Men with advanced prostate cancer are typically treated with androgen deprivation therapy, but most ultimately develop resistance and incurable disease (e.g., castration-resistant prostate cancer, CRPC). The majority of CRPCs overexpress the epigenetic enzyme EZH2 and harbor alterations in the PI3K pathway, providing 2 targetable pathways outside of the androgen receptor. Here, we show that EZH2 inhibitors synergize with PI3K, AKT, or mTORC1 inhibitors to kill CRPC in vitro and promote tumor regression in vivo. Strikingly, these agents trigger a catastrophic energy crisis by cooperatively suppressing glycolysis, the TCA cycle, and oxidative phosphorylation before cell death. EZH2 and PI3K pathway inhibitors achieve this by respectively inhibiting 2 key regulators of metabolism, MYC and HIF-1A, while derepressing a proapoptotic stress sensor. Together, these studies reveal a promising therapeutic strategy for CRPC and demonstrate how metabolic plasticity can be fatally impaired by cotargeting upstream oncogenic nodes that converge on this important process.

MYC overexpression, often associated with chromosome 8q24 amplification, is a well identified genetic alteration in aggressive prostate cancer, especially in metastatic castration-resistant prostate cancer (mCRPC). It has been reported that MYC amplification counteracts with androgen receptor (AR) signaling, which has significant impacts on androgen deprivation therapy efficacy. In this study, we developed a prostate cancer mouse model in which MYC overexpression is initially induced by AR but AR-independent during tumorigenesis and progression. We employed the Multiome technology integrating single-cell RNA-sequencing (scRNA-seq) and ATAC-sequencing (scATAC-seq) to profile late-stage MYC-driven non-metastatic and metastatic prostate cancers. Consistent with previous studies using AR-dependent MYC-driven models, we identified that primary tumors are composed of a large quantity of luminal cells. We have also observed a higher proportion of luminal cells in the tumors that developed metastasis, while localized primary tumors were more abundant in basal cells, and transitional cell types. Interestingly, we uncovered heterogeneous transitional populations featured by different cell cycle profiles and cell-type gene signatures. With gene set enrichment analysis (GSEA), we identified differential enrichment of inflammatory pathways in luminal cells in metastatic primary tumors relative to localized primary tumors. By integrating with scATAC-seq analysis, we also identified new differential transcriptional and epigenetic regulators that may drive the aggressiveness of these MYC-driven cancers in a tissue specific manner. In addition, we applied inferred copy number variation (CNV) analysis and showed that aggressive tumors and metastasis harbor higher levels of CNVs. Together, these findings reveal how MYC overexpression reshapes prostate epithelial lineage, chromatin landscape and genomic instability to promote AR-independent aggressiveness, providing mechanistic insights and a foundation for future therapeutic targeting of MYC-driven malignancies. Kathryn Echandía-Monroe, Sofia Hu, Daniel R. Schmidt, Kun-Lin Ho, Duanduan Ma, Elise G. DeArment, Faith Kim, Chloe Springer, Savannah Washburn, Madeline M. Wong, Kate Lu, Marianna Trakala, William D. Figg, Matthew G. Vander Heiden, Xiaofeng A. Su. Multiomic single-cell profiling of a novel MYC-driven mouse prostate cancer model [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Innovations in Prostate Cancer Research and Treatment; 2026 Jan 20-22; Philadelphia PA. Philadelphia (PA): AACR; Cancer Res 2026;86(2_Suppl):Abstract nr B017.

