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.

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.

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.

Technology implementation in care practices for community-dwelling older adults with mild cognitive decline: Perspectives of professional caregivers in Quebec and Brussels

OBJECTIVE

As worldwide population aging is accelerating, innovative technologies are being developed to support independent living among community-dwelling older adults with mild cognitive decline. However, the successful implementation of these interventions is often challenging. Until now, literature on implementation issues related to the specific context of older adults with mild cognitive decline is lacking and the few studies available do not focus specifically on the perspective of professional caregivers. Yet the perspective of these caregivers is important as they can be considered a key facilitator for technology implementation among this population. Therefore, this study was the first to examine technology implementation among community-dwelling older adults with mild cognitive decline from the broader perspective of professional caregivers.

METHODS

In this qualitative study, two focus groups consisting of a heterogeneous pool of professional caregivers were conducted: one in Quebec (Canada, n = 6) and one in Brussels (Belgium, n = 8). Braun and Clarke' method for thematic analysis, guided by a qualitative descriptive approach was applied to inductively identify themes from the data.

RESULTS

We identified factors influencing technology implementation in older adults with mild cognitive decline on three levels: an individual level (e.g., characteristics of older adults with mild cognitive decline and professional caregivers' attitude), an organizational level (e.g., lack of training among professional caregivers) and a level referring to the broader context (e.g., ethical considerations).

CONCLUSIONS

This study contributes to the research gap in knowledge on the needs of professional caregivers to facilitate technology implementation among the population of older adults with cognitive decline. Future directions for research, practice, and policy are given, more specifically to improve knowledge among caregivers and on the development of decision support to retrieve safe and effective technologies that suit patient-centered care.

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 1169: A potential tumor suppressive role of polo-like kinase 5 in specific neoplasms

Polo-like kinase 5 (PLK5) is a member of the serine/threonine family of polo-like kinases (PLKs) which have been shown to play important role in cell cycle regulation. The Plk5 gene was identified to encode an expressed protein in humans over a decade ago; however, limited information is available regarding the functional significance of PLK5. A search of the ProteinAtlas database showed that PLK5 was expressed in several types of normal human tissues including the brain, eye, lung, testis, fallopian tubes, endometrium, and cervix. However, research regarding the role of PLK5 in cancer is still in its infancy, with little available information regarding its functional significance in human biology. Interestingly, one published study has demonstrated that PLK5 was downregulated in brain tumors, suggesting a potential tumor suppressive function in this neoplasm. The objective of this study was to determine the expression profile of PLK5 in a variety of normal and malignant tissues types to gain an insight into its function in cancer. We performed quantitative immunostaining of PLK5 employing tissue microarrays (TMAs) containing tissue cores from six different organs viz. cervix, endometrium, fallopian tubes, ovary, lung, and testis. Following immunohistochemical staining, the TMA slides were scanned via Vectra Imaging System and analyzed using the Inform software, yielding quantitative information of PLK5 protein levels in each tissue core, which was then subjected to further statistical analysis. Our data demonstrated that PLK5 protein levels were significantly downregulated in most malignant tissues when compared to normal tissues (p<0.03). Further, we determined the expression profiles of PLK5 in cancer and normal tissues from the organs of interest using publicly available TCGA (The Cancer Genome Atlas) data via the Genomic Data Commons (GDC) Data Portal. Using this data source, we were able to compare PLK5 levels in tumor versus normal tissues from cervix, endometrium, and ovary. We found that PLK5 had significantly lower expression in cancer than normal in all three tissue types (p<0.003). Additionally, we used the Genotype-Tissue Expression (GTEx) portal, which contains data from non-diseased tissues, to compare the PLK5 expression in normal samples from GTEx to the tumor samples from TCGA. We found that the PLK5 levels were higher in normal versus the malignant tissues from cervix, endometrium, ovary, and testis; however, there was no difference in terms of PLK5 levels between the normal and malignant tissues from lung. Taken together, our results demonstrate that PLK5 levels are downregulated in multiple cancers, suggesting a potential tumor suppressive function of PLK5 in the tissue types studied. However, additional detailed studies are required to fully understand the role and functional significance of PLK5 in cancer.

Citation Format: Glorimar Guzmán-Pérez, Shengqin Su, Mary A. Ndiaye, Manish Patankar, Nihal Ahmad. A potential tumor suppressive role of polo-like kinase 5 in specific neoplasms [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 1169.

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.

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.

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.

Protective Effects of Dietary Grape on UVB-Mediated Cutaneous Damages and Skin Tumorigenesis in SKH-1 Mice

Non-melanoma skin cancers (NMSCs) are the most diagnosed cancers in the US and occur more frequently in males. We previously demonstrated chemoprotective effects of dietary grape powder (GP) against UVB-mediated skin tumorigenesis in female SKH-1 mice. To expand on this, here, we determined the effects of GP in a short-term UVB exposure protocol (0 or 5% GP, followed by UVB every other day for 2 weeks) in male and female SKH-1 mice, as well as explored any sex-related differences in UVB carcinogenesis via male SKH-1 mice (0, 3, or 5% GP; UVB twice weekly for 28 weeks). In the short-term study, we found that GP protects against early-stage epithelial hyperplasia and mast cell infiltration in both sexes. In the long term, GP markedly reduced tumor counts and malignant conversion, along with significant decreases in mast cell infiltration, serum IgE and Eotaxin. We also found inhibition of P38 phosphorylation and reduced PCNA, Ki67 and BCL2 levels, suggesting that the anti-inflammatory effects of GP inhibits P38, acting as an upstream regulator to inhibit proliferation and reduce tumor cell survival. Together, GP appears to protect against UVB-mediated skin damage and carcinogenesis in SKH-1 mice and should be explored further as a supplement for NMSC prevention.

