Radioresistant Prostate Cancer Research Articles

Abstract 702: Development of a radioresistant PDX prostate cancer model to evaluate potential radiosensitizing compounds

Abstract Prostate cancer is the second most common cancer diagnosis worldwide and the fifth leading cause of cancer related death among men. Several treatment strategies are used including the FDA approved 177Lu-vipivotide tetraxetan (177Lu-PSMA-617) for the treatment of prostate-specific membrane antigen (PSMA)-positive metastatic castration-resistant prostate cancer. However, not all patients respond to treatment due to tumor intrinsic resistance mechanisms. Therefore, the combination of targeted radionuclide therapy with inhibitors against e.g. DNA damage response, cell cycle progression or cell survival pathways are investigated to enhance the radiosensitivity of the tumor. Current models to study radioresistance in prostate cancer are based on cancer cell lines or cell-line derived xenograft models, but these models do not account for the heterogenous and complex biology of the disease. To overcome this issue, we have developed a radioresistant patient-derived xenograft (PDX) prostate cancer model (ST1273, XenoSTART), that is positive for PSMA. Resistance to radiation was initially established by sequential irradiation of the tumors with external beam radiation. Moreover, the model has proven to be resistant towards treatment with 30 MBq 177Lu-PSMA-617. Utilizing this radioresistant model we are now able to investigate the treatment response of 177Lu-PSMA-617 in combination with different drug inhibitor classes to evaluate their potential radiosensitizing effect. The PARP inhibitor, Olaparib, was administered at 50 mg/kg QDx48 alone or in combination with a single dose of 177Lu-PSMA-617 in radioresistant ST1273 tumor bearing NMRI nude mice. First results showed a prolonging treatment effect of Olaparib given in combination with 177Lu-PSMA-617 compared to 177Lu-PSMA-617 alone. Tumor relapse was observed 29 days after treatment with 177Lu-PSMA-617 alone, whereas it was observed 49 days after combination treatment. Olaparib given alone did not influence tumor growth. To further investigate the mechanism of resistance we are currently investigating the radiosensitizing potential of additional compounds and evaluating the tumors by RNA- and whole-exome- sequencing. Altogether, we successfully established a PSMA positive prostate cancer model resistant to PSMA targeted radionuclide therapy. With this model we are able to investigate the radiosensitizing effect of different drug classes. Citation Format: Maria Zeiler Alfsen, Maria Thaysen, Nikoline Nielsen, Michael Wick, Luke Piggott, Sebastian Gnosa, Carsten Haagen Nielsen. Development of a radioresistant PDX prostate cancer model to evaluate potential radiosensitizing compounds [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 702.

Epigenetic regulation of TP53 is involved in prostate cancer radioresistance and DNA damage response signaling

External beam radiotherapy (RT) is a leading first-line therapy for prostate cancer (PCa), and, in recent years, significant advances have been accomplished. However, RT resistance can arise and result in long-term recurrence or disease progression in the worst-case scenario. Thus, making crucial the discovery of new targets for PCa radiosensitization. Herein, we generated a radioresistant PCa cell line, and found p53 to be highly expressed in radioresistant PCa cells, as well as in PCa patients with recurrent/disease progression submitted to RT. Mechanism dissection revealed that RT could promote p53 expression via epigenetic modulation. Specifically, a decrease of H3K27me3 occupancy at TP53 gene promoter, due to increased KDM6B activity, was observed in radioresistant PCa cells. Furthermore, p53 is essential for efficient DNA damage signaling response and cell recovery upon stress induction by prolonged fractionated irradiation. Remarkably, KDM6B inhibition by GSK-J4 significantly decreased p53 expression, consequently attenuating the radioresistant phenotype of PCa cells and hampering in vivo 3D tumor formation. Overall, this work contributes to improve the understanding of p53 as a mediator of signaling transduction in DNA damage repair, as well as the impact of epigenetic targeting for PCa radiosensitization.

CDC20 promotes radioresistance of prostate cancer by activating Twist1 expression.

