The Molecular 'Myc-anisms' Behind Myc-Driven Tumorigenesis and the Relevant Myc-Directed Therapeutics.

MYC, a well-studied proto-oncogene that is overexpressed in >20% of tumors across all cancers, is classically known as "undruggable" due to its crucial roles in cell processes and its lack of a drug binding pocket. Four decades of research and creativity led to the discovery of a myriad of indirect (and now some direct!) therapeutic strategies targeting Myc. This review explores the various mechanisms in which Myc promotes cancer and highlights five key therapeutic approaches to disrupt Myc, including transcription, Myc-Max dimerization, protein stability, cell cycle regulation, and metabolism, in order to develop more specific Myc-directed therapies.

Evaluating class III antiarrhythmic agents as novel MYC targeting drugs in ovarian cancer.

OBJECTIVE: To evaluate the utility of amiodarone and its derivative dronedarone as novel drug repositioning candidates in EOC and to determine the potential pathways targeted by these drugs. METHODS: Drug-predict bioinformatics platform was used to assess the utility of amiodarone as a novel drug-repurposing candidate in EOC. EOC cells were treated with amiodarone and dronedarone. Cell death was assessed by Annexin V staining. Cell viability and cell survival were assessed by MTT and clonogenics assays respectively. c-MYC and mTOR/Akt axis were evaluated as potential targets. Effect on autophagy was determined by autophagy flux flow cytometry. RESULTS: "DrugPredict" bioinformatics platform ranked Class III antiarrhythmic drug amiodarone within the top 3.9% of potential EOC drug repositioning candidates which was comparable to carboplatin ranking in the top 3.7%. Amiodarone and dronedarone were the only Class III antiarrhythmic drugs that decreased the cellular survival of both cisplatin-sensitive and cisplatin-resistant primary EOC cells. Interestingly, both drugs induced degradation of c-MYC protein and decreased the expression of known transcriptional targets of c-MYC. Furthermore, stable overexpression of non-degradable c-MYC partially rescued the effects of amiodarone and dronedarone induced cell death. Dronedarone induced higher autophagy flux in EOC cells as compared to amiodarone with decreased phospho-AKT and phospho-4EBP1 protein expression, suggesting autophagy induction due to inhibition of AKT/mTOR axis with these drugs. Lastly, both drugs also inhibited the survival of EOC tumor-initiating cells (TICs). CONCLUSIONS: We provide the first evidence of class III antiarrhythmic agents as novel c-MYC targeting drugs and autophagy inducers in EOC. Since c-MYC is amplified in >40% ovarian tumors, our results provide the basis for repositioning amiodarone and dronedarone as novel c-MYC targeting drugs in EOC with potential extension to other cancers.

Integrated stress response plasticity governs normal cell adaptation to chronic stress via the PP2A-TFE3-ATF4 pathway.

The integrated stress response (ISR) regulates cell fate during conditions of stress by leveraging the cell's capacity to endure sustainable and efficient adaptive stress responses. Protein phosphatase 2A (PP2A) activity modulation has been shown to be successful in achieving both therapeutic efficacy and safety across various cancer models; however, the molecular mechanisms driving its selective antitumor effects remain unclear. Here, we show for the first time that ISR plasticity relies on PP2A activation to regulate drug response and dictate cellular fate under conditions of chronic stress. We demonstrate that genetic and chemical modulation of the PP2A leads to chronic proteolytic stress and triggers an ISR to dictate cell fate. More specifically, we uncovered that the PP2A-TFE3-ATF4 pathway governs ISR cell plasticity during endoplasmic reticular and cellular stress independent of the unfolded protein response. We further show that normal cells reprogram their genetic signatures to undergo ISR-mediated adaptation and homeostatic recovery thereby successfully avoiding toxicity following PP2A-mediated stress. Conversely, oncogenic specific cytotoxicity induced by chemical modulation of PP2A is achieved by activating chronic and irreversible ISR in cancer cells. Our findings propose that a differential response to chemical modulation of PP2A is determined by intrinsic ISR plasticity, providing a novel biological vulnerability to selectively induce cancer cell death and improve targeted therapeutic efficacy.

