Ferroptosis Inducers in Thyroid Cancer.

PURPOSE: Papillary thyroid carcinoma (PTC) progression imparts reduced patient survival. Tumor resistance and progression can be influenced by Glutathione (GSH) metabolism. Glutathione peroxidase 4 (GPX4) regulates GSH oxidation to prevent lipid peroxidation of cell membranes during increased oxidative stress and regulates ferroptosis cell death pathway in tumor cells. This study examines the differential ferroptosis effects by GPX4 inhibitors in thyroid cancer cell and 3-D spheroid in vitro models. MATERIALS AND METHODS: We examined differential effects of GPX4 inhibitors on PTC cells (K1, MDA-T32, MDA-T68) with BRAF and RAS mutations, and TERT promoter and PIK3CA co-mutations. The effects of GPX4 inhibitors on ferroptosis activation, proliferation, oxidative stress, and activation of signaling pathways were assessed by Western blot, total (GSH) and oxidized glutathione (GSSG) levels, ROS induction, RT-qPCR, migration, and proliferation assays. RESULTS: GPX4 inhibitors induced ferroptosis, rising ROS, GSH depletion, arrested tumor cell migration, increased DNA damage, suppressed mTOR pathway and DNA repair response in PTC cells in vitro. Differential responses to DNA damage and GPX4 levels were observed between 3-D PTC spheroids and thyroid cancer cells in a monolayer model. CONCLUSION: Effective GPX4 inhibition with various inhibitors induced a robust but differential activation of ferroptosis in monolayer thyroid tumor cell and 3-D PTC spheroid models. Our study is the first of its kind to determine the differential effects of GPX4 inhibitors on thyroid cancer cells with diverse mutational signatures. We have identified a novel mechanism of action of GPX4 inhibition in preclinical in vitro models of thyroid cancer that can be further exploited for therapeutic benefit in advanced therapy-resistant thyroid cancers.

Integrative computational immunogenomic profiling of cortisol-secreting adrenocortical carcinoma.

Adrenocortical carcinoma (ACC) is a rare but highly aggressive malignancy. Nearly half of ACC tumours overproduce and secrete adrenal steroids. Excess cortisol secretion, in particular, has been associated with poor prognosis among ACC patients. Furthermore, recent immunotherapy clinical trials have demonstrated significant immunoresistance among cortisol-secreting ACC (CS-ACC) patients when compared to their non-cortisol-secreting (nonCS-ACC) counterparts. The immunosuppressive role of excess glucocorticoid therapies and hypersecretion is known; however, the impact of the cortisol hypersecretion on ACC tumour microenvironment (TME), immune expression profiles and immune cell responses remain largely undefined. In this study, we characterized the TME of ACC patients and compared the immunogenomic profiles of nonCS-ACC and CS-ACC tumours to assess the impact of differentially expressed genes (DEGs) by utilizing The Cancer Genome Atlas (TCGA) database. Immunogenomic comparison (CS- vs. nonCS-ACC tumour TMEs) demonstrated an immunosuppressive expression profile with a direct impact on patient survival. We identified several primary prognostic indicators and potential targets within ACC tumour immune landscape. Differentially expressed immune genes with prognostic significance provide additional insight into the understanding of potential contributory mechanisms underlying failure of initial immunotherapeutic trials and poor prognosis of patients with CS-ACC.

Development and validation of a novel assay to identify radiosensitizers that target nucleophosmin 1.

A series of indole analogs that are synthesized using the scaffold of a potent radiosensitizer, YTR107, were tested for their ability to alter the solubility of phosphorylated nucleophosmin 1 (pNPM1). NPM1 is critical for DNA double strand break (DSB) repair. In response to formation of DNA DSBs, phosphorylated T199 NPM1 binds to ubiquitinated chromatin, in a RNF8/RNF168-dependent manner, forming irradiation-induced foci (IRIF) that promote repair of DNA DSBs. A Western blot assay was developed using lead molecule, YTR107, for the purpose of screening newly synthesized molecules that target pNPM1 in irradiated cells. A colony formation assay was used to demonstrate the radiosensitization properties of the compounds. Compounds that enhanced the extractability of pNPM1 upon radiation treatment possessed radiosensitization properties.