Identification of Molecular Targets of Dietary Grape-Mediated Chemoprevention of Ultraviolet B Skin Carcinogenesis: A Comparative Quantitative Proteomics Analysis

We recently showed that dietary grape powder (GP) imparts considerable protection against ultraviolet B (UVB)-mediated skin carcinogenesis in SKH-1 mice. To determine molecular mechanisms of this response, we employed tandem mass tag (TMT) quantitative global proteomics approach on skin tumors from mice exposed to 180 mJ/cm² UVB twice per week and fed control or 5% GP diet. We found 2629 proteins modulated by GP feeding, with 34 identified using stringent cutoffs (false discovery rate (FDR) q-value ≤ 0.1, fold change ≥ 1.2, p-value ≤ 0.05, ≥ 3 unique peptides). Ingenuity Pathway Analysis helped identify seven proteins involved in protein ubiquitination, including the deubiquitinase UCHL5 and 6 subunits of the 20S proteasome (PSMA1,3,4,6 and PSMB4,7). A second data set without the FDR q-value identified 239 modulated proteins, seven of which are involved in protein ubiquitination. Further, 14 proteins involved in acute phase response signaling were modulated >1.5-fold, including acute phase proteins APCS, FGA, FGB, HP, HPX, and RBP1. Evaluation of upstream regulators found inhibition of ERK1/2 phosphorylation and NF-κB p65, and an increase in IκBα in GP-treated tumors. Overall, our data suggested that GP consumption may mitigate tumorigenesis by enhancing protein ubiquitination and degradation caused by oxidative stress, and manipulates an otherwise tumor-promoting anti-inflammatory environment.

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<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.

Abstract 1251: Potential tumor suppressor function of polo-like kinase 5 in ovarian cancers

Ovarian cancer remains one of the leading causes of cancer-related deaths in women worldwide, with an estimated 295,414 new cases and 184,799 deaths to occur in 2018. In the United States, although this malignancy is not in the top 10 for number of estimated new cases, it is the 5th leading cause of cancer-related deaths in women. This disparity is due to the fact that most ovarian cancers are not diagnosed until late stages when only limited options for treatment are available. Therefore, it is important to uncover novel molecular mechanisms that can be targeted to control this deadly cancer. The polo-like kinases (PLKs 1-5) are a family of serine/threonine kinases that that primarily play key roles in cell cycle progression, and have been linked to cancer pathogenesis. Limited information is available regarding the role of PLK5 in cancer. PLK5 is structurally unique, in that it has been shown to be missing the majority of the kinase domain that the other family members have. Interestingly, although PLK5 is not expressed in many tissues, it has been found to be present in appreciable levels in fallopian tube tissue, which suggests that PLK5 may be important in fallopian tube biology. Contrary to previous dogma, recent research has suggested that most ovarian cancers may actually have their origin in the fallopian tubes. Keeping this in mind, we wanted to explore the role of PLK5 in fallopian cancer. To this end, we performed a quantitative immunostaining of PLK5 in a fallopian tube disease tissue microarray (TMA) containing 5 normal tissues, 10 cases of inflammation, 10 fallopian adenocarcinoma, and 4 adjacent normal tissues. Following staining, the TMA was scanned with the Vectra platform and immunostaining was analyzed using InForm software that allows us to quantitatively measure the PLK5 intensity in each tissue and subcellular compartment. Our data demonstrated that PLK5 protein levels were significantly decreased in fallopian tumors compared to normal fallopian tissue (p = 0.01). Interestingly, although there was no significant difference between inflamed tissue and normal tissue, PLK5 levels were significantly reduced in the fallopian tube adenocarcinomas compared to the inflamed fallopian tissue (p<0.001), suggesting a potential role for PLK5 in fallopian tube carcinogenesis. Further, our data demonstrated that PLK5 was enriched in the nucleus (p<0.001) versus the cytoplasm, which is the opposite of what has been previously published in human neurons and glial cells. Taken together, our data suggests that PLK5 may be a tumor suppressor in fallopian tube cancer, and potentially ovarian cancers, as a majority of them are derived from the fallopian tube epithelium. However, further studies are needed to understand the exact roles played by this kinase in these reproductive tissues.

Citation Format: Mary A. Ndiaye, Shengqin Su, Rebecca M. Baus, Wei Huang, Manish S. Patankar, Nihal Ahmad. Potential tumor suppressor function of polo-like kinase 5 in ovarian cancers [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 1251.

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.