Cooperativity of c-MYC with Krüppel-Like Factor 6 Splice Variant 1 induces phenotypic plasticity and promotes prostate cancer progression and metastasis.

Metastasis remains a major cause of morbidity and mortality in men with prostate cancer, and the functional impact of the genetic alterations, alone or in combination, driving metastatic disease remains incompletely understood. The proto-oncogene c-MYC, commonly deregulated in prostate cancer. Transgenic expression of c-MYC is sufficient to drive the progression to prostatic intraepithelial neoplasia and ultimately to moderately differentiated localized primary tumors, however, c-MYC-driven tumors are unable to progress through the metastatic cascade, suggesting that a "second-hit" is necessary in the milieu of aberrant c-MYC-driven signaling. Here, we identified cooperativity between c-MYC and KLF6-SV1, an oncogenic splice variant of the KLF6 gene. Transgenic mice that co-expressed KLF6-SV1 and c-MYC developed progressive and metastatic prostate cancer with a histological and molecular phenotype like human prostate cancer. Silencing c-MYC expression significantly reduced tumor burden in these mice supporting the necessity for c-MYC in tumor maintenance. Unbiased global proteomic analysis of tumors from these mice revealed significantly enriched vimentin, a dedifferentiation and pro-metastatic marker, induced by KLF6-SV1. c-MYC-positive tumors were also significantly enriched for KLF6-SV1 in human prostate cancer specimens. Our findings provide evidence that KLF6-SV1 is an enhancer of c-MYC-driven prostate cancer progression and metastasis, and a correlated genetic event in human prostate cancer with potential translational significance.

Modeling of Intracellular Taurine Levels Associated with Ovarian Cancer Reveals Activation of p53, ERK, mTOR and DNA-Damage-Sensing-Dependent Cell Protection.

Taurine, a non-proteogenic amino acid and commonly used nutritional supplement, can protect various tissues from degeneration associated with the action of the DNA-damaging chemotherapeutic agent cisplatin. Whether and how taurine protects human ovarian cancer (OC) cells from DNA damage caused by cisplatin is not well understood. We found that OC ascites-derived cells contained significantly more intracellular taurine than cell culture-modeled OC. In culture, elevation of intracellular taurine concentration to OC ascites-cell-associated levels suppressed proliferation of various OC cell lines and patient-derived organoids, reduced glycolysis, and induced cell protection from cisplatin. Taurine cell protection was associated with decreased DNA damage in response to cisplatin. A combination of RNA sequencing, reverse-phase protein arrays, live-cell microscopy, flow cytometry, and biochemical validation experiments provided evidence for taurine-mediated induction of mutant or wild-type p53 binding to DNA, activation of p53 effectors involved in negative regulation of the cell cycle (p21), and glycolysis (TIGAR). Paradoxically, taurine's suppression of cell proliferation was associated with activation of pro-mitogenic signal transduction including ERK, mTOR, and increased mRNA expression of major DNA damage-sensing molecules such as DNAPK, ATM and ATR. While inhibition of ERK or p53 did not interfere with taurine's ability to protect cells from cisplatin, suppression of mTOR with Torin2, a clinically relevant inhibitor that also targets DNAPK and ATM/ATR, broke taurine's cell protection. Our studies implicate that elevation of intracellular taurine could suppress cell growth and metabolism, and activate cell protective mechanisms involving mTOR and DNA damage-sensing signal transducti.

Ligand-dependent corepressor (LCoR) recruitment by Kruppel-like factor 6 (KLF6) regulates expression of the cyclin-dependent kinase inhibitor CDKN1A gene.