1-Benzyl-2-methyl-3-indolylmethylene barbituric acid derivatives: Anti-cancer agents that target nucleophosmin 1 (NPM1).

In the present study, we have designed and synthesized a series of 1-benzyl-2-methyl-3-indolylmethylene barbituric acid analogs (7a-7h) and 1-benzyl-2-methyl-3-indolylmethylene thiobarbituric acid analogs (7 i-7 l) as nucleophosmin 1 (NPM1) inhibitors and have evaluated them for their anti-cancer activity against a panel of 60 different human cancer cell lines. Among these analogs 7 i, 7 j, and 7 k demonstrated potent growth inhibitory effects in various cancer cell types with GI50 values <2 µM. Compound 7 k exhibited growth inhibitory effects on a sub-panel of six leukemia cell lines with GI50 values in the range 0.22-0.35 µM. Analog 7 i also exhibited GI50 values <0.35 µM against three of the leukemia cell lines in the sub-panel. Analogs 7 i, 7 j, 7 k and 7 l were also evaluated against the mutant NPM1 expressing OCI-AML3 cell line and compounds 7 k and 7 l were found to cause dose-dependent apoptosis (AP50 = 1.75 µM and 3.3 µM, respectively). Compound 7k also exhibited potent growth inhibition against a wide variety of solid tumor cell lines: that is, A498 renal cancer (GI50 = 0.19 µM), HOP-92 and NCI-H522 lung cancer (GI50 = 0.25 µM), COLO 205 and HCT-116 colon cancer (GI50 = 0.20 and 0.26 µM, respectively), CNS cancer SF-539 (GI50 = 0.22 µM), melanoma MDA-MB-435 (GI50 = 0.22 µM), and breast cancer HS 578T (GI50 = 0.22 µM) cell lines. Molecular docking studies suggest that compounds 7 k and 7 l exert their anti-leukemic activity by binding to a pocket in the central channel of the NPM1 pentameric structure. These results indicate that the small molecule inhibitors 7 i, 7 j, 7 k, and 7 l could be potentially developed into anti-NPM1 drugs for the treatment of a variety of hematologic malignancies and solid tumors.

The novel antiangiogenic VJ115 inhibits the NADH oxidase ENOX1 and cytoskeleton-remodeling proteins.

Targeting tumor vasculature represents a rational strategy for controlling cancer. (Z)-(+/-)-2-(1-benzylindol-3-ylmethylene)-1-azabicyclo[2.2.2]octan-3-ol (denoted VJ115) is a novel chemical entity that inhibits the enzyme ENOX1, a NADH oxidase. Genetic and small molecule inhibition of ENOX1 inhibits endothelial cell tubule formation and tumor-mediated neo-angiogenesis. Inhibition of ENOX1 radiosensitizes tumor vasculature, a consequence of enhanced apoptosis. However, the molecular mechanisms underlying these observations are not well understood. Herein, we mechanistically link ENOX1-mediated regulation of cellular NADH concentrations with proteomics profiling of endothelial cell protein expression following exposure to VJ115. Pathway Studios network analysis of potential effector molecules identified by the proteomics profiling indicated that a VJ115 exposure capable of altering intracellular NADH concentrations impacted proteins involved in cytoskeletal reorganization. The analysis was validated using RT-PCR and immunoblotting of selected proteins. RNAi knockdown of ENOX1 was shown to suppress expression of stathmin and lamin A/C, proteins identified by the proteomics analysis to be suppressed upon VJ115 exposure. These data support the hypothesis that VJ115 inhibition of ENOX1 can impact expression of proteins involved in cytoskeletal reorganization and support a hypothesis in which ENOX1 activity links elevated cellular NADH concentrations with cytoskeletal reorganization and angiogenesis.

Nucleophosmin Plays a Role in Repairing DNA Damage and Is a Target for Cancer Treatment.

