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H M Coley

Publications and source records attributed to H M Coley.

At least 19 recordsLinked to original sources
PubMed2000

Copper bis(diphosphine) complexes: radiopharmaceuticals for the detection of multi-drug resistance in tumours by PET.

Experience with imaging of the multi-drug resistance (MDR) phenotype in tumours using technetium-99m sestamibi, a substrate of the P-glycoprotein (Pgp) transporter, suggests that better quantification of images and separation of MDR from other variables affecting tracer uptake in tumours are required. One approach to these problems is the development of short half-life positron-emitting tracers which are substrates of Pgp. Several lipophilic cationic copper(I) bis(diphosphine) complexes labelled with copper-64 have been synthesised and evaluated in vitro as substrates for Pgp. The synthesis is rapid and efficient with no need for purification steps. The chemistry is suitable for use with very short half-life radionuclides such as copper-62 (9.7 min) and copper-60 (23.7 min). Incubation of the complexes with human serum in vitro showed that they are sufficiently stable in serum to support clinical imaging, and the more lipophilic members of the series are taken up rapidly by cells (Chinese hamster ovary and human ovarian carcinoma) in vitro with great avidity. Uptake in human ovarian carcinoma cells is significantly reduced after several months of conditioning in the presence of doxorubicin, which induces increased Pgp expression. Uptake in hooded rat sarcoma (HSN) cells, which express Pgp, is significantly increased in the presence of the MDR modulator cyclosporin A. Biodistribution studies in hooded rats show rapid blood clearance, excretion through both kidneys and liver, and low uptake in other tissues. The one complex investigated in HSN tumour-bearing rats showed uptake in tumour increasing up to 30 min p.i. while it was decreasing in other tissues. We conclude that diphosphine ligands offer a good basis for development of radiopharmaceuticals containing copper radionuclides, and that this series of complexes should undergo further evaluation in vivo as positron emission tomography imaging agents for MDR.

Animals↗
PubMed2000

Incidence of P-glycoprotein overexpression and multidrug resistance (MDR) reversal in adult soft tissue sarcoma.

Multidrug resistance (MDR) is a widespread problem in the treatment of neoplastic diseases and may limit the effectiveness of treatment of adult soft tissue sarcomas (STS). We examined the levels of expression of the MDR marker P-glycoprotein (Pgp) in fresh, surgical material and matched paraffin-embedded tissue using MRK-16 and JSB-1 monoclonal antibodies. Using fresh tumour material in short-term culture an assessment of doxorubicin sensitivity (MTT assay) and MDR modulation using PSC-833 in daunorubicin (DNR) accumulation experiments (FACS analysis) was carried out. 44 patients were studied at various disease stages with a mean follow-up duration of 487 days (range: 45-1095 days). Immunocytochemistry and immunohistochemistry showed 62% and 58%, respectively, of STS samples were positive for Pgp. Patients showing negative Pgp expression had a median survival of 544 days versus 431 days for Pgp-positive patients (P=0.311), with disease-free survival medians of 508 and 355 days, respectively (P=0.203). In vitro doxorubicin sensitivity was not informative in this respect and there was no apparent relationship between this and Pgp expression. Eleven out of 29 samples evaluated for MDR modulation showed enhanced tumour cell DNR accumulation. However, the effects of PSC-833 on drug accumulation in clinical material were modest compared with those seen for MDR cell lines, with a maximum of only 20% enhancement. Moreover, there was no relationship between the extent of PSC-833 effects on accumulation and the levels of Pgp seen in the STS samples. Nevertheless, we show evidence that a proportion of cases of STS express moderate to high levels of Pgp. There may be a role for MDR modulating agents in association with doxorubicin in the treatment of these tumours, either in the adjuvant setting or at first relapse.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1997

N-(Hydroxymethyl) melamines.

