The role of collagen triple helix repeat containing 1 (CTHRC1) in cancer development and progression

INTRODUCTION

Collagen triple helix repeat containing 1 (CTHRC1) is a protein that has been implicated in pro-migratory pathways, arterial tissue-repair processes, and inhibition of collagen deposition via the regulation of multiple signaling cascades. Studies have also demonstrated an upregulation of CTHRC1 in multiple cancers where it has been linked to enhanced proliferation, invasion, and metastasis. However, the understanding of the exact role and mechanisms of CTHRC1 in cancer is far from complete.

AREAS COVERED

This review focuses on analyzing the role of CTHRC1 in cancer as well as its associations with clinicopathologies and cancer-related processes and signaling. We have also summarized the available literature information regarding the role of CTHRC1 in tumor microenvironment and immune signaling. Finally, we have discussed the mechanisms associated with CTHRC1 regulations, and opportunities and challenges regarding the development of CTHRC1 as a potential target for cancer management.

EXPERT OPINION

CTHRC1 is a multifaceted protein with critical roles in cancer progression and other pathological conditions. Its association with lower overall survival in various cancers, and impact on the tumor immune microenvironment make it an intriguing target for further research and potential therapeutic interventions in cancer.

The fusion of light and immunity: Advancements in photoimmunotherapy for melanoma

Metastatic melanoma is an aggressive skin cancer with high mortality and recurrence rates. Despite the clinical success of recent immunotherapy approaches, prevailing resistance rates necessitate the continued development of novel therapeutic options. Photoimmunotherapy (PIT) is emerging as a promising immunotherapy strategy that uses photodynamic therapy (PDT) to unleash systemic immune responses against tumor sites while maintaining the superior tumor-specificity and minimally invasive nature of traditional PDT. In this review, we discuss recent advances in PIT and strategies for the management of melanoma using PIT. PIT can strongly induce immunogenic cell death, inviting the concomitant application of immune checkpoint blockade or adoptive cell therapies. PIT can also be leveraged to selectively remove the suppressive immune populations associated with immunotherapy resistance. The modular nature of PIT therapy design combined with the potential for patient-specific antigen selection or drug co-delivery makes PIT an alluring option for future personalized melanoma care.

Immune escape and metastasis mechanisms in melanoma: breaking down the dichotomy

Melanoma is one of the most lethal neoplasms of the skin. Despite the revolutionary introduction of immune checkpoint inhibitors, metastatic spread, and recurrence remain critical problems in resistant cases. Melanoma employs a multitude of mechanisms to subvert the immune system and successfully metastasize to distant organs. Concerningly, recent research also shows that tumor cells can disseminate early during melanoma progression and enter dormant states, eventually leading to metastases at a future time. Immune escape and metastasis have previously been viewed as separate phenomena; however, accumulating evidence is breaking down this dichotomy. Recent research into the progressive mechanisms of melanoma provides evidence that dedifferentiation similar to classical epithelial to mesenchymal transition (EMT), genes involved in neural crest stem cell maintenance, and hypoxia/acidosis, are important factors simultaneously involved in immune escape and metastasis. The likeness between EMT and early dissemination, and differences, also become apparent in these contexts. Detailed knowledge of the mechanisms behind "dual drivers" simultaneously promoting metastatically inclined and immunosuppressive environments can yield novel strategies effective in disabling multiple facets of melanoma progression. Furthermore, understanding progression through these drivers may provide insight towards novel treatments capable of preventing recurrence arising from dormant dissemination or improving immunotherapy outcomes.

Role of PLK1/NUMB/NOTCH in epithelial-mesenchymal transition in human melanoma

Polo-like kinase 1 (PLK1), a serine/threonine kinase, is overexpressed in melanoma and its expression has been associated with poor disease prognosis. PLK1 has been shown to interact with NUMB, a NOTCH antagonist. However, the exact role of PLK1, NUMB, and NOTCH signaling in epithelial-mesenchymal transition (EMT) in melanoma progression is unclear. In this study, Affymetrix microarray analysis was performed to determine differentially expressed genes following shRNA-mediated knockdown of PLK1 in human melanoma cells that showed significant modulations in EMT and metastasis-related genes. Using multiple PLK1-modulated melanoma cell lines, we found that PLK1 is involved in the regulation of cell migration, invasion, and EMT via its kinase activity and NOTCH activation. In vitro kinase assay and mass spectrometry analysis demonstrated a previously unknown PLK1 phosphorylation site (Ser413) on NUMB. Overexpression of non-phosphorylatable (S413A) and phosphomimetic (S413D) mutants of NUMB in melanoma cells implicated the involvement of NUMB-S413 phosphorylation in cell migration and invasion, which was independent of NOTCH activation. To determine the clinical relevance of these findings, immunohistochemistry was performed using melanoma tissue microarray, which indicated a strong positive correlation between PLK1 and N-cadherin, a protein required for successful EMT. These findings were supported by TCGA analysis, where expression of high PLK1 with low NUMB or high NOTCH or N-cadherin showed a significant decrease in survival of melanoma patients. Overall, these results suggest a potential role of PLK1 in EMT, migration, and invasion of melanoma cells. Our findings support the therapeutic targeting of PLK1, NUMB, and NOTCH for melanoma management.

Abstract 466: A potential pro-oncogenic role of SERPINB4 in melanoma

Despite recent therapeutic advancements, melanoma remains one of the deadliest forms of skin cancer. Melanoma metastasis and recurrence is associated with the existence of heterogeneous cell populations within tumors that have the ability to both initiate metastatic programs and bypass immune recognition. Tumor cells achieve immune evasion by interfering with immune signaling to limit immune cell infiltration, allowing tumor cell proliferation and growth. SERPINB4 (Squamous Cell Carcinoma Antigen 2 or SCCA2), a serine protease inhibitor, has been shown to regulate the host immune response against tumor cells by inhibiting immune cell activity. Interestingly, certain cancer cell types have been reported to overexpress SERPINB4. However, the expression profile and the functional significance of SERPINB4 in melanoma is not known. In this study, employing ‘The Cancer Genome Atlas’ (TCGA), we found that SERPINB4 is overexpressed and significantly associated with lower overall survival in patients with melanoma. Next, employing a panel of human melanoma cell lines, we demonstrated that SERPINB4 is overexpressed in melanoma cells when compared to normal human melanocytes. In addition, CRISPR knockout of SERPINB4 in high-SERPINB4-expressing A375 melanoma cells resulted in a significant decrease in proliferation of melanoma cells in comparison to control cells. Conversely, forced overexpression of SERPINB4 in low-SERPINB4-expressing SK-MEL-2 and SK-MEL-28 melanoma cells significantly increased melanoma cell proliferation. Moreover, RT-qPCR analyses suggested that SERPINB4 overexpression significantly increased, while its knockout significantly decreased epithelial-mesenchymal transition (EMT) markers (N-cadherin, β-catenin, Snail and Zeb1) in melanoma cells. Additionally, SERPINB4 manipulation significantly modulated the expression of genes involved in antigen-presentation (MHC Class I molecules, HLA-A, -B, and -C) in melanoma cells. Taken together, our data suggested a potential oncogenic role of SERPINB4 in melanoma. Our study also suggested that SERPINB4 might be a promising therapeutic target for melanoma. Indeed, additional in vitro mechanistic and in vivo studies are needed to firmly establish the mechanism and therapeutic potential of SERPINB4 for melanoma management.

Citation Format: Gagan Chhabra, Carl A. Shirley, Rachel K. Robarge, Hassan A. Rizvi, Mary A. Ndiaye, Nihal Ahmad. A potential pro-oncogenic role of SERPINB4 in melanoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 466.

Protective effects of dietary grape against atopic dermatitis-like skin lesions in NC/NgaTndCrlj mice

Atopic dermatitis (AD) is a chronic inflammatory skin disease with significant health/economic burdens. Existing therapies are not fully effective, necessitating development of new approaches for AD management. Here, we report that dietary grape powder (GP) mitigates AD-like symptoms in 2,4-dinitrofluorobenzene (DNFB)-induced AD in NC/NgaTndCrlj mice. Using prevention and intervention protocols, we tested the efficacy of 3% and 5% GP-fortified diet in a 13-weeks study. We found that GP feeding markedly inhibited development and progression of AD-like skin lesions, and caused reduction in i) epidermal thickness, mast cell infiltration, ulceration, excoriation and acanthosis in dorsal skin, ii) spleen weight, extramedullary hematopoiesis and lymph nodes sizes, and iii) ear weight and IgE levels. We also found significant modulations in 15 AD-associated serum cytokines/chemokines. Next, using quantitative global proteomics, we identified 714 proteins. Of these, 68 (normal control) and 21 (5% GP-prevention) were significantly modulated (≥2-fold) vs AD control (DNFB-treated) group, with many GP-modulated proteins reverting to normal levels. Ingenuity pathway analysis of GP-modulated proteins followed by validation using ProteinSimple identified changes in acute phase response signaling (FGA, FGB, FGG, HP, HPX, LRG1). Overall, GP supplementation inhibited DNFB-induced AD in NC/NgaTndCrlj mice in both prevention and intervention trials, and should be explored further.

Trichloroisocyanuric Acid (TCIC), A Swimming Pool Disinfectant: New Developments and Role in UV-Induced Skin Inflammation

This article is a highlight of the paper by Snell et al. in the current issue of Photochemistry and Photobiology (Snell et al. Photochem. Photobiol. 2022). The authors utilized an organotypic human skin model as well as transgenic SKH-1 mice to determine the oxidative stress response induced by topical treatment of trichloroisocyanuric acid (TCIC), a common disinfectant used in swimming pool. Additionally, they determined molecular mechanisms associated with topical TCIC pre-treatment followed by ultraviolet (UV) radiation exposure. This work provides the first example that cutaneous delivery of TCIC significantly increases UV-induced skin inflammation, suggesting a previously unidentified potential of TCIC. If translatable to human skin, these findings could be important for human skin health implications.

