In vitro drug sensitivity testing for the individual patient: an ideal adjunct to current methods of treatment choice

Patient-Derived Ex Vivo Cultures and Endpoint Assays with Surrogate Biomarkers in Functional Testing for Prediction of Therapeutic Response

Prediction of therapeutic outcomes is important for cancer patients in order to reduce side effects and improve the efficacy of anti-cancer drugs. Currently, the most widely accepted method for predicting the efficacy of anti-cancer drugs is gene panel testing based on next-generation sequencing. However, gene panel testing has several limitations. For example, only 10% of cancer patients are estimated to have druggable mutations, even if whole-exome sequencing is applied. Additionally, even if optimal drugs are selected, a significant proportion of patients derive no benefit from the indicated drug treatment. Furthermore, most of the anti-cancer drugs selected by gene panel testing are molecularly targeted drugs, and the efficacies of cytotoxic drugs remain difficult to predict. Apart from gene panel testing, attempts to predict chemotherapeutic efficacy using ex vivo cultures from cancer patients have been increasing. Several groups have retrospectively demonstrated correlations between ex vivo drug sensitivity and clinical outcome. For ex vivo culture, surgically resected tumor tissue is the most abundant source. However, patients with recurrent or metastatic tumors do not usually undergo surgery, and chemotherapy may be the only option for those with inoperable tumors. Therefore, predictive methods using small amounts of cancer tissue from diagnostic materials such as endoscopic, fine-needle aspirates, needle cores and liquid biopsies are needed. To achieve this, various types of ex vivo culture and endpoint assays using effective surrogate biomarkers of drug sensitivity have recently been developed. Here, we review the variety of ex vivo cultures and endpoint assays currently available.

Differential Staining Cytotoxicity assay: a review

Differential Staining Cytotoxicity (DiSC) assay is the prototype for a closely related family of assays based on the concept of total cell kill, or, in other words, cell death occurring in the entire population of tumor cells. It is probably the most versatile of the cell-death end points, in that it (1) can be applied to both solid and hematologic neoplasms, (2) can be applied to specimens in which it is not possible to obtain a pure population of highly enriched tumor cells, and (3) can be applied to a wide variety of drugs, ranging from traditional cytotoxic agents to biological response modifiers with activity mediated through tumor-infiltrating effector cells, to "targeted" kinase inhibitors, and to antivascular agents, such as bevacizumab and pazopanib. The basic principles of the assay are to culture three-dimensional fresh tumor cell clusters in anchorage-independent conditions. At the conclusion of the culture period, Fast Green dye is added to the microwells, the contents of which are then sedimented onto permanent Cytospin centrifuge slides and then counterstained with hematoxylin-eosin or Wright-Giemsa. "Living" cells stain with the cytologic stain in question and can be identified as either normal or neoplastic, based on standard morphologic criteria. "Dead" cells stain blue-green. Nonviable endothelial cells appear as strikingly hyperchromatic, blue-black, and often refractile objects, which may be readily distinguished from other types of dead cells. This assay has been biologically and clinically validated in a number of ways, as described in this chapter.

Prediction of individual response to chemotherapy in patients with acute myeloid leukaemia using the chemosensitivity index Ci

As the response to chemotherapy in patients with acute myeloid leukaemia (AML) may still not be accurately determined by known prognostic factors, such as karyotype, the ex vivo chemosensitivity profile may help to predict the individual response. The predictive accuracy of an ex vivo assay should be assessed by correlation of assay results with both response rate and survival. We prospectively investigated the prognostic relevance of pre-therapeutic ex vivo chemosensitivity testing in primary cell cultures from adult AML patients by applying a new evaluation methodology, designated the chemosensitivity index, C(i). This C(i) was designed as a prognostic index by taking the area under the curve as an exact measure of the total dose-response relationship. We found an overall predictive accuracy of 98.2% concerning treatment response, which compares favourably with previously published data ranging from 75% to 92%. Moreover, the C(i) proved to be the strongest prognostic factor for overall survival in a multivariate Cox regression analysis including karyotype grouping and age (P < 0.001), and enabled the evaluation of response to combination therapies and selection of possible treatment alternatives. Our data suggest that ex vivo chemosensitivity testing evaluated by the C(i) could serve as a powerful tool for assay-directed therapy strategies in AML.

