HbA1c of 5.8% or higher as the most useful indicator for recommendation of ultrasonography to detect nonalcoholic fatty liver disease

Background and Aim

Nonalcoholic fatty liver disease (NAFLD) is closely associated with metabolic syndrome. This study was performed to examine the association between NAFLD and each factor of metabolic syndrome and to identify the factors that are most strongly associated with NAFLD in participants undergoing health checkups.

Methods

We studied 6538 participants who underwent a health checkup from 2017 to 2018 in our institution. Participants with alcohol intake exceeding 20 g/day or with other chronic liver diseases were excluded. Fatty liver was detected by ultrasonography.

Results

In total, 4310 participants were enrolled, and 28.4% had fatty liver (NAFLD). The prevalence of NAFLD was highest in the diabetes mellitus (DM)-only group than in the dyslipidemia-only or hypertension-only group. The DM-only group was the only group whose prevalence of NAFLD was >50% in the overall study and in males. The prevalence of NAFLD was higher in males than in females in the DM-only, hypertension-only, and dyslipidemia-only groups. The prevalence of NAFLD was >70% in the dyslipidemia and DM combined group. Multivariate analysis showed that gender and HbA1c were the independent factors most strongly associated with NAFLD. The cutoff value for HbA1c by receiver operating characteristic curve analysis was 5.8% (sensitivity, 57.9%; specificity, 72.6%; area under the curve, 0.70).

Conclusion

NAFLD was most strongly associated with DM, among the various components of metabolic syndrome. We strongly recommend abdominal ultrasonography to detect NAFLD in patients with an HbA1c of ≥5.8% in general practice and during health checkups.

Beige mucosa observable under narrow-band imaging indicates the active sites of eosinophilic esophagitis

BACKGROUND AND AIM

The majority of patients with eosinophilic esophagitis (EoE) are likely to have observable features under narrow-band imaging, namely beige mucosa. However, the histological features and clinical implications of beige mucosa have not been investigated. The aim of this study was to determine whether beige mucosa could serve as an endoscopic marker for predicting active inflammatory sites of EoE.

METHODS

We retrospectively analyzed both the narrow-band images and biopsied specimens of 77 esophageal lesions from 35 consecutive patients with EoE. We divided these specimens into two groups: target biopsied specimens from beige mucosa (beige group) and specimens biopsied from non-beige mucosa (non-beige group). The number of eosinophils per high-powered field, thickness of the superficial differentiated cell layer, and depth of the hemoglobin component from the surface layer were compared between the two groups.

RESULTS

Forty-four out of the 45 specimens were diagnosed as histological active lesions in the beige group. The sensitivity, specificity, and overall accuracy of beige mucosa in predicting EoE activity were 97.8%, 96.9%, and 97.8%, respectively. Compared with the non-beige group, specimens in the beige group had a significantly thinner superficial differentiated cell layer.

CONCLUSIONS

Beige mucosa is associated with thinning of the normal superficial differentiated cell layer, and these histological changes in the active inflammatory sites of EoE could be recognized endoscopically as color differences. Beige mucosa may serve as an endoscopic indicator for predicting the histological activity of EoE.

Reversal of multidrug resistance by novel nitrophenyl pyrones, SNF4435C and D

SNF4435C and D, novel immunosuppressants produced by a strain of Streptomyces spectabilis, were examined for their reversing effects in vitro on various multidrug-resistant (MDR) tumor cells overexpressing P-glycoprotein. These two compounds in the range of 3-10 microM completely reversed the resistance of MDR variant cells, mouse leukemia P388 cells [vincristine (VCR)-resistant P388/VCR and adriamycin (ADM)-resistant P388/ADM], human myelogenous leukemia K562 cells (VCR-resistant K562/VCR and ADM-resistant K562/ADM) and human ovarian cancer A2780 cells (ADM-resistant AD(10)), against VCR. Both compounds moderately potentiated the sensitivity of the MDR cells to ADM but the reversal was not complete. SNF4435C and D significantly increased the intracellular accumulation of VCR in AD(10) cells as potently as verapamil, cyclosporin A (CysA) and FK506, whereas the compounds exerted no effect on the accumulation of VCR in the drug-sensitive parent cells. Moreover, SNF4435C improved the chemotherapeutic efficacy of VCR in the treatment of P388/VCR-bearing mice. When 10 mg/kg SNF4435C was administered intraperitoneally to the mice concurrently with 0.2 mg/kg VCR for every 5 days, a treated/control (T/C) value of 143% was obtained. These results suggest that the compounds are useful candidates or tools for MDR modification in cancer chemotherapy.

Dephosphorylated hypoxia-inducible factor 1alpha as a mediator of p53-dependent apoptosis during hypoxia

Under hypoxia, HIF-1alpha binds to aryl hydrocarbon receptor nuclear translocator (ARNT, also called HIF-1beta) to activate expression of genes important for cell survival. Alternatively, HIF-1alpha can bind to the tumor suppressor p53 and promote p53-dependent apoptosis. Here we show that the opposite functions of HIF-1alpha are distinguished by its phosphorylation status. Two distinguishable forms of HIF-1alpha, phosphorylated and dephosphorylated, were induced during hypoxia-induced apoptosis. The phosphorylated HIF-1alpha was the major form that bound to ARNT. Ectopically expressed ARNT was consistently able to enhance HIF-1alpha phosphorylation in a binding-dependent manner. In contrast, the dephosphorylated HIF-1alpha was the major form that bound to p53. Depletion of the dephosphorylated HIF-1alpha, by using the Hsp90 inhibitor geldanamycin A that had little effect on the phosphorylated HIF-1alpha expression, suppressed p53 induction and subsequent apoptosis. Depletion of dephosphorylated HIF-1alpha also prevented hypoxia-induced nuclear accumulation of HDM2, a negative regulator of p53. Our results indicate that the functions of HIF-1alpha varied with its phosphorylation status and that dephosphorylated HIF-1alpha mediated apoptosis by binding to and stabilizing p53.

