Epigenetic disruption of the RARγ complex impairs its function to bookmark AR enhancer interactions required for enzalutamide sensitivity in prostate cancer.

The current study in prostate cancer (PCa) focused on the genomic mechanisms at the cross-roads of pro-differentiation signals and the emergence of lineage plasticity. We explored an understudied cistromic mechanism involving RARγ's ability to govern AR cistrome-transcriptome relationships, including those associated with more aggressive PCa features. The RARγ complex in PCa cell models was enriched for canonical cofactors, as well as proteins involved in RNA processing and bookmarking. Identifying the repertoire of miR-96 bound and regulated gene targets, including those recognition elements marked by m6A, revealed their significant enrichment in the RARγ complex. RARγ significantly enhanced the AR cistrome, particularly in active enhancers and super-enhancers, and overlapped with the binding of bookmarking factors. Furthermore, RARγ expression led to nucleosome-free chromatin enriched with H3K27ac, and significantly enhanced the AR cistrome in G2/M cells. RARγ functions also antagonized the transcriptional actions of the lineage master regulator ONECUT2. Similarly, gene programs regulated by either miR-96 or antagonized by RARγ were enriched in alternative lineages and more aggressive PCa phenotypes. Together these findings reveal an under-investigated role for RARγ, modulated by miR-96, to bookmark enhancer sites during mitosis. These sites are required by the AR to promote transcriptional competence, and emphasize luminal differentiation, while antagonizing ONECUT2.

The effects of glycemic index on prostate cancer progression in a xenograft mouse model.

BACKGROUND: Previously, we found low-carbohydrate diets slowed prostate cancer (PC) growth and increased survival vs. a Western diet in mice, by inhibiting the insulin/IGF-1 axis. Thus, we tested whether modifying carbohydrate quality to lower glycemic index (GI) without changing quantity results in similar benefits as with reduced quantity. METHODS: Male SCID mice injected with LAPC-4 cells were single-housed and randomized when their tumors reached 200 mm3 on average to a LoGI (48% carbohydrate kcal, from Hylon-VII) or HiGI Western diet (48% carbohydrate kcal, from sucrose). Body weight and tumor volume were measured weekly. Body composition was assessed 35 days after randomization. Blood glucose and serum insulin, IGF-1 and IGFBP3 were measured at study end when tumor volumes reached 800 mm3. We analyzed gene expression of mice tumors by RNA-sequencing and human tumors using the Prostate Cancer Transcriptome Atlas. RESULTS: There were no significant differences in tumor volume (P > 0.05), tumor proliferation (P = 0.29), and overall survival (P = 0.15) between groups. At 35 days after randomization, the LoGI group had 30% lower body fat (P = 0.007) despite similar body weight (P = 0.58). At sacrifice, LoGI mice had smaller livers (P < 0.001) and lower glucose (P = 0.15), insulin (P = 0.11), IGF-1 (P = 0.07) and IGF-1:IGFBP3 ratio (P = 0.05), and higher IGFBP3 (P = 0.09) vs. HiGI, although none of these metabolic differences reached statistical significance. We observed differential gene expression and pathway enrichment in mice tumors by diet. The most upregulated and downregulated gene in the LoGI group showed expression patterns more closely resembling expression in human benign prostate tissue vs. PC. CONCLUSIONS: In this single mouse xenograft model, consuming a low GI diet did not delay PC growth or survival vs. a high GI diet despite suggestions of decreased activation of the insulin/IGF-1 pathway. These data suggest that improving carbohydrate quality alone while consuming a high carbohydrate diet may not effectively slow PC growth.

Genetic and biological drivers of prostate cancer disparities in Black men.

Black men with prostate cancer have historically had worse outcomes than white men with prostate cancer. The causes of this disparity in outcomes are multi-factorial, but a potential basis is that prostate cancers in Black men are biologically distinct from prostate cancers in white men. Evidence suggests that genetic and ancestral factors, molecular pathways involving androgen and non-androgen receptor signalling, inflammation, epigenetics, the tumour microenvironment and tumour metabolism are contributing factors to the racial disparities observed. Key genetic and molecular pathways linked to prostate cancer risk and aggressiveness have potential clinical relevance. Describing biological drivers of prostate cancer disparities could inform efforts to improve outcomes for Black men with prostate cancer.

