Characterization of newly established human myeloid leukemia cell line (KF-19) and its drug resistant sublines

Mechanisms of cross-resistance between nucleoside analogues and vincristine or daunorubicin in leukemic cells

The aim of this study was to clarify the biochemical and molecular mechanisms behind the cross-resistance to nucleoside analogues (NAs) in four erythroleukemic cell lines with acquired resistance to the anthracycline daunorubicin and to the vinca alkaloid vincristine, expressing high levels of p-glycoprotein (P-gp, MDR1). All resistant strains exhibited cross-resistance to NA (cladribine and cytosine arabinoside)-induced apoptosis, assessed by caspase-3-like activation and were less sensitive to NA cytotoxicity in MTT assay. Real-time PCR and enzyme activity analysis showed reduced amounts of deoxycytidine kinase (35-80%) and elevated levels of 5'-nucleotidases (50-100%). The ratio 5'-nucleotidase to deoxycytidine kinase increased between 2.5- and 7.5-folds in resistant cells. This is in agreement with the observation that 5'-nucleotidase/deoxycytidine kinase ratio might be an important factor in predicting resistance to NAs. Implications of this finding for combining anthracyclines or vinca alkaloids with NAs toward leukemic cells are discussed.

Persistent reversal of P-glycoprotein-mediated daunorubicin resistance by tetrandrine in multidrug-resistant human T lymphoblastoid leukemia MOLT-4 cells

Multidrug resistance (MDR) represents a major problem in cancer chemotherapy. P-glycoprotein (P-gp), the drug efflux pump that mediates this resistance, can be inhibited by compounds with a variety of pharmacological functions, thus circumventing the MDR phenotype. The present study was performed to evaluate a unique MDR-reversal feature of a bisbenzylisoquinoline alkaloid tetrandrine (TET) in a P-gp expressing MOLT-4 MDR line (MOLT-4/DNR) established in our laboratory. Cell viability was determined by an MTT assay. P-gp function was characterized by determining the Rh123 accumulation/efflux capacity. P-gp overexpression in resistant MOLT-4/DNR cells was confirmed by flow cytometry analysis after staining with phycoerythrin-conjugated anti-P-gp monoclonal antibody 17F9. Compared to ciclosporin A (CsA), TET exhibited stronger activity to reverse drug resistance to daunorubicin (DNR), vinblastine (VLB) and doxorubicin (DOX) in MOLT-4/DNR cells. TET showed no cytotoxic effects on parental MOLT-4 cells lacking P-gp expression or on the resistant MOLT-4/DNR cells. TET modulated DNR cytotoxicity even after it was washed with the medium for 24 h, while CsA almost completely lost its reversal capability 24 h after washing. TET and CsA similarly increased the accumulation of Rh123 in resistant MOLT-4/DNR cells. However, TET inhibited Rh123 efflux from resistant cells even after washing with the medium, while CsA rapidly lost its ability to inhibit Rh123 efflux after washing. The current study suggests that TET enhances the cytotoxicity of anticancer drugs in the P-gp expressing MDR cell line by modulating P-gp in a different manner to the well-known P-gp inhibitor CsA.

Potent Killing of Paclitaxel- and Doxorubicin-resistant Breast Cancer Cells by Calphostin C Accompanied by Cytoplasmic Vacuolization

