A rapid in vitro screening system for the identification and evaluation of anticancer drugs

Telomeric DNA induces apoptosis and senescence of human breast carcinoma cells

INTRODUCTION

Cancer is a leading cause of death in Americans. We have identified an inducible cancer avoidance mechanism in cells that reduces mutation rate, reduces and delays carcinogenesis after carcinogen exposure, and induces apoptosis and/or senescence of already transformed cells by simultaneously activating multiple overlapping and redundant DNA damage response pathways.

METHODS

The human breast carcinoma cell line MCF-7, the adriamycin-resistant MCF-7 (Adr/MCF-7) cell line, as well as normal human mammary epithelial (NME) cells were treated with DNA oligonucleotides homologous to the telomere 3' overhang (T-oligos). SCID mice received intravenous injections of MCF-7 cells followed by intravenous administration of T-oligos.

RESULTS

Acting through ataxia telangiectasia mutated (ATM) and its downstream effectors, T-oligos induced apoptosis and senescence of MCF-7 cells but not NME cells, in which these signaling pathways were induced to a far lesser extent. In MCF-7 cells, experimental telomere loop disruption caused identical responses, consistent with the hypothesis that T-oligos act by mimicking telomere overhang exposure. In vivo, T-oligos greatly prolonged survival of SCID mice following intravenous injection of human breast carcinoma cells.

CONCLUSION

By inducing DNA damage-like responses in MCF-7 cells, T-oligos provide insight into innate cancer avoidance mechanisms and may offer a novel approach to treatment of breast cancer and other malignancies.

Glucocorticoid use in prostate cancer and other solid tumours: implications for effectiveness of cytotoxic treatment and metastases

Glucocorticoids have been used widely in conjunction with other treatment for patients with cancer because they have potent proapoptotic properties in lymphoid cells, can reduce nausea, and alleviate acute toxic effects in healthy tissue. However, glucocorticoids are used in a supportive-care role, even though to our knowledge no prospective clinical studies have assessed the effect of these steroids on the growth of solid tumours. Data from preclinical and, to some extent, clinical studies, suggest that glucocorticoids induce treatment resistance in solid tumours, including prostate cancer. Research has focussed on disseminated cells that have been shed by the tumour: the potential of glucocorticoids to render these cells resistant to apoptosis--and to downregulate the immune response--might contribute to tumour metastasis. Here, we review the benefits of glucocorticoids and their negative effects, such as induction of resistance in tumour cells and concomitant induction of apoptosis in immune cells, with particular emphasis on prostate cancer.

Antagonism between tamoxifen and doxorubicin in the MCF-7 human breast tumor cell line

Tamoxifen, an antiestrogen, and doxorubicin, an anthracycline antibiotic, are each utilized alone and in combination in the treatment of breast carcinoma. In view of conflicting reports relating to the interaction between these drugs, studies were undertaken to characterize the influence of tamoxifen on growth inhibition by doxorubicin in the MCF-7 breast tumor cell line in vitro. Studies combining 5 microM tamoxifen, a clinically relevant concentration, with various concentrations of doxorubicin, indicated that this drug combination produces antiproliferative effects that appear to be less than additive. Concentration-dependent growth inhibition was analyzed further using various concentrations of tamoxifen and doxorubicin by the combination index-isobologram method; this quantitative approach provided clear evidence of antagonism between these agents, a finding with potential relevance to the treatment of breast cancer.

An organoid culture assay (OCA) for determining the drug sensitivity of human tumors

A model for testing chemotherapeutic agents in vitro is described. It is based on an organoid culture method which allows human carcinomas to grow in vitro and to maintain many typical in vivo properties, including 3-dimensional architecture, growth of multiple cell types, expression of morphological differentiation and formation of histotypical structures. The preservation of drug sensitivity and resistance under the conditions of our organoid culture assay (OCA) was demonstrated by investigating 3 strains of a human hypopharynx carcinoma which differed by different sensitivity to cisplatin in in vivo conditions. These differences were retained in vitro and the modified neutral-red (NR) assay was especially suitable for revealing drug-induced cytotoxic damage in OCA. On the basis of our findings, the following approach is proposed for the in vitro testing of cytostatic drugs before they are administered to patients. (1) Removal of carcinomas from patients; (2) dense cell suspensions of these carcinomas to be dropped on membrane filters at the air-medium interface, resulting in growth of solid nodules of organized carcinoma tissues; (3) addition of cytostatic drugs to the growth medium for 2 or 3 days; (4) detachment and bisection of the culture nodules; (5) determination of viable cells by NR uptake and total cell mass by the sulforhodamin B (SRB) assay; (6) determination of quotient NR:SRB absorbance, related as percentage to control value: this indicates the fraction of viable cells and gives a measure of the cytotoxic injury caused by the applied cytotoxic drug. Thus, the OCA seems to be suitable for defining the patterns of drug sensitivity and resistance of individual human carcinomas in vitro within a few days.

