No description available.

No description available.

Introduction: Most cancers show heterogeneity of response to chemotherapy. This may be due in part to the differential expression of drug resistance proteins and the molecular targets of the drugs concerned. Methods: An ex vivo ATP-based Tumour Chemosensitivity Assay (ATP-TCA), immunohistochemistry and quantitative RT-PCR have been used to assess the chemosensitivity and resistance of a variety of solid tumours and cell lines. Results: (a) Melanoma cell lines showed higher chemosensitivity than tumour-derived cells, partially reversible by lowering the serum concentration, and hence the proliferation rate of the cells. (b) Studies of retinoblastoma samples confirmed that this malignancy is susceptible to cytotoxic drugs of all types, though multidrug resistance may occur in some cases. (c) The ATP-TCA was used to study the activity of high-dose doxorubicin in combination with other cytotoxic agents in ovarian adenocarcinoma samples. The combination of liposomal doxorubicin + vinorelbine was selected for further development. (d) A number of experimental drugs with varying sensitivity to resistance mechanisms were also assessed. One drug, XR5944, has entered phase I/II clinical trials during the course of this project, and the data have provided clinical indications. (e) An inhibitor of multi-drug resistance, tariquidar, has been tested in combination with doxorubicin, vinorelbine or paclitaxel, and has been shown to reverse this resistance. (f) Molecular studies have determined the expression of topoisomerases and drug transporters in tumour cells before and after exposure to chemotherapeutic agents. P-gp expression has been found to be a determinant of sensitivity to a certain number of drugs. Conclusion: The results suggest that drug resistance contributes to heterogeneity of chemosensitivity in many solid tumour types, as well as other mechanisms. Reversal of such resistance may benefit a subset of patients undergoing chemotherapy.

No description available.

No description available.

No description available.

Telomere shortening is a major mechanism to induce telomere uncapping and thus to signal growth arrest and/ or apoptosis and can be caused by different mechanisms, one of which is damage to DNA, to which telomeres appear to be particularly sensitive. Contradictory data exists on the relationship between conventionally used chemotherapeutic drugs and the telomere/ telomerase complex. The aim of the work described in this thesis was to determine whether or not damage to telomeres played a significant role in the cytotoxic action of the anti-cancer drugs cisplatin and etoposide. Two cell lines were used with either short (neuroblastorna cell line SHSY5Y) or long (lymphoblastic T cell line 1301) telomeres. Cytotoxic effects of the drugs were assessed by growth inhibition assays and measurement of apoptosis and cell cycle progression by flow cytometry. Etoposide caused readily detectable DNA strand breakage and led to formation of nuclear foci of phosphorylated histone y-H2A. X. Cisplatin treatment did not induce strand breaks after initial drug exposure but strand breaks and DNA damage foci were detected after further incubation. For cells with either long or short telomeres, no detectable changes in total telomere length or overhang length were observed before apoptosis became manifest. Preferential occurrences of single strand breaks in the G-rich strand of telorneres were not found. Through the development of a dual staining method it was established that drug-induced histone H2A. X foci did not colocalise to the telomeres. Telomerase was transiently activated by lower concentrations of etoposide and its activity decreased only after onset of apoptosis. Taken together, the results show no indication that telorneres and/ or telomeric damage play any preferential role as signal transducers towards apoptosis and/ or growth arrest in either of these cell lines. Also, the protective function of telornerase &-I - seems to be telomere independent. The data are consistent with a model of druginduced growth arrest and apoptosis being triggered by damage elsewhere in the genome.

P ARP-l inhibitors enhance DNA topoisomerase I (Topo I) poison-induced cytotoxicity and anti-tumour activity in vitro and in vivo but the underlying mechanism has not been defined. Two hypotheses have been proposed to explain this a) PARP-I modulates topo I activity via poly(ADP-ribosylation), or b) P ARP-l participates in the repair of topo 1- induced DNA lesions. To explore these mechanisms we have investigated the cellular effects of a novel potent P ARP-l inhibitor, AG 14361 (Ki < 5 nM), in combination with the topo I poisons, camptothecin and topotecan. PARP-l null mouse embryonic fibroblasts (MEFs) were 3-fold more sensitive to topotecan than P ARP-l wild type MEFs. AG 14361 significantly enhanced topotecaninduced growth inhibition by 3-fold in PARP-l wild-type cells but not PARP-l null cells. This confirms that P ARP-l activity promotes survival after topo I poison-induced cytotoxicity and the cellular effects of AG 14361 are due to P ARP-l inhibition. AG 14316 also increased camptothecin-induced growth inhibition in human K562 cells ~2-fold. AG14361 did not affect topo I-DNA cleavable complexes or topo I relaxation activity. In contrast, AG 14361 increased camptothecin-induced DNA strand breaks by 20% and significantly retarded DNA repair following camptothecin removal, (620/0 inhibition of repair 10 mins). These data indicate a role for PARP-l in the repair of topo I poison-mediated damage. The repair pathways by which P ARP-l acts to repair this damage was investigated using repair-deficient cells. AG 14361 significantly potentiated the cytotoxicity of camptothecin in AA8 repair-proficient and V3 nonhomologous end joining-deficient cells, but not the irs 1 SF homologous recombinationdeficient or EM9 base excision repair-deficient cells. AG 14361 also failed to retard the repair of camptothecin-induced DNA damage in EM9 cells. This suggests that P ARP-l may act via BER and possibly HR to repair topo I poison-mediated DNA damage.

No description available.

No description available.