Drug resistance is a major impediment to the successful treatment of breast cancer using chemotherapy. The photoactivatable drug calphostin C has shown promise in killing select drug-resistant tumor cells lines in vitro. To assess the effectiveness of this agent in killing doxorubicin- or paclitaxel-resistant breast tumor cells and to explore its mode of action, MCF-7 cells were exposed to increasing concentrations of either doxorubicin or paclitaxel until maximum resistance was obtained. This resulted in the creation of isogenic drug-resistant MCF-7TAX and MCF-7DOX cell lines, which were approximately 50- and 65-fold resistant to paclitaxel and doxorubicin, respectively. Interestingly, calphostin C was able to kill MCF-7TAX cells as efficiently as wildtype MCF-7 cells (IC50s were 9.2 and 13.2 nM, respectively), while MCF-7DOX cells required a 5-fold higher concentration of calphostin C to achieve the same killing (IC50 = 64.2 nM). Consistent with their known mechanisms of action, paclitaxel killed tumor cells by inducing mitotic arrest and cell multinucleation, while doxorubicin induced plasma membrane blebbing and decreased nuclear staining with propidium iodide. In contrast, cytoplasmic vacuolization accompanied cell killing by calphostin C in these cell lines, without the induction of caspase-8 or PARP cleavage or the release of cytochrome c from mitochondria. Calphostin C had little effect on the uptake of either paclitaxel or doxorubicin by the cells. Taken together, the above data suggests that calphostin C is able to potently kill drug-resistant breast tumor cells through a mechanism that may involve the induction of cytoplasmic vacuolization, without activation of typical apoptotic pathways. Consequently, calphostin C may prove useful clinically to combat tumor growth in breast cancer patients whose tumors have become unresponsive to anthracyclines or taxanes, particularly in association with photodynamic therapy.

Cross-resistance to cytosine arabinoside in a multidrug-resistant human promyelocytic cell line selected for resistance to doxorubicin: implications for combination chemotherapy

The pyrimidine analogue cytosine arabinoside (AraC) is one of the most effective drugs used in the treatment of acute leukaemia. Overexpression of the multidrug resistance (MDR-1) gene and its product, P-glycoprotein (P-gp), is associated with cellular resistance to drugs, such as anthracyclines and vinca alkaloids. This resistance can be reversed by cyclosporine analogues or verapamil (ver). We investigated the in vitro cross-resistance to AraC in a doxorubicin-resistant HL60 cell line, with an elevated expression of the MDR-1 gene. The resistant clone showed an eightfold increased resistance to AraC and a two- to fourfold resistance to the other analogues, as measured by cytotoxicity test. There was no significant increase in the activity of 5'-nucleotidase or in the amount of deoxyribonucleotide pools between cell lines. We could, however, detect a reduction in deoxycytidine kinase (dCK) activity (30%, P = 0.021, using deoxycytidine as substrate) and the level of AraC triphosphates was significantly reduced in the resistant cells (70%, P = 0.009). When the cells were exposed to cyclosporin A (CsA) or the cyclosporine analogue PSC 833 (PSC) in combination with AraC, there was more extensive apoptosis, as measured by formation of oligonucleosomal DNA fragmentation and caspase-3-like activity, than with exposure to AraC alone. We also found an increased retention of AraC in the resistant cells when incubated with AraC in combination with CsA. Ver in combination with AraC, failed to increase apoptosis for the resistant cell line. Our data suggests that the resistance to AraC for the P-gp-expressing cells is a result of a reduction of dCK activity and an increase in efflux, the latter possibly depending on P-gp. A combination of CsA or PSC with AraC may improve the effect of AraC in vivo.

Pharmacological basis for cladribine resistance in a human acute T lymphoblastic leukaemia cell line selected for resistance to etoposide

