Plasma membrane proteins and glycoproteins from Chinese hamster cells sensitive and resistant to actinomycin D

Drug resistance in cancer: mechanisms and tackling strategies

Drug resistance developed towards conventional therapy is one of the important reasons for chemotherapy failure in cancer. The various underlying mechanism for drug resistance development in tumor includes tumor heterogeneity, some cellular levels changes, genetic factors, and others novel mechanisms which have been highlighted in the past few years. In the present scenario, researchers have to focus on these novel mechanisms and their tackling strategies. The small molecules, peptides, and nanotherapeutics have emerged to overcome the drug resistance in cancer. The drug delivery systems with targeting moiety enhance the site-specificity, receptor-mediated endocytosis, and increase the drug concentration inside the cells, thus minimizing drug resistance and improve their therapeutic efficacy. These therapeutic approaches work by modulating the different pathways responsible for drug resistance. This review focuses on the different mechanisms of drug resistance and the recent advancements in therapeutic approaches to improve the sensitivity and effectiveness of chemotherapeutics.

Profound differences in the transport of steroids by two mouse P-glycoproteins

There are two mouse P-glycoproteins that convey multidrug resistance, mdr1 (mdr1b) and mdr3 (mdr1a), by serving as drug efflux transporters. These proteins each exhibit tissue-specific expression. There is relatively high expression of the mdr1 gene in the adrenals, the site of glucocorticoid and mineralocorticoid hormone synthesis. We previously demonstrated that mdr1 gene expression in murine thymoma cells correlated well with a decrease in their ability to accumulate the glucocorticoid dexamethasone and their increased resistance to glucocorticoid-induced apoptosis. Additional evidence is presented that supports the proposition that the mdr1 P-glycoprotein can transport glucocorticoids. Specifically, introduction and expression of the mouse mdr1 gene in the human HEK 293T cell line conveys a multidrug resistance phenotype that includes a reduced capacity to accumulate dexamethasone. Moreover, isolation of additional mdr1-expressing mouse lymphoid cells, without using steroids in the selection, confirms the linkage between multidrug resistance conveyed by the mdr1 P-glycoprotein and resistance to dexamethasone. In contrast, two newly isolated lymphoid lines, selectively expressing the mdr3 gene, were not found to have increased dexamethasone resistance or the capacity to accumulate significantly lower levels of hormone. The results support the concept that the mdr1 and mdr3 P-glycoproteins may serve alternative roles in the transport of endogenous substances such as steroids.

Reversal of doxorubicin resistance by the amiloride analogue EIPA in multidrug resistant human colon carcinoma cells

Although multidrug resistance (mdr) may arise through a variety of mechanisms, the most widely studied and accepted form is associated with an increased concentration of P-glycoprotein (P-gp), a 170 kd protein found in the membrane fraction of a number of mammalian cells. Since mdr seems to be related to the ability of resistant cells to extrude drugs and the circumvention of mdr is supposed to be due to the restored ability to accumulate drugs, membrane has been regarded as the crucial site for such a regulation and an important role for membrane ion exchangers has been suggested. The aim of this work was to elucidate whether the Na+/H+ antiporter is involved in the mechanism of regulation and circumvention of mdr and if 5-(N-ethyl-N-isopropyl) amiloride (EIPA), a selective inhibitor of the Na+/H+ exchanger, can modulate the functional expression of the mdr phenotype. The effect of EIPA on doxorubicin (DX) resistant cells (LoVo/DX) obtained from a human colon adenocarcinoma cell line (LoVo) was studied. EIPA at concentrations ranging from 10 to 50 mu M was able to increase the antibiotic cytotoxicity in the resistant Lovo/DX cells. The reversal of DX resistance paralleled an increase of the ability of the cells to accumulate the drug. Both drug loading and sensitivity to the inhibitory effect of DX on cell proliferation were restored by EIPA in a dose-dependent way. These results suggest a new mechanism of mdr reversal and indicate that amiloride and its derivatives may be useful in reversing DX resistance and in enhancing the clinical effectiveness of chemotherapeutics.

The human type 1 inositol 1,4,5-trisphosphate receptor from T lymphocytes. Structure, localization, and tyrosine phosphorylation

Inositol 1,4,5-trisphosphate receptors (IP3R) are intracellular calcium release channels involved in diverse signaling pathways. An IP3R is thought to play a role in mobilizing calcium required for activation of T lymphocytes. The IP3R is a tetrameric structure comprised of four approximately 300-kDa subunits encoded by a approximately 10-kilobase mRNA. In the present study we determined the structure of the human type 1 IP3R expressed in T lymphocytes (Jurkats). The IP3R in human T cells had a predicted molecular mass of 308 kDa and was most similar to the non-neuronal form of the rodent type 1 IP3R. Two putative tyrosine phosphorylation sites were identified, one near the amino terminus and one near the putative channel pore at the carboxyl terminus. During T cell activation the IP3R was tyrosine phosphorylated. A site-specific anti-IP3R antibody was used to localize the carboxyl terminus of the IP3R to the cytoplasm in T cells.

A phase I trial of intrahepatic verapamil and doxorubicin. Regional therapy to overcome multidrug resistance

BACKGROUND

Verapamil can modulate multidrug resistance in vitro, but only at levels that are not tolerable when administered systemically. Regional strategies of drug administration may permit the delivery of high concentrations of a drug to specific areas with lower systemic levels. Colorectal cancers typically express the multidrug resistance phenotype.

METHODS

A Phase I trial was performed to determine the maximum tolerable dose (MTD) and dose limiting toxicities of verapamil by hepatic artery infusion, together with doxorubicin, to patients with hepatic metastases of colorectal cancer. Fourteen patients with metastatic colorectal cancer received a 14-hour intrahepatic infusion of verapamil. Six hours after the start of the infusion, a fixed dose of doxorubicin (50 mg/m2) was given, also via the hepatic artery, over a 30-minute period. Patients were followed by cardiac telemetry but were not in an intensive care setting, and no invasive monitoring was used. All patients had received prior intrahepatic chemotherapy.