Background and purpose:To evaluate the dosimetric and toxicity profiles of stereotactic body radiotherapy (SBRT) for prostate cancer, comparing cohorts with and without intraprostatic boost (IPB) to assess feasibility and safety of IPB, with particular attention to urethral and bladder dose and toxicity. Materials and methods:This retrospective cohort study analyzed 349 patients with localized prostate cancer treated between 2018 and 2023. Of these, 266 received SBRT with IPB, and 83 received SBRT without IPB. Patients were treated using a robotic SBRT platform with fiducial tracking. Dosimetric parameters for the urethra, including D0.03cc, D0.3cc, and V40Gy, and for the bladder, including D0.03cc, D5cc, D10cc, and V37Gy, were evaluated. Acute and late toxicities were assessed using CTCAE criteria. Results:For the urethra, median values for D0.03cc, D0.3cc, and V40Gy, and for the bladder, median values D0.03cc, D5cc, D10cc, and V37Gy were compared and no statistically significant differences were observed between the two cohorts. Late urinary toxicity of grade 3 or higher occurred in 2.25 % of patients in the IPB group and 2.47 % in the no IPB group, with no grade 3 acute toxicities reported. Discussion:These findings support the use of SBRT using an IPB as a feasible and safe approach to achieve focal dose escalation to dominant intra-prostatic lesions (DILs) without significantly increasing urethra or bladder dose or toxicity. Future research should focus on standardizing DIL contouring, exploring adaptive planning techniques to increase accuracy, and prospectively studying toxicity and quality of life in patients treated with IPB with SBRT.

Purpose/objectives:SBRT is a standard of care treatment for localized prostate cancer. Whole gland dose escalation remains controversial. Concomitant intraprostatic boost (IPB) may offer an acceptable compromise for dose escalation. In this series, we report changes in International Prostate Symptom Scores (IPSS) over a 12-month period following SBRT with IPB in patients treated in a large academic institution. Materials/methods:Seventy-four patients treated from October 2018 to March 2022 with robotic stereotactic body radiotherapy completed IPSS questionnaires. IPSS were evaluated for patients at three timepoints: pre-treatment, post-treatment (defined as 3 months after SBRT completion), and at follow-up (defined as within 12 months after SBRT completion). The patients were stratified into two cohorts: patients who experienced minimally important difference (MID) in their post-treatment IPSS and those who did not. Urethral and bladder doses were retrospectively extracted from the treatment planning software and compared between the two cohorts using Wilcoxon rank sum test. Results:Of the 74 patients, 46 (62%) experienced MID in scores (cohort A), while 28 (38%) did not (cohort B). Patient characteristics in the two cohorts such as risk stratification and initial PSA were well-balanced. Median IPSS for cohort A were 5 (range: 0-21) pre-treatment, 12 (range: 3-28) post-treatment, and 8 (range: 1-32) at 12 months. For cohort B, the scores were 9.5 (range: 0-29), 7 (range: 1-19), and 8.5 (range: 0-32), respectively. In addition, there was a statistically significant difference in D0.03cc to the bladder in cohort A compared to cohort B (41.9 Gy vs 40.2 Gy; p < 0.001). Conclusion:IPB is well tolerated with acceptable change in urinary quality of life metrics as measured by IPSS. Max dose to the bladder remains the only significant difference in patients who experienced MID in their urinary quality of life.

