Fluorometric Microculture Cytotoxicity Assay Research Articles

ACTIVITY OF STANDARD AND INVESTIGATIONAL CYTOTOXIC DRUGS IN PRIMARY CULTURES OF TUMOR CELLS FROM PATIENTS WITH KIDNEY AND URINARY BLADDER CARCINOMAS

In vitro tumor models could support the process of development of new cytotoxic drugs and selection of suitable drugs for the individual patient. We investigated whether the testing of tumor cells from patients with kidney or urinary bladder carcinoma by fluorometric microculture cytotoxicity assay (FMCA) could provide clinically relevant data for these tumor types. A total of 45 tumor samples from patients with kidney or urinary bladder carcinoma were compared with 247 samples of other tumor types with respect to sensitivity to 8 standard and 6 investigational cytotoxic drugs in the FMCA, a 72 hour assay based on the concept of total cell kill. In bladder carcinomas, sensitivity to standard drugs was correlated to various tumor characteristics. The technical success rate for kidney and bladder carcinomas was high; approximately 90% of the samples could be analyzed successfully. Kidney carcinomas were highly resistant to standard drugs and bladder carcinomas essentially as sensitive as carcinomas of the breast and ovary but with a steeper dose-response relationship. In bladder carcinoma there was no clear relationship between tumor stage, grade, ploidy, mitoses or p53 expression and drug sensitivity. Except for suramin, kidney carcinomas were poorly sensitive to the investigational drugs CdA, gemcitabine, paclitaxel, vinorelbine and topotecan. In bladder carcinomas paclitaxel, gemcitabine and suramin showed promising activity. The FMCA seems suitable for cytotoxic drug sensitivity testing of urinary tract carcinomas. This technique may have a role in new drug development in these tumor types.

Relationship between diagnosis-specific activity of cytotoxic drugs in fresh human tumour cells ex vivo and in the clinic

The aim of this investigation was to evaluate the relationship between the disease-specific activity of cytotoxic drugs in the clinic and in fresh human tumour cells from patients, as detected by a non-clonogenic cytotoxicity assay. The activity of 18 different cytotoxic drugs in fresh human tumour cells ex vivo was analysed in up to 15 samples from each of 13 different diagnoses using the fluorometric microculture cytotoxicity assay (FMCA). For each drug and diagnosis, relative activity indices (RAIs) were calculated, defined as the fraction of samples within the diagnosis having a survival index (SI) less than the median SI for the drug in all tested samples. Clinical response rates for the drug in the same diagnoses were collected from published phase II trials and were compared with the RAIs using Spearman's rank correlation (Rho) and Pearson's correlation coefficient ( R). Correlation coefficients could be calculated for 12 drugs. The coefficients varied between 0.02 and 0.92 (Rho) and between 0.07 and 0.91 ( R), but for most drugs the correlation between RAI and clinical response rates was good, with Rho >0.6 and R>0.7. Weak correlations were observed for cyclophosphamide and vincristine (Rho=0.32 and 0.16, respectively), which might be due to old clinical data, and for paclitaxel (Rho=0.02), which perhaps could be explained by in vitro activity of the solvent, Cremophor EL. The 18 drugs were also categorised according to their suggested clinical use in solid or haematological tumours, and were then compared regarding the activity in solid compared with haematological tumours ex vivo, expressed as the ratio between the number of responders among solid and haematological tumours (S/H ratio). The mean ex vivo S/H ratios in the group of drugs registered for use in haematological tumours was only 0.09 and was significantly different ( P=0.05) from the mean S/H ratios for the drugs used in both haematological and solid tumours (0.31) and in solid tumours only (0.47). Furthermore, the FMCA could identify the 50% most and least sensitive diagnoses with respect to clinical phase II activity with 74% (78/106) correct classifications. The results indicate that the relative activity of cytotoxic drugs in different diagnoses may be detected by the FMCA. Thus, ‘phase II trials ex vivo’ using non-clonogenic cytotoxicity assays might be used to make clinical trials more effective by targeting trials to diagnoses in which a new agent is most likely to be active.

In vitro cytotoxic drug activity and in vivo pharmacokinetics in childhood acute myeloid leukemia.

Since May 1996 all Nordic countries have been participating in a study of childhood acute myeloid leukemia (AML). The aim is to correlate the in vitro sensitivity of leukemic cells and individual plasma concentrations of cytotoxic drugs with clinical effect. Blast cells from bone marrow and/or peripheral blood are tested against a panel of cytotoxic agents using the fluorometric microculture cytotoxicity assay (FMCA). Plasma concentrations of cytotoxic drugs are analysed during induction therapy. Bone marrow samples from the participating centres generally reached the analysing laboratory within 24 hours. 61 out of 71 (86%) samples were successfully analysed, 47 de novo AML and 14 relapses. Relapsing patients tended to have a more resistant test profile than newly diagnosed patients. Steady state plasma levels of doxorubicin, etoposide and 6-thioguanine nucleotide varied about 10-fold between patients. The intra-individual variation was much less, suggesting that dose adjustment based on pharmacokinetic data might be useful in the future.

