Sukaina Rashid

DNA Mismatch Repair and Oxidative DNA Damage: Implications for Cancer Biology and Treatment

Many components of the cell, including lipids, proteins and both nuclear and mitochondrial DNA, are vulnerable to deleterious modifications caused by reactive oxygen species. If not repaired, oxidative DNA damage can lead to disease-causing mutations, such as in cancer. Base excision repair and nucleotide excision repair are the two DNA repair pathways believed to orchestrate the removal of oxidative lesions. However, recent findings suggest that the mismatch repair pathway may also be important for the response to oxidative DNA damage. This is particularly relevant in cancer where mismatch repair genes are frequently mutated or epigenetically silenced. In this review we explore how the regulation of oxidative DNA damage by mismatch repair proteins may impact on carcinogenesis. We discuss recent studies that identify potential new treatments for mismatch repair deficient tumours, which exploit this non-canonical role of mismatch repair using synthetic lethal targeting.

Carbonic Anhydrase 9 Expression Increases with Vascular Endothelial Growth Factor–Targeted Therapy and Is Predictive of Outcome in Metastatic Clear Cell Renal Cancer

Background There is a lack of biomarkers to predict outcome with targeted therapy in metastatic clear cell renal cancer (mccRCC). This may be because dynamic molecular changes occur with therapy. Objective To explore if dynamic, targeted-therapy-driven molecular changes correlate with mccRCC outcome. Design, setting, and participants Multiple frozen samples from primary tumours were taken from sunitinib-naïve (n = 22) and sunitinib-treated mccRCC patients (n = 23) for protein analysis. A cohort (n = 86) of paired, untreated and sunitinib/pazopanib-treated mccRCC samples was used for validation. Array comparative genomic hybridisation (CGH) analysis and RNA interference (RNAi) was used to support the findings. Intervention Three cycles of sunitinib 50 mg (4 wk on, 2 wk off). Outcome measurements and statistical analysis Reverse phase protein arrays (training set) and immunofluorescence automated quantitative analysis (validation set) assessed protein expression. Results and limitations Differential expression between sunitinib-naïve and treated samples was seen in 30 of 55 proteins (p < 0.05 for each). The proteins B-cell CLL/lymphoma 2 (BCL2), mutL homolog 1 (MLH1), carbonic anhydrase 9 (CA9), and mechanistic target of rapamycin (mTOR) (serine/threonine kinase) had both increased intratumoural variance and significant differential expression with therapy. The validation cohort confirmed increased CA9 expression with therapy. Multivariate analysis showed high CA9 expression after treatment was associated with longer survival (hazard ratio: 0.48; 95% confidence interval, 0.26–0.87; p = 0.02). Array CGH profiles revealed sunitinib was associated with significant CA9 region loss. RNAi CA9 silencing in two cell lines inhibited the antiproliferative effects of sunitinib. Shortcomings of the study include selection of a specific protein for analysis, and the specific time points at which the treated tissue was analysed. Conclusions CA9 levels increase with targeted therapy in mccRCC. Lower CA9 levels are associated with a poor prognosis and possible resistance, as indicated by the validation cohort. Patient summary Drug treatment of advanced kidney cancer alters molecular markers of treatment resistance. Measuring carbonic anhydrase 9 levels may be helpful in determining which patients benefit from therapy.

An indirect comparison of the toxicity of sunitinib and pazopanib in metastatic clear cell renal cancer

BACKGROUND Both sunitinib and pazopanib are widely used as first line therapy in metastatic renal cancer (mRCC). The efficacy of these agents appears similar but they may have distinct toxicity profiles. In this study we compare the severity of symptomatic and asymptomatic toxicity associated with sunitinib and pazopanib. METHODS Two sequential prospective single arm phase II studies investigated either 12 weeks of sunitinib (n=43) or pazopanib (n=34) prior to nephrectomy in untreated mRCC. Toxicity was defined as either symptomatic (hand and foot syndrome, mucositis, nausea, fatigue, diarrhoea, oedema, headache, pain, anorexia and change in taste) or asymptomatic (liver toxicity or haematological toxicity). Pazopanib (800 mg once daily (OD)) and sunitinib (50 mg 4/2) were given. Regular Common Toxicity Criteria (CTC) toxicity assessment was performed during the first 12 weeks of therapy. RESULTS There was no significant difference in the overall number of toxic events (grade 1-4) for sunitinib and pazopanib (mean number of toxic events/patients: 1.97 versus 1.96: p>0.05). Increased grade 2-4 symptomatic toxicity events occurred with sunitinib (hazard ratio (HR) 1.67 [95% confidence interval (CI): 1.11-2.56] p<0.03). Sunitinib was associated with an increased grade 2-4 mucositis (16% versus 0% p=0.02) and fatigue (42% versus 15% p=0.01). Pazopanib was associated with more frequent grade 1 diarrhoea (39% versus 12%: p=0.03). Dose reductions for symptomatic toxicity occurred more frequently with sunitinib (26% versus 6% p<0.05). There was no difference in the occurrence of asymptomatic toxicity. CONCLUSION This indirect analysis suggests sunitinib and pazopanib have distinct toxicity profiles which may help guide patients choice. Further comparative data from randomised trials are awaited.