RESULTS

The MTD of intrahepatic verapamil on this schedule in this patient population was 1.2 mg/kg/hour. Hypotension was the dose limiting toxicity. No major objective responses were noted in this heavily pretreated patient population. A dose of 1.0 mg/kg/hour is recommended for Phase II trials.

CONCLUSIONS

Based on estimations of normal hepatic artery blood flow, the estimated concentration of verapamil delivered to the hepatic tumors at 1.0 mg/kg/hour is 3.6 micrograms/ml (7.3 microM), which is comparable to concentrations at which an in vitro reversal of MDR is seen. This study demonstrates that the systemic toxicities of an MDR reversal agent can be overcome by regional drug delivery, establishing this approach as an important model system for further study of MDR modulation.

Reverse transformation of multidrug-resistant cells

Spontaneously transformed Chinese hamster lung cells with high levels of resistance (approximately 100-fold to 70,000-fold) to actinomycin D, daunorubicin, or vincristine exhibit morphology and growth patterns characteristic of normal cells in vitro and reduced tumorigenicity in vivo. These reverse transformed, multidrug-resistant cells amplify and highly overexpress one or more genes encoding P-glycoprotein. Similarly, hydrocarbon-induced mouse sarcoma cells selected with actinomycin D, vincristine, or ethidium bromide developed high levels of resistance associated with reduced drug accumulation and suppression of malignancy. To determine whether human tumor cells would undergo similar changes and whether reverse transformation reflected an altered state of differentiation, nine multidrug-resistant sublines were selected with four agents from human neuroblastoma cells with well defined pathways of differentiation. Those five with resistance levels above about 125-fold showed a reduced tumor frequency as compared to control cells. All resistant sublines showed altered differentiation. The changes in transformation phenotype appear to be intrinsic and not the result of altered immunogenicity. Two additional consequences of high level multidrug resistance have been observed: change in ganglioside composition in the Chinese hamster cells, manifested as a block in higher ganglioside biosynthesis and/or a relative increase in GM3, and increase in epidermal growth factor receptor in all three cell systems. A tentative hypothesis links ganglioside and growth factor receptor changes to the change in transformation phenotype. The basis of the reverse transformation phenomenon is not known, but the major alterations in expression of P-glycoprotein, gangliosides, and the epidermal growth factor receptor implicate, in some way, the plasma membrane.

Genetic aspects of multidrug resistance

Mammalian cells exposed to a single cytotoxic natural product drug, such as vincristine or dactinomycin, can develop resistance to the selective agent and cross-resistance to a broad spectrum of structurally and functionally distinct antibiotics and alkaloids. This phenomenon, termed multidrug resistance (MDR), has been widely studied experimentally. The most consistent feature of cells with high-level MDR is amplification and overexpression of genes encoding an integral plasma membrane protein known as P-glycoprotein. The MDR genes belong to a small family (two members in humans and three members in mouse and Chinese hamster). Based on several lines of evidence, P-glycoprotein is thought to act as an adenosine triphosphate-dependent efflux pump that decreases accumulation of drugs and increases resistance to their effects. The normal function of P-glycoprotein, apart from its role in MDR, is not known. Proposed roles in detoxification and steroid transport systems are speculative but suggest that the membrane protein may have distinct functions in normal tissues and in tumor cells with acquired MDR. Although possible endogenous substrates for P-glycoprotein have not been identified, insight into normal function may be gained from tissue distribution studies. For example, studies using molecular probes to P-glycoprotein messenger RNA and monoclonal antibodies to different epitopes of the molecule have shown that P-glycoprotein is expressed at high levels in the more differentiated or specialized cells of the colon or kidney. Amplification of MDR genes in vivo has not been observed. Whether intrinsic or acquired MDR plays a causal and potentially modifiable role in clinical nonresponsiveness to cancer chemotherapeutic agents is a topic of current interest. Prospective studies and serial determinations during the course of disease are needed to clarify the importance of this membrane protein in clinical drug resistance.

The gene encoding vacuolar H+-ATPase subunit C is overexpressed in multidrug resistant HL60 cells

Previous studies have suggested that vacuolar H(+)-ATPase activity may play a role in modulating drug transport mechanism in multidrug resistant HL60 cells. In the present study we have used a cDNA of human vacuolar H(+)-ATPase subunit C (SC-H(+)-ATPase) to analyze expression of this gene in HL60 cells isolated for resistance to adriamycin or vincristine. The results demonstrate that development of resistance to either agent results in a major increase in the levels of SC-H(+)-ATPase mRNA. Furthermore in resistant cells which have partially reverted to drug sensitivity there is a parallel reduction in SC-H(+)-ATPase mRNA levels. Southern blot analysis shows that the SC-H(+)-ATPase gene is not amplified in the resistant cells. These results therefore demonstrate a correlation between the development of multidrug resistance and enhanced expression of the SC-H(+)-ATPase gene.

Reduced ouabain-sensitive potassium entry as a possible mechanism of multidrug-resistance in P388 cells

Multidrug-resistant P388 cells were found to be resistant also to a variety of ammonium, phosphonium and arsonium compounds. As previously shown for anthracyclines and vinca alkaloids, the resistance to the permanently charged lipophilic cationic compounds could be circumvented by verapamil. Relative to drug-sensitive cells, K+ uptake and plasma membrane Mg-ATPase activity in multidrug-resistant cells are ouabain resistant. The intracellular K+ concentration in drug-resistant cells is maintained at a normal level by increased activity of the furosemide sensitive transport system. It is suggested that the reduced activity of the electrogenic Na(+)-K+ pump in multidrug-resistant, cells could result in a lower transmembrane potential and therefore reduced accumulation of cationic lipophilic compounds.

