Restored in vitro sensitivity of adriamycin- and vincristine-resistant P388 leukemia with reserpine

Gallic acid enhances pirarubicin‑induced anticancer in living K562 and K562/Dox leukemia cancer cells through cellular energetic state impairment and P‑glycoprotein inhibition

Leukemia is a common malignancy affecting humans worldwide. Pirarubicin (Pira) is one of the anticancer agents used for the treatment of leukemia. Although Pira is effective, drug resistance may develop in cancer cells exposed to this drug, whereas the combination of natural products with Pira may help to overcome this problem. The aim of the present study was to focus on the effect of gallic acid (GA) on the anticancer activity of Pira in K562 leukemia cells and K562/doxorubicin (Dox)‑resistant leukemia cells in order to investigate the possible underlying mechanisms. The cell viability, mitochondrial activity, mitochondrial membrane potential (ΔΨm) and ATP levels were assessed in living K562 and K562/Dox cancer cells following treatment with GA/Pira combination, GA alone or Pira alone. P‑glycoprotein‑mediated efflux of Pira was determined in GA‑treated K562/Dox cancer cells. The results demonstrated that GA/Pira combination decreased cell viability, mitochondrial activity, ΔΨm and ATP levels in K562 and K562/Dox cancer cells in a GA concentration‑dependent manner compared with non‑treated or Pira‑treated cells. GA inhibited P‑glycoprotein‑mediated efflux of Pira in GA‑treated K562/Dox cancer cells. Therefore, GA enhanced the anticancer effect of Pira on K562 and K562/Dox cancer cells through cellular energy status impairment, and was able to reverse drug resistance in living K562/Dox cancer cells by inhibiting the function of P‑glycoprotein.

Differential Effect of Clofibrate on Adriamycin Cytotoxicity in P388 Murine Leukemia Cells Sensitive and Resistant to Adriamycin

Clofibrate (CPIB), an antihyperlipidemic agent, was utilized as a drug response modulator to modify the cytotoxicity of adriamycin (ADR) in vitro in P388 murine lymphocytic leukemia cells sensitive (P388/S) and resistant (P388/ADR) to ADR. CPIB elicited concentration and time dependent DNA biosynthesis inhibition which was completely reversible up to the concentration of 0.0025 % in P388/S. However, only a partial reversibility of DNA biosynthesis inhibition was observed in P388/ADR cells treated with 0.0025 % of CPIB. In both P388/S and P388/ADR there was complete and irreversible DNA biosynthesis inhibition at CPIB concentration of 0.005%. These findings were further confirmed by tumorigenicity anaysis. CPIB was ineffective in altering ADR cytotoxicity in P388/S ceils. However, in P388/ADR, CPIB enhanced ADR cytotoxicity at the lower concentrations of ADR and decreased the cytotoxicity upon increase in ADR concentrations. The enhancement in ADR cytotoxicity by CPIB in P388/ADR was due to increased ADR accumulation which was absent in P388/S cells. The present findings suggest the utility of CPIB as a selective agent to circumvent ADR resistance and to reduce host toxicity due to the drug.

Reversion of P-glycoprotein-mediated multidrug resistance by diallyl trisulfide in a human osteosarcoma cell line

Diallyl trisulfide (DATS), the main sulfuric compound in garlic, has been shown to have antitumor effects. The present study aimed to ascertain whether DATS reverses the drug resistance of human osteosarcoma cells in vitro and to investigate its potential mechanisms. Human osteosarcoma U2-OS cells were treated with different concentrations of DATS. Cell proliferation was measured by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, while P-glycoprotein (P-gp) expression and the proportion of apoptotic cells were measured by flow cytometry. Morphological changes were observed under an optical microscope. Νuclear factor-κB (NF-κB) and inhibitor of NF-κB (IκB) activities were measured by PCR and western blot analysis. Results showed that the proliferation of U2-OS cells treated with different concentrations of DATS was significantly decreased in a concentration- and time-dependent manner. DATS increased the toxic effect of adriamycin on U2-OS cells. Moreover, P-gp expression was decreased and the apoptosis rate was increased in a concentration-dependent manner following treatment of DATS. Additionally, NF-κB activity was inhibited by DATS while expression of IκB was increased. Our data clearly suggest that DATS has significant anticancer effects on human osteosarcoma cells. The potential mechanisms include reducing the multidrug resistance and inducing apoptosis. NF-κB suppression may be involved in DATS-induced inhibition of cell proliferation.

