give rise to very different DNA profiles it is possible that different combinations of parameter values give rise to virtually identical profiles. Experimental estimates of the rate of transition from the G1-phase (growth) to the S-phase (DNA synthesis) enable us to uniquely determine other model parameters of interest that give the least square error between the model and data. We finally apply our model to each of the 11 different cell lines and compare cell cycle phase transit times. Although the DNA histograms of each of the cell lines have similar shapes these cell lines have different combinations of transit times to each other, which could explain why they often react very differently when exposed to anti-cancer therapies during laboratory experiments. An understanding of the in vitro situation may give an insight into why some human cancer patients do not respond to cancer therapy.

Synthesis and cytotoxic activity of N-[(alkylamino)alkyl]carboxamide derivatives of 7-oxo-7H-benz[de]anthracene, 7-oxo-7H-naphtho[1,2,3-de]quinoline, and 7-oxo-7H-benzo[e]perimidine

7-Oxo-7H-naphtho[1,2,3-de]quinoline-11-carboxamides and analogues were prepared and evaluated for in vitro and in vivo antitumor activity. Chromophore variations included 'deaza' (7-oxo-7H-benz[de]anthracene) and 'diaza' (7-oxo-7H-benzo[e]perimidine) analogues, and side chain variations included chiral alpha-methyl compounds. The naphthoquinolines were the most cytotoxic, with IC(50) values of 5-20 nM, and showed the strongest DNA binding, with high selectivity for G-C rich DNA. The chiral alpha-methyl analogues were 10-20-fold more cytotoxic than the parent des-methyl compound. Both enantiomers provided substantial growth delays against s.c. colon 38 tumors in mice, with the R-enantiomer more active than the S (tumor growth delays of >35 and 12 days, respectively).

Disrupting tumour blood vessels

Low-molecular-weight vascular-disrupting agents (VDAs) cause a pronounced shutdown in blood flow to solid tumours, resulting in extensive tumour-cell necrosis, while they leave the blood flow in normal tissues relatively intact. The largest group of VDAs is the tubulin-binding combretastatins, several of which are now being tested in clinical trials. DMXAA (5,6-dimethylxanthenone-4-acetic acid) - one of a structurally distinct group of drugs - is also being tested in clinical trials. A full understanding of the action of these and other VDAs will provide insights into mechanisms that control tumour blood flow and will be the basis for the development of new therapeutic drugs for targeting the established tumour vasculature for therapy.

Synthesis and cytotoxic activity of carboxamide derivatives of benzo[b][1,6]naphthyridin-(5H)ones

A previous reaction leading to 2-substituted 6-methyl-1-oxo-1,2-dihydrobenzo[b][1,6]naphthyridine-4-carboxylic acids has been extended to encompass a broad range of 2-substituents. Derived carboxamides, particularly 4-N-[2-(dimethylamino)ethyl], were tested for growth inhibitory properties. Potent cytotoxicity against murine P388 leukemia and Lewis lung carcinoma (LLTC) was retained for compounds bearing a remarkably diverse range of 2-substituents with a number having IC50 values <10 nM. Five of the new compounds were tested in vivo against subcutaneous colon 38 tumors in mice; a single dose (1.8 mg/kg) proved curative for the 2-(4-fluorophenyl) derivative, a further increase in potency over the very effective 2-methyl analogue reported previously.

Mechanisms of tumor vascular shutdown induced by 5,6-dimethylxanthenone-4-acetic acid (DMXAA): Increased tumor vascular permeability

The novel vascular targeting agent 5,6-dimethylxanthenone-4-acetic acid (DMXAA) has completed phase 1 clinical trial and has shown tumor antivascular activity in both mice and humans. We have investigated its ability to change tumor vascular permeability, relating it to tumor vascular perfusion and other responses. The murine colon 38 adenocarcinoma was grown in C57Bl wild-type mice and mice lacking expression of either tumor necrosis factor receptor-1 (TNFR1(-/-)) or TNF (TNF-/-). Tumor vascular permeability, as measured by extravasation of albumin-Evans Blue complexes 4 hr after DMXAA treatment, was significantly increased in tumor tissue in C57Bl, TNFR1-/- and TNF-/- mice but not in normal (skin) tissue. Significant linear relationships were found between increased tumor vascular permeability, decreased functioning tumor blood vessels (measured by Hoechst 33342 staining at 4 hr), increased plasma 5-hydroxyindole-3-acetic acid concentrations (as a measure of serotonin release by platelets) and the degree of induced tumor hemorrhagic necrosis. The results support the hypothesis that DMXAA increases tumor vascular permeability both directly and through the induction of other vasoactive mediators, including TNF. DMXAA might be useful clinically to potentiate the vascular permeability of other anticancer modalities such as cytotoxic drugs, antibodies, drug conjugates and gene therapy.

Thalidomide Pharmacokinetics and Metabolite Formation in Mice, Rabbits, and Multiple Myeloma Patients

PURPOSE

Thalidomide has a variety of biological effects that vary considerably according to the species tested. We sought to establish whether differences in pharmacokinetics could form a basis for the species-specific effects of thalidomide.

EXPERIMENTAL DESIGN

Mice and rabbits were administered thalidomide (2 mg/kg) p.o. or i.v., and plasma concentrations of thalidomide were measured after drug administration using high performance liquid chromotography. Plasma samples from five multiple myeloma patients over 24 hours after their first dose of thalidomide (200 mg) were similarly analyzed and all data were fitted to a one-compartment model. Metabolites of thalidomide in plasma were identified simultaneously using liquid chromatography-mass spectrometry.

