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P Workman

Publications and source records attributed to P Workman.

At least 127 records · Page 7Linked to original sources
PubMed1992

The impact of pharmacokinetically guided dose escalation strategies in phase I clinical trials: critical evaluation and recommendations for future studies.

Phase I studies requiring multiple dose escalation steps have led to the development of pharmacokinetically guided dose escalation (PGDE) strategies to expedite the conduct of early clinical trials. This article critically reviews PGDE strategies for a number of new anticancer agents including amphethinile, brequinar sodium, iodo-doxorubicin, the anthrapyrazoles (DuP 941, DuP 942 and DuP 937), rhizoxin, and aphidicolin glycinate. The benefits and problems associated with PGDE are examined. Recommendations are made for the optimal deployment of pharmacological information in future phase I studies.

Antineoplastic Agents↗
PubMed1992

Laboratory and phase I studies of new cancer drugs.

New drug discovery continues to follow the time-honored paths of screening and novel target identification combined with analogue development and serendipity. The agents selected here reflect these various approaches. They include drugs already showing significant antitumor activity, eg, anthrapyrazoles, temozolomide, camptothecin analogues, and taxotere, and updated information is provided on their development. Other drugs just entering or currently in phase I trials include rhizoxin, which seems capable of overcoming multidrug resistance; the novel bioreductive agent EO9 [corrected]; and bryostatin, a highly potent protein kinase C agonist. Sequence specificity could well prove to be an important factor in the development of DNA-interactive agents, and information is provided on the progress with distamycin mustard and the new cyclopropylpyrroloindole analogues carzelesin and adozelesin.

Antineoplastic Agents↗
PubMed1992

The use of parallel EEL spectral imaging and elemental mapping in the rapid assessment of anti-cancer drug localization.

Both electron spectroscopic imaging (ESI) and electron energy-loss spectroscopy (EELS) have great potential for use in several areas of cancer research. In biologically targeted radiotherapy, cytotoxic drug therapy and boron neutron capture therapy the effectiveness of many drugs is often critically dependent upon the intracellular localization of the agent employed. We describe the use of parallel EEL spectral imaging to assess the penetration and location of the iodine-containing drug meta-iodobenzyl guanidine, of potential value in targeted radiotherapy, and for the rapid detection of boron within borate-adsorbed polystyrene beads, of potential value in boron neutron capture therapy. We also describe elemental mapping of boron following low-temperature embedding. These results show how the techniques could be applied to many forms of cancer research by discussing the validity and limitations of the techniques experimentally. We also provide an outline of other areas in this field which could benefit from the future application of ESI and EELS.

3-Iodobenzylguanidine↗
PubMed1992

Tyrosine kinase inhibitors.

Tyrosine kinases are associated with the cytoplasmic domains of growth factor receptors as well as oncoproteins and many have the potential to cause transformation if mutated or hyperexpressed. Tyrosine kinases therefore represent an excellent target for the development of cancer drugs. A large number of inhibitors have now been identified and many show promising cytostatic activity, particularly using in vitro models. Some in vivo activity has been reported. Progress with various structural classes is reviewed. It is not clear whether specific or broad spectrum tyrosine kinase inhibitors should be developed as potential anticancer drugs. It does seem likely, however, that tyrosine inhibitors will enter clinical trial in cancer patients.

Drug Design↗
PubMed1992

Further examination of 9-alkyl- and sugar-modified anthracyclines in the circumvention of multidrug resistance.