Reversion of p-glycoprotein-mediated multidrug resistance in human leukemic cell line by diallyl trisulfide

Multidrug resistance (MDR) is the major obstacle in chemotherapy, which involves multiple signaling pathways. Diallyl trisulfide (DATS) is the main sulfuric compound in garlic. In the present study, we aimed to explore whether DATS could overcome P-glycoprotein-(P-gp-)mediated MDR in K562/A02 cells, and to investigate whether NF-κB suppression is involved in DATS-induced reversal of MDR. MTT assay revealed that cotreatment with DATS increased the response of K562/A02 cells to adriamycin (the resistance reversal fold was 3.79) without toxic side effects. DATS could enhance the intracellular concentration of adriamycin by inhibiting the function and expression of P-gp, as shown by flow cytometry, RT-PCR, and western blot. In addition, DATS resulted in more K562/A02 cell apoptosis, accompanied by increased expression of caspase-3. The expression of NF-κB/p65 (downregulation) was significantly linked to the drug-resistance mechanism of DATS, whereas the expression of IκBα was not affected by DATS. Our findings demonstrated that DATS can serve as a novel, nontoxic modulator of MDR, and can reverse the MDR of K562/A02 cells in vitro by increasing intracellular adriamycin concentration and inducing apoptosis. More importantly, we proved for the first time that the suppression of NF-κB possibly involves the molecular mechanism in the course of reversion by DATS.

Reversal of vinblastine resistance in human leukemic cells by haloperidol and dihydrohaloperidol

Haloperidol, an antipsychotic, was investigated in cells overexpressing P-glycoprotein to detemine whether it was a clinically effective drug to reverse for reversing multidrug resistance (MDR) mediated by P-glycoprotein. A nontoxic concentration of haloperidol (1-30 microM) enhanced the cytotoxic effects of vinblastine (VBL) concentration-dependently in VBL-resistant human leukemia (K562/VBL) cells, but had no effect in the parent cells. Haloperidol also enhanced the cytotoxicities of epirubicin, doxorubicin and actinomycin D in the K562/VBL cells, but not those of idarubicin or cisplatin; this enhancement was less than that of the VBL toxicity in the VBL-resistant tumor line. Haloperidol increased the intracellular accumulation of VBL in the K562/VBL cells, and the binding of [3H]-azidopine to the cell-surface protein, P-glycoprotein, was inhibited by haloperidol in a concentration-dependent manner. Haloperidol was less potent than verapamil. Thus, haloperidol appeared to potentiate anticancer agents through the reversal of MDR by competitively inhibiting drug-binding to P-glycoprotein. In contrast, the main metabolite of haloperidol, dihydrohaloperidol, without antipsychotic activity, had less of an effect. Therefore, haloperidol might be useful in reversing drug-resistance.

Multidrug-resistance modulators from Stephania japonica

An alkaloidal extract of the vines of Stephania japonica showed multidrug-resistance-reversing activity as demonstrated by the bicinchoninic acid assay. Two known bisbenzylisoquinoline alkaloids, isotrilobine (1) and trilobine (2), were isolated by bioassay-directed fractionation and separation. Isotrilobine (1) was shown to be as active as verapamil (3) in reversing doxorubicin resistance in human breast cancer cells.

Overcoming of multidrug resistance by VA-033, a novel derivative of apovincaminic acid ester

We have studied the effects of a novel derivative of apovincaminic acid ester, VA-033, on the resistance of tumors to chemotherapeutic agents. VA-033 increased the sensitivity of drug-resistant cell lines (P388/VCR, P388/ADM, AD10, and K562/ADM) to adriamycin or vincristine. The potency of VA-033 was stronger than verapamil. The drug lengthened the survival time of the P388/VCR-implanted mice treated with vincristine. VA-033 increased the intracellular accumulation of vincristine in the tumor cells, and the photolabeling of P-glycoprotein by [3H]azidopine was inhibited by VA-033. VA-033 showed a slight inhibitory effect on the L-type Ca2+ current in the ventricular myocytes, and had less effect on the cardiovascular parameters such as blood pressure, contractile force and atrio-ventricular conduction time than verapamil when administered systemically in the dog. These results suggest that VA-033 may become a beneficial compound as a modifier to the neoplastic cell resistant to multidrugs.