Currently, radiotherapy is one of the most attractive treatments for prostate cancer (PCa) patients. However, radioresistance remains a challenging issue and the underlying mechanism is unknown. Growing evidence has demonstrated that CDC20 (Cell division cycle protein 20) plays a pivotal role in a variety of tumors, including PCa. Here, GEPIA database mining and western blot analysis showed that higher expression of CDC20 was observed in PCa tissues and cells. We demonstrated that the expression of CDC20 was increased in PCa cells by irradiation, and knockdown of CDC20 resulted in inhibition of cell proliferation, migration, tumor formation, induced cell apoptosis and increased radiosensitivity in PCa in vitro and in vivo. Furthermore, we observed that CDC20 regulated Twist1 pathway, influencing cell proliferation and migration. These results suggest that targeting CDC20 and Twist1 may be an effective way to improve the radiosensitivity of PCa.

Inducing apoptosis by using microRNA in radio-resistant prostate cancer: an in-silico study with an in-vitro validation.

One of the problems with radiation therapy (RT) is that prostate tumor cells are often radio-resistant, which results in treatment failure. This study aimed to determine the procedure involved in radio-resistant prostate cancer apoptosis. For a deeper insight, we devoted a novel bioinformatics approach to analyze the targeting between microRNAs and radio-resistant prostate cancer genes. This study uses the Tarbase, and the Mirtarbase databases as validated experimental databases and mirDIP as a predicted database to identify microRNAs that target radio-resistant anti-apoptotic genes. These genes are used to construct the radio-resistant prostate cancer genes network using the online tool STRING. The validation of causing apoptosis by using microRNA was confirmed with flow cytometry of Annexin V. The anti-apoptotic gene of radio-resistant prostate cancer included BCL-2, MCL1, XIAP, STAT3, NOTCH1, REL, REL B, BIRC3, and AKT1 genes. These genes were identified as anti-apoptotic genes for radio-resistant prostate cancer. The crucial microRNA that knockdown all of these genes was hsa-miR-7-5p. The highest rate of apoptotic cells in a cell transfected with hsa-miR-7-5p was (32.90 ± 1.49), plenti III (21.99 ± 3.72), and the control group (5.08 ± 0.88) in 0Gy (P < 0.001); also, this rate was in miR-7-5p (47.01 ± 2.48), plenti III (33.79 ± 3.40), and the control group (16.98 ± 3.11) (P < 0.001) for 4Gy. The use of this new treatment such as gene therapy to suppress genes involved in apoptosis can help to improve the treatment results and increase the quality of life of patients with prostate cancer.

Abstract 5039: Development of a prostate cancer PDX model radioresistant to PSMA targeted radionuclide therapy

