Evaluation of anticancer drug schedule dependency using an in vitro human tumor clonogenic assay

Summary A human tumor clonogenic assay (HTCA) has been used to evaluate standard and experimental anticancer drugs with respect to thrir inhibition of clonogenicity of both fresh human cancers and human tumor cell lines. By comparing the inhibitory effect on tumor colony-forming unit (TCFU) growth of 1-h and continuous drug exposures in the HTCA we were able to identify and separate schedule-dependent (e.g., bleomycin, vinblastine, and etoposide) and schedule-independent drugs (e.g., actinomycin D, adriamycin, basantrene, and cis-platinum). Vinblastine, bleomycin, and etoposide, which are known to have cell cycle-specific characteristics, caused exponential reduction in tumor colony formation when given by continuous exposure, whereas when given with a short exposure each of these drugs caused plateau-type dose-response curves. For comparison of the relative efficacy of the two dosing schedules, a ratio (1-h versus continuous exposures) was calculated of the drug concentrations which reduced growth of TCFU to 50% of the control values (ID₅₀) for fresh human tumors and human tumor cell lines. For fresh tumors, ID₅₀ ratios for adriamycin, actinomycin D, and bisantrene ranged between 2 and 60 (median 14), whereas the ID₅₀ ratios for bleomycin, vinblastine, and etoposide ranged between 100 and 3,000 (median 600). The fact that actinomycin D, adriamycin, and bisantrene (a new anthracene-type drug) had similarly shaped dose-response curves and very low ID₅₀ ratios suggests that the cytotoxicity of these compounds may not be schedule-dependent. On the other hand, the steep dose-survival curves we observed after continuous drug exposure and the high ID₅₀ ratios of bleomycin, vinblastine, and etoposide suggest that these drugs may possess schedule-dependent cytotoxicity characteristics. Before final conclusions are drawn concerning a drug's schedule dependency it is essential to evaluate its in vitro stability and protein-binding characteristics. Finally, it must be emphasized that unlike the results obtained with 1-h exposure studies, the in vitro continuous exposure schedules have yet to be shown to be predictive of clinical response for any agent or tumor type.     

Chemical and biological stability of anticancer drugs used in a human tumor clonogenic assay

Summary Human tumor clonogenic assays (HTCA) are being used to evaluate the chemosensitivity of human cancers to both standard and experimental anticancer drugs as well as to predict clinical tumor response and resistance to these agents. To enable us to design and accurately interpret drug assay data we quantitated the chemical and biological stability characteristics of various cell cycle-specific and cell cyle-nonspecific drugs commonly used in our laboratory for chemosensitivity testing in the HTCA. Aliquots of the culture media were obtained immediately after drug addition and after 6 and 24 h and 2, 4, and 10 days of incubation, and then frozen in liquid nitrogen for later chemical (HPLC or RIA) and biological (HTCA) assay. Adriamycin, actinomycin D, bisantrene, bleomycin, and vinblastine retained 80–100% of their biological activity against human tumor colony-forming units even after 10 days of incubation in culture media. In contrast, etoposide lost 60% of its in vitro antitumor activity over the same period. There was no loss in the chemical concentration of actinomycin D. bisantrene, bleomycin, or vinblastine in the culture media, but etoposide concentrations as measured by HPLC decreased to zero over 10 days. We conclude that the HTCA can be used as a simple test for biological stability of new investigational agents prior to the development of adequate chemical assay methodology, and that it can help clarify whether a drug's in vitro antitumor activity is due to the parent compound or to a degradation products.     

In vitro drug-sensitivity test using human tumor clonogenic assay in lung cancer patients

It would be helpful for successful chemotherapy in cancer patients if a drug-sensitivity test in vitro could predict the exact response of an individual patient's tumor. We have investigated a drug-sensitivity test using human tumor clonogenic assay since 1980. In this paper, results obtained in lung cancer patients are discussed. Specimens for testing were obtained from primary tumor, metastatic mass, malignant pleural and pericardial effusion, and affected bone marrow. Drugs tested in this study were adriamycin, aclarubicin , THP-adriamycin, mitoxantrone, mitomycin C, cis-platinum, 40497 S (an active compound derived from ifosfamide), and methotrexate. Out of 88 specimens tested, 41 (47%) successfully yielded more than 30 colonies per control dish, and were able to evaluate drug-sensitivity. Of those, 32 instances were valid for examination in an in vitro-in vivo association. As a result, 3 were in vitro sensitive-in vivo sensitive, 2 were in vitro sensitive-in vivo resistant, and 27 were in vitro resistant-in vivo resistant. Accordingly, the true positive rate was 60%, and the true negative rate was 100%. In summary, the human tumor clonogenic assay appeared to be an excellent method for testing drug-sensitivity for an individual patient with lung cancer.     

