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

Quantitative Proteomics Identifies Secreted Diagnostic Biomarkers as well as Tumor-Dependent Prognostic Targets for Clear Cell Renal Cell Carcinoma

Clear cell renal cell carcinoma (ccRCC) is the third most common and most malignant urological cancer, with a 5-year survival rate of 10% for patients with advanced tumors. Here, we identified 10,160 unique proteins by in-depth quantitative proteomics, of which 955 proteins were significantly regulated between tumor and normal adjacent tissues. We verified four putatively secreted biomarker candidates, namely, PLOD2, FERMT3, SPARC, and SIRPα, as highly expressed proteins that are not affected by intratumor and intertumor heterogeneity. Moreover, SPARC displayed a significant increase in urine samples of patients with ccRCC, making it a promising marker for the detection of the disease in body fluids. Furthermore, based on molecular expression profiles, we propose a biomarker panel for the robust classification of ccRCC tumors into two main clusters, which significantly differed in patient outcome with an almost three times higher risk of death for cluster 1 tumors compared with cluster 2 tumors. Moreover, among the most significant clustering proteins, 13 were targets of repurposed inhibitory FDA-approved drugs. Our rigorous proteomics approach identified promising diagnostic and tumor-discriminative biomarker candidates which can serve as therapeutic targets for the treatment of ccRCC. IMPLICATIONS: Our in-depth quantitative proteomics analysis of ccRCC tissues identifies the putatively secreted protein SPARC as a promising urine biomarker and reveals two molecular tumor phenotypes.

Streptomycin sulphate loaded solid lipid nanoparticles show enhanced uptake in macrophage, lower MIC in Mycobacterium and improved oral bioavailability

Present study addresses the challenge of incorporating hydrophilic streptomycin sulphate (STRS; log P -6.4) with high dose (1 g/day) into a lipid matrix of SLNs. Cold high-pressure homogenization technique used for SLN preparation achieved 30% drug loading and 51.17 ± 0.95% entrapment efficiency. Polyethylene glycol 600 as a supporting-surfactant assigned small size (218.1 ± 15.46 nm) and mucus-penetrating property. It was conceived to administer STRS-SLNs orally rather than intramuscularly. STRS-SLNs remained stable on incubation for varying times in SGF or SIF. STRS-SLNs were extensively characterised for microscopic (TEM and AFM), thermal (DSC), diffraction (XRD) and spectroscopic (NMR and FTIR) properties and showed zero-order controlled release. Enhanced (60 times) intracellular uptake was observed in THP-1 and Pgp expressing LoVo and DLD-1 cell lines, using fluorescein-SLNs. Presence of SLNs in LoVo cells was also revealed by TEM studies. STRS-SLNs showed 3 times reduction in MIC against Mycobacterium tuberculosis H37RV (256182) in comparison to free STRS. It also showed better activity against both M. bovis BCG and Mycobacterium tuberculosis H37RV (272994) in comparison to free STRS. Cytotoxicity and acute toxicity studies (OECD 425 guidelines) confirmed in vitro and in vivo safety of STRS-SLNs. Single-dose oral pharmacokinetic studies in rat plasma using validated LCMS/MS technique or the microbioassay showed significant oral absorption and bioavailability (160% - 710% increase than free drug).

P-glycoprotein and its inhibition in tumors by phytochemicals derived from Chinese herbs

P-glycoprotein belongs to the family of ATP-binding cassette (ABC) transporters. It functions in cellular detoxification, pumping a wide range of xenobiotic compounds, including anticancer drugs out of the cell. In cancerous cells, P-glycoprotein confers resistance to a broad spectrum of anticancer agents, a phenomenon termed multidrug resistance. An attractive strategy for overcoming multidrug resistance is to block the transport function of P-glycoprotein and thus increase intracellular concentrations of anticancer drugs to lethal levels. Efforts to identify P-glycoprotein inhibitors have led to numerous candidates, none of which have passed clinical trials with cancer patients due to their high toxicity. The search for naturally inhibitory products from traditional Chinese medicine may be more promising because natural products are frequently less toxic than chemically synthesized substances. In this review, we give an overview of molecular and clinical aspects of P-glycoprotein and multidrug resistance in the context of cancer as well as Chinese herbs and phytochemicals showing inhibitory activity towards P-glycoprotein.