Abstract 3979: CRISPR/Cas9-mediated knockout of PLK4 results in antiproliferative response in human epidermoid carcinoma cells in vitro and in implanted xenografts

Non-melanoma skin cancers (NMSCs) constitute the largest number of cancers diagnosed in the United States, with an estimated 1 in 5 people affected by the age of 70. The most notable NMSCs are squamous cell carcinomas (SCCs) and basal cell carcinomas (BCCs), which are considered keratinocyte cancers due to their origin. Although the majority of NMSCs can be removed with surgery or curettage, these options are not always available if the tumor occurs in an inoperable location or becomes metastatic. While non-surgical treatment modalities are also currently available, they have not been fully effective in NMSC management. Therefore, novel mechanistic-based therapeutic strategies are needed. The polo-like kinases (PLKs) are a family of serine/threonine kinases that have been found to play multiple roles in regulating the cell cycle. PLK4 is a structurally unique member of this family, which has been shown to be essential for precise centriole duplication. However, PLK4 has been shown to be dysregulated in certain cancers. Though the role of PLK4 in NMSC is not fully understood, we previously showed that PLK4 was significantly overexpressed in NMSC cell lines at both mRNA and protein levels as compared to normal keratinocytes, and its small molecule inhibition resulted in anti-proliferative responses in NMSC cell lines (Cancer Res 2018; 78 [13 Suppl]: Abstract nr 547). Here, we further validated our previous observation by determining the effects of CRISPR/Cas9-mediated knockout (KO) of PLK4 in the A431 human SCC line, both in vitro and in vivo. Our data demonstrated significantly reduced cell growth of multiple A431 PLK4 KO clones compared to wild-type (WT) cells, as measured by RealTime-Glo MT cell viability and trypan blue exclusion assays. In addition, we found significant reduction in clonogenic survival of A431 PLK4 KO cells, as measured by colony formation assays. Using a Human Cancer Pathway Finder RT2 Profiler PCR array, we identified 18 of the 84 genes tested to be greater than 1.6-fold differentially regulated after PLK4 KO in these cells. Employing Ingenuity Pathway Analysis (IPA) software, we identified that the regulation of the epithelial-mesenchymal transition by growth factors was one of the top canonical pathways modulated by PLK4 KO. To determine the in vivo relevance of our in vitro data, we compared the tumorigenicity of the A431 WT and PLK4 KO cells in nu/nu mice. The mice (n=7 per group) were injected subcutaneously with 5 x 105 A431 WT or PLK4 KO cells and tumors were allowed to grow for further analyses. We found a significant reduction in tumor volume in A431 PLK4 KO xenografts as compared to A431 PLK4 WT xenografts. Taken together, these findings support our previous results that suggest PLK4 has pro-proliferative roles in NMSC and should be further studied as a potential novel target for skin cancer management.

Citation Format: Mary A. Ndiaye, Debra R. Garvey, Gagan Chhabra, Chandra K. Singh, Nihal Ahmad. CRISPR/Cas9-mediated knockout of PLK4 results in antiproliferative response in human epidermoid carcinoma cells in vitro and in implanted xenografts [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 3979.

Mechanisms of Immunotherapy Resistance in Cutaneous Melanoma: Recognizing a Shapeshifter

Melanoma is one of the seven most common cancers in the United States, and its incidence is still increasing. Since 2011, developments in targeted therapies and immunotherapies have been essential for significantly improving overall survival rates. Prior to the advent of targeted and immunotherapies, metastatic melanoma was considered a death sentence, with less than 5% of patients surviving more than 5 years. With the implementation of immunotherapies, approximately half of patients with metastatic melanoma now survive more than 5 years. Unfortunately, this also means that half of the patients with melanoma do not respond to current therapies and live less than 5 years after diagnosis. One major factor that contributes to lower response in this population is acquired or primary resistance to immunotherapies via tumor immune evasion. To improve the overall survival of melanoma patients new treatment strategies must be designed to minimize the risk of acquired resistance and overcome existing primary resistance. In recent years, many advances have been made in identifying and understanding the pathways that contribute to tumor immune evasion throughout the course of immunotherapy treatment. In addition, results from clinical trials focusing on treating patients with immunotherapy-resistant melanoma have reported some initial findings. In this review, we summarize important mechanisms that drive resistance to immunotherapies in patients with cutaneous melanoma. We have focused on tumor intrinsic characteristics of resistance, altered immune function, and systemic factors that contribute to immunotherapy resistance in melanoma. Exploring these pathways will hopefully yield novel strategies to prevent acquired resistance and overcome existing resistance to immunotherapy treatment in patients with cutaneous melanoma.

PLK1 inhibition-based combination therapies for cancer management

Polo-like kinase I (PLK1), a cell cycle regulating kinase, has been shown to have oncogenic function in several cancers. Although PLK1 inhibitors, such as BI2536, BI6727 (volasertib) and NMS-1286937 (onvansertib) are generally well-tolerated with a favorable pharmacokinetic profile, clinical successes are limited due to partial responses in cancer patients, especially those in advanced stages. Recently, combination therapies targeting multiple pathways are being tested for cancer management. In this review, we first discuss structure and function of PLK1, role of PLK1 in cancers, PLK1 specific inhibitors, and advantages of using combination therapy versus monotherapy followed by a critical account on PLK1-based combination therapies in cancer treatments, especially highlighting recent advancements and challenges. PLK1 inhibitors in combination with chemotherapy drugs and targeted small molecules have shown superior effects against cancer both in vitro and in vivo. PLK1-based combination therapies have shown increased apoptosis, disrupted cell cycle, and potential to overcome resistance in cancer cells/tissues over monotherapies. Further, with successes in preclinical experiments, researchers are validating such approaches in clinical trials. Although PLK1-based combination therapies have achieved initial success in clinical studies, there are examples where they have failed to improve patient survival. Therefore, further research is needed to identify and validate novel biologically informed co-targets for PLK1-based combinatorial therapies. Employing a network-based analysis, we identified potential PLK1 co-targets that could be examined further. In addition, understanding the mechanisms of synergism between PLK1 inhibitors and other agents may lead to a better approach on which agents to pair with PLK1 inhibition for optimum cancer treatment.

BRAF Inhibitors in Melanoma Management: When Friends Become Foes

The BRAF inhibitor (BRAFi) vemurafenib improves survival of patients with melanoma with BRAF^V600E mutations. However, effects of sustained BRAFis on BRAFi-resistant melanomas with dual mutations in BRAF and NRAS are not well characterized. Jandova and Wondrak (2021) report that vemurafenib selectively enhances expression of genes involved in the epithelial-to-mesenchymal transition in BRAF^V600E/NRAS^Q61K melanoma cells, paradoxically promoting tumor growth and metastasis in mice. This preclinical study provides compelling reasons to be cautious in the use of BRAFis in patients with NRAS-driven melanoma.

Anti-melanoma effects of concomitant inhibition of SIRT1 and SIRT3 in BrafV600E/PtenNULL mice

Novel therapeutic strategies are required for the effective and lasting treatment of metastatic melanoma, one of the deadliest skin malignancies. In this study, we determined the anti-melanoma efficacy of 4'-bromo-resveratrol (4'-BR), which is a small molecule dual inhibitor of SIRT1 and SIRT3 in a Braf^V600E/Pten^NULL mouse model that recapitulates human disease, including metastases. Tumors were induced by topical application of 4-hydroxy-tamoxifen on shaved backs of 10-week-old mice, and the effects of 4'-BR (5-30 mg/kg b.wt.; intraperitoneally; 3d/week for 5 weeks) were assessed on melanoma development and progression. We found that 4'-BR at a dose of 30 mg/kg significantly reduced size and volume of primary melanoma tumors, as well as lung metastasis, with no adverse effects. Further, mechanistic studies on tumors showed significant modulation in markers of proliferation, survival and melanoma progression. As SIRT1 and SIRT3 are linked to immunomodulation, we performed differential gene expression analysis via NanoString PanCancer Immune Profiling panel (770 genes). Our data demonstrated that 4'-BR significantly downregulated genes related to metastasis-promotion, chemokine/cytokine-regulation, and innate/adaptive immune functions. Overall, inhibition of SIRT1 and SIRT3 by 4'-BR is a promising anti-melanoma therapy with anti-metastatic and immunomodulatory activities warranting further detailed studies, including clinical investigations.