Nucleophosmin (NPM1) is frequently mutated in acute myeloid leukemia, and NPM1 expression is elevated in several cancer types. NPM1 is a multifunctional oligomeric protein involved in numerous cellular functions that include participating in liquid-liquid phase separation, ribosome biogenesis, chaperoning of histones, and modulation of transcription. In this review, we discuss the underappreciated role of NPM1 in DNA damage repair, specifically Polη-mediated translesion synthesis, base excision, and homologous recombination and highlight the therapeutic potential of NPM1 targeting in cancer treatment.

Metabolism of parathyroid organoids.

Introduction: We successfully developed a broad spectrum of patient-derived endocrine organoids (PDO) from benign and malignant neoplasms of thyroid, parathyroid, and adrenal glands. In this study, we employed functionally intact parathyroid PDOs from benign parathyroid tissues to study primary hyperparathyroidism (PHPT), a common endocrine metabolic disease. As proof of concept, we examined the utility of parathyroid PDOs for bioenergetic and metabolic screening and assessed whether parathyroid PDO metabolism recapitulated matched PHPT tissues. Methods: Our study methods included a fine-needle aspiration (FNA)-based technique to establish parathyroid PDOs from human PHPT tissues (n=6) in semi-solid culture conditions for organoid formation, growth, and proliferation. Mass spectrometry metabolomic analysis of PHPT tissues and patient-matched PDOs, and live cell bioenergetic profiling of parathyroid PDOs with extracellular flux analyses, were performed. Functional analysis cryopreserved and re-cultured parathyroid PDOs for parathyroid hormone (PTH) secretion was performed using ELISA hormone assays. Results and discussion: Our findings support both the feasibility of parathyroid PDOs for metabolic and bioenergetic profiling and reinforce metabolic recapitulation of PHPT tissues by patient-matched parathyroid PDOs. Cryopreserved parathyroid PDOs exhibited preserved, rapid, and sustained secretory function after thawing. In conclusion, successful utilization of parathyroid PDOs for metabolic profiling further affirms the feasibility of promising endocrine organoid platforms for future metabolic studies and broader multiplatform and translational applications for therapeutic advancements of parathyroid and other endocrine applications.

Engineering functional 3-dimensional patient-derived endocrine organoids for broad multiplatform applications.

BACKGROUND: Recent advancements in 3-dimensional patient-derived organoid models have revolutionized the field of cancer biology. There is an urgent need for development of endocrine tumor organoid models for medullary thyroid carcinoma, adrenocortical carcinoma, papillary thyroid carcinoma, and a spectrum of benign hyperfunctioning parathyroid and adrenal neoplasms. We aimed to engineer functionally intact 3-dimensional endocrine patient-derived organoids to expand the in vitro and translational applications for the advancement of endocrine research. METHODS: Using our recently developed fine needle aspiration-based methodology, we established patient-derived 3-dimensional endocrine organoid models using prospectively collected human papillary thyroid carcinoma (n = 6), medullary thyroid carcinoma (n = 3), adrenocortical carcinoma (n = 3), and parathyroid (n = 5). and adrenal (n = 5) neoplasms. Multiplatform analyses of endocrine patient-derived organoids and applications in oncoimmunology, near-infrared autofluorescence, and radiosensitization studies under 3-dimensional in vitro conditions were performed. RESULTS: We have successfully modeled and analyzed the complex endocrine microenvironment for a spectrum of endocrine neoplasms in 3-dimensional culture. The endocrine patient-derived organoids recapitulated complex tumor microenvironment of endocrine neoplasms morphologically and functionally and maintained cytokine production and near-infrared autofluorescence properties. CONCLUSION: Our novel engineered endocrine patient-derived organoid models of thyroid, parathyroid and adrenal neoplasms represent an exciting and elegant alternative to current limited 2-dimensional systems and afford future broad multiplatform in vitro and translational applications, including in endocrine oncoimmunology.

Glutathione peroxidase 4 inhibition induces ferroptosis and mTOR pathway suppression in thyroid cancer.