1. The N-(hydroxymethyl) melamines are analogs of the antitumor agent hexamethylmelamine (HMM) which do not require bioactivation to exert their antitumor effects. 2. Trimelamol (N2,N4,N6-trihydroxymethyl-N2,N4,N6-trimethylmelamine; TM) was developed as a water-soluble antitumor agent for intravenous administration. 3. Phase I and II trials of TM showed promising activity versus platinum-refractory ovarian cancer, but unfortunately further clinical development was halted due to formulation difficulties. 4. Stable analogs of TM were synthesized in an effort to overcome this shortcoming and these were evaluated in a number of in vitro and in vivo studies. 5. While the stable analogs showed good in vitro cytotoxicity in tumor cell lines, only one analog, CB7646 [bis-N-(hydroxymethyl)trimethylmelamine], showed comparable in vivo antitumor activity to that seen for TM. 6. Both TM and CB7646 were curative in human ovarian and breast cancer xenograft models, including the HX110P ovarian cancer xenograft with acquired resistance to carboplatin. 7. As CB7646 possesses favorable formulation characteristics, relating to its superior stability over that for TM, it is currently being developed for phase I clinical trial. 8. The N-(hydroxymethyl) melamines are capable of overcoming many forms of drug resistance, based on data obtained in in vitro and in vivo studies, and thus show promise as agents in the treatment of heavily pretreated, refractive tumors.

Altretamine↗
PubMed1997

Drug resistance studies using fresh human ovarian carcinoma and soft tissue sarcoma samples.

The relevance of continuous cell line cultures to the problem of clinical anticancer drug resistance is unclear. There is also mounting scepticism regarding the use of tumour cell lines with in vitro acquired drug resistance, possessing high levels of resistance unlikely to be seen in the clinical setting. To overcome some of these problems we have initiated a study of drug resistance using fresh tumour material obtained from patients suffering from ovarian cancer and soft tissue sarcoma (STS). Studies involving ovarian cancer have involved over 30 specimens of stage III-IV disease. For these samples we have specifically focused on the multidrug-resistant (MDR) phenotype, examining the role of proteins P-glycoprotein (Pgp), multidrug resistance-protein (MRP) and lung-resistance-associated protein (LRP). Techniques have involved chemosensitivity testing, immunocytochemistry and flow cytometry, to measure Pgp function (drug efflux capacity with modulator reversal). Pgp was the most commonly expressed marker and its expression correlated with survival. MDR modulation using cyclosporins was shown to chemosensitise a proportion of the samples. Hence, in vitro screening can help to identify patients likely to benefit from resistance reversal strategies. Studies involving STS have looked at a combination of MDR and p53 disruption (commonly seen in this disease). Data have been examined alongside clinical data and the course of disease has been closely monitored. Although our studies are ongoing, we have identified a group of patients with aggressive disease showing marked drug resistance in vitro. All patients have relapsed with persistent disease following chemotherapy or radiotherapy. A number of chemoresistant patients showed a combination of p53 disruption in the presence of an MDR phenotype. Feedback from these translational studies should be used to guide the selection of patients for clinical trials using resistance reversal strategies and may suggest new targets for drug development.

Drug Resistance, Neoplasm↗
PubMed1996

Pre-clinical development of the anti-tumour agent CB 7646, bis N-(hydroxymethyl) trimethylmelamine, a stable analogue of trimelamol.

Formulation difficulties prevented the otherwise promising clinical development of the anti-tumour agent trimelamol (TM; tris-[hydroxymethyl]trimethylmelamine]). A synthetic analogue programme resulted in the identification of CB 7646 (bis N-[hydroxymethyl]trimethylmelamine) as a compound with improved stability and favourable formulation characteristics. The in vitro and in vivo activity of CB 7646 was shown to be very similar to that of TM. In addition, curative activities were shown in the PXN/65 human ovarian cancer xenograft and the MX-1 and T-61 human breast cancer xenograft models. The effectiveness of the N-(hydroxymethyl)melamines against platinum-refractory disease was noted in the phase I clinical trial of TM. In line with this finding, the present study confirmed the effective activity of both TM and CB 7646 against various forms of platinum resistance in in vitro models. Curative activity for TM and CB 7646 was seen in the HX110P human ovarian cancer xenograft with acquired carboplatin resistance. Animal studies indicated less neurotoxicity for CB 7646 than for TM. The pharmacokinetic profile of CB 7646 indicated a decreased plasma elimination, indicative of slower in vivo degradation than for TM. CB 7646, therefore, represents a promising candidate for clinical development, designed to supersede TM.