Abstract Prostate cancer is the second most common cancer diagnosis worldwide and the fifth leading cause of cancer related death among men. Lutetium Lu 177 vivivotide tetraxetetan was recently approved by the FDA for treatment of prostate-specific membrane antigen (PSMA)-positive metastatic castration-resistant prostate cancer. However, not all patients respond to treatment and combination therapies may improve outcomes. One approach is to combine targeted radionuclide therapy with inhibitors targeting DNA damage response pathways such as ATM/ATR inhibitors to enhance the radiosensitivity of the cancer cells. Currently, models used to study radioresistance in prostate cancer are based on cancer cell lines or cell-line derived xenograft models, but these models do not account for the heterogenous and complex biology of the disease. To overcome this issue, we aimed at developing a radioresistant PSMA positive prostate cancer patient-derived xenograft (PDX) model based on the ST1273 model (XenoSTART). ST1273 originates from a sixty-five-year-old Hispanic male that did not receive treatment prior to sampling. The model is characterized by overexpression of androgen receptor and PSMA. Tumors were implanted in nude mice and radioresistance was induced by external beam radiation therapy (3 × 2Gy per cycle) until tumor growth was unresponsive to the treatment. Flow cytometry were applied to evaluate if altered proliferation rate or changes in the tumor microenvironment (TME) convers the resistance. Out of five initially treated tumors, one tumor re-occurred after 19 days. Repeating the treatment led to an initial decrease in tumor volume but the growth delay was reduced to 12 days. A third treatment rendered the tumor resistant as tumor growth was unaffected. Current evidence confirms that radioresistance was maintained when passaging, and PSMA expression was unaffected. Next, we tested whether the tumor would also withstand targeted radionuclide therapy. Animals implanted with parental or radioresistant ST1273 tumors were treated with Lu177-PSMA-617 (5MBq, QW x2). The treatment reduced tumor size in both tumor types, but significantly less in the resistant model. Moreover, parental tumors had a significantly slower recurrence of 45 days compared to the resistant tumors that relapsed 24 days after the first dosing. Flow cytometry analysis of control and treated tumors (parental and radioresistant) showed that the radioresistance might be attributed to alterations in the cell cycle control. Altogether, we developed a PDX prostate cancer model that is resistance to external beam radiation and PSMA targeted radionuclide therapy. This model will allow us to further characterize radioresistance and evaluate combinatorial therapy in a clinically relevant model. Citation Format: Maria Thaysen, Esben Christensen, Rikke N. Nielsen, Michael Wick, Mette M. Wessel, Lotte K. Kristensen, Sebastian Gnosa, Carsten H. Nielsen. Development of a prostate cancer PDX model radioresistant to PSMA targeted radionuclide therapy. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 5039.

Circular RNA LPAR3 targets JPT1 via microRNA-513b-5p to facilitate glycolytic activation but repress prostate cancer radiosensitivity

A great many circular RNAs (circRNAs) are considered key modulators of human malignancies. However, the function of circRNA lysophosphatidic acid receptor 3 (LPAR3) in the radioresistance of prostate cancer (PCa) cells is still uncertain. circLPAR3, microRNA (miR)-329-3p, and JPT1 expression in PCa tissues and cells were detected by real-time quantitative PCR or western blot. Cell proliferation was detected by CCK-8 (cell proliferation assay) and colony formation assay, apoptosis was by flow cytometry, and migration and invasion ability were by Transwell assay. Cell glycolysis was analyzed by glucose uptake, lactate production, and ATP metabolism. Under different doses of radiation, the radiosensitivity of PCa cells was detected by colony formation assay. The relationship between circLPAR3, miR-513b-5p, and JPT1 was confirmed by dual luciferase reporter gene detection and RIP assay. The data presented that circLPAR3 and JPT1 expression was elevated in PCa, while miR-513b-5p expression was reduced. Repression of circLPAR3 depressed cell advancement, and restrained glycolysis, but enhanced the radiosensitivity of PCa cells. CircLPAR3's target miRNA was miR-513b-5p which targeted JPT1. Elevated JPT1 reversed the repressive effects of circLPAR3 knockdown or miR-513b-5p overexpression on PCa advancement, glycolysis, and radiosensitivity. In summary, the knockdown of circLPAR3 reduces glycolysis, but promotes PCa radiosensitivity via the miR-513b-5p/JPT1 axis, discovering a novel mechanism in PCa progression.

Euchromatic histone lysine methyltransferase 2 facilitates radioresistance in prostate cancer by repressing endoplasmic reticulum protein 29 transcription.