Cross-resistance between different classes of anti-neoplastic agents can jeopardize successful combination cancer chemotherapy. In this study, we observed an unexpected cross-resistance between the podophyllotoxine derivative etoposide (VP) and the nucleoside analogue cladribine (CdA) in CCRF-CEM cells developed for resistance to VP. The resistant cells also displayed 14- and twofold resistance to cytarabine (ara-C) and gemcitabine respectively. Closer analysis of these cells showed that they contained lower amounts of topoisomerase (topo) IIalpha (P < 0.001) and beta protein (P < 0.026), formed substantially lower amounts of the topo II-DNA complex, and had a markedly decreased level of Fas (CD95/APO-1)-ligand mRNA expression. Interestingly, Fas expression in the resistant cells did not differ from that in the parental cell line. No differences were observed in the accumulation/efflux of daunorubicin or in the gene expressions of P-glycoprotein, multidrug resistance-associated protein and the lung resistance-related protein. The activity of deoxycytidine kinase (dCK), responsible for activation of CdA and ara-C, was the same for resistant and wild-type cells. However, there was an increase in the activity of the cytosolic 5'-nucleotidases (5'-NT), responsible for deactivation of nucleotides, amounting to 206% (P < 0.001) for the high Km and 134% (P < 0.331) for the low Km 5'-NT in resistant cells. The high Km 5'-NT is probably responsible for the decreased amount of the active metabolite CdA 5'-triphosphate [40% decreased (P < 0.045)], as well as for other purine ribonucleosides and deoxyribonucleosides triphosphates in the resistant cells. In contrast, a significantly higher deoxycytidine triphosphate (dCTP) level (167%, P < 0.001) was observed in the resistant cells. Thus, this study suggests that the major cause of resistance to the nucleoside analogues CdA and ara-C in cells selected for resistance to VP is a result of metabolic alterations producing increased activity of 5'-NT and higher dCTP levels. Furthermore, these results indicate that there is a common factor in the regulation of nucleotide-degrading enzymes and DNA topoisomerases, which may be altered in cross-resistant cells.

Drug resistance mechanisms in acute leukemia

Markers of anticancer drug resistance are predictive of treatment response and outcome in patients with acute myeloid leukemia. Immunologic detection of the drug efflux pumps, P-glycoprotein (Pgp) and multidrug resistance-associated protein 1 (MRP1), correlate with functional assays of drug resistance. These accumulation defects also appear operable in acute lymphoblastic leukemia. Many of the efflux pumps identified share significant structural homology with the large superfamily of ATP-binding cassette transporters. Other markers such as lung-resistance protein, bcl-2, and breast cancer-resistance protein, have been described in acute myeloid leukemia patients although their pathophysiology and clinical relevance are less clear and the methodology for their quantification are not well standardized. Preclinical studies have shown that small molecules capable of reversing efflux can restore drug sensitivity in resistant tumor models. Although initial clinical studies were limited by both potency and specificity of the reverser, later studies with more effective reversers have in many instances been limited by pharmacokinetic interactions exacerbating the clinical toxicities of chemotherapy. Although one large randomized study has demonstrated a proven survival advantage without increased toxicity using cyclosporine, the inconsistent results with other modulators raise doubt as to the utility and overall strategy of using drug efflux blockers in patients with established Pgp overexpression. Many of these patients have additional resistance mechanisms, and achieving meaningful clinical responses will likely require more complex clinical strategies. Preventing or delaying development of drug resistance in chemosensitive patients represents another therapeutic strategy to be tested.

In vitro leukemia cell models of Ara-C resistance

Cells of the human leukemia line K562 were continuously exposed to cytosine arabinoside (Ara-C) at increasing concentrations for 3 months. The resulting cell line, termed K562/AC, showed 48-fold resistance to Ara-C, compared with the parental K562 cells. The sensitivities of K562/AC to adriamycin (ADR), vincristine (VCR) and etoposide (VP16) were similar to those of parental K562. Gene analysis revealed that this cell line lacked expression of the deoxycytidine kinase (dCK) gene, which was evident in Ara-C-sensitive cells. As in K562 cells, multidrug resistance (MDR-1) and multidrug resistance protein (MRP) genes were not expressed in K562/AC. We also established an in vitro model of Ara-C resistance using phosphorothioate antisense oligonucleotides to dCK (dCK-AS). Treatment of K562 with dCK-AS caused decreased dCK expression and 6- to 10-fold increases in resistance to Ara-C, compared with that in cells treated with sense oligonucleotides to dCK (dCK-S) or in non-transfected cells. The cells described here may contribute to the study of a novel mechanism associated with Ara-C resistance, in which reduced dCK activity may play an important role.