Animals↗
PubMed1995

The role of the N-(hydroxymethyl)melamines as antitumour agents: mechanism of action studies.

The hexamethylmelamine analogue trimelamol (tris-hydroxymethyl[trimethyl]melamine) and its equicytotoxic stable analogues CB 7547, CB 7639 and CB 7669 have been used to clarify the mechanism of action for the N-(hydroxymethyl)melamines as antitumour agents. Two main mechanisms have been proposed and explored: (i) formation of a reactive iminium species forming covalent adducts with DNA; and (ii) local formaldehyde release leading to cytotoxic damage. 32P-postlabelling and thermal denaturation experiments showed these compounds to be interactive with cytosine and guanine. Trimelamol gave rise to DNA-interstrand crosslinks in naked plasmid DNA and in cultured cell lines, whereas the analogues failed to do so under a variety of experimental conditions. Along with our observations that cell lines with acquired resistance to the N-(hydroxymethyl)melamines showed no significant cross-resistance to classical bifunctional alkylating agents, DNA crosslinking may play only a minor role in their mechanism of action. In cultured cell lines treatment with formaldehyde, trimelamol and CB 7639 gave rise to high levels of DNA-protein crosslinks with a gradual disappearance over a 24 hr period. Along with our earlier observation that resistance to trimelamol coincides with cross-resistance to formaldehyde, we conclude that formaldehyde-release may be an important factor in their cytotoxicity. Further, the cytotoxicity of trimelamol or formaldehyde towards human ovarian cancer cells was not influenced by glutathione depletion. As the precise mechanism of action for the N-(hydroxymethyl)melamines is apparently not shared by many commonly used anticancer agents, this may confer their broad-spectrum activity versus heavily pretreated tumours.

Alkylating Agents↗
PubMed1995

DNA sequence-specific adenine alkylation by the novel antitumor drug tallimustine (FCE 24517), a benzoyl nitrogen mustard derivative of distamycin.

FCE 24517, a novel distamycin derivative possessing potent antitumor activity, is under initial clinical investigation in Europe. In spite of the presence of a benzoyl nitrogen mustard group this compound fails to alkylate the N7 position of guanine, the major site of alkylation by conventional nitrogen mustards. Characterisation of DNA-drug adducts revealed only a very low level of adenine adduct formation. Using a modified Maxam-Gilbert sequencing method the consensus sequence for FCE 24517-adenine adduct formation was found to be 5'-TTTTGA-3'. A single base modification in the hexamer completely abolishes the alkylation of adenine. Using a Taq polymerase stop assay alkylations were confirmed at the A present in the hexamer TTTTGA and, in addition, in one out of three TTTTAA sequences present in the plasmid utilized. The sequence specificity of alkylation by FCE 24517 is therefore the most striking yet observed for an alkylating agent of small molecular weight.

Adenine↗
PubMed1994

Stable analogues of the antitumour agent trimelamol retain in vitro cytotoxicity in drug-sensitive and resistant rodent and human cell lines.

In spite of clinical activity in heavily-pretreated ovarian cancer, the antitumour s-triazine trimelamol [TM; tris(hydroxymethyl)-tris(methyl)melamine] had to be withdrawn from further clinical studies due to formulation difficulties related to instability. A synthetic programme has produced tris(hydroxymethyl) analogues containing electron-withdrawing groups in place of methyl-triscyanomethyl CB 7669, tristrifluoroethyl CB 7639, CB 7529 and trispropargyl CB 7547, all showing markedly superior stability to TM. Chemosensitivity testing of analogues (MTT assay, continuous exposure) using a panel of rodent and human cell lines showed activity close to that of TM, e.g. for the CH1 human ovarian cancer cell line. IC50 values were TM 23.4 microM, CB 7639 30.5 microM, CB 7529 29.5 microM, CB 7547 28.5 microM and CB 7669 27.3 microM. CB 7669 and CB 7639 required prolonged exposure (> 12 h) in order to exhibit equivalent cytotoxicity to a 2-h exposure to TM. Thus, rather than administration as a single daily dose, the stable analogues may be more suited to prolonged infusion, which was suggested as being a more beneficial regimen in clinical trials with TM. In line with clinical observations indicating the efficacy of TM in platinum-refractory ovarian cancer, we saw no significant cross-resistance to TM or CB 7529 in a range of platinum-sensitive and acquired-resistant cell line pairs or in an alkylating-agent resistant cell line, despite TM's ability to crosslink DNA. Data obtained using cell lines with acquired resistance to TM, CB 7669 and formaldehyde (released in the breakdown of TM) suggest a pivotal role for formaldehyde and a more minor role for alkylating activity in the mechanism of action of the N-(hydroxymethyl)melamines in vitro. Further clinical trials of these compounds are eagerly awaited, and their usefulness as second-line chemotherapy for heavily pretreated ovarian cancer deserves further investigation.