Inhibition of nuclear factor kappa B transcription activity drives a synergistic effect of pyrrolidine dithiocarbamate and cisplatin for treatment of renal cell carcinoma

One of the impeding factors in the effective treatment of metastatic renal cell carcinoma (RCC) is their intrinsic and acquired resistance to chemotherapeutics. Many studies have shown that drug resistance, at least in part, is mediated by the upregulation of anti-apoptotic (Bcl-2) and multidrug resistance molecules (MDR-1 and MRP-1) by the transcription factor nuclear factor kappa B (NF-kappaB). Combining NF-kappaB inhibitors with conventional chemotherapeutics could overcome resistance of cancer cells. In this study, we examined the synergistic effect of pyrrolidine dithiocarbamate (PDTC), a NF-kappaB inhibitor, and cisplatin, on two human metastatic RCC cell lines ACHN and SN12K1. Individual non-toxic concentrations of PDTC and cisplatin, when combined, synergistically induced a significant increase in apoptosis of the two RCC cell lines. In ACHN cells, the groups with nuclear translocation of NF-kappaB showed resistance to apoptosis, but in SN12K1 cells, the groups with NF-kappaB translocation were susceptible to apoptosis. The combination treatment significantly decreased the transcription activity of all NF-kappaB subunits in both cell lines. Anti-apoptotic proteins Bcl-2 and Bcl-(XL) were significantly decreased in the combination therapy group of both cell lines, but MDR-1 was decreased only in the ACHN cells. No changes in MRP-1 were observed in any of the treatment groups. The results demonstrate the potential of PDTC to be an adjunct therapeutic agent. The major mechanism of the synergistic effect appears to be mediated by the inhibition of transcription activity of NF-kappaB rather than its expression, and the resultant decrease in the anti-apoptotic proteins Bcl-2 and Bcl-(XL).

Molecular biology of cantharidin in cancer cells

Herbal medicine is one of the forms of traditional medical practice. Traditional Chinese medicine (TCM) and traditional Vietnamese medicine (TVM) are well-known for their long-standing tradition of herbal medicine. Secreted by many species of blister beetle, most notably by the 'Spanish fly' (Lytta vesicatoria), cantharidin inhibits protein phosphatases 1 and 2A (PP1, PP2A). Blister beetle has been used in Asian traditional medicine to treat Molluscum contagiosum virus (MCV) infections and associated warts, and is now also used for cancer treatment. A combination of both genomic and postgenomic techniques was used in our studies to identify candidate genes affecting sensitivity or resistance to cantharidin. Cantharidin was not found to be related to multidrug resistance phenotype, suggesting its potential usefulness for the treatment of refractory tumors. Oxidative stress response genes diminish the activity of cantharidin by inducing DNA strand breaks which may be subject to base excision repair and induce apoptosis in a p53- and Bcl2-dependent manner. Cantharidin is one of many natural products used in traditional Chinese medicine and traditional Vietnamese medicine for cancer treatment. Combined methods of pharmaceutical biology and molecular biology can help elucidate modes of action of these natural products.

Reversal of P-glycoprotein mediated multidrug resistance in K562 cell line by a novel synthetic calmodulin inhibitor, E6

The overexpression of P-glycoprotein (P-gp) is associated with multidrug resistance (MDR) of tumor cells to a number of chemotherapeutic drugs. P-gp inhibitors have been shown to effectively reverse P-gp-mediated MDR in both in vitro and in vivo. Our previous studies demonstrated that E6, a novel synthetic calmodulin inhibitor, exhibited potent inhibitory effect on P-gp in rat brain microvessel endothelial cells (RBMECs). In the present study, the effect of E6 on MDR in a K562 MDR cell line (K562/DOX) highly expressing P-gp was studied and compared with that of a conventional P-gp inhibitor, verapamil (VER). E6 at concentrations of 1, 3, 10, 30 microM reduced the IC50 value of doxorubicin in K562/DOX cells from 79.19 microM to 35.18, 21.86, 6.31 and 1.97 microM, respectively. However, the IC50 value of doxorubicin in K562 sensitive subline was not significantly changed by E6. Using a DNA content analysis and an annexin V binding assay, the effects of E6 on doxorubicin-induced apoptosis were also examined. The results indicated that E6 effectively reversed the resistance to doxorubicin-induced apoptosis in K562/DOX cells. In addition, co-treatment of E6 and doxorubicin resulted in a remarkably G2/M blocking effect in K562/DOX cells. Furthermore, the treatment of K562/DOX cells with 10 microM E6 led to increased intracellular accumulation and decreased efflux of doxorubicin. Overall, the pharmacological effects of E6 on P-gp-mediated MDR is much stronger than that of positive control drug VER. These results suggested that E6 is a novel and potent MDR reversal agent and may be a potential adjunctive agent for tumor chemotherapy.