Neutral taxoids from Taxus cuspidata as modulators of multidrug-resistant tumor cells

Two taxoids, taxinine NN-7 (1) and 3,11-cyclotaxinine NN-2 (2), were isolated from the neutral fraction of the EtOAc extract of a mixture of needles and young stems of Taxus cuspidata. The structures were determined by spectroscopic analysis. Both compounds showed some activity as modulators of multidrug-resistant tumor cells.

Proteasome inhibition circumvents solid tumor resistance to topoisomerase II-directed drugs

Physiological cell conditions, such as glucose deprivation and hypoxia, play a role in developing drug resistance in solid tumors. These tumor-specific conditions cause decreased expression of DNA topoisomerase IIalpha (topo IIalpha), rendering cells resistant to topo II-targeted drugs, such as etoposide and doxorubicin. We show here that inhibition of proteasome attenuated drug resistance by inhibiting topo IIalpha depletion induced by glucose starvation and hypoxia. topo IIalpha restoration was seen only at the protein levels, indicating that the topo IIalpha protein depletion occurred through a proteasome-mediated degradation mechanism. The stress-induced etoposide resistance was effectively prevented in vitro by the proteasome inhibitor lactacystin in both intrinsically resistant and sensitive tumor cells (colon cancer HT-29 and ovarian cancer A2780 cells, respectively). Furthermore, lactacystin effectively enhanced the antitumor activity of etoposide in the refractory HT-29 xenograft. These results indicate that lactacystin could serve as a new therapeutic agent to circumvent resistance to topo II-targeted chemotherapy in solid tumors.

Antitumor activity and novel DNA-self-strand-breaking mechanism of CNDAC (1-(2-C-cyano-2-deoxy-beta-D-arabino-pentofuranosyl) cytosine) and its N4-palmitoyl derivative (CS-682)

We have studied the antitumor activity and the novel DNA-self-strand-breaking mechanism of CNDAC (1-(2-Ccyano-2-deoxy-beta-D-arabino-pentofuranosyl)cytosine) and its N4-palmitoyl derivative (CS-682). In vitro, CS-682 showed strong cytotoxicity against human tumor cells comparable with that of CNDAC; both compounds displayed a similar broad spectrum. In vivo, however, orally administered CS-682 showed a more potent activity against human tumor xenografts than CNDAC, 5'-deoxy-5-fluorouridine, 5-fluorouracil and 2',2'-difluorodeoxycytidine. Moreover, CS-682 was effective against various human organ tumor xenografts at a wide dose range and with low toxicity, and was effective against P388 leukemic cells resistant to mitomycin-C, vincristine, 5-fluorouracil or cisplatin in syngeneic mice. CNDAC, an active metabolite of CS-682, had a prolonged plasma half-life after repeated oral administrations of CS-682 but not after oral administrations of CNDAC itself. This difference may partially explain the higher antitumor activity of CS-682 relative to CNDAC. In both CNDAC- and CS-682-treated carcinoma cells, CNDAC 5'-triphosphate (CNDACTP) was generated and incorporated into a DNA strand. High performance liquid chromatography (HPLC) and mass spectrometric analysis of the nucleosides prepared by digestion of the DNA from the CNDAC-treated cells detected ddCNC (2'-Ccyano-2',3 '-didehydro-2',3 '-dideoxycytidine), which was shown to be generated only when the self-strand-breakage of CNDACTP-incorporated DNA occurred. The cytotoxicity of CNDAC was completely abrogated by the addition of 2'-deoxycytidine and was low against cells with decreased deoxycytidine kinase. Our results suggest that CNDAC is converted to CNDACMP by deoxycytidine kinase and that the resulting CNDACTP incorporated into a DNA strand as CNDACMP may induce DNA-self-strand-breakage. This novel DNA-self-strand-breaking mechanism may contribute to the potent antitumor activity of CS-682.

Hypoxia up-regulates telomerase activity via mitogen-activated protein kinase signaling in human solid tumor cells

Solid tumor cells are often exposed to hypoxia in vivo, which has been suggested to promote genetic instability in those cells. Telomere elongation by telomerase is implicated in chromosome stabilization in immortal cells. Here we found that hypoxia enhanced telomerase activity in the solid tumor A2780 and HT-29 cells but not in the leukemia U937 cells. The telomerase activation correlated with activation of mitogen-activated protein kinase (MAPK) and c-fos expression. The MEK1 inhibitor PD98059 repressed telomerase activation in the hypoxic cells. Consistently, a dominant negative MEK1 inhibited telomerase activation by hypoxia. Finally, we found a good correlation between telomerase activation and resistance to apoptotic cell death under hypoxic conditions. These findings indicate that hypoxia up-regulates telomerase activity via MAPK cascade signaling especially in solid tumor cells and suggest that solid tumor cells might enhance the telomerase activity as a stress response against genotoxicity induced by hypoxia.