The widely expressed transcriptional coregulator, ligand-dependent corepressor (LCoR), initially characterized as a regulator of nuclear receptor-mediated transactivation, functions through recruitment of C-terminal binding proteins (CtBPs) and histone deacetylases (HDACs) to its N-terminal and central domains, respectively. We performed a yeast two-hybrid screen for novel cofactors, and identified an interaction between the C-terminal domain of LCoR and the transcription factor Krüppel-like factor 6 (KLF6), a putative tumor suppressor in prostate cancer. Subsequent experiments revealed LCoR regulation of several KLF6 target genes notably p21(WAF1/CIP1) (CDKN1A) and to a lesser extent E-cadherin (CDH1), indicating that LCoR regulates gene transcription through multiple classes of transcription factors. In multiple cancer cells, LCoR and KLF6 bind together on the promoters of the genes encoding CDKN1A and CDH1. LCoR contributes to KLF6-mediated transcriptional repression in a promoter- and cell type-dependent manner. Its inhibition of reporter constructs driven by the CDKN1A and CDH1 promoters in PC-3 prostate carcinoma cells is sensitive to treatment with the HDAC inhibitor trichostatin A. Additionally, the LCoR cofactor CtBP1 bound the same promoters and augmented the LCoR-dependent repression in PC-3 cells. Consistent with their inferred roles in transcriptional repression, siRNA-mediated knockdown of KLF6, LCoR, or CtBP1 in PC-3 cells induced expression of CDKN1A and CDH1 and additional KLF6 target genes. We propose a novel model of LCoR function in which promoter-bound KLF6 inhibits transcription of the CDKN1A gene and other genes as well by tethering a transcriptional corepressor complex containing LCoR, with specific contributions by CtBP1 and HDACs.

Phosphorylation of the myosin IIA tailpiece regulates single myosin IIA molecule association with lytic granules to promote NK-cell cytotoxicity.

Natural killer (NK) cells are innate immune lymphocytes that provide critical defense against virally infected and transformed cells. NK-cell cytotoxicity requires the formation of an F-actin rich immunologic synapse (IS), as well as the polarization of perforin-containing lytic granules to the IS and secretion of their contents at the IS. It was reported previously that NK-cell cytotoxicity requires nonmuscle myosin IIA function and that granule-associated myosin IIA mediates the interaction of granules with F-actin at the IS. In the present study, we evaluate the nature of the association of myosin IIA with lytic granules. Using NK cells from patients with mutations in myosin IIA, we found that the nonhelical tailpiece is required for NK-cell cytotoxicity and for the phosphorylation of granule-associated myosin IIA. Ultra-resolution imaging techniques demonstrated that single myosin IIA molecules associate with NK-cell lytic granules via the nonhelical tailpiece. Phosphorylation of myosin IIA at residue serine 1943 (S1943) in the tailpiece is needed for this linkage. This defines a novel mechanism for myosin II function, in which myosin IIA can act as a single-molecule actin motor, claiming granules as cargo through tail-dependent phosphorylation for the execution of a pre-final step in human NK-cell cytotoxicity.

MiR-181a targets STING to drive PARP inhibitor resistance in BRCA- mutated triple-negative breast cancer and ovarian cancer.

BACKGROUND: Poly (ADP-ribose) polymerase inhibitors (PARPi) are approved for the treatment of BRCA-mutated breast cancer (BC), including triple-negative BC (TNBC) and ovarian cancer (OvCa). A key challenge is to identify the factors associated with PARPi resistance; although, previous studies suggest that platinum-based agents and PARPi share similar resistance mechanisms. METHODS: Olaparib-resistant (OlaR) cell lines were analyzed using HTG EdgeSeq miRNA Whole Transcriptomic Analysis (WTA). Functional assays were performed in three BRCA-mutated TNBC cell lines. In-silico analysis were performed using multiple databases including The Cancer Genome Atlas, the Genotype-Tissue Expression, The Cancer Cell Line Encyclopedia, Genomics of Drug Sensitivity in Cancer, and Gene Omnibus Expression. RESULTS: High miR-181a levels were identified in OlaR TNBC cell lines (p = 0.001) as well as in tumor tissues from TNBC patients (p = 0.001). We hypothesized that miR-181a downregulates the stimulator of interferon genes (STING) and the downstream proinflammatory cytokines to mediate PARPi resistance. BRCA1 mutated TNBC cell lines with miR-181a-overexpression were more resistant to olaparib and showed downregulation in STING and the downstream genes controlled by STING. Extracellular vesicles derived from PARPi-resistant TNBC cell lines horizontally transferred miR-181a to parental cells which conferred PARPi-resistance and targeted STING. In clinical settings, STING levels were positively correlated with interferon gamma (IFNG) response scores (p = 0.01). In addition, low IFNG response scores were associated with worse response to neoadjuvant treatment including PARPi for high-risk HER2 negative BC patients (p = 0.001). OlaR TNBC cell lines showed resistance to platinum-based drugs. OvCa cell lines resistant to platinum showed resistance to olaparib. Knockout of miR-181a significantly improved olaparib sensitivity in OvCa cell lines (p = 0.001). CONCLUSION: miR-181a is a key factor controlling the STING pathway and driving PARPi and platinum-based drug resistance in TNBC and OvCa. The miR-181a-STING axis can be used as a potential marker for predicting PARPi responses in TNBC and OvCa tumors.