Papillary thyroid carcinoma (PTC) demonstrates significantly reduced patient survival with metastatic progression. Tumor progression can be influenced by metabolism, including antioxidant glutathione (GSH). Glutathione peroxidase 4 (GPX4) is a selenoenzyme that uses GSH as a co-factor to regulate lipid peroxidation of cell membranes during increased oxidative stress. GPX4 suppression in tumor cells can induce ferroptosis. This study aims to examine ferroptosis as a potentially critical pathway in effective targeting of thyroid cancer (TC) cells. We treated human TC cells (K1, MDA-T68, MDA-T32, TPC1) with (1S,3R)-RSL3 (RSL3), a small-molecule inhibitor of GPX4 and examined the effects on ferroptosis, tumor cell survival and migration, spheroid formation, oxidative stress, DNA damage repair response, and mTOR signaling pathway in vitro. GPX4 inhibition activated ferroptosis, inducing TC cell death, rapid rise in reactive oxygen species and effectively arrested cell migration in vitro. Suppression of mTOR signaling pathway triggered autophagy. GPX4 genetic knockdown mirrored RSL3 effect on mTOR pathway suppression. RSL3 subdued DNA damage repair response by suppressing phosphorylation of nucleophosmin 1 (NPM1). Thus, observed potent induction of ferroptosis, GPX4-dependent novel suppression of mTOR pathway and DNA damage repair response in preclinical in vitro model of TC supports GPX4 targeting for therapeutic benefit in advanced therapy-resistant thyroid cancers.

Multiplatform computational analysis of mast cells in adrenocortical carcinoma tumor microenvironment.

BACKGROUND: Immunotherapeutic response failure of adrenocortical carcinomas highlights a need for novel strategies targeting immune cell populations in the tumor microenvironment to overcome tumor resistance and enhance therapeutic response. A recent study explored a new link between tumor mast cell infiltration and improved outcomes in patients with adrenocortical carcinomas. We further dissect the role of mast cells in the tumor microenvironment of adrenocortical carcinomas by examining the tumor mast cell expression signatures and mast cell activity within the tumor microenvironment to provide additional insight into potential novel immunotherapeutic targets. METHODS: Using the CIBERSORTx computational immunogenomic deconvolution algorithm to analyze adrenocortical carcinoma tumor gene messenger RNA expression data (The Cancer Genome Atlas, N = 79), we estimated the abundance of tumor immune infiltrating mast cells and assessed prognostic potential of mast cell signaling genes as pro or antitumor signatures, as well as examined the impact on overall and disease-free survival. RESULTS: We stratified mast cell signaling genes with survival prognostic values (overall survival, disease-free survival, P < .05) into antitumor (ALOX5, CCL2, CCL5, CXCL10, HDC, IL16, TNF, TPSAB1, VEGFD) and protumor (CXCL1, CXCL3, CXCL8, IL4, IL13, PTGS3, TNSF4, VEGFD) groups. Antitumor mast cell signature, as the predominant phenotype, was associated with improved overall and disease-free survival. CONCLUSION: The deconvolution analysis of The Cancer Genome Atlas data identified mast cell infiltration in the adrenocortical carcinoma microenvironment as predominantly associated with antitumor activity. Future studies stemming from our findings may help define the role of mast cells in the tumor microenvironment and the impact on patient survival in patients with adrenocortical carcinomas. Modulation of tumor mast cell infiltration may serve as a potential target for novel synergistic immunotherapies for the treatment and improved survival of patients with adrenocortical carcinomas.

Inhibition of cyclic nucleotide phosphodiesterases by methylxanthines and related compounds.

Naturally occurring methylxanthines were the first inhibitors of cyclic nucleotide (cN) phosphodiesterases (PDEs) to be discovered. To improve potency and specificity for inhibition of various PDEs in research and for treatment of diseases, thousands of compounds with related structures have now been synthesized. All known PDE inhibitors contain one or more rings that mimic the purine in the cN substrate and directly compete with cN for access to the catalytic site; this review focuses on inhibitors that contain a nucleus that is closely related to the xanthine ring of theophylline and caffeine and the purine ring of cNs. The specificity and potency of these compounds for blocking PDE action have been improved by appending groups at positions on the rings as well as by modification of the number and distribution of nitrogens and carbons in those rings. Several of these inhibitors are highly selective for particular PDEs; potent and largely selective PDE5 inhibitors are used clinically for treatment of erectile dysfunction [sildenafil (Viagra™), tadalafil (Cialis™) and vardenafil (Levitra™)] and pulmonary hypertension [sildenafil (Revatio™) and tadalafil (Adenocirca)]. Related compounds target other PDEs and show therapeutic promise for a number of maladies.