Abstract 2157: Potential correlations between PLK1, BRAF and MITF in melanoma

Melanoma is one of the most aggressive types of cancer and extremely difficult to treat after metastasis. BRAFV600E-activating mutations give rise to ∼80% of melanocytic nevi, yet only one-third of melanocytic nevi result in melanoma, suggesting the involvement of other factors. Polo-like kinase 1 (PLK1), an important regulator of cell cycle progression, is overexpressed in melanoma and its expression has been shown to correlate with patient prognosis. Microphthalmia-associated transcription factor (MITF) is a melanocytic lineage-specific transcription factor that regulates a variety of genes critical for melanin synthesis as well as melanoma progression. The goal of this study was to define potential interactions between PLK1, BRAFV600E, and MITF in human melanoma. First, we employed a commercially available human tissue microarray (TMA) coupled with high-throughput, multispectral Vectra scanning and inForm analysis to study a number of clinical tissue cores (nevus, malignant and metastatic melanoma). The TMA was simultaneously immunostained for PLK1, BRAFV600E, MITF, proliferation marker Ki67, melanoma biomarker S100 and DAPI, and was subjected to Vectra scanning and inForm analyses. Using Simple Linear Regression analyses, we found significant correlations among each pair of the selected four proteins (PLK1, BRAFV600E, MITF and Ki67) with correlation co-efficient ranging 0.24-0.84. To analyze if PLK1, and BRAFV600E are contributing to cell proliferation (Ki67 expression) or affecting MITF expression, we employed a Multiple Linear Regression analysis. Our data suggested that high expressions of both BRAFV600E and PLK1 are correlated positively with the expression of Ki67. However, when fitting both PLK1 and BRAFV600E versus MITF, only high PLK1 had significant positive correlation with MITF, while BRAFV600E did not show correlation with MITF. These results suggest that PLK1 and MITF could contribute to melanoma progression independent to BRAFV600E. To further validate our findings, we analyzed The Cancer Genome Atlas (TCGA) database containing a large melanoma cohort of 432 melanoma patients with information on overall survival (OS). To visualize the survival plots, the expression level of PLK1 and MITF was sorted and equally separated to two groups using the median value as a cutoff. Kaplan-Meier analyses showed that high mRNA expression of both PLK1 and MITF were individually associated with significant reductions in OS. Interestingly, when we sorted the data for both high PLK1 and high MITF in the same patient, the OS was shorter than that of patients with low PLK1 and low MITF. Overall, our study suggests an association between PLK1 and MITF pathways during melanoma progression, which may affect overall survival in melanoma patients. Thus, concomitant targeting of PLK1 and MITF could provide an advantage over monotherapy towards melanoma management. However, in-depth studies are required to validate our findings.

Citation Format: Gagan Chhabra, Shengqin Su, Chandra K. Singh, Mary A. Ndiaye, Nihal Ahmad. Potential correlations between PLK1, BRAF and MITF in melanoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2157.

Abstract 873: Identification of key immune-related genes in the pathogenesis of metastatic melanoma via bioinformatic approaches

Melanoma is one of the most aggressive forms of cancer with a meager 5-year survival rate of 25%, for metastatic melanoma. These necessitates new efforts to fully understand the pathogenesis of melanoma metastasis and identify new targets. In recent years, researchers have been taking advantage of TCGA and other publicly available databases to perform high-throughput data-mining aimed at identifying mechanisms and potential biomarkers of progression of different cancers, including melanoma. Although a limited number of bioinformatics studies have attempted to predict the genes that may be involved in the pathogenesis of metastatic melanoma, these are yet to be rigorously validated by other computational methodologies or databases. The purpose of this study was to identify key genes in the pathogenesis of metastatic melanoma by a comprehensive analysis of TCGA and other available databases. We first downloaded 470 TCGA melanoma patient's data, including clinical information and mRNA expression. Employing survival analysis within a multiple comparison correction of FDR<=0.05, we identified 1355 genes that have a significant effect on the overall survival (OS) of melanoma patients. Using “TCGAbiolinks” package in R, we further classified 1317 genes that are differentially expressed between primary and metastatic melanoma (FDR<=0.05, |log2 fold change|>=1). By taking the intersection, we narrowed down to 236 genes that i) have significant effects on patient OS and ii) differentially expressed between primary and metastatic melanoma. To study the functionalities of these 236 genes, we performed Gene Ontology (GO) analysis with FDR<=0.05 using the ClueGO application in Cytoscape. Interestingly, the most significantly deregulated GO term was the regulation of immune system process (GO:0002682, FDR=1.1e-39) that contained 62 out of the 236 genes, suggesting the significance of immune pathways in melanoma metastasis. To further cross-validate these 62 immune-related genes, we assessed whether these genes were differentially expressed between primary and metastatic melanoma using an external GEO database (GSE46517, 31 primary melanoma and 73 metastatic melanoma). Finally, we narrowed down to 21 candidate genes, including KLK8, SERPINB4, AQP3, S100A9, S100A8, S100A7, S100A7A, CLEC10A, FCGR3A, CD8B, CD84, CXCL13, MZB1, KIT, CD4, EBI3, NCKAP1L, SAMSN1, CD80, SIT1, and CCR2. In summary, we have identified 21 genes that i) regulate immune process, ii) have significant effects on melanoma patient survival, and iii) are differentially expressed between primary and metastatic melanoma. Further studies are required to validate our findings in metastatic melanoma cells and tissues.

Citation Format: Shengqin Su, Gagan Chhabra, Ting Ye, Nihal Ahmad. Identification of key immune-related genes in the pathogenesis of metastatic melanoma via bioinformatic approaches [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 873.

Dietary Phytochemicals in Zinc Homeostasis: A Strategy for Prostate Cancer Management

Studies have suggested an important role of the trace element zinc (Zn) in prostate biology and functions. Zn has been shown to exist in very high concentrations in the healthy prostate and is important for several prostatic functions. In prostate cancer (PCa), Zn levels are significantly decreased and inversely correlated with disease progression. Ideally, restoration of adequate Zn levels in premalignant/malignant prostate cells could abort prostate malignancy. However, studies have shown that Zn supplementation is not an efficient way to significantly increase Zn concentrations in PCa. Based on a limited number of investigations, the reason for the lower levels of Zn in PCa is believed to be the dysregulation of Zn transporters (especially ZIP and ZnT family of proteins), metallothioneins (for storing and releasing Zn), and their regulators (e.g., Zn finger transcription factor RREB1). Interestingly, the level of Zn in cells has been shown to be modulated by naturally occurring dietary phytochemicals. In this review, we discussed the effect of selected phytochemicals (quercetin, resveratrol, epigallocatechin-3-gallate and curcumin) on Zn functioning and proposes that Zn in combination with specific dietary phytochemicals may lead to enhanced Zn bioaccumulation in the prostate, and therefore, may inhibit PCa.

Genetic Manipulation of Sirtuin 3 Causes Alterations of Key Metabolic Regulators in Melanoma

The mitochondrial sirtuin SIRT3 plays key roles in cellular metabolism and energy production, which makes it an obvious target for the management of cancer, including melanoma. Previously, we have demonstrated that SIRT3 was constitutively upregulated in human melanoma and its inhibition resulted in anti-proliferative effects in vitro in human melanoma cells and in vivo in human melanoma xenografts. In this study, we expanded our data employing knockdown and overexpression strategies in cell culture and mouse xenografts to further validate and establish the pro-proliferative function of SIRT3 in melanocytic cells, and its associated potential mechanisms, especially focusing on the metabolic regulation. We found that short-hairpin RNA (shRNA) mediated SIRT3 knockdown in G361 melanoma cells showed diminished tumorigenesis in immunodeficient Nu/Nu mice. Conversely, SIRT3 overexpressing Hs294T melanoma cells showed increased tumor growth. These effects were consistent with changes in markers of proliferation (PCNA), survival (Survivin) and angiogenesis (VEGF) in xenografted tissues. Further, in in vitro culture system, we determined the effect of SIRT3 knockdown on glucose metabolism in SK-MEL-2 cells, using a PCR array. SIRT3 knockdown caused alterations in a total of 37 genes involved in the regulation and enzymatic pathways of glucose (32 genes) and glycogen (5 genes) metabolism. Functions annotation of these identified genes, using the ingenuity pathway analysis (IPA), predicted cumulative actions of decreased cell viability/proliferation, tumor growth and reactive oxygen species (ROS), and increased apoptosis in response to SIRT3 knockdown. Further, IPA gene network analysis of SIRT3 modulated genes revealed the interactions among these genes in addition to several melanoma-associated genes. Sirtuin pathway was identified as one of the top canonical pathways showing the interaction of SIRT3 with metabolic regulatory genes along with other sirtuins. IPA analysis also predicted the inhibition of HIF1α, PKM, KDM8, PPARGC1A, mTOR, and activation of P53 and CLPP; the genes involved in major cancer/melanoma-associated signaling events. Collectively, these results suggest that SIRT3 inhibition affects cellular metabolism, to impart an anti-proliferative response against melanoma.

Role of Polo-Like Kinase 4 (PLK4) in Epithelial Cancers and Recent Progress in its Small Molecule Targeting for Cancer Management

The polo-like kinases (PLKs) are a family of serine/threonine kinases traditionally linked to cell-cycle regulation. A structurally unique member of this family, PLK4, has been shown to regulate centriole duplication during the cell cycle via interactions with a variety of centrosomal proteins. Recent findings suggest that PLK4 is overexpressed in various human cancers and associated with poor cancer prognosis. Although several studies have shown that PLK4 inhibition may lead to cancer cell death, the underlying mechanisms are largely unknown. In this review, we discuss the structure, localization, and function of PLK4, along with the functional significance of PLK4 in epithelial cancers and some preliminary work suggesting a role for PLK4 in the key cancer progression process epithelial-mesenchymal transition. We also discuss the potential of PLK4 as a druggable target for anticancer drug development based on critical analysis of the available data of PLK4 inhibitors in preclinical development and clinical trials. Overall, the emerging data suggest that PLK4 plays an essential role in epithelial cancers and should be further explored as a potential biomarker and/or therapeutic target. Continued detailed exploration of available and next-generation PLK4 inhibitors may provide a new dimension for novel cancer therapeutics following successful clinical trials.

