Stopsack, Konrad H.

5038 Background: Platinum-based chemotherapy has shown palliative and radiographic benefit in small unselected studies of metastatic castration-resistant prostate cancer (mCRPC). Alterations in DNA damage repair genes (DDRmut), which occur in ~25% of patients with mCRPC, may sensitize to platinum-based chemotherapy, and may aid in the selection of patients for this therapy. We sought to evaluate the efficacy of platinum-based chemotherapy in DDRmut mCRPC. Methods: We performed a retrospective review of patients with prostate cancer who underwent tumor genomic profiling and received platinum-based chemotherapy. Deleterious alterations in a panel including BRCA2, BRCA1, ATM, FANCA, CDK12 or PALB2 were classified as DDRmut. Absence of deleterious alterations in those genes was classified as DDRwt. MSI-H cases were excluded from analysis. Electronic charts, PSA values, and scans were reviewed to assess for outcomes. Results: From October 2013 to July 2018, 109 patients with mCRPC received platinum-based chemotherapy. 64/109 had prior taxane progression and were PARP inhibitor (PARPi) naïve at the time of platinum-based chemotherapy. DDRmut was found in 16/64 (25%) of patients ( BRCA2, n = 6; ATM, n = 2; CDK12, n = 4; FANCA, n = 4; PALB2, n = 1). Visceral metastasis occurred in 4/16 (25%) of DDRmut patients and in 22/48 (46%) of DDRwt patients. PSA50 responses were more common among DDRmut (8/15 evaluable = 53%, 95% CI, 30-75%) than among DDRwt patients (5/42 evaluable = 12%, 95% CI, 5-25%). Time on platinum-based chemotherapy tended to be longer in the DDRmut group (median 3.1 vs 1.8 months; HR 0.73, 95% CI 0.42-1.26). Of 8 DDRmut patients ( BRCA2, n = 6; BRCA1, n = 1; ATM, n = 2) who received platinum-based chemotherapy after progression on a PARPi, 3/7 evaluable patients (43%) had RECIST response or stable disease, and 2/7 evaluable patients (29%) had a PSA50 response. Of 4 patients with ATM deleterious mutations, none had a radiographic or PSA50 response to platinum-based chemotherapy. Conclusions: Platinum-based chemotherapy showed activity in DDRmut mCRPC patients before and after PARPi treatment.

Abstract Background: We recently discovered that mRNA expression of SQLE, coding for squalene monooxygenase, the second rate-limiting enzyme of cholesterol synthesis, is associated with lethality after prostate cancer diagnosis. Here, we investigate how expression of SQLE and other key regulators of cholesterol homeostasis, identified by prior mechanistic studies, aid risk prediction for lethal prostate cancer. Methods: The Health Professionals Follow-up Study and the Physicians' Health Study prostate cancer tissue cohorts collected tissue from prostatectomy or transurethral resection of the prostate at cancer diagnosis. Whole-transcriptome profiling was performed. The outcome of interest was lethal cancer defined as prostate cancer mortality or development of metastases in contrast to non-lethal cancer without evidence of metastases after at least eight years of follow up. Discrimination for prostate lethal cancer was assessed by comparing c-statistics using bootstrap resampling. Results: Combining both cohorts, 112 men had lethal prostate cancer; 290 men had non-lethal cancer. A prognostic model for lethal cancer including Gleason grade, pathologic stage, age, and year of diagnosis had a high c = 0.885; adding body mass index, smoking status, family history of prostate cancer, and diabetes diagnosis increased c to 0.889. A model containing only SQLE (linear) achieved c = 0.663. Adding SQLE to the fully adjusted model increased c to 0.903 (p = 0.027). None of the other cholesterol regulators ABCA1, ACAT1, LDLR, and SCARB1 improved discrimination. Conclusions: SQLE performs well as a single biomarker of prostate cancer lethality after primary therapy, in contrast to other markers of intratumoral cholesterol regulation. Improvements in prognostication are minimal when SQLE is added to a model that contains a centrally re-reviewed Gleason grade. Most importantly, SQLE may be an actionable, predictive biomarker of benefit from statin therapy, which addresses the cholesterol synthesis pathway regulated by SQLE. Citation Format: Konrad H. Stopsack, Travis A. Gerke, Lorelei A. Mucci, Jennifer R. Rider. Prostate cancer prognostication based on an actionable metabolic pathway. [abstract]. In: Proceedings of the AACR Special Conference: Improving Cancer Risk Prediction for Prevention and Early Detection; Nov 16-19, 2016; Orlando, FL. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2017;26(5 Suppl):Abstract nr PR09.