In vitro antitumor activity of teniposide against carcinoma of the lung in human tumor clonogenic assay

The antitumor activity of teniposide (VM26) on carcinoma of the lung was tested by comparing it with its congener, etoposide (VP16) in an in vitro soft agar clonogenic assay system (HTCA). Of 56 tumor biopsies placed in culture, 40 tumors were evaluable for drug sensitivity information (i.e., greater than or equal to 30 colonies in the control plate). The overall in vitro response rate (defined as less than or equal to 50% survival of TCFU) at the standard dose (10% peak plasma concentration) was 35%, which is higher than that of VP16 (28%). In cell lines derived from human carcinoma of the lung, VM26 showed 50% inhibition against colony formation of PC-7 cells at 0.45 microgram/ml which is less than that of VP16. A superior antitumor activity of VM26 on PC-9 cells was also observed. VM26 was observed to act faster than VP16 thus indicating its possible superior antitumor activity in vivo.     

Contributions of human tumor xenografts to anticancer drug development

Mouse models of cancer have consistently been used to qualify new anticancer drugs for study in human clinical trials. The most used models include transplantable murine tumors grown in syngeneic hosts and xenografts of human tumors grown in immunodeficient mice. For the latter systems, retrospective preclinical-clinical correlation studies are available, which suggest that improvements must be made to increase their value. Transgenic, knock-out, and knock-in mouse models and their intercrosses are more recent developments that mirror defined steps of human carcinogenesis. However, their value in predicting clinical results remains to date poorly defined. We take the position that properly used and interpreted human tumor xenografts grown in immunodeficient mice can be useful, although not absolutely predictive of behavior in the clinic, and continue to make contributions to critical clinical development choices.     

Thermochemosensitivity: augmentation by hyperthermia of cytotoxicity of anticancer drugs against human colorectal cancers, measured by the human tumor clonogenic assay

Thermochemosensitivity was examined in vitro by a human tumor clonogenic assay (HTCA) using specimens obtained surgically from 43 patients with colorectal cancer. We found that the percentages of patients whose cells showed higher sensitivity (greater than 70% inhibition of colony formation) to hyperthermia alone were 29.6 and 55.6% at 42 and 43 degrees C each for 1 h, respectively. Similarly, percentages of patients whose cells were sensitive to drugs alone were 13.8, 24.1 and 48.3%, for cis-diamminedichloroplatinum(II), 5-fluorouracil and mitomycin C, respectively. These sensitivities were augmented when hyperthermia was combined with administration of anticancer agents. Even in tumor cells that were insensitive to anticancer drugs alone or to hyperthermia alone, sensitivity was enhanced when administration of drugs was combined with hyperthermia. Our results demonstrate that HTCA of tumor cells, obtained from suitable patients, may be useful as a predictive test for application of thermotherapy and for individualization of chemotherapy.     

Microencapsulated tumor assay: new short-term assay for in vivo evaluation of the effects of anticancer drugs on human tumor cell lines

A new in vivo has been developed for evaluating the antitumor activity of chemotherapeutic drugs. The assay is based on a microencapsulation technology developed by Damon Biotech, Inc., Boston, MA, which makes it possible to encapsulate human tumor cells in small (about 1 mm in diameter) microcapsules with semipermeable membranes. Microcapsules containing human tumor cells were injected i.p. into nude or C57BL/6 mice and drugs were administered i.v. The microcapsules were recovered at various intervals following treatment and determinations of drug effects were made based on the differences in the number of tumor cells recovered from the treated and nontreated animals. Using this assay we found that (a) encapsulated tumor cells grew better in the in vivo system than in vitro under the conditions tested; (b) drugs crossed the capsular membrane and killed or inhibited the proliferation of tumor cells; and (c) the antitumor effect was consistent with the relative therapeutic efficacy of drugs or level of resistance of tumor cells detected by other in vitro or in vivo tests. The tumor microencapsulation assay offers several properties which make it attractive for use in new drug development: (a) the antitumor activity of drugs can be tested against human tumor cells under conditions which provide for three-dimensional growth and in vivo supply of nutrients; (b) the sensitivity of tumor cells can be assessed following exposure to drugs at concentrations which are achievable in vivo; (c) compounds requiring in vivo metabolic activation can be tested; (d) the effect of each drug injection can be quickly evaluated; (e) inhibition of tumor cell proliferation versus cytoreductive effects of drugs can be discriminated; (f) the test is applicable to virtually all histological types of human tumor cells; and (g) the tumor microencapsulation assay is a short-term, simple, and relatively inexpensive assay.     