Multidrug resistance in human neuroblastoma cells

Neuroblastoma remains a significant problem in pediatric oncology. Recently a "multidrug-resistance" gene that may cause cells to become resistant to various chemotherapeutic agents has been cloned. The gene encodes the high-molecular-weight plasma membrane protein known as P-glycoprotein. To study the expression of this gene in cells exhibiting the multidrug-resistant phenotype, a panel of sublines selected with several different natural product drugs was established. The drug-sensitive parental BE(2)-C cells were clonally isolated from the human neuroblastoma SK-N-BE(2) line and exhibit a 150-fold increase in the copy number of the N-myc protooncogene. Sublines were selected by stepwise increases in the concentration of actinomycin-D, doxorubicin, vincristine, or colchicine. Gene amplification was assessed using Southern analysis, and RNA levels were determined by Northern and dot-blot analysis. Western blotting was used to determine protein levels. N-myc amplification and expression were simultaneously determined to assess possible alterations associated with development of multidrug resistance. Amplified P-glycoprotein-encoding genes were not seen in control lines but were clearly present in those that had undergone exposure to each of the chemical agents. Similarly, steady-state messenger RNA and protein levels were greatly increased in the drug-resistant sublines. We conclude that human neuroblastoma cells can acquire the multidrug-resistant phenotype after exposure to various chemotherapeutic agents.

A possible role for a mammalian facilitative hexose transporter in the development of resistance to drugs

We show that D- but not L-hexoses modulate the accumulation of radioactive vinblastine in injected Xenopus laevis oocytes expressing the murine Mdr1b P-glycoprotein. We also show that X. laevis oocytes injected with RNA encoding the rat erythroid/brain glucose transport protein (GLUT1) and expressing the corresponding functional transporter exhibit a lower accumulation of [3H]vinblastine and show a greater capacity to extrude the drug than do control oocytes not expressing the rat GLUT1 protein. Cytochalasin B and phloretin, two inhibitors of the mammalian facilitative glucose transporters, can overcome the reduced drug accumulation conferred by expression of the rat GLUT1 protein in Xenopus oocytes but have no significant effect on the accumulation of drug by Xenopus oocytes expressing the mouse Mdr1b P-glycoprotein. These drugs also increase the accumulation of [3H]vinblastine in multidrug-resistant Chinese hamster ovary cells. Cytochalasin E, an analog of cytochalasin B that does not affect the activity of the facilitative glucose transporter, has no effect on the accumulation of vinblastine by multidrug-resistant Chinese hamster cells or by oocytes expressing either the mouse Mdr1b P-glycoprotein or the GLUT1 protein. In all three cases, the drug verapamil produces a profound effect on the cellular accumulation of vinblastine. Interestingly, although immunological analysis indicated the presence of massive amounts of P-glycoprotein in the multidrug-resistant cells, immunological and functional studies revealed only a minor increase in the expression of a hexose transporter-like protein in resistant versus drug-sensitive cells. Taken together, these results suggest the participation of the mammalian facilitative glucose transporter in the development of drug resistance.

A possible role for a mammalian facilitative hexose transporter in the development of resistance to drugs

We show that D- but not L-hexoses modulate the accumulation of radioactive vinblastine in injected Xenopus laevis oocytes expressing the murine Mdr1b P-glycoprotein. We also show that X. laevis oocytes injected with RNA encoding the rat erythroid/brain glucose transport protein (GLUT1) and expressing the corresponding functional transporter exhibit a lower accumulation of [3H]vinblastine and show a greater capacity to extrude the drug than do control oocytes not expressing the rat GLUT1 protein. Cytochalasin B and phloretin, two inhibitors of the mammalian facilitative glucose transporters, can overcome the reduced drug accumulation conferred by expression of the rat GLUT1 protein in Xenopus oocytes but have no significant effect on the accumulation of drug by Xenopus oocytes expressing the mouse Mdr1b P-glycoprotein. These drugs also increase the accumulation of [3H]vinblastine in multidrug-resistant Chinese hamster ovary cells. Cytochalasin E, an analog of cytochalasin B that does not affect the activity of the facilitative glucose transporter, has no effect on the accumulation of vinblastine by multidrug-resistant Chinese hamster cells or by oocytes expressing either the mouse Mdr1b P-glycoprotein or the GLUT1 protein. In all three cases, the drug verapamil produces a profound effect on the cellular accumulation of vinblastine. Interestingly, although immunological analysis indicated the presence of massive amounts of P-glycoprotein in the multidrug-resistant cells, immunological and functional studies revealed only a minor increase in the expression of a hexose transporter-like protein in resistant versus drug-sensitive cells. Taken together, these results suggest the participation of the mammalian facilitative glucose transporter in the development of drug resistance.

Characteristics of erythroleukemia cells selected for vincristine resistance that have accelerated inducer-mediated differentiation

The induction of murine erythroleukemia cells (MELC; DS19/Sc9) to terminal differentiation by hexamethylenebisacetamide (HMBA) is characterized by a latent period of 10-12 hr before onset of commitment to terminal-cell division and increased transcription of globin genes. MELC variants, derived from this parental cell line, selected for resistance to vincristine (VC), can be induced to differentiate with little or no latent period. This study shows that accelerated HMBA-induced commitment is characteristic of MELC with a low level (2- to 5-fold) of VC resistance in four independently derived cell lines. Both resistance to VC and accelerated differentiation are stable phenotypes for at least 50 passages (approximately 5 months) in the absence of VC. Low-level VC-resistant MELC do not display increased levels of P-glycoprotein or mdr1, mdr2, and mdr3 mRNAs, nor do they exhibit cross-resistance to colchicine or doxorubicin. These cells do show (i) increased level of protein kinase C activity, (ii) reduced accumulation of [3H]VC, and (iii) restoration of VC sensitivity in the presence of verapamil. MELC selected for higher levels of VC resistance (approximately 500-fold) do express high levels of P-glycoprotein and the mdr3 gene. During HMBA-induced differentiation, DS19/Sc9 decrease [3H]VC accumulation, but P-glycoprotein content does not change. A VC-transport-associated protein, also critical for the process of induced differentiation, may be constitutively present in VC-resistant MELC, accounting for their enhanced sensitivity to inducer. This protein accumulates by exposure of VC-sensitive cells to HMBA, contributing to their differentiation and decreased level of VC accumulation.

