Further investigation of the relation between the clinical and tissue culture response to chemotherapeutic agents on human cancer

Use of patient-derived explants as a preclinical model for precision medicine in colorectal cancer: A scoping review

PURPOSE

Whilst the treatment paradigm for colorectal cancer has evolved significantly over time, there is still a lack of reliable biomarkers of treatment response. Treatment decisions are based on high-risk features such as advanced TNM stage and histology. The role of the tumour microenvironment, which can influence tumour progression and treatment response, has generated considerable interest. Patient-derived explant cultures allow preservation of native tissue architecture and tumour microenvironment. The aim of the scoping review is to evaluate the utility of patient-derived explant cultures as a preclinical model in colorectal cancer.

METHODS

A search was conducted using Ovid MEDLINE, EMBASE, Web of Science, and Cochrane databases from start of database records to September 1, 2022. We included all peer-reviewed human studies in English language which used patient-derived explants as a preclinical model in primary colorectal cancer. Eligible studies were grouped into the following categories: assessing model feasibility; exploring tumour microenvironment; assessing ex vivo drug responses; discovering and validating biomarkers.

RESULTS

A total of 60 studies were eligible. Fourteen studies demonstrated feasibility of using patient-derived explants as a preclinical model. Ten studies explored the tumour microenvironment. Thirty-eight studies assessed ex vivo drug responses of chemotherapy agents and targeted therapies. Twenty-four studies identified potential biomarkers of treatment response.

CONCLUSIONS

Given the preservation of tumour microenvironment and tumour heterogeneity, patient-derived explants has the potential to identify reliable biomarkers, treatment resistance mechanisms, and novel therapeutic agents. Further validation studies are required to characterise, refine and standardise this preclinical model before it can become a part of precision medicine in colorectal cancer.

Three-dimensional models of cancer for pharmacology and cancer cell biology: capturing tumor complexity in vitro/ex vivo

Cancers are complex and heterogeneous pathological "organs" in a dynamic interplay with their host. Models of human cancer in vitro, used in cancer biology and drug discovery, are generally highly reductionist. These cancer models do not incorporate complexity or heterogeneity. This raises the question as to whether the cancer models' biochemical circuitry (not their genome) represents, with sufficient fidelity, a tumor in situ. Around 95% of new anticancer drugs eventually fail in clinical trial, despite robust indications of activity in existing in vitro pre-clinical models. Innovative models are required that better capture tumor biology. An important feature of all tissues, and tumors, is that cells grow in three dimensions. Advances in generating and characterizing simple and complex (with added stromal components) three-dimensional in vitro models (3D models) are reviewed in this article. The application of stirred bioreactors to permit both scale-up/scale-down of these cancer models and, importantly, methods to permit controlled changes in environment (pH, nutrients, and oxygen) are also described. The challenges of generating thin tumor slices, their utility, and potential advantages and disadvantages are discussed. These in vitro/ex vivo models represent a distinct move to capture the realities of tumor biology in situ, but significant characterization work still remains to be done in order to show that their biochemical circuitry accurately reflects that of a tumor.

Prediction of response to drug therapy of cancer. A review of in vitro assays

Cancer chemotherapy has witnessed a great deal of progress since the introduction of the nitrogen mustards in the 1940s. Unfortunately, individual patients with apparently identical tumour histologies do not always respond identically to the same drug regimen. Determining the sensitivity and resistance of an organism before treatment has been the standard of care in infectious diseases for many years, while in oncology treatment has been initiated according to tumour histology rather than the tumour's sensitivity to a given agent. Attempts to individualise therapy have been the goal of oncologists since the 1950s. Since that time a number of in vitro assays have been developed to predict therapeutic outcome prior to the start of therapy. In the 1970s, with the introduction of the human tumour stem cell assay, it was generally believed that oncology was on the threshold of entering an era of predictive in vitro chemosensitivity testing. Unfortunately, this assay was shown to have a number of technical drawbacks including the low plating efficiencies of many primary tumour samples which thus limits the percentage which can be evaluated, leaving us still at this threshold today. Several recent developments, such as the Kern assay, which measures inhibition of radioactive precursors into tumour cells in the presence of antineoplastic agents, ATP bioluminescence assays, and the fluorescent cytoprint assay offer the promise of rapid and sensitive results. Other assays, such as the tetrazolium-based MTT and the sulphorhodamine blue assay appear to hold more promise in the screening and evaluation of potential new agents in established tumour cell lines than for evaluating chemosensitivity of clinical specimens. However, before a particular assay can be considered as an in vitro test of chemosensitivity or resistance, controlled prospective studies must be carried out to validate the assay in a number of different tumour types.