Glucose-regulated stresses cause degradation of DNA topoisomerase IIalpha by inducing nuclear proteasome during G1 cell cycle arrest in cancer cells

The glucose-regulated stress response of cancer cells leads to a decreased expression of DNA topoisomerase IIalpha (topo IIalpha) and a cell cycle arrest at the G1 phase. In this study, we found that the topo IIalpha decrease occurred specifically during the G1 arrest in human colon adenocarcinoma HT-29 cells. The intracelluar level of topo IIalpha in HT-29 cells was relatively constant regardless of cell cycle position in the exponentially growing state, determined using a centrifugal elutriation technique and synchronizing the cells with a mitotic inhibitor nocodazole. Interestingly, when the cell cycle was arrested in the M phase by nocodazole, the topo IIalpha level remained high even in stressed cells. After the stressed cells were released from the M phase, topo IIalpha steeply decreased along with cell cycle progression followed by the next G1 arrest. This decrease in nuclear topo IIalpha protein was completely inhibited by selective inhibitors for proteasome. Furthermore, we found that proteasome activity was elevated three to fourfold in the nuclear extract of stressed cells over unstressed cells. Accordingly, there were increased amounts of nuclear proteasome subunits, although total intracellular content of the subunits did not change in stressed cells. These findings indicate that the expression of topo IIalpha in stressed cells is downregulated at the G1 phase by proteasome-mediated degradation and that the proteolysis of topo IIalpha can be facilitated by the nuclear accumulation of proteasome.

Cellular sensitization to cisplatin and carboplatin with decreased removal of platinum-DNA adduct by glucose-regulated stress

PURPOSE

Stress conditions, such as glucose starvation and hypoxia, that induce glucose-regulated proteins (GRPs) in cells, are seen in most solid tumors. These conditions have been shown to cause cellular resistance to multiple anticancer drugs, such as etoposide, doxorubicin, and camptothecin. We examined the effect of the GRP-inducing conditions on cellular sensitivity to cisplatin and carboplatin, which are widely used drugs against solid tumors.

METHODS

We generated the GRP-inducing culture conditions by exposing cells to 2-deoxyglucose (2DG), calcium ionophore A23187 and tunicamycin, and examined cellular sensitivity to cisplatin and carboplatin under these conditions. We next measured platinum accumulation and DNA-bound platinum in 2DG-stressed cells after cisplatin exposure.

RESULTS

The GRP-inducing stress conditions led to cellular sensitization to cisplatin and carboplatin. This sensitization was reversible, as the cellular sensitivity returned to normal levels 12 h after removal of 2DG. Platinum accumulation and DNA-bound platinum that were found immediately after exposure to cisplatin for 1 h were slightly increased in 2DG-stressed cells as compared with nonstressed cells. After a drug-free recovery incubation of 8 h, the DNA-bound platinum in the nonstressed cells was reduced by 33% while the amount in the 2DG-stressed cells was sustained at the initial levels.

CONCLUSIONS

These results indicated that the decreased removal of platinum-DNA adducts was associated with increased sensitivity to cisplatin and carboplatin in the stressed cells. The sensitization of cancer cells under the GRP-inducing stress conditions would explain, in part, the clinical potency of platinum drugs against solid tumors.

Glucose starvation and hypoxia induce nuclear accumulation of proteasome in cancer cells

Solid tumors commonly contain regions with glucose-starved and hypoxic conditions. Tumor cells under the adverse conditions can survive through the stress response, such as cell cycle arrest. In this study, we found that the stress conditions stimulated nuclear accumulation of proteasomes, large multicatalytic protease complexes, in human colon cancer HT-29 cells. The nuclear proteasome levels both in amount and in activity were increased approximately 4 and 2 times by glucose starvation and hypoxia, respectively. No changes were detected in the total expression levels of proteasome. The nuclear proteasome accumulation was also observed in ovarian cancer A2780 cells under glucose starvation, suggesting that this response was regardless of the origin of cancer cells. Our results indicate that the nuclear proteasome distribution is enhanced by glucose starvation and hypoxia, and suggest that the proteolysis by proteasome in the nucleus may play roles in the stress response of solid tumor cells.

Drug resistance mediated by cellular stress response to the microenvironment of solid tumors

Most solid tumors show resistance to current chemotherapy. This drug resistance can be associated with the unique physiology of solid tumors. Solid tumors generally have regions of low oxygen (hypoxia), low pH and low levels of glucose, which are not observed in normal tissues. These tumor-specific conditions commonly cause the glucose-regulated stress response of cancer cells. Accumulating evidence shows that the stress response leads to induction of resistance to multiple drugs, such as etoposide, doxorubicin, camptothecin and vincristine. This type of drug resistance is reversible and decays rapidly when stress conditions are removed. The induction of drug resistance can be partly explained by cell cycle arrest at the G1 phase in stressed cells because most anticancer drugs are primarily effective against rapidly dividing cells. Specific mechanisms, such as the decreased expression of DNA topoisomerase (topo) II alpha for the resistance to topo II poisons, are also involved in the drug resistance. Stressed cells, however, become hypersensitive to cisplatin, one of the most effective drugs against solid tumors, suggesting that preferential cytotoxicity to stressed cells may be important for the clinical efficacy against solid tumors. Further characterization of stressed cells will provide a unique target to circumvent the drug resistance of solid tumors.

Modulation of multidrug resistance in tumor cells by taxinine derivatives

Among a series of taxinine (1) and its designed derivatives (2-33), two taxoids (29 and 33) increased cellular accumulation of vincristine in multidrug-resistant tumor cells more potently than verapamil, while the activities of eight taxoids (11, 14-16, 22, and 30-32) were comparable with that of verapamil. These results reveal that some taxinine derivatives are good modifiers of multidrug resistance in tumor cells.