Production, cross reactivity, and epitope analysis of monoclonal antibodies against rat kidney gamma glutamyltransferase

Eighteen IgG1 monoclonal antibodies (Mabs) have been produced against gamma-glutamyl transferase (GGT) from rat kidney. They were specific to the light subunit of the enzyme with affinity constants ranging from 0.3 to 7.5 10(8) M-1, while they did not react with GGT from other sources i.e. human and pig kidney, rat and guinea pig liver, suggesting species and organ specificity. Two of the Mabs (No 11 and 21) lost their immunoreactivities towards rat kidney GGT in the presence of N-acetyl-neuraminic acid, while immunoreactivities of the other Mabs were unchanged. Furthermore, Mabs No 11 and 21 did not react with desialylated rat kidney GGT. These findings suggest that N-acetyl-neuraminic acid is involved in the epitopes recognized by these two Mabs.

Murine monoclonal antibody recognizing a 90-kDa cell-surface determinant selectively lost by multi-drug-resistant variants of CEM cells

We describe a murine IgG1 monoclonal antibody (MAb56), specific for a cell-surface protein structure (MC56 determinant) expressed by the human CEM cell line. A large band of approximately 90 kDa was identified as the main specific component of the MC56 determinant. Such a 90-kDa protein is significantly associated with the drug-sensitive phenotype, its expression being progressively reduced quantitatively in multi-drug-resistant (MDR) variants of CEM cells, according to the extent of drug resistance. In addition, the MC56 determinant is expressed de novo in drug-sensitive revertant cell lines derived from MDR cells and unreactive with the MAb56. The MAb56 shows a high affinity towards the immunizing drug-sensitive CEM cell line (Ka = 1.86 x 10(9) L/mole) while not binding to MDR cell variants. The expression of the MC56 molecule on a variety of human cells and tissues makes such a cellular determinant a candidate as a marker for studying the MDR phenomenon both in vivo and in vitro.

P-glycoproteins in pathology: the multidrug resistance gene family in humans

Many cancers do not respond to chemotherapy on primary exposure to drugs, thus manifesting intrinsic drug resistance. Other cancers that do initially respond subsequently become resistant to the same drugs and simultaneously to other drugs to which the patient has had no previous exposure. This is a form of acquired drug resistance. There is a pressing need to better understand the mechanisms of drug resistance and to use this information to develop strategies for the chemosensitization of drug-resistant tumors. A goal of the pathology laboratory is to offer chemosensitivity tests that identify intrinsic or acquired resistance of tumors to specific drugs or classes of drugs to enable the clinician to tailor therapy to the biology of cancers in individual patients. Multidrug resistance is one type of drug resistance. It can be present in either an intrinsic or acquired form. The human gene that confers human multidrug resistance, the MDR1 gene, has been cloned and classified as a member of the MDR gene family. Its encoded protein, called Mdr1, is an energy-driven membrane efflux transporter that maintains intracellular concentrations of certain chemotherapeutic drugs at nontoxic levels. Useful model systems for studying multidrug resistance have been developed in several research laboratories. Applying selection pressure by exposing cultured cancer cells to escalating doses of natural product anti-cancer drugs allows cross-resistant cell lines to be produced which share patterns of drug resistance with human cancers. A common feature of these drug-resistant lines is the expression of Mdr1. Using techniques of genetic engineering, molecular probes have been developed that can be used to measure MDR1 mRNA and MDR1 gene amplification. Mdr can be measured by immunochemistry methods. Currently, such measurements are being used to stratify patients in clinical trials designed to determine if chemosensitization by inhibition of the pump function of Mdr is a clinically useful therapeutic strategy. If successful, Mdr/MDR1 mRNA laboratory testing might significantly increase the clinical laboratory's role in cancer patient management.

Mechanisms of multidrug resistance in HL60 cells. Analysis of resistance associated membrane proteins and levels of mdr gene expression

HL60 cells isolated for resistance to Adriamycin do not contain P-glycoprotein, as determined with immunological probes. These cells, however, are multidrug resistant and defective in the cellular accumulation of drug. In view of these findings, we have examined in greater detail certain properties of the HL60/Adr cells and have compared these properties to an HL60 drug-resistant isolate (HL60/Vinc) which contains high levels of P-glycoprotein. The results of these studies demonstrated that verapamil induces a major increase in cellular drug accumulation in both HL60/Adr and HL60/Vinc isolates. An 125I-labeled photoaffinity analog of verapamil labeled P-glycoprotein contained in membranes of HL60/Vinc cells. In contrast, this agent did not label any protein selectively associated with drug resistance in membranes of the HL60/Adr isolate. The photoactive dihydropyridine calcium channel blocker [3H]azidopine and [125I]NASV, a photoaffinity analog of vinblastine, labelled P-glycoprotein in membranes from HL60/Vinc cells, whereas in experiments with the HL60/Adr isolate there was no detectable labeling of a drug resistance associated membrane protein. Additional studies have been carried out to analyze membrane proteins of HL60/Adr cells labeled with the photoaffinity agent 8-azido-alpha-[32P]ATP (AzATP32). The results demonstrate that this agent labeled a resistance associated membrane protein of 190 kilodaltons (P190). P190 is essentially absent in membranes of drug-sensitive cells. Labeling of P190 with AzATP32 in membranes of resistant cells was blocked completely when incubations were carried out in the presence of excess unlabeled ATP. Additional studies were carried out to analyze mdr gene amplification and expression in sensitive and resistant cells. Experiments carried out with human 5',mdr1 (1.1 kb) and mdr3 (1.0 kb) cDNAs demonstrate that both of these sequences were highly amplified in the HL60/Vinc isolate. Only the mrd1 gene sequence however, was overexpressed. In contrast, there was no detectable amplification or overexpression of mdr1 or mdr3 sequences in HL60/Adr cells. The results of this study thus identify a new nucleotide binding protein which is overexpressed in membranes of HL60 cells isolated for resistance to Adriamycin. P190, which exhibits properties distinct from P-glycoprotein, possibly functions in the energy-dependent drug efflux system contained in the HL60/Adr resistant isolate.