Organoid reorganization of human tumors under in vitro conditions

In the present study we describe a new method to cultivate human tumors, which allows organoid differentiation under in vitro conditions. Diverse tumors of different origin and various histopathology which had been heterotransplanted to athymic mice were dissociated into single cells and seeded at high cell density onto a membrane filter consisting of cellulose nitrate at the gas-medium interface. Within a few days, the tumor cells reorganized and differentiated into organoid structures which exhibited the typical histological characteristics of the original tissues. Due to the formation of organoid aggregates, which was also previously seen with normal fetal cells, this type of culture has been described as 'organoid culture'. In the case of adenocarcinomas of the lung and the colon including the rectum, glandular structures with central lumina, adjacent microvilli, and junctional complexes were formed. Numerous specific intercellular contacts such as desmosomes and tight junctions occurred as well as interdigitations of adjacent cell membranes. In a tumor of the rectum, a typical brush border differentiated at the surface of the reorganized tumor-tissue aggregate. Epidermoid carcinomas of the head and neck developed structures resembling the spinous layer of the epidermis, exhibiting numerous desmosomes and intracytoplasmic bundles of tonofilaments radiating into the desmosomes. Most tumors produced a fragmentary monolayered or multilayered basal lamina of similar morphological appearance as under in vivo conditions. These results illustrate the organoid reorganization and differentiation of human tumor cells under the experimentally rather simple conditions of the organoid culture systems and clearly demonstrate that this in vitro system comes close to the in vivo situation as far as certain differentiation phenomena are concerned.

Human ovarian cancers specifically bind daunorubicin-OC-125 conjugate: an immunofluorescence study

This study was designed to test the specific binding to human ovarian serous adenocarcinomas of a drug-antibody conjugate [daunorubicin (DNR-OC-125], made from a new analog (PIPP-DNR) of daunorubicin that chemically links the drug to monoclonal antibodies. We recently reported that the DNR-OC-125 conjugate is selectively toxic in vitro to dividing cell populations of the human ovarian cancer cell lines SK-OV-3 and OVCAR-3 that express the CA-125 antigen [F. Sweet, L. O. Rosik, G. M. Sommers, and J. L. Collins, Gynecol. Oncol. 34, 305-311 (1989)]. In the present study, immunofluorescence data show that the DNR-OC-125 conjugate has high affinity and specificity for proliferating malignant cells from human ovarian tumors. The results demonstrate that the DNR-OC-125 conjugate retains the specific binding to CA-125 antigenic sites characteristic of the OC-125 monoclonal antibody moiety. The DNR-OC-125 conjugate selectively binds to CA-125 antigen-positive ovarian cancerous tissue in both cryostat and paraffin-embedded tissue sections. This is consistent with the earlier in vitro data from dividing populations of two human ovarian cancer cell lines that revealed retention by the DNR-OC-125 conjugate of both the specificity due to OC-125 and the cytotoxicity of daunorubicin. The present immunofluorescence studies in the DNR-OC-125 conjugate is tested on human ovarian serous tumors indicate that the OC-125 monoclonal antibody can indeed serve as a cancer-targeting carrier for daunorubicin and its analogs.

In vitro analysis of the anticancer potential of tumor necrosis factor in combination with cisplatin

We have recently shown that cisplatin increases the natural cytotoxic (NC) cell-mediated lysis of a variety of human adenocarcinoma cell lines that are resistant to cisplatin or NC activity alone. Because NC lysis is mediated by tumor necrosis factor alpha (TNF) bound to the surface of NC effector cells, we analyzed the ability of TNF in combination with cisplatin to increase the lysis of tumor cells. The in vitro anticancer potential of the combination of TNF and cisplatin was determined for both dividing and nondividing populations of two human ovarian carcinoma cell lines, SK-OV-3 and OVCAR-3. Nondividing SK-OV-3 and OVCAR-3 cells are resistant to cisplatin and TNF when used as single agents. Dividing OVCAR-3 cells are approximately two times more sensitive to TNF than dividing SK-OV-3 cells, whereas dividing SK-OV-3 cells are approximately ten times more sensitive to cisplatin than dividing OVCAR-3 cells. TNF at 1000 units/ml in the presence of clinically low concentrations of cisplatin (0.6-0.25 micrograms/ml) increased the lysis of dividing OVCAR-3 cells above the value expected for the sum lysis mediated by cisplatin alone and lysis mediated by TNF alone. Similar results were obtained with dividing populations of the SK-OV-3 cell line. The combination of cisplatin and TNF did not increase the lysis of the nondividing populations of either cell line. The increased lysis of tumor cells combined with the maintenance of specificity for only dividing cells indicates that the combination of cisplatin and TNF may be useful for the treatment of tumors that are resistant to either cisplatin or TNF.