Disclosure: C. Springer: None. T. Janas: None. K.H. Stopsack: None. D.R. Schmidt: None. D. Ma: None. Z. Li: None. M.G. Vander Heiden: None. K.L. Penny: None. P.A. Scheet: None. T.L. Lotan: None. A. Amon: None. L.A. Mucci: None. X. Su: None. Prostate cancer (PCa) remains the second leading cause of cancer-related mortality among men in the United States. Aneuploidy, characterized by imbalanced chromosome numbers, correlates with lethal PCa progression. Chromosome 8q (chr8q) gain is one of the most frequent aneuploidy events, occurring in 23% of PCa cases. Recently, we ranked odds ratio (OR) for each chr8q gene to assess the long-term risk of metastases and death from PCa (lethal disease) within 403 patients in the HPFS and PHS cohorts. We observed that the squalene monooxygenase (SQLE) is one of the top ranked genes on chr8q, with an OR of 2.2. SQLE, encoding the key enzyme in cholesterol biosynthesis pathway, has been shown to be associated with poor prognosis in PCa, suggesting it as a potential target to treat aggressive PCa. Datasets such as The Cancer Genome Atlas (TCGA) and the Prostate Cancer Atlas were used to correlate the copy number and mRNA expression levels and the progression of PCa. We focused on mouse prostate organoids (both normal and cancer-like) and human metastatic prostate cell line, VCaP cell, expressing TMPRSS2-ERG gene, which approximately 50% of PCa cases harbors. We used lentiviral transduction to introduce either SQLE overexpression in prostate organoids (which harbor euploid SQLE) or SQLE shRNA in VCaP cells (which harbor increased SQLE). Molecular and cellular approaches were employed to study the influences of altered SQLE levels on target prostate cells. Ultra performance liquid chromatography (UPLC) with mass spectrometry (MS) was used to analyze the changed levels of squalene and lipid profiles when SQLE levels were altered. Overexpression of SQLE in cancer-like mouse prostate organoid models led to increased invasive structures and proliferation. RNA sequencing data suggested that alteration in SQLE levels changes gene signatures related to lipid metabolisms. Interestingly, SQLE overexpression decreased TMPRSS2-ERG protein levels in the organoids. In contrast, SQLE knockdown in VCaP cells resulted in significantly increased TMPRSS2-ERG protein levels. ERG is associated with fatty acid metabolism in PCa cohorts. Our findings suggest that aneuploidy-associated overexpression of SQLE drives PCa aggressiveness by modulating lipid metabolism, particularly through its impact on cholesterol biosynthesis and TMPRSS2-ERG regulation. Targeting SQLE could present a novel therapeutic approach to treat aggressive PCa. Presentation: Saturday, July 12, 2025

Abstract Prostate cancer (PCa) is the second leading cause of cancer-related death in men in the US. Epidemiology studies on primary PCa cohorts in Physicians' Health Study and Health Professionals Follow-up Study (PHS and HPFS) have shown that high levels of whole-genome aneuploidy, featured by imbalanced chromosome numbers, correlate with lethal progression in PCa. However, details of the mechanisms of how aneuploidy drives PCa aggressiveness are still unclear. Here, we used the case of chromosome 8q (chr 8q, the long arm of chr 8) gain to study aneuploidy-associated prostatic malignancies. Chr 8q gains are the most frequent gain events that occur in approximately 23% of PCa cases. By using the PHS and HPFS cohorts, we modeled the increased expression of each gene located on chr 8q, for predicting the risks for lethal progression, and obtained each corresponding gene’s odds ratio (OR). By ranking the ORs, we revealed that a cholesterol biosynthesis gene, squalene monooxygenase (SQLE), is one of the top associators with lethal progression, amongst all chr 8q genes. SQLE plays a pivotal role in cholesterol synthesis. Previous lymphoma studies have shown that loss of SQLE contributes to cholesterol auxotrophy, and squalene build-up protects against oxidative cell death. In our experimental study, we have used normal and cancerous TMPRSS2-ERG-driven organoid models and found that over-expression of SQLE promotes formation of invasive structures and proliferation in cancer organoids. Interestingly, overexpression of SQLE decreased the protein levels of TMPRSS2-ERG, which appeared to be independent of androgen receptor levels. We also utilized the TMPRSS2-ERG positive VCaP cell line, which harbors gains of SQLE gene copies. We found that knocking down SQLE expression significantly upregulated ERG protein levels. Our recent study has shown that ERG (or other ETS) positive prostate cancers have a strong correlation with downregulation of fatty acid metabolism signature. We speculate that gain of SQLE can drive aggressiveness of prostate cancer by modulating lipid metabolism for growth and migration. Inhibition of SQLE could translate to better clinical outcomes regarding prostate cancer lethality. Citation Format: Thomas Walter Janas, Xiaofeng A. Su, Konrad H. Stopsack, Daniel R. Schmidt, Duanduan Ma, Zhe Li, Kathryn L. Penny, Tamara L. Lotan, Lorelei A. Mucci, Matthew G. Vander Heiden, Elise DeArment, Angelika Amon, Paul A. Scheet. Aneuploidy-associated SQLE gain promotes prostate cancer aggressiveness by altering lipid metabolism [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 402.

