Surgery (Austin & Northern Health) - Research Publications
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ItemMetformin may offer no protective effect in men undergoing external beam radiation therapy for prostate cancer(WILEY, 2019-05)OBJECTIVES: To assess whether metformin reduces radio-resistance and increases survival in men undergoing external beam radiation therapy (EBRT) for prostate cancer (PCa), and to determine its effect on hypoxia inducible factor 1-α (HIF1α). PATIENTS AND METHODS: All patients treated with curative intent with EBRT for PCa at a major cancer centre between 2000 and 2007 were included in this study. The outcome measures of time to biochemical failure (BF), metastasis, PCa-specific mortality and overall survival (OS) were analysed in those taking metformin vs those not, using competing risk and Cox regression models. To determine metformin's effect on HIF1α expression and survival in vitro, PC3 cells with high basal HIF1α levels were subjected to increasing doses of metformin after H2 O2 -induced oxidative stress. RESULTS: A total of 2055 eligible cases, including 113 who were on metformin, were identified, with a median follow-up of 95.7 months. There were no differences in age, initial prostate-specific antigen level, Gleason score, T-stage, D'Amico risk class or duration of androgen deprivation therapy (ADT) between patients who were or were not on metformin. Treatment with metformin did not result in any apparent improvement in time to BF, time to metastasis detection or OS, but there was a 1.5-fold increase in PCa-specific deaths (P = 0.045) in patients on metformin and ADT when adjusted for cancer risk and comorbidities. When comparing patients on high-dose metformin (>1 g/d) with those on low-dose metformin (≤1 g), there was no difference in either time to metastases or time to BF. In vitro metformin at a high concentration of 100 μM did not reduce HIF1α expression, nor did metformin affect the PC3 cell survival when exposed to oxidative stress (H2 O2 ). CONCLUSIONS: No association was found between the use of metformin and time to metastasis detection, time to BF or OS in patients undergoing radiation therapy with or without ADT for PCa. In vitro, low therapeutic concentrations of metformin had no effect on HIF1α, and this observation could explain the conflicting evidence for the effectiveness of metformin in men undergoing EBRT for PCa. Higher, more toxic doses of metformin may be required to inhibit the mammalian target of rapamycin-HIF1α pathway in this patient group.
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ItemTargeting HIF-1α to Prevent Renal Ischemia-Reperfusion Injury: Does It Work?(Hindawi Limited, 2018)Partial nephrectomy (open or minimally invasive) usually requires temporary renal arterial occlusion to limit intraoperative bleeding and improve access to intrarenal structures. This is a time-critical step due to the critical ischemia period of renal tissue. Prolonged renal ischemia may lead to irreversible nephron damage in the remaining tissue and, ultimately, chronic kidney disease. This is potentiated by the incompletely understood ischemia-reperfusion injury (IRI). A key mechanism in IRI prevention appears to be the upregulation of an intracellular transcription protein, Hypoxia-Inducible Factor (HIF). HIF mediates metabolic adaptation, angiogenesis, erythropoiesis, cell growth, survival, and apoptosis. Upregulating HIF-1α via ischemic preconditioning (IPC) or drugs that simulate hypoxia (hypoxia-mimetics) has been investigated as a method to reduce IRI. While many promising chemical agents have been trialed for the prevention of IRI in small animal studies, all have failed in human trials. The aim of this review is to highlight the techniques and drugs that target HIF-1α and ameliorate IRI associated with renal ischemia. Developing a technique or drug that could reduce the risk of acute kidney injury associated with renal IRI would have an immediate worldwide impact on multisystem surgeries that would otherwise risk ischemic tissue injury.
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ItemCorrigendum to "Targeting HIF-1α to Prevent Renal Ischemia-Reperfusion Injury: Does It Work?".(Hindawi Limited, 2019)[This corrects the article DOI: 10.1155/2018/9852791.].
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ItemThe effects of nonspecific HIF1α inhibitors on development of castrate resistance and metastases in prostate cancer(WILEY-BLACKWELL, 2014-04)Expression of hypoxia-inducible factor (HIF)1α increases the risk of castrate-resistant prostate cancer (CRPC) and metastases in patients on androgen deprivation therapy (ADT) for prostate cancer (PC). We aimed to investigate the effects of nonspecific HIF1α inhibitors (Digoxin, metformin, and angiotensin-2 receptor blockers) on development of CRPC and metastases while on ADT. A retrospective review of prospectively collected medical records was conducted of all men who had continuous ADT as first-line therapy for CRPC at the Austin Hospital from 1983 to 2011. Association between HIF1α inhibitor medications and time to develop CRPC was investigated using actuarial statistics. Ninety-eight patients meeting the criteria were identified. Eighteen patients (21.4%) were treated with the nonspecific HIF1α inhibitors. Both groups had similar characteristics, apart from patients on HIF1α inhibitors being older (70 years vs. 63.9 years). The median CRPC-free survival was longer in men using HIF1α inhibitors compared to those not on inhibitors (6.7 years vs. 2.7 years, P = 0.01) and there was a 71% reduction in the risk of developing CRPC (HR 0.29 [95% CI 0.10-0.78] P = 0.02) after adjustment for Gleason score, age, and prostate-specific antigen (PSA). The median metastasis-free survival in men on HIF1α inhibitors was also significantly longer compared to those on no inhibitors (5.1 years vs. 2.6 years, P = 0.01) with an 81% reduction in the risk of developing metastases (HR 0.19 [CI 0.05-0.76] P = 0.02) after adjustment for Gleason score, age, and PSA. Nonspecific HIF1α inhibitors appear to increase the progression-free survival and reduce the risk of developing CRPC and metastases in patients on continuous ADT.
