Biomedical subjects

J A Double

Publications and source records attributed to J A Double.

At least 55 records · Page 3Linked to original sources

PubMed1992

In vitro activity of the novel indoloquinone EO-9 and the influence of pH on cytotoxicity.

The novel indoloquinone compound EO-9 is shortly to undergo phase I clinical evaluation as a potential bioreductive drug. Preclinical studies have shown that EO-9 has greater activity against cells derived from human solid tumours than leukaemias in vitro. The results of this study extend the preclinical data available on EO-9 by demonstrating that EO-9 induces a broad spectrum of activity (IC50 values range from 8 to 590 ng ml-1) against a panel of human and murine tumour cell lines. Some evidence exists of selectivity towards leukaemia and human colon cell lines as opposed to murine colon cells. The response of cells to Mitomycin C were not comparable to EO-9 suggesting that the mechanism of action of these compounds is different. The cytotoxic properties of EO-9 under aerobic conditions are significantly influenced by extracellular pH. Reduction of pH from 7.4 to 5.8 increases cell kill from 40% to 95% in DLD-1 cells. In addition, EO-9 is unstable at acidic pH (T1/2 = 37 min at pH 5.5) compared to neutral pH T1/2 = 6.3 h). The major breakdown product in vitro was identified as EO-5A which proved relatively inactive compared to EO-9 (IC50 = 50 and 0.6 ug ml-1 respectively). These studies suggest that if EO-9 can be delivered to regions of low pH within solid tumours, a therapeutic advantage may be obtained.

Animals↗

PubMed1991

The relationship between the in vitro chemosensitivity of tumor cells and tumor response in vivo in an experimental tumor model.

Cell lines derived from a panel of five histologically distinct murine adenocarcinomas of the colon (MAC) were used to assess whether or not a colony-forming assay could have retrospectively predicted the wide range of in vivo responses to chlorambucil (CHL). The predictive value of the clonogenic assay was significantly improved when fractions (one-tenth) of the plasma drug AUC (from the area under the drug clearance curves); were used to determine clonogenic cell kill in vitro, instead of one-tenth peak plasma drug concentration and total plasma drug AUC exposures. Despite the good correlation between in vitro and in vivo responses observed, the clonogenic assay could not forecast the site-dependent response of MAC 15A to CHL. These site-dependent responses cannot be explained in terms of the inherent sensitivity of tumor cells themselves, suggesting that caution must be applied in the interpretation of in vitro chemosensitivity assays.

Animals↗

PubMed1991

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.

Adenocarcinoma↗

PubMed1991

The relationship between tissue levels of flavone acetic acid (NSC 347512) and site dependent anti-tumour activity in murine colon tumours.

Flavone acetic acid (FAA) is extremely active against subcutaneous transplantable tumours in mice, but disappointingly there has been no demonstrable clinical activity. Previous studies have shown that lung tumour deposits are less responsive than the same cells implanted subcutaneously. The aim of this study is to examine the tissue disposition of FAA in an attempt to explain this site-dependent activity. The data show clearly that FAA clearance curves are influenced by the presence of MAC 15A tumours growing either subcutaneously or systemically. The decreased clearance of FAA from MAC 15A tumour bearing animals does not however explain the resistance of lung deposits. Neither can this be explained by differences in metabolism in these different sites. Cytotoxic metabolites have not been detected either in vitro or in vivo and their role in the mechanism of action of FAA is questionable.

Adenocarcinoma↗

PubMed1990

A critical appraisal of the predictive value of in vitro chemosensitivity assays.

The ultimate value of a screening program based on the response of cell lines in vitro will depend on the demonstration of a strong correlation between in vitro and in vivo responses to cytotoxic drugs. However, marked discrepancies in the predictive value of in vitro chemosensitivity assays have been described, suggesting that factors other than the inherent chemosensitivity of tumor cells significantly influence the outcome of chemotherapy in vivo. These factors include the influence of drug pharmacokinetics and metabolism, together with numerous problems associated with the biology of solid tumors in vivo (e.g., drug penetration barriers, proliferation gradients, and microenvironmental conditions). These additional factors may be highly significant in explaining the site-dependent nature of the responses of solid tumors to cytotoxic drugs, the poor prediction of responses in experimental tumor models, and the differences in the responses of multicellular spheroids and monolayers. These discrepancies suggest that the selection of compounds for phase II clinical trials on the basis of disease-specific activity in vitro may be premature.