ONECUT2 Activates Diverse Resistance Drivers of Androgen Receptor-Independent Heterogeneity in Prostate Cancer.

Androgen receptor- (AR-) indifference is a mechanism of resistance to hormonal therapy in prostate cancer (PC). Here we demonstrate that the HOX/CUT transcription factor ONECUT2 (OC2) activates resistance through multiple drivers associated with adenocarcinoma, stem-like and neuroendocrine (NE) variants. Direct OC2 targets include the glucocorticoid receptor and the NE splicing factor SRRM4, among others. OC2 regulates gene expression by promoter binding, enhancement of chromatin accessibility, and formation of novel super-enhancers. OC2 also activates glucuronidation genes that irreversibly disable androgen, thereby evoking phenotypic heterogeneity indirectly by hormone depletion. Pharmacologic inhibition of OC2 suppresses lineage plasticity reprogramming induced by the AR signaling inhibitor enzalutamide. These results demonstrate that OC2 activation promotes a range of drug resistance mechanisms associated with treatment-emergent lineage variation in PC. Our findings support enhanced efforts to therapeutically target this protein as a means of suppressing treatment-resistant disease.

Targeting Key Players of Neuroendocrine Differentiation in Prostate Cancer.

Neuroendocrine prostate cancer (NEPC) is a highly aggressive subtype of prostate cancer (PC) that commonly emerges through a transdifferentiation process from prostate adenocarcinoma and evades conventional therapies. Extensive molecular research has revealed factors that drive lineage plasticity, uncovering novel therapeutic targets to be explored. A diverse array of targeting agents is currently under evaluation in pre-clinical and clinical studies with promising results in suppressing or reversing the neuroendocrine phenotype and inhibiting tumor growth and metastasis. This new knowledge has the potential to contribute to the development of novel therapeutic approaches that may enhance the clinical management and prognosis of this lethal disease. In the present review, we discuss molecular players involved in the neuroendocrine phenotype, and we explore therapeutic strategies that are currently under investigation for NEPC.

The homeodomain drives favorable DNA binding energetics of prostate cancer target ONECUT2.

The ONECUT transcription factors feature a CUT and a homeodomain, evolutionarily conserved elements that bind DNA cooperatively, but the process remains mechanistically enigmatic. Using an integrative DNA binding analysis of ONECUT2, a driver of aggressive prostate cancer, we show that the homeodomain energetically stabilizes the ONECUT2-DNA complex through allosteric modulation of CUT. Further, evolutionarily conserved base-interactions in both the CUT and homeodomain are necessary for the favorable thermodynamics. We have identified a novel arginine pair unique to the ONECUT family homeodomain that can adapt to DNA sequence variations. Base interactions in general, including by this arginine pair, are critical for optimal DNA binding and transcription in a prostate cancer model. These findings provide fundamental insights into DNA binding by CUT-homeodomain proteins with potential therapeutic implications. One-Sentence Summary: Base-specific interactions regulate homeodomain-mediated stabilization of DNA binding by the ONECUT2 transcription factor.

Autonomous action and cooperativity between the ONECUT2 transcription factor and its 3' untranslated region.