Prostate cancer is one of the most common cancers in men. This study was conducted to investigate the role of euchromatic histone lysine methyltransferase 2 (EHMT2) and endoplasmic reticulum protein 29 (ERP29) in the progression of radioresistance in prostate cancer. The expression of EHMT2 and ERP29 in prostate cancer cells and during the progression of radioresistance was detected using quantitative reverse transcription-polymerase chain reaction and western blotting, and the interaction between EHMT2 and ERP29 was investigated. The proliferation of transfected cells under x-ray irradiation was determined using the methyl thiazolyl tetrazolium and colony formation assays. Flow cytometry was used to analyze the apoptosis of the transfected cells under x-ray irradiation. Nude mice were subcutaneously injected with prostate cancer (DU145) cells stably transfected with sh-ERP29 or sh-NC. The effect of ERP29 expression on radioresistance in nude mice was assessed by x-ray irradiation. The expression of EHMT2 was upregulated and that of ERP29 was downregulated in prostate cancer cells during radioresistance progression. EHMT2 downregulation suppressed radioresistance in DU145 and androgen-sensitive prostate cancer (LNCaP) cells. In irradiated DU145 cells, EHMT2 inhibition decreased the number of colonies and accelerated apoptosis. The transcription of ERP29 was suppressed by EHMT2 by upregulating H3K9me2 and downregulating H3K4me3, thereby regulating radioresistance in prostate cancer cells. In addition, the downregulation of ERP29 promoted the progression of radioresistance in prostate cancer cells in nude mice. EHMT2 promotes radioresistance in prostate cancer cells by repressing ERP29 transcription.

Generation of Radioresistant Prostate Cancer Cells.

The development of in vitro isogenic models of radioresistance through exposure to fractionated radiation is an increasingly used approach to investigate the mechanisms of radioresistance in cancer cells. Owing to the complex nature of the biological effect of ionizing radiation, the generation and validation of these models requires the careful consideration of radiation exposure protocols and cellular endpoints. This chapter presents a protocol we used to derive and characterize an isogenic model of radioresistant prostate cancer cells. This protocol may be applicable to other cancer cell lines.

Dose-Response Prediction for SBRT of Prostate Cancer Based on Measured Cell Survival Curves Using a Unified Multi-Activation Model

<h3>Purpose/Objective(s)</h3> Hypofractionated external beam radiotherapy with 10 to 30 fractions (fx) and stereotactic body radiation therapy (SBRT) for prostate cancer (PC) have similar rates of cancer control and toxicity at 5 years as compared to conventional treatment. There is a lack of a radiobiological modeling from lab experiments to guide this transition. By assuming a unified multi-activation (UMA) model of lab-measured radiosensitivity (RS) of the cell lines to the entire dose range, we explored the clinical dose-response, modeling tumor-control probability (TCP) and normal-tissue complication probability (NTCP). <h3>Materials/Methods</h3> Published cell survival curves (CSC) with experimental error bars for PC of 5 DU145 CSCs, 3 CP3 CSCs, 6 LNCaP + 2 LnCaP with BCL2 overexpressed or down-regulated CSCs, 3 wild-type (WT)-22RV1 CSCs, 3 post-radiation radioresistant (RR)-22RV1 CSCs, 2 hypoxia-22RV1 CSCs, 3 urothelial HCV-29 CSCs and 4 large intestine (LI) or small intestine (SI) stem cell and organoid CSCs were fitted with a UMA model by using a logit transformation and c²-regression to obtain the model parameters of g and n and their deviations. Cell survival at any fractional dose (=total dose/fx) and TCP and NTCP for the total number of cancer cells or normal tissue cells corresponding to a grade of toxicity were analytically determined from the parameters. <h3>Results</h3> All of the CSCs had been excellently fitted with R² > 0.95 and Q-factor > 0.2 excepting for two in-vivo LI/SI crypt CSCs each with an outline point. We identified radiobiological parameters and predicted TCP/NTCP curves and listed the data for the 8Gyx5 SBRT of PC in Table 1 that are comparable with the results listed in the HyTEC papers. The 0% TCP to RR or hypoxia PC and 100% NTCP to SI are similar to conventional EBRT. The Dg reflects the major uncertainties in the lab-measured RS. D50, the total dose at 50% TCP or NTCP, correlated with RS and number of cells. Cell heterogeneity greatly changed RS and shapes of TCP and NTCP curves. <h3>Conclusion</h3> These findings may be useful for the design and evaluation of new clinical treatment schemes in PC translating lab work into clinical application.

Silibinin Radiosensitizes EGF Receptor-knockdown Prostate Cancer Cells by Attenuating DNA Repair Pathways.