Effects of isoquinolinesulphonamide compounds on multidrug-resistant P388 cells

The effects of eight isoquinolinesulphonamide compounds on resistance to vinblastine in adriamycin-resistant mouse leukaemia cells (P388/ADR) which overexpress the relative molecular weight (M(r)) 140 kDa P-glycoprotein in the plasma membrane were investigated. N-[2-(Methylamino)ethyl]-5-isoquinolinesulphonamide (H-8) and N-(2-aminoethyl)-5-isoquinolinesulphonamide (H-9) did not reverse vinblastine resistance. N-[2-[N-[3-(4-Chlorophenyl)-2-propenyl]amino] ethyl]-5-isoquinolinesulphonamide (H-86) and N-[2-[N-[3-(4-chlorophenyl)-1-methyl-2-propenyl] amino]ethyl]-5-isoquinolinesulphonamide (H-87) caused accumulation of intracellular vinblastine and inhibition of vinblastine efflux from the cells and reversed the resistance. Addition of an aminoethyl group to the nitrogen atom of the sulphonamide group (W-66) or a formyl group at the terminal amino group (H-85) of H-86 reduced those activities. Conversion of the chlorophenyl group of H-87 to pyridinyl (H-31) or furanyl (H-34) markedly decreased activities against the drug resistance. The activity against vinblastine accumulation closely correlated with the apparent partition coefficient of compounds. These compounds dose-dependently inhibited photoaffinity labelling of a photosensitive analogue of vinblastine, N-(p-azido-(3-[125I)salicyl)-N'-beta-aminoethyl-vindesine ([125I]NASV), and there was a good correlation between inhibition of [125I]NASV-photolabelling and hydrophobicity. Although these isoquinolinesulphonamides inhibited protein kinase A with different magnitudes, this activity did not correlate with the effect on the drug resistance. These results indicate that isoquinolinesulphonamide compounds with a hydrophobic group interact with antitumour drugs on P-glycoprotein and reverse multidrug resistance without involvement of their activity on protein kinase A.

Phase II trial of doxorubicin and trifluoperazine in metastatic breast cancer

Pre-clinical and clinical studies have shown that trifluoperazine (TFP) can modulate multidrug resistance. We have performed a Phase II trial of TFP and doxorubicin in doxorubicin-naive patients with metastatic breast cancer. We hypothesized that TFP would inhibit the development of doxorubicin resistance, resulting in an increased rate of complete response or a prolongation in response duration. Twenty patients with metastatic breast cancer were treated every 3 weeks with TFP 5 mg by mouth every 6 hours on days 0-5 and doxorubicin 60 mg/m2/96 hr on days 1-4 by continuous intravenous infusion. The first 5 patients were treated with TFP 15 mg by mouth every 6 hours, but the dose was reduced to 5 mg every 6 hours when grade 3-4 extrapyramidal toxicity was noted in 3 of the first 5 patients. Thereafter, neurologic toxicity was grade 0-2. No complete and 9 partial responses were produced in 20 patients (45%). The median response duration was 17 weeks (range 7-112). The combination of trifluoperazine and doxorubicin did not seem to produce a response rate or duration markedly different than that expected for doxorubicin alone in patients with metastatic breast cancer. Alternative trial designs may be necessary in future clinical trials investigating the inhibition of acquisition of drug resistance.

Modulation of drug cytotoxicity in wild-type and multidrug-resistant tumor cells by stereoisomeric series of C-20'-vinblastine congeners that lack antimicrotubule activity

Seven binary vinca alkaloid congeners were newly synthesized as the C14' or C16'(20') or C14'16'(20') stereoisomers of C20'-modified VBL. These congeners lacked detectable antimicrotubule activity in assays of polymerization of purified microtubule protein and of mitotic arrest induction. The compounds modulated the cytotoxicity of VBL, VCR, and DOX in sarcoma and colon-tumor cell lines. In wild-type cell lines, each congener elicited a concentration-dependent enhancement of cytotoxicity that was drug- and cell-type-selective. For example, C20'-deoxy C14'16'20'-epi VBL sensitized sarcoma S180 cells 19-fold to DOX and 11-fold to VCR but had no effect on VBL cytotoxicity. In the rat colon-cancer cell lines there was preferential enhancement of VCR cytotoxicity by most congeners. In two MDR cell strains of S180, the modulation potency of each congener was independent of specific drug or of resistance level. As a result, the amount of modulator (concentration) required for reversal was proportional to the drug-resistance level. Such properties were not displayed by the monomeric vinca alkaloid modulator vindoline. The potency of drug modulation in both wild-type and MDR cells strains was dependent on the stereoisomeric form of the congener and its C20'-substituents.