Characterization of a newly established human acinic cell adenocarcinoma cell line (HACC) originating from the salivary gland: morphological features and role of various growth factors on the growth of the HACC cell line

Human acinic cell adenocarcinoma cell (HACC) line was established from the pleural effusion that contains metastatic tumor cells of acinic cell adenocarcinoma of papillary and microcystic type originating from the parotid gland. The HACC cells grew in an adherent monolayer with a doubling time of 66 h. Implanted tumor of SCID mice revealed similar histological findings to that of the primary tumor. The HACC cells produced mucin and expressed epithelial markers as well as alpha1-antitrypsin and lysozyme, whereas salivary peptide P-C was expressed in cultured HACC cells but not in the primary and implanted HACC cell tumors. S-100 protein was also expressed in both the primary tumor and HACC cell line. Neither amplification of common oncogenes nor expression of p53 was observed. The receptor for epidermal growth factor (EGF) was expressed, indicating EGF and transforming growth factor-alpha (TGF-alpha) enhanced the growth of the HACC line. Unexpectedly, tumor necrosis factor-a (TNF-alpha) also enhanced the growth of the HACC line significantly. However, there was no evidence of autocrine growth using these growth factors. In contrast, TGF-beta1 inhibited the growth of the HACC cell line through apoptosis. The HACC cell line has features similar to both acinar and intercalated ductal cells of the salivary gland. Epidermal growth factor, TGF-alpha and TNF-alpha are potential growth factors for the HACC cell line. The HACC cell line may be a good model for studying the biological behavior of salivary gland neoplasms.

Reactivity of antibody YU-311 in formalin-fixed, paraffin-embedded specimens of normal organs, non-hematopoietic tumors, and mast cell tumors

YU-311 is a monoclonal antibody that reacts with a human leukemia cell line resistant for cytosine arabinoside and that identifies a 92 kDa membrane protein. The reactivity of YU-311 in normal organs, various non-hematopoietic tumors and in mast cell tumors in formalin-fixed, paraffin-embedded specimens was examined using immunohistochemical methods. In normal organs, YU-311 reacted with fundic glands of the stomach, the intercalated duct of the pancreas, the distal portion and the loop of Henle of renal tubules and tissue mast cells. Benign neoplasms of various organs showed no immunoreaction with YU-311, except for mast cell tumors. Some types of malignant neoplasms were occasionally positive against YU-311, suggesting neoplasms arising from or differentiating along normal YU-311-positive counterparts. Some other types of malignancies were rarely positive for YU-311, although their normal counterparts showed no immunoreactivity with YU-311. None of the non-epithelial tumors reacted with YU-311, except for one case of malignant melanoma. In contrast, normal tissue mast cells and their related tumors, such as urticaria pigmentosa or solitary mastocytoma, were constantly positive for YU-311. None of the non-hematopoietic human tumor cell lines examined in the present study was reactive with YU-311. These findings indicate that YU-311 is a good marker of some types of tumors and mast cell tumors and that an aberrant expression of YU-311 rarely occurs.

Reactivity of anti-AraC-resistant cell monoclonal antibody, YU-311, in formalin-fixed paraffin-embedded specimens of various hematopoietic disorders

YU-311 is a monoclonal antibody reacting with cytosine arabinoside (AraC)-resistant human leukemic cell line and identifies a 92 kDa membrane protein. We have examined YU-311 reactivity with various hematopoietic disorders by an immunohistochemical method and evaluated a correlation between YU-311 expression and refractoriness to chemotherapy, retrospectively. YU-311 reacted with AraC-resistant human leukemia cell lines, in which a 92 kDa membrane protein was identified by Western blotting, whereas drug-resistant cell lines to other than AraC failed to express YU-311 antigen. The frequency of YU-311 positivity was significantly increased in relapsed cases. Only five cases were positive for YU-311 at diagnosis and 24 cases at relapse. Unexpectedly, only eight cases of relapsed leukemia/lymphoma expressed YU-311 and P-glycoprotein simultaneously. Most of the YU-311-positive relapsed cases showed clinical refractoriness for chemotherapy and then failed to induct complete remission or relapsed at short periods with short disease-free duration. These findings indicate that YU-311 expression is closely associated with some aspects of drug resistance, especially with AraC resistance.