The transcription factor ONECUT2 (OC2) is a master transcriptional regulator operating in metastatic castration-resistant prostate cancer that suppresses androgen receptor activity and promotes neural differentiation and tumor cell survival. OC2 mRNA possesses an unusually long (14,575 nt), evolutionarily conserved 3' untranslated region (3' UTR) with many microRNA binding sites, including up to 26 miR-9 sites. This is notable because miR-9 targets many of the same genes regulated by the OC2 protein. Paradoxically, OC2 expression is high in tissues with high miR-9 expression. The length and complex secondary structure of OC2 mRNA suggests that it is a potent master competing endogenous RNA (ceRNA) capable of sequestering miRNAs. Here, we describe a novel role for OC2 3' UTR in lethal prostate cancer consistent with a function as a ceRNA. A plausible ceRNA network in OC2-driven tumors was constructed computationally and then confirmed in prostate cancer cell lines. Genes regulated by OC2 3' UTR exhibited high overlap (up to 45%) with genes driven by the overexpression of the OC2 protein in the absence of 3' UTR, indicating a cooperative functional relationship between the OC2 protein and its 3' UTR. These overlapping networks suggest an evolutionarily conserved mechanism to reinforce OC2 transcription by protection of OC2-regulated mRNAs from miRNA suppression. Both the protein and 3' UTR showed increased polycomb-repressive complex activity. The expression of OC2 3' UTR mRNA alone (without protein) dramatically increased the metastatic potential by in vitro assays. Additionally, OC2 3' UTR increased the expression of Aldo-Keto reductase and UDP-glucuronyl transferase family genes responsible for altering the androgen synthesis pathway. ONECUT2 represents the first-described dual-modality transcript that operates as both a key transcription factor driving castration-resistant prostate cancer and a master ceRNA that promotes and protects the same transcriptional network.

Targeting Glutamine Metabolism in Prostate Cancer.

Glutamine is a conditionally essential amino acid important for cancer cell proliferation through intermediary metabolism leading to de novo synthesis of purine and pyrimidine nucleotides, hexosamine biosytnehsis, fatty acid synthesis through reductive carboxylation, maintenance of redox homeostasis, glutathione synthesis, production of non-essential amino acids, and mitochondrial oxidative phosphorylation. Prostate cancer has increasingly been characterized as a tumor type that is heavily dependent on glutamine for growth and survival. In this review, we highlight the preclinical evidence that supports a relationship between glutamine signaling and prostate cancer progression. We focus on the regulation of glutamine metabolism in prostate cancer through key pathways involving the androgen receptor pathway, MYC, and the PTEN/PI3K/mTOR pathway. We end with a discussion on considerations for translation of targeting glutamine metabolism as a therapeutic strategy to manage prostate cancer. Here, it is important to understand that the tumor microenvironment also plays a role in facilitating glutamine signaling and resultant prostate cancer growth. The druggability of prostate cancer glutamine metabolism is more readily achievable with our greater understanding of tumor metabolism and the advent of selective glutaminase inhibitors that have proven safe and tolerable in early-phase clinical trials.

ONECUT2 regulates RANKL-dependent enterocyte and microfold cell differentiation in the small intestine; a multi-omics study.

Microfold (M) cells reside in the intestinal epithelium of Peyer's patches (PP). Their unique ability to take up and transport antigens from the intestinal lumen to the underlying lymphoid tissue is key in the regulation of the gut-associated immune response. Here, we applied a multi-omics approach to investigate the molecular mechanisms that drive M cell differentiation in mouse small intestinal organoids. We generated a comprehensive profile of chromatin accessibility changes and transcription factor dynamics during in vitro M cell differentiation, allowing us to uncover numerous cell type-specific regulatory elements and associated transcription factors. By using single-cell RNA sequencing, we identified an enterocyte and M cell precursor population. We used our newly developed computational tool SCEPIA to link precursor cell-specific gene expression to transcription factor motif activity in cis-regulatory elements, uncovering high expression of and motif activity for the transcription factor ONECUT2. Subsequent in vitro and in vivo perturbation experiments revealed that ONECUT2 acts downstream of the RANK/RANKL signalling axis to support enterocyte differentiation, thereby restricting M cell lineage specification. This study sheds new light on the mechanism regulating cell fate balance in the PP, and it provides a powerful blueprint for investigation of cell fate switches in the intestinal epithelium.

27-hydroxycholesterol and DNA damage repair: implication in prostate cancer.