Circumvention of multi-drug resistance in human kidney and kidney carcinoma in vitro

This report investigated whether the calmodulin inhibitor, trifluoperazine, can circumvent multi-drug resistance both in primary tissue cultures of human kidney and kidney carcinoma. For detection of inherent multi-drug resistance, the expression of P-glycoprotein was determined by immunofluorescence and immunocytochemistry using the monoclonal antibody C219. For detection of doxorubicin resistance and reversal of this resistance by trifluoperazine, the incorporation of nucleic acid precursor was measured after addition of doxorubicin and trifluoperazine, respectively. Both P-glycoprotein expressing resistant normal and malignant kidney tissue cultures could be modified by trifluoperazine. However, sensitive normal kidney and kidney carcinoma cultures were little affected by trifluoperazine. Thus, circumvention of primary resistance to doxorubicin is not limited to tumor cells. This might have important implications for the use of resistance modifiers in the clinical setting.

Rationale for immunotherapy of renal cell carcinoma

Metastasis to distant organs is the principal cause of death from renal cell carcinoma (RCC). No commonly accepted therapy is available for disseminated RCC at present. Immunotherapy is a mode of therapy that either interferes with the immune system or makes use of drugs that have been derived from soluble mediators of the immune system. Several lines of evidence suggest that combinations of genetically engineered cytokines (e.g. interleukin-2 and interferon alpha) may be particularly active in the treatment of advanced RCC. There are two major rationales for considering immunotherapy for RCC: (1) there is currently no other therapy available, and (2) there is hardly any innovative approach besides immunotherapy. Still, immunotherapy is far from being a standard therapy for disseminated RCC.

Efflux of bis-carboxyethyl-carboxyfluorescein (BCECF) by a novel ATP-dependent transport mechanism in epithelial cells

The efflux of the intracellular pH fluorochrome 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein (BCECF) was quantified in four cultured epithelial cell lines; HCT-8, T84, HGT-1 and MDCK. BCECF efflux was time-dependent, and after 5 h 45-91% of the initial BCECF loaded was extracellular, efflux being greatest in MDCK cells. Depletion of cellular ATP approximately halved BCECF efflux. BCECF efflux was inhibited by indomethacin, vinblastine and verapamil, but not by nifedipine or reserpine. Certain features of BCECF efflux resemble drug efflux in multidrug resistant cells, but inhibition of efflux displays a distinct pharmacological profile suggesting BCECF is a substrate for a novel ATP-dependent transport system.

Synergistic effect of cyclosporin A and verapamil in overcoming vincristine resistance of multidrug-resistant cultured human leukemia cells

Reversal of vincristine (VCR) resistance by cyclosporin A (CyA) or the combination of CyA and verapamil (VER) was investigated by using four P-glycoprotein (P-gp)-associated human multidrug-resistant (MDR) cell lines (K562/ADM, KYO-1, HEL and CMK). Drug sensitivity was expressed as 50% inhibitory concentration (IC50). The degree of reversal of resistance was expressed as x-fold decrease by dividing the IC50 value without modifier(s) by that with modifier(s). CyA overcame P-gp-associated MDR significantly in all four MDR cell lines. Reversal of VCR resistance by CyA appeared to be dose-dependent. In the case of low-grade MDR cell lines (KYO-1, HEL and CMK), CyA at the low concentration of 0.5 microgram/ml was still effective. The degree of reversal of VCR resistance in this condition was greater (6.3- to 16-fold decrease) in the low-grade MDR cell lines than in a high-grade MDR cell line (K562/ADM) (2.9-fold decrease). At a high concentration (5 micrograms/ml) of CyA, however, it was greater (240-fold decrease) in the high-grade MDR cell lines than in the low-grade MDR cell line (20- to 100-fold decrease). This indicates that concentration of CyA required for overcoming drug resistance in MDR cells was dependent on the degree of drug resistance. CyA overcame VCR resistance more efficiently than VER. The combination of CyA and VER enhanced reversal of VCR resistance in a supra-additive or at least an additive manner and overcame VCR resistance at low concentrations of both modifiers that are clinically achievable with safety.