Targeting NPM1 in irradiated cells inhibits NPM1 binding to RAD51, RAD51 foci formation and radiosensitizes NSCLC.

The ability of chemo-radiation therapy to control locally advanced stage III non-small cell lung cancer (NSCLC) is poor. While addition of consolidation immunotherapy has improved outcomes in subsets of patients there is still an urgent need for new therapeutic targets. Emerging research indicates that nucleophosmin1 (NPM1) is over-expressed in NSCLC, promotes tumor growth and that over-expression correlates with a lower survival probability. NPM1 is critical for APE1 base excision activity and for RAD51-mediated repair of DNA double strand breaks (DSBs). YTR107 is a small molecule radiation sensitizer that has been shown to bind to NPM1, suppressing pentamer formation. Here we show that in irradiated cells YTR107 inhibits SUMOylated NPM1 from associating with RAD51, RAD51 foci formation and repair of DSBs. YTR107 acts synergistically with the PARP1/2 inhibitor ABT 888 to increase replication stress and radiation-induced cell lethality. YTR107 was found to radiosensitize tumor initiating cells. Congruent with this knowledge, adding YTR107 to a fractionated irradiation regimen diminished NSCLC xenograft growth and increased overall survival. These data support the hypothesis that YTR107 represents a therapeutic target for control of NSCLC.

Cysteine-based regulation of the CUL3 adaptor protein Keap1.

Nrf2 (NF-E2-related factor 2) is a master transcription factor containing a powerful acidic transcriptional activation domain. Nrf2-dependent gene expression impacts cancer chemoprevention strategies, inflammatory responses, and progression of neurodegenerative diseases. Under basal conditions, association of Nrf2 with the CUL3 adaptor protein Keap1 results in the rapid Nrf2 ubiquitylation and proteasome-dependent degradation. Inhibition of Keap1 function blocks ubiquitylation of Nrf2, allowing newly synthesized Nrf2 to translocate into the nucleus, bind to ARE sites and direct target gene expression. Site-directed mutagenesis experiments coupled with proteomic analysis support a model in which Keap1 contains at least 2 distinct cysteine motifs. The first is located at Cys 151 in the BTB domain. The second is located in the intervening domain and centers around Cys 273 and 288. Adduction or oxidation at Cys151 has been shown to produce a conformational change in Keap1 that results in dissociation of Keap1 from CUL3, thereby inhibiting Nrf2 ubiquitylation. Thus, adduction captures specific chemical information and translates it into biochemical information via changes in structural conformation.

Indolyl-quinuclidinols inhibit ENOX activity and endothelial cell morphogenesis while enhancing radiation-mediated control of tumor vasculature.

There is a need for novel strategies that target tumor vasculature, specifically those that synergize with cytotoxic therapy, in order to overcome resistance that can develop with current therapeutics. A chemistry-driven drug discovery screen was employed to identify novel compounds that inhibit endothelial cell tubule formation. Cell-based phenotypic screening revealed that noncytotoxic concentrations of (Z)-(+/-)-2-(1-benzenesulfonylindol-3-ylmethylene)-1-azabicyclo[2. 2.2]octan-3-ol (analog I) and (Z)-(+/-)-2-(1-benzylindol-3-ylmethylene)-1-azabicyclo[2.2.2]octan-3-ol (analog II) inhibited endothelial cell migration and the ability to form capillary-like structures in Matrigel by > or =70%. The ability to undergo neoangiogenesis, as measured in a window-chamber model, was also inhibited by 70%. Screening of biochemical pathways revealed that analog II inhibited the enzyme ENOX1 (EC(50) = 10 microM). Retroviral-mediated shRNA suppression of endothelial ENOX1 expression inhibited cell migration and tubule formation, recapitulating the effects observed with the small-molecule analogs. Genetic or chemical suppression of ENOX1 significantly increased radiation-mediated Caspase3-activated apoptosis, coincident with suppression of p70S6K1 phosphorylation. Administration of analog II prior to fractionated X-irradiation significantly diminished the number and density of tumor microvessels, as well as delayed syngeneic and xenograft tumor growth compared to results obtained with radiation alone. Analysis of necropsies suggests that the analog was well tolerated. These results suggest that targeting ENOX1 activity represents a novel therapeutic strategy for enhancing the radiation response of tumors.