In vitro sensitivity assays in cancer: a review, analysis, and prognosis

Tumors are complex systems consisting of heterogeneous cancer cells as well as normal cells with each exhibiting unique drug sensitivity spectra. There have been many attempts to design in vitro systems to determine drug response to tumors. The most widely used system is the clonogenic assay. which has demonstrated some clinical predictivity. However, the clonogenic assay has been shown to have negative aspects, including low frequency of evaluation, clump artifacts, lack of cytotoxic end-points and disruption of normal cell-cell interactions existing in a true tissue environment. Newer models are described utilizing cytotoxic as well as cell-proliferation end-points, and maintenance of three-dimensional tissue architecture in vitro. It is concluded that less artifactual, more realistic models can be used to select more tumor-specific drugs which themselves in turn will make in vitro chemosensitivity assays more useful for cancer patients.

Advances in rational combination chemotherapy

Due to the high frequency of micro- or macrometastatic disease at the time of diagnosis of cancer, and to the increasing prevalence of cancer in this country, the use of chemotherapy to evoke cure or prolongation of survival has become critically important. In addition, the growth kinetics of large tumor burdens and the high probability of drug-resistant cells in a tumor mass at the time of diagnosis necessitate combinations of chemotherapeutic agents rather than single agents as the most effective mode of treatment. Since there are 40 to 50 active anticancer drugs now utilized, and since synergy between drug combinations is often dose and/or schedule dependent, the number of possible drug combinations and permutations is vast. Thus, screening for effective drug combinations requires a rational approach which will allow for accurate predictions of synergy. Most advances in this scientific approach have utilized biochemical modulation in conjunction with in vitro cytotoxicity assays, in particular, clonogenic assays. Such an approach has generated a number of drug combinations, such as sequential MTX-5FU, with widely applicable clinical efficacy. The continued use of biochemical modulation should rapidly generate new effective drug combinations which will, hopefully, allow us to cure even those cancers presently considered incurable.

Predictive testing in cancer chemotherapy. II. In vitro

During the last thirty years several in vitro techniques have been developed to predict sensitivity of individual tumours. When the results of these techniques were correlated with the clinical response in larger groups of patients, the accuracy for predicting resistance was greater than for predicting sensitivity. Amongst the culture techniques the colony-forming assays have received much attention. Research with tumour cell lines and the sound biological basis do support this preference on other techniques. Studies on these assays have come from several independent laboratories, who report comparable results. Improvement of the culture technique and more insight into the in vitro pharmacology is needed, before application on wider scale is justified. Colony-forming culture techniques have not only been propagated for individualized chemotherapy, but also for drug screening. New antitumour agents and analogous can be screened in a short time for their sensitivity in many histologic tumour types.

In vitro sensitivity and resistance of cultured human squamous carcinoma cells to cis-platinum and methotrexate

To determine whether resistance to chemotherapy in advanced head and neck squamous cell carcinoma stems from biochemical mechanisms and to assess the potential usefulness of new anticarcinogens, an in vitro test would be highly desirable. In the past 4 years our laboratory has developed methodology to establish squamous carcinoma cell lines in tissue culture from patients with squamous cancer of the head and neck. We used some of these lines to compare the in vitro effects of methotrexate on squamous carcinoma, fibrosarcoma, and melanoma cells. Three of the squamous carcinoma lines were tested for sensitivity to both methotrexate and cis-platinum; all but one squamous carcinoma cell line exposed to methotrexate showed growth inhibition at the physiologically attainable concentration of 10(-7) M. In contrast, a tenfold higher concentration was required to produce similar effects in the melanoma, while no concentration inhibited fibrosarcoma growth. Cis-platinum showed consistent squamous carcinoma cytotoxicity in 10(-5) M and 10(-6) M concentrations. This approach should be useful for determining the relative sensitivity and resistance of head and neck cancers to chemotherapeutic agents in vitro.

Prediction of response to cancer chemotherapy

Cytotoxic chemotherapy plays a key role in the treatment of carcinoma for thousands of patients annually who either present with metastatic disease or relapse after surgical excision of apparently localised disease. Unfortunately, there is such a wide range of responsiveness to drug therapy within individual tumour types that response of an individual patient's tumour to cytotoxic therapy cannot be accurately predicted. Intensive efforts to increase the accuracy of selection of effective chemotherapy have recently culminated in an in vitro system which employs soft agar and standard laboratory tissue culture techniques to predict drug sensitivity and resistance for an individual patient's tumour with reasonable accuracy. Research in this system is being actively pursued at several centres and further modifications and refinements may well make cancer chemotherapy more precise than previously possible. This review surveys methods of studying in vitro drug sensitivity which have been tested and for which clinical correlations are available. The technique and results of the more recently developed human tumour stem cell assay and the potential applications of this system are also discussed.

In vitro sensitivity test of stomach cancer tissues by the use of metal grid method

Ninety-nine specimens obtained from 53 patients with stomach cancer were cultured for about 3 days by means of the stainless steel grid method. In vitro effects of antitumor drugs on the cancer cells were evaluated autoradiographically or biochemically using a liquid scintillation counter to measure the uptake of 3H-thymidine. The radioactivity of the labeled tumor cells of both control fragments and fragments affected by drugs varied greatly among individual tumors. Therefore, the in vitro efficacy of antitumor drugs was represented as a comparison with that of control fragments. Positive correlation between in vitro tests and the clinical effects of antitumor drugs was observed in the specimens of 18 cases.