Aspergillus species strain M39 produces two naphtho-gamma-pyrones that reverse drug resistance in human KB cells

One thousand fungi and Actinomycetes were investigated to see whether they produced compounds that reverse multi-drug resistance in KB cells. Only one Aspergillus strain M39 produced agents with resistance-reversing activity and these compounds were identified to be rubrofusarin B and dianhydro-aurasperone C. Rubrofusarin B only slightly reversed the resistance of KB-C2 cells to Adriamycin and daunomycin, partially reversed the resistance to chromomycin A3, and almost completely reversed the resistance to vincristine and mitomycin C. Purified dianhydro-aurasperone C and rubrofusarin B had similar effects on drug resistance in KB-8-5 cells. Dianhydro-aurasperone C enhanced the accumulation of vinblastine in KB-8-5 cells and inhibited the efflux of vinblastine from the cells. Dianhydro-aurasperone C and rubrofusarin B at 10 microM completely inhibited 3H-azidopine photolabelling of P-glycoprotein. The two products of Aspergillus strain M39 appear to reverse multi-drug resistance by interacting with P-glycoprotein and inhibiting its role as an active efflux pump.

Effect of calcium antagonists on the chemosensitivity of two multidrug-resistant human tumour cell lines which do not overexpress P-glycoprotein

We have examined the ability of eight compounds to enhance adriamycin (ADM) sensitivity of two human tumour cell lines (a small cell lung cancer cell line, NCI-H69, and a fibrosarcoma cell line, HT1080) and their multidrug-resistant variants. The resistant cell lines (H69AR and HT1080/DR4) do not overexpress P-glycoprotein. Verapamil, nicardipine, perhexiline maleate, chloroquine, tamoxifen, clomiphene, prenylamine and trifluoperazine were tested alone and in combination with ADM for their cytotoxic effects. No major differences in sensitivity between the parent and resistant cell lines were noted when these agents were tested alone, except for HT1080/DR4 cells which exhibited a slight collateral sensitivity to nicardipine and H69AR cells which showed cross-resistance to chloroquine and clomiphene. When the chemosensitisers were combined with ADM no enhanced cytotoxicity of either parent cell line was observed. In HT1080/DR4 cells, verapamil showed only a modest dose-dependent chemosensitising effect while the other compounds had no effect. Verapamil and nicardipine enhanced ADM cytotoxicity in H69AR cells slightly but these effects were not dose-dependent. These results demonstrate that the reversal of drug resistance by verapamil and other calcium antagonists in a dose-dependent fashion is not an invariable property of multidrug-resistant tumour cells.

Vincristine-resistant human cancer KB cell line and increased expression of multidrug-resistance gene

A multidrug-resistant clone of human cancer KB cells was isolated by stepwise selection on exposure to increasing doses of vincristine. The final clone, VJ-300, obtained after ethylmethane sulfonate mutagenesis showed 400-fold higher resistance to vincristine than did KB cells. Cellular accumulation of vincristine in VJ-300 was decreased to less than one-tenth of that in KB. The cells were also cross-resistant to daunomycin, adriamycin, actinomycin D, colchicine and VP-16. During continuous culturing in the absence of any drug for several months, a different colchicine-resistant and multidrug-resistant clone, KB-C1, reverted almost completely to drug sensitivity, whereas drug resistance in VJ-300 was stably maintained. Amplification of the multidrug-resistance-1 (mdr-1) gene was more than 20-fold in KB-C1, but less than 2-fold in VJ-300. mdr-1 mRNA was, however, expressed in VJ-300 at a rate comparable to KB-C1. Acquisition of high multidrug resistance in VJ-300 might be correlated with both activated transcription of mdr-1 gene and amplification.

The membrane transport system responsible for multidrug resistance is operating in nonresistant cells

Cultured hamster fibroblasts of the DM-15 cell line stained by rhodamine 123 gradually release the dye when placed in dye-free medium. Here we demonstrate that reserpine, verapamil, and trifluoperazine are capable of blocking this release. We also show that reserpine can inhibit the efflux of another dye, phosphine 3R, from DM-15 cells and the release of rhodamine 123 from mouse embryo fibroblasts, four mouse cell lines, and MDCK cells. The three substances that block the release of the dyes are potent inhibitors of the membrane transport system implicated in the phenomenon of multidrug resistance (MDR). By using this system MDR cells can pump many structurally unrelated drugs and dyes, including rhodamine 123 and phosphine 3R, from the cytoplasm to the outer medium. It appears from our results that the membrane transport system responsible for MDR operates slowly in nonresistant cells and can play a role in normal cell physiology.