Down-regulation of epidermal growth factor receptor-signaling pathway by binding of GRP78/BiP to the receptor under glucose-starved stress conditions

GRP78/BiP, a molecular chaperone in the endoplasmic reticulum, is induced under such adverse conditions for cell survival as glucose starvation. Induction of GRP78 has been shown to coincide with G1 cell cycle arrest, which is an important cellular defense system. In this study, we investigated involvement of GRP78 in the mechanism of growth arrest by using human epidermoid carcinoma A431 cells. Under a chemical stress condition with 2-deoxyglucose, GRP78 was induced 3-4-fold. In the stressed cells, an underglycosylated form of epidermal growth factor receptor (EGFR) was produced and the mature form was decreased. We found that the molecular chaperone GRP78 in the endoplasmic reticulum formed a stable complex with the underglycosylated EGFR but did not with the mature form. This complex formation occurred specifically under the stress conditions, and the complex was dissociated upon removal of the stress. Treatment of the GRP78-underglycosylated EGFR complex with ATP resulted in a release of the underglycosylated EGFR from GRP78, indicating that the complex could be formed through the chaperone function of GRP78. In accordance with the complex formation with endoplasmic reticulum-resident GRP78, the underglycosylated EGFR could not be translocated to the cell surface. As a result, EGF could not induce expression of cyclin D3, a G1 cyclin, in the stressed cells, whereas it did in non-stressed cells. These results indicated that, in the stressed cells, GRP78 participated in down-regulation of EGF-signaling pathway by forming a stable complex with EGFR and inhibiting EGFR translocation to the cell surface.

A novel mutant from apoptosis-resistant colon cancer HT-29 cells showing hyper-apoptotic response to hypoxia, low glucose and cisplatin

Solid tumors usually have regions of hypoxia and glucose deprivation. Human colon carcinoma HT-29 cells show an apoptosis-resistant phenotype in response to microenvironmental stresses. In this study, we isolated a novel mutant of HT-29, designated as HA511, that showed a high apoptotic response to hypoxia, glucose deprivation and treatment with the chemical stressors tunicamycin and glucosamine. The mutant HA511 cells exhibited nuclear condensation and fragmentation and activation of CPP32 (caspase-3) protease under the stress conditions, while the parental HT-29 cells did not. We found that apoptosis occurred in HA511 cells after prolonged cell cycle arrest at the G1 phase, while in the parental cells a progression to S phase occurred after the G1 arrest. Upon exposure to an anti-Fas antibody, HA511 cells underwent apoptosis, whereas the parental cells proliferated without substantial cell death. Furthermore, HA511 cells were preferentially hypersensitive to cisplatin. We found no alteration in expression of GRP78, anti-apoptotic protein Bcl-XL, or p53, of which the gene was mutated in HT-29 cells. The mutant HA511 cells could provide useful information on the mechanism of apoptosis of solid tumors.

Immunological quantitation of DT-diaphorase in carcinoma cell lines and clinical colon cancers: advanced tumors express greater levels of DT-diaphorase

NAD(P)H:quinone oxidoreductase (DT-diaphorase; DTD) plays a major role in activating mitomycin C (MMC) in human colon and gastric carcinoma cell lines. Thus, measurement of DTD in clinical tumor samples could be beneficial in designing adjuvant chemotherapy. We explored immunological quantitation of DTD protein using a monoclonal antibody against DTD, demonstrating a close correlation between protein expression and enzyme activity of DTD in colon and gastric carcinoma cell lines and in colorectal tumor samples. This indicates that such immunoblot analysis is a simple alternative method for quantitating DTD in clinically excised samples. In most colorectal tumor samples, the tumors expressed larger amounts of DTD than did the peripheral normal tissues, suggesting a selective toxicity of MMC toward tumor cells. Also tumors with nodal metastases showed significantly higher DTD levels than did tumors without metastasis. These results raise the possibility that DTD expression is related to tumorigenesis and malignant progression of colorectal tumors. Measurement of DTD by the immunological method described here could be beneficial in designing a rational adjuvant chemotherapy with MMC.

Inhibition of P-glycoprotein and recovery of drug sensitivity of human acute leukemic blast cells by multidrug resistance gene (mdr1) antisense oligonucleotides

To overcome the problem of multidrug resistance, we investigated the effectiveness of phosphrothioate antisense oligonucleotides (MDR1-AS) in suppressing multidrug resistance gene (mdr1) expression in drug-resistant acute myelogenous leukemia (AML) blast cells and the K562 adriamycin-resistant cell line K562/ADM. The percentage of cells with the mdr1 gene product P-glycoprotein (P-gp) was decreased from 100% to 26% by 20 micromol/L MDR1-AS in the K562/ADM cells, and from 48.1% to 10.2% by 2.5 micromol/L MDR1-AS in the AML blast cells. Western blot analysis also showed a decrease in the amount of P-gp in the MDR1-AS-treated K562/ADM cells. This effect was specific to MDR1-AS, and not observed with sense or random control oligonucleotides. The expression of mdr1 mRNA in K562/ADM and AML blast cells treated with MDR1-AS was decreased compared with the random control. Intracellular rhodamine retention and [3H]daunorubicin also increased after antisense treatment. Chemosensitivity to daunorubicin increased in MDR1-AS-treated blast cells up to 5.9-fold in the K562/ADM cells and 3.0- to 6.4-fold in the AML blast cells. The expression of mdr1 mRNA derived from colony cells decreased in the MDR1-AS-treated groups. No inhibitory effect of the oligonucleotides on normal bone marrow progenitors was observed. These findings suggest that MDR1-AS is useful to overcome multidrug resistance in the treatment of leukemia.