Multiple mechanisms of adriamycin resistance in the human leukemia cell line CCRF-CEM

CEM cells exhibiting a 25-fold (C25X) or 80-fold (C80X) increase in resistance to adriamycin were isolated and characterized. C25X cells were cross-resistant to daunomycin and etoposide (VP-16) but not to vincristine or colchicine. These cells were not defective in the cellular accumulation of drug and did not contain detectable levels of P-glycoprotein. Continued exposure of C25X cells to adriamycin resulted in increased levels of resistance and additional phenotypic changes. These cells (C80X) now contained high levels of P-glycoprotein and were cross-resistant to a variety of agents including vincristine and colchicine. A fluorometric assay for DNA unwinding was used to measure levels of drug-induced DNA breaks in sensitive and C25X resistant cells. Studies carried out with VP-16, 4'9-acridinyl-aminomethanesulfon-m-anisidide (m-AMSA), adriamycin, or daunomycin showed that the level of drug-induced DNA strand breakage in resistant cells was considerably less than that occurring in drug-treated sensitive cells. These studies, therefore, show that treatment of CEM cells with adriamycin resulted in a nuclear alteration that contributed to drug resistance. They also demonstrate that prolonged treatment of cells with adriamycin resulted in membrane alterations that affect cellular drug accumulation. Adriamycin resistance in CEM cells can thus occur as a result of at least two distinct mechanisms.

Photoaffinity labeling of the multidrug-resistance-related P-glycoprotein with photoactive analogs of verapamil

Verapamil, a phenylalkylamine calcium channel blocker, has been shown to reverse multidrug resistance in tumor cells, possibly by increasing drug retention through interaction with an outward drug transporter of the resistant cells. In this study two photoactive radioactive analogs of verapamil, N-(p-azido[3,5-3H]benzoyl)aminomethyl verapamil and N-(p-azido[3-125I]salicyl)aminomethyl verapamil, were synthesized and used to identify the possible biochemical target(s) for verapamil in multidrug-resistant DC-3F/VCRd-5L Chinese hamster lung cells selected for resistance to vincristine. The results show that a specifically labeled 150- to 180-kDa membrane protein in resistant cells was immunoprecipitated with a monoclonal antibody specific for P-glycoprotein. Phenylalkylamine binding specificity was established by competitive blocking of specific photolabeling with the nonradioactive photoactive analogs as well as with verapamil. Photoaffinity labeling was also inhibited by 50 microM concentrations of the calcium channel blockers nimodipine, nifedipine, nicardipine, azidopine, bepridil, and diltiazem and partially by prenylamine. Bay K8644, a calcium channel agonist, also inhibited P-glycoprotein photolabeling. Moreover, P-glycoprotein labeling was inhibited in a dose-dependent manner by vinblastine with half-maximal inhibition at 0.2 microM compared to that by verapamil at 8 microM. Photolabeling was also partially inhibited by two of the drugs to which these cells are cross-resistant, doxorubicin and actinomycin D, at 100 microM, but not by colchicine. These data provide direct evidence that P-glycoprotein has broad drug recognition capacity and that it serves as a molecular target for calcium channel blocker action in reversing multidrug resistance.

Increased epidermal growth factor receptor in multidrug-resistant human neuroblastoma cells

Multidrug-resistant human neuroblastoma cell lines obtained by selection with vincristine or actinomycin D from two independent clonal lines, SH-SY5Y and MC-IXC, have 3- to 30-fold more cell surface epidermal growth factor (EGF) receptors than the drug-sensitive parental cells as indicated by EGF binding assays and immunoprecipitation, affinity-labeling, and phosphorylation studies. Reversion to drug sensitivity in one line was accompanied by a return to the parental level of EGF receptor. SH-EP cells, a clone derived from the same neuroblastoma cell line as SH-SY5Y but which displays melanocyte rather than neuronal lineage markers, also express significantly more EGF receptor than SH-SY5Y cells. By nucleic acid hybridization analysis with a molecularly cloned probe, increased receptor level in multidrug-resistant cells was shown to be the result of higher levels of EGF receptor mRNA in drug-resistant than in drug-sensitive cells. The increased steady state amount of specific RNA did not result from amplification of receptor-encoding genes. A small difference was observed in the electrophoretic mobility under denaturing conditions of EGF receptor immunoprecipitated from drug-resistant and drug-sensitive cells. Quantitative and qualitative modulation of the EGF receptor might reflect alterations in the transformation and/or differentiation phenotype of the resistant cells or might result from unknown selective pressures associated with the development of multidrug resistance.

Increase of daunorubicin and vincristine accumulation in multidrug resistant human ovarian carcinoma cells by a monoclonal antibody reacting with P-glycoprotein

An overexpression of plasma membrane 170-180 kDa P-glycoproteins is consistently found in multidrug-resistant (MDR) cell lines. In this study MRK-16, a monoclonal antibody (mAb) reacting with P-glycoprotein is used to study the putative functional role of this protein in vincristine (VCR) and daunorubicin (DNR) cellular accumulation in the MDR human ovarian carcinoma cell line 2780AD. We established that this cell line is highly cross-resistant to vincristine and daunomycin, related to a greatly reduced drug accumulation. Verapamil (Vp) (8 microM) caused a 3.6-fold increase in DNR as well as VCR accumulation. Exposition of 2780AD cells to MRK-16 led to an increase of 30% in cellular accumulation of VCR, both in normal growth medium as well as in medium without added glucose and with sodium azide, which largely depleted cellular ATP levels. No increase in DNR accumulation was found under these conditions. However, in the presence of 8 microM Vp, MRK-16 increased not only VCR but also DNR accumulation with about 30%. The relative increase of DNR accumulation was constant in a concentration range of 0.2-4 microM DNR. These data indicate that mAbs against P-glycoprotein might potentiate the action of calcium antagonists like Vp to increase cellular anthracycline accumulation.