Small-Molecule-Mediated Stabilization of PP2A Modulates the Homologous Recombination Pathway and Potentiates DNA Damage-Induced Cell Death.

High-grade serous carcinoma (HGSC) is the most common and lethal ovarian cancer subtype. PARP inhibitors (PARPi) have become the mainstay of HGSC-targeted therapy, given that these tumors are driven by a high degree of genomic instability (GI) and homologous recombination (HR) defects. Nonetheless, approximately 30% of patients initially respond to treatment, ultimately relapsing with resistant disease. Thus, despite recent advances in drug development and an increased understanding of genetic alterations driving HGSC progression, mortality has not declined, highlighting the need for novel therapies. Using a small-molecule activator of protein phosphatase 2A (PP2A; SMAP-061), we investigated the mechanism by which PP2A stabilization induces apoptosis in patient-derived HGSC cells and xenograft (PDX) models alone or in combination with PARPi. We uncovered that PP2A genes essential for cellular transformation (B56α, B56γ, and PR72) and basal phosphatase activity (PP2A-A and -C) are heterozygously lost in the majority of HGSC. Moreover, loss of these PP2A genes correlates with worse overall patient survival. We show that SMAP-061-induced stabilization of PP2A inhibits the HR output by targeting RAD51, leading to chronic accumulation of DNA damage and ultimately apoptosis. Furthermore, combination of SMAP-061 and PARPi leads to enhanced apoptosis in both HR-proficient and HR-deficient HGSC cells and PDX models. Our studies identify PP2A as a novel regulator of HR and indicate PP2A modulators as a therapeutic therapy for HGSC. In summary, our findings further emphasize the potential of PP2A modulators to overcome PARPi insensitivity, given that targeting RAD51 presents benefits in overcoming PARPi resistance driven by BRCA1/2 mutation reversions.

The nutritional supplement taurine activates p53-dependent and independent tumor suppressor mechanisms in various cellular models of ovarian cancer.

Loss of treatment-induced ovarian carcinoma (OC) growth suppression poses a major clinical challenge because it leads to disease recurrence. Therefore, there is a compelling need for well- -tolerated approaches that can support tumor growth-suppression after therapy is stopped. We have profiled ascites as OC tumor microenvironments to search for potential non-toxic soluble components that would activate tumor suppressor pathways in OC cells. Our investigations revealed that low levels of taurine, a non-proteogenic sulfonic amino acid, were present within OC ascites. Taurine supplementation, beyond levels found in ascites, induced growth suppression without causing cytotoxicity in various OC cells, including chemotherapy-resistant cell clones and patient-derived organoids representing primary or chemotherapy recovered disease. Inhibition of proliferation by taurine was linked to increased mutant or wild-type p53 proteins binding to DNA, induction of p21, and independently of p53, TIGAR expression. Taurine-induced activation of p21 and TIGAR was associated with suppression of cell-cycle progression, glycolysis, and mitochondrial respiration. Expression of p21 or TIGAR in OC cells mimicked taurine-induced growth suppression. Our studies support the potential therapeutic value of taurine supplementation in OC.