Animals↗
PubMed1993

Synthesis and cytotoxicity of potential tumor-inhibitory analogues of trimelamol (2,4,6-tris[(hydroxymethyl)methylamino]-1,3,5-triazine) having electron-withdrawing groups in place of methyl.

In exploring the structural features which determine the antitumor activity of 2,4,6-tris-[(hydroxymethyl)methylamino]-1,3,5-triazine (trimelamol, 1), we have synthesized analogues in which the methyl groups have been replaced by the electron-withdrawing substituents 2,2,2-trifluoroethyl (5), propargyl (13), and cyanomethyl (15) via the respective tris(alkylamino)triazines 3, 12, and 14. Three mono[(hydroxymethyl)amino]triazines (4, 7, and 10) were also prepared. All the new tris(hydroxymethyl) derivatives showed cytotoxicities toward a variety of experimental rodent and human ovarian tumor cell lines similar to those shown by 1, the cyanomethyl analogue (15) having the most favorable profile. Mono(hydroxymethyl) derivatives (4 and 7) were ca. one-third as toxic. The new tris(hydroxymethyl) analogues were more stable to aqueous hydrolysis than was 1. Half-life (pH 7.5) values were, for 1, 120 min, for 5, 690 min, for 13, 450 min, and for 15, 275 min, but at pH 2.0, 15 (t1/2 350 min) was the most stable. This cyanomethyl analogue was also the most water-soluble, being comparable to 1 whereas 5 and 13 were poorly soluble.

Animals↗
PubMed1993

The efflux of anthracyclines in multidrug-resistant cell lines.

In order to address the association of enhanced drug efflux with the multidrug-resistant (MDR) phenotype, we have studied the cellular pharmacokinetics of anthracyclines in the P-glycoprotein (Pgp)-positive MDR cell lines H69/LX4 (human small cell lung cancer) and EMT6/AR1.0 (mouse mammary tumour). Both doxorubicin (DOX) and daunorubicin (DNR) were accumulated to a lesser extent and effluxed at a higher rate by MDR cells than by their drug-sensitive counterparts. In contrast, the 9-alkyl substituted compound, aclacinomycin A (ACL), was accumulated and effluxed from parent and MDR cells at an identical rate. In experiments designed to examine energy-dependent efflux, DOX and DNR were shown to be efficiently effluxed against the concentration gradient in the presence of glucose. However, in the same experiments the analogues ACL and Ro 31-3294 (9-alkyl and morpholinyl substituted), which have previously been shown to retain activity against MDR cell lines, were accumulated and effluxed at identical rates in parent and MDR EMT6 cells. Hence, 9-alkyl and morpholinyl substituted compounds appear to behave less favourably as substrates for energy-driven drug efflux by Pgp-positive MDR cells than do DOX or DNR. Resistance modifiers verapamil and cyclosporin A appeared to abolish energy-dependent efflux for DOX and DNR in both the EMT6 and H69 MDR lines whereas they had no effect on the cellular efflux of ACL. The altered cellular pharmacology in MDR cell lines may provide a rational basis for the use of modified anthracycline analogues (e.g. 9-alkyl and morpholinyl (substituted) and resistance of modifying agent in the treatment of tumours expressing a Pgp-mediated phenotype.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1993

The effects of a benzoic acid mustard derivative of distamycin A (FCE 24517) and related minor groove-binding distamycin analogues on the activity of major groove-binding alkylating agents.