2-Deoxyglucose inhibits chemotherapeutic drug-induced apoptosis in human monocytic leukemia U937 cells with inhibition of c-Jun N-terminal kinase 1/stress-activated protein kinase activation

Human monocytic leukemia U937 cells undergo apoptosis when treated with antitumor drugs, such as etoposide, camptothecin and mitomycin C. The molecular mechanism of the drug-induced apoptosis is not well understood. In this study, we found that 2-deoxyglucose (2DG), an analog of D-glucose and an inducer of glucose-regulated stress, inhibited anticancer drug-induced but not tumor necrosis factor-alpha-induced apoptosis of U937 cells. 2DG did not reduce initial cellular damage caused by etoposide, an inhibitor of topoisomerase II, suggesting that 2DG affected subsequent cellular responses involved in apoptosis. 2DG inhibited the etoposide-induced activation of c-Jun N-terminal kinase 1/stress-activated protein kinase (JNK1/SAPK) and the subsequent activation of CPP32, both of which are positive regulators for etoposide-induced apoptosis of U937 cells. Our results indicate that 2DG inhibits apoptosis by blocking the signals from cellular DNA damage for JNK1/SAPK activation.

Overexpression of thioredoxin does not confer resistance to cisplatin in transfected human ovarian and colon cancer cell lines

PURPOSE

We have previously reported increased expression of thioredoxin (TRX) in cell lines with both acquired and intrinsic cisplatin (cDDP) resistance. We found that the expression levels of TRX correlate with cellular resistance to the drug. The purpose of this study was to elucidate whether TRX induces cDDP resistance in the absence of other intracellular changes.

METHODS

We developed cell lines stably expressing high levels of TRX by transfection of human ovarian cancer A2780 and colon cancer HT-29, and examined their sensitivity to cDDP.

RESULTS

The TRX transfectants expressed two- to threefold more TRX with corresponding activities than the parental cells or mock transfectants. TRX-transfected HT-29 cells expressed higher levels of TRX than cDDP-resistant variant cells. Both TRX-transfected A2780 and HT-29 cells showed no resistance to cDDP. Though TRX-transfected A2780 cells showed 1.8-fold increased resistance to H2O2, resistance to adriamycin and mitomycin C, which generate oxygen radicals, was not observed in the transfectants.

CONCLUSIONS

These results suggest that TRX may be necessary but insufficient to induce resistance against cDDP as well as other chemotherapeutic drugs.

Glucose-regulated stresses induce resistance to camptothecin in human cancer cells

The glucose-regulated stress response in mammalian cells is characterized by the increased synthesis of glucose-regulated proteins (GRPs). In this study, we found that GRP-inducing conditions in culture led to induction of resistance to the topoisomerase I-targeted drug camptothecin in human colon cancer HT-29 and ovarian cancer A2780 cells. The induction of camptothecin resistance was accompanied by decreased levels of camptothecin-induced cleavable complexes, as measured by a topoisomerase I band depletion assay. However, topoisomerase I protein levels were the same in both stressed and non-stressed cells. Furthermore, when isolated nuclei from stressed and non-stressed cells were treated with camptothecin, similar levels of cleavable complexes were obtained, suggesting that the activity of topoisomerase I did not change in stressed cells. In contrast, intracellular accumulation of camptothecin decreased in stressed cells. Our results indicate that stress-induced camptothecin resistance could be explained by reduced camptothecin accumulation, leading to decreased numbers of cleavable complexes, without quantitative or qualitative changes in topoisomerase I levels. In addition, cell cycle analysis revealed that the GRP-inducing treatments resulted in an accumulation of G1/G0-phase cells. As camptothecin shows an S-phase-specific cytotoxicity, the G1/G0-phase accumulation is another mechanism for camptothecin resistance. Since a glucose-regulated response is produced by hypoxia and nutrient deprivation that occur naturally in solid tumors, the resistance observed here can occur in some solid tumors and can be an obstacle to chemotherapy.

Glucose-regulated stresses cause decreased expression of cyclin D1 and hypophosphorylation of retinoblastoma protein in human cancer cells

Glucose-regulated stress response of cancer cells occurs during the growth of solid tumors and is induced in culture by treatments with various agents, including 2-deoxyglucose, glucosamine, and calcium ionophore A23187. We previously reported that the three stressors commonly induced cell-cycle arrest in the G1 phase and resistance to antitumor drugs in human cancer A2780 and HT-29 cells. In this study, we investigated the mechanisms of stress-induced G1 arrest by determining the expression of cell-cycle-regulating proteins. Among G1 cyclins and cyclin-dependent kinases (cdk) examined, the expression levels of cyclin D1 preferentially decreased in the stressed cells. A time-course study showed that the decrease in cyclin D1 coincided with the appearance of hypophosphorylated retinoblastoma protein (pRb), which is the growth suppressive form. These findings suggest that the stress-induced G1 arrest is mediated through the down-regulation of cyclin D1-associated kinases (cdk4/6), pRb kinases during G1 phase. This was also supported by decreased cdk4 expression in stressed HT-29 cells. In addition, p21WAF1, a cdk inhibitor, was induced in the stressed cells, particularly A23187-treated cells. A23187, compared with the other stressors, caused extreme pRb hypophosphorylation, suggesting that p21WAf1 is involved in the regulation of pRb phosphorylation in the stressed cells. Our present findings could explain a molecular-based mechanism of a growth-arrested quiescent state and also resistance to chemotherapy of solid tumor cells.