Emergence of radioresistance in prostate cancer (PCa) cells is a major obstacle in cancer therapy and contributes to the relapse of the disease. EGF receptor (EGFR) signaling plays an important role in the development of radioresistance. Herein, we have assessed the modulatory effects of silibinin on radiation-induced resistance via DNA repair pathways in EGFR-knockdown DU145 cells. shRNA-based silencing of EGFR was done in radioresistant human PCa DU145 cells and effects of ionizing radiation (IR) and silibinin were assessed using clonogenic and trypan blue assays. Furthermore, radiosensitizing effects of silibinin on PCa in context with EGFR were analyzed using flow cytometry, comet assay, and immunoblotting. Silibinin decreased the colony formation ability with an increased death of DU145 cells exposed to IR (5 Gray), with a concomitant decrease in Rad51 protein expression. Silibinin (25 μM) augmented the IR-induced cytotoxic effect in EGFR-knockdown PCa cells, along with induction of G2/M phase cell cycle arrest. Further, we studied homologous recombination (HR) and non-homologous end joining (NHEJ) pathways in silibinin-induced DNA double-strand breaks in EGFR-knockdown DU145 cells. Silibinin down-regulated the expression of Rad51 and DNA-dependent protein kinase proteins without any considerable effect on Ku70 and Ku80 in IR-exposed EGFR-knockdown PCa cells. The pro-survival signaling proteins, phospho-extracellular signal-regulated kinases (ERK)1/2, phospho-Akt and phospho-STAT3 were decreased by silibinin in EGFR-deficient PCa cells. These findings suggest a novel mechanism of silibinin-induced radiosensitization of PCa cells by targeting DNA repair pathways, HR and NHEJ, and suppressing the pro-survival signaling pathways, ERK1/2, Akt and STAT3, in EGFR-knockdown PCa cells.

Drivers of Radioresistance in Prostate Cancer.

Prostate cancer (PCa) is the second most commonly diagnosed cancer worldwide. Radiotherapy remains one of the first-line treatments in localised disease and may be used as monotherapy or in combination with other treatments such as androgen deprivation therapy or radical prostatectomy. Despite advancements in delivery methods and techniques, radiotherapy has been unable to totally overcome radioresistance resulting in treatment failure or recurrence of previously treated PCa. Various factors have been linked to the development of tumour radioresistance including abnormal tumour vasculature, oxygen depletion, glucose and energy deprivation, changes in gene expression and proteome alterations. Understanding the biological mechanisms behind radioresistance is essential in the development of therapies that are able to produce both initial and sustained response to radiotherapy. This review will investigate the different biological mechanisms utilised by PCa tumours to drive radioresistance.

Peroxiredoxin IV plays a critical role in cancer cell growth and radioresistance through the activation of the Akt/GSK3 signaling pathways

High levels of redox enzymes have been commonly observed in various types of human cancer, although whether and how the enzymes contribute to cancer malignancy and therapeutic resistance have yet to be understood. Peroxiredoxin IV (Prx4) is an antioxidant with bona fide peroxidase and molecular chaperone functions. Here, we report that Prx4 is highly expressed in prostate cancer patient specimens, as well as established prostate cancer cell lines, and that its levels can be further stimulated through the activation of androgen receptor signaling. We used lentivirus-mediated shRNA knockdown and CRISPR-Cas9 based KO techniques to establish Prx4-depleted prostate cancer cells, which showed delayed cell cycle progression, reduced rate of cell proliferation, migration, and invasion compared to control cells. In addition, we used proteome profiler phosphokinase arrays to identify signaling changes in Prx4-depleted cells; we found that loss of Prx4 results in insufficient phosphorylation of both Akt and its downstream kinase GSK3α/β. Moreover, we demonstrate that Prx4-depleted cells are more sensitive to ionizing radiation as they display compromised ability to scavenge reactive oxygen species and increased accumulation of DNA damage. In mouse xenograft models, we show depletion of Prx4 leads to significant suppression of tumor growth, and tumors formed by Prx4-depleted cells respond more effectively to radiation therapy. Our findings suggest that increased levels of Prx4 contribute to the malignancy and radioresistance of prostate cancer through the activation of Akt/GSK3 signaling pathways. Therefore, strategies targeting Prx4 may be utilized to potentially inhibit tumor growth and overcome radioresistance in prostate cancer.