Introduction: We previously reported that cholesterol homeostasis in prostate cancer (PC) is regulated by 27-hydroxycholesterol (27HC) and that CYP27A1, the enzyme that converts cholesterol to 27HC, is frequently lost in PCs. We observed that restoring the CYP27A1/27HC axis inhibited PC growth. In this study, we investigated the mechanism of 27HC-mediated anti-PC effects. Methods: We employed in vitro models and human transcriptomics data to investigate 27HC mechanism of action in PC. LNCaP (AR+) and DU145 (AR-) cells were treated with 27HC or vehicle. Transcriptome profiling was performed using the Affymetrix GeneChip™ microarray system. Differential expression was determined, and gene set enrichment analysis was done using the GSEA software with hallmark gene sets from MSigDB. Key changes were validated at mRNA and protein levels. Human PC transcriptomes from six datasets were analyzed to determine the correlation between CYP27A1 and DNA repair gene expression signatures. DNA damage was assessed via comet assays. Results: Transcriptome analysis revealed 27HC treatment downregulated Hallmark pathways related to DNA damage repair, decreased expression of FEN1 and RAD51, and induced "BRCAness" by downregulating genes involved in homologous recombination regulation in LNCaP cells. Consistently, we found a correlation between higher CYP27A1 expression (i.e., higher intracellular 27HC) and decreased expression of DNA repair gene signatures in castration-sensitive PC (CSPC) in human PC datasets. However, such correlation was less clear in metastatic castration-resistant PC (mCRPC). 27HC increased expression of DNA damage repair markers in PC cells, notably in AR+ cells, but no consistent effects in AR- cells and decreased expression in non-neoplastic prostate epithelial cells. While testing the clinical implications of this, we noted that 27HC treatment increased DNA damage in LNCaP cells via comet assays. Effects were reversible by adding back cholesterol, but not androgens. Finally, in combination with olaparib, a PARP inhibitor, we showed additive DNA damage effects. Discussion: These results suggest 27HC induces "BRCAness", a functional state thought to increase sensitivity to PARP inhibitors, and leads to increased DNA damage, especially in CSPC. Given the emerging appreciation that defective DNA damage repair can drive PC growth, future studies are needed to test whether 27HC creates a synthetic lethality to PARP inhibitors and DNA damaging agents in CSPC.

Actionable Driver Events in Small Cell Lung Cancer.

Small cell lung cancer (SCLC) stands out as the most aggressive form of lung cancer, characterized by an extremely high proliferation rate and a very poor prognosis, with a 5-year survival rate that falls below 7%. Approximately two-thirds of patients receive their diagnosis when the disease has already reached a metastatic or extensive stage, leaving chemotherapy as the remaining first-line treatment option. Other than the recent advances in immunotherapy, which have shown moderate results, SCLC patients cannot yet benefit from any approved targeted therapy, meaning that this cancer remains treated as a uniform entity, disregarding intra- or inter-tumoral heterogeneity. Continuous efforts and technological improvements have enabled the identification of new potential targets that could be used to implement novel therapeutic strategies. In this review, we provide an overview of the most recent approaches for SCLC treatment, providing an extensive compilation of the targeted therapies that are currently under clinical evaluation and inhibitor molecules with promising results in vitro and in vivo.

Variation in Molecularly Defined Prostate Tumor Subtypes by Self-identified Race.

Background: Socioeconomic and health care utilization factors are major drivers of prostate cancer (PC) mortality disparities in the USA; however, tumor molecular heterogeneity may also contribute to the higher mortality among Black men. Objective: To compare differences in PC subtype frequency and genomic aggressiveness by self-identified race. Design setting and participants: Five molecular subtype classifiers were applied for 426 Black and 762 White PC patients in the Decipher Genomics Resource Information Database (GRID). Outcome measurements and statistical analysis: Differences in subtype frequency and tumor genomic risk (Decipher score >0.6) by race were evaluated using χ2 tests and multivariable-adjusted logistic regression models. Results and limitations: Subtype frequencies differed by race for four classifiers. Subtypes characterized by the presence of SPOP mutations, SPINK1 overexpression, and neuroendocrine differentiation were more common among Black men. ERG and ETS fusion-positive subtypes were more frequent among White men, with no clear differences for subtypes reflecting luminal versus basal lineage. The hypothesized low-risk Kamoun S2 subtype was associated with a lower Decipher score among White men only (p = 0.01 for heterogeneity), while the aggressive You PCS1 subtype was associated with a higher Decipher score among White men only (p = 0.001 for heterogeneity). The Tomlins ERG+ subtype was associated with a higher Decipher score relative to all other subtypes among Black men, with no association among White men (p = 0.007 for heterogeneity). Conclusions: The frequency of PC molecular subtypes differed by self-identified race. Additional studies are required to evaluate whether our observations suggest differences in the tumor genomic risk of progression by self-identified race. Patient summary: We studied five classifiers that identify subtypes of prostate tumors and found that subtypes differed in frequency between Black and White patients. Further research is warranted to evaluate how differences in tumor subtypes may contribute to disparities in prostate cancer mortality.