Abstract 547: The potential role of polo-like kinase 4 in non-melanoma skin cancers

Nonmelanoma skin cancers (NMSC), including basal cell carcinoma (BCC) and squamous cell carcinoma (SCC), are the most common malignancies in the United States, with over 5.4 million cases treated in more than 3.3 million people each year. The existing preventive and therapeutic strategies have not been fully effective in NMSC management. Therefore, an enhanced knowledge of the molecular mechanisms of NMSC may provide novel targets for prevention and treatment of these cancers. This study was undertaken to determine the potential role of the serine/threonine kinase, polo-like kinase 4 (PLK4) in NMSC. PLK4 plays an important role in cell division by regulating centriole duplication during the cell cycle. Essentially, PLK4 is a low abundance suicidal kinase capable of auto-phosphorylating itself to cause its own destruction to limit centriole duplication once per cell cycle phase. Since centrosome aberrations are frequently seen in cancer, the central role of PLK4 in centriole duplication suggests its significance as a potential target for cancer management. In this study, employing in vitro and ex vivo approaches, we tested the hypothesis that PLK4 is differentially expressed in NMSC and may be used as a potential new target for the management of these neoplasms. Employing real time quantitative polymerase chain reaction as well as immunoblot analyses, we found that compared to normal human epidermal keratinocytes (NHEKs), PLK4 was significantly overexpressed in human epidermoid carcinoma A431 cells and basal cell carcinoma UW-BCC1 cell lines at both mRNA and protein levels. Further, we determined the expression profile of PLK4 in NMSC using immunohistochemical analysis of multiple tissue microarrays containing cores of normal skin, BCC and SCC. Our data demonstrated a marked overexpression of PLK4 in cancerous tissues, compared to normal skin. To further assess the role of PLK4 overexpression in NMSC, we determined the effects of small molecule inhibitors of PLK4, centrinone-B and CFI-400945 in vitro. We found that treatment with centrinone-B or CFI-400945 resulted in dose- as well as time-dependent decreases in the growth and viability. Further, centrinone-B and CFI-400945 treatments also resulted in a marked reduction in the clonogenic survival of skin cancer cells. Taken together, our study suggests that PLK4 has a pro-proliferative function in NMSC. Additional detailed studies are ongoing in our laboratory to determine the functional significance of PLK4 in NMSC. Based on our data, we suggest that PLK4 should be further evaluated as a potential target and prognostic biomarker for the management of NMSC.

Citation Format: Debra R. Garvey, Mary A. Ndiaye, Chandra K. Singh, Ambria Noll, Nihal Ahmad. The potential role of polo-like kinase 4 in non-melanoma skin cancers [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 547.

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 5830: Combination of volasertib (BI6727) and abemaciclib (LY2835219) for melanoma management: Concomitant targeting of multiple cell cycle phases

Melanoma is one of the most lethal forms of skin cancer that kills an average of around one person every hour in the United States alone. Melanoma can be surgically removed if diagnosed early, however, undiagnosed or untreated melanomas can rapidly metastasize to become lethal. Significant progress has been made in the treatment of metastatic melanoma over the past decade, especially with novel targeted therapeutic approaches (such as BRAF- and MEK- inhibitors or immunotherapies). However, even with these newer therapies, melanoma can acquire resistance and become untreatable, with fatal consequences. Therefore, novel therapeutic approaches are required for the management of this neoplasm. It is commonly accepted that mechanism-based combination therapeutics could be better for an efficient and complete elimination of cancer cells, thereby limiting the chances of recurrence and resistance. Based on this rationale, we reasoned that a simultaneous targeting of G2/M and G1 phases of the cell cycle could provide a more efficacious response against melanoma. Studies in our laboratory have suggested that polo-like kinase 1 (PLK1), which is a mitotic regulator acting in the G2/M phase of the cell cycle, is overexpressed in melanoma and is a potentially druggable target for melanoma management. We demonstrated that BI6727, a small-molecule PLK1 inhibitor, resulted in delay and regression of melanoma xenografts. Similarly, dysregulation of the p16-cyclin D1-CDK4/6-Rb pathway has been shown to frequently occur in melanoma, and CDK4/6 inhibition is being extensively investigated in the management of several cancers, including melanoma. In this study, we evaluated the anti-proliferative efficacy of a combination of G2/M-phase targeting by BI6727 and G1-phase targeting by the CDK4/6 inhibitor LY2835219 in human melanoma cells. We determined the effect of BI6727 and/or LY2835219 on growth and viability of human melanoma cells using the RealTime-Glo Cell Viability- and Trypan Blue exclusion- assays. We found that the combination of BI6727 and LY2835219 resulted in a better anti-proliferative response, when compared to either of the agents alone. Further, the combination treatment was found to result in a marked decrease in the clonogenic survival of melanoma cells, as assessed by colony formation assay. Cell cycle analysis showed a G2/M-phase arrest in BI6727 treated cells and G1-phase arrest in LY2835219 treated cells. Interestingly, the combination was found to cause G2/M as well as G1- phase arrest of melanoma cells. Overall, our data suggests that a concomitant inhibition of PLK1 with CDK4/6 provides a superior anti-proliferative response, suggesting that dual inhibition should be further evaluated in detailed in vitro and in vivo experiments. Additional studies to determine the mechanisms of this combination are currently underway in our laboratory.

Citation Format: Sanghamitra Nethramurthy, Mary A. Ndiaye, Chandra K. Singh, Nihal Ahmad. Combination of volasertib (BI6727) and abemaciclib (LY2835219) for melanoma management: Concomitant targeting of multiple cell cycle phases [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 5830.