PLK1 and NOTCH Positively Correlate in Melanoma and Their Combined Inhibition Results in Synergistic Modulations of Key Melanoma Pathways

Melanoma is one of the most serious forms of skin cancer, and its increasing incidence coupled with nonlasting therapeutic options for metastatic disease highlights the need for additional novel approaches for its management. In this study, we determined the potential interactions between polo-like kinase 1 (PLK1, a serine/threonine kinase involved in mitotic regulation) and NOTCH1 (a type I transmembrane protein deciding cell fate during development) in melanoma. Employing an in-house human melanoma tissue microarray (TMA) containing multiple cases of melanomas and benign nevi, coupled with high-throughput, multispectral quantitative fluorescence imaging analysis, we found a positive correlation between PLK1 and NOTCH1 in melanoma. Furthermore, The Cancer Genome Atlas database analysis of patients with melanoma showed an association of higher mRNA levels of PLK1 and NOTCH1 with poor overall, as well as disease-free, survival. Next, utilizing small-molecule inhibitors of PLK1 and NOTCH (BI 6727 and MK-0752, respectively), we found a synergistic antiproliferative response of combined treatment in multiple human melanoma cells. To determine the molecular targets of the overall and synergistic responses of combined PLK1 and NOTCH inhibition, we conducted RNA-sequencing analysis employing a unique regression model with interaction terms. We identified the modulations of several key genes relevant to melanoma progression/metastasis, including MAPK, PI3K, and RAS, as well as some new genes such as Apobec3G, BTK, and FCER1G, which have not been well studied in melanoma. In conclusion, our study demonstrated a synergistic antiproliferative response of concomitant targeting of PLK1 and NOTCH in melanoma, unraveling a potential novel therapeutic approach for detailed preclinical/clinical evaluation.

Abstract 4052: Effects of CRISPR/Cas9-mediated knockout of SIRT6 in human melanoma cells, in vitro and in vivo

Melanoma is one of the most aggressive and fatal forms of skin cancer, with dismal 5-year survival if not diagnosed early. Although recent advances have led to better targeted- and immuno- therapeutic approaches, many patients develop resistance and recurrence. Therefore, it is crucial to develop newer druggable molecular targets that could be exploited towards the management of this deleterious neoplasm. Earlier studies from our laboratory have shown that SIRT6, a member of the sirtuin family of class III histone deacetylases, possesses a potential pro-proliferative role in melanoma. Extending on these novel findings, the objective of this study was to determine the effects of CRISPR/Cas9-mediated knockout (KO) of SIRT6 in melanoma cells, both in vitro and in vivo. First, we evaluated the effects of SIRT6 KO on growth, viability, and clonogenic survival in the A375 human melanoma cell line. We found that KO of SIRT6 resulted in a significant anti-proliferative response in melanoma cells, as measured by trypan blue and RealTime-Glo assays. Further, SIRT6 KO also resulted in a significant decrease in the long-term clonogenic survival of melanoma cells, as measured by a colony formation assay. Additionally, we used DNA cell cycle analysis by flow cytometry to assess the effect of SIRT6 KO on cell cycle perturbation in melanoma cells. Our data demonstrated that SIRT6 KO induced a G1-phase arrest in the A375 melanoma cells. Furthermore, we employed a PCR array (RT2 Profiler Cancer Pathway Array; with 84 genes) to understand the molecular mechanisms associated with the observed anti-proliferative response of SIRT6 KO. We found that SIRT6 KO caused statistically significant alteration in genes involved in important cellular pathways, including angiogenesis (CCL2, KDR, SERPINF1, and FLT1), hypoxia signaling (ADM and CA9), cellular senescence (IGFBP5 and TBX2), apoptosis (CFLAR), epithelial-to-mesenchymal transition (EMT) (SNAI2), and telomere maintenance (TEP1). Finally, to validate the in vitro findings to in vivo situation, we determined the growth of SIRT6 KO A375 human melanoma cells-implanted tumors in immunocompromised mice. We observed a significant slow growth of SIRT6 KO tumors compared to wild-type A375 tumors, suggesting that SIRT6 reduction decreases cell survival in melanoma both in vitro and in vivo. Overall, our results re-emphasize the tumor promoter role of SIRT6 in melanoma. Further detailed studies are required to determine the potential of SIRT6 inhibition as a novel treatment regimen against melanoma.

Citation Format: Liz M. Garcia-Peterson, Mary A. Ndiaye, Glorimar Guzman-Perez, Chandra K. Singh, Gagan Chhabra, Nihal Ahmad. Effects of CRISPR/Cas9-mediated knockout of SIRT6 in human melanoma cells, in vitro and in vivo [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 4052.

Abstract 2918: Concomitant inhibition of SIRT1 and SIRT3 reduces melanoma growth and metastasis in BRAFV600E/PTENNULL transgenic mice

Metastatic melanoma, one of the most aggressive types of skin cancer, is extremely difficult to treat, with a median overall survival of less than one year. Despite recent advances in targeted- and immune- therapies, the treatment options have either failed to achieve >25% response or the responses have been short-lived with the emergence of resistance. Therefore, newer approaches are needed for the management of this deadly neoplasm. 4′-bromo-resveratrol [5-(2-(4-hydroxyphenyl)vinyl)-1,3-benzenediol; 4′-BR], an analog of resveratrol, is a dual small molecule inhibitor of sirtuins 1 and 3 (SIRTs 1 & 3), which have pro-proliferative functions in melanoma. In a recently published study, we demonstrated that 4′-BR induced apoptosis and caused metabolic reprogramming in human melanoma cells, leading to reduced proliferation and growth of melanoma cells in vitro. In order to validate our in vitro findings to in vivo situations, in this study, we evaluated the therapeutic efficacy of 4′-BR on melanoma growth and metastasis in a genetically engineered transgenic (BRAFV600E/PTENNull) mouse model of melanoma. This mouse model shows melanoma's cardinal features and is an excellent model to test drug efficacy in pre-clinical settings. To induce melanoma tumors, 4-hydroxytamoxifen was applied on shaved backs of 10-week-old mice topically once per day for 3 consecutive days. Highly pigmented tumors appeared 10 days after tamoxifen application. At this point, treatment with 4′-BR (0, 5, 10, 20 and 30 mg/kg b.wt.; intraperitoneal; 3d/week; n=6 mice/group) was started. Body weight, tumor size and volume were measured weekly. At the termination of the study (~17 weeks of age), we observed significant reduction in tumor volume and tumor weight in mice treated with 30 mg/kg 4'-BR with no noticeable adverse effects. Further, we analyzed markers for cell proliferation and survival (Ki67, PCNA, and Survivin), metastasis (Vimentin), oxidative stress (Nrf2 and Keap1) and growth factor signaling (IGF1 and IGFBP5) using immunohistochemistry (IHC) or real-time quantitative PCR (RT-qPCR) in tumors. IHC analysis revealed that 4′-BR treatment markedly decreased Ki67 positive tumor cells. RT-qPCR analysis showed that 4'-BR treatments significantly decreased expression of PCNA, Survivin, and IGF1 (a melanoma promoting growth factor), as well as significantly increased expression of IGFBP5, a tumor suppressor gene. Furthermore, we observed that 4'-BR treatment significantly decreased the ratio of Nrf2/Keap1. In addition, our data demonstrated a significant decrease in lung metastasis and the levels of metastasis marker Vimentin in 4'-BR treatment group. Overall, these data show the ability of 4′-BR to exert anti-proliferative, anti-tumorigenic, and anti-metastatic effects in a human-relevant melanoma mouse model, thus warranting further pre-clinical and clinical investigations in this direction.

Citation Format: Gagan Chhabra, Chandra K. Singh, Mary A. Ndiaye, Kenneth A. Iczkowski, Nihal Ahmad. Concomitant inhibition of SIRT1 and SIRT3 reduces melanoma growth and metastasis in BRAFV600E/PTENNULL transgenic mice [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 2918.

Abstract 222: RNA-seq analysis of differential gene expression in melanoma cells after combined inhibition of Plk1 and Notch

Melanoma is one of the most brutal forms of skin cancer, and its increasing incidence coupled with non-lasting therapeutic options for metastatic tumor highlight the need for additional strategies for the management of this neoplasm. Using tissue microarray analysis, we previously found that the expression of polo-like kinase 1 (Plk1, a serine/threonine kinase involved in mitotic regulation) and Notch1 (a type I transmembrane protein deciding cell fate during development) were positively correlated in melanoma (Cancer Res 2018; 78 [13 Suppl]: Abstract nr 2530), and their combined inhibition resulted in a synergistic anti-proliferative response in human melanoma cells (Cancer Res 2019; 79 [13 Suppl]: Abstract nr 302). In this study, to determine the possible mechanisms behind this observed synergism, we used RNA-seq technology to obtain the differential gene expression following treatment of SK-MEL-2 human metastatic melanoma cells with Plk1 inhibitor volasertib (BI6727, 20 nM) and Notch1 inhibitor MK-0752 (100 μM) for 48 h. After data pre-processing by RSEM algorithm, the DESeq2 package was implemented to identify differentially expressed genes (DEGs, |log2-fold change| >= 1, false positive rate ⇐ 0.05) when comparing the individual and combined treatments to vehicle (DMSO), as well as the interaction between volasertib:MK-0752. As a result, we identified 909 DEGs from volasertib treatment, 675 DEGs from MK-0752 treatment, 2142 genes from the combined treatment of volasertib and MK-0752, as well as 304 DEGs from the interaction of volasertib and MK-0752. In addition, employing GOstats and KEGGprofile packages in R programming, we conducted Gene Ontology (GO) and KEGG pathway analysis of the various DEGs. In GO analysis (counts >= 2, p ⇐ 10−5), we identified 202 downregulated GO terms affected by the combined inhibition of Plk1 and Notch1, including metabolism, cell proliferation, and migration. In KEGG pathway analysis, the combined inhibition of Plk1 and Notch1 was found to be associated with downregulation of several pathways shared with single drug treatments, such as PI3K-Akt, extracellular matrix receptor interaction, and protein digestion and absorption, as well as some novel pathways that were only affected by combined treatment, such as MAPK, Ras, and Rap1 pathways. Interestingly, our analysis predicted that the combined inhibition of Plk1 and Notch may make the melanoma cells more sensitive to immune responses. Overall, our data demonstrated that not only does targeting both Plk1 and Notch1 signaling pathways alters multiple melanoma progression pathways, but it may also potentially result in an increased sensitivity to other therapeutic targets, such as immune checkpoint blockade. However, these mechanistic findings need to be validated further in other relevant in vitro and in vivo models.