Targeting Ribonucleotide Reductase Induces Synthetic Lethality in PP2A-Deficient Uterine Serous Carcinoma.

Uterine serous carcinoma (USC) is a highly aggressive endometrial cancer subtype with limited therapeutic options and a lack of targeted therapies. While mutations to PPP2R1A, which encodes the predominant protein phosphatase 2A (PP2A) scaffolding protein Aα, occur in 30% to 40% of USC cases, the clinical actionability of these mutations has not been studied. Using a high-throughput screening approach, we showed that mutations in Aα results in synthetic lethality following treatment with inhibitors of ribonucleotide reductase (RNR). In vivo, multiple models of Aα mutant uterine serous tumors were sensitive to clofarabine, an RNR inhibitor (RNRi). Aα-mutant cells displayed impaired checkpoint signaling upon RNRi treatment and subsequently accumulated more DNA damage than wild-type (WT) cells. Consistently, inhibition of PP2A activity using LB-100, a catalytic inhibitor, sensitized WT USC cells to RNRi. Analysis of The Cancer Genome Atlas data indicated that inactivation of PP2A, through loss of PP2A subunit expression, was prevalent in USC, with 88% of patients with USC harboring loss of at least one PP2A gene. In contrast, loss of PP2A subunit expression was rare in uterine endometrioid carcinomas. While RNRi are not routinely used for uterine cancers, a retrospective analysis of patients treated with gemcitabine as a second- or later-line therapy revealed a trend for improved outcomes in patients with USC treated with RNRi gemcitabine compared with patients with endometrioid histology. Overall, our data provide experimental evidence to support the use of ribonucleotide reductase inhibitors for the treatment of USC. SIGNIFICANCE: A drug repurposing screen identifies synthetic lethal interactions in PP2A-deficient uterine serous carcinoma, providing potential therapeutic avenues for treating this deadly endometrial cancer.

Metabolic collateral lethal target identification reveals MTHFD2 paralogue dependency in ovarian cancer.

Recurrent loss-of-function deletions cause frequent inactivation of tumour suppressor genes but often also involve the collateral deletion of essential genes in chromosomal proximity, engendering dependence on paralogues that maintain similar function. Although these paralogues are attractive anticancer targets, no methodology exists to uncover such collateral lethal genes. Here we report a framework for collateral lethal gene identification via metabolic fluxes, CLIM, and use it to reveal MTHFD2 as a collateral lethal gene in UQCR11-deleted ovarian tumours. We show that MTHFD2 has a non-canonical oxidative function to provide mitochondrial NAD+, and demonstrate the regulation of systemic metabolic activity by the paralogue metabolic pathway maintaining metabolic flux compensation. This UQCR11-MTHFD2 collateral lethality is confirmed in vivo, with MTHFD2 inhibition leading to complete remission of UQCR11-deleted ovarian tumours. Using CLIM's machine learning and genome-scale metabolic flux analysis, we elucidate the broad efficacy of targeting MTHFD2 despite distinct cancer genetic profiles co-occurring with UQCR11 deletion and irrespective of stromal compositions of tumours.

KLF6-SV1 overexpression accelerates human and mouse prostate cancer progression and metastasis.

Metastatic prostate cancer (PCa) is one of the leading causes of death from cancer in men. The molecular mechanisms underlying the transition from localized tumor to hormone-refractory metastatic PCa remain largely unknown, and their identification is key for predicting prognosis and targeted therapy. Here we demonstrated that increased expression of a splice variant of the Kruppel-like factor 6 (KLF6) tumor suppressor gene, known as KLF6-SV1, in tumors from men after prostatectomy predicted markedly poorer survival and disease recurrence profiles. Analysis of tumor samples revealed that KLF6-SV1 levels were specifically upregulated in hormone-refractory metastatic PCa. In 2 complementary mouse models of metastatic PCa, KLF6-SV1-overexpressing PCa cells were shown by in vivo and ex vivo bioluminescent imaging to metastasize more rapidly and to disseminate to lymph nodes, bone, and brain more often. Interestingly, while KLF6-SV1 overexpression increased metastasis, it did not affect localized tumor growth. KLF6-SV1 inhibition using RNAi induced spontaneous apoptosis in cultured PCa cell lines and suppressed tumor growth in mice. Together, these findings demonstrate that KLF6-SV1 expression levels in PCa tumors at the time of diagnosis can predict the metastatic behavior of the tumor; thus, KLF-SV1 may represent a novel therapeutic target.