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 1260: Mechanism of skin cancer chemoprevention by dietary grape: A global proteomics approach

Non-melanoma skin cancer (NMSC), composed mainly of squamous cell carcinomas (SCC) and basal cell carcinomas (BCC), is the most commonly diagnosed form of cancer in the United States, with more than 5 million cases diagnosed each year. Ultraviolet (UV) radiation, a major component of sunlight, is the primary contributing factor in the development of NMSCs. Based on research in the past few decades, the naturally occurring dietary antioxidants have shown considerable promise towards preventing or delaying the process of carcinogenesis. We have previously demonstrated that dietary grape powder (GP) imparts considerable chemopreventive effects against UVB exposure-mediated skin carcinogenesis in SKH-1 hairless mice (AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5263). Here, we extended our study to determine the molecular mechanisms associated with the observed chemopreventive response of grapes. We employed a quantitative proteomics approach to identify the mechanism of observed protective effects of GP against UVB exposure-mediated skin carcinogenesis. The trypsin-digested protein extracts from UVB exposure-mediated skin tumors excised from control and 5% GP-fed mice were labeled using TMT10plex isobaric mass tagging reagents, fractionated, and analyzed by high-resolution Orbitrap LC-MS/MS. Post-acquisition analysis was performed using MaxQuant and Perseus computational software. We found that approximately 2600 total proteins were modulated by GP consumption. In our first set of data reduction, we used cut-off parameters of a p-value less than 0.05, 3 unique peptides, and greater than 1.2 fold change. A low fold change threshold was selected due to ratio compression, a known phenomenon in isobaric mass tagging which leads to underestimation of quantitative ratios. The resulting subset of 239 proteins were then subjected to Ingenuity Pathway Analysis (IPA), which identified Acute Phase Response (APR), a systemic response to trauma which is linked to poor cancer prognosis when prolonged, as a pathway affected by GP. We observed modulations in nine APR proteins (APCS, HP, RBP1, FGB, FGA, CRABP2, C1S, HPX, IL36G, AMBP). Application of a more stringent data filter (permutation FDR q-value less than 0.07) exposed a subset of 20 proteins. When analyzed by IPA, the results suggested that GP affects signaling proteins associated with the 20s proteasome (PSMA6, PSMA3, and PSMB7) and 19s proteasome (UCHL5), both components of the 26s proteasome signaling, which plays an important role in cancer. Further studies are underway to validate our proteomics data.

Citation Format: Charlotte A. Mintie, Chandra K. Singh, Mary A. Ndiaye, Gregory A. Barrett-Wilt, Nihal Ahmad. Mechanism of skin cancer chemoprevention by dietary grape: A global proteomics approach [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 1260.

Abstract 2530: An analysis of correlative interactions between Plk1, Notch1 and FoxM1 in melanoma

Melanoma is one of the most aggressive forms of skin cancer, and existing therapies have not been effective in managing this neoplasm. Therefore, a deeper understanding of the mechanisms of melanoma development/progression is required. The goal of this study was to define the potential interactions between several key melanoma-linked proteins, namely Polo-like kinase 1 (Plk1; a cell cycle regulator involved in G2/M transition), Notch (Notch1; a type I transmembrane protein that decides cell fate during development), and forkhead box M1 (FoxM1; a transcription factor regulating S and G2/M phases of cell cycle) in human melanoma. Previously, we have shown that Plk1 is overexpressed in melanoma, and its inhibition results in G2/M phase arrest and apoptosis in multiple melanoma cells. Recent studies have shown that both Notch1 and FoxM1 may be involved in the pathogenesis of certain cancers, including melanoma. In this study, employing an in-house human tissue microarray (TMA) coupled with high-throughput, multispectral Vectra scanning and inForm analysis, we analyzed 126 clinical tissue specimens of normal skin and localized cutaneous melanoma. The TMA was co-immunostained for Plk1, Notch1, FoxM1, and the melanoma biomarker S100, followed by Vectra scanning and analyses with inForm software. Using this system, we determined the levels of Plk1, Notch1, and FoxM1 in both the nucleus and cytoplasm of melanoma cells which were positive for S100 staining. By applying statistical tools of Wilcoxon Signed-Rank Test and Pearson's Correlation Coefficient in R programming, we found that while all the proteins are detected in both nucleus and cytoplasm, FoxM1 and Notch1 are enriched in the nucleus, and Plk1 is enriched in the cytoplasm. Visualization of the correlation coefficients on a heat-map showed that all 3 sets of proteins (Plk1:Notch1, Plk1:FoxM1, and Notch1:FoxM1) are positively correlated, with Plk1:Notch1 having the strongest correlation, and FoxM1 having a weaker correlation with the other two proteins. The associative relationship between Plk1 and Notch1 leads to the hypothesis that Plk1 and Notch1 may be positively correlated in melanoma. We further studied how Breslow thickness, a measure of melanoma aggressiveness, is related to Plk1, Notch1 and FoxM1. By analyzing the TMA cores with available clinical data, we found a positive correlation between Breslow thickness and Notch1, as well as Plk1. Interestingly, although Breslow thickness was significantly correlated with FoxM1 in the nucleus, no correlation was found in the cytoplasm, suggesting that FoxM1 levels may be independent of Plk1 and Notch1. Overall, our study found novel correlative interactions between Plk1 and Notch1 in melanoma, which may have relevance to melanoma progression. Additional studies are needed to validate our findings and dissect the possible interaction between Plk1 and Notch1 during melanoma development and progression.

Citation Format: Shengqin Su, Chandra K. Singh, Mary A. Ndiaye, Vijayasaradhi Setaluri, Nihal Ahmad. An analysis of correlative interactions between Plk1, Notch1 and FoxM1 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 2530.

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.

