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

A Nonclonogenic Cytotoxicity Assay Using Primary Cultures of Patient Tumor Cells for Anticancer Drug Screening

Primary cultures of cells from patients with chronic lymphocytic leukemia (CLL) and ovarian carcinoma (Ovca) were compared with the renal carcinoma ACHN and the lymphocytic CCRF-CEM human tumor cell lines in response to 63 toxic or nontoxic compounds. The experiments were conducted at 1, 10, and 100 μ/ml in 96-well microtiter plates for an assay time of 72 h. The plates were analyzed by the fully automated Dynatech Immuno Assay System (DIAS) using Alamar blue as a fluorometric/colorimetric indicator of metabolic activity. Drug response data were reported as the area under the tumor cell survival-concentration curve (AUC). Noncytotoxic compounds were classified as inactive by all cell systems. According to the AUC, CCRF-CEM and CLL cells were the most sensitive, followed by ACHN, and then Ovca. Many of the clinically active drugs were detected by all cell systems. However, the sensitivity pattern differed considerably between the cell types as judged from correlation analysis, and a higher proportion of clinically inactive drugs were scored as active by the cell lines compared with the primary cultures. Ovca showed the highest ratio of clinically solid tumor active/clinically inactive agents followed by CLL. The results indicate that primary cultures of human tumor cells may be a useful and valuable model for anticancer drug screening.

Cladribine enhances apoptotic cell death in lung carcinoma cells over-expressing DNase γ

Worldwide, lung cancer is the most common form of cancer and often has a poor prognosis. Establishment of effective therapies for lung cancer is a major concern in clinical cancer research. We compared the cytotoxic effects of chemotherapeutic agents including cisplatin, 5-fluorouracil, vinorelbine and cladribine, on a human lung cancer cell line, A549, and its derivative transfected with the DNase γ gene. We observed selective cytotoxicity of cladribine on the DNase γ-expressing sub-cell line of A549. Cladribine induces selective apoptosis in DNase γ-expressing A549 cells, which depends on activation of caspases. These results suggest that a combination therapy that includes cladribine along with the introduction of DNase γ has potential as a new therapeutic strategy for lung cancer.

Activity of Cladribine Combined with Etoposide in Heavily Pretreated Patients with Indolent Lymphoid Malignancies

We determined the effectiveness and toxicity of combined chemotherapy consisting of etoposide 100 mg/m(2)/day i.v. and cladribine (2-CdA) 0.12 mg/kg/day i.v. each for 5 days (EC regimen) in the treatment of refractory or relapsed low-grade non-Hodgkin's lymphoma and chronic lymphocytic leukemia. The cycles were repeated every 28 days, reaching a maximum of six courses. Twenty patients entered the study. All patients had received three or more cycles of chemotherapy before the EC regimen (median 8, range 3-19). Thirteen patients received 2-CdA before the EC regimen. Seven out of 20 patients (35%) responded, including one complete response. Median overall survival time of responding patients was 22 months (range 3-30). Myelosuppression and infections were the major toxicity of the EC regimen.

In vitro evaluation of the efficacy of idarubicin in human tumour cells from patients with low-grade non-Hodgkin's lymphoma

Evaluating the potential benefit of the new anthracycline, idarubicin (Ida), in lymphoma, 58 tumour samples from patients suffering from low-grade non-Hodgkin's lymphoma (L-NHL), were analysed in vitro for their sensitivity to 0.5 microg/ml Ida. This was compared with the sensitivity to other anthracyclines (0.5 microg/ml), using the fluorometric microculture cytotoxicity assay. A total of 132 samples from patients with acute leukaemia and a cell-line panel representing different resistance mechanisms was included for comparison. The median cell survival of L-NHL cells did not differ after exposing the cells to Ida or daunorubicin (Dnr), whereas epirubicin, doxorubicin (Dox) and mitoxantrone (Mitox) were significantly less cytotoxic than Ida (P < 0.001). The median cell survival in L-NHL cells did not differ from that of acute leukaemia cells after exposure to 0.5 microg/ml Ida, Dnr, Dox and Mitox. Cells from previously treated patients with L-NHL had a higher median survival than cells from untreated patients after exposure to all drugs, except for Ida. In samples from previously untreated patients, Spearman rank correlations were high (Rho = 0.81-0.90) between cell survival after exposure to Ida and the other anthracyclines. The same pattern was observed in the cell-line panel (Rho = 0.78-0.91) (P < 0.05). In contrast, low correlations (Rho = 0.24-0.42) were observed among samples from previously treated patients. Our results indicate a potential benefit of Ida in previously drug-treated patients with L-NHL.

Cytotoxicity of digitoxin and related cardiac glycosides in human tumor cells

The saponin digitonin, the aglycone digitoxigenin and five cardiac glycosides were evaluated for cytotoxicity using primary cultures of tumor cells from patients and a human cell line panel (representing different cytotoxic drug-resistance patterns). Of these seven compounds, proscillaridin A was the most potent (IC(50): 6.4--76 nM), followed by digitoxin, and then ouabain, digoxin, lanatoside C, digitoxigenin and digitonin. Correlation analysis of the log IC(50) values for the cell lines in the panel showed that compound cytotoxicity was only slightly influenced by resistance mechanisms that involved P-glycoprotein, topoisomerase II, multidrug resistance-associated protein and glutathione-mediated drug resistance. Digitoxin and digoxin expressed selective toxicity against solid tumor cells from patients, while proscillaridin A expressed no selective toxicity against either solid or hematological tumor cells. The results revealed marked differences in cytotoxicity between the cardiac glycosides, both in potency and selectivity, and modes of action for cytotoxicity that differ from that of commonly used anticancer drugs.

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.