Is in vitro sensitivity of blast cells correlated to therapeutic effect in childhood acute lymphoblastic leukemia?

Our aim is to study whether or not in vitro sensitivity of leukemic cells correlates with clinical effect; if so, in vitro testing might used for stratification of treatment. During 1995-1997 bone marrow samples from 145 Swedish children with newly diagnosed acute lymphoblastic leukemia were analysed by the automated fluorometric microculture cytotoxicity assay. Therapeutic effect was evaluated by bone marrow morphology day 15 and 29. Preliminary results indicate that marrow samples from patients with poor response to induction therapy show a higher degree of in vitro resistance to several cytotoxic drugs at diagnosis than good responders.

Synergistic interactions of combinations of topotecan with standard drugs in primary cultures of human tumor cells from patients.

Combination therapies are important in the treatment of many tumor types. This study was undertaken to find candidates for combination therapy with the novel topoisomerase I inhibitor topotecan. The cytotoxic effect of topotecan alone and in combination with five standard cytotoxic drugs was studied in 27 primary cultures of human tumor cells from patients with various diagnoses using the fluorometric microculture cytotoxicity assay (FMCA). The combinations were analysed according to the multiplicative concept of drug interaction. The additive model was shown to be a better descriptor than the effect of the most effective agent (Dmax) for all drug combinations tested. Topotecan in combination with cisplatin (CisP) was the drug combination showing synergy in the highest percentage of samples (54%), followed by topotecan in combination with doxorubicin (Dox: 39%), etoposide (P16; 23%), paclitaxel in the formulation Taxol (22%) and cytarabine (AraC; 12%). The high percentage of synergistic interactions was especially pronounced in solid tumors. In 28% of the samples tested, drug sensitivity testing of only single drugs failed to predict response to the drugs in combination. Cisplatin and doxorubicin showed promising effects in combination with topotecan, and clinical trials with these combinations seem warranted. The results also indicate the value of testing drug combinations in in vitro drug sensitivity testing.

In vitro determination of cytotoxic drug response in ovarian carcinoma using the fluorometric microculture cytotoxicity assay (FMCA)

The fluorometric microculture cytotoxicity assay (FMCA), a short-term in vitro assay based on the concept of total tumor cell kill, was used for testing the cytotoxic drug sensitivity of tumor cells from patients with ovarian carcinoma. A total of 125 fresh specimens was obtained, 98 (78%) of which were analyzed successfully. Data from 45 patients were available for clinical correlations. The FMCA appeared to yield clinically relevant cytotoxic drug sensitivity data for ovarian carcinoma as indicated by a comparison with tumor samples obtained from patients with non-Hodgkin's lymphoma or kidney carcinoma. Considering the most active single agent in vitro actually given in vivo, and using the median drug activity among all ovarian carcinoma samples as a cut-off, the sensitivity of the assay and its specificity were 75 and 52%, respectively. Cross-resistance in vitro was frequently observed between standard drugs but not between standard drugs and Taxol. Ten percent of the specimens showed an extreme resistance for at least 4 of 6 of the drugs investigated. Int. J. Cancer 72:1008–1012, 1997. © 1997 Wiley-Liss, Inc.

Cytotoxic activity of topotecan in human tumour cell lines and primary cultures of human tumour cells from patients.

The cytotoxic activity and cross-resistance pattern of the novel topoisomerase I inhibitor topotecan (Topo) were investigated in ten cell lines, representing different mechanisms of cytotoxic drug resistance, and in 218 fresh human tumour samples using the fluorometric microculture cytotoxicity assay (FMCA). Resistance to Topo in the cell lines was associated with expression of the multidrug resistance-associated protein (MRP), whereas the cell lines with P-glycoprotein (P-gp), topoisomerase II and glutathione-associated resistance did not show decreased sensitivity to the drug. Topo was more active in haematological than in solid tumour samples, but substantial activity was observed in carcinomas of the ovary and breast, sarcoma and childhood solid tumours. Cross-resistance to standard drugs representing different mechanisms of action was generally low in patient cells. The effect of Topo was better after longer exposure, but this time-dependent effect was largely abolished when adjustment for in vitro exposure was made. Topo showed activity both in proliferative and non-proliferative cell systems. The results indicate that Topo is insensitive to major mechanisms of resistance except for MRP. Proliferation does not seem to be necessary for the effect of Topo, and no superiority for protracted dosing schedules was observed. The results also suggest that, for example, leukaemias, lymphomas, sarcomas and childhood solid tumours may be suitable targets for future phase II trials.

