Evaluation of the cytotoxic activity of gemcitabine in primary cultures of tumor cells from patients with hematologic or solid tumors

Gemcitabine (2'-deoxy-2',2'-difluorocytidine; dFdC) is a novel nucleoside analog that has shown clinical activity against solid tumors. The semiautomated fluorometric microculture cytotoxicity assay (FMCA) was used for evaluation of the cytotoxicity of gemcitabine in vitro in primary cultures of human cells from patients with hematologic or solid tumors. The activity pattern of cytarabine (ara-C), 2-chlorodeoxyadenosine (CdA), etoposide (VP-16), doxorubicin, and cisplatin were included for comparison. One hundred forty samples were tested using continuous drug exposure. Gemcitabine showed high activity against hematologic samples, whereas little or no activity was observed in the solid tumor groups. A similar pattern of activity also was observed for ara-C and CdA, whereas etoposide, cisplatin, and doxorubicin were relatively more active in solid tumors. Cross-resistance analysis between gemcitabine and the standard drugs revealed the following rank order of correlation coefficients: ara-C > doxorubicin > CdA > cisplatin > VP-16. The results indicate that gemcitabine is differentially active against hematologic tumors and that the activity pattern of gemcitabine resembles that of ara-C. However, these results also indicate that gemcitabine may be more active against some solid tumor groups in comparison to ara-C and CdA.

The cytotoxic activity of Taxol in primary cultures of tumour cells from patients is partly mediated by Cremophor EL

In patient tumour samples the activity in vitro of Taxol corresponded fairly well to the known clinical activity and Taxol showed low cross-resistance to standard cytotoxic drugs. However, the Taxol solvent Cremophor EL--ethanol was considerably active alone, whereas paclitaxel formulated in ethanol was less active. Taxol thus seems to contain two components active against patient tumour cells in vitro.

Relationship between pharmacokinetic parameters in patients and cytotoxicity in vitro of standard and investigational anticancer drugs

The selection of the starting dose for initial clinical trials of anticancer agents is mostly determined by toxicological endpoints in mice (LD10). So far, very few attempts have been made to evaluate the potential value of cytotoxicity assays for this purpose. The present study was undertaken as a first attempt to investigate the relationship between cytotoxicity of anticancer drugs in vitro and pharmacokinetic parameters in vivo in patients, at suggested maximum tolerated doses. Using the fluorometric microculture cytotoxicity assay (FMCA), we determined the concentration giving 50% cell survival (IC50) in vitro, for 25 cytotoxic drugs in fresh preparations of normal peripheral blood mononuclear cells (PBMC) and of tumor cells from patients with acute or chronic lymphocytic leukemia (ALL or CLL). Using linear regression, we investigated the relationship between the IC50s and clinically achievable peak plasma concentrations (Cmax) or concentration-time products (C x T) in humans. The clinical data was obtained from the literature. Based on all drugs tested, good correlations were obtained between IC50s for CLL cells, and both Cmax and C x T (R approximately 0.7, p < 0.0002), and for ALL cells and normal PBMC between IC50 and Cmax, while the two latter cell types showed somewhat weaker relationships to C x T. Using the IC50 data of CLL cells, predictions of Cmax and C x T exceeded 1 log for only four drugs. No tendencies to under- or overprediction within different classes of drugs were noted. The results demonstrate a significant relationship between toxicity in vitro and achievable systemic exposure of anticancer drugs in humans, which suggests that non-clonogenic in vitro assays for drug sensitivity testing may provide pharmacokinetic information useful in the development of investigational cytotoxic drugs.

Leaf CO(2) exchange of Erythrina poeppigiana (Leguminosae: Phaseolae) in humid tropical field conditions

An idealized model was developed to describe leaf CO(2) exchange in the leguminous tree Erythrina poeppigiana (Walpers) O.F. Cook under well-watered field conditions. Photosynthetic rate in mature leaves (p) was modeled as a rectangular hyperbolic function of photon flux density (q) and ambient CO(2) concentration (c(a)), relative photosynthetic capacity (pi) was modeled as a logistic s-function of leaf age (l(a)), metabolic dark respiration rate (r(m)) was modeled as an exponential function of leaf temperature (T(l)), and photorespiration rate (r(p)) was modeled as a hyperbolic function of c(a). Assimilation rate (a(c)) was modeled as the difference between the product of p and pi and the sum of r(m) and r(p): a(c) = p(q,c(a))pi(l(a)) - [r(m)(T(l)) + r(p)(c(a))]. The model parameters were estimated separately for five sources of E. poeppigiana (Clones 2660, 2662, 2687 and 2693 and half-sib Family 2431) from field data measured with a portable closed-loop gas exchange system at a humid tropical site in Costa Rica. The between-source differences in leaf CO(2) exchange characteristics were small, but statistically significant. Aboveground biomass production was highest in sources that maintained high relative photosynthetic capacity throughout the leaf life span. Quantum yield varied between 0.046 and 0.067, and light-saturated assimilation rate (q = 2000 micro mol m(-2) s(-1) and T(l) = 28 degrees C) at natural atmospheric c(a) (350 micro mol mol(-1)) was 16.8-19.9 micro mol m(-2) s(-1). Increasing c(a) to 1000 micro mol mol(-1) resulted in an approximate doubling of the light-saturated assimilation rate. Foliole nitrogen concentration, which was 45.3-51.2 mg g(-1) in mature leaves, was positively correlated with relative photosynthetic capacity. Foliole nitrogen concentration, quantum yield and maximum assimilation rate of E. poeppigiana are among the highest values observed in tropical woody legumes.

Expression of the 85-kd membrane protein in primary human breast cancer: relationship to hormone receptor levels, DNA ploidy, and tumor grade

Using the monoclonal antibody (MAb) MRK20 the immunohistochemical expression of the 85-kd membrane protein (MP)/cell adhesion molecule (CAM) CD36 was investigated in tumors from 41 patients with untreated breast adenocarcinoma. DNA ploidy as measured by flow cytometry and estrogen (ER) and progesterone receptor (PgR) tumor contents also were determined. Immunohistochemistry on frozen tissue showed expression of 85-kd MP localized to the carcinoma cells in tumors from 16 patients (39%). These samples also displayed variable staining of the capillary endothelium. Twenty-one samples (51%) showed 85-kd MP expression in small blood vessels. Thus, a total of 37 of 41 tumors (90%) were MAb MRK20 positive in carcinoma and/or mesenchymal cells. Expression of 85-kd MP in carcinoma cells was negatively associated with expression of ER (P < .05) and PgR (P < .01) receptors and positively associated with nondiploid tumors (P < 0.05) and tumor grade (P < .05). Axillary lymph node status, tumor size, and (patient) age were not associated with expression of 85-kd MP. In cytological smears obtained by fine-needle aspiration (FNA) cytology from 19 of the samples, expression of 85-kd MP in carcinoma cells showed a good correlation with tumor cell positivity in the corresponding histological section. Expression of 85-kd MP in breast carcinoma cells thus was associated with some recognized adverse prognostic factors. Future studies of its pathophysiological and prognostic roles in breast cancer seem warranted.

Cytotoxic activity of topoisomerase II inhibitors in primary cultures of tumor cells from patients with human hematologic and solid tumors

BACKGROUND

Little is known about the in vitro activity and cross-resistance patterns of topoisomerase II (topo II) inhibitors in primary cultures of tumor cells from patients with different diagnoses.

METHODS

The in vitro activity of the topo II inhibitors daunorubicin, doxorubicin, idarubicin, epirubicin, amsacrine, mitoxantrone, and etoposide was determined using the fluorometric microculture cytotoxicity assay. Four hundred seventy-six samples from patients with various diagnoses were tested with continuous drug exposure.

RESULTS

Hematologic samples were more sensitive than solid tumors to all tested drugs. Etoposide was the most active drug in solid tumors followed by epirubicin, with amsacrine the least active. The anthracyclines doxorubicin, daunorubicin, and epirubicin showed similar in vitro activity. Conversely, idarubicin showed low to moderate cross-resistance with all tested topo II inhibitors. Mitoxantrone and amsacrine showed high in vitro activity and displayed cross-resistance to the anthracyclines in the hematologic neoplasms. In the solid tumor group, mitoxantrone and amsacrine had lower activity and weak correlations with the anthracyclines. Etoposide had intermediate to weak correlations with the other drugs.