Time-schedule dependency of the inhibiting activity of various anticancer drugs in the clonogenic assay

Summary To analyze the discrepancy between the in vitro response in the clonogenic assay and the clinical response, the time-schedule dependencies of various anticancer drugs were determined by comparing the inhibiting effect against colony formation by PC-7 cells treated with the drugs for 1 h with that of those treated for 24h. According to their schedule dependency the drugs can be divided into a schedule-dependent drug group (5-fluorouracil, methotrexate, bleomycin, pepleomycin, etoposide, cisplatin, teniposide, vindesine, and vinblastine) and a non-schedule-dependent drug group (adriamycin, actinomycin D, ranomustine, mitomycin C, aclacinomycin, daunomycin, nimustine, melphalan, and KW 2083). In the clonogenic assay, the 1-h exposure schedule is appropriate for predicting clinical response for the non-schedule-dependent drugs. However, the effect of the schedule-dependent drugs was underestimated in the same conditions. Therefore, it is necessary to test these drugs in the assay by 24-h exposure for a more accurate assessment of their antitumor activity.     

The human tumor clonogenic assay in human breast cancer

The human tumor clonogenic assay (HTCA) was evaluated in 407 fresh samples of breast cancer from 288 patients. Seventy samples were inadequate for testing. Adequate in vitro growth for drug testing (greater than 30 colonies/plate) was obtained in 91 (27%) of the 337 viable samples, inadequate growth for drug evaluation (5 to 30 colonies/plate) in 17%, and no colony formation (less than 5 colonies/plate) in 56%. Operationally defining a greater than or equal to 50% inhibition of colony formation as in vitro drug sensitivity, the in vitro response rates to 12 anticancer drugs tested against ten to 36 different cancers (arranged in decreasing order according to the number of tests performed) were as follows: doxorubicin (14%), bisantrene (54%), vinblastine (33%), mitomycin (36%), interferon clone A (23%), 5-fluorouracil (20%), methotrexate (17%), leukocyte interferon (33%), mitoxantrone (42%), cyclophosphamide (25%), m-AMSA (16%), and melphalan (10%). Among 25 patients receiving single-agent therapy, there were ten (59%) of 17 with in vitro sensitivity who responded; resistance was correctly predicted in nine patients (100%), P = .01. Among 34 patients treated with combination chemotherapy, seven (50%) of 14 with in vitro sensitivity responded, and resistance was predicted in 13 (65%) of 20 patients. Difficulties in using the HTCA in breast cancer (including small specimen size, difficulties in disaggregation, and inadequacy of growth) will require additional research. Nonetheless, the assay appears to detect in vitro activity as well as resistance of a variety of anticancer agents and appears to predict clinical responsiveness to standard as well as some investigational single agents.     

Pharmacologic studies of anticancer drugs with the human tumor stem cell assay

Summary To optimize the human tumor stem cell assay (HTSCA) for clinical and research purposes we have carried out in vitro pharmacology studies. Useful observations were made in four areas. (1) Drug assay design: The predictive accuracy of the HTSCA depends on the in vitro testing of drug concentrations of less than 10% of those which are pharmacologically achievable with standard in vivo drug doses. The use of unrealistically high in vitro concentrations can accurately predict clinical drug resistance, but is likely to yield high false-positive rates of clinical response prediction. (2) Drug scheduling: For certain schedule-dependent drugs, as well as those with a prolonged plasma half-life and those used according to a repeated daily schedule, prolonged in vitro exposure (rather than 1 h) may be needed to provide an adequate in vitro design. For an accurate prediction of sensitivity of tumor colony-forming units (TCFUs) to continuous drug contact in the agar, concentrations should be in the range of 1/300 that used for the standard 1-h exposure prior to plating. (3) Drug combinations: In preliminary studies of combination chemotherapy in vitro we commonly observed at least additive effects with low doses of cis-platinum plus either vinblastine or adriamycin. (4) Drug bioactivation: Rat liver microsomes or S-9 fraction were used to activate cyclophosphamide for in vitro effect, and satisfactory dose-response curves were observed for the inhibition of TCFUs. Such pharmacologic studies will be required for a wide variety of standard and new agents and will probably become a regular aspect of investigation of new anticancer drugs.     