Citation Format: Shengqin Su, Gagan Chhabra, Mary A. Ndiaye, Chandra K. Singh, Colin N. Dewey, Nihal Ahmad. RNA-seq analysis of differential gene expression in melanoma cells after combined inhibition of Plk1 and Notch [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 222.

Quercetin-Resveratrol Combination for Prostate Cancer Management in TRAMP Mice

Prostate Cancer (PCa) is a leading cause of cancer-related morbidity and mortality in men. Therefore, novel mechanistically-driven approaches are needed for PCa management. Here, we determined the effects of grape antioxidants quercetin and/or resveratrol (60 and 600 mg/kg, respectively, in diet) against PCa in Transgenic Adenocarcinoma of Mouse Prostate (TRAMP)-model in prevention and intervention settings. We found resveratrol alone and in combination significantly inhibited prostate tumorigenesis in prevention setting, while the same was seen only in combination after intervention. The observed effects were associated with marked inhibition in proliferation, oxidative stress, and tumor survival markers, and induced apoptosis markers. Utilizing PCa PCR array analysis with prevention tumor tissues, we identified that quercetin-resveratrol modulates genes involved in promoter methylation, cell cycle, apoptosis, fatty acid metabolism, transcription factors, androgen response, PI3K/AKT and PTEN signaling. Ingenuity Pathway Analysis (IPA) identified IGF1 and BCL2 as central players in two gene networks. Functional annotation predicted increased apoptosis and inhibited cell viability/proliferation, hyperplasia, vasculogenesis, and angiogenesis with dual treatment. Furthermore, IPA predicted upstream inhibition of major PCa signaling VEGF, Ca2+, PI3K, CSF2, PTH). Based on PCR array, we identified decreased levels of EGFR, EGR3, and IL6, and increased levels of IGFBP7 and NKX3.1, overall supporting anti-PCa effects of quercetin-resveratrol.

Prospective Nonrandomized Comparison Between Open and Robot-Assisted Kidney Transplantation: Analysis of Midterm Functional Outcomes

Introduction: To compare short- and midterm outcomes of the first 55 patients undergoing robot-assisted kidney transplant (RAKT) with patients undergoing open kidney transplant (OKT) during the same period in a tertiary care hospital. Materials and Methods: Data of all end-stage renal disease patients undergoing renal transplant were prospectively maintained. All graft kidneys were harvested laparoscopically. Both RAKT and OKT were performed using standardized techniques, and all RAKTs were performed by a single experienced robotic surgeon. Chi-square test/Fisher exact test was done for categorical data, and Mann-Whitney U test was done for continuous data. Discrete variables were expressed in absolute numbers and percentages. For all tests, p < 0.05 was considered significant. All results were expressed as mean ± standard deviation or median with range. Results: Between April 2016 and September 2018, 55 patients underwent RAKT. The same was compared with 152 patients who underwent OKT. The two groups were comparable in terms of age, gender, and body mass index. Duration on hemodialysis was significantly higher in the RAKT group, and hemoglobin and donor kidney glomerular filtration rate was significantly better in the RAKT group. Requirement of perioperative analgesia was significantly less in the RAKT group. Rewarm ischemia time was significantly longer in the RAKT group. The fall in serum creatinine was slower in RAKT group till 3 months. The serum creatinine levels were statistically similar in the two cohorts at 3 months (p = 0.082), which was maintained at median 29 months of follow-up (p = 0.067). Tacrolimus levels on postoperative day 2 were found to be significantly higher in RAKT cohort (17.98 ± 14.41) vs OKT cohort (11.38 ± 6.93). Surgical-site infections were rare in the RAKT group. Conclusions: RAKT confers advantage of decreased wound morbidity with similar functional outcomes compared with OKT in midterm. It looks promising; however, long-term follow-up of larger numbers of patients is needed.

CRISPR/Cas9-mediated Knockout of SIRT6 Imparts Remarkable Antiproliferative Response in Human Melanoma Cells in vitro and in vivo

Melanoma is one of the most aggressive, potentially fatal forms of skin cancer and has been shown to be associated with solar ultraviolet radiation-dependent initiation and progression. Despite remarkable recent advances with targeted and immune therapeutics, lasting and recurrence-free survival remain significant concerns. Therefore, additional novel mechanism-based approaches are needed for effective melanoma management. The sirtuin SIRT6 appears to have a pro-proliferative function in melanocytic cells. In this study, we determined the effects of genetic manipulation of SIRT6 in human melanoma cells, in vitro and in vivo. Our data demonstrated that CRISPR/Cas9-mediated knockout (KO) of SIRT6 in A375 melanoma cells resulted in a significant (1) decrease in growth, viability and clonogenic survival and (2) induction of G1-phase cell cycle arrest. Further, employing a RT² Profiler PCR array containing 84 key transformation and tumorigenesis genes, we found that SIRT6 KO resulted in modulation of genes involved in angiogenesis, apoptosis, cellular senescence, epithelial-to-mesenchymal transition, hypoxia signaling and telomere maintenance. Finally, we found significantly decreased tumorigenicity of SIRT6 KO A375 cells in athymic nude mice. Our data provide strong evidence that SIRT6 promotes melanoma cell survival, both in vitro and in vivo, and could be exploited as a target for melanoma management.

Abstract 5085: Molecular analysis of chemopreventive effects of grape antioxidants resveratrol and quercetin in transgenic adenocarcinoma of the mouse prostate

Prostate cancer (PCa) is one of the most frequently diagnosed cancers of the male population and current treatments are insufficient to fully manage this neoplasm. Therefore, identification of novel mechanism-based approaches are needed for PCa management. Earlier, we demonstrated that a combination of the grape antioxidants resveratrol and quercetin impart superior anti-proliferative responses in multiple human PCa cell lines, as well as a significant anti-tumor response in transgenic adenocarcinoma of the mouse prostate (TRAMP) (Cancer Res 75(15 Suppl):2801). The rationale of the study was based on the fact that i) both resveratrol and quercetin are naturally present in several plants ii) quercetin improves bioavailability of resveratrol by inhibiting its sulfation, and iii) separately, both agents have shown potential for management of PCa in previously published studies. This study extended our previous work and determined the mechanisms of chemopreventive effects of resveratrol-quercetin combination employing a mouse PCa RT² Profiler PCR array that profiles 84 key PCa-related genes. For this, we employed tumor tissues generated in a chemoprevention protocol where TRAMP mice were given AIN76A diet supplemented with resveratrol (600 mg/kg), quercetin (60 mg/kg), or a combination of both. PCR array analysis found significant modulation (≥2-fold) in 14, 15, and 10 genes in the quercetin, resveratrol, and combination groups, respectively. To explore the involved gene networks using Ingenuity Pathway Analysis (IPA), we selected total 22 genes with ≥2-fold change in any one group and ≥1.5-fold change in other group(s). IPA analysis identified that resveratrol-quercetin modulated genes supported the cumulative actions of increased apoptosis, as well as inhibition of cell viability/proliferation, hyperplasia, vasculogenesis, and angiogenesis. Further, IPA predicted inhibition of major PCa promoting upstream signaling molecules viz. Pi3k, Vegf, Csf2, Ca2+, and Pth. This PCR array also identified decreased levels of Igf1, Egfr, Egr3, and Il6, which are known to support PCa progression, as well as found increased levels of Nkx3-1, which is a tumor suppressor in PCa. Furthermore, IPA exploration identified a gene network where decreased Igf1 emerged as a central regulatory player, interacting with most of the resveratrol-quercetin modulated genes. Additionally, employing IHC, immunoblot, and RT-qPCR analyses, we found marked decrease in the levels of cell proliferation markers Ki67 and PCNA, oxidative stress biomarker 4-HNE, EMT marker vimentin, and prosurvival marker Bcl2. These results suggest that this natural combination of grape polyphenols may be useful as a chemopreventive regimen for PCa. Further detailed studies including clinical trials are needed to determine the translational significance of our findings.

Citation Format: Chandra K. Singh, Mary A. Ndiaye, Gagan Chhabra, Charlotte A. Mintie, Nihal Ahmad. Molecular analysis of chemopreventive effects of grape antioxidants resveratrol and quercetin in transgenic adenocarcinoma of the mouse prostate [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 5085.