CONCLUSIONS

There is a marked difference in tumor-type specificity and cross resistance patterns among the different topo II inhibitors tested. This may indicate that minor differences in topo II interaction and/or other mechanisms of drug action may substantially determine the cytotoxic activity of topo II-targeted drugs.

Effects of lovastatin on a human myeloma cell line: increased sensitivity of a multidrug-resistant subline that expresses the 170 kDa P-glycoprotein

Using a fluorometric microculture cytotoxicity assay for measuring cell viability and proliferation we examine the cytotoxic effect of lovastatin on a drug sensitive myeloma cell line (RPMI 8226) and a multidrug resistant (MDR) clone (8226/Dox40), that was approximately 100-fold less sensitive to doxorubicin. The RPMI 8226 cells were sensitive to lovastatin with an IC50 of 15.8 micrograms/ml. However, the MDR subline exhibited a collateral sensitivity to lovastatin, with an IC50 of 1.7 microM, thus having a 9.3-fold greater sensitivity to lovastatin than the parental cell line. The combination of doxorubicin and lovastatin did not show any synergistic or antagonistic effects on any of the cell lines. The increased sensitivity to lovastatin of the P-gp 170-expressing MDR cells 8226/Dox40 might be part of a more general phenomenon that merits further investigation.

Interactions between cladribine (2-chlorodeoxyadenosine) and standard antileukemic drugs in primary cultures of human tumor cells from patients with acute myelocytic leukemia

The semiautomated fluorometric microculture cytotoxicity assay (FMCA), based on the measurement of fluorescence generated from cellular hydrolysis of fluorescein diacetate (FDA) to fluorescein in microtiter plates, was used for in vitro evaluation of Cladribine (2-chlorodeoxyadenosine, CdA) interactions with five standard antileukemic drugs: amsacrine (Am), etoposide (VP16), daunorubicin (Dnr), cytosine arabinoside (AraC), and mitoxantrone (Mit). Samples from 31 patients with acute myelocytic leukemia (AML) were tested with continuous drug exposure. A large heterogeneity with respect to cell kill was observed for all combinations tested. An additive model provided a significantly better fit of the data compared to the effect of the most active single agent of the combination (Dmax) only for CdA+AraC. When the frequency of additive and synergistic interactions were calculated according to the multiplicative concept for drug interactions, the highest frequencies were observed for CdA+AraC and CdA+Dnr. This interaction pattern was confirmed by isobologram analysis. Cross-resistance analysis revealed high correlations between CdA and AraC whereas the correlations were weaker between CdA and the other drugs. The highest frequency of synergistic interactions was obtained for AraC+CdA, despite their cross-resistance. Of the non-cross-resistant drugs tested, Dnr appears to be the most effective adjunct to CdA in terms of interactions at the cellular level.

Variable p-glycoprotein immunoreactivity unrelated to cytotoxic drug-resistance in-vitro of human adrenocortical carcinoma

Human adrenocortical tissue was immunohistochemically investigated with monoclonal antibodies C219 and JSB-1 for expression of P-glycoprotein (Pgp) associated with resistance to multiple cytotoxic drugs. All normal (n=7) and adenomatous (n=3) glands strongly expressed the protein, while the cancers (n=15) demonstrated variable Pgp reactivity. Cytotoxic drug sensitivity testing in vitro on freshly dispersed cells from one normal adrenal gland and from 6 carcinomas with no to extensive Pgp reactivity demonstrated universally poor sensitivity to 9 standard drugs including those with Pgp mediated resistance. The findings indicate that immunohistochemical staining for Pgp cannot be used to predict cytotoxic drug resistance and that other mechanisms mediate cytotoxic drug resistance in adrenocortical carcinoma.

Cytotoxic drug sensitivity testing of tumor cells from patients with ovarian carcinoma using the fluorometric microculture cytotoxicity assay (FMCA)

The automated fluorometric microculture cytotoxicity assay (FMCA) is based on the measurement of fluorescence generated from cellular hydrolysis of fluorescein diacetate (FDA) to fluorescein by viable cells after a 72-hr culture period in microtiter plates. The FMCA was adopted for chemosensitivity testing of tumor cells from patients with ovarian carcinoma. Thirty-seven samples of solid tumors and malignant effusions were obtained from 35 patients at diagnosis or relapse. Tumor cells from solid samples and effusions were prepared by enzymatic digestion and centrifugation, respectively, followed by Percoll or Ficoll purification. The fluorescence was proportional to the number of cells/well and considerably higher in tumor cells than in contaminating normal cells. The effect of up to 19 cytotoxic drugs was successfully assessed in 70% of the samples and there was a good correlation between drug sensitivity data reported by the FMCA and the DiSC assay performed in parallel. The overall drug sensitivity pattern in vitro corresponded well to the clinical experience. The effect of cisplatin varied considerably between patients and resistance was found also in cases not previously exposed to cytotoxic drugs. The FMCA is a rapid and simple method that seems to report clinically relevant cytotoxic drug sensitivity data in ovarian carcinomas. In the future, this method may contribute to optimizing chemotherapy by assisting in individualized drug selection and new drug development.

Development of vincristine resistance and increased sensitivity to cyclosporin A and verapamil in the human U-937 lymphoma cell line without overexpression of the 170-kDa P-glycoprotein

A vincristine (Vcr)-resistant subline of the human histiocytic lymphoma cell line U-937 (U-937-vcr) has been established and characterized with respect to its phenotypic features, including growth rate, surface marker expression and ability to respond to differentiation-inducing agents. The sensitivity of U-937-vcr cells to the direct cytotoxicity of cyclosporin A (CsA) and verapamil (Ver), and the capacity of these drugs to modify Vcr resistance, were also examined. The U-937-vcr cells exhibited a more than 200-fold resistance to Vcr, and cross-resistance to vinorelbin and taxol. Also, there was a slight cross-resistance to colchicine, doxorubicin and VP16. However, the response of U-937-vcr to CsA or Ver alone was substantially altered, with a marked decrease in their respective IC50s. The U-937-vcr cells did not show increased levels of pgp 170. We conclude that the development of Vcr resistance was not associated with a change in the major phenotypic properties of the U-937 cell line, and that resistance modifier hypersensitivity was not associated with increase in pgp 170 expression.

Polyamines regulate human medullary thyroid carcinoma TT-cell proliferation and secretion of calcitonin and calcitonin gene-related peptide

The significance of polyamines for the neoplastic proliferation and secretion of calcitonin (CT) and calcitonin-gene-related peptide (CGRP) by the human medullary thyroid carcinoma TT cell line was investigated. TT cells were cultured in vitro for 6 days with or without additions of pathway inhibitors of polyamine biosynthetic enzymes. Treatment of the cells with 1 mM of the specific L-ornithine decarboxylase (ODC) inhibitor DL-alpha-difluoromethylornithine (DFMO) resulted in a 97% decrease in ODC activity, lowered contents of putrescine (96%) and spermidine (85%) and cell proliferation rates (90%) along with a compensatory 15-fold increase in S-adenosyl-L-methionine decarboxylase (SAMDC) activity. DFMO treatment also led to a decrease in cellular content of CT (33%) and CGRP (26%), while the drug enhanced secretion of CT (31%) but depressed that of CGRP (26%), and elevated the ratio of CT to CGRP secreted into the medium by 74%. Ethylglyoxal bis(guanylhydrazone) (EGBG), a SAMDC inhibitor, at 100 microM evoked a similar reduction of cell proliferation and lowered the content of spermine by 81%. Furthermore, EGBG treatment caused a 34-fold increase in ODC activity and a subsequent 35-fold build-up of putrescine, but also seemed to stabilize SAMDC as evidenced by a highly enhanced SAMDC activity (approximately 200-fold) during enzyme assays in the absence of the inhibitor. EGBG exposure resulted in an increase in cellular CT content (110%) and secretion of the hormone (82%), while not affecting CGRP content or release.2+ EGBG effects were partially counteracted by DFMO.(ABSTRACT TRUNCATED AT 250 WORDS)