Human tumor clonogenic assay in human breast cancer

The human tumor clonogenic assay (HTCA) developed by Hamburger and Salmon was evaluated in 135 fresh samples of breast cancer. Successful tumor colony growth (greater than or equal to 5 colonies/plate) was obtained in 100 (74%) of the 135 samples, and adequate growth for drug testing (greater than or equal to 30 colonies/plate) in 75 (56%). With regard to the success rates of growing colonies categorized by specimen source, tumor sites, histology, prior chemotherapy and estrogen receptor (ER), specimens from solid tumors and primary tumors showed higher success rates than those from pleural effusions and metastatic tumors. The effects of prior chemotherapy, histology type and ER status on the success rate of colony formation were not significant. The overall median plating efficiency was 0.012%. Higher plating efficiencies were found in pleural effusion, metastatic tumors and samples from patients with prior chemotherapy. These findings appeared to indicate that aggressiveness of disease might be related to plating efficiency. Defining a greater than or equal to 50% inhibition of colony formation (ICF) as in vitro drug sensitivity, the in vitro response rates to anticancer drugs tested were as follows: adriamycin 33%, mitomycin C 39%, 5-fluorouracil 32%, methotrexate 42%, L-PAM 31%, cisplatin 38%, vincristine 32%, vinblastine 54%. The group of patients without prior chemotherapy showed higher sensitivity in vitro compared with the group of patients who had prior chemotherapy (38% vs. 27%). Correlation between in vitro drug sensitivity (greater than or equal to 70% ICF) and clinical response in 12 patients treated with the same drugs were analyzed retrospectively. The predictive accuracy was 0% (0/1) for true positive and 91% (10/11) for resistance. Thus, overall predictive accuracy was 83%. Based on these results, HTCA appeared to be useful chemosensitivity test for evaluation of antitumor drugs for human cancers in vitro and prediction of the chemotherapeutic effect in clinical use.     

In vitro evaluation of the anticancer drug modulatory effect of hyaluronidase in human gastrointestinal cell lines

In an attempt to establish whether the combination of anticancer drugs with hyaluronidase would result in enhanced cytotoxicity, we have tested a range of 6 continuous cell lines against 4 different chemotherapeutic drugs with or without the addition of various concentrations of the enzyme. Measurement of cytotoxic drug effects has been performed using the Bactec system, a new semiautomated radiometric technique. In only 15 of a total of 144 experiments (11%) was a significant hyaluronidase-mediated potentiation of the single agents' activity seen. In the large majority of experiments, the antiproliferative effect of the combined treatment was classified as additive or subadditive, while in 23% it was antagonistic. Evaluation of the drug modulatory mechanism of hyaluronidase suggested that the combined drug-hyaluronidase effects were independent of the nature of the drug, the exposure mode and the concentration of the enzyme employed. Among the various tumor cell lines tested there was a marked heterogeneity in the sensitivity to the combined effect (P less than 0.0001). In summary, we have not been able to confirm the promising results of early reports of in vitro and in vivo enhancement of the cytotoxicity of antitumor agents by hyaluronidase. Our data emphasize the need for further controlled clinical studies in order to prove or disprove this new therapeutic approach.     

The clonogenic assay with human tumor xenografts: evaluation, predictive value and application for drug screening

The feasibility, evaluation and predictive value of the colony-forming assay with human tumor xenografts for screening anticancer drugs have been studied. Using human tumors grown in serial passage in nude mice, adequate colony formation was observed in 215 of 251 (86%) different solid human tumors of various histologies. Based on in vitro growth characteristics, a quality-controlled assay protocol was developed. With the proposed criteria for standardized evaluation of individual experiments a substantial increase in assay reliability was achieved. The five clinically established agents, cisplatin, doxorubicin, etoposide, mitomycin-C and vindesine, were studied for anticancer activity in the clonogenic assay. Drugs were applied over a wide dose range by continuous exposure, yielding clear dose-response effects with coefficients of correlation between r = 0.946 and 0.995. Relevant dose levels predicting correctly for the clinical efficacy of the agents were determined by comparison of in vitro anticancer activity to in vitro toxicity on human bone marrow as follows: cisplatin 0.1 micrograms/ml, doxorubicin 0.01 micrograms/ml, etoposide 0.1 micrograms/ml, mitomycin-C 0.005 micrograms/ml, vindesine 0.01 micrograms/ml. At these concentrations, clinically sensitive tumor types showed inhibition of colony formation in 99 of 240 cases (41%), whereas 11% (19/176) of clinically resistant tumors were responsive. The relevant dose levels used equal between 0.3% and 4.0% of the achievable peak plasma concentrations in man. The predictive value of the clonogenic assay was determined by treatment of the same tumors in vitro and in vivo in tumor-bearing nude mice. In 174/220 comparisons (79%), in vitro data predicted correctly for the in vivo sensitivity of the xenografted malignancies.(ABSTRACT TRUNCATED AT 250 WORDS)     