RNA interference-mediated knockdown of SIRT1 and/or SIRT2 in melanoma: Identification of downstream targets by large-scale proteomics analysis

Melanoma is the most notorious and fatal of all skin cancers and the existing treatment options have not been proven to effectively manage this neoplasm, especially the metastatic disease. Sirtuin (SIRT) proteins have been shown to be differentially expressed in melanoma. We have shown that SIRTs 1 and 2 were overexpressed in melanoma and inhibition of SIRT1 imparts anti-proliferative responses in human melanoma cells. To elucidate the impact of SIRT 1 and/or 2 in melanoma, we created stable knockdowns of SIRTs 1, 2, and their combination using shRNA mediated RNA interference in A375 human melanoma cells. We found that SIRT1 and SIRT1&2 combination knockdown caused a decreased cellular proliferation in melanoma cells. Further, the knockdown of SIRT 1 and/or 2 resulted in a decreased colony formation in melanoma cells. To explore the downstream targets of SIRTs 1 and/or 2, we employed a label-free quantitative nano-LC-MS/MS proteomics analysis using the stable lines. We found aberrant levels of proteins involved in many vital cellular processes, including cytoskeletal organization, ribosomal activity, oxidative stress response, and angiogenesis. These findings provide clear evidence of cellular systems undergoing alterations in response to sirtuin inhibition, and have unveiled several excellent candidates for future study.

SIGNIFICANCE

Melanoma is the deadliest form of skin cancer, due to its aggressive nature, metastatic potential, and a lack of sufficient treatment options for advanced disease. Therefore, detailed investigations into the molecular mechanisms of melanoma growth and progression are needed. In the search for candidate genes to serve as therapeutic targets, the sirtuins show promise as they have been found to be upregulated in melanoma and they regulate a large number of proteins involved in cellular processes known to affect tumor growth, such as DNA damage repair, cell cycle arrest, and apoptosis. In this study, we used a large-scale label-free comparative proteomics system to identify novel protein targets that are affected following knockdown of SIRT1 and/or 2 in A375 metastatic melanoma cell line. Our study offers important insight into the potential downstream targets of SIRTs 1 and/or 2. This may unravel new potential areas of exploration in melanoma research.

Abstract 5263: Chemopreventive effects of dietary grapes on skin cancer

Non-melanoma skin cancer (NMSC) is the most commonly diagnosed malignancy in the United States, affecting more than 3 million Americans each year. Ultraviolet (UV) radiation from the sun, particularly its UVB component (290-320 nm), is an established causative factor for ~90% of skin cancers. The two most common forms of skin cancer, basal- and squamous- cell carcinomas, are treatable if detected early. However, they can be difficult to treat and potentially fatal if left until late stages. Further, epidemiological studies have suggested an amplified risk of other deadly cancers in individuals with a history of skin cancer. Therefore, it is important to design novel approaches, especially focusing on prevention, for the management of skin cancers. Studies from our laboratory and by others have shown that topical application of the grape antioxidant resveratrol possesses promise in the prevention of skin cancer. However, ideally cancer preventive agents need to be orally administrable for ease of use and broader human acceptability. With this in mind, in this study, we determined the efficacy of dietary grape powder (containing resveratrol in natural amalgamation with catechins, anthocyanins, polyphenols and flavonols) against UVB-mediated skin tumorigenesis in the SKH-1 hairless mouse model, which is regarded to have relevance to human NMSC. We employed a UVB initiation-promotion protocol in which the mice were subjected to chronic UVB exposure (180 mJ/cm2; twice weekly, for 28 weeks). The animals received either AIN-76A or grape powder (GP) fortified diet (3% and 5% GP, obtained from the California Table Grape Commission), all of which were sugar-matched to the highest GP content. Our data demonstrated that the consumption of GP at both 3% and 5% resulted in a significant inhibition in skin tumor incidence and delay in the onset of tumorigenesis. The average consumption of feed per mouse was 3.5 g/day, corresponding to 105 and 174 mg GP/day in the 3% and 5% GP treatment groups. This dosing regimen seems to be easily achievable for human consumption, as it corresponds to 25.5 and 42.4 g/day, which are equivalent to 1.1 and 1.8 serving of fresh grapes, respectively. Our data also demonstrated that the observed skin cancer chemopreventive effects of grape powder were accompanied by significant i) decreases in cellular proliferation markers Ki67 and PCNA, ii) decreases in the oxidative stress marker 4-HNE, and iii) increases in the levels of cleaved caspase 7 and poly (ADP-ribose) polymerase (PARP). Interestingly, NRF2, an activator of cellular antioxidant response, was found to be downregulated in GP treated tumors, compared to UVB alone groups, suggesting a potential protective role of NRF2 in the survival of tumor cells. Overall, our study suggests a strong chemopreventive effect of dietary grape and provides a basis for future human studies.