Activity of cyclosporins as resistance modifiers in primary cultures of human haematological and solid tumours

The semiautomated fluorimetric microculture cytotoxicity assay (FMCA) was used for evaluation of the ability of cyclosporin A (CsA) and its novel non-immunosuppressive derivative SDZ PSC 833 (PSC) to modify the response to doxorubicin or vincristine in vitro in different haematological and solid human tumour types. Primary cultures of 322 tumour samples were analysed. Both cyclosporins showed resistance-modifying activity in all haematological tumours tested, and in solid tumours activity was observed in ovarian carcinoma and childhood tumours. Little or no effect was found in the remaining tumour types, including breast, renal and adrenal cortical carcinomas and adult sarcomas. In most of the responsive cases the interaction between the modifier and the cytotoxic drug was synergistic. There was a tendency to higher activity in samples from previously treated patients, and an inverse relationship between degree of cytotoxic drug resistance and resistance-modifying activity was noted. No difference in potency between CsA and PSC could be discerned. The results indicate differential in vitro resistance-modifying activity of the cyclosporins depending on tumour type. The results also suggest that treatment with resistance modifiers should be considered also for primary therapy of drug-sensitive tumours. Drug resistance assays such as the FMCA may become useful in preclinical evaluation of resistance modifiers.

A non-P-glycoprotein-mediated mechanism of vincristine transport which is affected by resistance modifiers and present in chemosensitive cells

The accumulation and cytotoxicity of vincristine (Vcr), etoposide (VP16), and daunorubicin (Dau) and effect of the resistance modifiers (RM) verapamil (Ver; 10 microM) and cyclosporin A (CyA; 3 microM) were studied in isolated rat cardiac myocytes, peripheral lymphocytes from seven patients with chronic lymphocytic leukemia (CLL), in the human leukemic cell line K562 and its two Vcr resistant mdr1 gene expressing sublines, K562/Vcr30, K562/Vcr150. Both RMs increased the accumulation and cytotoxic effect of Vcr and Dau in the resistant sublines. In K562 cells, lymphocytes from patients with CLL and rat cardiac myocytes, which all were mdr1 RNA negative RMs increased the cellular accumulation and potentiated the cytotoxic effect of Vcr but not that of Dau. K562/Vcr30 and K562/Vcr150 were cross resistant to Dau but not to VP16 and RMs had no effect on the cytotoxicity of VP16 in any of cell lines. The results indicate that chemosensitive cells also have a transport mechanism, not mediated by P-glycoprotein, which transports Vcr but not Dau and VP16. This suggests that addition of RMs to Vcr-containing chemotherapy may enhance the antineoplastic effect also by inhibition of non-P-glycoprotein mediated transport mechanisms.

Microfluorometric evaluation of calcein acetoxymethyl ester as a probe for P-glycoprotein-mediated resistance: effects of cyclosporin A and its nonimmunosuppressive analogue SDZ PSC 833

A microtiter plate-based fluorometric assay for functional measurement of 170-kDa P-glycoprotein (Pgp)-mediated transport using fluorescent calcein as a probe is described. The myeloma RPMI 8226 cell line and two of its doxorubicin-resistant Pgp-expressing sublines, dox40 (high expression) and dox6 (low expression), were used as models. Nonfluorescent calcein acetoxymethyl ester (calcein/AM) was added to the cells and subsequent accumulation of calcein was measured in a 96-well scanning fluorometer after 30 min. There was an inverse relationship between Pgp expression and calcein/AM accumulation, which increased dose-dependently in the presence of cyclosporin A (CsA) and the nonimmunosuppressive analogue SDZ PSC 833 (PSC) in the Pgp-expressing cell lines. PSC appeared to restore uptake more effectively than CsA at low concentrations. Calcein accumulation was also increased in Pgp-expressing cells by the addition of the Pgp substrate vincristine and the metabolic inhibitor potassium cyanide, KCN. No effect was observed in parental cell lines. When parental and dox40 cells were mixed, 10% of dox40 cells could reproducibly be detected. The results indicate that microtiter-plate determination of calcein accumulation is a simple and sensitive method for functional determination of Pgp-mediated drug transport. The method may become useful, not only for preclinical screening for novel and improved resistance modifiers, but also for determination of Pgp activity in individual clinical tumor samples.

P-glycoprotein expression and activity of resistance modifying agents in primary cultures of human renal and adrenocortical carcinoma cells

Tumor cells from patients with renal or adrenocortical carcinomas were tested in vitro for sensitivity to doxorubicin (Dox) and vincristine (Vcr), as well as for the modulation of this sensitivity by resistance modifiers and the immunohistochemical expression of the multidrug resistance associated P-glycoprotein (Pgp). Normal adrenocortical cells from one patient and Pgp-expressing cells of Dox-resistant myeloma RPMI 8226 sublines were included for comparison. The normal adrenocortical cells and cells from one adrenocortical carcinoma showed high Pgp expression, comparable to the most Dox-resistant myeloma cell line, whereas the other tumor samples showed variable but lower expression. The normal adrenocortical as well as the adrenocortical and renal tumor cells were highly resistant to Dox and Vcr. Whereas the cytotoxic effect of Dox was considerably increased by verapamil, cyclosporin A and its non-immunosuppressive analogue SDZ PSC 833 in the Pgp-expressing Dox-resistant sublines, comparatively small effects on the Dox and Vcr sensitivity were observed in the patient samples, irrespective of their Pgp expression. The results indicate that the Dox and Vcr resistance in human adrenocortical and renal carcinomas is mediated by mechanisms other than Pgp and that resistance modulating agents targeting Pgp may be much less efficient in the clinic than in Pgp-expressing cell lines, at least for the tumor types described in the present study.

Detection of tumor-specific cytotoxic drug activity in vitro using the fluorometric microculture cytotoxicity assay and primary cultures of tumor cells from patients

The semi-automated fluorometric microculture cytotoxicity assay (FMCA), based on the measurement of fluorescence generated from cellular hydrolysis of fluorescein diacetate (FDA) by viable cells, was employed for cytotoxic drug sensitivity testing of tumor cells from patients with hematological or solid tumors. In total, 390 samples from 20 diagnoses were tested with up to 12 standard cytotoxic drugs. The technical success rate for different tumor types ranged from 67 to 95%. Fluorescence was linearly related to cell number but variably steep depending on tumor type. Samples from most solid tumors thus showed higher signal-to-noise ratios than hematological samples. A wide spectrum of in vitro drug activity was obtained, with acute leukemias and non-Hodgkin's lymphomas being sensitive to almost all tested drugs, whereas renal and adrenocortical carcinomas were essentially totally resistant. Between these extremes were samples of breast and ovarian carcinomas and sarcomas. When in vitro response was compared with known clinical response patterns, a good correspondence was observed. The results indicate that the FMCA is a rapid and efficient method for in vitro measurement of tumor-specific drug activity both in hematological and in solid tumors. The assay may be suitable for new drug development and direction of phase-2 trials to suitable patients.

In vitro activity of 2-chlorodeoxyadenosine (CdA) in primary cultures of human haematological and solid tumours

2-Chlorodeoxyadenosine (CdA) is a deaminase-resistant purine analogue which has shown clinical activity against various haematological tumours, and is currently undergoing phase II trials. In the present study, the semiautomated fluorometric microculture cytotoxicity assay (FMCA) was used for in vitro evaluation of CdA activity in cell suspensions from both haematological and solid tumours. A total of 133 samples from various diagnoses were successfully tested with continuous drug exposure. CdA showed high in vitro activity against samples from chronic and acute lymphocytic leukaemia and acute myelocytic leukaemia, but little or no response was observed in the solid tumour groups. Cross-resistance analysis with standard drugs revealed the following rank order of correlation coefficients: cytosine arabinoside (AraC) > daunorubicin > doxorubicin > vincristine > prednisolone > 4-hydroperoxycyclophosphamide > etoposide > cisplatin. The high correlation between CdA and AraC was maintained even if the analysis was based only on the haematological tumours. The results indicate that CdA is differentially active against haematological tumours with little or no activity against solid tumours. CdA also appears highly cross resistant with AraC. If this disease-specific information is substantiated in further clinical trials and extended to other phase I-II drugs, non-clonogenic drug resistance assays such as the FMCA may become useful in new drug evaluation, and in targeting specific diagnoses and patients for phase II trials.