Animals↗

PubMed1989

Therapeutic index: a vital component in selection of anticancer agents for clinical trial.

In an attempt to identify anticancer agents more active in the major groups of solid cancers, the National Cancer Institute has replaced the primary murine tumor systems with an in vitro system using human cancer cell lines. A broader approach is being followed in Europe, where considerable reliance will still be placed on data from animal tumor systems. We argue the case for broader preclinical evaluation using animal model systems that are resistant to standard anticancer agents and thus reflect the clinical disease. Selection of compounds for clinical trials should be based on a therapeutic index that will give a more realistic representation of the margin between antitumor activity and toxicity to normal cells. Furthermore, preclinical evaluation can establish understanding of the factors responsible for treatment efficacy, including pharmacokinetics, metabolism, and drug bioavailability.

Animals↗

PubMed1989

Characterization of the major metabolites of flavone acetic acid and comparison of their disposition in humans and mice.

Flavone acetic acid represents a novel chemical structure currently undergoing clinical investigation. Broad spectrum activity has been observed in preclinical animal screens, but at doses close to toxic in mice. Phase I clinical trials have established that equivalent plasma drug levels can be achieved in humans, but to date Phase II trials have not demonstrated significant activity in a range of tumor types. Little is known about the drug's biotransformation, although metabolites have been implicated in proposed mechanisms of action. In this paper, we have purified the two major human metabolites present in urine (also the only two metabolites detected in plasma) and characterized their structure, chemical properties, activity, and pharmacokinetics. Metabolite 1 (M1) was a glucuronide conjugated to the 8-acetic acid grouping (Mr 456), was chemically labile, and showed a strong tendency to undergo chemical rearrangement at mildly alkaline pH. Metabolite 2 (M2) was also a glucuronide (Mr 456) but appeared to be an unusual isomer of M1. Both were noncytotoxic. In patients, biotransformation represented the predominant mechanism of drug clearance with as much as 80% of a low dose (0.5 g/m2) recovered in urine as M1 and M2 after only 6 h. At high dose (4.8 to 8.6 g/m2, 1- to 6-h infusion) the appearance of peak concentrations of metabolites in plasma and urine was delayed, apparently due to saturation of glucuronidation pathways. This resulted in an overall reduction in drug clearance by 3- to 4-fold. Mice cleared flavone acetic acid much more slowly than patients (289 ml/h/m2 after 600 mg/m2 i.p. versus 2.3 liters/h/m2 after 4.8 g/m2-1-h i.v. infusion) without producing M1 or M2. A different metabolite, exhibiting characteristics of a conjugate, was detected at low concentrations in plasma, tissues, and tumor. Extensive metabolism to inactive products followed by their rapid clearance may contribute to the lack of activity so far seen in humans.

Animals↗

PubMed1989

Reduction of tumor blood flow by flavone acetic acid: a possible component of therapy.

Flavone acetic acid (FAA) is active against normally refractory murine sc tumors. Clinical studies are disappointing despite achievement of plasma profiles associated with the antitumor murine activity in man. To clarify the mechanism of action, we have followed histologic changes, tumor blood volume, and drug concentrations in a well-differentiated, slow-growing cystic adenocarcinoma in mice. FAA causes massive tumor necrosis beginning 2 hours after treatment. Tumor plasma volumes are reduced by 2 hours after treatment and tumor blood vessels are shutdown, which suggests that tumor vasculature plays a role in the dramatic response of sc tumors in pure-strain male NMRI mice.

Adenocarcinoma↗

PubMed1989

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.

Adenocarcinoma↗

PubMed1989

Synthesis, mechanism of action, and biological evaluation of mitosenes.