Cross resistance pattern towards anticancer drugs of a human carcinoma multidrug-resistant cell line

Puromycin-resistant (PurR) mutants/variants of a human carcinoma cell line (HeLa), which show greatly reduced cellular uptake of 3H-puromycin and 3H-daunomycin have been isolated after one- and two-step selections in presence of the drug. The cross-resistance pattern of these mutant cell lines towards numerous anticancer drugs and other inhibitors has been examined. Both the first- and the second-step mutants exhibited increased resistance to a number of antimitotic drugs (viz. vinblastine, vincristine, colchicine, taxol and maytansine), several protein synthesis inhibitors (viz. chalcomycin, bruceantin, harringtonine, homoharringtonine), a large number of DNA interactive compounds (viz. aclacinomycin A, actinomycin D, adriamycin, m-AMSA, chromomycin A3, coralyne sulphoacetate, daunomycin, ellipticine, mithramycin, mitoxantrone, 5-methoxysterigmatocystin, rubidazone, variamycin, VM26 and VP16-213) and a number of other drugs acting via other mechanisms (viz. Baker's antifol, nitidine chloride and rhodamine 123). Whereas the first-step mutants showed stable resistance to these drugs, the second-step lines partially reverted upon growth in non-selective medium. Further, treatment of these mutant lines with non-cytotoxic doses of the calcium channel blocker verapamil reverted or abolished their resistance to the above drugs in a dose-dependent manner. In contrast to the above compounds, the PurR mutants showed no significant cross-resistance to a large number of other drugs which included asaley, AT-125, 5-azacytidine, azaserine, cyclocytidine, cis-platin, cytosine arabinoside, chlorambucil, chlorpromazine, alpha-difluoromethyl ornithine, 5-fluorouracil, ftorafur, gallium nitrate, hydroxyurea, ICRF-159, ICRF-187, imipramine, methotraxate, 6-methylmercaptopurine riboside, mycophenolic acid, melphalan, mitomycin C, methyl GAG, nafoxidine, reumycin, 6-selenoguanosine, 6-thioguanine, tiazofurin, tamoxifen, thalicarpine, tiapamil and verapamil). These cross-resistance data should prove useful in developing suitable drug combinations to which cellular resistance would not develop readily.

Use of fluorescent dyes as molecular probes for the study of multidrug resistance

Fluorescence microscopy has shown that 18 different fluorescent dyes, staining various intracellular structures in transformed hamster fibroblasts (DM-15), did not stain or stained weakly multidrug-resistant cells selected from DM-15 by colchicine. Reduced staining by fluorescent dyes was characteristic also of five other tested multidrug-resistant cell lines of hamster and mouse origin, selected by actinomycin D, colcemid, rubomycin, and ruboxyl. The intensity of staining of two revertant cell lines was similar to that of parental sensitive cells. All tested inhibitors of multidrug resistance, including weak detergent, metabolic inhibitors, calcium channel blockers, calmodulin inhibitors, and reserpine, restored normal staining of multidrug-resistant cells. The dyes accumulated in resistant cells in presence of these inhibitors left the cells several minutes after the removal of the inhibitor from the incubation medium. Sensitive cells retained the dyes for several hours. The efflux of the dyes from resistant cells is an active process since it occurred even in the presence of the dyes in the incubation medium. The efflux could be blocked by all tested inhibitors of multidrug resistance and it is possibly a basic mechanism of the reduced staining of resistant cells. These data support the idea that multidrug resistance is based on active nonspecific efflux of the drugs and indicate that the simple procedure of cell staining can be used for the detection of resistant cells and further study of the phenomenon of multidrug resistance.

Restoration of drug sensitivity by nitroxazepine hydrochloride in P388 murine leukemia cells resistant to adriamycin

Attempts were made to reverse the acquired resistance of P388 murine leukemia utilizing non-toxic concentration of nitroxazepine hydrochloride, an antidepressant. The effect of nitroxazepine hydrochloride on the intracellular accumulation of adriamycin and the inhibition of DNA synthesis were studied in these cells. The survival of mice bearing adriamycin-resistant P388 murine leukemia cells treated in vitro with nitroxazepine hydrochloride, adriamycin and a combination of the two drugs was also investigated. The results show that treatment of these cells with nitroxazepine hydrochloride significantly enhanced (1) the intracellular accumulation of adriamycin, (2) inhibition of DNA biosynthesis, and (3) the survival of mice transplanted with adriamycin-resistant P388 murine leukemia cells treated in vitro with a combination of nitroxazepine hydrochloride and adriamycin. The mechanism of restoration of drug sensitivity by nitroxazepine hydrochloride in adriamycin-resistant P388 cells could be due to an enhanced intracellular accumulation of adriamycin. The implications of the present investigations are promising, leaving hope for the utility of nitroxazepine hydrochloride in restoring drug sensitivity in adriamycin-resistant tumors.