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ItemProtective effect of zinc preconditioning against renal ischemia reperfusion injury is dose dependent(PUBLIC LIBRARY SCIENCE, 2017-07-07)OBJECTIVES: Ischemia-reperfusion injury (IRI) is a major cause of acute kidney injury and chronic kidney disease. Two promising preconditioning methods for the kidney, intermittent arterial clamping (IC) and treatment with the hypoxia mimetic cobalt chloride, have never been directly compared. Furthermore, the protective efficacy of the chemically related transition metal Zn2+ against renal IRI is unclear. Although Co2+ ions have been shown to protect the kidney via hypoxia inducible factor (HIF), the effect of Zn2+ ions on the induction of HIF1α, HIF2α and HIF3α has not been investigated previously. MATERIALS AND METHODS: The efficacy of different preconditioning techniques was assessed using a Sprague-Dawley rat model of renal IRI. Induction of HIF proteins following Zn2+ treatment of the human kidney cell lines HK-2 (immortalized normal tubular cells) and ACHN (renal cancer) was measured using Western Blot. RESULTS: Following 40 minutes of renal ischemia in rats, cobalt preconditioning offered greater protection against renal IRI than IC as evidenced by lower peak serum creatinine and urea concentrations. ZnCl2 (10 mg/kg) significantly lowered the creatinine and urea concentrations compared to saline-treated control rats following a clinically relevant 60 minutes of ischemia. Zn2+ induced expression of HIF1α and HIF2α but not HIF3α in HK-2 and ACHN cells. CONCLUSION: ZnCl2 preconditioning protects against renal IRI in a dose-dependent manner. Further studies are warranted to determine the possible mechanisms involved, and to assess the benefit of ZnCl2 preconditioning for clinical applications.
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ItemZinc ion dyshomeostasis increases resistance of prostate cancer cells to oxidative stress via upregulation of HIF1α.(Impact Journals, 2018-02-02)Zinc ions (Zn2+) are known to influence cell survival and proliferation. However the homeostatic regulation of Zn2+ and their role in prostate cancer (PC) progression is poorly understood. Therefore the subcellular distribution and uptake of Zn2+ in PC cells were investigated. Inductively coupled plasma mass spectroscopy and fluorescent microscopy with the Zn2+-specific fluorescent probe FluoZin-3 were used to quantify total and free Zn2+, respectively, in the normal prostate epithelial cell line (PNT1A) and three human PC cell lines (PC3, DU145 and LNCaP). The effects of Zn2+ treatment on proliferation and survival were measured in vitro using MTT assays and in vivo using mouse xenografts. The ability of Zn2+ to protect against oxidative stress via a HIF1α-dependent mechanism was investigated using a HIF1α knock-down PC3 model. Our results demonstrate that the total Zn2+ concentration in normal PNT1A and PC cells is similar, but PC3 cells contain significantly higher free Zn2+ than PNT1A cells (p < 0.01). PNT1A cells can survive better in the presence of high concentrations of Zn2+ than PC3 cells. Exposure to 10 µM Zn2+ over 72 hours significantly reduces PC3 cell proliferation in vitro but not in vivo. Zn2+ increases PC3 cell survival up to 2.3-fold under oxidative stress, and this protective effect is not seen in PNT1A cells or in a HIF1α-KD PC3 cell model. A state of Zn2+ dyshomeostasis exists in PC. HIF1α is an integral component of a Zn2+-dependent protective mechanism present in PC3 cells. This pathway may be clinically significant through its contribution to castrate-resistant PC survival.
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ItemThe Role of Hypoxia-Inducible Factor 1α in Determining the Properties of Castrate-Resistant Prostate Cancers(PUBLIC LIBRARY SCIENCE, 2013-01-16)BACKGROUND: Castrate-resistant prostate cancer (CRPC) is a lethal condition in patients receiving androgen deprivation therapy for prostate cancer (PC). Despite numerous studies showing the expression of HIF1α protein under normoxia in PC cell lines, the role of this normoxic HIF1α expression in chemo-resistance and migration has not been investigated previously. As no method is currently available to determine which tumors will progress to CRPC, the role of HIF1α in PC and its potential for predicting the development of CRPC was also investigated. METHODS: The effect of HIF1α protein knockdown on chemo-resistance and migration of PC3 cells was assessed by cell counting and Transwell assays, respectively. Translation efficiency of HIF1α mRNA was determined in PC cells using a HIF1α 5'UTR-luciferase construct. Clinical outcomes were correlated following the staining of 100 prostate tumors for HIF1α expression. RESULTS: The CRPC-like cell lines (PC3 and DU145) expressed more HIF1α protein than an androgen sensitive cell line (LNCaP). Migration rate and chemo-resistance were higher in the PC3 cells and both were decreased when HIF1α expression was reduced. Increased translation of HIF1α mRNA may be responsible for HIF1α overexpression in PC3 cells. Patients whose tumors expressed HIF1α had significantly decreased metastasis-free survival and the patients who were on androgen-deprivation therapy had decreased CRPC-free survival on Kaplan-Meier analysis. On multivariate analysis HIF1α was an independent risk factor for progression to metastatic PC (Hazard ratio (HR) 9.8, p = 0.017) and development of CRPC (HR 10.0, p = 0.021) in patients on androgen-deprivation therapy. Notably the tumors which did not express HIF1α did not metastasize or develop CRPC. CONCLUSIONS: HIF1α is likely to contribute to metastasis and chemo-resistance of CRPC and targeted reduction of HIF1α may increase the responsiveness of CRPCs to chemotherapy. Expression of HIF1α may be a useful screening tool for development of CRPC.