Expression patterns of cell cycle and apoptosis-related genes in a multidrug-resistant human colon carcinoma cell line

BACKGROUND

An in vitro multidrug resistance (MDR) system from a human colonic cancer cell line (SW620-MDR) has been established. To further study the mechanisms at molecular level and prevention of multidrug resistance in clinical practice, it was demonstrated that the expressions of several apoptosis-related and cell cycle regulator genes were changed in the cells.

METHODS

A multidrug-resistant colonic cell line (SW620-MDR) was established, and the Atlas human cDNA expression array was used for studying the pattern of gene expression in this cell line. Furthermore, Northern hybridization or real-time PCR analysis confirmed the pattern of gene expression.

RESULTS

In the SW620-MDR cell line the pro-apoptosis genes, CASP4, BIK, PDCD2, and TACE were expressed with decreased levels, and the antiapoptosis genes CD27-L and IGFBP2 were over-expressed. Furthermore, the cell cycle regulator genes such as CDK6, CCND1, CDC27HS, CDC16HS, Wee1Hu, MAPKK1, and IGFBP6 were expressed with decreased levels in the drug-resistant cell line.

CONCLUSIONS

It is worthwhile investigating whether the differentially expressed pattern of the aforementioned genes exists in the drug-resistant cancer specimens, and to further understand their functions in the cancer drug-resistance mechanism.

Heterogeneity of chemosensitivity of esophageal and gastric carcinoma

Esophageal and gastric cancer have a poor prognosis, and chemotherapy is rarely of long-term benefit. This may be related in part to heterogeneity of chemosensitivity and to constitutive resistance to individual cytotoxic drugs. This study aimed to demonstrate the degree of heterogeneity of chemosensitivity between tumors. We have examined the heterogeneity of chemosensitivity in esophageal and gastric cancer specimens (n=85) using an ex vivo ATP-based chemosensitivity assay (ATP-TCA). A variety of chemotherapeutic agents were tested. Sixty-four specimens were endoscopic biopsy samples; the remainder were from resection specimens. Cells were obtained from 62 specimens (73%). Eight assays were infected due to contamination/infection of the biopsy material, giving an evaluability rate of 87%. Analysis of the data showed considerable heterogeneity of chemosensitivity. The most active single agents identified by the assay were mitomycin C (56% sensitivity) and 5-fluorouracil (5-FU; 42% sensitivity). Exposure of tumor cells to combinations of drugs showed ECF (epirubicin, cisplatin, 5-FU) and mitomycin C+5-FU to be moderately active regimens. Other experimental drug combinations showed greater activity. There is a marked heterogeneity of chemosensitivity in esophageal and gastric cancers. The degree of heterogeneity observed suggests that the ATP-TCA could be used to individualize chemotherapy by selecting agents for particular patients. This approach provides the rationale for a trial of ATP-TCA-directed therapy to determine whether individualization of chemotherapy might improve patient response and survival.

Establishment of two vaccine-associated feline sarcoma cell lines and determination of in vitro chemosensitivity to doxorubicin and mitoxantrone

OBJECTIVE

To establish 2 vaccine-associated feline sarcoma (VAFS) cell lines and to determine their in vitro sensitivity to the chemotherapeutic agents doxorubicin and mitoxantrone.

SAMPLE POPULATION

Tumor specimens collected from 2 cats undergoing surgery for removal of vaccine-associated sarcomas.

PROCEDURES

Tumor specimens were minced and treated with trypsin under aseptic conditions to obtain single-cell suspensions, which were then cultured in vitro in medium supplemented with 5% heat-inactivated fetal bovine serum. Growth rates and sensitivity after 24 hours of exposure to various concentrations (0.1 to 100 microg/ml) of doxorubicin and mitoxantrone were assessed for each cell line. Survival of cells was estimated 3 days after exposure to the 2 agents, and the concentration of each drug that resulted in a 50% reduction in the number of viable cells (IC50) was calculated.

RESULTS

Two tumor-derived cell lines (FSA and FSB) were successfully established and determined to be sensitive to doxorubicin and mitoxantrone. Under the conditions tested, the IC50 of doxorubicin were 0.6 and 1.5 microg/ml for cell lines FSB and FSA, respectively. The IC50 of mitoxantrone was 0.4 microg/ml for both cell lines.