Receptor-interacting protein kinase 2 (RIPK2) stabilizes c-Myc and is a therapeutic target in prostate cancer metastasis.

Despite progress in prostate cancer (PC) therapeutics, distant metastasis remains a major cause of morbidity and mortality from PC. Thus, there is growing recognition that preventing or delaying PC metastasis holds great potential for substantially improving patient outcomes. Here we show receptor-interacting protein kinase 2 (RIPK2) is a clinically actionable target for inhibiting PC metastasis. RIPK2 is amplified/gained in ~65% of lethal metastatic castration-resistant PC. Its overexpression is associated with disease progression and poor prognosis, and its genetic knockout substantially reduces PC metastasis. Multi-level proteomics analyses reveal that RIPK2 strongly regulates the stability and activity of c-Myc (a driver of metastasis), largely via binding to and activating mitogen-activated protein kinase kinase 7 (MKK7), which we identify as a direct c-Myc-S62 kinase. RIPK2 inhibition by preclinical and clinical drugs inactivates the noncanonical RIPK2/MKK7/c-Myc pathway and effectively impairs PC metastatic outgrowth. These results support targeting RIPK2 signaling to extend metastasis-free and overall survival.

Cholesterol-Lowering Intervention Decreases mTOR Complex 2 Signaling and Enhances Antitumor Immunity.

PURPOSE: There is a need for strategies to prevent prostate cancer. Cholesterol-lowering interventions are employed widely and safely to reduce risk of cardiovascular disease and has been proposed for chemoprevention. Using preclinical models and a window-of-opportunity clinical trial, we describe an adaptive antitumor immunity resulting from cholesterol lowering. EXPERIMENTAL DESIGN: Statins do not reliably lower serum cholesterol in mice. Therefore, oral ezetimibe was administered to mice to lower serum cholesterol to clinically relevant levels and evaluated the final adaptive immune response. T-lymphocytes-specific mTORC2 knockout mice were used to evaluate mTOR signaling and antitumor immunity. Pretreatment and posttreatment prostate tumors and lymphocytes were examined from a window-of-opportunity clinical trial where men with prostate cancer were treated with 2 to 6 weeks of aggressive cholesterol-lowering intervention prior to radical prostatectomy. RESULTS: Mice treated with oral ezetimibe exhibited enhanced antitumor immunity against syngeneic cancers in a CD8+ lymphocyte-dependent manner, produced immunity that was transferrable through lymphocytes, and had enhanced central CD8+ T-cell memory. In mice and in patients undergoing prostatectomy, lowering serum cholesterol inhibited mTORC2 signaling in lymphocytes and increased infiltration of CD8+ lymphocytes into prostate tumors. T-lymphocyte-specific mTORC2 knockout mice demonstrated enhanced CD8+ lymphocyte function and antitumor capacity. In patients, cholesterol-lowering intervention prior to prostatectomy decreased the proliferation of normal prostate and low-grade adenocarcinomas. CONCLUSIONS: Lowering serum cholesterol decreased signaling through mTORC2 and enhanced antitumor CD8+ T-cell memory. We provide a rationale for large-scale clinical testing of cholesterol lowering strategies for prostate cancer chemoprevention.

BoxCar and shotgun proteomic analyses reveal molecular networks regulated by UBR5 in prostate cancer.