Radiosensitization of cancer cells by hydroxychalcones.

Radiation sensitization is significantly increased by proteotoxic stress, such as a heat shock. We undertook an investigation, seeking to identify natural products that induced proteotoxic stress and then determined if a compound exhibited radiosensitizing properties. The hydroxychalcones, 2',5'-dihydroxychalcone (D-601) and 2,2'-dihydroxychalcone (D-501), were found to activate heat shock factor 1 (Hsf1) and exhibited radiation sensitization properties in colon and pancreatic cancer cells. The radiosensitization ability of D-601 was blocked by pretreatment with α-napthoflavone (ANF), a specific inhibitor of cytochrome P450 1A2 (CYP1A2), suggesting that the metabolite of D-601 is essential for radiosensitization. The study demonstrated the ability of hydroxychalcones to radiosensitize cancer cells and provides new leads for developing novel radiation sensitizers.

Antiangiogenic properties of substituted (Z)-(±)-2-(N-benzylindol-3-ylmethylene)quinuclidin-3-ol/one analogs and their derivatives.

In the past half century research efforts have defined a critical role for angiogenesis in tumor growth and metastasis. We previously reported that inhibition of a novel target, ENOX1, by a (Z)-2-benzylindol-3-ylmethylene) quinuclidin-3-ol, suppressed tumor angiogenesis. The present study was undertaken in order to establish structure-activity relationships for quinuclidine analogs. The angiogenesis inhibiting activity of a series of substituted (Z)-(±)-2-(N-benzylindol-3-ylmethylene)quinuclidin-3-ols (1a-1k), (Z)-2-benzylindol-3-ylmethylene)quinuclidin-3-ones (2a-2h), (Z)-(±)-2-(1H/N-methyl-indol-3-ylmethylene)quinuclidin-3-ols (3a-3b), and substituted (Z)-(±)-2-(N-benzenesulfonylindol-3-yl-methylene)quinuclidin-3-ols and their derivatives (4a-4d) that incorporate a variety of substituents in both the indole and N-benzyl moieties was evaluated using Human Umbilical Vein Endothelial Cells (HUVECs) subjected to in vitro cell migration scratch assays, tubule formation in Matrigel, cell viability and proliferation assays. In total, 25 different analogs were evaluated. Based on in vitro cell migration scratch assays, eight analogs were identified as potent angiogenesis inhibitors at 10 µM, a concentration that was determined to be nontoxic by colony formation assay. In addition, this approach identified a potent antiangiogenic ENOX1 inhibitor, analog 4b.

Novel substituted (Z)-5-((N-benzyl-1H-indol-3-yl)methylene)imidazolidine-2,4-diones and 5-((N-benzyl-1H-indol-3-yl)methylene)pyrimidine-2,4,6(1H,3H,5H)-triones as potent radio-sensitizing agents.

A series of (Z)-5-((N-benzyl-1H-indol-3-yl)methylene)imidazolidine-2,4-dione (9a-9m) and 5-((N-benzyl-1H-indol-3-yl)methylene)pyrimidine-2,4,6(1H,3H,5H)-trione (10a-10i) derivatives that incorporate a variety of aromatic substituents in both the indole and N-benzyl moieties have been synthesized. These analogs were evaluated for their radiosensitization activity against the HT-29 cell line. Three analogs, 10a, 10b, and 10c were identified as the most potent radiosensitizing agents.