Targeted chemotherapy with cytotoxic bombesin analogue AN-215 can overcome chemoresistance in experimental renal cell carcinomas

BACKGROUND

Multidrug resistance (MDR) mediated by membrane transporters, such as P-glycoprotein (MDR-1) and MDR-associated protein (MRP), remains a challenge in the therapy of renal cell carcinoma (RCC). Chemotherapy targeted to hormone receptors may provide a new approach to overcome chemoresistance. The cytotoxic analogue of bombesin/gastrin-releasing peptide (GRP), AN-215, consists of a superactive derivative of doxorubicin, AN-201, which is linked to a bombesin analogue carrier: RC-3094.

METHODS

The authors examined the expression of bombesin/GRP receptors in 3 human RCC cell lines (A-498, ACHN. and 786-0) by using reverse-transcriptase-polymerase chain reaction (RT-PCR) analysis and radioligand-binding assays. They also evaluated the effects of AN-215 and its cytotoxic radical AN-201 in the same RCC models in vivo, and they studied the effects of AN-215 and AN-201 on the expression levels of MDR-1 and subtype 1 of MRP (MRP-1) by using real-time PCR.

RESULTS

A N-215 significantly (P < 0.05) inhibited the growth of A-498, ACHN, and 786-0 RCC xenografted into nude mice by 59.2-67.6%, whereas the cytotoxic radical AN-201 alone had no significant antitumor effects. The efficacy of AN-215 was independent of the expression patterns of MDR-1 and MRP-1 in these RCC cell lines. The induction of MDR-1 by AN-215 was similar (Experiment 2) or weaker (Experiment 1) compared with AN-201. Both AN-215 and AN-201 caused only a minor induction of MRP-1.

CONCLUSIONS

The current findings indicated that targeted chemotherapy with cytotoxic bombesin/GRP analogue AN-215 can inhibit the growth of RCC, providing a new treatment modality for patients with advanced RCC.

Clonal xenobiotic resistance during pollution-induced toxic injury and hepatocellular carcinogenesis in liver of female flounder (Platichthys flesus (L.))

Juvenile and adult female flounder (Platichthys flesus (L.)) were caught either in the estuary of the most polluted European river, the Elbe, or as controls in a reference site to study pollution-induced xenobiotic resistance in their livers in relation to pathological alterations. In juvenile fish, livers displayed reversible and irreversible degenerative toxipathic lesion types but never showed (pre)neoplastic changes. Tumour frequencies up to 70% were found macroscopically in livers of adult female flounder which had progressed to adenomas and carcinomas in the most polluted site. Because male adult flounder show only up to 50% of livers containing early preneoplastic foci but never malignancies, we focussed our study on female individuals. (Pre)neoplastic changes ranged from early eosinophilic foci to basophilic foci, adenomas and hepatocellular carcinomas. Adenomas were generally eosinophilic whereas carcinomas were mainly basophilic. These phenotypical sequential changes strongly resemble those found in chemically-induced liver carcinogenesis in mammals. Characteristic mutations known from mammalian cancers have not been found so far in these flounder livers. Therefore, we investigated whether epigenetic events had induced a metabolic "resistant phenotype" of (pre)malignant cancer cells during hepatocellular carcinogenesis. With a quantitative immunohistochemical approach, we studied expression of P-glycoprotein (P-gp)-mediated multixenobiotic resistance (MXR), cytochrome P4501A1, glutathione-S-transferase-A which are key proteins in xenobiotic metabolism and elimination. Glucose-6-phosphate dehydrogenase (G6PDH) activity, the major source of the reducing power NADPH which is needed for biotransformation, oxyradical scavenging and biosynthesis, was detected as well. We observed upregulation of G6PDH activity already in early preneoplastic eosinophilic foci and subsequent further upregulation in basophilic foci and carcinomas. P-gp started to become overexpressed in basophilic foci and was overexpressed even more strongly in carcinomas and their invasively-growing protrusions (satellites). In carcinomas, P-gp protein was predominantly present in membranes of lysosomes which are the intracellular sites of deposition of xenobiotics. CYP450 was reduced whereas GST-A was increased in these carcinomas. Progression towards malignancy was positively correlated with levels of mitogenic organochlorines in these livers which are "fingerprint contaminants" of the river Elbe. We conclude that (pre)neoplastic hepatocytes in female flounder acquire growth advantages over normal hepatocytes by epigenetic metabolic adaptations during liver carcinogenesis as a result of chronic exposure to (pro)carcinogens in the polluted habitat.