In vitro drug sensitivity testing of tumor cells from patients with non-Hodgkin's lymphoma using the fluorometric microculture cytotoxicity assay

BACKGROUND

Tumor cell drug sensitivity is an important determinant of chemotherapy response. Its measurement in vitro would aid in therapy individualization and new drug development.

MATERIALS AND METHODS

The fluorometric microculture cytotoxicity assay (FMCA), based on production by viable cells of fluorescent fluorescein after 3 days of culture, was used for cytotoxic drug sensitivity testing of 73 samples of tumor cells from patients with non-Hodgkin's lymphoma (NHL).

RESULTS

The technical success rate was 92%, and FMCA data showed good correlation to the Disc assay. NHL samples were considerably more drug sensitive than were samples from in vivo resistant tumors. There was no obvious difference in drug sensitivity for high- vs. low-grade or untreated vs. previously treated low-grade NHL. For 26 patients, clinical outcome was correlated to in vitro response giving a sensitivity and specificity of 93 and 48%, respectively. Cross-resistance between standard drugs was frequent in vitro. Resistance modulators potentiated the effect of vincristine and doxorubicin in 10-29% of the samples, most frequently from previously treated patients.

CONCLUSIONS

The FMCA seems to report clinically relevant drug sensitivity data for NHL, and thus it could serve as a tool for optimization of chemotherapy in the future.

Expression of the multidrug-resistance gene product in untreated human breast cancer and its relationship to prognostic markers

The immunohistochemical expression of the 170-kDa permeability glycoprotein (P-gp) was investigated in 41 primary untreated breast carcinomas, using the monoclonal antibodies C219 and MRK16. DNA ploidy by flow cytometry and estrogen (ER) and progesterone receptor (PgR) contents were also determined. P-gp expression, as revealed by C219 or MRK16, was observed in 6 (14%) of the investigated cancers. P-gp expression had a tendency to occur in non-diploid, high-grade tumors as well as in patients with lymph node negative disease. However, except for lymph node status, these associations were not statistically significant. No positive statistical relationships were observed between other prognostic parameters (age, tumor size, and receptor status) and P-gp expression. Considering the great heterogeneity observed in previous studies and the low expression of P-gp observed hereby, the utility of P-gp immunostaining as a guide for therapy planning in patients with breast cancer remains uncertain.

Prediction of individual patient response to chemotherapy by the fluorometric microculture cytotoxicity assay (FMCA) using drug specific cut-off limits and a Bayesian model

The semiautomated fluorometric microculture cytotoxicity assay (FMCA) based on the measurement of fluorescence generated from cellular hydrolysis of fluorescein diacetate (FDA) to fluorescein in microtiter plates, has been used for determination of cytotoxic drug resistance of tumor cells from patients with hematological and solid tumors. In the present study we describe a calibration procedure based on statistically derived cut-off limits and assay-predicted response probabilities using Bayes' theorem. Test results at a specified drug concentration were divided into three categories: low, intermediate or extreme drug resistance (LDR, IDR and EDR, respectively) using the median and median +1 standard deviation as the cut-off limits. When correlated with clinical outcome, LDR samples showed a higher response rate than expected, IDR a lower and EDR samples no response at all. The sensitivity and specificity of the test, using the median as cut-off limit, were 0.92 and 0.69 respectively. By fitting these test characteristics to a statistical model based on Bayes' theorem it is possible to calculate response probabilities for each individual patient taking into consideration not only the test characteristics and the particular assay result, but also the clinical and patient specific characteristics influencing the pre-test probability of response. EDR predicts clinical drug resistance with high specificity and is also observed in tumor types with high response rate.

Characterization of four doxorubicin adapted human breast cancer cell lines with respect to chemotherapeutic drug sensitivity, drug resistance associated membrane proteins and glutathione transferases

Four human breast cancer cell lines with or without estrogen and progesterone receptors were adapted to growth in the continuous presence of doxorubicin (Dox) at 10 (Zr-75-1), 15 (HTB-122), or 50 (MDA-MB-231 and Hs578T) ng/ml. The sublines of Zr-75-1, MDA-MB-231 and Hs578T showed 5-10-fold Dox resistance and also cross-resistance to vincristine (VCR) and etoposide (VP16). The sublines of Zr-75-1, MDA-MB-231 and Hs578T showed 5-10-fold Dox resistance and also cross-resistance to vincristine (VCR) and etoposide (VP16). The sublines maintained or slightly increased their cis-platinum (CDDP) sensitivity. The sublines of HTB-122 showed resistance only to VP16 combined with a paradoxical increased sensitivity to VCR. The phenotypic alteration in the sublines with respect to Dox sensitivity was maintained for at least two months in the absence of Dox. The glutathione depletor buthionine sulfoximine (BSO) and the calcium channel blocker verapamil (Ver) increased the Dox sensitivity slightly only in the MDA-MB-231 and Hs578T sublines, respectively. Ver also tended to protect some of the sublines from CDDP. The sublines of Zr-75-1 and Hs578T showed increased expression of the 170-kDa permeability glycoprotein (P-gp), whereas expression of a 85-kDa membrane protein determined by the MRK20 antibody was increased in the sublines of Zr-75-1, and HTB-122. Class pi glutathione transferase (GST) levels varied greatly between the cell lines but increased during Dox selection only in the subline of Zr-75-1. Class mu GST was detectable in the MDA-MB-231, Hs578T and HTB-122 cell lines, whereas class alpha GST was detectable in these sublines but undetectable in their parental cell lines. The Zr-75-1 subline showed a 5-fold increase in the class alpha concentration. Except for a correlation between increased P-gp expression and resistance to Dox, VCR and VP16, no obvious correlations between receptor status, increased P-gp expression, membrane proteins, GST levels and acquired drug resistance were found. Thus, except for a possible role for P-gp in multidrug-resistance, these findings indicate a pronounced mechanistic heterogeneity responsible for cytotoxic drug sensitivity also in cells with a common histologic origin and exposed to the same drug.

Difluoromethylornithine and ethylglyoxal bis(guanylhydrazone) as inhibitors of human renal carcinoma cell proliferation and polyamine metabolism

The significance of the polyamines putrescine, spermidine and spermine for the neoplastic proliferation of the human renal carcinoma cell line ACHN was investigated. For this purpose cells were cultured in vitro for 4 days with or without the addition of pathway inhibitors of polyamine biosynthetic enzymes. It was found that treatment of ACHN cells with the specific ornithine decarboxylase (ODC) inhibitor difluoromethylornithine (DFMO) resulted in profound decreases of ODC activity, polyamine content and cell proliferation rates along with a compensatory increase in S-adenosylmethionine decarboxylase (SAMDC) activity. Ethylglyoxal bis(guanylhydrazone) (EGBG), a SAMDC inhibitor, evoked a similar reduction of cell proliferation and contents of spermidine and spermine. EGBG also seemed to stabilize SAMDC, as evidenced by a highly enhanced SAMDC activity during enzyme assays in the absence of the inhibitor. Furthermore, EGBG treatment caused on activation of ODC and a subsequent build-up of putrescine. The impact on polyamine contents and proliferation rates were synergistic when the inhibitors were used in combination. None of the inhibitors alone exerted a cytocidal activity. It is concluded that polyamines may be implicated in the regulation of the neoplastic proliferation of cultured human renal carcinoma cells and that polyamine synthesis inhibitors may prove valuable in clinical treatment of this disease.