Application of in vivo and in vitro pharmacokinetics for physiologically relevant drug exposure in a human tumor clonogenic cell assay

The biological half-lives and decay rate constants under the conditions of a human brain tumor clonogenic cell assay were determined for six clinically used anticancer agents. The agents studied were: 1,3-bis(2-chloroethyl)-1-nitrosourea; 3-(2-chloroethyl-3-nitrosoureido-2-deoxy-D-glucopyranose; cis-diaminedichloroplatinum(II); 2,5-diaziridinyl-3,6-bis-(carboethoxyamino)-1,4-benzoquinone; 4-demethylepipodophylotoxin-D-thylidene glucoside; and 9-hydroxy-2-N-methylellipticine. In vitro decay of all six drugs was found to be according to first order kinetics. The half-lives of two drugs, namely, 1,3-bis(2-chloroethyl-1-nitrosourea and 3-(2-chloroethyl-3-nitrosoureido-2-deoxy-D-glucopyranose under the human tumor clonogenic cell assay (HTCA) conditions were found to be similar to their terminal in vivo half-lives in humans. For the other drugs, however, there was a very large difference between their in vitro and in vivo pharmacokinetics. In the case of 2,5-diaziridinyl-3,6-bis(carboethoxyamine)-1,4-benzoquinone, we observed about an 80-fold difference between its in vitro half-life of 40.76 h and its in vivo terminal half-life of 0.52 h. We describe the principles upon which these data can be used to design clinically more relevant in vitro drug exposure protocols in HTCAs. Since, generally, tumor cells are exposed to drugs in the HTCA either continuously or for a specified duration, e.g., 1 or 2 h, we computed the initial in vitro drug concentrations to which tumor cells should be exposed such that the resulting in vitro (c X t) after a 2-h or a continuous exposure will be within clinically achievable levels. The application of these in vivo and in vitro pharmacokinetic principles will provide for more physiological testing of patient tumor cell sensitivity to anticancer drugs in the HTCA, and is likely to result in lower rates of false positive responses in clinical trials using clonogenic cell assays.     

Update of human tumor clonogenic assay in carcinoma of the lung

The human tumor clonogenic assay (HTCA) is a double-layer agar technique, which provides an in vitro prediction of the response of an individual patient's tumor to an antitumor agent. This paper briefly provides an outline of HTCA and its potential use in chemotherapy on patients with lung cancer. In our experience with culturing 123 carcinomas of the lung, 105 specimens (85%) could be subject to more than 5 chemosensitivity tests each by modifying the preparation method of single cell suspension in this system. Growth rate was improved in all types of primary human lung cancer with reasonable consistency. Further, metastatic tumors were capable of being successfully grown in a high percentage of cases, which was comparable to the results obtained for other kinds of tumors. There was no correlation of growth or cloning efficiency with histology, source, or previous chemotherapy. Using 50% or more inhibition on to colony formation as the criterion for chemosensitivity, response rates to vindesine or mitomycin C were 19% or 16%, respectively. The in vitro response rates of these or almost all other antitumor drugs seemed to be comparable to the clinical responses reported by various investigators. Correlation between in vitro chemosensitivity in HTCA and clinical response has been evaluated by various investigators, and the pooled data have demonstrated a good association between in vitro drug sensitivity and clinical response or lack of response. In lung cancer, HTCA had a 57% true positive rate and an 85% true negative rate for the prediction of drug sensitivity and resistance, respectively, of cancer patients to specific chemotherapeutic drugs. Although the system still has to undergo modification to resolve a number of theoretical and practical problems, it has potential uses in lung cancer chemotherapy.     

Human tumor clonogenic assay in osteosarcoma and its clinical evaluation

On twenty-three specimens from patients with osteosarcoma (biopsied tissue, resected specimens from primary and metastatic lesions), the human tumor clonogenic assay (HTCA: standard assay) as well as cultivated HTCA involving short-term cultivation of a single-cell suspension, was carried out. The percentage colony-forming ability, which was very small for standard HTCA, increased significantly when cultivated HTCA was performed. With cultivated HTCA, sensitivity tests were possible in 87% of the specimens, in contrast to only 28.6% with standard HTCA. Retrospective evaluation of the results obtained by cultivated HTCA with the clinical efficacy of anticancer drugs showed a true positive rate, 66.7%, and a true negative rate, 88.9%. This analysis revealed that drugs shown to be ineffective and that tumor cells are refractory to those drugs, so that clinical use of such drugs should be avoided.