Abstract 1875: Polo-like kinase 1 positively correlates with N-cadherin and promotes epithelial-mesenchymal transition in melanoma

Polo-like kinase 1 (PLK1), a serine/threonine kinase and important cell cycle regulator, is overexpressed in melanoma and has been linked with enhanced cell proliferation. Recent studies have shown involvement of PLK1 in epithelial-mesenchymal transition (EMT) in certain cancer types. However, the role of PLK1 in EMT in melanoma is not well understood. EMT has been shown to promote metastasis, and is associated with an upregulation of the mesenchymal marker N-cadherin (CDH2), downregulation of the epithelial marker E-cadherin (CDH1), and increased cell migration and invasion ability. Earlier, we demonstrated that PLK1 is involved in EMT and its kinase activity is important for EMT-related modulations in A375 melanoma cells (Cancer Res 2018; 78 (13 Suppl): Abstract #2016). In this study, we employed a human tissue microarray (TMA) co-immunostained for PLK1, N-cadherin, E-cadherin and the melanoma biomarker S100 to determine the association between PLK1 and EMT effectors. This TMA, coupled with high-throughput, multispectral Vectra scanning and inForm analysis, allowed us to objectively analyze and quantify protein levels in 57 clinical tissue specimens of nevus (n=15), primary (n=22) and metastatic melanoma (n=20). We observed an increase in PLK1 expression in primary and metastatic melanoma as compared to benign nevi, with a significant increase in metastatic tumors compared to primary tumors (p=0.004). Similarly, N-cadherin expression was markedly higher in metastatic melanoma (fold-change=2.31; p=0.001) and primary melanoma (fold-change=1.8; p=0.03) when compared to benign nevi. Further, we observed a significant decrease in E-cadherin expression in metastatic tumors compared to primary melanoma (fold-change=2.53; p=0.02). Moreover, using single linear regression analyses between expression of two proteins, we found a significant strong positive correlation between PLK1 and mesenchymal marker N-cadherin (correlation co-efficient R=0.75; p&lt;0.01). We also found a weak but negative correlation between PLK1 and epithelial marker E-cadherin (correlation co-efficient R=-0.25). To further confirm the role of PLK1 in EMT, using shRNA-mediated PLK1 knockdown in SK-MEL-2 cells (a human melanoma line that possesses high metastatic potential), we performed cell migration and invasion assays, as well as immunofluorescence staining for expression of N-cadherin and E-cadherin. Interestingly, we found a decrease in expression of mesenchymal marker N-cadherin and an increase in expression of epithelial marker E-cadherin after PLK1 knockdown. These were accompanied by decreased cell migration and invasion, suggesting that inhibition of PLK1 in these human melanoma cells leads to inhibition of EMT. Overall, these results suggest that PLK1 is an important regulator of EMT in melanoma, and therefore can be exploited as a therapeutic target to inhibit melanoma metastasis.

Citation Format: Gagan Chhabra, Mary A. Ndiaye, Shengqin Su, Chandra K. Singh, Nihal Ahmad. Polo-like kinase 1 positively correlates with N-cadherin and promotes epithelial-mesenchymal transition in melanoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1875.

Abstract 302: The combined inhibition of Plk1 and Notch1 results in a synergistic anti-proliferative response in human melanoma cells

Melanoma is the most aggressive form of skin cancer, and its incidence and mortality have been increasing over the past thirty years. Therefore, additional therapeutic strategies are needed for an effective management of this neoplasm. We previously demonstrated that polo-like kinase 1 (Plk1, a serine/threonine kinase involved in mitotic regulation) and Notch1 (a type I transmembrane protein deciding cell fate during development) are strongly correlated in melanoma (Cancer Res 2018; 78 (13 Suppl): Abstract nr 2530). In addition, a number of studies from our lab and elsewhere have suggested the important functions of Plk1- as well as Notch- signaling in melanoma progression. Based on these observations, in this study, we determined the potential efficacy of a combined inhibition of Plk1 and Notch1 against melanoma cells. Employing Plk1 inhibitor volasertib (BI6727) and Notch1 inhibitor MK-0752, we determined the effects of concomitant targeting of these pathways in A375 (wild type TP53) and SK-MEL-2 (mutant TP53) human melanoma cell lines. Employing RealTime-Glo and trypan blue exclusion assays, we found that volasertib (10 and 20 nM) and MK-0752 (50 and 100 μM) resulted in a significant decrease (60-80%) in viability and growth of human melanoma cells A375 and SK-MEL-2. The Combination Index (CI), as calculated using the Chou-Talalay theorem, was less than 1 when volasertib at 10 nM was given with MK-0752 at 50 and 100 μM, indicating a synergism between these two drugs. As a result of the synergism, the melanoma cells treated with combined drugs showed decreased colony formation ability compared to individual drugs. In addition, the combined treatment also resulted in enhanced apoptosis of melanoma cells. Interestingly, cell cycle analysis by flow cytometry showed that combined inhibition of Plk1 and Notch1 caused a G2-M phase arrest of melanoma cells. Furthermore, our data demonstrated that volasertib and MK-0752 combination caused a marked increase of cleaved PARP (poly ADP ribose polymerase) and cleaved caspase-3 in both melanoma cell lines, as well as increased expression of tumor suppressor protein TP53 and its target p21 (CDKN1A) in A375 melanoma cells. Taken together, our data demonstrated that a combined targeting of Plk1- and Notch1- signaling pathways imparts a synergistic anti-proliferative response against melanoma. However, additional experiments are needed i) to validate our in vitro data to in vivo situations in human relevant melanoma models, and ii) to define the interactive mechanism(s) of the observed synergistic response.

Citation Format: Shengqin Su, Gagan Chhabra, Chandra K. Singh, Mary A. Ndiaye, Nihal Ahmad. The combined inhibition of Plk1 and Notch1 results in a synergistic anti-proliferative response in human melanoma cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 302.

Liraglutide modulates adipokine expression during adipogenesis, ameliorating obesity, and polycystic ovary syndrome in mice

PURPOSE

The incidence of obesity is increasing among all age groups throughout the world and it is highly associated with numerous other metabolic disorders, such as insulin resistance, polycystic ovarian syndrome (PCOS) etc. METHODS AND RESULTS: Using in vitro and in vivo approach, this study investigated the adipokine profile after liraglutide on differentiated murine 3T3-L1 pre-adipocytes. Effect of liraglutide on DHEA-induced PCOS mice were investigated. This study showed Liraglutide treatment resulted in up-regulation of adiponectin and IL-6 along with down-regulation of ICAM 1 in differentiated 3T3-L1 cells. Liraglutide in absence of other differentiating factors, significantly increased glucose, lipid uptake and PPARγ, C/EBPα expression in the adipocytes suggesting its ability to solely promote pre-adipocyte differentiation into mature adipocyte. Liraglutide treatment showed increased adiponectin expression and decreased number of cystic follicles, body weight, circulating glucose, triglyceride and testosterone levels in comparison to the PCOS induced mice.

CONCLUSION

This study suggests that adiponectin may act as a link between metabolic disorders and PCOS and that liraglutide might be a promising therapeutic agent for the treatment of PCOS in addition to obesity and insulin resistance.

Chemoprotective Effects of Dietary Grape Powder on UVB Radiation-Mediated Skin Carcinogenesis in SKH-1 Hairless Mice

Skin cancer is the most frequently diagnosed cancer in the United States, and solar UVR is an established causative factor for approximately 90% of these cases. Despite efforts aimed at UV protection, including use of sunscreen and clothing, annual cases of skin cancer continue to rise. Here, we report that dietary grape powder mitigates UVB-mediated skin carcinogenesis in an SKH-1 hairless mouse model. Using a UVB initiation-promotion protocol, whereby mice were exposed to 180 mJ/cm² UVB two times per week for 28 weeks, we determined the effects of a grape powder-fortified diet (3% or 5%) on skin carcinogenesis. Grape powder consumption at both doses resulted in marked inhibition in tumor incidence, as well as a delay in onset of tumorigenesis. Molecular analyses of skin and tumor tissue showed that grape powder-mediated protective response against UVB-induced skin cancer was accompanied by enhanced DNA damage repair, reduced proliferation, increased apoptosis, and modulations in several oxidative stress markers specifically related to inhibition of oxidative stress and increased reactive oxygen species metabolism. NRF2, an activator of cellular antioxidant response, was decreased by grape powder feeding, suggesting a supportive role in tumor cell survival. Overall, our study suggested that dietary grape, containing several antioxidants in natural amalgamation, may protect against UVB-mediated skin carcinogenesis.

Effects and Mechanism of Nicotinamide Against UVA- and/or UVB-mediated DNA Damages in Normal Melanocytes

Melanoma incidences are increasing rapidly, and ultraviolet (UV) radiation from the sun is believed to be its major contributing factor. UV exposure causes DNA damage in skin which may initiate cutaneous skin cancers including melanoma. Melanoma arises from melanocytes, the melanin-producing skin cells, following genetic dysregulations resulting into hyperproliferative phenotype and neoplastic transformation. Both UVA and UVB exposures to the skin are believed to trigger melanocytic hyperplasia and melanomagenesis. Melanocytes by themselves are deficient in repair of oxidative DNA damage and UV-induced photoproducts. Nicotinamide, an active form of vitamin B3 and a critical component of the human body's defense system has been shown to prevent certain cancers including nonmelanoma skin cancers. However, the mechanism of nicotinamide's protective effects is not well understood. Here, we investigated potential protective effects and mechanism of nicotinamide against UVA- and/or UVB- induced damage in normal human epidermal melanocytes. Our data demonstrated an appreciable protective effect of nicotinamide against UVA- and/or UVB- induced DNA damage in melanocytes by decreasing both cyclobutane pyrimidine dimers and 8-hydroxy-2'-deoxyguanosine levels. We found that the photoprotective response of nicotinamide was associated with the activation of nucleotide excision repair genes and NRF2 signaling. Further studies are needed to validate our findings in in vivo models.

Current Molecular-Targeted Therapies in NSCLC and Their Mechanism of Resistance

Lung cancer is treated with many conventional therapies, such as surgery, radiation, and chemotherapy. However, these therapies have multiple undesirable side effects. To bypass the side effects elicited by these conventional treatments, molecularly-targeted therapies are currently in use or under development. Current molecularly-targeted therapies effectively target specific biomarkers, which are commonly overexpressed in lung cancers and can cause increased tumorigenicity. Unfortunately, several molecularly-targeted therapies are associated with initial dramatic responses followed by acquired resistance due to spontaneous mutations or activation of signaling pathways. Acquired resistance to molecularly targeted therapies presents a major clinical challenge in the treatment of lung cancer. Therefore, to address this clinical challenge and to improve lung cancer patient prognosis, we need to understand the mechanism of acquired resistance to current therapies and develop additional novel therapies. This review concentrates on various lung cancer biomarkers, including EGFR, ALK, and BRAF, as well as their potential mechanisms of drug resistance.