Abstract Introduction: Epidemiologic data support an inverse association between statin use and risk of lethal prostate cancer, but contributing mechanisms have not been elucidated. Herein, using data from the Health Professionals Follow-up Study (HPFS), we updated our previous analysis of statins and lethal prostate cancer with a decade of additional follow-up, and incorporated immunohistochemistry (IHC)-based biomarkers and gene expression profiling to identify putative molecular mechanisms contributing to the association. Methods: We included data from 44,076 HPFS participants who were cancer free in 1990, with follow-up through 2012. Participants reported prediagnostic statin use on biennial questionnaires. Statin use was categorized as current vs. never/past use, with current users further categorized as long-term vs. short-term users (≥6 vs. <6 years). To classify prostate cancer molecular subtypes, genetically validated IHC assays for TMPRSS2:ERG fusion and PTEN loss were conducted on tissue microarrays for 891 and 660 cases, respectively. Whole-genome mRNA profiling of tumor and adjacent normal tissue was completed for 237 and 114 cases, respectively, using Affymetrix GeneChip Human Gene 1.0 ST arrays. We used Cox proportional hazards analysis to generate hazard ratios (HR) and 95% confidence intervals (CI) for associations between statin use and risk of overall, advanced (stage T3b or higher at diagnosis, metastatic or fatal), and lethal (metastatic or fatal) prostate cancer, as well as molecular subtypes, adjusted for PSA testing behavior and potential confounders including obesity and smoking. Moreover, we explored gene expression pathways in tumor and adjacent normal prostate tissue of statin users vs. nonusers using gene set enrichment analysis (GSEA). Results: During 22 years of follow-up, 6,144 men were diagnosed with prostate cancer; 1,051 (17%) had advanced disease and 827 (13%) developed lethal prostate cancer. Of cases with molecular subtype available, 48% were ERG-positive and 14% PTEN-null. In multivariable analysis, relative to never/past use, current statin use was inversely associated with risk of advanced (HR 0.84; 95% CI 0.68-1.04) and lethal (HR 0.78; 95% CI 0.68-1.01) prostate cancer. These associations were more pronounced in long-term users, where ≥6 years of prediagnosis statin use was significantly associated with a lower risk of advanced (HR 0.72; 95% CI 0.53-0.97) and lethal prostate cancer (HR 0.64; 95% CI 0.45-0.92), relative to nonuse. Long-term statin use was not associated with overall prostate cancer risk, whether ERG-positive (HR 0.89; 95% CI 0.59-1.35) or ERG-negative (HR 1.06; 95% CI 0.74-1.50). However, relative to nonuse, a longer duration of prediagnosis statin use was associated with reduced risk of PTEN-null cancers (HR 0.42; 95% CI 0.20-0.90), but not PTEN-intact disease (HR 1.18; 95% CI 0.95-1.46; p-heterogeneity=0.01). In GSEA, we identified T cell, B cell, and phosphatidylinositol (PI3K) signaling among the top pathways enriched in tumor-adjacent normal prostate tissue of current statin users, relative to never users. Intriguingly, no gene sets were differentially expressed by statin use in the tumor. Discussion: Our updated findings from the HPFS are consistent with our prior findings and other epidemiologic data supporting a role for statins in lethal prostate cancer prevention. Molecular classification of tumors identified PTEN/PI3K signaling and inflammation/immune activation as two potential mechanisms contributing to this association. Elucidating molecular mechanisms mediating the association between statin use and lower risk of lethal prostate cancer will provide support for a causal effect of statins on lethal prostate cancer risk and could inform statin clinical trials with appropriate intermediate endpoints. Citation Format: Emma H. Allott, Ericka M. Ebot, Amparo G. Gonzalez-Feliciano, Sarah C. Markt, Kathryn M. Wilson, Thomas U. Ahearn, Travis A. Gerke, Mary K. Downer, Konrad H. Stopsack, Jennifer R. Rider, Stephen J. Freedland, Elizabeth A. Platz, Meir J. Stampfer, Edward L. Giovannucci, Christopher J. Sweeney, Stephen P. Finn, Lorelei A. Mucci. Molecular tumor profiling to identify mechanisms linking statin use with lower risk of lethal prostate cancer: Results from the Health Professionals Follow-up Study [abstract]. In: Proceedings of the AACR Special Conference: Prostate Cancer: Advances in Basic, Translational, and Clinical Research; 2017 Dec 2-5; Orlando, Florida. Philadelphia (PA): AACR; Cancer Res 2018;78(16 Suppl):Abstract nr A015.