[The effect of cyclophosphamide on tumors in the sensitivity-test (author's transl)]

The sensitivity of tumors to cyclophosphamide was tested in vitro. For this purpose, the urine of cyclophosphamide-treated rats (90 min., 500 mg/kg) was used. This method of activating cyclophosphamid proved more advantageous than other methods; all cytostatically effective metabolites can be used in the test and the production of metabolites can easily be standardized. Consequently results with good reproducibility can be obtained. In various long-term and short-term test models with animal transplantation-tumors in vitro, the effects of the cyclophosphamide metabolites depended on the dose used. This test results in the various test models are comparable. In the tissue-culture of tumors (long-term test) sensitivity was evaluated by using morphological criteria as well as by counting cell numbers. In the short-term test the sensitivity of tumors was found out by influencing the nucleic acid syntheses (3-H-thymidine-, 3-H-uridine-incorporation). As the tissue-culture meets with difficulties as a routine clinical examination, the use of the short-term test is recommended. Using as model the fast proliferating WALKER-256-carcinosarcoma and a slowly proliferating rat adenocarcinoma, the results of the sensitivity-test in vitro were compared with the effects of therapy in animal tests. Tumor remissions corresponding with the results reached in vitro, which depended on dosis, could also be achieved in both transplantation-tumors. Human tumors, tested in in vitro studies (short-term-test), show a different sensitivity to cyclophosphamide.

Oxygen consumption by acrylamide polymerization: a method for rapid screening of anticancer agents

We have developed a rapid and sensitive method to measure oxygen consumption of tumor cells by acrylamide polymerization. This method could be used as an in vitro screen for potential chemotherapeutic agents. Previous techniques have lacked either the sensitivity or the speed required for use as an effective clinical tool. This method was modified from a technique previously developed in our laboratory for measuring oxygen in blood. Standard anticancer agents were tested against Walker 256 ascites tumor. Ascites was harvested from 20 rats on each of 50 days, incubated briefly with drugs, and acrylamide polymerization time was measured hourly. Individual controls were established for each drug-treated group, and oxygen uptake measured after one hour of incubation. Actinomycin, cyclohexamide, and cytosine arabinoside inhibited tumor cell oxygen consumption by 80%, 40%, and 30%, respectively. These results correlated with the known in vivo effects of these drugs on Walker carcinosarcoma. Therefore, this sensitive method could potentially be used directly on tumor cells removed from biopsy material so that the testing of anticancer drugs could be completed on the day of biopsy.

A predictive test for the selection of cancer chemotherapeutic agents for the treatment of human cancer

The use of animals for the screening of chemotherapeutic agents effective against cancer is not always satisfactory. In addition to the problems of cost, space, and care, the results obtained by animal screening do not always parallel those obtained by the clinical use of the agents. With the advent of more refined in vitro technics which can be applied directly to the patient's own tumor tissue, additional information may permit a more critical evaluation of the laboratory findings. The critical index of sensitivity probably lies in the combined evaluation of biochemical analysis and observed morphological damage. From this investigation it would appear that tissue culture of human tumors may serve as a valuable adjunctive method for the screening of chemicals in order to find drugs valuable in the treatment of cancer in man and to serve as a method in the selection of the most effective therapeutic agent for a given tumor in a given patient.

Treatment of leukemia with large doses of methotrexate and folinic acid: clinical-biochemical correlates

Patients with acute leukemia were given repeated cycles consisting of infusions of methotrexate followed by "rescue" with folinic acid. Peripheral blood leukemic cells were harvested from patients before cyclical treatment, and the rates of incorporation of thymidine and of deoxyuridine into deoxyribonucleic acid (DNA) were measuared in vitro. There was no relationship between the pretreatment incorporation of either deoxynucleoside into DNA and the clinical response to therapy. Methotrexate suppressed deoxyuridine incorporation into DNA by the leukemic blasts in vitro, but the patients whose cells were most sensitive to this effect did not necessarily go into remission when treated. Leukemic cells were sampled during methotrexate infusions and the deoxynucleoside incorporation rates were determined. Thymidine incorporation into DNA was variably affected. If, by the end of the first infusion, it remained elevated, remission rarely followed, whereas if it was below the pretreatment value, remission was much more likely. In all cases, deoxyuridine incorporation was suppressed during the infusion. The greatest suppression occurred in patients who went on to remission, but the suppression did not correlate with that expected from pretreatment in vitro tests unless due weight was given to the concomitant effects of the methotrexate therapy on thymidine incorporation. Leukemic blasts surviving successive cycles of therapy became progressively more resistant to the suppressing effects of methotrexate in vitro. This resistance became especially marked in the blasts of patients who did not go into remission. During methotrexate infusions, inhibition of leukemic cell dihydrofolate reductase activity was greatest in blasts of patients whose disease subsequently remitted.

Determinants of human tumor sensitivity to fluorinated pyrimidine chemotherapy

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