Mitosenes of both the pyrrolo- and pyrido[1,2-a]indole type have been prepared via modification of these heterotricyclic compounds. Several mitosenes have been studied for their reactions with nucleophiles under reductive conditions. The results of these experiments show that the biological activity of mitosenes is based on the mechanism of bioreductive activation. When both leaving groups at C-1 and C-10 in the mitosene are the same, the nucleophile preferably adds to C-10 under reductive conditions. All mitosenes were studied for their biological activities in vitro against L1210, WiDr, and A204. On the basis of these results a selection of three mitosenes was made for a more detailed biological evaluation. Several tumor model systems were used, viz. P388, human tumor xenografts, MAC 13, and MAC 16. The results of these studies show that mitosenes have a more limited range of activities than mitomycin C. Surprisingly, the in vivo activities of mitosene diol 8b and mitosene diacetate 10b against the gastric human tumor xenograft GXF 97 were very high and comparable with that of mitomycin C.

Animals↗

PubMed1989

Nucleoside analogues: 8. Some isomers of B.3839, the original 5-fluorouracil/nitrosourea molecular combination, and their effect on colon, breast and lung tumours in mice.

This study describes the manipulation of secondary products arising from the synthesis of the prototypical molecular combination of 5-fluorouracil (5-FU) and chloroethylnitrosourea (CNU), B.3839, in order to investigate the effects produced by connecting the C-S-C-C-CNU chain to the 5-FU ring in different ways. The isolation of phthalimide precursors of these compounds and the transformation into CNUs is described. Anti-tumour activity of these molecular combinations against a series of experimental murine colon, lung and mammary tumours is presented. The spectrum of anti-tumour activity displayed is interesting but defies simple explanation without further detailed in vivo pharmacokinetic and metabolism studies in order to define optimal profiles for activity.

Adenocarcinoma↗

PubMed1989

Nucleoside analogues. 9. Seco-nucleoside analogues of some 5-fluorouracil/nitrosourea molecular combinations having uracil as base: synthesis and anti-tumour activity.

The synthesis of representative seco-nucleoside analogues of 5-fluorouracil (5-FU)/nitrosourea molecular combinations having uracil (U) as base instead of 5-FU is described. The anti-tumour activity of corresponding pairs of drugs is compared in experimental tumours of the mouse colon, lung and breast. These studies have demonstrated that the presence of a hydrogen or fluorine atom at pyrimidine C-5 is unimportant for the activity shown against most of the experimental tumours employed, rather that the pyrimidine cyclic urea and/or alkylthio functionalities may constitute the critical factors. One exception is the prototypical compound B.3839 and its U analogue B.3912. B.3839 is highly active against colon 38 adenocarcinoma, a tumour which is highly responsive to 5-FU, whereas most of the activity is lost in B.3912. The 5-FU release profile of some of these molecular combinations could be adequate or effective in treatment of slow-growing clinical tumours.

Adenocarcinoma↗

PubMed1989

Nucleoside analogues: 7. Effect on colon, breast and lung tumours in mice of 5-fluorouracil/nitrosourea molecular combinations incorporating alkoxy and oxidized sulphur functions.

This study considers further changes in the carrier moiety of molecular combinations of the pyrimidine antimetabolite 5-fluorouracil (5-FU) and the alkylating group chloroethylnitrosourea (CNU). Detailed chemical syntheses are described of compounds incorporating (a) a simpler alkoxy group in the 'sugar' fragment, (b) attachment of the 5-FU residue to the C-X-C-C chain on the side of the heteroatom X distal from the CNU group, and (c) higher oxidation states of the sulphur atom in the prototypical compound B.3839. Anti-tumour activity of these analogues against a series of experimental murine colon, lung and mammary tumours is described. The pattern of activity reveals that the carrier moiety is important but further pharmacokinetics and metabolism studies are required to determine structure-activity relationships.

Adenocarcinoma↗

PubMed1988

Experimental correlations of in vitro drug sensitivity with in vivo responses to ThioTEPA in a panel of murine colon tumours.