Electrophoretic mobility studies on doxorubicin-resistant and -sensitive murine P388 leukemic cells

The electrokinetic properties of doxorubicin (DOX)-resistant (P388/R) and -sensitive (P388/S) murine leukemic cells were studied in a free-flow electrophoresis (FFE) system. The electrophoretic mobilities (EM) of P388/S and P388/R cells were 1.07 and 1.35 x 10(-4) cm2 V-1 s-1, respectively, suggesting a higher net negative charge on the P388/R cells. Neuraminidase treatment decreased the EM of both the P388/S and P388/R cells by 15-20% but had no effect on cellular doxorubicin retention. Total and cell surface sialic acid contents were similar in both the cell lines. Our studies show that no direct correlations may exist among surface charge, cell surface sialic acid content, and doxorubicin retention in DOX-resistant and -sensitive P388 cells; however, differences in cell surface charge between these cell types were used to separate them by preparative FFE.

Effects of verapamil on the cellular accumulations and toxicity of several antitumor drugs in 9-hydroxy-ellipticine-resistant cells

9-OH-Ellipticine (9-OH-E)-resistant cells are not only resistant to the DNA topoisomerase II inhibitors, but also to some other antitumor agents, such as actinomycin D (AD), adriamycin (ADM), daunorubicin and vincristine. It was previously shown that a decreased uptake accounts for the cross-resistance of these cells to AD and ADM which then suggested that the 9-OH-E-resistant cells might display some of the properties usually associated with the multidrug resistance phenotype. In this work, we have examined the effects of verapamil, a drug which is known to overcome the multidrug resistance, on the toxicity and the cellular accumulation of four cytotoxic agents: 9-OH-E, 2N-methyl-9-hydroxy-ellipticinium (NMHE), AD and ADM, either on 9-OH-E resistant cells or on a multidrug resistant subline derived from the same sensitive parental cells. Verapamil inhibited the cellular accumulation of the ellipticine derivatives in the sensitive DC-3F cells, and the toxicity of these drugs on these cells was correspondingly decreased. On either one of the resistant cell lines, verapamil had no effect on the toxicity and the cellular accumulation of 9-OH-E. In contrast, in the presence of verapamil, the cellular accumulation of NMHE by the 9-OH-E and the multidrug resistant cells was about 50% and 300% increased, respectively. The increased NMHE cellular concentration in the multidrug resistant cells was associated with an 8-fold increased toxicity. The major structural characteristics which might account for this difference between the sensitivities of both ellipticine derivatives to the effects of verapamil on the multidrug resistant cells is the presence of a positive charge on the nitrogen in position 2 of the 6H-pyridocarbazole molecule. Finally, verapamil circumvented partially the cross-resistance of DC-3F/9-OH-E cells to AD and ADM by increasing the accumulation of these drugs inside the cells.

Sorcin (V19), a soluble acidic calcium-binding protein overproduced in multidrug-resistant cells. Identification of the protein by anti-sorcin antibody

Sorcin (soluble resistance-related calcium-binding protein), an acidic (pI = 5.7) protein (Mr approximately 20 kDa) previously designated V19, was originally identified in cells selected for high levels of resistance to vincristine. Two-dimensional gel electrophoresis and/or Western blot techniques now show sorcin to be overproduced in cells selected for resistance to actinomycin D (QUA/ADj), colchicine (CHRC5), and adriamycin (BE(2)-C/ADR). Not all cell lines selected for resistance to these drugs overproduced sorcin; e.g. cells of an independently selected actinomycin D-resistant subline of QUA, QUA/ADsx, did not contain increased amounts of sorcin. Sorcin was purified by preparative gel electrophoresis from QUA/ADj cells and used to generate specific antiserum in chickens. By Western blot analyses the antiserum was shown to recognize sorcin in QUA/ADj and in vincristine-resistant mouse and Chinese hamster lung, colchicine-resistant Chinese hamster ovary, and adriamycin-resistant human neuroblastoma lines. Low level expression of the protein was detectable in control, drug-sensitive cells. Direct binding assays with 45Ca2+ showed that sorcin was a calcium-binding protein. QUA/ADj cells contained increased numbers of double minute chromosomes (DMs), cytogenetic indicators of gene amplification. As found for two other multidrug-resistant sublines, sorcin overproduction in QUA/ADj cells may be the result of amplification of the sorcin-encoding gene. The overproduction of this protein in multidrug-resistant cells of various species implies that sorcin plays a role in expression of the resistant phenotype.

Adriamycin resistance in HL60 cells in the absence of detectable P-glycoprotein

Previous studies have shown that the development of multi-drug resistance in cell lines treated with chemotherapeutic agents is closely associated with the overexpression of a 170-180 kilodalton surface membrane glycoprotein (P-glycoprotein). In the present study a monoclonal antibody against the P-glycoprotein was used to determine if this protein is overexpressed in multi-drug resistant HL60 cells. Using either indirect immunofluorescent staining or immunoblot analysis P-glycoprotein could not be detected in HL60 cells isolated for resistance to adriamycin. In contrast HL60 cells isolated for resistance to vincristine contain the P-glycoprotein and the amount of this material increases with increasing levels of resistance. These studies thus demonstrate adriamycin resistance in P-glycoprotein negative HL60 cells. Furthermore adriamycin and vincristine are found to have distinct effects in inducing overexpression of P-glycoprotein in the HL60 cell line. This information could be useful in the development of therapeutic strategies for the treatment of certain forms of cancer.