Glucose-regulated stresses induce resistance to camptothecin in human cancer cells

The glucose-regulated stress response in mammalian cells is characterized by the increased synthesis of glucose-regulated proteins (GRPs). In this study, we found that GRP-inducing conditions in culture led to induction of resistance to the topoisomerase I-targeted drug camptothecin in human colon cancer HT-29 and ovarian cancer A2780 cells. The induction of camptothecin resistance was accompanied by decreased levels of camptothecin-induced cleavable complexes, as measured by a topoisomerase I band depletion assay. However, topoisomerase I protein levels were the same in both stressed and non-stressed cells. Furthermore, when isolated nuclei from stressed and non-stressed cells were treated with camptothecin, similar levels of cleavable complexes were obtained, suggesting that the activity of topoisomerase I did not change in stressed cells. In contrast, intracellular accumulation of camptothecin decreased in stressed cells. Our results indicate that stress-induced camptothecin resistance could be explained by reduced camptothecin accumulation, leading to decreased numbers of cleavable complexes, without quantitative or qualitative changes in topoisomerase I levels. In addition, cell cycle analysis revealed that the GRP-inducing treatments resulted in an accumulation of G1/G0-phase cells. As camptothecin shows an S-phase-specific cytotoxicity, the G1/G0-phase accumulation is another mechanism for camptothecin resistance. Since a glucose-regulated response is produced by hypoxia and nutrient deprivation that occur naturally in solid tumors, the resistance observed here can occur in some solid tumors and can be an obstacle to chemotherapy.

DT-diaphorase as a critical determinant of sensitivity to mitomycin C in human colon and gastric carcinoma cell lines

Mitomycin C (MMC), a known cytotoxic agent, requires cellular enzyme-mediated activation for effective antitumor activity. To study the bioreductive enzymes responsible for MMC activation in tumor cells, we examined the enzyme activities of DT-diaphorase (DTD) and NADPH:cytochrome P-450 reductase in 13 colon and gastric carcinoma cell lines and then compared these activities to the respective cellular MMC sensitivity. We found that cell lines with nonexistent or marginal DTD activity, such as St-4 and MKN7, showed resistance to MMC, in comparison to cell lines with DTD activity ranging from 210 to 1420 nmol/min/mg protein. No correlation was found between NADPH:cytochrome P-450 reductase activity and MMC sensitivity in these cell lines. To confirm the role of DTD in cellular MMC sensitivity, we constructed an expression vector containing NQO1, a gene that codes for DTD, and transfected the vector into St-4 cells expressing no DTD activity. Several transfectant clones with DTD activity from 144 to 2085 nmol/min/mg protein were obtained. All of the transfectants showed 5-10-fold higher sensitivity to MMC compared to the parental St-4 cells. Consistent with the MMC sensitivity, we also found that MMC-DNA adduct was formed more extensively in the NQO1 transfectants than in the St-4 cells. These results indicate that DTD activity is required for effective cytotoxicity of MMC in colon and gastric carcinoma cells.

Increased expression of thioredoxin/adult T-cell leukemia-derived factor in cisplatin-resistant human cancer cell lines

Thioredoxin (TRX) is a widely distributed Mr 13,000 protein with a redox-active dithiol/disulfide in the active site. The TRX system, consisting of TRX, TRX reductase, and NADPH, has an intracellular reducing capacity. Another reducing capacity, glutathione (GSH), can be associated with cis-diaminedichloroplatinum (cDDP) resistance. Therefore, we examined the involvement of TRX in cDDP resistance using two cell lines designated St/DDP and HT/DDP, which were established from the human gastric cancer cell line St-4 and the colon cancer cell line HT-29. St/DDP and HT/DDP were seven and five times as resistant to cDDP as their parental lines, and the expression of TRX in these variants was increased by 2.5- and 2-fold, respectively. The expression of TRX in the complete revertant cells of St/DDP was reduced as low as that in St-4 cells. TRX reductase activity was also increased in St/DDP and HT/DDP, suggesting that activation of the TRX system was associated with in vitro-acquired cDDP resistance. Because cDDP is the first-line drug against ovarian cancer, we examined the expression of TRX in 11 human ovarian cancer cell lines not treated with cDDP in vitro. Positive correlation between TRX expression and cDDP resistance was observed in these cell lines (r = 0.76, P = 0.007). This correlation was comparable to that between GSH content and cDDP resistance (r = 0.69, P = 0.019). These results suggest a possible involvement of TRX, as well as GSH, in cDDP resistance.

Multidrug resistance

Since we found verapamil as a multidrug resistance (MDR) reversing agent in 1981, many MDR reversing compounds have been reported. This type of drug must have strong effects with little side effects. We recently found MS-209 and PSC-833 as reversing agents. These two compounds interacted directly with P-glycoprotein, and showed a good MDR reversing effect in vitro and in vivo. MRK16, an antibody against P-glycoprotein, also showed a good therapeutic effect against drug resistant human tumors. MS-209, PSC-833 and the antibody against P-glycoprotein are interesting candidates for clinical use in the future.

Acute induction of adriamycin-resistance in human colon carcinoma HT-29 cells exposed to a sublethal dose of adriamycin

To study the mechanisms of the acute induction of drug resistance in cancer cells, we have established a model system in which adriamycin (ADM) induces immediate drug resistance. In this system, human colon carcinoma HT-29 cells were pretreated for 1 h with a subtoxic dose of ADM (0.3 micrograms/ml) and incubated for 24 h in drug-free medium. Then the cells were treated for 1 h with ADM, and the cell survival was determined in terms of colony-forming ability. The survival of the pretreated cells was increased up to 100-fold, as compared with that of untreated cells. Such increased survival, however, was observed only after high doses of ADM (2 to 8 micrograms/ml); more than 99% of the cells were killed. These results indicate that only a small fraction of ADM-pretreated cells acquire the ADM-resistant phenotype. Similar induced resistance was observed in five of seven subclones isolated from HT-29 cells by limiting dilution, suggesting that the majority of cells in the parental HT-29 population could acquire the ADM-resistant phenotype. In the subclone HT-29T9, the ADM pretreatment induced concomitant resistance to daunomycin, VP-16, and VM-26 but not to agents other than topoisomerase II inhibitors. The ADM-induced drug resistance did not accompany MDR1 gene expression and could not be overcome by verapamil, a P-glycoprotein inhibitor. The present system could be useful to study the acute induction mechanism(s) of ADM-resistance, which could be relevant to clinical resistance in patients.