Abstract Bipolar androgen therapy (BAT) is the cyclical administration of supraphysiological androgen (SPA), which can be an effective treatment for 30-40% of patients with castration-resistant prostate cancer. We sought to improve the efficacy of BAT by better understanding its molecular consequences in prostate cancer. Given that the androgen receptor (AR) regulates cellular metabolism, we hypothesized that SPA induces dependencies on specific metabolic pathways that might be exploited therapeutically. A negative selection metabolism-focused CRISPR-KO screen in LNCaP cells treated with SPA suggested that the deletion of several enzymes involved in de novo nucleotide synthesis enhances growth suppression by SPA. A top hit was cytidine triphosphate synthase 1 (CTPS1). CTPS1 converts UTP to CTP in the final step of de novo pyrimidine synthesis. Exposure of SPA-treated prostate cancer cell lines to STP-B, a potent and highly selective inhibitor of CTPS1 (PMID 37008165), increased cell death in vitro and in vivo, indicating that CTPS1 constitutes a metabolic vulnerability in this context. Inhibition of CTPS1 with STP-B induced S phase cell cycle arrest and replication stress, as indicated by phosphorylation of RPA and CHEK proteins, which was augmented by treatment with SPA. CTPS1 likely becomes a vulnerability in SPA-treated prostate cancer due to the downregulation of MYC by SPA, which we found leads to a reduced abundance of enzymes required for nucleotide synthesis and nucleotides, particularly CTP. This rewires nucleotide synthesis and salvage pathway such that de novo synthesis of CTP is required to avoid replication stress and cell death. Altogether, this work suggests that inhibition of CTPS1 may enhance the efficacy of BAT through the induction of replication stress. Selective inhibitors of CTPS1 have entered clinical development (NCT05463263), increasing the feasibility of a combination therapy clinical trial design for patients with prostate cancer. Citation Format: Sheila Jonnatan, Rajendra Kumar, Varsha Vakkala, Karthik Vasan, Zachary R. Chalmers, Daniel R. Schmidt, Philip A. Beer, Matthew G. Vander Heiden, Samuel R. Denmeade, Navdeep S. Chandel, Laura A. Sena. CTP synthase 1 is a synthetic vulnerability in prostate cancer treated with supraphysiological androgen [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr LB405.

Higher levels of aneuploidy, characterized by imbalanced chromosome numbers, are associated with lethal progression in prostate cancer. However, how aneuploidy contributes to prostate cancer aggressiveness remains poorly understood. In this study, we assessed in patients which genes on chromosome 8q, one of the most frequently gained chromosome arms in prostate tumors, were most strongly associated with long-term risk of cancer progression to metastases and death from prostate cancer (lethal disease) in 403 patients and found the strongest candidate was cohesin subunit gene, RAD21 , with an odds ratio of 3.7 (95% CI 1.8, 7.6) comparing the highest vs. lowest tertiles of mRNA expression and adjusting for overall aneuploidy burden and Gleason score, both strong prognostic factors in primary prostate cancer. Studying prostate cancer driven by the TMPRSS2-ERG oncogenic fusion, found in about half of all prostate tumors, we found that increased RAD21 alleviated toxic oncogenic stress and DNA damage caused by oncogene expression. Data from both organoids and patients indicate that increased RAD21 thereby enables aggressive tumors to sustain tumor proliferation, and more broadly suggests one path through which tumors benefit from aneuploidy.

Control of cellular identity requires coordination of developmental programs with environmental factors such as nutrient availability, suggesting that perturbing metabolism can alter cell state. Here, we find that nucleotide depletion and DNA replication stress drive differentiation in human and murine normal and transformed hematopoietic systems, including patient-derived acute myeloid leukemia (AML) xenografts. These cell state transitions begin during S phase and are independent of ATR/ATM checkpoint signaling, double-stranded DNA break formation, and changes in cell cycle length. In systems where differentiation is blocked by oncogenic transcription factor expression, replication stress activates primed regulatory loci and induces lineage-appropriate maturation genes despite the persistence of progenitor programs. Altering the baseline cell state by manipulating transcription factor expression causes replication stress to induce genes specific for alternative lineages. The ability of replication stress to selectively activate primed maturation programs across different contexts suggests a general mechanism by which changes in metabolism can promote lineage-appropriate cell state transitions.