106 Background: Pharmacoepidemiologic studies suggest prognostic benefits of aspirin in prostate cancer. We hypothesized that prostate cancer tissue from regular aspirin users at cancer diagnosis compared to nonusers is characterized by specific transcriptional changes. Methods: We analyzed tumor whole-transcriptome data from men diagnosed with prostate cancer during prospective follow up of the Physicians Health Study 1 (PHS1, n1 = 150), initially a randomized-controlled trial of aspirin for prevention of cardiovascular disease and cancer. We compared the expression of putative aspirin target genes ( PTGS2, CTNNB1, MYC, AXIN2, PTGER3) between regular aspirin users ( ≥ 3 x 324 mg/week) and non-users at cancer diagnosis. We used Gene Set Enrichment Analysis to identify Gene Ontology biological process gene sets (total, 3609) associated with aspirin use. Leading edge genes of ≥ 3 functionally related gene sets were summarized in a meta-gene score. Results were validated among prostate cancer patients from the Health-Professionals Follow-up Study (HPFS, n2 = 254; aspirin use, ≥ 2 x/week). Results: Regular aspirin use was common (65% in PHS1; 45% in HPFS) and not associated with age, stage, and Gleason grade. In PHS1, none of the predefined genes were associated with aspirin use (all p > 0.05). 26 gene sets were downregulated in aspirin users at a false discovery rate (FDR) < 0.25 (9 at FDR < 0.05). 11 gene sets were clustered functionally around ribosome function and protein translation. A “ribosome” score of 96 genes was higher in aspirin users compared to nonusers (difference, 35.5 standard deviations [SD]; p = 0.0001). There was no dose-dependency for cumulative duration of aspirin use before cancer diagnosis ( ptrend = 0.17) or time since stopping use among non-users at diagnosis ( p = 0.32). In HPFS, neither the pre-defined target genes (all p > 0.18) nor the score were associated with aspirin use (difference, –9.8 SD; p = 0.18). Conclusions: Although RNA acetylation and resulting intratumoral gene expression changes due to aspirin use may be biologically plausible, we were unable to corroborate this association in two-long term prospective studies. Short-term trials might assess if aspirin has direct effects on tumor gene expression.