Prostate cancer (PC) is a major health and economic problem in industrialized countries, yet our understanding of the molecular mechanisms of PC progression and drug response remains limited. Accumulating evidence showed that certain E3 ubiquitin ligases such as SIAH2, RNF7, and SPOP play important roles in PC development and progression. However, the roles and mechanisms of other E3s in PC progression remain largely unexplored. Through an integration analysis of clinical genomic and transcriptomic profiles of PC tumors, this study identified UBR5 as a top PC-relevant E3 ubiquitin ligase whose expression levels are strongly associated with PC progression and aggressiveness. BoxCar and shotgun proteomic analyses of control and UBR5-knockdown PC3 cells complementarily identified 75 UBR5-regulated proteins. Bioinformatic analysis suggested that the 75 proteins form four molecular networks centered around FANCD2, PAF1, YY1, and LAMB3 via direct protein-protein interactions. Experimental analyses demonstrated that UBR5 associates with and downregulates two key DNA damage repair proteins (XRCC3 and FANCD2) and confers PC cell sensitivity to olaparib, a PARP inhibitor in clinical use for cancer therapy. This study represents the first application of BoxCar in PC research, provides new insights into the molecular functions of UBR5 in PC, and suggests that PC patients with UBR5-high tumors may potentially benefit from PARP inhibitor treatment.

Activation of ONECUT2 by RB1 loss in castration-resistant prostate cancer.

Functional loss of the two major tumor repressors, TP53 and RB1, is frequently involved in the emergence and progression of castration-resistant prostate cancer (CRPC). Inactivating mutations in TP53 and RB1 promote lineage variants that suppress the androgen receptor axis and enhance therapy resistance. The present study provides the first evidence that RB1 loss, and not TP53 loss, is sufficient to activate the master regulator transcription factor ONECUT2 (OC2) in mCRPC. OC2 upregulation is common in CRPC and drives metastasis and lineage plasticity, particularly neuroendocrine differentiation, in model systems. Pharmacologic inhibition of OC2 was reported to suppress established human CRPC metastases in mice. Here we show that RB1 silencing in human and mouse prostate cancer models is sufficient to upregulate OC2, at least in part through epigenetic regulation. OC2 expression downregulated TP53 transcription and inactivated RB1 via phosphorylation. OC2 expression and activation in human CRPC correlated with bi- or single-allelic loss of RB1 and inversely with RB1 expression and activity. A small molecule OC2 inhibitor blocked enzalutamide-induced lineage plasticity in vitro. These findings indicate that activation of OC2 in CRPC occurs in response to RB1 inactivation, and that biomarkers of RB1 activity may be useful for stratifying patients refractory to hormone therapy where OC2 is targeted pharmacologically.

miR-1227 Targets SEC23A to Regulate the Shedding of Large Extracellular Vesicles.

Cancer cells shed a heterogenous mixture of extracellular vesicles (EVs), differing in both size and composition, which likely influence physiological processes in different manners. However, how cells differentially control the shedding of these EV populations is poorly understood. Here, we show that miR-1227, which is enriched in prostate cancer EVs, compared to the cell of origin, but not in EVs derived from prostate benign epithelial cells, induces the shedding of large EVs (such as large oncosomes), while inhibiting the shedding of small EVs (such as exosomes). RNA sequencing from cells stably expressing miR-1227, a modified RISCTRAP assay that stabilizes and purifies mRNA-miR-1227 complexes for RNA sequencing, and in silico target prediction tools were used to identify miR-1227 targets that may mediate this alteration in EV shedding. The COPII vesicle protein SEC23A emerged and was validated by qPCR, WBlot, and luciferase assays as a direct target of miR-1227. The inhibition of SEC23A was sufficient to induce the shedding of large EVs. These results identify a novel mechanism of EV shedding, by which the inhibition of SEC23A by miR-1227 induces a shift in EV shedding, favoring the shedding of large EV over small EV.

Scaffold attachment factor B1 regulates androgen degradation pathways in prostate cancer.