Anthracyclines possessing either a 9-alkyl modification in the A-ring of the tetracyclic aglycone and/or specific changes to the amino sugar moiety retain effective cytotoxic activity against multidrug resistant (MDR) cell lines. To obtain a better understanding of the structural features responsible for this potentially valuable behaviour, we used the MTT tetrazolium dye reduction assay to calculate resistance factors (RF = the ratio of ID50 for the drug-resistant line to that for the parental line) for the EMT6/P mouse mammary tumour and its MDR variant EMT6/AR1.0, and the H69/P human small cell lung cancer line and its MDR counterpart H69/LX4. Both MDR lines exhibit marked resistance to doxorubicin, MDR 1 gene amplification, hyperexpression of the membrane P-glycoprotein and reduced drug accumulation. RF values for doxorubicin were 34 and 131 in the EMT6 and H69 cell line pairs, respectively. The 9-alkyl-substituted anthracyclines were confirmed as having RF values 9- to 15-fold lower than those for doxorubicin. The 9-ethyl analogues Ro 31-1966 (RF for EMT6 2.2, RF for H69 4.7) and Ro 31-1749 (RF for EMT6 3.9, RF for H69 9.5) were superior to the previously studied 9-methyl analogue Ro 31-1215 (RF for EMT6 8.1 RF for H69 12.4). A clear trend for RF values to decrease with increasing 9-alkyl chain length was also noted in the structurally more complex aclacinomycin series. For example, 13-methyl-aclacinomycin (RF for EMT6 1.0, RF for H69 2.2) featuring a 9-isopropyl moiety was superior to the 9-alkyl-containing aclacinomycin A (RF for EMT6 4.7, RF for H69 5.8), and this was in turn more effective than the 9-methyl analogue sulfurmycin A (RF for EMT6 6.4, RF for H69 14.2). The trisaccharide moiety was not an essential feature for activity against MDR lines in the aclacinomycins, as shown by the low RF value with aklavine (RF for EMT6 2.1, RF for H69 2.5). However, a small change in one of the sugar moieties of aclacinomycin A, as in marcellomycin, resulted in a considerable increase in RF values (RF for EMT6 18.5, RF for H69 25.3). The complex anthracyclines AD 32 (RF for EMT6 6.5, RF for H69 11.7) and particularly tetrahydropyranyl-doxorubicin (RF for EMT6 1.4, RF for H69 3.2) were effective against MDR lines.(ABSTRACT TRUNCATED AT 400 WORDS)

Aclarubicin↗
PubMed1991

Multiparametric flow cytometry of the modulation of tumor cell membrane permeability by developmental antitumor ether lipid SRI 62-834 in EMT6 mouse mammary tumor and HL-60 human promyelocytic leukemia cells.

(+-)-2-[Hydroxy[tetrahydro-2-(octadecyloxy)methylfuran-2- yl]methoxyl]phosphinyloxy-N,N,N-trimethylethaniminium hydroxide, inner salt (SRI 62-834) is a tetrahydrofuran analogue of platelet activating factor (PAF) that is currently entering clinical trial. Like other ether lipids it is of interest as a membrane-active antitumor agent. Here, we have used two-color multiparameter flow cytometry to study simultaneously its effects on cell membrane permeability, intracellular pH, and cell size/structure of EMT6 mouse mammary tumor cells and HL-60 human promyelocytic leukemia cells in vitro. Concentrations as low as 1 microM up to 100 microM SRI 62-834 caused a rapid, dose-dependent increase in membrane permeability, initially towards outward efflux of the preloaded fluorescein probe bis(carboxyethyl)carboxyfluorescein (green fluorescence) and then towards influx of extracellular propidium (red fluorescence). At the same time, median cell size from light scatter was reduced with an increased coefficient of variation, and the proportion of cell debris was elevated. In vitro antitumor activity was seen over the same concentration range, as measured by tetrazolium dye reduction and cell growth curves. Neither low concentrations of PAF (50 nM) nor the potent PAF antagonist 3-[4-(2-chlorophenyl)-9-methyl-6H-thieno[3,2-f][1,2,4]tria- zolo[4,3a][1,4]diazepin-2-yl]-1-(4-morpholinyl)-1-propanone (0.5-100 microM) had any influence on the membrane effects of SRI 62-834, and at higher concentrations (1-200 microM) PAF mimicked the behavior of SRI 62-834. In addition, the PAF antagonist did not modulate the cytotoxicity of SRI 62-834 or PAF. HL-60 cells were more sensitive to SRI 62-834 than were EMT6 cells in terms of both cytotoxicity and membrane permeability. However, PAF was more potent than SRI 62-834 in causing membrane permeabilization with both cell lines, whereas PAF was less active than SRI 62-834 in cytotoxicity assays. The results support a membrane-damaging role in the cytotoxicity of SRI 62-834 but suggest that additional factors are also involved. Membrane permeabilization may be related to its reported effects on protein kinase C-dependent intracellular calcium signaling but apparently does not involve a conventional PAF receptor in HL-60 or EMT6 cells.

Animals↗
PubMed1991

Pharmacokinetic contribution to the improved therapeutic selectivity of a novel bromoethylamino prodrug (RB 6145) of the mixed-function hypoxic cell sensitizer/cytotoxin alpha-(1-aziridinomethyl)-2-nitro-1H-imidazole-1-ethanol (RSU 1069).