Activity of drugs from traditional Chinese medicine toward sensitive and MDR1- or MRP1-overexpressing multidrug-resistant human CCRF-CEM leukemia cells

There is considerable interest among basic and clinical researchers in novel drugs with activity against leukemia. The vast history of experience of traditional Chinese medicine (TCM) with medicinal plants may facilitate the identification of novel antileukemic compounds. In the present investigation, we tested 22 drugs for their activity toward CCRF-CEM cell lines: artesunate, artemisinin, baicalein, baicalin, berberine, bufalin, cantharidin, cephalotaxine, curcumin, daidzein, daidzin, diallyl disulfide, ginsenoside Rh2, glycyrrhizic acid, isonardosinon, homoharringtonine, nardosinon, nardofuran, puerarin, quercetin, tannic acid, and tetrahydronardosinon. As compounds from folk medicinal remedies are sometimes looked upon as alternative medicine with some hesitation or criticism, we investigated only chemically pure compounds and tested the drugs independently in two different laboratories in Germany and Australia. We used CCRF-CEM parental cells and doxorubicin-selected P-glycoprotein (P-gp)/MDR1-expressing CEM/ADR5000, vinblastine-selected P-gp/MDR1-expressing CEM/VLB(100), and epirubicin-selected multidrug resistance-related protein 1 (MRP1)-expressing CEM/E1000 sublines thereof. While CEM/ADR5000, CEM/VLB(100), and CEM/E1000 cells were highly resistant to the corresponding selecting agents, no or only minimal degrees of cross-resistance were observed to TCM drugs in both growth inhibition assay and MTT assay (range from 0.4- to 8-fold). Homoharringtonine, artesunate, and bufalin were most active among this panel of compounds. As shown by flow cytometry, artesunate significantly increased daunorubicin accumulation in CEM/E1000 cells, but not in CEM/VLB(100) or CCRF-CEM parental cells. Bufalin caused a small, but significant increase in daunorubicin accumulation in CEM/VLB(100) and CEM/E1000 cells. As artesunate and bufalin showed both antileukemic activity if applied alone and modulation activity in combination with daunorubicin in multidrug-resistant (MDR) cells, these two drugs may be suitable for novel combination treatment regimens to improve leukemia cell killing.

Methylthioadenosine phosphorylase as target for chemoselective treatment of T-cell acute lymphoblastic leukemic cells