The nuclear matrix protein Scaffold Attachment Factor B1 (SAFB1, SAFB) can act in prostate cancer (PCa) as an androgen receptor (AR) co-repressor that functions through epigenetic silencing of AR targets, such as prostate specific antigen (PSA, KLK3). Genomic profiling of SAFB1-silenced PCa cells indicated that SAFB1 may play a role in modulating intracrine androgen levels through the regulation of UDP-glucuronosyltransferase (UGT) genes, which inactivate steroid hormones. Gene silencing of SAFB1 resulted in increased levels of free dihydrotesterosterone (DHT), and increased resistance to the AR inhibitor enzalutamide. SAFB1 silencing suppressed expression of the UDP-glucuronosyltransferase family 2 member B15 gene (UGT2B15) and the closely related UGT2B17 gene, which encode proteins that irreversibly inactivate testosterone (T) and DHT. Analysis of human data indicated that genomic loss at the SAFB locus, or down-regulation of expression of the SAFB gene, is associated with aggressive PCa. These findings identify SAFB1 as an important regulator of androgen catabolism in PCa and suggest that loss or inactivation of this protein may promote AR activity by retention of active androgen in tumor cells.

Loss of CDCP1 triggers FAK activation in detached prostate cancer cells.

A major metastasis suppressing mechanism is the rapid apoptotic death of cancer cells upon detachment from extracellular matrix, a process called anoikis. Focal adhesion kinase (PTK2/FAK) is a key enzyme involved in evasion of anoikis. We show that loss of the Cub-domain containing protein-1 (CDCP1), paradoxically stimulates FAK activation in the detached state of prostate cancer cells. In CDCP1low DU145 and PC3 prostate cancer cells, detachment-activation of FAK occurs through local production of PI(4,5)P2. PI(4,5)P2 is generated by the PIP5K1c-201 splicing isoform of PIP5K1c, which contains a unique SRC phosphorylation site. In the detached state, reduced expression of CDCP1 and an alternative CDCP1-independent SRC activation mechanism triggers PIP5K1c-pY644 phosphorylation by SRC. This causes a switch of Talin binding from ß1-integrin to PIP5K1c-pY644 and leads to activation of PIP5K1c-FAK. Reduced CDCP1 expression also inactivates CDK5, a negative regulator of PIP5K1c. Furthermore, immersion of prostate cancer cells in 10% human plasma or fetal bovine serum is required for activation of PIP5K1c-FAK. The PIP5K1c induced detachment-activation of FAK in preclinical models sensitizes CDCP1low prostate cancer cells to FAK inhibitors. In patients, CDCP1High versus CDCP1low circulating tumor cells differ in expression of AR-v7, ONECUT2 and HOXB13 oncogenes and TMPRSS2 and display intra-patient heterogeneity of FAK-pY397 expression. Taken together, CDCP1low and CDCP1high detached prostate cancer cells activate distinct cytoplasmic kinase complexes and targetable transcription factors, which has important therapeutic implications.

Clinical Utility of Olaparib in the Treatment of Metastatic Castration-Resistant Prostate Cancer: A Review of Current Evidence and Patient Selection.

Metastatic castration-resistant prostate cancer (mCRPC) is an aggressive and fatal disease with a median survival of 36 months. With the advent of genetic sequencing to identify individual genomic profiles and acquired tumor-specific pathways, targeted therapies have revolutionized cancer treatment, including the treatment strategy in mCRPC. Poly(adenosine 5'-diphosphate) ribose polymerase inhibitors (PARPi) are oral drugs that target mutations in the homologous recombination repair (HRR) pathway, which are found in approximately 27% of prostate cancer patients. In May 2020, the first PARP inhibitor, olaparib, was approved by the US Food and Drug Administration for men with mCRPC with HHR gene mutations based on the findings of the Phase III PROfound trial that showed improved overall survival in men with mCRPC who received olaparib and whose disease had progressed on a novel hormonal agent. This review summarizes the current evidence and clinical utility of olaparib as treatment in men with mCRPC. We describe the mechanism of action of PARPi, key clinical trials of olaparib in men with mCRPC, and ongoing Phase II and III clinical trials investigating olaparib in combination therapy and as front-line therapy in mCRPC.