Resistance to antitumor agent-induced apoptosis in a mutant of human myeloid leukemia U937 cells

Human monocytic leukemia U937 cells underwent apoptosis when the cells were treated with a variety of antitumor drugs. We isolated and characterized a mutant, UK711, that was resistant to apoptosis induced by antitumor agents. When U937 cells were treated with etoposide (VP-16), an inhibitor of DNA topoisomerase II, apoptosis occurred in a large number of cells, and flow-cytometric analysis revealed that the majority of cells in S phase underwent apoptosis within 2 h of the end of treatment. Such treatment, however, induced apoptosis in only a few UK711 cells. The levels of protein-DNA covalent links and DNA double-strand breaks caused by VP-16 were similar in both cell lines, indicating that the initial DNA damage caused by VP-16 were comparable, whereas the following cellular responses that resulted in apoptosis differed between these cell lines. UK711 cells also showed resistance to apoptosis induced by such antitumor agents as 1-(beta-D-arabinofuranosyl) cytosine (Ara-C), adriamycin, mitomycin C, camptothecin, and by cytotoxic stimuli such as staurosporine, cycloheximide, and uv irradiation. UK711 cells, however, were sensitive to apoptosis induced by tumor necrosis factor (TNF), as were U937 cells. In accordance with resistance to apoptosis induced by antitumor agents, UK711 cells showed significant actual drug resistance to these antitumor agents. The present results indicate that UK711 cells acquired resistance to apoptosis induced by a variety of cytotoxic stimuli resulting in actual anticancer drug resistance. This cell line may be useful in studying the mechanism of apoptosis induced by cytotoxic agents.

Enhancement of reversing effect of cyclosporin A on vincristine resistance by anti-P-glycoprotein monoclonal antibody MRK-16

The synergistic effect of MRK-16, a monoclonal antibody against P-glycoprotein, and cyclosporin A (CsA) on the modulation of vincristine resistance was studied by isobologram analysis in three different, highly multidrug-resistant tumor cells. In all cell lines, the synergistic effect was demonstrated at various concentrations of MRK-16 and CsA. While MRK-16 alone did not enhance the sensitivity of the moderately resistant KB-8-5 cells to vincristine, it increased two-fold the reversing effect of cyclosporin A at 1 microM, an achievable blood concentration. Since MRK-16 alone showed therapeutic effects against multidrug-resistant tumors, the combined use of MRK-16, CsA and antitumor agents should provide therapeutic benefits for the treatment of resistant tumors.

Enhancement of cellular accumulation of cyclosporine by anti-P-glycoprotein monoclonal antibody MRK-16 and synergistic modulation of multidrug resistance

BACKGROUND

Drug resistance is a major obstacle to successful cancer chemotherapy. P-glycoprotein, which transports certain antitumor agents out of resistant tumor cells, is known to be a major factor in some types of multidrug resistance. Studies have shown that verapamil and the immunosuppressors cyclosporine and FK-506 can reverse multidrug resistance in vitro and in vivo and that the P-glycoprotein monoclonal antibody MRK-16 increases drug toxicity in multidrug-resistant tumors.

PURPOSE

The purpose of this in vitro study was to establish effective treatment modalities for overcoming multidrug resistance. We assessed the synergistic effects of verapamil, cyclosporine, or FK-506 in combination with MRK-16 and antitumor agents.

METHODS

Human myelogenous leukemia K562 cells and multidrug-resistant K562/ADM cells were treated with vincristine or doxorubicin combined with MRK-16 and cyclosporine alone or together; MRK-16 and verapamil alone or together; or MRK-16 and FK-506. The effects of MRK-16 and cyclosporine or verapamil on the accumulation of vincristine and doxorubicin were examined in K562/ADM cells, and the mechanisms of action were analyzed.

RESULTS

MRK-16 and cyclosporine synergistically enhanced the antitumor effects of vincristine and of doxorubicin in K562/ADM cells. However, the combined use of MRK-16 with verapamil or FK-506 did not show such synergistic effects in these cells. Studies of the effect of MRK-16 on cellular accumulation of cyclosporine and verapamil revealed that MRK-16 substantially increased accumulation of cyclosporine in K562/ADM cells, but did not increase accumulation of verapamil.

CONCLUSIONS

MRK-16 and cyclosporine synergistically enhanced the antitumor effects of vincristine and doxorubicin because MRK-16 increased cellular accumulation of cyclosporine.

IMPLICATIONS

These results, together with our previous finding that intravenous administration of MRK-16 induced regression of multidrug-resistant subcutaneous tumors in athymic mice, support the hypothesis that the combined use of MRK-16 and cyclosporine might increase the efficacy of antitumor agents against multidrug-resistant tumors expressing P-glycoprotein. Clinical phase I trials of MRK-16 in the treatment of multidrug-resistant tumors are under consideration.