Citation Format: Chandra K. Singh, Mary A. Ndiaye, Charlotte A. Mintie, Gagan Chhabra, Nihal Ahmad. Chemopreventive effects of dietary grapes on skin cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5263. doi:10.1158/1538-7445.AM2017-5263

Abstract 5415: Targeted depletion of polo-like kinase 1 alters metabolic regulation in melanoma

Polo-like kinase 1 (PLK1), a critical regulator of mitosis, is shown to be overexpressed in a variety of cancers. PLK1 overexpression has also been linked to poor disease prognosis and a lessened survival in cancer patients. Previously, we have shown that PLK1 is overexpressed in human melanoma and its inhibition causes significant anti-proliferative response in vitro (in multiple melanoma cells) as well as in vivo (in human melanoma xenografts). Further, in another study we demonstrated, based on a large-scale label-free comparative proteomics analysis, that PLK1 inhibition via the small-molecule inhibitor BI 6727 (Volasertib) in human melanoma cells resulted in an alteration of certain metabolism-associated proteins with an associated decrease in cellular metabolism. In this study, to further explore the association between PLK1 and cellular metabolism, we utilized a doxycycline-inducible PLK1 knockdown approach in A375 melanoma cells coupled with a Human Glucose Metabolism PCR array that covers 84 key genes involved in the regulation and enzymatic pathways of glucose and glycogen metabolism. We found that PLK1 knockdown resulted in a significant downregulation of 29 genes and upregulation of 3 genes (more than 2 fold change) associated with cellular metabolism. IDH1, PDP2 and PCK1 were >3-fold downregulated while FBP1 was >7-fold upregulated. Through Ingenuity Pathway Analysis (IPA), we identified glycolysis and the pentose phosphate pathway as major canonical pathways altered by PLK1 inhibition. Further, IPA identified that PLK1 inhibition-modulated genes were largely associated with the proliferation of cells, where FBP1 appeared as a key regulatory player. PCK1 was found to be highly downregulated in our array, and IPA identified it as part of a monosaccharide regulation network. We further validated our data in vivo and found that BI 6727 treatment resulted in a decrease in PCK1 and increase in FBP1 in A375 melanoma cell implanted xenografts. In addition, we observed a strong inverse correlation between PLK1 and FBP1 in multiple melanoma cell lines, with FBP1 expression significantly downregulated in a panel of melanoma cells compared to normal melanocytes. Moreover, BI 6727 treatment resulted in an upregulation in FBP1 in A375, Hs 294T and G361 melanoma cells. Interestingly, in recent studies, FBP1 (fructose-bisphosphatase) that is a rate-limiting enzyme in gluconeogenesis, has been shown to function as a tumor suppressor in certain cancers. Overall, our study support the hypothesis that PLK1 is a regulator of metabolism maintenance that affects the melanoma cell growth.

Citation Format: Rosie E. Gutteridge, Chandra K. Singh, Mary A. Ndiaye, Nihal Ahmad. Targeted depletion of polo-like kinase 1 alters metabolic regulation in melanoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5415. doi:10.1158/1538-7445.AM2017-5415

Abstract 820: Potential pro-proliferative role of SIRT6 in melanoma

Melanoma is one of the deadliest form of skin cancer that can rapidly metastasize to become lethal, if not diagnosed early or left untreated. In 2016, approximately 76,380 new melanoma cases and 10,130 melanoma-related deaths are predicted in the United States. Current preventive and therapeutic strategies have not been sufficiently effective in the management of melanoma. Therefore, novel molecular targets and treatments are required for an effective management of this neoplasm. In our laboratory, we are assessing the role and functional and therapeutic significance of sirtuin family of proteins in melanoma. Sirtuins (SIRTs) have been conserved through evolution from prokaryotic to eukaryotic cells. SIRTs are nicotinamide adenine dinucleotide (NAD+) dependent protein deacetylases and belong to class III of the histone deacetylase (HDAC) family. Seven members of the mammalian SIRT family are known to date, and despite structural similarities, each SIRT has their own biological niche, performing unique functions via regulating critical mechanisms in the cell. The role of SIRTs in cancer is somewhat controversial, as they have exhibited conflicting functions (tumor promoter vs. tumor suppressor) depending on cell and tissue contexts. The sirtuin SIRT6, a predominantly nuclear protein, has been shown to conduct ADP-ribosyl transferase and histone deacetylase activities. SIRT6 plays key roles in DNA repair, inflammation and metabolic diseases such as cancer. Currently, the role of SIRT6 in melanoma is not known. The objective of this study was to determine the role of SIRT6 in melanoma. Using a panel of human melanoma cell lines (A375, Hs 294T, G361, SK-MEL-2, SK-MEL-28, SK-MEL-31, WM115 and WM35) differing in genetic complexity and disease progression stage, and normal human epidermal melanocytes (NHEMs), we determined the endogenous expression levels of SIRT6. We found that compared to NHEMs, SIRT6 is significantly upregulated in melanoma cell lines, at mRNA as well as protein levels, as shown by quantitative Real-Time PCR and western blot analyses. Further, employing a human tissue microarray (TMA) coupled with quantitative Vectra™ analysis, we determined the expression profile of SIRT6 protein in human melanoma and melanocytic nevus tissues. Our data demonstrated that SIRT6 is significantly overexpressed in human melanoma tissues when compared to nevi. Furthermore, lentiviral short hairpin RNA-mediated knockdown of SIRT6 in human melanoma cells was found to result in a marked anti-proliferative response in melanoma cells. Taken together, our data suggest that SIRT6 overexpression could potentially be a contributing factor in melanoma progression. Further detailed studies are underway to understand the functional significance of SIRT6 in melanoma development and progression.