CONCLUSIONS AND CLINICAL RELEVANCE

The establishment of VAFS cell lines provides a tool for the in vitro screening of antitumor drugs. Doxorubicin and mitoxantrone were effective in decreasing the number of viable cells in the 2 cell lines tested. Both of these anthracycline antibiotics have been used to treat various neoplasias in cats, and their efficacy for adjuvant treatment of vaccine-associated sarcomas should be further evaluated.

In vitro preclinical models for a rational design of chemotherapy combinations in human tumors

Today, drug combinations are frequently used in the treatment of cancer to increase therapeutic efficacy. Currently used clinical protocols for cancer combination therapies are mainly obtained empirically or on the basis of results from previous clinical trials. Information obtained from clinical protocols is invaluable, but it is time-consuming, expensive and does not provide data on the biochemical and molecular mechanisms of interaction of the drugs used in combination treatments at cellular level. Therefore, in vitro drug combination studies on established cell lines or primary cell cultures play an important role in designing and optimising combination protocols. A variety of in vitro assays and different mathematics models have been developed to investigate cytotoxic effects and to analyse the type of drug interactions. Increased knowledge of the cellular targets of traditional and new drugs and the development of new technologies have resulted in a new role for the in vitro tests which are no longer used only to evaluate the cytotoxic effects of drugs, but also to investigate the interference on cell cycle, induction of apoptosis and molecular or biochemical interactions. A review on in vitro preclinical tests used to evaluate the effects of drug combinations and to design the rationale of combined chemotherapy protocols is presented.

Relationship between expression of topoisomerase II isoforms and chemosensitivity in choroidal melanoma

Choroidal melanoma has a high mortality rate and responds poorly to existing chemotherapy, but unexpected ex vivo sensitivity of a subset of these tumours to topoisomerase II inhibitors has been noted. Since chemoresistance may be mediated by the molecular phenotype of tumours, immunohistochemistry has been used to study the expression of both isoforms of topoisomerase II (alpha and beta) in 29 choroidal melanomas for which chemosensitivity assay data for doxorubicin or mitoxantrone are also available. Of these, eight tumours were topoisomerase II beta-positive and 11 were topoisomerase II alpha-positive. Recent studies showing genetic abnormality (often monosomy of chromosome 3) in choroidal melanoma suggest that loss of immunostaining could be due to genomic loss rather than down-regulation of topoisomerase II beta in these tumours. There was no convincing excess of anthracycline resistance in the topoisomerase II beta-negative group. Addition of topoisomerase II alpha, MDR1 (11/17 positive), LRP (16/28 positive), and MRP (5/29 positive) data in multivariate analysis did not reliably predict sensitivity or resistance. Vincristine chemosensitivity showed no relation to MDR1, LRP or MRP in 18 tumours tested. While it is possible that some tumours which do express topoisomerase II beta may respond to anthracyclines, the molecular basis of resistance or sensitivity to anthracyclines or vincristine in uveal melanoma is complex and remains incompletely understood.

Prognosis in adult AML is precisely predicted by the DISC-assay using the chemosensitivity-index Ci

We prospectively investigated the correlation between DISC-assay results and clinical response and also survival in patients with AML using a new method of evaluation.

Airborne cytotoxicity in the DiSC assay caused by solutions of treosulfan but not busulphan

Treosulfan and busulphan are similar molecules, the former used in the treatment of ovarian cancer and the latter in chronic myelogenous leukaemia. We have used both in the differential staining cytotoxicity (DiSC) assay for in vitro drug sensitivity testing to aid in the choice of chemotherapy for individual patients. It was observed that occasionally the viability of control cells in one assay box was reduced compared with control cells in other boxes from the same assay. Treosulfan was suspected as the cause because cells throughout the microtitre box containing treosulfan had reduced viability in 28/62 (45%) experiments and in 9 of these, total kill of all cells in the box was observed. We tested the hypothesis that a metabolite of treosulfan might be the cause of this airborne cytotoxicity, and found that whilst 10 mg ml-1 of either methane sulphonic acid or tetrahydrofuran had no airborne cytotoxic effect, 1 mg ml-1 diepoxybutane killed over 95% of cells in all tubes in the same box. Treosulfan is another chemical (cf. azide, mafosfamide and possibly other cytotoxic agents) that can cause airborne cytotoxicity.