The distamycin derivative FCE 24517 is a potent antitumour agent. Efforts have been made towards elucidating the mechanism of action of this compound which, to date, have highlighted a high level of DNA sequence specificity for covalent adduct formation. Compared to classical alkylating agents, FCE 24517 forms very few covalent adducts with double-stranded DNA, and thus appears to be a weak alkylating agent. Examination of the effects of this minor groove-binding agent on the major groove of DNA have been facilitated by use of the alkylating agents mustine, melphalan, dabis maleate, quinacrine mustard and uracil mustard. Pretreatment of plasmid DNA with FCE 24517 followed by reaction with any one of these mustards gave rise to a marked abolition of N-7 guanine adduct formation, as assayed by Maxam and Gilbert sequencing gels. The smallest effect was seen for quinacrine mustard, whereas total abolition of N-7 guanine alkylation was seen with uracil mustard. Using related structural analogues of FCE 24517 in the same experiments, it was not possible to reproduce this effect, with very few exceptions. Some effects were seen when using distamycin A itself in these experiments, although these were marginal compared to those seen for FCE 24517. We were able to extrapolate our findings to a whole cell system using murine L-1210 leukaemia cells. Alkaline elution experiments showed that treatment of cultured cells with FCE 24517 followed by either mustine or uracil mustard caused a marked inhibition of DNA interstrand crosslink formation, compared to treatment with mustine or uracil mustard alone. The present study has demonstrated the marked effect that FCE 24517 has upon the reactivity of double-stranded DNA, an effect possibly separate from that of its alkylating function. This study has highlighted the complex nature of the DNA interactive compound FCE 24517 which possess potent and broad spectrum antitumour activity.

Alkylating Agents↗
PubMed1993

Examination by laser scanning confocal fluorescence imaging microscopy of the subcellular localisation of anthracyclines in parent and multidrug resistant cell lines.

This study highlights the usefulness of laser scanning confocal microscopy in the examination of subcellular disposition of anthracyclines in tumour cell lines. The distribution of anthracycline compounds has been studied in two pairs of parental and multidrug resistant (MDR) cell lines. For the parental EMT6 mouse mammary tumour cell line EMT6/P treated with doxorubicin (DOX) the anthracycline fluorescence was shown to be predominantly nuclear but with some particulate cytoplasmic fluorescence and very low levels of plasma membrane staining. In the same experiments much fainter fluorescence was seen for the EMT6/AR1.0 MDR subline which hyperexpresses P-glycoprotein. The loss of nuclear fluorescence was comparatively greater than loss of cytoplasmic fluorescence. For the human large cell lung cancer line COR-L23/P cellular DOX disposition was markedly nuclear with nuclear membrane staining and diffuse cytoplasmic fluorescence. For the MDR line COR-L23/R, which lacks P-glycoprotein expression, DOX fluorescence was reduced in the nucleus compared with the parental line, but an intense area of perinuclear staining was seen consistent with localisation to the Golgi apparatus. The morpholinyl-substituted analogue MR-DOX achieved very similar subcellular distribution in both parental and MDR lines, consistent with its retention of activity in the latter. The presence of verapamil during anthracycline exposure increased the intensity of fluorescence in the MDR lines, particularly in the nucleus. Relatively little effect was seen in the parental lines. Confocal microscopy provides high resolution images of the subcellular distribution of anthracyclines in parent and MDR cell lines. Differences in drug disposition in various cell lines may provide insights into the mechanism of multidrug resistance and suggest strategies for its therapeutic circumvention.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
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

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↗
PubMed1990

9-Alkyl, morpholinyl anthracyclines in the circumvention of multidrug resistance.

The intramolecular combination of 9-alkyl substitution in the anthracycline A-ring plus incorporation of the amino group of the daunosamine sugar within a morpholinyl ring led to the retention of almost complete activity against P-glycoprotein positive, multidrug resistant variants of a mouse mammary tumour line and a human small cell lung cancer line. Resistance factors were close to unity. These structural elements may prevent efflux by the P-glycoprotein multidrug transporter. The use of 9-alkyl, morpholinyl anthracyclines with resistance circumvention properties may have clinical application.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1989

Improved cellular accumulation is characteristic of anthracyclines which retain high activity in multidrug resistant cell lines, alone or in combination with verapamil or cyclosporin A.