RESULTS

Plasma concentration-time profiles for the individual patients were very similar to each other, but widely different pharmacokinetic properties were found between patients compared with those in mice or rabbits. Area under the concentration curve values for mice, rabbits, and multiple myeloma patients were 4, 8, and 81 micromol/L. hour, respectively, and corresponding elimination half-lives were 0.5, 2.2, and 7.3 hours, respectively. Large differences were also observed between the metabolite profiles from the three species. Hydrolysis products were detected for all species, and the proportion of hydroxylated metabolites was higher in mice than in rabbits and undetectable in patients.

CONCLUSIONS

Our results show major interspecies differences in the pharmacokinetics of thalidomide that are related to the altered degree of metabolism. We suggest that the interspecies differences in biological effects of thalidomide may be attributable, at least in part, to the differences in its metabolism and hence pharmacokinetics.

Determination of the investigational anti-cancer drug 5,6-dimethylxanthenone-4-acetic acid and its acyl glucuronide in Caco-2 monolayers by liquid chromatography with fluorescence detection: application to transport studies

5,6-Dimethylxanthenone-4-acetic acid (DMXAA) is a potent cytokine inducer, with a bioavailability of >70% in the mouse. The aim of this study was to develop and validate HPLC methods for the determination of DMXAA and DMXAA acyl glucuronide (DMXAA-G) in the human intestinal cell line Caco-2 monolayers. The developed HPLC methods were sensitive and reliable, with acceptable accuracy (85-115% of true values) and precision (intra- and inter-assay CV < 15%). The total running time was within 6.8 min, with acceptable separation of the compounds of interest. The limit of quantitation (LOQ) values for DMXAA and DMXAA-G were 14.2 and 24 ng/ml, respectively. The validated HPLC methods were applied to examine the epithelial transport of DMXAA and DMXAA-G by Caco-2 monolayers. The permeability coefficient (Papp) values (overall mean +/- S.D., n = 3-9) of DMXAA over 10-500 microM were independent of concentration for both apical (AP) to basolateral (BL) (4.0 +/- 0.4 x 10(-5)cm/s) and BL-AP (4.3 +/- 0.5 x 10(-5)cm/s) transport, and of similar magnitude in either direction, with net efflux ratio (Rnet) values of 1-1.3. However, the Papp values for the BL to AP transport of DMXAA-G were significantly greater than those for the AP to BL transport, with Rnet values of 17.6, 6.7 and 4.5 at 50, 100 and 200 microM, respectively. Further studies showed that the transport of DMXAA-G was Na+- and energy-dependent, and inhibited by MK-571 [a multidrug resistance associated protein (MRP) 1/2 inhibitor], but not by verapamil and probenecid. These data indicate that the HPLC methods for the determination of DMXAA and DMXAA-G in the transport buffer were simple and reliable, and the methods have been applied to the transport study of both compounds by Caco-2 monolayers. DMXAA across Caco-2 monolayers was through a passive transcellular process, whereas the transport of DMXAA-G was mediated by MRP1/2.

Modelling cell population growth with applications to cancer therapy in human tumour cell lines

In this paper we present an overview of the work undertaken to model a population of cells and the effects of cancer therapy. We began with a theoretical one compartment size structured cell population model and investigated its asymptotic steady size distributions (SSDs) (On a cell growth model for plankton, MMB JIMA 21 (2004) 49). However these size distributions are not similar to the DNA (size) distributions obtained experimentally via the flow cytometric analysis of human tumour cell lines (data obtained from the Auckland Cancer Society Research Centre, New Zealand). In our one compartment model, size was a generic term, but in order to obtain realistic steady size distributions we chose size to be DNA content and devised a multi-compartment mathematical model for the cell division cycle where each compartment corresponds to a distinct phase of the cell cycle (J. Math. Biol. 47 (2003) 295). We then incorporated another compartment describing the possible induction of apoptosis (cell death) from mitosis phase (Modelling cell death in human tumour cell lines exposed to anticancer drug paclitaxel, J. Math. Biol. 2004, in press). This enabled us to compare our model to flow cytometric data of a melanoma cell line where the anticancer drug, paclitaxel, had been added. The model gives a dynamic picture of the effects of paclitaxel on the cell cycle. We hope to use the model to describe the effects of other cancer therapies on a number of different cell lines.

In vitro modelling of human tumour behaviour in drug discovery programmes

Human tumour cell lines have played an important part in our understanding of cancer and have been used extensively in the discovery and characterisation of new chemotherapeutic drugs. A potential weakness of such cell lines is that they may have lost important properties originally possessed in vivo, including potential targets for therapy. This review discusses how possible differences between tumour cells in cancer patients and cell lines might be identified by the use of short-term cultures of human tumour cells taken directly from cancer tissue, termed here primary cultures. Cell-cycle time is one important difference between tumours and cell lines and it is known that the cell-cycle times of primary cultures cover the same wide range as estimated in vivo cell-cycle times. Because tumour cells have at least two pathways to cell death, one from interphase and one from mitosis, changes in cell-cycle length can modify the balance of such pathways. Responses of primary cultures to DNA-damaging drugs and inhibitors of growth factor receptors also differ from those of cell lines, suggesting that the process of developing a cell line can result in the loss of important cellular responses. Without an appreciation of these changes our ability to discover new targets for the development of improved cancer therapy may be jeopardised. The identification of cell lines that preserve potential targets is an important goal in cancer biology and research using primary cultures will help in this identification.