Supplementary Figure from Pyruvate Kinase M1 Suppresses Development and Progression of Prostate Adenocarcinoma

Prostate cancer (PCa) is one of the most common cancers among men, leading to the second cause of death for men with cancers in the US. Aneuploidy, featured by imbalanced chromosome numbers, is a hallmark of cancer. Epidemiology studies on primary PCa cohorts of Physicians' Health Study and Health Professionals Follow-up Study (PHS and HPFS) have shown that high levels of whole-genome aneuploidy correlate with lethal progression in PCa. However, the detail mechanisms of how aneuploidy drives aggressiveness of PCa are still unclear. Here, we used the case of chromosome 8q (chr 8q, the long arm of chr 8) gain to study aneuploidy-associated prostatic malignancies. Chr 8q gains are the most frequently gain events that occur in around 23% of PCa cases. By using the PHS and HPFS cohorts, we modeled the increased expression of each gene located on chr 8q, for predicting the risks for lethal progression, and obtained the odds ratio (OR) for each. Then, we ranked the ORs for lethal progression and identified several important genes highly associated with lethality when overexpressed. Among them, the cohesin subunit gene, RAD21, is one of the top associators. Increased RAD21 mRNA level, per se, is highly correlated with lethality in all PCa cases, and the lethality is synergistically aggravated in the cases with both increased RAD21 expression and chr 8q gains. indicating that RAD21 cooperates with other chr 8q genes to drive cancer progression and chr 8q gains. To determine how RAD21 overexpression promotes PCa, we studied the effect of overexpression of RAD21 in early prostatic oncogenic events. We utilized the isogenic mouse prostate organoid models carrying an inducible the fusion-oncogene, TMPRSS2-ERG (T-ERG), which 50% of PCa cases harbor. We found that induction of T-ERG leads to a strong oncogenic replication stress at an early stage. Such stress results in an increase in apoptosis and growth impairment in these primary organoids. Overexpression of RAD21, mimicking the chr 8q gain situation, mitigates such replication stress and rescues the growth defect caused by T-ERG. These data suggest the role of increased RAD21 in promoting oncogenic growth of PCa cells by reducing oncogenic toxicity at an early stage. In addition, we showed that such role of RAD21 overexpression sustains in the more advanced cancerous organoid (ERG positive and PTEN loss) and promotes the growth of the cancer organoids. Consistently, increased RAD21 expression correlates with increase proliferative markers in human prostate cancer cases. In conclusion, we identified that overexpression of multiple chr 8q genes are correlated with lethal progression in primary PCa, and RAD21 is one of such genes. Increased RAD21 plays a fundamental role in reducing toxic DNA damage caused by prostatic oncogenesis. Citation Format: Xiaofeng A. Su, Konrad H. Stopsack, Daniel R. Schmidt, Duanduan Ma, Zhe Li, Matthew G. Vander Heiden, Angelika Amon, Lorelei A. Mucci. Increased RAD21 promotes prostate cancer development [abstract]. In: Proceedings of the AACR Special Conference: Advances in Prostate Cancer Research; 2023 Mar 15-18; Denver, Colorado. Philadelphia (PA): AACR; Cancer Res 2023;83(11 Suppl):Abstract nr A018.

A challenge for screening new anticancer drugs is that efficacy in cell culture models is not always predictive of efficacy in patients. One limitation of standard cell culture is a reliance on non-physiological nutrient levels, which can influence cell metabolism and drug sensitivity. A general assessment of how physiological nutrients affect cancer cell response to small molecule therapies is lacking. To address this, we developed a serum-derived culture medium that supports the proliferation of diverse cancer cell lines and is amenable to high-throughput screening. We screened several small molecule libraries and found that compounds targeting metabolic enzymes were differentially effective in standard compared to serum-derived medium. We exploited the differences in nutrient levels between each medium to understand why medium conditions affected the response of cells to some compounds, illustrating how this approach can be used to screen potential therapeutics and understand how their efficacy is modified by available nutrients.