In vitro testing of chemotherapeutic drug combinations in acute myelocytic leukaemia using the fluorometric microculture cytotoxicity assay (FMCA)

The fluorometric microculture cytotoxicity assay (FMCA) was employed for analysing the effect of different chemotherapeutic drug combinations and their single constituents in 44 cases of acute myelocytic leukaemia (AML). A large heterogeneity with respect to cell kill was observed for all combinations tested, the interactions ranging from antagonistic to synergistic in terms of the multiplicative concept for drug interactions. However, an 'additive' model provided a significantly better fit of the data compared to the effect of the most active single agent of the combination (Dmax) for several common antileukaemic drug combinations. When the two interaction models were related to treatment outcome 38% of the non-responders showed preference for the additive model whereas the corresponding figure for responders was 80%. Overall, in 248 of 290 (85%) tests performed with drug combinations, there was an agreement between the effect of the combination and that of the most active single component. Direct comparison of Dmax and the combination for correlation with clinical outcome demonstrated only minor differences in the ability to predict drug resistance. The results show that FMCA appear to report drug interactions in samples from patients with AML in accordance with clinical experience. Furthermore, testing single agents as a substitute for drug combinations may be adequate for detection of clinical drug resistance to combination therapy in AML.

Laboratory prediction of clinical chemotherapeutic drug resistance: a working model exemplified by acute leukaemia

Recent research into mechanisms of resistance to chemotherapy in acute leukaemia has been focused on various protective mechanisms at the cellular level, such as drug uptake, efflux, metabolism and DNA repair mechanisms, while therapeutic failures due to other potentially important causes have received relatively little attention. Here we describe a simple model to account for three major determinants of tumour response in acute leukaemia: cellular drug sensitivity, leukaemic cell regrowth potential and systemic drug exposure. Possible ways of measuring these parameters are discussed. It is suggested that laboratory estimation of these parameters may provide valuable information on clinical drug resistance and may help to design more adequate treatment strategies for the individual patient.

SDZ PSC-833—a novel potent in vitro chemosensitizer in multiple myeloma

Multiple myeloma cell lines and patient tumor samples with and without the expression of the classical multidrug resistance (MDR) phenotype were investigated in vitro for drug induced cytotoxicity and modulation of drug resistance. Overall there was a good correlation in the cell lines between MDR expression, as measured by immunocytochemistry with monoclonal antibodies against P-glycoprotein 170 (Pgp), and in vitro resistance to doxorubicin (dox) and vincristin (vcr). Drug resistance in the cell line RPMI 8226 dox 40, expressing a high level of Pgp, was almost completely reversed by the novel non-immunosuppressive cyclosporin A (CsA) analog SDZ PSC-833 (PSC), while the chemosensitizers verapamil, CsA and quinine, in clinically achievable concentrations, were much less effective. In cell lines with low Pgp expression, PSC and the other chemosensitizers seem equally effective. The patient tumor samples were selected to represent different combinations of Pgp expression, drug resistance and effects of chemosensitizers. PSC and CsA appeared equally potent and resistance modulation was detected not only in Pgp positive, but also in Pgp negative tumor samples. Furthermore, in one case of a Pgp expression myeloma, chemosensitizers were without effect. These findings indicate the need to incorporate in vitro chemosensitivity assays with Pgp determination when the effects of MDR modulating chemosensitizers are to be studied in the clinic.

Selective cytotoxic activity of cyclosporins against tumor cells from patients with B cell chronic lymphocytic leukemia

A fluorometric microculture cytotoxicity assay was employed for the study of cyclosporin A induced cytotoxicity in tumor samples from patients with B type chronic lymphocytic leukemia (B-CLL). Tumor cells from patients with B-CLL were found to be significantly more sensitive to the cytotoxic actions of cyclosporin A than normal blood mononuclear cells and tumor cells obtained from patients with different types of acute leukemia and solid tumors. The effect of cyclosporin A on B-CLL samples could be reproduced by a non-immunosuppressive cyclosporin A analogue. One B-CLL patient treated with cyclosporin A responded with a significant decrease in tumor mass and alleviation of anemia and B symptoms. The results show that cyclosporin A and its non-immunosuppressive analogues appear selectively toxic to B-CLL cells, an observation which may have clinical implications.

Feasibility of the fluorometric microculture cytotoxicity assay (FMCA) for cytotoxic drug sensitivity testing of tumor cells from patients with acute lymphoblastic leukemia

The automated fluorometric microculture cytotoxicity assay (FMCA) was used for chemotherapeutic drug sensitivity testing of fresh and cryopreserved tumor cells from patients with acute lymphoblastic leukemia (ALL) at diagnosis and relapse. The technique success rate was 87% for fresh and 81% for cryopreserved samples. Up to 16 different cytotoxic drugs were routinely tested, but neither asparaginase nor methotrexate produced dose-response related cell kill. FMCA data showed good correlation to the well established Disc assay and the drug sensitivity reported by the FMCA was in good agreement with known clinical activity. Samples from children and initial ALL tended to be more drug sensitive than those from adults and ALL at relapse, respectively. For 36 samples clinical outcome was correlated to the quartile position in comparison to all other samples for the most in vitro active drug actually given to the patient. For patients with samples in the first, second, third, and fourth quartiles, the probabilities of complete remission were 89, 57, 38, and 0%, respectively. Using the median value as cut-off line, the sensitivity and specificity of the assay were 87 and 62%, respectively. It is concluded that the FMCA with a minimum of effort and with high success rate report clinically relevant drug sensitivity profiles for ALL.

Cytotoxic action of cyclosporins on human tumor cell lines is not dependent on immunosuppressive activity

The cytotoxic activity of cyclosporin A (CsA) and the three non-immuno-suppressive CsA analogues B3-243, WO-039 and B3-665 were studied in tumor cell lines representing both classical and atypical forms of multidrug resistance (MDR): T-ALL GM3639 L100 cells selected for vincristine (vcr) resistance and displaying characteristics of classical MDR, including P-glycoprotein (pgp) expression and increased drug efflux which can be inhibited by pgp blockers (e.g. verapamil), and U-1285/ADR, a small cell lung cancer (SCLC) cell line selected for doxorubicin resistance which lacks pgp, is insensitive to pgp-blockers and shows cross resistance to cis-platinum. At 1 micrograms/ml CsA was the most active agent in reversing Vcr resistance in L100 cells followed by B3-243 and WO-039, with no effect of B3-665. Parental LO cells were only marginally sensitized to Vcr by these agents. No reversing effect of any cyclosporin was observed in the U-1285/ADR or its parental cell line. Compared to LO cells, L100 cells showed a marked hypersensitivity to CsA > B3-243 > WO-039 with B3-665 being inactive. No collateral sensitivity was observed for cyclosporins in U-1285/ADR cells. Although of different magnitude, the pattern of cytotoxic activity for the different cyclosporins alone closely parallelled that of L100 cells for U-1285, U1285/ADR and LO cells. The results indicate that not only the collateral sensitivity in classical MDR but also the cytotoxic actions of cyclosporins per se on tumor cells alone are independent of immunosuppressive activity. The results also suggest a structure-activity relationship for cyclosporin-induced cytotoxicity similar to, but independent of, MDR reversing activity.

Regulation of parathyroid hormone release in normal and pathological parathyroid cells exposed to modulators of protein kinase C

Effects of the protein kinase C activating phorbol ester 12-O-tetradecanoyl phorbol 13-acetate and the inhibitor 1-(5-isoquinolinyl-sulfonyl)-2-methylpiperazine (H-7) on parathyroid hormone (PTH) release were studied in normal bovine and pathological human parathyroid cells. An increase of extracellular Ca2+ from 0.5 to 3.0 mmol/l inhibited PTH release by 60% in the bovine cells with half maximal effect (ED50) at 1.31 mmol/l. This inhibition reached less than 50% in the cells from patients with primary and uremic hyperparathyroidism, and the ED50 values were 1.49 and 1.42 mmol/l, respectively. The phorbol ester (0.1 mumol/l) made secretion insensitive to changes of extracellular Ca2+, an action counteracted by H-7 (50 mumol/l) in the bovine cells, whereas H-7 alone had no effects. The phorbol ester and H-7 had opposite actions on regulation of PTH release also from cells from patients with hyperparathyroidism. However, in pathological cells H-7 alone improved Ca2+ inhibition of secretion by stimulating release in low Ca2+ concentrations and decreasing the ED50 values. The magnitude of changes in ED50 values by H-7 increased with the severity of the secretory disturbance of the pathological cells. The results indicate that increased protein kinase C activity may be a factor of importance in the pathophysiology of hyperparathyroidism.

