http://hdl.handle.net/2123/2740 Search the Channel search http://ses.library.usyd.edu.au/simple-search http://hdl.handle.net/2123/5687 Title: Regrowth resistance: low-level platinum resistance mediated by rapid recovery from platinum-induced cell-cycle arrest<br/><br/>Authors: Stordal, Britta; Davey, Ross<br/><br/>Abstract: The H69CIS200 and H69OX400 cell lines are novel models of low-level platinum drug resistance developed from H69 human small-cell lung cancer cells with eight 4-day treatments of 200 ng/ml cisplatin and 400 ng/ml oxaliplatin, respectively. A recovery period was given between treatments to emulate the cycles of chemotherapy given in the clinic. The resistant cell lines were approximately twofold resistant to cisplatin and oxaliplatin, and were cross-resistant to both drugs. Platinum resistance was not associated with increased cellular glutathione, decreased accumulation of platinum or increased DNA repair capacity. The H69 platinum sensitive cells entered a lengthy 3-week growth arrest in response to low-level cisplatin or oxaliplatin treatment. This is an example of the coordinated response between the cell cycle and DNA repair. In contrast, the H69CIS200 and H69OX400 cells have an alteration in the cell cycle allowing them to rapidly proliferate post drug treatment. The resistant cell lines also have many chromosomal rearrangements most of which are not associated with the resistant phenotype, suggesting an increase in the genomic instability in the resistant cell lines. We hypothesized that there was a lack of coordination between the cell cycle and DNA repair in the resistant cell lines allowing proliferation in the presence of DNA damage which has created an increase in genomic instability. The H69 cells and resistant cell lines have mutant p53 and consequently decrease the expression of p21 in response to platinum drug treatment; promoting progression of the cell cycle instead of increasing p21 to maintain the arrest. A decrease in ERCC1 protein expression and an increase in RAD51B foci activity were observed with the platinum-induced cell-cycle arrest and did not correlate with resistance or altered DNA repair capacity. These changes may, in part, be mediating and maintaining the cell-cycle arrest in place of p21.The rapidly proliferating resistant cells have restored the levels of both these proteins to their levels in untreated cells. We use the term “regrowth resistance” to describe this low-level platinum resistance where cells survive treatment through increased proliferation. Regrowth resistance may play a role in the onset of clinical resistance. http://hdl.handle.net/2123/5686 Title: Treating cisplatin-resistant cancer: a systematic analysis of oxaliplatin or paclitaxel salvage chemotherapy.<br/><br/>Authors: Stordal, Britta; Pavlakis, Nick; Davey, Ross<br/><br/>Abstract: Objective: To examine the pre-clinical and clinical evidence for the use of oxaliplatinor paclitaxel salvage chemotherapy in patients with cisplatin-resistant cancer.Methods: Medline was searched for 1) Cell models of acquired resistance reportingcisplatin, oxaliplatin and paclitaxel sensitivities and 2) Clinical trials of single agentoxaliplatin or paclitaxel salvage therapy for cisplatin/carboplatin-resistant ovariancancer. Results: Oxaliplatin - Oxaliplatin is widely regarded as being active incisplatin-resistant cancer. In contrast, data in cell models suggests that there is crossresistancebetween cisplatin and oxaliplatin in cellular models with resistance levelswhich reflect clinical resistance (<10 fold). Oxaliplatin as a single agent had a poorresponse rate in patients with cisplatin-resistant ovarian cancer (8%, n=91).Oxaliplatin performed better in combination with other agents for the treatment ofplatinum-resistant cancer suggesting that the benefit of oxaliplatin may lie in its morefavourable toxicity and ability to be combined with other drugs rather than anunderlying activity in cisplatin resistance. Oxaliplatin therefore should not beconsidered broadly active in cisplatin-resistant cancer. Paclitaxel – Cellular data2suggests that paclitaxel is active in cisplatin-resistant cancer. 68.1% of cisplatinresistantcells were sensitive to paclitaxel. Paclitaxel as a single agent had a responserate of 22% in patients with platinum-resistant ovarian cancer (n = 1918), a significantincrease from the response of oxaliplatin (p<0.01). Paclitaxel-resistant cells were alsosensitive to cisplatin, suggesting that alternating between agents may be beneficial.Studies of single agent paclitaxel in platinum-resistant ovarian cancer where patientshad previously received paclitaxel had an improved response rate of 35.3% n=232(p<0.01), suggesting that pre-treatment with paclitaxel improves the response ofsalvage paclitaxel therapy.Conclusions: Cellular models reflect the resistance observed in the clinic as the crossresistant agent oxaliplatin has a lower response rate compared to the non-crossresistant agent paclitaxel in cisplatin-resistant ovarian cancer. Alternating therapywith cisplatin and paclitaxel may therefore lead to an improved response rate inovarian cancer. http://hdl.handle.net/2123/5685 Title: ERCC1 expression and RAD51B activity correlate with cell cycle response to platinum drug treatment not DNA repair<br/><br/>Authors: Stordal, Britta; Davey, Ross<br/><br/>Abstract: Background: The H69CIS200 and H69OX400 cell lines are novel models of low-level platinum-drug resistance. Resistance was not associated with increased cellularglutathione or decreased accumulation of platinum, rather the resistant cell lines havea cell cycle alteration allowing them to rapidly proliferate post drug treatment.Results: A decrease in ERCC1 protein expression and an increase in RAD51B fociactivity was observed in association with the platinum induced cell cycle arrest butthese changes did not correlate with resistance or altered DNA repair capacity. TheH69 cells and resistant cell lines have a p53 mutation and consequently decreaseexpression of p21 in response to platinum drug treatment, promoting progression ofthe cell cycle instead of increasing p21 to maintain the arrest.Conclusion: Decreased ERCC1 protein and increased RAD51B foci may in part bemediating the maintenance of the cell cycle arrest in the sensitive cells. Resistance inthe H69CIS200 and H69OX400 cells may therefore involve the regulation of ERCC1and RAD51B independent of their roles in DNA repair. The novel mechanism ofplatinum resistance in the H69CIS200 and H69OX400 cells demonstrates themultifactorial nature of platinum resistance which can occur independently ofalterations in DNA repair capacity and changes in ERCC1. http://hdl.handle.net/2123/5684 Title: A 39 kDa fragment of endogenous ASK1 suggests specific cleavage not degradation by the proteasome<br/><br/>Authors: Stordal, Britta; Davey, Ross<br/><br/>Abstract: Transfected human ASK1 produces a 150kDa protein. However, we have detectedendogenous ASK1 predominantly as 39kDa and 50kDa C-terminal and 75kDa and110kDa N-terminal fragments in a panel of non-transfected cancer cell lines and HUVECendothelial cells. This suggests that in non-apoptotic cells, endogenous ASK1 protein isnormally cleaved at a number of specific sites, some of which are in the kinase domain.Transfected ASK1 protein is known to be degraded by the proteasome. In contrast, thecleavage of endogenous ASK1 is independent of the proteasome as treatment with theproteasome inhibitor, lactacystin did not inhibit cleavage. Cisplatin treatment decreasedthe amount of 39kDa C-terminal ASK1 fragment in mutant p53 cell lines suggesting adecrease in cleavage associated with apoptosis. Transfected ASK1 may therefore notaccurately reflect the role of endogenous ASK1.