BACKGROUND:Genetically engineered mouse models (GEMMs) of cancer are powerful tools to study mechanisms of disease progression and therapy response, yet little is known about how these models respond to multimodality therapy used in patients. Radiation therapy (RT) is frequently used to treat localized cancers with curative intent, delay progression of oligometastases, and palliate symptoms of metastatic disease.METHODS:Here we report the development, testing, and validation of a platform to immobilize and target tumors in mice with stereotactic ablative RT (SART). Xenograft and autochthonous tumor models were treated with hypofractionated ablative doses of radiotherapy.RESULTS:We demonstrate that hypofractionated regimens used in clinical practice can be effectively delivered in mouse models. SART alters tumor stroma and the immune environment, improves survival in GEMMs of primary prostate and colorectal cancer, and synergizes with androgen deprivation in prostate cancer. Complete pathologic responses were achieved in xenograft models, but not in GEMMs.CONCLUSIONS:While SART is capable of fully ablating xenografts, it is unable to completely eradicate disease in GEMMs, arguing that resistance to potentially curative therapy can be modeled in GEMMs.

Prostate cancer (PCa) is one of the most common cancers among men, leading to the second cause of death for men with cancers in the US. Aneuploidy, featured by imbalanced chromosome numbers, is a hallmark of cancer. Epidemiology studies on primary PCa cohorts of Physicians' Health Study and Health Professionals Follow-up Study (PHS and HPFS) have shown that high levels of whole-genome aneuploidy correlate with lethal progression in PCa. However, the detail mechanisms of how aneuploidy drives aggressiveness of PCa are still unclear. Here, we used the case of chromosome 8q (chr 8q, the long arm of chr 8) gain to study aneuploidy-associated prostatic malignancies. Chr 8q gains are the most frequently gain events that occur in around 23% of PCa cases. By using the PHS and HPFS cohorts, we modeled the increased expression of each gene located on chr 8q, for predicting the risks for lethal progression, and obtained the odds ratio (OR) for each. Then, we ranked the ORs for lethal progression and identified several important genes highly associated with lethality when overexpressed. Among them, the cohesin subunit gene, RAD21, is one of the top associators. Increased RAD21 mRNA level, per se, is highly correlated with lethality in all PCa cases, and the lethality is synergistically aggravated in the cases with both increased RAD21 expression and chr 8q gains. indicating that RAD21 cooperates with other chr 8q genes to drive cancer progression and chr 8q gains. To determine how RAD21 overexpression promotes PCa, we studied the effect of overexpression of RAD21 in early prostatic oncogenic events. We utilized the isogenic mouse prostate organoid models carrying an inducible the fusion-oncogene, TMPRSS2-ERG (T-ERG), which 50% of PCa cases harbor. We found that induction of T-ERG leads to a strong oncogenic replication stress at an early stage. Such stress results in an increase in apoptosis and growth impairment in these primary organoids. Overexpression of RAD21, mimicking the chr 8q gain situation, mitigates such replication stress and rescues the growth defect caused by T-ERG. These data suggest the role of increased RAD21 in promoting oncogenic growth of PCa cells by reducing oncogenic toxicity at an early stage. In addition, we showed that such role of RAD21 overexpression sustains in the more advanced cancerous organoid (ERG positive and PTEN loss) and promotes the growth of the cancer organoids. Consistently, increased RAD21 expression correlates with increase proliferative markers in human prostate cancer cases. In conclusion, we identified that overexpression of multiple chr 8q genes are correlated with lethal progression in primary PCa, and RAD21 is one of such genes. Increased RAD21 plays a fundamental role in reducing toxic DNA damage caused by prostatic oncogenesis. Citation Format: Xiaofeng A Su, Konrad H Stopsack, Daniel R Schmidt, Duanduan Ma, Zhe Li, Thomas Janas, Matthew G Vander Heiden, Kathryn L Penny, Paul A Scheet, Tamara L Lotan, Angelika Amon, Lorelei A Mucci. Identification of cohesin RAD21 as a novel aneuploidy-associated marker driving prostate cancer progression by mitigating toxic DNA damage [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2023 Oct 11-15; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2023;22(12 Suppl):Abstract nr B059.