Abstract 1469: T-oligo mediates DNA damage responses by modulating telomere associated proteins and telomerase

T-oligo, a guanine-rich oligonucleotide (GRO) homologous to the 3′ overhang of telomeres, elicits potent DNA-damage responses (DDRs) in cancer cells. However, the detailed molecular mechanism of T-oligo in cancer cells remains elusive. Recent studies confirmed that T-oligo can form intermolecular G-quadruplexes (G4), which are stabilized by hydrogen bonding of guanine residues, and cause disruption of the protective shelterin complex of telomeres. We hypothesize that single-stranded (SS) T-oligo and G4 T-oligo may modulate the shelterin proteins TRF2 and POT2 and thus induce DDRs. In this study, we utilized a pull-down assay using T-oligo, showing that T-oligo is co-localized with TRF2 and POT1 and indicating that T-oligo may interact with these telomeric proteins. We further investigated the modulation of these proteins by western blotting, showing that T-oligo treatment upregulates TRF2 by 2.2 and 3.0-fold (p&lt;0.01) at 48h and 72h, respectively, and POT1 by 3.0-fold (p&lt;0.02) both at 48h and 72h in melanoma cells (MM-AN). Immunofluorescence studies confirmed upregulation of TRF2 (2.4-fold) and POT1 (2.0-fold). Additionally we found that T-oligo can co-localize with telomere binding proteins TRF2 (88.4±4.5%) and POT1 (84.5±8%) using immunofluorescence.

Using qRT-PCR, we found that T-oligo inhibited mRNA expression of hTERT, a catalytic subunit of telomerase, by 50%. It has been suggested that JNK activation may lead to downregulation of hTERT, hence we investigated the effect of the JNK inhibitor SP600125 on hTERT expression and found that treatment with SP600125 in presence of T-oligo partially reversed the downregulation of hTERT. We found a 16% decrease in hTERT expression in comparison to 50% reduction by T-oligo treatment alone. Recently, it has been reported that the novel drug 6-Thio-2'-Deoxyguanosine (6-thio-dG), a nucleoside analogue of the approved drug 6-thioguanine, inhibits growth of cancer cells by its incorporation into the telomere via telomerase followed by subsequent shelterin disruption. Furthermore, this study aims to investigate the potential of 6-thio-dG in combination with T-oligo as an anticancer therapeutic. We first studied the concentrations of 6-thio-dG that are effective in inhibiting the growth of melanoma cells. We found that 1.25μM and 2.5μM 6-thio-dG significantly inhibited growth of melanoma cells by 1.6 and 3.8-fold, respectively (p&lt;0.01). However, treatment of melanoma cells in combination with both 10μM T-oligo and 6-thio-dG (1.25μM or 2.5μM) did not significantly inhibit cell growth in comparison to T-oligo alone. T-oligo may downregulate hTERT, which is required for telomerase activity, and/or disrupt the shelterin complex, both of which are necessary for 6-thio-dG mediated inhibition of growth of melanoma cells. These results indicate that T-oligo and 6-thio-dG may induce their effects by a similar mechanism of action.

Citation Format: Nabiha Haleema Khan, Zachary Schrank, Joseph Kellen, Sanjana Singh, Chike Osude, Neelu Puri, Gagan Chhabra. T-oligo mediates DNA damage responses by modulating telomere associated proteins and telomerase [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1469.

Abstract 546: The nuclear sirtuin SIRT6 promotes epithelial-mesenchymal transition in human melanoma cells

According to the recent statistics, the incidence as well as mortality from malignant melanoma has risen steadily for the past two decades in the United States. In 2017, an estimated 87,110 new cases of melanoma will be diagnosed and 9,730 people will die due to invasive melanoma. Therefore, intense research is needed to enhance our understanding of the molecular mechanisms of melanoma development, progression and metastasis. We have previously shown that the sirtuin SIRT6 was significantly overexpressed in melanoma, and a transient short hairpin RNA (shRNA)-mediated knockdown of SIRT6 resulted in a marked anti-proliferative response in melanoma cells (Genes & Cancer; In Press). In this study, we tested a hypothesis that the nuclear sirtuin SIRT6 is involved in the regulation of epithelial-mesenchymal transition (EMT) in melanoma. Indeed, EMT is an important and well-choreographed process where cells transition from a non-mobile epithelial cell type to a more motile and invasive mesenchymal state, thereby enhancing the migratory capacity of cancer cells. Activation of the EMT process allows cancer cells to propagate from the primary tumor site to adjacent tissues and subsequently metastasize by spreading through the lymphatic system and/or bloodstream. The role of SIRT6 in EMT appears to be cell- and context- dependent, since it has been shown to either promote or inhibit EMT depending on cancer type. The role of SIRT6 in melanoma has not yet been explored. In this study, we determined the effect of SIRT6 manipulation on EMT-associated markers, employing lentiviral short hairpin RNA (shRNA) mediated stably transfected SIRT6 knockdown A375 melanoma cells. Our data demonstrated that SIRT6 knockdown resulted in a significant downregulation of the mesenchymal markers N-cadherin, β-catenin, and vimentin, with a concomitant upregulation of the epithelial marker E-cadherin, both at mRNA and protein levels. Further, a wound healing scratch assay showed a marked inhibition of cell migration potential following SIRT6 knockdown in melanoma cells. Interestingly, 72 h after performing the scratch, the wound was completely closed in control cells (stably transfected with nonsense shRNA), whereas SIRT6 knockdown cells showed limited migration and the wound was still visible. Similarly, compared to control cells, the A375 shSIRT6 cells showed a significant inhibition in invasive potential, as assessed by a Matrigel invasion assay. Taken together, our data suggests that SIRT6 may be a contributing factor in the EMT process and its downregulation may inhibit mesenchymal properties in melanoma. Further detailed studies are underway to understand the complete mechanism and the ways that SIRT6-associated signaling molecules affect the EMT process in melanoma.

Citation Format: Liz M. Garcia, Gagan Chhabra, Mary A. Ndiaye, Nihal Ahmad. The nuclear sirtuin SIRT6 promotes epithelial-mesenchymal transition in human melanoma cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 546.

Abstract 548: The effects of Sirtuin 6 inhibition on autophagy-related pathways in melanoma

Melanoma is an aggressive skin cancer that can rapidly metastasize to become fatal, if not diagnosed early. Despite therapeutic advances, clinical management of melanoma remains challenging. The existing chemotherapeutic drugs either fail to achieve greater than 25% response or ultimately develop resistance to therapy. Therefore, novel molecular targets and treatments are required for an effective management of melanoma. In order to design novel and more effective approaches for lasting cure of melanoma, a deeper understanding of the mechanisms involved in melanomagenesis are needed. In our laboratory, we are assessing the role and functional and therapeutic significance of sirtuin proteins in melanoma. We have previously demonstrated that Sirtuin 6 (SIRT6) is significantly overexpressed in human melanoma cells and clinical tissues, and its genetic knockdown resulted in a marked anti-proliferative response in human melanoma cells (Genes & Cancer; In Press). A limited number of studies have implicated SIRT6 in autophagy regulation. Autophagy forms part of a basic cellular process that copes with cellular stress and is considered to be an important metabolic mechanistic essential for degradation and recycling of unnecessary intracellular components. In melanoma autophagy is believed to be a tumor suppressing process in early stages of cancer, but tumor-promoting in established tumors. This study was designed to determine the connection between SIRT6 and autophagy in melanoma. Employing lentiviral short hairpin RNA-mediated knockdown of SIRT6 in A375 melanoma cells, we determined the modulation in autophagy related pathways. We employed a PCR array containing 84 genes that are involved in the regulation of autophagy. Our data demonstrated that 17 of the 84 genes were significantly modulated (two-fold or more) upon SIRT6 knockdown. Of these 17 genes, 2 were upregulated (ATG10 and GAA) and 15 were downregulated (AKT1, ATG12, ATG3, ATG7, BAK1, BCL2L1, CLN3, CTSB, CTSS, DRAM2, HSP90AA1, IRGM, NPC1, SQSTM1, and TNF). Modulated genes were analyzed using Ingenuity Pathway Analysis (IPA) for predicted gene-gene interactions and functional networks. Many of the network genes were found to have definitive links to cancer. These genes were found to be associated with cell transformation and tumor invasion. Further validation at mRNA and protein levels, confirmed the significant modulations in autophagy markers BECN1, SQSTM1, ATG3, ATG7, ATG10 and GAA, upon SIRT6 knockdown. Moreover, SIRT6 knockdown was found to cause a marked decrease in the LC3 II protein level, which is a central protein in the autophagy pathway. Taken together, our data suggest that SIRT6 knockdown significantly alters pathways related to autophagy in melanoma cells. Future studies are required to carefully study the role of SIRT6 and autophagy in early versus late melanomas.

Citation Format: Liz M. Garcia-Peterson, Mary A. Ndiaye, Chandra K. Singh, Gagan Chhabra, Nihal Ahmad. The effects of Sirtuin 6 inhibition on autophagy-related pathways in melanoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 548.