Anti-cancer drug characterisation using a human cell line panel representing defined types of drug resistance.

Differential drug response in a human cell line panel representing defined types of cytotoxic drug resistance was measured using the non-clonogenic fluorometric microculture cytotoxicity assay (FMCA). In total 37 drugs were analysed; eight topoisomerase II inhibitors, eight anti-metabolites, eight alkylating agents, eight tubulin-active agents and five compounds with other or unknown mechanisms of action, including one topoisomerase I inhibitor. Correlation analysis of log IC50 values obtained from the panel showed a high degree of similarity among the drugs with a similar mechanism of action. The mean percentage of mechanistically similar drugs included among the ten highest correlations, when each drug was compared with the remaining data set, was 100%, 92%, 88% and 52% for the topoisomerase II inhibitors, alkylators, tubulinactive agents and anti-metabolites respectively. Classification of drugs into the four categories representing different mechanisms of action using a probabilistic neural network (PNN) analysis resulted in 29 (91%) correct predictions. The results indicate the feasibility of using a limited number of cell lines for prediction of mechanism of action of anti-cancer drugs. The present approach may be well suited for initial classification and evaluation of novel anti-cancer drugs and as a potential tool to guide lead compound optimisation.

Cytotoxic activity of calcein acetoxymethyl ester (calcein/AM) on primary cultures of human haematological and solid tumours

The aim of this study was to determine the in vitro cytotoxicity of calcein acetoxymethyl ester (Calcein/AM) on primary cultures derived from solid and haematological human tumours. Calcein/AM is a fluorescent dye that localises intracellularly after esterase-dependent cellular trapping and which has shown cytotoxic activity against various established human tumour cell lines at relatively low concentrations. The semi-automated fluorometric microculture cytotoxicity assay, based on the measurement of fluorescence generated from cellular hydrolysis of fluorescein diacetate to fluorescein, in microtitre plates was used for the evaluation of Calcein/AM activity in tumour cell suspensions from patients. The cytotoxicity was measured as a survival index (SI), defined as the fluorescence as a percentage of control cultures. A total of 163 evaluable samples from various tumours were tested with continuous drug exposure. The activity of Calcein/AM was compared with representatives of six major classes of standard chemotherapeutic drugs. Calcein/AM was found to induce concentration-dependent decreases in the SI of both haematological and solid tumour cells. The ratio of solid over haematological tumour activity increased at a rate that was concentration dependent. Although it was relatively less active than cisplatin against solid tumours, Calcein/AM showed higher solid tumour activity compared to leukaemic specific agents (cytarabine and amsacrine), vincristine and doxorubicin (Dox). Among the solid tumours tested, childhood tumours, non-small cell lung cancer and sarcomas were the most sensitive to Calcein/AM. The best correlation between SI values was seen between Calcein/AM and Dox, with weaker correlations to representatives of antimetabolites, platinum compounds, topoisomerase II inhibitors, tubulin interactive agents and alkylators. Non-cytotoxic concentrations of cyclosporin A significantly potentiated calcein-induced cytotoxicity. The results show that Calcein/AM is differentially active against haematological tumours, but with substantial activity against solid tumours. The drug may represent a new class of anticancer compound with a unique means of drug delivery.

Selective sensitivity of solid tumors to suramin in primary cultures of tumor cells from patients.

The antineoplastic activity of suramin is currently the subject of clinical trials. We therefore used the semi-automated fluorometric microculture cytotoxicity assay (FMCA) to evaluate the cytotoxicity of suramin in vitro in primary cultures of cells from patients with hematological or solid tumors. The activity patterns of some standard cytotoxic agents were included for comparison. A total of 159 samples were tested using continuous drug exposure. Suramin showed relatively high activity against solid tumors, with colorectal, adrenal and kidney carcinomas being the most sensitive, whereas hematological malignancies were more resistant. Suramin and standard drugs showed very low cross-resistance. The results indicate that suramin is differentially active against some solid tumors with comparatively little activity against hematological tumors. The study provides an experimental motive for evaluation of suramin therapy in patients with solid tumors and exploration of less toxic suramin analogues.

Cytotoxic drug sensitivity testing of tumor cells from patients with ovarian carcinoma using the fluorometric microculture cytotoxicity assay (FMCA): Csoka K.; Larsson R.; Tholander B.; Gerdin E.; De la Torre M.; Nygren P. SWE Gynecol Oncol 1994 54/2 (163–170)

Cytotoxic drug sensitivity testing of tumor cells from patients with ovarian carcinoma using the fluorometric microculture cytotoxicity assay (FMCA): Csoka K.; Larsson R.; Tholander B.; Gerdin E.; De la Torre M.; Nygren P. SWE Gynecol Oncol 1994 54/2 (163–170)

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

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. 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. 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. 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.

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.

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

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

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 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.

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.

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.