The RelB-BLNK Axis Determines Cellular Response to a Novel Redox-Active Agent Betamethasone during Radiation Therapy in Prostate Cancer.

Aberrant levels of reactive oxygen species (ROS) are potential mechanisms that contribute to both cancer therapy efficacy and the side effects of cancer treatment. Upregulation of the non-canonical redox-sensitive NF-kB family member, RelB, confers radioresistance in prostate cancer (PCa). We screened FDA-approved compounds and identified betamethasone (BET) as a drug that increases hydrogen peroxide levels in vitro and protects non-PCa tissues/cells while also enhancing radiation killing of PCa tissues/cells, both in vitro and in vivo. Significantly, BET increases ROS levels and exerts different effects on RelB expression in normal cells and PCa cells. BET induces protein expression of RelB and RelB target genes, including the primary antioxidant enzyme, manganese superoxide dismutase (MnSOD), in normal cells, while it suppresses protein expression of RelB and MnSOD in LNCaP cells and PC3 cells. RNA sequencing analysis identifies B-cell linker protein (BLNK) as a novel RelB complementary partner that BET differentially regulates in normal cells and PCa cells. RelB and BLNK are upregulated and correlate with the aggressiveness of PCa in human samples. The RelB-BLNK axis translocates to the nuclear compartment to activate MnSOD protein expression. BET promotes the RelB-BLNK axis in normal cells but suppresses the RelB-BLNK axis in PCa cells. Targeted disruptions of RelB-BLNK expressions mitigate the radioprotective effect of BET on normal cells and the radiosensitizing effect of BET on PCa cells. Our study identified a novel RelB complementary partner and reveals a complex redox-mediated mechanism showing that the RelB-BLNK axis, at least in part, triggers differential responses to the redox-active agent BET by stimulating adaptive responses in normal cells but pushing PCa cells into oxidative stress overload.

A radiation resistance related index for biochemical recurrence and tumor immune environment in prostate cancer patients

PurposeTo establish and verify a novel radiation resistance related index for predicting biochemical recurrence and tumor immune environment in prostate cancer (PCa) patients. Materials and methodsThe transcriptome information of PCa were obtained from GEO and TCGA portal. We identified radiation resistance related genes (RRGs) between radioresistant and radiosensitive PCa cells. We conducted multivariate Cox analysis to construct a novel radiation resistance related index for predicting biochemical recurrence (BCR)-free survival (BCRFS). Internal and external validations were conducted. Preliminary experimental verifications were performed. ResultsWe identified 194 differentially expressed RRGs and three radiation resistance related molecular clusters for PCa. Moreover, we established a novel radiation resistance related index and succeeded in conducting internal and external validations. High-risk populations meant significantly worse BCRFS in training, testing and validating cohort. The area under receiver operating characteristic curve were 0.809, 0.698, and 0.712 in training, testing, and validating cohort. The immune microenvironment was significantly different between high and low-risk score patients. Preliminary experiment identified and validated three potential biomarkers related to radiation resistance (ZNF695, TM4SF19, CCDC3) of PCa. ConclusionsThis study successfully established and verified a novel radiation resistance related index, which had an excellent performance in predicting BCR and tumor immune microenvironment in patients with PCa.

Antagonizing Glutamine Bioavailability Promotes Radiation Sensitivity in Prostate Cancer.