In vitro analysis of drug resistance in tumor cells from patients with acute myelocytic leukemia

A 72 hours fluorometric microculture cytotoxicity assay (FMCA) was used for the study of chemotherapeutic drug resistance in tumor cell suspensions from patients with acute myelocytic leukemia (AML). A marked heterogeneity with respect to sensitivity was observed for a panel of cytotoxic drugs tested in 76 samples from 60 patients with treated or untreated AML. Primary resistance to vincristine (Vcr) and prednisolone in untreated AML was observed as well as 'acquired' resistance to several other antileukemic drugs. Cross resistance patterns for AML active drugs revealed significant positive relationships between anthracyclines, VP16 and amsacrine (Amsa), whereas mitoxantrone (Mitox) was more weakly correlated. Sensitivity to cytosine arabinoside was unrelated to the anthracyclines, VP16, Amsa and Mitox but showed a significant relationship to 6-thioguanine. Several resistance modifying agents, including the novel non-immunosuppressive cyclosporin A analogue PSC 833, were able to potentiate the effects of doxorubicin and Vcr at concentrations achievable in the clinic. However, the pattern of activity was heterogenous and the frequency of responsive samples was higher in relapse compared to de novo cases. Individual in vitro/in vivo correlations based on quartile distributions of all accumulated drug sensitivity data from AML patients indicated a high specificity with respect to the identification of drug resistance. The results suggest that the FMCA may provide clinically valuable information on chemotherapeutic drug resistance in AML.

Laboratory determination of chemotherapeutic drug resistance in tumor cells from patients with leukemia, using a fluorometric microculture cytotoxicity assay (FMCA)

An automated fluorometric microculture cytotoxicity assay (FMCA) based on the measurement of fluorescence generated from cellular hydrolysis of fluorescein diacetate (FDA) to fluorescein was employed for chemotherapeutic-drug-sensitivity testing of tumor-cell suspensions from patients with leukemia. Fluorescence was linearly related to cell number, and reproducible measurements of drug sensitivity could be performed using fresh or cryopreserved leukemia cells. A marked heterogeneity with respect to chemotherapeutic drug sensitivity was observed for a panel of cytotoxic drugs tested in 43 samples from 35 patients with treated or untreated acute and chronic leukemia. For samples obtained from patients with chronic lymphocytic and acute myelocytic leukemia, sensitivity profiles for standard drugs corresponded to known clinical activity and the assay detected primary and acquired drug resistance. Individual in vitro/in vivo correlations indicated high specificity with respect to the identification of drug resistance. The results suggest that the FMCA may be a simple and rapid method for in vivo-representative determinations of chemotherapeutic drug resistance in tumor cells obtained from patients with leukemia.

Doxorubicin selected multidrug-resistant small cell lung cancer cell lines characterised by elevated cytoplasmic Ca2+ and resistance modulation by verapamil in absence of P-glycoprotein overexpression

Sublines from the small cell lung cancer (SCLC) cell lines U1285 and U1690, denoted U1285-100, U1285-250, U1690-40 and U1690-150, were adapted to grow in the continuous presence of 100, 250, 40 and 150 ng ml-1 doxorubicin (Dox), respectively. The Dox resistance was accompanied by cross-resistance to vincristine (Vcr), Vp-16 and for U1285-100 also to cisplatinum. Sublines of U1690-40 and U1285-100, cultured in absence of Dox for 4 months were only partially reversed with respect to Dox resistance. Neither the parental nor the most Dox resistance sublines had detectable levels of mdr 1 RNA but a small fraction of cells in all cell lines stained weakly positive for P-glycoprotein (P-gp). Verapamil (Ver) at 5 microM reversed the Dox resistance completely and partly in the U1690 and U1285 sublines, respectively, but did not increase the cellular accumulation of Dox. The cytoplasmic free Ca2+ concentration (Ca2+i) was close to 100 nM in both parental cell lines but elevated in the U1285-100 and U1690-40 sublines by 21 and 44%, respectively, and in U1285-250 and U1690-150 by 51 and 91%, respectively. The partly reverted sublines still showed significant but smaller elevations in Ca2+i of 10-30%. Ver was without acute or long term effects of Ca2+i in the U1285-100 and U1690-40 sublines. Selection for Dox resistance in SCLC may thus result in atypical multidrug-resistance characterised by absence of P-gp overexpression and atypical cross-resistance. Although Ver did not seem to affect Dox accumulation it may still work as a resistance modulator.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential in vitro sensitivity of human tumor and normal cells to chemotherapeutic agents and resistance modulators

The intrinsically Vincristine(Vcr)-resistant human kidney adenocarcinoma cell line ACHN, the human acute lymphoblastic leukemia cell line L0, its more-than-100-fold Vcr-resistant subline LI00, normal human fibroblasts and lymphocytes, also tumor cells from patients with chronic lymphocytic leukemia (CLL), acute myeloblastic leukemia (AML) and solid tumors, were compared for sensitivity to cytotoxic drugs and resistance modulators (RMs). The LI00 cells showed pronounced sensitivity to the RMs verapamil (Ver), cyclosporin A (CsA) and buthionine sulfoximine (BSO) alone as well as to cisplatinum, whereas the L0 and ACHN cells, also slowly growing fibroblasts and non-proliferating lymphocytes, were considerably less sensitive. Compared with AML cells and lymphocytes, CLL cells were more sensitive to Ver and CsA alone. The cytotoxicity of Vcr was significantly increased in the Vcr-resistant ACHN and LI00, but also in sensitive L0 cells by Ver and CsA, with smaller effects on Dox and Vp-16 toxicity. Fibroblasts and lymphocytes were generally resistant to the cytotoxic agents and RM addition had only minor effects. CLL cells were more sensitive to Dox and Vcr as compared with normal lymphocytes, with potentiation of the Vcr effect by Ver and CsA. The Vcr effect in non-proliferating Vcr-resistant cells from a malignant schwannoma was potentiated by Ver and CsA, which had no effect in cells from a kidney adenocarcinoma. We conclude that cytotoxicity of RMs alone is not dependent on the proliferation rate of tumor cells and that potentiation of cytotoxic drugs by RMs may be selective for tumor cells irrespective of their initial level and mode of drug resistance.

Combination of cyclosporin A and buthionine sulfoximine (BSO) as a pharmacological strategy for circumvention of multidrug resistance in small cell lung cancer cell lines selected for resistance to doxorubicin

The small cell lung cancer (SCLC) cell lines U-1285 and U-1690 were adapted to growth in continuous presence of doxorubicin (Dox). The resulting cell lines U-1285R and U-1690R were investigated with respect to sensitivity to the glutathione (GSH) depleting agent buthionine sulfoximine (BSO) and the immunosuppressant cyclosporin A (CsA) as well as the Dox resistance modifying ability of these agents. The parental U-1285 cells were more sensitive to BSO compared to parental U-1690 and the multidrug resistant (MDR) sublines, whereas no difference in sensitivity to CsA was observed between parental and MDR lines. BSO (10 microM) or CsA (1 microgram/ml) alone were able to partially reverse Dox resistance in the MDR cell lines, CsA being only marginally active in U-1285R cells. However, the combination of these two drugs at the same concentrations completely reversed Dox resistance in the MDR U-1690R cells whereas the combination was less effective in the U-1285R cells. The results demonstrate that a combination of low concentrations of BSO and CsA, only partially active by themselves in modifying Dox resistance, may be used as a pharmacological strategy to increase Dox sensitivity in some MDR SCLC cells.