Carboplatin AUC 10 for IGCCCG good prognosis metastatic seminoma

Abstract Objective. Metastatic seminoma is a highly curable disease. Standard treatment comprises of combination chemotherapy. The short- and long-term toxicities of this treatment are increasingly recognised and the possibility of over treatment in such a curable disease should be considered. We have therefore assessed the use of single agent carboplatin at a dose of AUC 10 in patients with good prognosis metastatic seminoma. Materials and methods. Patients with good prognosis metastatic seminoma treated with carboplatin (AUC 10) were identified at our institution and affiliated institutions. Treatment was three weekly for a total of three or four cycles. Outcome and toxicities were analysed. Results. With a median follow-up of 36 months, 61 patients in total were treated with carboplatin AUC 10, all good prognosis by the IGCCCG criteria. Forty-eight percent had stage IIA/IIB disease and 52% had greater than stage IIB disease. Thirty-one patients (51%) had a complete response following treatment. Three-year survival was 96.3% with a three-year progression free survival of 93.2%. The main treatment toxicity was haematological with 46% having grade 3, 24% having grade 4 neutropenia and 54% experiencing grade 3/4 thrombocytopenia. There were no treatment related deaths. Conclusion. Single agent carboplatin at a dose of AUC 10 is an effective treatment for good prognosis metastatic seminoma. The outcome compares favourably to previously published outcomes of combination chemotherapy. Although haematological toxicity is a concern, single agent carboplatin treatment for good prognosis metastatic seminoma could be considered a treatment option and is associated with less toxicity than combination regimens currently used.

Abstract 4713: Targeting the mitochondria for the treatment of MLH1-deficient disease

The DNA Mismatch repair (MMR) pathway is responsible for the repair of base-base mismatches and insertion/deletion loops that arise during DNA replication. MMR deficiency is currently estimated to be present in 15-17% of colorectal cancer cases and 30% of endometrial cancers. MLH1 is one of the key proteins involved in the MMR pathway. MMR deficient tumours are often resistant to standard chemotherapies, therefore there is a critical need to identify new therapeutic strategies to treat MMR deficient disease. We have performed synthetic lethal compound and RNAi screens to identify potential therapeutic targets for the treatment of MLH1 deficient tumours. Strikingly, upon analysis, a number of the hit compounds have been shown to target mitochondrial function. Our previous work has shown that MLH1 can localize to the mitochondria and silencing of the mitochondrial genes, POLG and PINK1 are synthetically lethal with MLH1 deficiency. We demonstrate that MLH1 deficient tumours are synthetically lethal with mitochondrial targeted agents (Menadione, Parthenolide) which are known to induce reactive oxygen species and cause oxidative stress as one of their main mechanisms of action. Upon functional analysis we show that loss of MLH1 is associated with a reduction in Complex I activity, reduced basal oxygen consumption rate, reduced spare respiratory capacity and reactive mitochondrial biogenesis (upregulation of pgc1β), suggesting that mitochondrial function is deregulated upon loss of MLH1. Taken together, our results thus far suggest that targeting the mitochondria may be a potential therapeutic strategy for the treatment of MLH1 deficient disease. Citation Format: Sukaina Rashid, Gemma Bridge, Zhi Yao, Gyorgy Szabadkai, Sarah A. Martin. Targeting the mitochondria for the treatment of MLH1-deficient disease. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4713. doi:10.1158/1538-7445.AM2015-4713