RB 6145 is a novel hypoxic cell sensitizer and cytotoxin containing both an essential bioreductive nitro group and a bromoethylamino substituent designed to form an alkylating aziridine moiety under physiological conditions. In mice, RB 6145 is 2.5 times less toxic but only slightly less active than the aziridine analogue RSU 1069, giving rise to an improved therapeutic index. However, the mechanism for the enhanced selectivity is not clear. Reasoning that this may lie in a more beneficial pharmacokinetic profile, we investigated the plasma pharmacokinetics, tissue distribution and metabolism of RB 6145 in mice using a specially developed reversed-phase HPLC technique. An i.p. dose of 190 mg kg-1 (0.5 mmol kg-1) RB 6145 produced peak plasma concentrations of about 50 micrograms ml-1 of the pharmacologically active target molecule RSU 1069 as compared with levels of around twice this value that were obtained using an equimolar i.p. dose of RSU 1069 itself. The plasma AUC0-infinity value for administered RSU 1069 was ca. 47 micrograms ml-1 h and that for the analogue RSU 1069 was ca. 84 micrograms ml-1 h. No prodrug was detectable. Another major RB 6145 metabolite in plasma was the corresponding oxazolidinone, apparently formed on interaction of the drug with hydrogen carbonate. The oxazolidinone initially occurred at higher concentrations than did RSU 1069, with the levels becoming very similar from 30 min onwards. Post-peak plasma concentrations of both RB 6145 metabolites declined exponentially, displaying an elimination t1/2 of ca. 25 min, very similar to the 30-min value observed for injected RSU 1069. The plasma AUC0-infinity value for the metabolite RSU 1069 was about 1.3 and 1.6 times higher following i.p. injection of 95 mg kg-1 (0.25 mmol kg-1) of the prodrug as compared with administration via the oral and i.v. routes, respectively. After i.v. injection, peak levels of the oxazolidinone metabolite were twice those observed following both i.p. and oral dosing and possibly contributed to the acute toxicity. After an i.p. dose of 190 mg kg-1 RB 6145, concentrations of RSU 1069 and the oxazolidinone metabolites rose to 40% and 33%, respectively, of the ambient plasma level in i.d. KHT tumours. The peak level of metabolite RSU 1069 was ca. 6 micrograms g-1 as compared with 10 micrograms g-1 following an equimolar dose of RSU 1069 itself; the tumour AUC0-infinity value for the metabolite RSU 1069 was some 35% lower.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1991

Lack of stereoselectivity in the pharmacokinetics and metabolism of the radiosensitizer Ro 03-8799 in man.

During a clinical toxicity study it was possible to obtain urine samples from six patients receiving either the R-(-)- or S-(+)-stereoenantiomeric forms of the developmental 2-nitroimidazole radiosensitizer Ro 03-8799 (pimonidazole). Paired plasma samples were also obtained from four patients. The pharmacokinetic data were compared with those for the racemic mixture in the same individuals. The results revealed no major differences in the plasma pharmacokinetics, urinary clearance or N-oxidation of the individual enantiomers as compared with the racemic mixture. A similar lack of stereoselectivity with respect to the acute dose-limiting CNS toxicity syndrome suggests that this may not involve a specific CNS receptor interaction.

Adenocarcinoma↗
PubMed1991

The combination of multiple doses of etanidazole and pimonidazole in 48 patients: a toxicity and pharmacokinetic study.

The two radiosensitizers etanidazole and pimonidazole, currently in clinical phase 3 trials, have different toxicities. The former produces a peripheral neuropathy after cumulative doses and the latter presents an accurate but transient central nervous system syndrome after each dose. A strategy for improving on the maximum radiosensitization achievable using either drug alone, has been investigated in the study reported in this paper. Escalating doses of the two drugs were given together to determine toxicity up to a maximum of 15 doses of 2.0 g/m2 etanidazole and 0.75 g/m2 pimonidazole/dose. 25 neuropathies were seen in the total of 48 patients (48%). This included 6 grade 2 neuropathies (12.5%) or 15% of those receiving 9 or more infusions. There were no significant correlations between the incidence of neuropathy and various dose and AUC parameters for the 31 patients receiving 10 or more infusions. However, in the selected group of 26 patients planned to receive multiple doses of etanidazole at 2 g/m2/dose with pimonidazole at 0.75 g/m2, significant correlations were seen with the cumulative dose, with single and cumulative AUCs for pimonidazole and also for the cumulative dose and the cumulative AUC for etanidazole, but not its single AUC. In the light of these observations and the recent reports of higher peripheral neuropathy rates than previously reported in studies in the USA, it is concluded that it is not possible at this time to determine whether there is toxicity interaction between the two drugs. There remains the possibility that, on the basis of the combined drug dosage achieved, an increased therapeutic efficacy can be reached with either drug alone.

Adult↗
PubMed1991

Retention of activity by selected anthracyclines in a multidrug resistant human large cell lung carcinoma line without P-glycoprotein hyperexpression.