Vasoactive intestinal polypeptide stimulates parathyroid hormone release by interaction with cyclic adenosine monophosphate production of bovine parathyroid cells

Influence of vasoactive intestinal polypeptide, neuropeptide Y, calcitonin gene-related peptide, and substance P was investigated on dispersed parathyroid cells of adult cattle. At a physiological concentration of extracellular calcium, vasoactive intestinal polypeptide stimulated the parathyroid hormone release in a dose-dependent manner, whereas no effects were noted for the other peptides. The dependency of PTH secretion upon extracellular calcium was shifted to the right by vasoactive intestinal polypeptide at 10(-6) mol/l, with a tendency for greater effects at low (0.5 mmol/l) than high concentrations (2.0-3.0 mmol/l) of the cation. Vasoactive intestinal polypeptide significantly enhanced cAMP release of the parathyroid cells, whereas no influence was noted on cytoplasmic calcium or pH within the cells. The results suggest that vasoactive intestinal polypeptide stimulates the PTH release by interaction with cAMP production of the parathyroid cells. This effect may contribute to the development of hypercalcemia in patients with neuroendocrine tumours secreting vasoactive intestinal polypeptide.

Verapamil and cyclosporin A potentiate the effects of chemotherapeutic drugs in the human medullary thyroid carcinoma TT cell line not expressing the 170 kDa P-glycoprotein

The TT-cell line, derived from a patient with metastatic medullary thyroid carcinoma (MTC), was found to exhibit intrinsic resistance to vincristine (VCR) despite the absence of immunohistochemically detectable 170 kDa P-glycoprotein (PGP 170) associated with multidrug resistance (MDR). Verapamil and cyclosporin A, two well known resistance modifiers of MDR, were found to significantly potentiate the action of VCR (60-fold) and to a lesser degree also of VP-16 and daunorubicin (dnr). The present results suggests that resistance of MTC to chemotherapy may be at least partly circumvented by the addition resistance modifiers to chemotherapeutic regimens.

Chemotherapeutic drug sensitivity testing of human leukemia cells in vitro using a semiautomated fluorometric assay

A simple and reproducible semiautomated fluorometric method for drug sensitivity testing of leukemic cells in microculture is described. The assay is based on hydrolysis of nonfluorescent fluorescein diacetate (FDA) to a strongly fluorescent product (fluorescein) by cells with intact plasma membranes after 72 hr of culture and was in the present study applied to acute lymphocytic leukemia (ALL) cell lines and specimens from patients with lymphocytic and myelocytic leukemia. FDA fluorescence was linearly related to viable cell number within a wide range of cell densities (3-4 logs) as well as in the presence of different added proportions of dead cells. The assay reliably detects high and low grade resistance to vincristine (vcr) and daunorubicin, respectively, as well as the subsequent reversal of vcr resistance by cyclosporin A and the calcium channel blocker verapamil. Using ALL cell lines, drug sensitivity was in good correspondence with data obtained by the microculture tetrazolium assay. Furthermore, drug sensitivity data of fresh leukemia cells from patients with leukemia were readily obtained. The results indicate that the presently described method is applicable for simple and reliable chemosensitivity testing of leukemia cell lines as well as tumor specimens from patients with leukemia.

Pharmacological modification of multi-drug resistance (MDR) in vitro detected by a novel fluorometric microculture cytotoxicity assay. Reversal of resistance and selective cytotoxic actions of cyclosporin A and verapamil on MDR leukemia T-cells

A novel fluorometric microculture cytotoxicity assay (FMCA), based on measurements of fluorescein diacetate (FDA) hydrolysis and DNA staining by Hoechst 33342, was used for drug sensitivity testing and detection of resistance reversal in acute lymphoblastic leukemia (ALL) cell lines. The 72-hr assay was found to be sensitive, reproducible and linearly related to the number of viable cells within a broad range of cell concentrations. At clinically achievable drug concentrations, the calcium channel blocker Verapamil (ver) and the immunosuppressant Cyclosporin A (csA) were found to partly reverse acquired Vincristine (vcr) resistance in multi-drug resistant (MDR) T-ALL L100 cells with little or no effect on the drug-sensitive parental L0 cell line. By combining the fluorometric indices, we found that low concentrations of csA were growth-inhibitory, whereas higher concentrations (greater than 10 micrograms/ml) were progressively cytotoxic for drug-sensitive L0 cells. In MDR L100 cells, on the other hand, csA produced significant cell kill even at low drug concentrations. Ver had no effects on sensitive L0 cells but showed considerable cytotoxic action towards MDR L100 cells. There was no apparent relationship between drug reversal of vcr resistance and the cytotoxic actions of the drug per se since the calcium channel blocker diltiazem (dil) significantly potentiated the actions of vcr on MDR L100 cells without being more toxic to these cells (compared to vcr-sensitive L0 cells).

Modulation of vincristine sensitivity of human kidney tumor cells by pharmacological agents interfering with intracellular signals. No apparent relationship to changes in cytoplasmic Ca2+ or pH

The effect of substances proposed to modulate intracellular signal systems on growth and sensitivity to vincristine in the human kidney tumor cell line ACHN was investigated and related to changes in cytoplasmic free Ca2+ concentration ([Ca2+]i) and cytoplasmic pH (pHi). Presence during culture of the protein kinase C (PKC) activator 12-O-tetradecanoyl phorbol 13-acetate (TPA) had no effect on cell growth but significantly increased the EC50 concentration for vincristine inhibited cell growth. There was no indication for endogenous PKC activity being responsible for basal vincristine insensitivity since it was not affected by the PKC inhibitor H-7. The Ca2+ ionophore ionomycin tended to increase cell growth and induced vincristine resistance, whereas the calmodulin inhibitor W-7 had opposite effects. Presence during culture of the adenylate cyclase activator forskolin did not affect basal cell growth but dose-dependently made the cells more sensitive to vincristine. The modulators of vincristine sensitivity had no immediate effect on pHi, whereas after 3 days of incubation ionomycin and forskolin tended to increase pHi. Ionomycin and forskolin induced an immediate increase in [Ca2+]i which remained after 3 days only for ionomycin, whereas TPA decreased [Ca2+]i, a change which tended to remain after 3 days of incubation. It is concluded that perturbation of the intracellular signal system may affect both cell growth and cytotoxic drug sensitivity. However, there is no apparent relationship between immediate or late changes in [Ca2+]i and pHi and vincristine sensitivity.

Verapamil and cyclosporin A sensitize human kidney tumor cells to vincristine in absence of membrane P-glycoprotein and without apparent changes in the cytoplasmic free Ca2+ concentration

Vincristine (Vcr) dose dependently inhibited growth of the kidney adenocarcinoma cell line ACHN during 4 days of culture. Verapamil (Ver) at 10 microM and cyclosporin A (CsA) at 1 microgram/ml had no effect on cell growth but significantly potentiated the action of Vcr, despite the absence of the multidrug resistance associated membrane P-glycoprotein (P-gp). Neither Ver nor CsA had any acute or long term effects on cytoplasmic free Ca2+ concentration (Ca2+i), except for a small Ver induced increase after 36 h of incubation. The results indicate that Ver and CsA may have a sensitizing effect on chemotherapeutic drug sensitivity also in absence of P-gp. However, these effects are probably not mediated by changes in Ca2+i.

A rapid fluorometric method for semiautomated determination of cytotoxicity and cellular proliferation of human tumor cell lines in microculture

A fluorometric method for the determination of cellular growth and cytotoxicity of human tumor cell lines in 96-well microculture plates is described. The assay is based on the combined use of the DNA-binding dye Hoechst 33342 and the fluorogenic substrate fluorescein diacetate (FDA). Hoechst 33342 undergoes a dramatic enhancement of fluorescence when specifically intercalated with cellular DNA, whereas the FDA fluorescence is dependent on cellular hydrolysis of the non-fluorescent substrate into its fluorescent product. Fluorescence from both dyes was linearly related to the density of freshly seeded cells (6 x 10(3)-1 x 10(5)/well) and correlated well with physical cell count of cells under normal culture conditions as well as in response to the vinca alkaloid vincristine. However, the amount of FDA fluorescence produces and retained by the cultures was clearly dependent on the fraction of intact and viable cells, whereas the fluorescence reported by Hoechst 33342 was not. The assay was found to be simple, reliable and many samples could be analysed in a short period of time with minimal waste of cells and biological reagents. Apart from giving an estimate of cell density, the protocol described also provides a separate index of viability which in certain situations may be of importance for distinguishing between cytocidal and cytostatic drug actions. The method may be well suited for several applications, including the large scale screening for antitumor activity of compounds with potential cytocidal or cytostatic actions.