Verapamil enhanced in vitro chemosensitivity of a murine bladder carcinoma, FCB

The in vitro enhancement of chemotherapeutic efficacy by verapamil, a calcium antagonist, was assessed using FCB, a transplantable murine transitional cell carcinoma. Exponentially growing FCB cells were partially resistant to treatment with both thiotepa (10(-4) M) and Adriamycin (10(-5) M), however, there was a significant reduction in cell growth when either agent was administered in combination with verapamil (10(-5) M); the effect was evident over a wide range of drug concentrations (10(-4) - 10(-9) M). There was also a pronounced inhibition of DNA precursor incorporation when verapamil was used in combination with either agent. Fluorometric analysis of Adriamycin uptake indicated that verapamil caused an increase in the intracellular concentration of the agent. The data presented are consistent with the postulate that verapamil enhances chemotherapeutic efficacy by altering cellular permeability to the cytotoxic agents. Our study indicates that the use of verapamil in combination with cytotoxic agents for intravesical chemotherapy of bladder tumors may prove to be beneficial in human patients.

Enhanced effect of reserpine upon growth-inhibitory action of ACNU on ACNU-resistant C6 glioma

Reserpine was found to enhance the cytotoxicity of ACNU on ACNU-resistant C6 glioma (C6/ACNU) cells in vitro. When reserpine was added along with ACNU to the C6/ACNU cells in vitro. When reserpine was added along with ACNU to the C6/ACNU culture in vitro at a concentration of 10 microM, the IC50 of ACNU for C6/ACNU cells decreased to the level of that for C6 cells and ACNU resistance was completely overcome in vitro. Furthermore, intracellular uptake of ACNU increased in both sensitive (C6) and resistant (C6/ACNU) glioma cells when 20 microM reserpine was added to the culture medium. Reserpine (20 microM) enhanced the cellular level of ACNU in C6 cells 1.5-fold and enhanced the level of ACNU in C6/ACNU cells 4-fold. The amount of ACNU incorporated into C6/ACNU cells reached the same level as that incorporated into C6 cells. The enhanced cytotoxicity of ACNU in vitro could be explained by the effective intracellular accumulation of ACNU resulting from the increase of intracellular uptake of ACNU in C6/ACNU cells by reserpine.

The calcium channel blocker verapamil and cancer chemotherapy

Verapamil is an agent which inhibits the transmembrane flux of calcium ions and is used clinically in the management of cardiac arrhythmias. Combination of this calcium antagonist with antineoplastic agents results in the establishment of chemosensitivity in tumor cells resistant to accepted chemotherapeutic agents and, to a lesser degree, potentiates the efficacy of such compounds in drug-sensitive malignancies. Preliminary indications are that the clinical role of such a potentiation of efficacy would not be limited by an increase in generalized toxicity in non-malignant tissues. Data accumulated indicates a verapamil-induced inhibition of the ability of resistant cells to actively extrude chemotherapeutic agents, possibly due to a decrease in calmodulin activity as a result of a drug-induced alteration of the intracellular calcium environment. The results of preclinical trials to date indicate a role for verapamil in augmenting currently accepted chemotherapeutic regimens.

Tumour cell resistance to anthracyclines--a review

Resistance to anthracyclines is the major factor limiting their clinical utility. Laboratory studies using cultured experimental and human tumour cells have indicated that reduced intracellular drug accumulation is one important factor underlying resistance. In some systems this results from enhanced active drug efflux, a process which may be circumvented experimentally, for example by calcium antagonists. A specific glycoprotein which is produced in excess and is inherited has been identified in the cell membrane of certain anthracycline-resistant cells, while gene amplification with the appearance of double-minute chromosomes has been noted in others. Thus it is possible that anthracycline resistance arises following inherited changes in the cell membrane resulting in failure of drug accumulation. However, other possibilities exist, including differences in drug binding, either to the cell membrane or to nuclei, differences in metabolism to the semiquinone free radical, and differences in drug penetration related to tumour morphology. For each human tumour type the factor(s) involved may differ, but sufficient clues now exist to suggest that clinical testing of some of the therapeutic possibilities for circumventing anthracycline resistance may soon be appropriate.