Novel chemical enhancers of heat shock increase thermal radiosensitization through a mitotic catastrophe pathway.

Radiation therapy combined with adjuvant hyperthermia has the potential to provide outstanding local-regional control for refractory disease. However, achieving therapeutic thermal dose can be problematic. In the current investigation, we used a chemistry-driven approach with the goal of designing and synthesizing novel small molecules that could function as thermal radiosensitizers. (Z)-(+/-)-2-(1-Benzenesulfonylindol-3-ylmethylene)-1-azabicyclo[2.2.2]octan-3-ol was identified as a compound that could lower the threshold for Hsf1 activation and thermal sensitivity. Enhanced thermal sensitivity was associated with significant thermal radiosensitization. We established the structural requirements for activity: the presence of an N-benzenesulfonylindole or N-benzylindole moiety linked at the indolic 3-position to a 2-(1-azabicyclo[2.2.2]octan-3-ol) or 2-(1-azabicyclo[2.2.2]octan-3-one) moiety. These small molecules functioned by exploiting the underlying biophysical events responsible for thermal sensitization. Thermal radiosensitization was characterized biochemically and found to include loss of mitochondrial membrane potential, followed by mitotic catastrophe. These studies identified a novel series of small molecules that represent a promising tool for the treatment of recurrent tumors by ionizing radiation.

Radiosensitization by enzalutamide for human prostate cancer is mediated through the DNA damage repair pathway.

Radiation therapy is often combined with androgen deprivation therapy in the treatment of aggressive localized prostate cancer. However, castration-resistant disease may not respond to testosterone deprivation approaches. Enzalutamide is a second-generation anti-androgen with high affinity and activity that is used for the treatment of metastatic disease. Although radiosensitization mechanisms are known to be mediated through androgen receptor activity, this project aims to uncover the detailed DNA damage repair factors influenced by enzalutamide using multiple models of androgen-sensitive (LNCaP) and castration-resistant human prostate cancer (22Rv1 and DU145). Enzalutamide is able to radiosensitize both androgen-dependent and androgen-independent human prostate cancer models in cell culture and xenografts in mice, as well as a treatment-resistant patient-derived xenograft. The enzalutamide-mediated mechanism of radiosensitization includes delay of DNA repair through temporal prolongation of the repair factor complexes and halting the cell cycle, which results in decreased colony survival. Altogether, these findings support the use of enzalutamide concurrently with radiotherapy to enhance the treatment efficacy for prostate cancer.

Inhibition of mammalian target of rapamycin or apoptotic pathway induces autophagy and radiosensitizes PTEN null prostate cancer cells.

The phosphatidylinositol 3-kinase/Akt pathway plays a critical role in oncogenesis, and dysregulation of this pathway through loss of PTEN suppression is a particularly common phenomenon in aggressive prostate cancers. The mammalian target of rapamycin (mTOR) is a downstream signaling kinase in this pathway, exerting prosurvival influence on cells through the activation of factors involved in protein synthesis. The mTOR inhibitor rapamycin and its derivatives are cytotoxic to a number of cell lines. Recently, mTOR inhibition has also been shown to radiosensitize endothelial and breast cancer cells in vitro. Because radiation is an important modality in the treatment of prostate cancer, we tested the ability of the mTOR inhibitor RAD001 (everolimus) to enhance the cytotoxic effects of radiation on two prostate cancer cell lines, PC-3 and DU145. We found that both cell lines became more vulnerable to irradiation after treatment with RAD001, with the PTEN-deficient PC-3 cell line showing the greater sensitivity. This increased susceptibility to radiation is associated with induction of autophagy. Furthermore, we show that blocking apoptosis with caspase inhibition and Bax/Bak small interfering RNA in these cell lines enhances radiation-induced mortality and induces autophagy. Together, these data highlight the emerging importance of mTOR as a molecular target for therapeutic intervention, and lend support to the idea that nonapoptotic modes of cell death may play a crucial role in improving tumor cell kill.