Early ionic events associated with phorbol ester induced differentiation and inhibition of cell growth in hematopoietic tumor cell lines

The effects of 12-O-tetradecanoylphorbol-13 acetate (TPA) on DNA synthesis, phenotypic expression, cytoplasmic Ca2+ (Ca2+i), intracellular pH (pHi) and membrane potential were studied in the monoblastic U-937 and the erythroleukemic K-562 cells. In both cell lines DNA synthesis was inhibited and in the U-937 cells this was accompanied by the appearance of macrophage differentiation markers. The erythroid characteristics of K-562 cells, on the other hand, were markedly suppressed. Intracellular pH (pHi) was increased by TPA treatment; however, while the alkalinization of K-562 cells was dependent on the presence of extracellular Na+, the response of U-937 cells was unaffected by the removal of this cation. In each cell type the protein kinase C (PKC) inhibitor H-7 largely attenuated the TPA induced increase of pHi. Moreover, the alpha-stereoisomer of TPA, which does not activate PKC, had no effects. TPA caused a dose-dependent decrease in Ca2+i which was more pronounced in U-937 cells. Measurements of membrane potential revealed a marked TPA depolarization of the K-562 cells, but no such effects were observed in the U-937 cell line. The depolarizing response of K-562 cells could be abolished by substituting extracellular Na+ with choline+, indicating the presence of a TPA sensitive Na+ permeability. The results show that the phorbol ester TPA, which inhibits proliferation and causes phenotypic modulation, also induced a number of early, apparently PKC dependent and cell type specific, changes of intracellular ion activities. The possible role of intracellular ion fluxes in the regulation of cell growth and differentiation is discussed.

Dimethyl sulfoxide inhibits proliferation but not hypertrophy and functional dedifferentiation of bovine parathyroid cells in culture

Primary cultures of bovine parathyroid cells were used to study the relationship between parathyroid hormone (PTH) release, regulation of the cytoplasmic Ca2+ concentration (Ca2+i) and cell growth. Parathyroid cells were seeded into fibronectin-coated culture wells in the absence (control) or presence of 2% (v/v) dimethyl sulfoxide (DMSO). Both groups of cells attached and flattened out, and during 4 days of culture the cell diameters and protein content increased. However, whereas the number of cells in the control group increased by 60% and their 3H-thymidine incorporation tenfold, the DMSO cultured cells exhibited no signs of cell proliferation. Despite this difference in cell replication rate both groups of cells developed similar functional dedifferentiation. There was consequently a decreased Ca2+ suppressibility of PTH release, and Ca2+i did not follow the ambient Ca2+ concentration in a usual manner. It is concluded that during culture bovine parathyroid cells develop morphological and functional abnormalities similar those in parathyroid cells from patients with hyperparathyroidism. Moreover, this functional dedifferentiation could be dissociated from increased cell proliferation but may be related to cell hypertrophy.

1,25(OH)2D3 inhibits hormone secretion and proliferation but not functional dedifferentiation of cultured bovine parathyroid cells

Increasing the extracellular Ca2+ concentration from 0.5 to 3.0 mM induced marked increments in cytoplasmic Ca2+ concentration (Ca2+i) and inhibition of parathyroid hormone (PTH) release of freshly isolated bovine parathyroid cells. 1,25-dihydroxycholecalciferol (1,24(OH)2D3; 0.1-100 ng/ml) did not affect (Ca2+i) and was also without acute effect on the secretion. During 4 days of monolayer culture, the parathyroid cells underwent significant increases in both number and size, and presence of 10-100 ng/ml 1,25(OH)2D3 almost completely inhibited the cell proliferation, whereas the hypertrophy was unaffected. One day of culture with 0.1-100 ng/ml 1,25(OH)2D3 was without effect on PTH release but after 4 days there was a dose-related reduction of secretion. At this time point and irrespective of the culture condition, PTH release was no longer suppressed by high extracellular Ca2+. Furthermore, Ca2+i increased little upon increments in the extracellular Ca2+ concentration as compared with freshly isolated cells. It is concluded that after prolonged exposure to 1,25(OH)2D3, PTH release is inhibited and, at high concentrations, the parathyroid cells cease to proliferate. However, 1,25(OH)2D3 does not affect the development of functional dedifferentiation of parathyroid cells during monolayer culture.

Phorbol-ester-induced stable changes in the regulation of DNA synthesis and intracellular pH are accompanied by altered expression of protein kinase C in the monoblastoid cell line U-937

12-O-tetradecanoylphorbol-13-acetate (TPA)-induced changes in cytoplasmic pH, cytoplasmic Ca2+-concentration, rate of DNA synthesis, and concentration and activity of protein kinase C (PKC) were studied in human monoblastoid cell lines. The cell line U-937 GTB was compared to the subline U-937 RES (adapted to growth in the presence of 10(-9) M TPA) and another subline U-937 RESREV (U-937 RES grown in TPA-free medium) established in order to analyze the stability of the TPA-induced differences. TPA induced half maximal inhibition of DNA synthesis in the wild-type U-937 GTB cell line at 10(-9) M, whereas 10 times higher concentrations of phorbol ester were needed for a corresponding inhibition of the U-937 RES and U-937 RESREV lines. Furthermore, the U-937 RES cells exhibited a decreased sensitivity to TPA, and the U-937 RESREV cells did not respond at all to this agent with regard to cytoplasmic alkalinization by an intracellular mechanism independent of Na+/H+ exchange. A Na+-dependent system for extrusion of protons, which was activated by the Ca2+ ionophore ionomycin, was also severely depressed as a result of TPA-adaptation. The concentration of PKC, measured by immunoblotting, was reduced by 34 and 24% in U-937 RES and U-937 RESREV cells, respectively, as compared to the wild-type U-937 GTB line. The corresponding reductions in PKC activity were 32 and 54% when histone III-S was used as substrate. The data suggest that adaptation to growth in the presence of TPA results in stable modifications of several parameters, which are assumed to be involved in the regulation of proliferation and differentiation. Furthermore, the data from the U-937 RESREV cells question a causal relationship between cytoplasmic alkalinization and control of proliferation.

Inhibition of cell growth retains differentiated function of bovine parathyroid cells in monolayer culture

Monolayer culture of bovine parathyroid cells for up to 4 days in medium containing 10% serum resulted in cell hypertrophy and proliferation as well as functional dedifferentiation. Compared to freshly isolated cells there was a right-shifted dose-effect relationship for calcium-inhibited parathyroid hormone (PTH) release, a decreased suppressibility of secretion and an inability of the cytoplasmic Ca2+ concentration (Ca2+i) to follow changes in the extracellular Ca2+ concentration. The functional changes seemed not to be due to culture per se, since human parathyroid cells exhibited an essentially unchanged regulation of Ca2+i even after 8 days of culture in 10% serum. During culture in medium containing 0.1% serum, the bovine cells did not proliferate and there was only slight cell hypertrophy. These cells retained much of their ability to regulate Ca2+i and PTH release. The results indicate that functional dedifferentiation of parathyroid cells is related to cell growth.

Hyperparathyroidism is associated with reduced expression of a parathyroid calcium receptor mechanism defined by monoclonal antiparathyroid antibodies

Parathyroid tissue from patients with hyperparathyroidism (HPT) exhibited reduced immunohistochemical reactivity with monoclonal antiparathyroid antibodies, previously shown to stain intensely the surface of normal human parathyroid cells and to interfere with a receptor mechanism of these cells which is involved in the sensing and gating of Ca2+. Parathyroid hormone (PTH) release and cytoplasmic Ca2+ concentrations (Ca2+i) of dispersed cells from the pathological parathyroid glands had right-shifted dependencies on extracellular Ca2+, and exposure to the antibodies rendered both Ca2+i and PTH release almost completely insensitive to changes in ambient Ca2+. The results suggest that reduced expression of a parathyroid calcium receptor mechanism may be an important cause for the aberrant PTH release in HPT.