We have examined the cellular accumulation of anthracycline compounds, alone or in conjunction with resistance modifiers, in an attempt to identify mechanisms by which multidrug resistance (MDR) can be circumvented. This was facilitated by using the EMT6 mouse mammary tumour cell line EMT6/P and its MDR subline EMT6/AR1.0 with 30-fold resistance to Adriamycin (ADM), and the human small cell lung cancer line H69/P together with its MDR subline H69/LX4 with 100-fold resistance to ADM. Both MDR lines hyperexpress membrane P-170 glycoprotein. The accumulation of ADM was compared to that seen for the anthracycline analogues aclacinomycin A (ACL), Ro 31-1215 and 4'-deoxy-4'-iodo-Adriamycin (iodo-ADM). These analogues were selected because of their high activity against MDR sublines, including H69/LX4 and EMT6/AR1.0. Both MDR cell lines exhibited a deficiency in ADM accumulation compared to the parent lines. Smaller differentials were seen using Ro 31-1215 or iodo-ADM. Both resistant sublines were able to accumulate ACL in identical amounts to their respective parental sublines. Improved drug accumulation is likely to contribute to the improved activity of the analogues against MDR cell lines. However, the relative accumulation defects in the resistant lines did not correlate exactly with the degree of resistance to a particular compound. Cyclosporin A (5 micrograms/ml) or verapamil (3.3 micrograms/ml) caused a preferential increase in uptake in both MDR sublines, with a small or negligible effect for the parental line. A smaller effect was observed with iodo-ADM and Ro 31-1215, and levels of ACL were unchanged in the MDR lines in the presence of either resistance modifier. These results indicate two mechanisms for circumventing drug resistance due to reduced drug accumulation. Structurally modified derivatives can partially or completely eliminate uptake differentials between parent and drug resistant cell lines. Any residual uptake can be eliminated using resistance modifiers. The two mechanisms may both operate via inhibition or circumvention of P-170 mediated efflux. The situation is complex, however, and this study indicates the possible involvement of additional resistance mechanisms.

Aclarubicin↗
PubMed1989

Identification of anthracyclines and related agents that retain preferential activity over adriamycin in multidrug-resistant cell lines, and further resistance modification by verapamil and cyclosporin A.

A range of anthracyclines and related compounds were evaluated for activity against murine and human cell lines exhibiting multidrug resistance (MDR). Cell lines used were the NCI-H69 human small-cell lung cancer line and the EMT6 murine mammary tumour line, together with their multidrug-resistant counterparts produced by in vitro exposure to Adriamycin (ADM). Chemosensitivity testing was carried out using the tetrazolium (MTT) dye assay. Results were expressed as the ratio of the ID50 for the resistant line to that obtained in the parent, i.e. the resistance factor (RF). Compounds exhibiting much lower RF values than ADM in both resistant cell lines were identified as those anthracyclines with 9-alkyl substituents and those with certain changes to the amino sugar residue at position 3' and 4', together with the anthracenedione mitoxantrone (MIT). In a further attempt to overcome resistance, we used four of these compounds, Ro 31-1215, 4'-deoxy-4'-iodo-ADM (iodo-ADM), aclacinomycin A (ACL) and MIT (all yielding low RF values), in combination with the resistance modifiers verapamil (VRP) and cyclosporin A (CYA). Additional enhancement of chemosensitivity was achieved in the ADM-resistant sublines, as shown by the further decrease in RF values. At the concentrations used, the largest effects were generally seen with CYA, and the combination of this modifier with ACL and MIT was particularly effective. For the H69/LX4 resistant line, the latter combinations gave RF values approaching unity. These findings point to the use of analogues with the 9-alkyl substituent and/or specific changes to the sugar residue in combination with resistance modifiers as a therapeutic strategy for circumvention of the MDR phenotype.

Animals↗