Abstract 539: Pro-proliferative function of the histone deacetylase SIRT3 in prostate cancer

Worldwide, prostate cancer (PCa) is the second most frequently diagnosed cancer and fifth leading cause of cancer death in males. The existing treatments, as well as surgical approaches, have not been fully effective either for prevention or treatment of PCa. This necessitates a need to intensify our efforts towards the understanding of genetics and mechanism(s) of PCa. This may lead to the identification of the novel molecular target(s) and mechanism-based approaches for the management of this neoplasm. Sirtuin-3 (SIRT3) is a nicotinamide adenine dinucleotide (NAD)-dependent deacetylase primarily located in the mitochondria and known to play important roles in the regulation of a variety of cellular processes, including transcription and programmed cell death. The fact that SIRT3 can regulate several cellular processes those are critical in cancer cell proliferation, makes it a potential therapeutic target for cancer management. Moreover, SIRT3 is a central regulator of mitochondrial adaptive responses that relate to metabolic reprogramming of cancer cells. However, the role of SIRT3 in cancer, including PCa, is not well understood and it has been shown to act both as a tumor suppressor as well as a tumor promoter. In this study, we determined the role of SIRT3 in PCa, employing in vitro and ex vivo approaches. The first step in our efforts to understand the role of SIRT3 in PCa was to check the expression profile of SIRT3 in a panel of human PCa cell line (DU145, 22Rν1, PC3, LNCaP, C4-2, MDA PCa 2b, E006AA-Par and E006AA-hT) by RT-qPCR and immunoblot analyses. Compared to normal human prostate epithelial cells (NrPEC), PCa cells showed higher expression of SIRT3, both at mRNA and protein levels. Further, we determined the expression profile of SIRT3 by immunostaining of a tissue microarray (TMA) containing paraffin-embedded sections of 40 cases of prostate adenocarcinoma and 8 normal prostate tissues. Our data demonstrated a significant upregulation of SIRT3 in cancerous prostatic tissues compared to the normal tissues. We next determined the effect of chemical inhibition of SIRT3 using a recently described SIRT3 inhibitor viz. 4'-Bromo-Resveratrol (4BR), in human PCa cells (DU145 and 22Rν1). 4BR treatment at 10, 20 and 40 μM concentrations for 48 and 72 h resulted in a dose- and time-dependent decrease in cell growth and proliferation. Further, 4BR treatment resulted in a marked decrease in clonogenic survival of DU145 and 22Rν1 PCa cells. Furthermore, 4BR treatment resulted in a marked cleavage of PARP, an indicator of apoptosis induction; and a decrease in the level of PCNA, a marker of cellular proliferation, in human PCa cells. Overall, our data suggest a possible pro-proliferative function of SIRT3 in PCa. Further studies are underway to unravel the role and functional significance of SIRT3 during PCa development and progression.

Citation Format: Chandra K. Singh, Gagan Chhabra, Minakshi Nihal, Kenneth A. Iczkowski, Nihal Ahmad. Pro-proliferative function of the histone deacetylase SIRT3 in prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 539.

Abstract 2016: Potential role of polo-like kinase 1 in epithelial-mesenchymal transition in melanoma

Mammalian polo-like kinase 1 (Plk1), an important serine/threonine kinase, has been shown to be a critical regulator of mitosis and cytokinesis. A number of studies, including those from our laboratory, have shown that Plk1 is significantly overexpressed in several cancers, including melanoma. Plk1 has also been linked with poor disease prognosis in cancer patients. A limited number of recent studies have suggested that Plk1 may be involved in epithelial-mesenchymal transition (EMT) in different cancers. However, the role of Plk1 in EMT process in melanoma has not been studied. Indeed, EMT plays a driving role in the acquisition of cancer metastasis and an important hallmark of EMT is downregulation of epithelial marker E-cadherin, and upregulation of mesenchymal marker, N-cadherin. In this study, we investigated whether the kinase activity of Plk1 plays a role in EMT process by modulating EMT markers in melanoma cells. To determine this, we performed western blots, RT-qPCR, cell migration and cell invasion assays using A375 melanoma cells stably transfected with plasmids for wild-type (WT) Plk1 overexpression, constitutively active Plk1 (T210D) and kinase-inactive (K82R) Plk1, as well as shRNA-mediated Plk1 knockdown. We observed that overexpression of WT Plk1 upregulated the mesenchymal markers N-cadherin, Vimentin, and Fibronectin, and downregulated the epithelial marker E-cadherin. We also found that the modulation in EMT markers by Plk1 in melanoma cells was associated with the upregulation of transcription factors Snail and Zeb1. Interestingly, downregulation of endogenous Plk1 by specific shRNA resulted in a downregulation of N-cadherin, Vimentin, Fibronectin, Snail and Zeb1. Further, when we assessed the EMT-related molecular changes in A375 melanoma cells containing constitutively active and kinase-inactive Plk1, the cells containing constitutively active Plk1 showed a significant decrease in epithelial marker as well as marked increases in mesenchymal markers. However, the cells containing kinase-inactive Plk1 showed the opposite trend. Moreover, A375 melanoma cells containing constitutively active Plk1 showed higher migration and invasion potential, whereas cells containing kinase-inactive Plk1 showed limited cell migration and invasion. Overall, these results suggest that Plk1 is involved in the EMT process and its kinase activity is important for EMT-related changes in melanoma cells. Further studies are in progress to determine the cause-and-effect molecular mechanisms of Plk1 mediated EMT regulation.

Citation Format: Gagan Chhabra, Chandra K. Singh, Mary A. Ndiaye, Nihal Ahmad. Potential role of polo-like kinase 1 in epithelial-mesenchymal transition in melanoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2016.

The Role of Sirtuins in Antioxidant and Redox Signaling

SIGNIFICANCE

Antioxidant and redox signaling (ARS) events are regulated by critical molecules that modulate antioxidants, reactive oxygen species (ROS) or reactive nitrogen species (RNS), and/or oxidative stress within the cell. Imbalances in these molecules can disturb cellular functions to become pathogenic. Sirtuins serve as important regulators of ARS in cells. Recent Advances: Sirtuins (SIRTs 1-7) are a family of nicotinamide adenine dinucleotide (NAD)-dependent histone deacetylases with the ability to deacetylate histone and nonhistone targets. Recent studies show that sirtuins modulate the regulation of a variety of cellular processes associated with ARS. SIRT1, SIRT3, and SIRT5 protect the cell from ROS, and SIRT2, SIRT6, and SIRT7 modulate key oxidative stress genes and mechanisms. Interestingly, SIRT4 has been shown to induce ROS production and has antioxidative roles as well.

CRITICAL ISSUES

A complete understanding of the roles of sirtuins in redox homeostasis of the cell is very important to understand the normal functioning as well as pathological manifestations. In this review, we have provided a critical discussion on the role of sirtuins in the regulation of ARS. We have also discussed mechanistic interactions among different sirtuins. Indeed, a complete understanding of sirtuin biology could be critical at multiple fronts.

FUTURE DIRECTIONS

Sirtuins are emerging to be important in normal mammalian physiology and in a variety of oxidative stress-mediated pathological situations. Studies are needed to dissect the mechanisms of sirtuins in maintaining redox homeostasis. Efforts are also required to assess the targetability of sirtuins in the management of redox-regulated diseases. Antioxid. Redox Signal. 28, 643-661.

Prostate cancer chemoprevention by natural agents: Clinical evidence and potential implications

Prostate cancer (PCa) is the most common non-skin cancer and the second leading cause of cancer-related deaths in American men. Due to its long latency period, PCa is considered as an ideal cancer type for chemopreventive interventions. Chemopreventive agents include various natural or synthetic agents that prevent or delay cancer development, progression and/or recurrence. Pre-clinical studies suggest that many natural products and dietary agents have chemopreventive properties. However, a limited number of these agents have been tested in clinical trials, with varying success. In this review, we have discussed the available clinical studies regarding the efficacy of natural chemopreventive agents against PCa, including tea polyphenols, selenium, soy proteins, vitamins and resveratrol. We have also provided a discussion on the clinical challenges and opportunities for the potential use of chemopreventive agents against PCa. Based on available literature, it appears that the variable outcomes of the chemopreventive clinical studies necessitate a need for additional studies with more rigorous designs and methodical interpretations in order to measure the potential of the natural agents against PCa.

Mechanism of Action of G-Quadruplex-Forming Oligonucleotide Homologous to the Telomere Overhang in Melanoma

T-oligo, a guanine-rich oligonucleotide homologous to the 3'-telomeric overhang of telomeres, elicits potent DNA-damage responses in melanoma cells; however, its mechanism of action is largely unknown. Guanine-rich oligonucleotides can form G-quadruplexes (G4), which are stabilized by the hydrogen bonding of guanine residues. In this study, we confirmed the G4-forming capabilities of T-oligo using nondenaturing PAGE, nuclear magnetic resonance, and immunofluorescence. Using an anti-G-quadruplex antibody, we showed that T-oligo can form G4 in the nuclei of melanoma cells. Furthermore, using DNase I in a nuclease degradation assay, G4-T-oligo was found to be more stable than single-stranded T-oligo. G4-T-oligo had decreased antiproliferative effects compared with single-stranded T-oligo. However, G4-T-oligo has similar cellular uptake as single-stranded T-oligo, as shown by FACS analysis. Inhibition of JNK, which causes DNA damage-induced apoptosis, partially reversed the antiproliferative activity of T-oligo. T-oligo also inhibited mRNA expression of human telomerase reverse transcriptase, a catalytic subunit of telomerase that was reversed by JNK inhibition. Furthermore, two shelterin complex proteins TRF2/POT1 were found to be up-regulated and bound by T-oligo, suggesting that T-oligo may mediate dissociation of these proteins from the telomere overhang. These studies show that T-oligo can form a G-quadruplex and that the antitumor effects of T-oligo may be mediated through POT1/TRF2 and via human telomerase reverse transcriptase inhibition through JNK activation.