Search

Nuclear membrane blebbing in amoeboid cells. Time-lapse analysis of DU145 DIAPH3-depleted cells treated with EGF and IL6 (exacerbates amoeboid features (13)) and stained with lipid fluorescent dye CellMask Orange.

Abnormalities in nuclear shape are a well-known feature of cancer, but their contribution to malignant progression remains poorly understood. Here, we show that depletion of the cytoskeletal regulator, Diaphanous-related formin 3 (DIAPH3), or the nuclear membrane–associated proteins, lamin A/C, in prostate and breast cancer cells, induces nuclear shape instability, with a corresponding gain in malignant properties, including secretion of extracellular vesicles that contain genomic material. This transformation is characterized by a reduction and/or mislocalization of the inner nuclear membrane protein, emerin. Consistent with this, depletion of emerin evokes nuclear shape instability and promotes metastasis. By visualizing emerin localization, evidence for nuclear shape instability was observed in cultured tumor cells, in experimental models of prostate cancer, in human prostate cancer tissues, and in circulating tumor cells from patients with metastatic disease. Quantitation of emerin mislocalization discriminated cancer from benign tissue and correlated with disease progression in a prostate cancer cohort. Taken together, these results identify emerin as a mediator of nuclear shape stability in cancer and show that destabilization of emerin can promote metastasis.Significance: This study identifies a novel mechanism integrating the control of nuclear structure with the metastatic phenotype, and our inclusion of two types of human specimens (cancer tissues and circulating tumor cells) demonstrates direct relevance to human cancer.Graphical Abstract: http://cancerres.aacrjournals.org/content/canres/78/21/6086/F1.large.jpg. Cancer Res; 78(21); 6086–97. ©2018 AACR.

Emerin deregulation links nuclear shape instability to metastatic potential

Emerin deregulation links nuclear shape instability to metastatic potential

Prostate cancer is the second most common cause of cancer related deaths in men in the United States. Pathogenesis is driven by the androgen receptor (AR), which has led to front-line treatment modalities that are based on androgen deprivation therapy (ADT). About 10-20% of all prostate cancers evolve to resist ADT and are classified as castration-resistant prostate cancer (CRPC) indicating the continued need for new treatment options. Bromodomain-containing protein 4 (BRD4) is an acetylated-chromatin associating protein that is involved in transcriptional elongation, mRNA splicing, epigenetic bookmarking, and super-enhancer activity. The BRD4 protein has been shown to both bind and colocalize with AR at androgen response elements (AREs) on chromatin. Furthermore, elevated BRD4 expression is prognostic of increased prostate specific antigen (PSA) levels following radical prostatectomy and is correlated with higher Gleason scores and poor overall survival. The intertwined activity of BRD4 with multiple essential driver mechanisms of prostate cancer suggests it may be a key target for developing novel therapeutics. Using our ultra-high throughput cell-based screening platform, which directly measures degradation of pathogenic proteins upon exposure to diverse chemical libraries, we identified a series of novel monovalent BRD4 degraders that was optimized to produce our lead compound PLX-3618. A cancer cell panel screen for antiproliferative effects of PLX-3618 indicated enhanced sensitivity in subsets of prostate cancer lines. PLX-3618 elicited selective, rapid, and deep degradation of BRD4 protein in prostate cancer cell models, without degrading the closely related BRD2 and BRD3 proteins. Addition of either proteosome or neddylation inhibitors blocked BRD4 degradation indicating a ubiquitin-proteosome system mediated clearance mechanism. Degradation of BRD4 led to sustained multimodal inhibition of the AR pathway and disruption of key oncogene enhancer networks. When compared to pan-BET inhibitors, treatment of select prostate cancer cell lines with PLX-3618 resulted in increased levels of the tumor suppressors p53 and p21, an aberrant DNA damage response, and substantially amplified apoptosis. Finally, in in vivo preclinical models of prostate cancer, PLX-3618 showed far superior efficacy over a pan-BET inhibitor. Taken together, the selective degradation of BRD4 via the potent monovalent degrader PLX-3618 represents a novel strategy in treating prostate cancer. Citation Format: Kenneth Steadman, Gregory S. Parker, Geoffray Leriche, Sarah Fish, Julia Toth, Mary E. Spalding, Elizabeth Daniele, Aleksandar Jamborcic, Xiaoming Li, E Adam Kallel, Farhana Barmare, Kenneth Chng, Erika Green, Michael Hocker, Elliot Imler, Yi Zhang, Peggy A. Thompson, Simon Bailey. PLX-3618, a potent, selective monovalent BRD4 degrader demonstrates activity in models of prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 421.