Background and Purpose. Chronic rectal toxicity significantly decreases the quality of life for men who receive radiotherapy for prostate cancer. The most significant predictor of rectal toxicity is rectal dose-volume exceeding tolerance. To minimize the volume of rectum in the high dose field, it is essential to accurately define the prostate-rectum interface. This can be challenging to do by computed tomography (CT) imaging alone. The current study was undertaken to formally demonstrate in a clinical trial setting that image-guided intensity-modulated radiation therapy (IG-IMRT) planning using magnetic resonance imaging (MRI) can reduce the volume of rectum exceeding 70 Gy, a validated metric that predicts the risk of late rectal toxicity. Materials and Methods. This prospective single-arm study enrolled 15 men treated with IG-IMRT for localized prostate cancer. All participants received a dedicated 3 Tesla MRI examination of the prostate in addition to a pelvic CT examination for treatment planning. Two volumetric modulated arc therapy (VMAT) plans with a prescription dose of 79.2 Gy were designed using identical constraints based on CT- and MRI-defined consensus volumes. The volume of rectum exposed to 70 Gy or more was compared using the Wilcoxon paired signed rank test. Results. For CT-based treatment plans, the median volume of rectum receiving 70 Gy or more was 9.3 cubic centimeters (cc) (IQR 7.0 to 10.2) compared with 4.9 cc (IQR 4.1 to 7.8) for MRI-based plans. This resulted in a median volume reduction of 2.1 cc (IQR 0.5 to 5.3, P < .001). Conclusions. Using MRI to plan prostate IG-IMRT to a dose of 79.2 Gy reduces the volume of rectum receiving radiation dose in excess of tolerance (70 Gy or more) and should be considered in men who are at high risk for late rectal toxicity and are not good candidates for other rectal sparing techniques such as hydrogel spacer. This trial is registered with NCT02470910.

Abstract Altered metabolism helps sustain cancer cell proliferation and survival. Most cancers, including prostate cancers, express the M2 splice isoform of pyruvate kinase (PKM2), which can support anabolic metabolism to support cell proliferation. However, Pkm2 expression is dispensable for the formation and growth of many cancers in vivo. Expression of pyruvate kinase isoform M1 (Pkm1) is restricted to relatively few tissues and has been reported to promote growth of select tumors, but the role of PKM1 in cancer has been less studied than PKM2. To test how differential expression of pyruvate kinase isoforms affects cancer initiation and progression, we generated mice harboring a conditional allele of Pkm1 and crossed these mice, or those with a Pkm2 conditional allele, with a Pten loss-driven prostate cancer model. Pkm1 loss led to increased PKM2 expression and accelerated prostate cancer development, whereas Pkm2 deletion led to increased PKM1 expression and suppressed tumor progression. Metabolic profiling revealed altered nucleotide levels in tumors with high PKM1 expression, and failure of these tumors to progress was associated with DNA replication stress and senescence. Consistent with these data, a small molecule pyruvate kinase activator that mimics a high activity PKM1-like state suppressed progression of established prostate tumors. Analysis of human specimens showed PKM2 expression is retained in most human prostate cancers. Overall, this study uncovers a role for pyruvate kinase isoforms in prostate cancer initiation and progression, and argues that pharmacologic pyruvate kinase activation may be beneficial for treating prostate cancer. Significance: Differential expression of PKM1 and PKM2 impacts prostate tumorigenesis and suggests a potential therapeutic vulnerability in prostate cancer.