12 Background: Cholesterol is needed in prostate cancer cells for cell proliferation and for androgen biosynthesis. Cholesterol-lowering statin drug use is associated with a lower risk of total and advanced prostate cancer and lower prostate cancer-specific mortality (PCSM). We hypothesized that tumor expression of cholesterol synthesis enzymes, transporters and regulators is associated with PCSM. Methods: We studied mRNA expression of 43 cholesterol metabolism genes in surgical specimens from 249 participants in the Health Professionals' Follow-up Study diagnosed with prostate cancer between 1986 and 2004. We included 81 cases of lethal prostate cancer and 168 indolent cases who survived >8 years without metastases. After multivariate dimensionality reduction for the synthesis, transport and regulator pathways using principal components analysis, we estimated odds ratios (ORs) and 95% confidence intervals (CIs) using logistic regression. We adjusted for age, year of diagnosis, body mass index, smoking status, family history, multivitamin use, high serum cholesterol and cholesterol-lowering drug use. Results: Reflecting the impact of the synthesis pathway and of the regulator pathway, respectively, the expression of squalene epoxidase (SQLE) and low-density lipoprotein receptor (LDLR) were significantly associated with lethal cancer in opposing directions. Compared to men with the mean level of SQLE expression, men with SQLE expression >1 standard deviation (SD) above the mean were 15.4 times more likely to have lethal cancer (95% CI: 3.31–71.53). For LDLR, expression >1 SD above the mean was associated with 96% lower odds of lethal cancer (95% CI: 0.01–0.70). Higher SQLE expression and lower LDLR expression were associated with higher Gleason grades (Fisher's test, p < 0.001 and p = 0.036, respectively) and were also predictive of PCSM independently from grade and tumor stage. Conclusions: These results suggest that the local cholesterol metabolism of the prostate tumor is tightly linked with mortality. Lethal cancers have higher activity of the second rate-controlling enzyme of cholesterol synthesis and are less dependent on cholesterol uptake.

77 Background: Prostate cancer cells rely on cholesterol for proliferation and androgen production. We recently demonstrated that increased expression of the second key enzyme of cholesterol synthesis, squalene monooxygenase (SQLE), is associated with higher prostate cancer-specific mortality (PCSM). We here validate findings in two additional prospective studies and investigate putative mechanisms. Methods: We analyzed the prospective prostatectomy cohorts within the Health Professionals Follow-up Study (HPFS) and the Physicians’ Health Study (PHS) as well as initially expectantly managed patients in the Swedish Watchful Waiting Study (SWWS). 258 lethal cancer cases and 469 patients who survived > 8 years without metastases were included. SQLE mRNA was measured in tumor specimens at diagnosis of all patients and in benign prostate tissue of 197 patients. Markers of tumor angiogenesis were assessed via immunohistochemistry in 169 HPFS patients. We estimated multivariable-adjusted odds ratios (ORs) and 95% confidence intervals (CIs) using logistic regression. Results: Higher SQLE expression was confirmed to be predictive of higher PCSM in the validation prostatectomy cohort PHS. Combining the two prostatectomy cohorts, men with high SQLE expression ( > 1 standard deviation above the mean) were 6.7 times (95% CI, 2.9 to 15.8; p < 0.001) more likely to die from their cancer compared to men with the mean level of SQLE expression. A 10% higher ratio of SQLE mRNA expression in tumor vs. benign prostate tissue of the same patient was predictive of 42% higher PCSM (95% CI, 15% to 74%). Higher SQLE expression was strongly associated with increased angiogenesis markers (all p ≤ 0.001). This increased risk associated with high SQLE expression was not modified by statin use (p ≥ 0.52). In initially untreated patients in SWWS, a more modest association of tumor SQLE expression with PCSM was observed (p = 0.047). Conclusions: SQLE, the second rate-limiting enzyme of cholesterol synthesis, is associated with prostate cancer progression. Its expression at cancer diagnosis is predictive of lethal disease both after curative-intent prostatectomy and in a watchful waiting setting, possibly by facilitating micrometastatic disease.