Treatment of prostate cancer (PC) by androgen suppression promotes the emergence of aggressive variants that are androgen receptor- (AR-) independent. Here we identify the transcription factor ONECUT2 (OC2) as a master regulator of AR networks in metastatic castration-resistant prostate cancer (mCRPC). OC2 acts as a survival factor in mCRPC models, suppresses the AR transcriptional program by direct regulation of AR target genes and the AR licensing factor FOXA1, and activates genes associated with neural differentiation and progression to lethal disease. OC2 appears active in a substantial subset of human prostate adenocarcinoma and neuroendocrine tumors. Inhibition of OC2 by a newly identified small molecule suppresses metastasis in mice. These findings suggest that OC2 displaces AR-dependent growth and survival mechanisms in many cases where AR remains expressed, but where its activity is bypassed. OC2 is also a potential drug target in the metastatic phase of aggressive PC.

Abnormalities in nuclear shape are a well-known feature of cancer, but their contribution to malignant progression remains poorly understood. Here, we show that depletion of the cytoskeletal regulator, Diaphanous-related formin 3 (DIAPH3), or the nuclear membrane–associated proteins, lamin A/C, in prostate and breast cancer cells, induces nuclear shape instability, with a corresponding gain in malignant properties, including secretion of extracellular vesicles that contain genomic material. This transformation is characterized by a reduction and/or mislocalization of the inner nuclear membrane protein, emerin. Consistent with this, depletion of emerin evokes nuclear shape instability and promotes metastasis. By visualizing emerin localization, evidence for nuclear shape instability was observed in cultured tumor cells, in experimental models of prostate cancer, in human prostate cancer tissues, and in circulating tumor cells from patients with metastatic disease. Quantitation of emerin mislocalization discriminated cancer from benign tissue and correlated with disease progression in a prostate cancer cohort. Taken together, these results identify emerin as a mediator of nuclear shape stability in cancer and show that destabilization of emerin can promote metastasis. Significance: This study identifies a novel mechanism integrating the control of nuclear structure with the metastatic phenotype, and our inclusion of two types of human specimens (cancer tissues and circulating tumor cells) demonstrates direct relevance to human cancer. Graphical Abstract: http://cancerres.aacrjournals.org/content/canres/78/21/6086/F1.large.jpg. Cancer Res; 78(21); 6086–97. ©2018 AACR.

BACKGROUND Acquired resistance to antiepidermal growth factor receptor (anti-EGFR) therapy may be caused by EGFR–v-erb-b2 avian erythroblastic leukemia viral oncogene homolog 2 (ErbB2) heterodimerization and pathway reactivation. In preclinical studies, inhibiting ErbB2 blocked this resistance mechanism and resensitized cells to anti-EGFR therapy. Cetuximab targets EGFR, whereas lapatinib inhibits both EGFR and ErbB2. The objective of this phase 1 trial was to assess the safety, dose-limiting toxicities (DLTs), and maximum tolerated doses (MTDs) of cetuximab and lapatinib in patients with solid tumors. METHODS Patients received standard weekly cetuximab with escalating lapatinib doses of 750 mg, 1000 mg, or 1250 mg daily in 3-week cycles. DLTs were monitored through the end of cycle 2. Pretreatment and post-treatment tumor biopsies and germline DNA samples were obtained for correlative studies. RESULTS Twenty-two patients were enrolled, and 18 patients each were evaluable for toxicity and response. Fifty-nine percent of patients had received prior anti-EGFR therapy. Common toxicities included rash and diarrhea. No patient experienced a DLT at the highest dose level, and no grade 4 toxicity was observed. Response included no complete responses, 3 partial responses, 9 patients with stable disease, and 6 patients with disease progression, for an overall response rate of 17% and a clinical benefit rate of 67%. The clinical benefit rate in patients who had previously received anti-EGFR therapy was 70%. The mean treatment duration was 4.7 cycles (range, 1-14 cycles). Decreased expression of EGFR/ErbB2 pathway components after treatment was correlated with response, whereas increased expression in the PI3K, Jak/Stat, and MAPK pathways occurred in nonresponders. CONCLUSIONS The combination of cetuximab and lapatinib was well tolerated, had the expected toxicities, and exhibited notable clinical activity, including in patients who had received previous anti-EGFR therapy. Further clinical study of this combination is warranted. Cancer 2015;121:1645–1653. © 2015 American Cancer Society.

Taxanes are widely employed chemotherapies for patients with metastatic prostate and breast cancer. Here, we show that loss of Diaphanous-related formin-3 (DIAPH3), frequently associated with metastatic breast and prostate cancers, correlates with increased sensitivity to taxanes. DIAPH3 interacted with microtubules (MT) and its loss altered several parameters of MT dynamics as well as decreased polarized force generation, contractility and response to substrate stiffness. Silencing of DIAPH3 increased the cytotoxic response to taxanes in prostate and breast cancer cell lines. Analysis of drug activity for tubulin-targeted agents in the NCI-60 cell line panel revealed a uniform positive correlation between reduced DIAPH3 expression and drug sensitivity. Low DIAPH3 expression correlated with improved relapse-free survival in breast cancer patients treated with chemotherapeutic regimens containing taxanes. Our results suggest that inhibition of MT stability arising from DIAPH3 downregulation enhances susceptibility to MT poisons and that the DIAPH3 network potentially reports taxane sensitivity in human tumors.