Cell lines derived from three histologically different murine colon tumours (MAC) were used to assess whether or not a tumour colony-forming assay could have retrospectively predicted the wide range of in vivo responses to the alkylating agent, ThioTEPA. Tumour responses ranged from sensitive (MAC 26) to resistant (MAC 15A), with MAC 13 showing only moderate sensitivity. In vitro chemosensitivity studies, in conjunction with pharmacokinetic data, suggest that plasma levels of the drug's primary metabolite, TEPA, should be sufficient to induce significant cell kills in all three tumour lines in vivo. Preliminary studies on the effect of pH on the cytotoxic properties of ThioTEPA in vitro have demonstrated an improved cell kill when cells were exposed to the drug under acidic conditions. As these tumours differ histologically in terms of vascularisation, tumoural pH may play an important part in determining drug efficacy and go some way towards explaining the poor in vitro/in vivo correlation in this model.

Adenocarcinoma↗

PubMed1988

Effects of routes of administration of TCNU on its plasma, tissue and tumour concentrations.

Tissue and plasma samples were taken from normal and tumour bearing mice at various time intervals following a dose of 30 mg kg-1 TCNU given by various routes. TCNU levels were measured by HPLC. The results show that the route of administration influences plasma concentrations, bioavailability and tissue and tumour concentrations. Intravenous administration gave 100% plasma bioavailability but only 15% of this level was seen following oral administration with consequently lower levels in tissues and tumours. The effect of gastric contents played a major role in this reduced bioavailability and plasma levels increased to 65% following overnight fasting. The differences in concentrations of TCNU observed here in plasma, tumour and normal tissues after oral and intravenous administration may have important clinical implications and may influence both anti-tumour activity and toxicity.

Adenocarcinoma↗

PubMed1988

Anti-tumour activity of TCNU in a panel of transplantable murine colon tumours.

The novel nitrosourea, 1-(2-chloroethyl)-3-[2-(dimethylaminosulphonyl)ethyl]-1-nitrosoure a (TCNU) is active against a panel of three transplantable murine adenocarcinomas of the colon of varying growth characteristics and morphology (MAC system). It shows greater activity than previously tested nitrosoureas in this system and the routes of administration of TCNU do not significantly alter its anti-tumour activity. These data suggest that TCNU may be useful in the management of large bowel cancer as the MAC system has been previously shown to be a good model of human disease.

Adenocarcinoma↗

PubMed1988

In vitro and in vivo responses of a panel of murine colon tumours to TCNU: a positive correlation.

TCNU is highly active against a panel of three histologically distinct transplantable murine adenocarcinomas of the colon (MAC tumours). Significant reductions in colony formation (greater than 70%) were observed in vitro in all three cell lines following a 1 h exposure to TCNU at experimentally achievable drug C X t values. A good correlation exists between in vivo tumour responses and in vitro cell responses in all cases. Dose-response curves generated at increasing exposure times suggest that no active or long lived products of TCNU are formed as a result of the drug's spontaneous breakdown in vitro (rate of breakdown was 0.078 micrograms min-1 at 37 degrees C). Preliminary studies with the HT-29 human colon cell line have demonstrated that multi-cellular spheroids are more responsive to TCNU (2 X) than the same cells cultured as monolayers.

Animals↗

PubMed1988

The logistics of broader pre-clinical evaluation of potential anti-cancer agents with reference to anti-tumour activity and toxicity of mitozolomide.

Anti-tumour responses with CCRG81010, M & B 39565, NSC 353451, 8-carbamoyl-3-(2-chloroethyl)imidazo [5,1-d]-1,2,3,5-tetrazin-4(3H)-one (Mitozolomide) in a panel of 4 murine colon tumours of varying growth characteristics and chemosensitivity and a spontaneous murine lymphoma are similar to those seen with standard nitrosoureas. The moderately well differentiated colon adenocarcinoma MAC 16 is nonresponsive to mitozolomide and methylCCNU. Responses in the other 4 lines studied are only achieved near to maximum tolerated dose and at this level there is severe host toxicity. Haemopoietic toxicity is clearly demonstrated by analysis of peripheral blood counts and by CFU-S assays and severe testicular and ovarian toxicity was also seen at dose levels necessary to achieve anti-tumour effects. Using mitozolomide as an example, the study has demonstrated the feasibility of conducting simple but thorough toxicity evaluation for the determination of the therapeutic index. This approach would provide invaluable guidelines for the selection for clinical trial of the most appropriate members of a series of new cytotoxic compounds.

Adenocarcinoma↗