Simple SummaryRadiation is the standard of care for prostate cancer, but almost half the patients develop resistant disease. It is imperative to understand the reasons behind disease progression to develop more effective strategies of treatment. We determined that glutamine is a crucial nutrient in driving prostate cancer tumors as people with more glutamine have poorer outcomes. We hypothesized that directly depriving cancer cells of this precious resource will further sensitize them to radiation. We sought to repurpose the drug L-asparaginase, which has been used extensively to treat leukemia patients, to complement radiation therapy for prostate cancer patients. This drug depletes glutamine in the blood and hinders an aspect of cell growth that makes cancer cells that are otherwise resistant vulnerable to irradiation. Ultimately, mouse models of prostate cancer given L-asparaginase in combination with irradiation were more effective at reducing tumor size than radiation alone.Nearly half of localized prostate cancer (PCa) patients given radiation therapy develop recurrence. Here, we identified glutamine as a key player in mediating the radio-sensitivity of PCa. Glutamine transporters and glutaminase are upregulated by radiation therapy of PCa cells, but respective inhibitors were ineffective in radio-sensitization. However, targeting glutamine bioavailability by L-asparaginase (L-ASP) led to a significant reduction in clonogenicity when combined with irradiation. L-ASP reduced extracellular asparagine and glutamine, but the sensitization effects were driven through its depletion of glutamine. L-ASP led to G2/M cell cycle checkpoint blockade. As evidence, there was a respective delay in DNA repair associated with RAD51 downregulation and upregulation of CHOP, contributing to radiation-induced cell death. A radio-resistant PCa cell line was developed, was found to bypass radiation-induced mitotic catastrophe, and was sensitive to L-ASP/radiation combination treatment. Previously, PCa-associated fibroblasts were reported as a glutamine source supporting tumor progression. As such, glutamine-free media were not effective in promoting radiation-induced PCa cell death when co-cultured with associated primary fibroblasts. However, the administration L-ASP catalyzed glutamine depletion with irradiated co-cultures and catalyzed tumor volume reduction in a mouse model. The clinical history of L-ASP for leukemia patients supports the viability for its repurposing as a radio-sensitizer for PCa patients.

OC-0426 ALDH genes as regulators of prostate cancer radioresistance, stemness and bone metastases

OC-0426 ALDH genes as regulators of prostate cancer radioresistance, stemness and bone metastases

MO-0140 Glutamine transporters as regulators of prostate cancer radioresistance

MO-0140 Glutamine transporters as regulators of prostate cancer radioresistance

Early PSA density kinetics predicts biochemical and local failure following extreme hypofractionated radiotherapy in intermediate-risk prostate cancer

PurposeThe present study explores PSA density (PSA-D) as predictor of biochemical and local failure in organ-confined prostate cancer at 3–6 months after hypofractionated stereotactic ablative radiotherapy (SABR). Methods and materialsA cohort of 219, hormone-naïve, NCCN intermediate-risk prostate cancer patients were derived from a phase 2 study of 5 × 9 Gy prostate cancer SABR. PSA-D was calculated at 3 and 6 months by dividing serum PSA by the MR-derived prostate CTV, while the slope of the 3–6 months curve was used to express the kinetics of PSA-D decay. ResultsThe median follow-up was 60.3 (range 46–76) months, and the actuarial 7-year bRFS was 98.0% for intermediate-risk favorable (FIR) patients versus 84.5% for the unfavorable (UIR) subgroup (P = 0.02). Fourteen patients developed a Phoenix-defined biochemical PSA relapse (bRFS) at a median of 34.2 months, 11 confirmed with 68Ga-PSMA PET/CT scan that revealed tracer uptake at the site of dominant intraprostatic pretreatment lesion in 8 patients. The 3-month PSA-D concertation (cut-off 0.08 ng/ml2) and 3–6 months decay slope (cut-off −0.45) values were predictive of long-term bRFS. A dual adverse PSA-D permutation was detected in 25/148 UIR patients, exhibiting 47.5% 7-year bRFS compared with 94.1% for the remaining 123 UIR patients with favorable PSA-D kinetics (P = 0.0006). Intraprostatic local relapse in patients with a 3-month PSA-D > 0.080 ng/ml2 was 11.0% vs. 1.7% for patients with PSA-D ≤ 0.080 ng/ml2 (P = 0.01) and 2.3% vs. 4.3%, respectively, for nodal progression (P = 0.68). ConclusionsEarly post-treatment PSA-D kinetics transcends pre-treatment risk stratification of tumor relapse and adds a nuance in the biological characterization of intermediate-risk prostate cancer phenotypes. The dual adverse PSA-D algorithm may serve as a tool to validate current search of classifiers of radioresistance in prostate cancer with therapeutic implications.