Abstract BACKGROUND: We previously showed that mRNA expression of squalene monooxygenase (SQLE), part of the cholesterol synthesis pathway, is associated with lethal prostate cancer. In-vitro studies suggest that loss of PTEN expression and resulting PI3K pathway activation drive cholesterol ester accumulation in aggressive prostate cancers through sterol regulatory element-binding protein (SREBP) and acyl coenzyme A-cholesterol acyltransferase (ACAT1) activity. In two prospective cohorts, we studied whether lower PTEN expression is associated with cholesterol metabolism and how this relates to lethal prostate cancer. METHODS: We analyzed men with prostate cancer from the prospective prostatectomy Health Professionals Follow-up Study and Physicians’ Health Study. 105 men had lethal cancer and 284 men non-lethal disease without metastases at 8 years of follow-up. Whole-transcriptome mRNA expression profiling data was available from diagnostic prostate tumor specimens. Linear regression models were used to assess continuous and categorical associations, and Pearson correlation coefficients were calculated. Logistic regression was used to obtain odds ratios (ORs) and 95% confidence intervals (CIs) of lethal prostate cancer. RESULTS: Both lower PTEN and higher SQLE expression were associated with higher Gleason grade (p trend &lt; 0.001 each). Correlations of PTEN with SREBF1 (r = -0.08, p = 0.1), SREBF2 (r = -0.09, p = 0.07), and ACAT1 (r = 0.04, p = 0.4) were weak. SREBF2 was correlated with SQLE (r = 0.33, p &lt; 0.001) but not with ACAT1 (r = -0.01, p = 0.8). Low PTEN was associated with lethal cancer (OR, 1.50 per 1 standard deviation [SD] decrease; 95% CI, 1.20 to 1.87; p = 0.001). High SQLE was associated with lethal cancer (OR 2.13 per 1 SD increase, 95% CI, 1.63 to 2.79; p &lt; 0.001). SREBF1, SREBF2, and ACAT1 were not associated with lethal cancer (all p &gt; 0.05). Adjusting for PTEN mildly attenuated the association of SQLE with lethal cancer (OR, 2.07; 95% CI, 1.57 to 2.73), as did additional adjustment for age, Gleason grade, and stage (SQLE: OR, 1.75; 95% CI, 1.29 to 2.40). In the lowest quartile of PTEN expression, SQLE was less strongly associated with lethal cancer (OR 1.74; 95% CI, 1.20 to 2.52) compared to the upper three quartiles (OR 2.47; 95% CI, 1.69 to 3.60; p interaction = 0.2). CONCLUSION: Low PTEN mRNA expression and high SQLE are features of aggressive prostate cancers. However, at the time of prostatectomy, SREBF1/2 expression and resulting ACAT1 expression do not appear to be major characteristics of prostate cancers with lethal outcomes. Citation Format: Konrad H. Stopsack, Travis A. Gerke, Lorelei A. Mucci, Jennifer R. Rider. PTEN expression, cholesterol metabolism, and lethal prostate cancer. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 60.

Abstract Cholesterol metabolism has been implicated in prostate cancer pathogenesis. Here, we assessed the association of intratumoral mRNA expression of cholesterol synthesis enzymes, transporters, and regulators in tumor specimen at diagnosis and lethal prostate cancer, defined as mortality or metastases from prostate cancer in contrast to nonlethal disease without evidence of metastases after at least 8 years of follow-up. We analyzed the prospective prostate cancer cohorts within the Health Professionals Follow-up Study (n = 249) and the Physicians' Health Study (n = 153) as well as expectantly managed patients in the Swedish Watchful Waiting Study (n = 338). The expression of squalene monooxygenase (SQLE) was associated with lethal cancer in all three cohorts. Men with high SQLE expression (&gt;1 standard deviation above the mean) were 8.3 times (95% confidence interval, 3.5 to 19.7) more likely to have lethal cancer despite therapy compared with men with the mean level of SQLE expression. Absolute SQLE expression was associated with lethal cancer independently from Gleason grade and stage, as was a SQLE expression ratio in tumor versus surrounding benign prostate tissue. Higher SQLE expression was tightly associated with increased histologic markers of angiogenesis. Collectively, this study establishes the prognostic value of intratumoral cholesterol synthesis as measured via SQLE, its second rate-limiting enzyme. SQLE expression at cancer diagnosis is prognostic for lethal prostate cancer both after curative-intent prostatectomy and in a watchful waiting setting, possibly by facilitating micrometastatic disease. Cancer Res; 76(16); 4785–90. ©2016 AACR.