We analyzed the role of methylthioadenosine phosphorylase (MTAP) for chemoselective treatment of T-cell acute lymphoblastic leukemia (T-ALL). MTAP converts methylthioadenosine into adenine which serves as an alternative purine source, if de novo purine biosynthesis is inhibited by antimetabolites (i.e., methotrexate). The idea of the chemoselectivity concept is that tumors with MTAP deletion at chromosome 9p21 are more susceptible to antimetabolites than normal cells without such a deletion. First, we screened 13 T-ALL lines for 9p21 deletions by comparative genomic hybridization. Five cell lines revealed deletions at the short arm of chromosome 9, dim(9p21pter). Further analyses were performed with CEM cells in which the 9p21 deletion was corroborated by fluorescence in situ hybridization. CEM cells were transfected with an MTAP expression vector. A green fluorescent protein (GFP) plasmid was cotransfected, to monitor the transfection efficacy by flow cytometry. The response of MTAP-transfected cells to the antimetabolites methotrexate (MTX), trimetrexate (TMX), and L-alanosine (ALA) was decreased compared to mock control transfectants using growth inhibition assays. The activity of doxorubicin (DOX) which is not involved in DNA biosynthesis was not changed in MTAP transfectants. As the p16(INK4a) tumor suppressor gene resides also at 9p21, we transfected CEM cells with a p16(INK4a) expression vector. These transfectant cells were more resistant to all four drugs indicating that p16(INK4a) did not specifically affect antimetabolites. The chemoselective effect of antimetabolites in MTAP-deleted tumor cells may, however, be compensated by the development of drug resistance. To prove this possibility, we analyzed an MTX-resistant subline, CEM/MTX1500LV, in which the MTX-resistance conferring dihydrofolate reductase (DHFR) gene was amplified. While TMX exhibited considerable cross-resistance in CEM/MTX1500LV cells, ALA did not. Thus, ALA could exhibit chemoselectivity in 9p21/MTAP-deleted cells, even if DHFR amplification occurs. We conclude that ALA may be more suitable than MTX or TMX for MTAP-mediated chemoselective treatment of T-ALL. Pretherapeutical detection of 9p21 and MTAP deletion may be helpful in developing a predictive molecular chemosensitivity test for T-ALL.

Circumvention of multidrug resistance in genitourinary tumors

Chemotherapy is the principal strategy to systemically challenge metastasized cancers of genitourinary origin. Unfortunately, the efficacy of chemotherapy is often hampered by multidrug resistance, the resistance to a variety of structurally and functionally distinct cytotoxic agents. Multidrug resistance can be either intrinsic or acquired, and can be caused by several mechanisms. The so-called classical multidrug resistance, mediated by the MDR1 gene product P-glycoprotein, has been held mainly responsible for inferring the multidrug resistance phenotype on urologic malignancies. However, several other multidrug resistance pathways have been identified. Multidrug resistance can be caused by the membrane-bound multidrug-resistance-associated protein, the detoxifying glutathione metabolism, the antiapoptotic protein BCL2, and changes in levels or activity of the topoisomerase enzymes. Strategies to overcome multidrug resistance of genitourinary tumors have arisen from the better understanding of the biologic and molecular mechanisms of multidrug resistance, and have been studied in experimental and clinical settings. However, attempts to modulate multidrug resistance in clinical renal cell, bladder, prostate, and testicular cancer have not been very rewarding so far, despite the optimism that had arisen from experimental data. Nevertheless, application of novel therapies to reverse multidrug resistance and to increase efficacy of chemotherapy for urologic cancers should be further pursued, within the setting of controlled clinical trials, to improve on current strategies.

Tubular PAH transport capacity in human kidney tissue and in renal cell carcinoma: correlation with various clinical and morphological parameters of the tumor

In vitro accumulation of p-aminohippurate (PAH) was investigated in "intact" human renal cortical slices of normal kidney tissue and in tissue slices of renal cell carcinoma (RCC). The technique used was established in preliminary experiments on rat kidney tissue slices. In principle, the accumulation capacity is comparable in renal tissue slices of both species (slice to medium accumulation ratios between 4 and 8). In man sex differences in accumulation capacity do not exist. But, as shown in detail for rats, accumulation capacity drops with age. Tissue slices of RCC are unable to accumulate PAH actively; slice to medium ratio reaches about 1 and indicates passive PAH uptake only. Surprisingly, in tumors of stage pT1 PAH uptake is lowest. perhaps as a sign of PAH transport out of the cells. There is no difference between peripheral and central parts of RCC. Age and sex are without influence on PAH uptake in RCC tissue slices. Interestingly, the accumulation capacity of "intact" tissue of kidneys infested with RCC also depends on the severity of the tumor (stage, diameter), but not on grading and formation of metastases.

Zidovudine induces the expression of cellular resistance affecting its antiviral activity

We have previously shown that multidrug-resistant cells expressing the multidrug transporter P-glycoprotein are less sensitive to the antiviral activity of AZT. Subsequently, we addressed the question whether AZT itself is able to induce cellular resistance to the drug. Indeed, CEM cells propagated in the presence of increasing concentrations of AZT become resistant to the antigrowth and antiviral activity of AZT but do not express detectable level of P-glycoprotein. Sensitivity of these cells to other compounds, such as vinblastine, vincristine, ddI, and ddC remained unchanged, indicating that, in contrast to P-glycoprotein-positive cells, AZT-induced resistance is specific for AZT. Interestingly, in AZT-induced resistant cells the intracellular accumulation of AZT and exogenous deoxythymidine, as well as thymidine kinase activity, are significantly reduced when compared with the parental cell line. Our findings show that AZT itself may directly induce the expression of cellular mechanisms leading to the acquisition of specific cellular resistance that can affect its antiviral activity.