Comparison of the cytotoxic activity of melphalan with L-prolyl-m-L-sarcolysyl-L-p-fluorophenylalanine in human tumour cell lines and primary cultures of tumour cells from patients

m-L-sarcolysin (m-L-SL) is an isomer of melphalan (Mel) with the di(2-chloroethyl) amino group being substituted in the meta position of phenylalanine. By covalent conjugation of amino acids to m-L-SL, a peptide complex consisting of six m-L-SL-based oligopeptides known as peptichemio (PTC) was developed previously. In the present study, the cytotoxic activity pattern of the different oligopeptides of PTC was investigated in ten human tumour cell lines representing different mechanisms of cytotoxic drug resistance using the fluorometric microculture cytotoxicity assay (FMCA). In the cell line panel, L-prolyl-m-L-sarcolysyl-L-p-fluorophenylalanine (P2) was the most active oligopeptide, showing slightly lower mean IC50 values (2.6 vs 3.9 and 4.1 microg ml(-1)) than Mel and m-L-SL. The other five oligopeptides were less active than Mel. All active oligopeptides showed mechanistic similarity to Mel as judged by the correlation analysis of the cell line panel log IC50 values (R > or = 0.90), although P2 appeared to be less sensitive to GSH-mediated drug resistance. The relative activity of Mel and P2 was found to be related to degree of proliferation, P2 being more active towards low-proliferating cell lines. P2 and Mel were then further characterized in 49 fresh human tumour samples. In these samples P2 was considerably more active than Mel and showed a higher relative solid tumour activity (2.7 to 4.5-fold). However, the correlation of log IC50s between P2 and Mel in patient cells was high (R = 0.79), indicating a similar mechanism of action in this tumour model too. Cross-resistance with other standard drugs was lower for P2 than Mel. The results show that P2 is the most potent component of PTC and demonstrates a favourable activity profile compared with Mel. These data suggest that further investigation of P2 as a potential anti-tumour agent is warranted.

Ex vivo cytotoxic drug evaluation by DiSC assay to expedite identification of clinical targets: results with 8-chloro-cAMP

There is a pressing need to reduce the time and cost of developing new cytotoxic agents and to accurately identify clinically active agents at an early stage. In this study, the differential staining cytotoxicity (DiSC) assay was used to assess the efficacy of the novel antitumour cAMP analogue, 8-chloro-cAMP (8-Cl-cAMP) (and its metabolite 8-Cl-adenosine) against 107 fresh specimens of human neoplastic and normal cells. Diagnoses included chronic and acute leukaemias, myeloma, non-Hodgkin's lymphoma (NHL) and miscellaneous solid tumours. The aim was to identify targets for subsequent phase I, II and III trials. 8-Cl-cAMP was tested at 4-985 microM, along with standard chemotherapeutic drugs. 8-Cl-cAMP and its metabolite caused no morphologically observable cell differentiation but induced dose-dependent cytotoxicity. Compared with untreated patients, previously treated chronic lymphocytic leukaemia (CLL) patients showed no increase in ex vivo resistance to 8-Cl-cAMP (P = 0.878); minimal cross-resistance with other cytotoxic drugs was detected. Compared with normal cells (mean LC90 = 1803 microM), 8-Cl-cAMP showed significant ex vivo activity against CLL (117.0 microM; P < 0.0001) and NHL (140.0 microM; P < 0.0001), of which eight were mantle cell NHL (84.7 microM), and greatest activity against cells from patients with acute myeloid leukaemia (AML; mean LC90 = 24.3 microM; in vitro therapeutic index 74-fold, P < 0.0001). Solid tumour specimens were comparatively resistant to 8-Cl-cAMP. The results highlight the clinical potential of 8-Cl-cAMP, point to several new phase I, II and III trial possibilities and provide a rationale for the inclusion of ex vivo cytotoxic drug evaluation in the drug development process.

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.

Investigation of the comparative effects of 2-chlorodeoxyadenosine on tumor colony forming units in vitro

2-CdA is a deaminase-resistant purine analogue which has shown clinical activity against various hematological tumors, and is currently undergoing clinical phase II trials. The objectives of our study were to determine the activity of 2-CdA against freshly explanted clonogenic cells from non-hematological human tumors and compare this agent with other clinically useful anticancer agents. We also compared short-term (1 hour) and long-term (21-28 days) exposures. For short-term exposure (1-hour), final concentrations were 0.57, 5.7, 57, and 114 ng/ml. Inhibition of tumor specimens was concentration-dependent: 0.57 ng/ml: 1/51 (2%), 5.7 ng/ml: 4/52 (7%), 57 ng/ml: 11/52 (21%), 114 ng/ml: 27/50 (54%). At concentrations > or = 57 ng/ml, 2-CdA was as active as cisplatin, doxorubicin, 5-fluorouracil, mitomycin-C, vinblastine, and etoposide. For long-term exposures (21-28 days), final concentration of 2-CdA were 0.57, 5.7, and 57 ng/ml. At 0.57 ng/ml, 2-CdA was active in 4/54 (7%) specimens [5.7 ng/ml: 13/54 (24%), 57 ng/ml: 40/54 (74%)]. A head-to-head comparison with short-term exposures demonstrated greater activity if the drug exposure time was extended. Using the strategy for testing other standard agents (in vitro dose of 1/10th achievable peak plasma concentration), one would predict clinical response rates for single agent bolus or short-term administration of 2-CdA to be in the neighborhood of 7%. Longer durations of infusion or multiple doses might increase the response rate to about 24%. If higher peak plasma concentration could be achieved, dose-dependent increases in clinical responses might be achievable. We conclude that 2-CdA is active against clonogenic cells from freshly explanted non-hematological human tumor specimens at high concentrations.