A subline (COR-L23/R) of the human large cell lung line [corrected] COR-L23, derived by in vivo exposure to doxorubicin, exhibits an unusual multidrug resistant (MDR) phenotype. This subline shows cross-resistance to daunorubicin, vincristine, colchicine and etoposide but does not express P-glycoprotein. Interestingly, COR-L23/R [corrected] shows little or no resistance to a range of structurally-modified analogues of doxorubicin comprising 9-alkyl and/or sugar modified anthracyclines. We have previously identified these same compounds as effective agents against P-glycoprotein-positive MDR cell lines. In contrast to typical MDR cell lines, COR-L23/R [corrected] shows only minimal chemosensitisation by verapamil and no collateral sensitivity to verapamil. Compared to the parental cell line, COR-L23/R [corrected] displays reduced accumulation of doxorubicin and daunorubicin. Accumulation defects were apparent only after 0.5-1 h of incubation of cells with these agents. The rate of daunorubicin efflux was shown to be enhanced by COR-L23/R [corrected] and this efflux was demonstrated to be energy-dependent. The use of anthracyclines which retain activity in MDR cells thus appears to be a valid approach for the circumvention of MDR, not only in cells which express P-glycoprotein, but also where defective drug accumulation is due to other mechanisms possibly involving an alternative multidrug transporter.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1991

The role of NAD(P)H: quinone reductase (EC 1.6.99.2, DT-diaphorase) in the reductive bioactivation of the novel indoloquinone antitumor agent EO9.

EO9 [3-hydroxymethyl-5-aziridinyl-1-methyl-2-(H-indole-4, 7-indione)-propenol] is a novel indoloquinone structurally related to mitomycin C, a quinone anticancer drug that requires reductive bioactivation. NAD(P)H: (quinone-acceptor) oxidoreductase (quinone reductase, DT-diaphorase, EC 1.6.99.2) is an obligate 2-electron donating enzyme that can reduce a variety of quinones resulting either in bioactivation or bioprotection. Using quinone reductase (QR) preparations from rat Walker 256 mammary tumor cells and human HT29 colon carcinoma cells, we have characterized the role of this enzyme in EO9 reductive metabolism. QR activity was assayed under optimal conditions by following cytochrome c reduction at 550 nm in the presence of enzyme, quinone substrate, NADH, and bovine albumin, and confirmed by loss of EO9 absorbance at 550 nm. Both the rat and human tumor cell enzymes catalyzed reduction of the benchmark quinone menadione with a similar Km of 1.4-3.1 microM, although the Vmax was 7 to 8-fold lower for the human preparation. EO9 was readily reduced by the rat Walker QR. The mean Km was about 5-fold higher than for menadione at around 15 microM and the Vmax was 6-fold lower at around 2.5 mumol of cytochrome c reduced mg-1 of protein. EO9 was also metabolized by QR from HT29 human colon carcinoma cells but rather less efficiently than by the rat tumor enzyme. For example, the rate was 6-fold lower than that for the Walker tumor enzyme at 100 microM substrate concentration after correcting for the 7- to 8-fold difference in specific activity for the two preparations.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Gradient high-performance liquid chromatographic assay for the determination of the novel indoloquinone antitumour agent E09 in biological specimens.

A high-performance liquid chromatographic method for the determination of the novel indoloquinone antitumour agent E09, 3-hydroxymethyl-5-aziridinyl-1-methyl-2-(1H-indole-4,7-dione)prop-beta-e n-alpha - ol, in mouse plasma and urine is described. Following protein precipitation by means of methanol (2 volumes), separation and quantification of parent drug, metabolites and internal standard E012 (5-morpholine substituted analogue) were achieved on a 5-microns Resolve C18 Rad-Pak with a 15-min linear gradient of 10-30% acetonitrile in a 0.02 M pH 7.4 sodium phosphate buffer with UV detection at 280 and 310 nm. The utility of the assay is also demonstrated for the aziridine ring-opened analogue E05A. 3-hydroxymethyl-5-beta-hydroxyethylamino-2-(1H-indole-4,7-dione)pr op-beta-en- alpha-ol. Plots of area ratios of analytes versus internal standard were linear in the range 50-15,000 ng/ml. The detection limit for indoloquinones in plasma was ca. 30 ng/ml. The within-assay and day-to-day variation were consistently lower than 12.5%. The assay was applied in preliminary pharmacokinetic investigations. One minor metabolite of E09 could be identified; further metabolites were characterized by ultraviolet-visible spectra.

Animals↗