Chemoresistance of renal cell carcinoma: 1986-1994

Multidrug resistance (MDR) in a variety of human tumors such as renal cell carcinoma (RCC) is thought to be caused by expression of the mdr1 gene and may be reversed by applying chemosensitizers such as Dexverapamil that inhibit the mdr1 gene product P-glycoprotein. On the basis of our preclinical analysis, we initiated a clinical (GCP) study with vinblastine (VBL), the most effective--if at all--chemotherapeutic agent; dexverapamil; and dexamethasone in patients with RCC. All patients had histologically proven RCC that was metastatic and progressive at study entry. The statistical design featured a preliminary study of two cycles of VBL alone followed by tumor evaluation. If no response was documented, with all patients thus serving as their own control, dexverapamil and dexamethasone were added for a minimum of three cycles of combination therapy. Having obtained institutional permission by the ethical review committee (MEC 124, 106-1993/12), we enrolled 24 patients on this protocol starting on May 3, 1993. In the preliminary study, 1 complete response (CR) was achieved with VBL alone, and myelotoxicity led to an adequate dose reduction from 2 mg/m2 VBL per day given as a 5-day continuous infusion (days 1-5) in 6/10 yet evaluable patients to 1.4 mg/m2 per day. In 8/11 yet evaluable patients, dexverapamil doses reached > or = 3000 mg/day by 7-day oral uptake (days 0-6, supported by 20 mg dexamethasone given twice daily), which is significantly higher than those previously reported. The combination of VBL given at 1.4 mg/m2 per day plus, dexverapamil given at 3000 mg per day was felt to be safe and well tolerated. Nine patients were yet evaluable for response. One partial response and three minor responses were noted in this heavily pretreated study population. It appears that this innovative approach may have some activity in RCC and may eventually lead to a rational treatment modality. Careful evaluation in ongoing studies is warranted.

Modulation of doxorubicin-toxicity by tamoxifen in multidrug-resistant tumor cells in vitro and in vivo

Modulation of the resistance of tumors offers new strategies to improve the therapeutical treatment of cancer. In this report, the anti-oestrogen tamoxifen was investigated in multidrug-resistant tumor cells in vitro and in vivo. The doxorubicin-resistance of L 1210/DOX-tumor cells, which express the multidrug-resistance phenotype, could be completely circumvented by addition of 1 microgram/ml tamoxifen. In contrast, no increased effect could be observed in the parental L 1210 tumor cells or in cytosine arabinoside-resistant L 1210 cells not expressing the multidrug-resistance phenotype. Thus, the enhancing effect of tamoxifen was restricted only to the multidrug-resistant L 1210/DOX tumor cells. Similar to the in vitro experiments, a significant reduction in the growth in solid tumors of mice by the combined treatment of doxorubicin and tamoxifen was again observed only in the multidrug-resistant L 1210/DOX tumors.

In vitro effects of pentoxifylline and doxorubicin on cell survival and DNA damage in sensitive and MDR-P388 leukemia cells

The utility of chemosensitizers to improve efficacy of chemotherapy is now gaining importance. This report investigated whether an active hemorheological agent, pentoxifylline (PTX), can circumvent drug resistance in parental (P388/S) and multidrug resistant (P388/DOX) P388 leukemia cells. For detection of doxorubicin (DOX) resistance and reversal of this resistance by PTX, the incorporation of nucleic acid precursor was measured after addition of DOX and PTX, respectively. The effect of PTX on the induction of DNA strand breaks by DOX was also examined. Increased fragmentation of DNA was illustrated in P388/DOX leukemia cells exposed to the combination of DOX and PTX. The most prominent feature of the multidrug-resistant cell is the reduced accumulation of the drug intracellularly. P388/DOX cells showed less accumulation of DOX in the cell as compared to that of the parental cell line. Further studies demonstrated that PTX significantly enhanced the intracellular accumulation of DOX in both the cell lines. These studies warrant the use of PTX as an adjuvant in cancer chemotherapy.