Cancer chemotherapy. Progress and expectations, 1984

Progress in the treatment of cancer with drugs has radically altered the clinical approach to patients with malignancy. Not only have new drugs produced promising results in hitherto untreatable tumors, but they have extended and enhanced the effectiveness of other modalities, including surgery and radiotherapy. In this article, the authors consider avenues of research that likely to aid in the discovery of new anticancer drugs and improve the effectiveness of established agents. Promising new efforts in drug development include the use of new screening systems, particularly those employing human tumor material; the development of improved analogs of existing active agents particularly those of the anthracycline and platinum complex types; and the search for agents that which promote differentiation or prevent metastasis. In an effort to improve the effectiveness of established agents, the authors consider the application of pharmacokinetic principles in developing regional perfusion routes, intraperitoneal chemotherapy, and central nervous system penetration. Finally, the contribution of biochemical pharmacology to the current understanding of drug action, mechanisms of resistance, and drug interactions are considered, and the impact of this knowledge on clinical protocol design is assessed.

Restoration of doxorubicin responsiveness in doxorubicin-resistant P388 murine leukaemia cells

The effects of certain compounds on the in vitro growth rate and the sensitivity to doxorubicin of P388 murine leukaemia cell line and of a doxorubicin-resistant subline (P388/ADR) were studied. The calcium channel blocking activity of these compounds was evaluated by measuring their effects on the sodium-dependent and membrane potential-dependent calcium uptake in synaptic plasma membrane vesicles. At non-inhibitory concentrations, verapamil, dipyridamole, meclizine and nicardipine were highly active in restoring the sensitivity to doxorubicin of P388/ADR cells. Moderately active were propranolol, N-(beta-diethylaminoethyl)-N-(beta-hydroxy-beta-phenylethyl)-2,5-dich loranaline (MDL-6792), thioridazine and chlorocyclizine, while nifedipine, guanethidine, phentolamine, chloroquine and papaverine had zero or only minimal synergistic activity to doxorubicin in this cell line. Doxorubicin synergistic activity could not be demonstrated in the parent drug-sensitive cell line. No sodium-dependent or membrane potential-dependent calcium uptake could be demonstrated in vesicles prepared from plasma membranes of either cell line. There is no correlation between the ability of these compounds to inhibit calcium uptake in synaptic vesicles and their potency in restoring the sensitivity of P388/ADR cells to doxorubicin.

Verapamil enhancement of chemotherapeutic efficacy in human bladder cancer cells

The calcium influx blocker verapamil has been used to overcome drug resistance in several tumor systems. The possible in vitro enhancement of drug efficacy was assessed in bladder cancer cell line T24. Combination of thiotepa and doxorubicin hydrochloride with verapamil significantly reduced the survival and growth of T24 cells after as little as 1 hour of drug exposure. An increase in doxorubicin hydrochloride-induced inhibition of [3H]thymidine uptake resulted when verapamil was administered. However, this trend was not demonstrated when combined with thiotepa. It appears that verapamil enhances thiotepa-induced cytotoxicity while it potentiates the antimitotic nature of doxorubicin hydrochloride. The data presented is consistent with the postulate that verapamil alters active efflux of drug from malignant cells and suggests that verapamil has a role in the clinical management of bladder cancer.

Cellular pharmacology of Vinca alkaloid resistance and its circumvention

Vinca alkaloid-resistant human leukemic cells express the multiple drug-resistant phenotype, characterized by cross resistance to natural product compounds of unrelated structure and action. While there are also distinct biochemical lesions associated with this phenotype, their role(s) in the expressions of resistance is not known at this time. More clear, however, is our understanding of the pharmacologic determinants of this resistance--apparent decreased drug uptake and decreased drug retention. This latter phenomenon has been attributed to the workings of an active efflux pump, but data presented here and elsewhere permit an alternative explanation--that of altered drug binding to an as yet unidentified target(s). Elucidation of the mechanism of multiple drug resistance is important in the design of new chemotherapeutic strategies to overcome it. In this regard, calcium channel blocking agents and calmodulin inhibitors can cause an apparent reversal of resistance by enhancing the cytotoxic effectiveness of the anticancer drugs, possibly by increasing the amount of drug retained by the tumor cells. The basis for this enhanced retention and cytotoxicity is not presently known, but it may be related to cellular calcium fluxes, calmodulin content or membrane fluidity and permeability. The meaning of these findings is unclear at the present time, but they may provide new insights into the mechanism of action and ultimate cellular target(s) for Vinca alkaloids. Whether these modifying drugs sensitize the cells to the action of the alkaloids or potentiate the oncolytic drug effect in the cell remains to be determined. Regardless of the mechanism, calcium channel blocking agents may have a role in the combination chemotherapy of the leukemias with Vinca alkaloids.