Citation Format: Liz Garcia-Peterson, Mary A. Ndiaye, Chandra K. Singh, Wei Huang, Nihal Ahmad. Potential pro-proliferative role of SIRT6 in melanoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 820. doi:10.1158/1538-7445.AM2017-820

Small molecule inhibition of polo-like kinase 1 by volasertib (BI 6727) causes significant melanoma growth delay and regression in vivo

The objective of this study was to determine the therapeutic potential of polo-like kinase 1 (Plk1) inhibition in melanoma, in vivo. Employing Vectra technology, we assessed the Plk1 expression profile in benign nevi, malignant (stages I-IV) and metastatic melanomas. We found a significant elevation of Plk1 immunostaining in melanoma tissues. Further, a second generation small molecule Plk1 inhibitor, BI 6727, resulted in reductions in growth, viability and clonogenic survival, as well as an increase in apoptosis of A375 and Hs 294T melanoma cells. BI 6727 treatment also resulted in a G2/M-as well as S-phase cell cycle arrest in melanoma cells. Importantly, BI 6727 (intravenous injection; 10 and 25 mg/kg body weight) treatment resulted in significant tumor growth delay and regression in vivo in A375-and Hs 294T-implanted xenografts in athymic nude mice. These anti-melanoma effects were accompanied with a decreased cellular proliferation (Ki-67 staining) and induction of apoptosis (caspase 3 activation). In addition, BI 6727 treatment caused a marked induction of p53 and p21 in vitro as well as in vivo. Overall, we suggest that Plk1 inhibition may be a useful approach as a monotherapy as well as in combination with other existing therapeutics, for melanoma management.

Abstract 1143: Pro-proliferative function of SIRT3 in a human melanoma xenograft mouse model

Melanoma is one of the most aggressive forms of skin cancer and is often lethal, if not treated early. Therefore, it is necessary to try to develop novel target-based strategies to combat this neoplasm. SIRT3 is a nicotinamide adenine dinucleotide (NAD+) -dependent mitochondrial protein deacetylase involved in metabolism- and aging- related disorders, including certain cancers. Interestingly, studies have suggested both tumor suppressor as well as tumor promoter roles of SIRT3 in cancer. However, its role in melanoma is not well-established. Previously, we have shown that SIRT3 was upregulated in human melanoma cells and its lentiviral knockdown resulted in anti-proliferative effects in human melanoma cells. We also found that SIRT3 knockdown resulted in the G1-phase arrest of the cell cycle, induction of senescence, and decrease in cell migration. This study was designed to determine the relevance of our in vitro findings to the in vivo situation, in human melanoma xenograft models. Employing immunodeficient mice (Crl:NU-Foxn1nu, homozygous; Strain 088), we first determined the effect of SIRT3-knockdown on melanoma tumorigenesis. The mice were subcutaneously implanted with shNS-SK-MEL-2 (control) and shSIRT3-SK-MEL-2 (SIRT3-knockdown) melanoma cells, followed by assessing tumorigenesis of melanoma cells. We found that compared to shNS-SK-MEL-2 cells, shSIRT3-SK-MEL-2 cells showed a significantly decreased tumorigenic potential in these mice, in terms of average tumor volume (measured weekly) and average tumor weight (measured at termination of the study). Further, the Kaplan-Meier analysis showed that SIRT3 knockdown resulted in a significant survival advantage, in terms of reaching the cutoff tumor size (2.0 cm in one dimension). In an additional strategy, we determined the tumorigenicity of SIRT3 overexpressing melanoma cells (Hs294T-SIRT3) in NU/NU mice. Our data demonstrated that compared to control Hs294T-pcDNA cells, the SIRT3 overexpressing Hs294T-SIRT3 cells demonstrated a significantly enhanced tumorigenic potential (average tumor volume and tumor weight) in NU/NU mice. Overall, our study provides evidence supporting a pro-proliferative role of SIRT3 in melanoma and suggests that SIRT3 needs to be further evaluated as a potential druggable therapeutic target for melanoma management. However, detailed mechanistic and in vivo studies in relevant melanoma models are needed to further validate our findings.

Citation Format: Jasmine George, Minakshi Nihal, Mary A. Ndiaye, Nihal Ahmad. Pro-proliferative function of SIRT3 in a human melanoma xenograft mouse model. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1143.

Sirtuin deacetylases: a new target for melanoma management

Melanoma continues to cause more deaths than any other skin cancer, necessitating the development of new avenues of treatment. One promising new opportunity comes in the form of mechanism-based therapeutic targets. We recently reported the overexpression and delocalization of the class III histone deacetylase SIRT1 in melanoma, and demonstrated that its small molecule inhibition via Tenovin-1 decreased cell growth and viability of melanoma cells, possibly by a p53 mediated induction of p21. Here, we support our data using additional SIRT inhibitors, viz. Sirtinol and Ex-527, which suggests possible benefits of concomitantly inhibiting more than one Sirtuin for an effective cancer management strategy. This "Extra View" paper also includes a discussion of our results in the context of similar recent and concurrent studies. Furthermore, we expand upon our findings in an analysis of new research that may link the cellular localization and growth effects of SIRT1 with the PI3K signaling pathway.