The role of microRNAs in the development of radioresistance of prostate cancer cells (experimental study)

Background. Radiation therapy is one of the leading treatments for early and late stage prostate cancer. Radiation therapy is one of the leading treatments for early and late stage prostate cancer. The significant frequency of prostate cancer progression after radiation therapy makes it relevant to study the molecular mechanisms of the development of radioresistance, to identify prognostic markers of its development.Objective: identification and analysis of the mechanism of action of microRNAs regulating radioresistance of prostate cancer cells on the model of the androgen-independent DU145 cell line.Materials and methods. We used human prostate adenocarcinoma cell lines: DU145-hormone-independent prostate cancer cell line and DU145-RR - its radioresistant variant. Differential microRNA expression was measured in cultured DU145 and DU145-RR cells 1, 8 days after a single gamma irradiation at a dose of 4 Gy. To analyze the differential expression of microRNAs in the initial and radioresistant variants of DU145 cells, the HiSeq 2000 platform (Illumina Inc., USA) was used. The miRBase v.21 database was used to identify microRNAs. The miRTarbase 7.0 and KEGG PATHWAY databases were used for bioinformatic analysisResults. The results of the study showed that the aberrant expression of miR-101-3p, -148a-3p, -21-3p, -532-5p, -92a-3p in DU145-RR cells upregulated compared to that in DU145 cells, and miR-125b-5p, -23a-3p, -424-3p - downregulated. It has been shown that the role of these microRNAs is associated with the provision of functional interaction between DNA methyltransferases, the transcriptional regulator of the proto-oncogenic protein Myc, and PTEN phosphatase in the regulation of the activity of MAPK and PI3K protein kinase signaling cascades. Constitutive activation of these cascades leads to an increase in cell survival, migration, proliferation, and growth.Conclusion. A wide range of target genes and a significant change in the expression profiles of microRNAs in various conditions, including the transition of malignant cells to a radioresistant status, makes microRNAs promising prognostic markers of radioresistance in prostate cancer.

Caffeic acid phenethyl ester induces radiosensitization via inhibition of DNA damage repair in androgen-independent prostate cancer cells.

In the present study, we evaluated the radiomodulatory potential of caffeic acid phenethyl ester (CAPE), an active component of traditional herbal medicine propolis. CAPE has been identified as a potent anticancer agent in multiple cancer types and is reported to have the dual role of radioprotection and radiosensitization. However, the radiomodulatory potential of CAPE in prostate cancer (PCa), which eventually becomes radioresistant is not known. Therefore, we studied the effect of co-treatment of CAPE and gamma radiation on androgen-independent DU145 and PC3 cells. The combination treatment sensitized PCa cells to radiation in a dose-dependent manner. The radiosensitizing effect of CAPE was observed in both cell lines. CAPE enhanced the level of ionizing radiation (IR)-induced gamma H2AX foci and cell death by apoptosis. The combination treatment also decreased the migration potential of PCa cells. This was confirmed by increased expression of E-cadherin and decrease in vimentin expression. CAPE sensitized PCa cells to radiation in vitro and induced apoptosis, augmented phosphorylation of Akt/mTOR, and hampered cell migration. At the mechanistic level, co-treatment of CAPE and IR inhibited cell growth by decreasing RAD50 and RAD51 proteins involved in DNA repair. This resulted in enhanced DNA damage and cell death. CAPE might represent a promising new adjuvant for the treatment of hormone-refractory radioresistant PCa.