Resistance gene expression determines the in vitro chemosensitivity of non-small cell lung cancer (NSCLC).

BACKGROUND: NSCLC exhibits considerable heterogeneity in its sensitivity to chemotherapy and similar heterogeneity is noted in vitro in a variety of model systems. This study has tested the hypothesis that the molecular basis of the observed in vitro chemosensitivity of NSCLC lies within the known resistance mechanisms inherent to these patients' tumors. METHODS: The chemosensitivity of a series of 49 NSCLC tumors was assessed using the ATP-based tumor chemosensitivity assay (ATP-TCA) and compared with quantitative expression of resistance genes measured by RT-PCR in a Taqman Array following extraction of RNA from formalin-fixed paraffin-embedded (FFPE) tissue. RESULTS: There was considerable heterogeneity between tumors within the ATP-TCA, and while this showed no direct correlation with individual gene expression, there was strong correlation of multi-gene signatures for many of the single agents and combinations tested. For instance, docetaxel activity showed some dependence on the expression of drug pumps, while cisplatin activity showed some dependence on DNA repair enzyme expression. Activity of both drugs was influenced more strongly still by the expression of anti- and pro-apoptotic genes by the tumor for both docetaxel and cisplatin. The doublet combinations of cisplatin with gemcitabine and cisplatin with docetaxel showed gene expression signatures incorporating resistance mechanisms for both agents. CONCLUSION: Genes predicted to be involved in known mechanisms drug sensitivity and resistance correlate well with in vitro chemosensitivity and may allow the definition of predictive signatures to guide individualized chemotherapy in lung cancer.

Cancer cell adaptation to chemotherapy.

BACKGROUND: Tumor resistance to chemotherapy may be present at the beginning of treatment, develop during treatment, or become apparent on re-treatment of the patient. The mechanisms involved are usually inferred from experiments with cell lines, as studies in tumor-derived cells are difficult. Studies of human tumors show that cells adapt to chemotherapy, but it has been largely assumed that clonal selection leads to the resistance of recurrent tumors. METHODS: Cells derived from 47 tumors of breast, ovarian, esophageal, and colorectal origin and 16 paired esophageal biopsies were exposed to anticancer agents (cisplatin; 5-fluorouracil; epirubicin; doxorubicin; paclitaxel; irinotecan and topotecan) in short-term cell culture (6 days). Real-time quantitative PCR was used to measure up- or down-regulation of 16 different resistance/target genes, and when tissue was available, immunohistochemistry was used to assess the protein levels. RESULTS: In 8/16 paired esophageal biopsies, there was an increase in the expression of multi-drug resistance gene 1 (MDR1) following epirubicin + cisplatin + 5-fluorouracil (ECF) chemotherapy and this was accompanied by increased expression of the MDR-1 encoded protein, P-gp. Following exposure to doxorubicin in vitro, 13/14 breast carcinomas and 9/12 ovarian carcinomas showed >2-fold down-regulation of topoisomerase IIalpha (TOPOIIalpha). Exposure to topotecan in vitro, resulted in >4-fold down-regulation of TOPOIIalpha in 6/7 colorectal tumors and 8/10 ovarian tumors. CONCLUSION: This study suggests that up-regulation of resistance genes or down-regulation in target genes may occur rapidly in human solid tumors, within days of the start of treatment, and that similar changes are present in pre- and post-chemotherapy biopsy material. The molecular processes used by each tumor appear to be linked to the drug used, but there is also heterogeneity between individual tumors, even those with the same histological type, in the pattern and magnitude of response to the same drugs. Adaptation to chemotherapy may explain why prediction of resistance mechanisms is difficult on the basis of tumor type alone or individual markers, and suggests that more complex predictive methods are required to improve the response rates to chemotherapy.

Chemosensitization of solid tumors by modulation of resistance mechanisms.

The number of drugs available for chemotherapy is growing exponentially, and this trend looks set to continue. Chemosensitization strategies use the administration of one drug or agent to render cancer cells more susceptible to a second agent. Modulation of resistance mechanisms due to xenobiotic membrane pumps such as the multidrug resistant proteins, MDR1/P-glycoprotein or MRP is feasible and a number of new agents have been produced to inhibit drug efflux resulting from expression of these molecules. However, tumor cells may express or upregulate more than one such molecule at one time, and this approach is unlikely to benefit every patient. Detoxification mechanisms mediated by glutathione conjugation or metallothionein are also responsible for resistance--the former has been linked to MRP-mediated resistance. Again, modulation is possible but may increase the toxicity of drugs to normal tissues and an increased therapeutic index is not guaranteed. Tumors exposed to DNA damaging agents often upregulate DNA repair mechanisms and this contributes to resistance. Different pathways perform the repair of different forms of DNA damage, and it is difficult to inhibit all of these. Nevertheless, inhibition of DNA repair can re-sensitize tumors to chemotherapy and is increasingly exploited. One of the most successful and widely used approaches is to combine gemcitabine with an alkylating or platinating agent. While gemcitabine may inhibit DNA polymerases directly, this cytidine analog is also likely to be incorporated by DNA repair leading to activity against non-cycling cells, which form the majority of the neoplastic cell population in most solid tumors. Oncologists should take account of potential resistance mechanisms when treating patients: it is often feasible to design combinations with old or new drugs which exploit these apparent weaknesses to the patient's advantage.

Chemosensitization of solid tumor cells by alteration of their susceptibility to apoptosis.

Chemosensitization strategies use the administration of one drug or agent to render cancer cells more susceptible to a second agent. Usually this involves enhanced drug metabolism, improvement of drug uptake or blockage of resistance mechanisms. Alteration of the susceptibility of cancer cells to apoptosis, the process of individual cell death by which many chemotherapeutic drugs act, shows particular promise for therapy in the future, and is the focus of this review. The dependence of cancer cells on non-neoplastic cells to form solid tumors allows anti-angiogenic therapy to be used in conjunction with chemotherapy to increase the therapeutic index. Chemosensitization strategies are set to become increasingly important in cancer therapy, allowing rational design of synergistic drug combinations at an earlier stage in drug development.