Novel mechanism of N-solanesyl-N,N'-bis(3,4-dimethoxybenzyl)ethylenediamine in potentiation of antitumor drug action on multidrug-resistant and sensitive Chinese hamster cells

The mechanism of the synthetic isoprenoid N-solanesyl-N,N'-bis(3,4-dimethoxybenzyl)ethylenediamine (SDB-ethylenediamine) in potentiating antitumor drug action against multidrug-resistant cells was comparatively studied with other potentiators such as verapamil and cepharanthine. SDB-ethylenediamine increased the accumulation of [3H]daunorubicin (DNR) in Chinese hamster V79 (V79/S) and its multidrug-resistant mutant (V79/ADM) cells. Even after SDB-ethylenediamine was removed from the medium, its effect continued. But when verapamil was removed from the medium, its effect disappeared immediately. Unlike verapamil and cepharanthine, SDB-ethylenediamine did not greatly inhibit the efflux of [3H]DNR from V79/ADM, the binding of [3H]vinblastine to membrane vesicles of V79/ADM, or the binding of [3H]azidopine to P-glycoprotein in the cytoplasmic membrane of V79/ADM. It did stimulate the influx of [3H]DNR into the ATP-depleted cells of V79/S and V79/ADM. Thus, SDB-ethylenediamine uniquely potentiates antitumor drugs. The increased intracellular accumulation of antitumor drugs in the presence of SDB-ethylenediamine is due not only to the inhibition of active efflux but also to the stimulation of the influx of antitumor drugs.

Synergistic effect in culture of bleomycin-group antibiotics and N-solanesyl-N,N'-bis(3,4-dimethoxybenzyl)ethylenediamine, a synthetic isoprenoid

Like bleomycin and peplomycin, libromycin, a newly developed bleomycin-group antibiotic, was potentiated 130-fold against Chinese hamster V79 cells (V79/S) and 47-fold against its multidrug-resistant mutant (V79/ADM) by N-solanesyl-N,N'-bis(3,4-dimethoxybenzyl)ethylenediamine (SDB-ethylenediamine) at 10 and 3 micrograms/ml, respectively. But neocarzinostatin, known to cause DNA strand scission as bleomycins do, was potentiated only twofold. This suggests that the high potentiation by SDB-ethylenediamine is unique to the bleomycin-group antibiotics. Isobologram analysis revealed that the combined effect of peplomycin and SDB-ethylenediamine was highly synergistic. SDB-ethylenediamine did not increase the intracellular accumulation of [3H]peplomycin in V79/S cells. Analyses by an alkaline elution method demonstrated that single strand scission in DNA of intact V79/S cells caused by 1-h incubation with peplomycin was greatly stimulated by pre- and co-existence of SDB-ethylenediamine, but DNA strand breaks in isolated nuclei were not affected. Apparently some cytoplasmic constituent(s) is involved in the potentiation mechanism. SDB-ethylenediamine did not block the DNA repair which occurred after the removal of peplomycin from the medium. Two fragments of SDB-ethylenediamine, solanesol (polyprenoid moiety) and a diamine component (verapamil-like moiety), were not synergistic with peplomycin, even when they were mixed together. This indicates that the steric conformation of the intact SDB-ethylenediamine molecule is important for the activity.

Cytocidal activity of a synthetic isoprenoid, N-solanesyl-N,N'-bis(3,4-dimethoxybenzyl)ethylenediamine, and its potentiation of antitumor drugs against multidrug-resistant and sensitive cells in vitro

A synthetic isoprenoid, N-solanesyl-N,N'-bis(3,4-dimethoxybenzyl)ethylenediamine (SDB-ethylenediamine), inhibited the colony formation of multidrug-resistant mutant cell lines derived from Chinese hamster V79 (V79/ADM) and human hepatoma PLC/PRF/5 (PLC/COL) cells to a greater extent than that of the parental cells. When combined with other clinically useful antitumor agents, it potentiated the cytotoxic activity of almost all kinds of drugs tested including adriamycin (ADM), actinomycin D, vincristine, cytosine arabinoside, and 5-fluorouracil (5-FU), and the potentiation ratios were higher against V79/ADM cells than against V79/S cells. Among the antitumor agents tested, the activities of bleomycin-group antibiotics were more strongly enhanced by SDB-ethylenediamine and the potentiation was higher in the parental cells than in V79/ADM cells. SDB-ethylenediamine enhanced the uptake of ADM and daunorubicin into V79/ADM and its parental cells, but it did not increase the uptake of 5-FU or peplomycin, indicating that different mechanisms operate for potentiation in the cases of the latter drugs, i.e., not simply an increase of intracellular drug uptake. Two fragments of SDB-ethylenediamine, solanesol (polyprenoid moiety) and the diamine component (verapamil-like moiety), showed neither cytotoxic activity nor potentiator activity, even if they were mixed together, indicating that the steric conformation of intact SDB-ethylenediamine molecule is important for these two activities.

Resorthiomycin, a novel antitumor antibiotic. III. Potentiation of antitumor drugs and its mechanism of action

Resorthiomycin suppressed the clonogenic activity of a multidrug-resistant mutant cell line of Chinese hamster V79 cells more potently than its parental cells. Moreover, resorthiomycin at 40 micrograms/ml potentiated the cytotoxic activity of vincristine and actinomycin D on V79 cells over 3-fold. Uptake of [3H]actinomycin D into V79 cells was stimulated 2-fold by 40 micrograms/ml of resorthiomycin during 2 hours incubation. On the other hand, incorporation of [3H]thymidine and [3H]uridine into mouse leukemia L5178Y cells was inhibited in a dose-dependent manner at resorthiomycin concentrations ranging from 5 to 40 micrograms/ml. In ATP-depleted L5178Y cells, membrane transport of [3H]thymidine and 2-[3H]deoxyglucose was strongly suppressed by resorthiomycin. These results suggest that resorthiomycin acts on the plasma membrane and perturbes some membrane function.