Myosin IIA associates with NK cell lytic granules to enable their interaction with F-actin and function at the immunological synapse.

NK cell cytotoxicity requires the formation of an actin-rich immunological synapse (IS) with a target cell and the polarization of perforin-containing lytic granules toward the IS. Following the polarization of lytic granules, they traverse through the actin-rich IS to join the NK cell membrane in order for directed secretion of their contents to occur. We examined the role of myosin IIA as a candidate for facilitating this prefinal step in lytic NK cell IS function. Lytic granules in and derived from a human NK cell line, or ex vivo human NK cells, were constitutively associated with myosin IIA. When isolated using density gradients, myosin IIA-associated NK cell lytic granules directly bound to F-actin and the interaction was sensitive to the presence of ATP under conditions of flow. In NK cells from patients with a truncation mutation in myosin IIA, NK cell cytotoxicity, lytic granule penetration into F-actin at the IS, and interaction of isolated granules with F-actin were all decreased. Similarly, inhibition of myosin function also diminished the penetration of lytic granules into F-actin at the IS, as well as the final approach of lytic granules to and their dynamics at the IS. Thus, NK cell lytic granule-associated myosin IIA enables their interaction with actin and final transit through the actin-rich IS to the synaptic membrane, and can be defective in the context of naturally occurring human myosin IIA mutation.

Loss of matrix metalloproteinase-2 amplifies murine toxin-induced liver fibrosis by upregulating collagen I expression.

BACKGROUND AND AIMS: Matrix metalloproteinase-2 (MMP-2), a type IV collagenase secreted by activated hepatic stellate cells (HSCs), is upregulated in chronic liver disease and is considered a profibrotic mediator due to its proliferative effect on cultured HSCs and ability to degrade normal liver matrix. Although associative studies and cell culture findings suggest that MMP-2 promotes hepatic fibrogenesis, no in vivo model has definitively established a pathologic role for MMP-2 in the development and progression of liver fibrosis. We therefore examined the impact of MMP-2 deficiency on liver fibrosis development during chronic CCl(4) liver injury and explored the effect of MMP-2 deficiency and overexpression on collagen I expression. METHODS: Following chronic CCl(4) administration, liver fibrosis was analyzed using Sirius Red staining with quantitative morphometry and real-time polymerase chain reaction (PCR) in MMP-2-/- mice and age-matched MMP-2+/+ controls. These studies were complemented by analyses of cultured human stellate cells. RESULTS: MMP-2-/- mice demonstrated an almost twofold increase in fibrosis which was not secondary to significant differences in hepatocellular injury, HSC activation or type I collagenase activity; however, type I collagen messenger RNA (mRNA) expression was increased threefold in the MMP-2-/- group by real-time PCR. Furthermore, targeted reduction of MMP-2 in cultured HSCs using RNA interference significantly increased collagen I mRNA and protein, while overexpression of MMP-2 resulted in decreased collagen I mRNA. CONCLUSIONS: These findings suggest that increased MMP-2 during the progression of liver fibrosis may be an important mechanism for inhibiting type I collagen synthesis by activated HSCs, thereby providing a protective rather than pathologic role.

Mistletoe Extract Viscum Fraxini-2 for Treatment of Advanced Hepatocellular Carcinoma: A Case Series.