The relationship between cisplatin sensitivity and drug uptake into mammalian cells in vitro

Clonogenic survival of HeLa, Chinese hamster and HaK cells after treatment with a range of cisplatin concentrations and exposure times was determined and cellular platinum concentrations were measured by PIXE. It was demonstrated that cisplatin cytotoxicity of the three cell lines varied considerably as a function of drug exposure dose. These differences are related to differential cellular drug uptake.

Epidermal growth factor receptor is increased in multidrug-resistant Chinese hamster and mouse tumor cells

Multidrug-resistant sublines of Chinese hamster lung and mouse tumor cells selected for high levels of resistance to vincristine or actinomycin D have increased numbers of epidermal growth factor (EGF) receptors compared to control cells. Evidence for this increase was found in six of six resistant cell lines with the use of receptor binding or immunoprecipitation techniques. Levels of 125I-labeled EGF binding to intact actinomycin D-resistant cells derived from DC-3F or CLM-7 Chinese hamster lines are increased 3- to 10-fold compared to controls. Scatchard analysis of these data suggests that increased binding is a result of increased receptor number rather than altered affinity of receptor for ligand. Affinity-labeling and immunoprecipitation studies confirmed the finding of increased receptor amount in resistant hamster and mouse cells. Multidrug-resistant variants of DC-3F cells overproduce a plasma membrane glycoprotein (gp150-180) with several physicochemical properties that resemble those of EGF receptor. However, electrophoretic transfer blots with a polyclonal antibody to gp150-180 show that EGF receptor and gp150-180 are probably different molecules. Resistant cells described in this report manifest a normalized phenotype compared to transformed, tumorigenic, drug-sensitive parental cells. EGF receptor increase in resistant variants may be associated with this reverse transformation.

Amplification and expression of genes associated with multidrug resistance in mammalian cells

In multidrug resistance, which is observed clinically and in tissue culture, cells that are challenged with certain cytotoxic drugs develop resistance not only to the selective agent but also to other, seemingly unrelated, agents. The multidrug-resistant phenotype is associated with DNA sequence amplification and with the overproduction of a number of cytosolic and membrane glycoproteins. The differential amplification and altered expression of at least two related genes, termed multidrug-resistant associated genes has been shown in multidrug-resistant Chinese hamster cells. In multidrug-resistant mouse and human cells, genes homologous to those in Chinese hamster cells are also amplified. The level of expression of these genes varied and did not correlate with their copy number. Furthermore, in Chinese hamster cells, the development of resistance to a single drug and multidrug resistance were closely related, but uncoupled, events. The overexpression of the multidrug-resistant genes was better correlated with the degree of resistance to the selective agent than it was with the extent of multidrug resistance.

Membrane-associated proteins of adriamycin sensitive and resistant murine leukemic P388 cells

We have isolated an 84-fold adriamycin resistant subline, P388/R84, from mouse leukemia P388 cells by serial cultivation in methylcellulose in the presence of increasing drug concentrations. Electrophoresis of detergent soluble fractions of radiolabeled sensitive and resistant cells suggested marked alterations in the protein fractions of 160, 100, 60, 45, and 30 kd. In resistant clones labeled with 125I an increase in 160 and 100 kd proteins was accompanied by concomitant reduction in the 60, 45, and 30 kd proteins. In 35S methionine-labeled resistant cells, similar increases in the 160 and 100 kd components were observed but in contrast to 125I-labeled cells the 30 kd component was also higher. Alterations in surface proteins were confirmed in experiments where the cell extracts were adsorbed to concanavalin A polymers and extracted with 0.26 M methyl-alpha-D-mannopyranoside. Our data confirm earlier reported observations on cell-surface protein changes in cells resistant to anthracyclines and alkaloids.

Gene amplification in Djungarian hamster cell lines possessing decreased plasma membrane permeability for colchicine and some other drugs

By multistep selection a set of clones and sublines possessing different levels of resistance to colchicine or adriablastin was obtained from the SV40-transformed Djungarian hamster cell lines, DM-15 and DMcap. Resistance to both colchicine and adriablastin is associated with an alteration of plasma membrane permeability leading to a decreased uptake of various drugs (3H-colchicine, 3H-cytochalasin B, 3H-actinomycin D, 3H-puromycin, 3H-vinblastine, 14C-chloramphenicol). The DNA of cells highly resistant to cholchicine can transmit resistance only to low dosages of the drug. Comparison of DNAs from wild-type and resistant cells digested by restriction endonucleases revealed new classes of repeated DNA sequences in resistant cell lines. The degree of DNA repetition was correlated with the level of drug resistance. The repeated DNA sequences evidently represent parts of the genome that are amplified in resistant cells. The size of the amplified sequences is 200-250 kilobase pairs (kb). Cell lines highly resistant to colchicine contain amplified DNA, which like mitochondrial DNA replicate asynchronously with the main portion of the cellular DNA and related but not identical DNA sequences are amplified in independent cell lines selected for resistance to colchicine, adriablastin, and actinomycin D. These cell lines display similar patterns of alterations of plasma membrane permeability. The amplified DNA sequences may contain a gene or genes the overexpression of which leads to change in plasma membrane permeability and a development of resistance to various drugs.

Heterogeneous distribution of drug metabolism in elutriated rat hepatocytes

Centrifugal elutriation was used to separate isolated rat hepatocytes into five fractions containing cells of different sizes. These fractions were compared with regard to cell size, morphology and function. Analyzed by flow cytometry, the small cells were found to be enriched in fraction 1 and the large cells in fraction 5. Evaluation by light and electron microscopy indicated that the fractions contained single hepatocytes of normal structure. The cytochrome P-450 content and the 7-ethoxycoumarin O-deethylase activity were assessed in hepatocytes from untreated animals, those treated with phenobarbital, and those treated with phenobarbital plus allylisopropylacetamide. In both untreated and phenobarbital-treated animals, cytochrome P-450 content and 7-ethoxycoumarin O-deethylase activity rose significantly from fraction 1 to fraction 5. The P-450 content gradually rose up to 2-fold. The enzyme activity rose 5-fold, and it increased steeply between fractions 2 and 3. The cytochrome P-450 content in phenobarbital-plus-allylisopropylacetamide-treated animals was decreased in all fractions but more extensively in fraction 5 than in fraction 1.