Multidrug-resistant colonic cancer cell line LoVoDx is efficiently killed by lymphokine-activated killer cells from patients with carcinoma of the colon

Multidrug-resistant (MDR+) cancer cells have the ability to grow in the presence of cytotoxic concentrations of antineoplastic drugs as a result of possessing the transmembrane drug efflux pump p-glycoprotein. The MDR+ colonic cancer cell line LoVoDx (derived from the drug-sensitive line LoVo) was tested for sensitivity to lymphokine-activated killer (LAK) cell-mediated toxicity. LAK cells were cultured from patients with colonic cancer and from matched controls with benign disorders. LAK cells from patients with cancer were as effective as those from controls in mediating cytotoxicity. The MDR+ cell line was significantly more sensitive to LAK cell-mediated cell killing than its parental drug-sensitive line LoVo (P < 0.05). These results indicate a possible role for adoptive immunotherapy in MDR+ tumours expressing p-glycoprotein.

Human cell lines as models for multidrug resistance in solid tumours

In spite of our expanding knowledge on the molecular biology of cancer, relatively little progress has been made in improving therapy for the solid tumours which are major killers, e.g., lung, colon, breast. Significant advances over the past 10-15 years in chemotherapy of some tumours such as testicular cancer and some leukaemias indicates that, in spite of the undesirable side-effects, chemotherapy has the potential to effect cure in the majority of patients with certain types of cancer. Multidrug resistance, inherent or acquired, is one important limiting factor in extending this success to most solid tumours. In vitro studies described in this review are now uncovering a diversity of possible mechanisms of cross-resistance to different types of drug. Sensitive methods such as immunocytochemistry, RT-PCR or in situ RNA hybridisation may be necessary to identify corresponding changes in clinical material. Only by classifying individual tumours according to their specific resistance mechanisms will it be possible to define the multidrug resistance problem properly. Such rigorous definition is a prerequisite to design (and choice on an individual basis) of specific therapies suited to individual patients. Since a much larger proportion of cancer biopsies should be susceptible to accurate analysis by the immunochemical and molecular biological techniques described above than to direct assessment of drug response, it seems reasonable to hope that this approach will succeed in improving results for cancer chemotherapy of solid tumours where other approaches such as individualised in vitro chemosensitivity testing have essentially failed. Results from clinical trials using cyclosporin A or verapamil are encouraging, but these agents are far from ideal, and reverse resistance in only a subset of resistant tumours. Proper definition of the other mechanisms of MDR, and how to antagonize them, is an urgent research priority.

Resistance of HIV-1 to AZT might also involve the cellular expression of multidrug resistance P-glycoprotein

Resistance of tumor cells to the antigrowth activity of several cytotoxic compounds has been associated with the expression of the so-called multidrug resistance protein or P-glycoprotein. This article addresses the question whether the expression of such protein could also affect the sensitivity of HIV to AZT. Our data indicate that this possibility does exist. In fact, multidrug-resistant CEM VBL100 cells, which express high levels of P-glycoprotein, are less sensitive to both the antiproliferative activity and the antiviral action of AZT. Additionally, our data suggest that this phenomenon is specifically mediated by P-glycoprotein since trifluoroperazine, which is known to circumvent multidrug resistance due to the action on P-glycoprotein, increases the intracellular accumulation of AZT and affects the sensitivity of HIV to AZT. Although the biological and clinical significance of these observations has still to be established, this study suggests that cellular factors, other than virus itself, should be taken into account to address the phenomenon of drug resistance of HIV.

Antibody-directed therapy of multidrug-resistant tumor cells

The major obstacle to effective cancer chemotherapy is the resistance of tumor cells to cytostatic agents. Tumor cells frequently express a multidrug-resistance (MDR) phenotype. In an effort to devise new strategies to overcome MDR, antibody-directed approaches for the eradication of MDR cells have been developed. Experimental data have shown that multidrug-resistant tumor cells can be efficiently killed by monoclonal antibodies, immunotoxins, or bispecific antibodies. The current experimental results indicate that an antibody-directed therapeutic approach to eradication of MDR cells might be a promising adjunct to conventional chemotherapy of cancer patients.