BACKGROUND: Hepatocellular carcinoma (HCC) is the fourth leading cause of death from cancer worldwide, and for advanced HCC the prognosis is poor. Preliminary studies indicate mistletoe extracts may have anticancer activity for HCC. METHODS: A prospective observational case series of advanced HCC patients that chose to take a mistletoe extract called viscum fraxini-2 (VF-2) alone for treatment. Time on treatment, imaging, and laboratory values were collected for descriptive analyses. RESULTS: A total of 12 patients with advanced HCC enrolled onto the protocol, and 10 patients had data available for evaluation. The majority were male (10/12) with a median age of 64 (SD 11). Most patients had received sorafenib therapy (9/12) and had varying Child-Pugh classes (A-4, B-6, C-2). Treatment with VF-2 ranged from 1 to 36 weeks with a mean of 12.3 weeks (SD 12). Six patients received 8 weeks of treatment, and 3 patients received 12 or more weeks of treatment. For patients that received at least 4 weeks of treatment, the average AFP value stabilized during the first 4 weeks of treatment. Two patients experienced an AFP decrease of >30%, approximately 37 and 40% decreases at the nadir. One patient had stable disease of 9 months. Major side effects were fever, fatigue, rash, and local injection site reaction of swelling, redness, and tenderness. CONCLUSION: This case series of advanced HCC indicates that mistletoe extract VF-2 may have potential biological activity against HCC for selected patients. Research is needed to identify the active compound and predictive markers of response.

Detection of Tumor-Specific PTPmu in Gynecological Cancer and Patient Derived Xenografts.

BACKGROUND: We developed a fluorophore-conjugated peptide agent, SBK4, that detects a tumor-specific proteolyzed form of the cell adhesion molecule, PTPmu, found in the tumor microenvironment. We previously demonstrated its tissue specific distribution in high-grade brain tumors. To extend those studies to other aggressive solid tumor types, we assessed the tissue distribution of PTPmu/SBK4 in a set of matched gynecologic cancer patient derived xenografts (PDXs) and primary patient tumors, as well as a limited cohort of tumors from gynecological cancer patients. PDXs isolated from the tissues of cancer patients have been shown to yield experimentally manipulatable models that replicate the clinical characteristics of individual patients' tumors. In this study, gynecological cancer PDXs and patient biopsies were examined to determine if tumor-specific proteolyzed PTPmu was present. METHODS: We used the peptide agent SBK4 conjugated to the fluorophore Texas Red (TR) to label tumor tissue microarrays (TMAs) containing patient and/or PDX samples from several high-grade gynecologic cancer types, and quantified the level of staining with Image J. In one TMA, we were able to directly compare the patient and the matched PDX tissue on the same slide. RESULTS: While normal tissue had very little SBK4-TR staining, both primary tumor tissue and PDXs have higher labeling with SBK4-TR. Matched PDXs and patient samples from high-grade endometrial and ovarian cancers demonstrated higher levels of PTPmu by staining with SBK4 than normal tissue. CONCLUSION: In this sample set, all PDXs and high-grade ovarian cancer samples had increased labeling by SBK4-TR compared with the normal controls. Our results indicate that proteolyzed PTPmu and its novel peptide detection agent, SBK4, allow for the visualization of tumor-specific changes in cell adhesion molecules by tissue-based staining, providing a rationale for further development as an imaging agent in aggressive solid tumors, including gynecological cancers.

STING pathway expression in low-grade serous carcinoma of the ovary: an unexpected therapeutic opportunity?

Ovarian carcinoma histotypes are distinct diseases with variable clinical outcomes and response to treatment. There is a need for new subtype-specific treatment modalities, especially for women with widespread and chemo-resistant disease. Stimulator of interferon genes (STING) is a part of the cGAS-STING pathway that mediates innate immune defence against infectious DNA-containing pathogens and also detects tumour-derived DNA and generates intrinsic antitumour immunity. The STING signalling pathway is suppressed by several mechanisms in a variety of malignant diseases and, in some cancers that may be a requirement for cellular transformation. The aim of this study was to use immunohistochemistry to evaluate STING protein expression across normal tissue, paratubal and ovarian cysts, and ovarian tumour histotypes including ovarian carcinomas. Herein, we show that the fallopian tube ciliated cells express STING protein, whereas the secretory cells are negative. STING expression differs among ovarian cancer histotypes; low-grade serous ovarian carcinomas and serous borderline tumours have uniform high STING expression, while high-grade serous and endometrioid carcinomas have heterogeneous expression, and clear cell and mucinous carcinomas show low expression. As low-grade serous carcinomas are known to be genomically stable and typically lack a prominent host immune response, the consistently high STING expression is unexpected. High STING expression may reflect pathway activation or histogenesis and the mechanisms may be different in different ovarian carcinoma histotypes. Further studies are needed to determine whether the STING signalling pathway is active and whether these tumours would be candidates for therapeutic interventions that trigger innate immunity activation.