Co-amplification of double minute chromosomes, multiple drug resistance, and cell surface P-glycoprotein in DNA-mediated transformants of mouse cells

A genetic system comprised of mammalian cell mutants which demonstrate concomitant resistance to a number of unrelated drugs has been described previously. The resistance is due to reduced cell membrane permeability and is correlated with the presence of large amounts of a plasma membrane glycoprotein termed P-glycoprotein. This system could represent a model for multiple drug resistance which develops in cancer patients treated with chemotherapeutic drugs. We demonstrate here that the multiple drug resistance phenotype can be transferred to mouse cells with DNA from a drug-resistant mutant and then amplified quantitatively by culture in media containing increasing concentrations of drug. The amount of P-glycoprotein was correlated directly with the degree of drug resistance in the transformants and amplified transformants. In addition, the drug resistance and expression of P-glycoprotein of the transformants were unstable and associated quantitatively with the number of double minute chromosomes. We suggest that the gene for multiple drug resistance and P-glycoprotein is contained in these extrachromosomal particles and is amplified by increases in double minute chromosome number. The potential use of this system for manipulation of mammalian genes in general is discussed.

Co-amplification of double minute chromosomes, multiple drug resistance, and cell surface P-glycoprotein in DNA-mediated transformants of mouse cells

A genetic system comprised of mammalian cell mutants which demonstrate concomitant resistance to a number of unrelated drugs has been described previously. The resistance is due to reduced cell membrane permeability and is correlated with the presence of large amounts of a plasma membrane glycoprotein termed P-glycoprotein. This system could represent a model for multiple drug resistance which develops in cancer patients treated with chemotherapeutic drugs. We demonstrate here that the multiple drug resistance phenotype can be transferred to mouse cells with DNA from a drug-resistant mutant and then amplified quantitatively by culture in media containing increasing concentrations of drug. The amount of P-glycoprotein was correlated directly with the degree of drug resistance in the transformants and amplified transformants. In addition, the drug resistance and expression of P-glycoprotein of the transformants were unstable and associated quantitatively with the number of double minute chromosomes. We suggest that the gene for multiple drug resistance and P-glycoprotein is contained in these extrachromosomal particles and is amplified by increases in double minute chromosome number. The potential use of this system for manipulation of mammalian genes in general is discussed.

Identification and characterization of a plasma membrane phosphoprotein which is present in Chinese hamster lung cells resistant to adriamycin

Studies have been carried out to analyze the phosphoprotein composition of plasma membranes from Chinese hamster lung cells resistant to the action of adriamycin. Gel electrophoretic analysis of [32Pi]-labeled proteins revealed that plasma membranes from resistant cells contain a phosphoprotein of 180,000 molecular weight (P180) which is not detected in drug sensitive cells. Protein P180 can also be identified after phosphorylation of resistant plasma membranes in an in vitro protein kinase system. Pulse-chase experiments indicated that the P180 was metabolically active and underwent cycles of phosphorylation and dephosphorylation in the cell. Additional studies showed that, in the presence of N-ethylmaleimide (NEM), there was a major increase in the uptake of adriamycin in resistant cells. A similar effect was observed with KCN but not with sodium azide. When resistant cells were grown in the presence of [32Pi] and then incubated in the presence of NEM, there was a considerable increase in the phosphorylation of P180. In contrast, many other plasma membrane proteins were dephosphorylated under these incubation conditions. The results suggest the possibility that, as P180 was hyperphosphorylated, the protein was inactivated and this contributed to the ability of resistant cells to accumulate adriamycin.

Cell surface P-glycoprotein associated with multidrug resistance in mammalian cell lines

The plasma membranes of hamster, mouse, and human tumor cell lines that display multiple resistance to drugs were examined by gel electrophoresis and immunoblotting. In every case, increased expression of a 170,000-dalton surface antigen was found to be correlated with multidrug resistance. This membrane component is of identical molecular size and shares some immunogenic homology with the previously characterized P-glycoprotein of colchicine-resistant Chinese hamster ovary cells. This finding may have application to cancer therapy.

Evidence that adriamycin resistance in Chinese hamster lung cells is regulated by phosphorylation of a plasma membrane glycoprotein

Incubation of adriamycin resistant Chinese hamster lung cells with low levels of N-ethylmaleimide (NEM) results in a major increase in the cellular accumulation of drug. When resistant cells are prelabeled with [32Pi] and thereafter treated with NEM there also occurs a selective superphosphorylation of an 180K plasma membrane glycoprotein (P-180). This phosphorylation reaction occurs at both serine and threonine residues. In similar experiments with drug sensitive cells only minor levels of this protein can be detected. Detailed studies have established that in cells which have reverted to drug sensitivity there is a parallel loss in the presence of phosphorylated P-180. Also in cells which have undergone partial reversion to drug sensitivity there is a correlation between levels of superphosphorylated P-180 and adriamycin resistance. These results provide evidence that adriamycin resistance is dependent on the presence of P-180. The results also suggest that the biological activity of this protein is highly regulated by phosphorylation and that in the superphosphorylated state P-180 is inactive and under these conditions the resistant cell is converted to a drug sensitive phenotype.

Effect of tunicamycin on receptors for tumor promoters

A progressive decline in the specific binding of [20-3H]phorbol 12,13-dibutyrate ([3H]PDBu) and glycoprotein synthesis was observed following treatment of primary mouse epidermal cells with tunicamycin, a specific inhibitor of dolichol-mediated glycosylation. Following 18 h of treatment, the specific binding of [3H]PDBu was reduced to 33-56% of the control value. The total protein synthesis determined by leucine incorporation into acid-insoluble material was not altered by this antibiotic drug. These results suggest that the receptor for phorbol diesters is, or is functionally linked to, a glycoprotein on the cell surface.