The miR-181a-SFRP4 Axis Regulates Wnt Activation to Drive Stemness and Platinum Resistance in Ovarian Cancer.

Wnt signaling is a major driver of stemness and chemoresistance in ovarian cancer, yet the genetic drivers that stimulate its expression remain largely unknown. Unlike other cancers, mutations in the Wnt pathway are not reported in high-grade serous ovarian cancer (HGSOC). Hence, a key challenge that must be addressed to develop effective targeted therapies is to identify nonmutational drivers of Wnt activation. Using an miRNA sensor-based approach, we have identified miR-181a as a novel driver of Wnt/ß-catenin signaling. miR-181ahigh primary HGSOC cells exhibited increased Wnt/ß-catenin signaling, which was associated with increased stem-cell frequency and platinum resistance. Consistent with these findings, inhibition of ß-catenin decreased stem-like properties in miR-181ahigh cell populations and downregulated miR-181a. The Wnt inhibitor SFRP4 was identified as a novel target of miR-181a. Overall, our results demonstrate that miR-181a is a nonmutational activator of Wnt signaling that drives stemness and chemoresistance in HGSOC, suggesting that the miR-181a-SFRP4 axis can be evaluated as a novel biomarker for ß-catenin-targeted therapy in this disease. SIGNIFICANCE: These results demonstrate that miR-181a is an activator of Wnt signaling that drives stemness and chemoresistance in HGSOC and may be targeted therapeutically in recurrent disease.

The role of KLF6 and its splice variants in cancer therapy.

The Krüppel-like zinc finger transcription factor (KLF6) gene encodes a family of proteins generated through alternative splicing involved in the regulation of cancer development and progression. Alternative splicing of the KLF6 gene results in the production of at least four alternatively spliced isoforms, two of which are extensively discussed in this review. The full length form of the KLF6 gene is a tumor suppressor gene that is frequently inactivated by loss of heterozygozity (LOH), somatic mutation, and/or decreased expression in human cancer. While the exact mechanisms underlying KLF6's tumor suppressor roles are not completely known, a number of highly relevant, overlapping pathways have been described: transactivation of p21 in a p53-independent manner, reduction of cyclin D1/cdk4 complexes via interaction with cyclin D1, inhibition of c-Jun proto-oncoprotein activities, decreased VEGF expression, and induction of apoptosis. Kruppel-like factor 6 splice variant 1 (KLF6-SV1) is an oncogenic splice variant of the KLF6 tumor suppressor gene that is specifically overexpressed in a number of human cancers. Increased KLF6-SV1 expression is associated with poor prognosis in prostate, lung, and ovarian cancer. Furthermore, KLF6-SV1 has been shown to be biologically active, antagonizing the tumor suppressor function of KLF6 and promoting tumor growth and dissemination in both ovarian and prostate cancer models. In addition, a common germline polymorphism in the KLF6 gene associated with increased prostate cancer risk in a large multi-institutional study of 3411 men results in increased expression of KLF6-SV1. Furthermore, recent studies have demonstrated that targeted reduction of KLF6-SV1 results in the induction of spontaneous apoptosis in cell culture, synergizes with chemotherapeutic agents like cisplatin, and results in significant tumor regression in vivo. Combined, these data make the KLF6 gene family a compelling therapeutic target for both the treatment of localized as well as metastatic cancer.