Methaneseleninic acid and γ-Tocopherol combination inhibits prostate tumor growth in Vivo in a xenograft mouse model

Studies have shown that vitamin E and selenium possess antiproliferative effects against prostate cancer (PCa). However, results from the Selenium and Vitamin E Cancer Prevention Trial (SELECT) suggest that vitamin E (α-tocopheryl acetate; 400 mg) and/or selenium (L-selenomethionine; 200 μg) were ineffective against PCa in humans. It is arguable that the selected dose/formulation of vitamin E/selenium were not optimal in SELECT. Thus, additional studies are needed to define the appropriate formulations/dose regimens of these agents. Here, we investigated the effect of methaneseleninic acid (MSA; 41 μg/kg) and/or γ-tocopherol (γT; 20.8 mg/kg or 41.7 mg/kg) in Nu/J mice implanted with 22Rν1 tumors. MSA (41 μg/kg) and γT (20.8 mg/kg) combination was most consistent in imparting anti-proliferative response; resulting in a significant decrease in i) tumor volume/weight, ii) serum PSA, and iii) Ki-67 immunostaining. Further, we observed i) an upregulation of pro-apoptosis Bax and a down-regulation of the pro-survival Bcl2, and ii) an increase in pro-apoptosis Bad. Furthermore, the combination resulted in a modulation of apolipoprotein E, selenoprotein P and Nrf2 in a fashion that favors antiproliferative responses. Overall, our study suggested that a combination of MSA and γT, at lower dose regimen, could be useful in PCa management.

Resveratrol and cancer: Challenges for clinical translation

Significant work has been done towards identifying the health-beneficial effects of the grape antioxidant resveratrol in a variety of bioassay- and disease- models, with much research being focused on its possible application to cancer management. Despite the large number of preclinical studies dealing with different aspects of the biological effects of resveratrol, its translation to clinics is far from reality due to a variety of challenges. In this review, we discuss the issues and questions associated with resveratrol becoming an effective in vivo anticancer drug, from basic metabolic issues to the problems faced by incomplete understanding of the mechanism(s) of action in the body. We also explore efforts taken by researchers, both public and private, to contend with some of these issues. By examining the published data and previous clinical trials, we have attempted to identify the problems and issues that hinder the clinical translation of resveratrol for cancer management. This article is part of a Special Issue entitled: Resveratrol: Challenges in translating pre-clinical findings to improved patient outcomes.

Skin, reactive oxygen species, and circadian clocks

SIGNIFICANCE

Skin, a complex organ and the body's first line of defense against environmental insults, plays a critical role in maintaining homeostasis in an organism. This balance is maintained through a complex network of cellular machinery and signaling events, including those regulating oxidative stress and circadian rhythms. These regulatory mechanisms have developed integral systems to protect skin cells and to signal to the rest of the body in the event of internal and environmental stresses.

RECENT ADVANCES

Interestingly, several signaling pathways and many bioactive molecules have been found to be involved and even important in the regulation of oxidative stress and circadian rhythms, especially in the skin. It is becoming increasingly evident that these two regulatory systems may, in fact, be interconnected in the regulation of homeostasis. Important examples of molecules that connect the two systems include serotonin, melatonin, vitamin D, and vitamin A.

CRITICAL ISSUES

Excessive reactive oxygen species and/or dysregulation of antioxidant system and circadian rhythms can cause critical errors in maintaining proper barrier function and skin health, as well as overall homeostasis. Unfortunately, the modern lifestyle seems to contribute to increasing alterations in redox balance and circadian rhythms, thereby posing a critical problem for normal functioning of the living system.

FUTURE DIRECTIONS

Since the oxidative stress and circadian rhythm systems seem to have areas of overlap, future research needs to be focused on defining the interactions between these two important systems. This may be especially important in the skin where both systems play critical roles in protecting the whole body.

Abstract 3693: Methaneseleninic acid and γ-tocopherol combination inhibits prostate tumor growth in a xenograft model

Prostate Cancer (PCa) is the second leading cause of cancer-related deaths in American males. Several in vitro and in vivo studies have suggested that vitamin E as well as selenium possesses potential in the management of PCa. However, results from the large-scale Selenium and Vitamin E Cancer Prevention Trial (SELECT) found that vitamin E (α-tocopheryl acetate; 400 mg) and/or selenium (L-selenomethionine; 200 μg) were ineffective in preventing PCa. Based on these seemingly contradictory outcomes, we believe that the dose and formulation of both these agents were sub-optimal in the SELECT trial, and may be critical in providing appropriate biological response in PCa. Thus, additional studies are needed to define the most appropriate formulations of vitamin E and selenium as well as the optimal dosages of these two agents. Following a careful analysis of literature, we evaluated the effect of methylseleninic acid (MSA in sterile water; oral gavage) and/or γ-tocopherol (γT in tocopherol-stripped corn oil; oral gavage), at a dose much lower than used in SELECT, against prostate tumors in an immunecompromised mouse model. Sixty Nu/J mice were implanted with 22Rν1 cells, tumors were allowed to grow to an average volume of 36 mm3, followed by treatment in 6 groups (10 animals each): 1) Control (vehicle alone); 2) MSA (41 μg/kg); 3) γT (20.8 mg/kg); 4) γT (41.7 mg/kg); 5) MSA (41 μg/kg) + γT (20.8 mg/kg); and 6) MSA (41 μg/kg) + γT (41.7 mg/kg). The mice were treated for 2 weeks (5 days per week) and followed for tumor growth. At the end of experiment, the mice were sacrificed and further studies were done. Our data demonstrated that the combination of γT (20.8 mg/kg) and MSA (41 μg/kg) resulted in a significant decrease in i) serum prostate specific antigen levels, ii) tumor volume and tumor wet weight, and iii) Ki-67 proliferation index. We found that this combination also resulted in i) an up-regulation of pro-apoptotic Bax coupled with a down-regulation of the pro-survival protein Bcl2, thereby resulting in an increased Bax/Bcl2 ratio, and ii) an increase in pro-apoptotic protein Bad. Further, γT and MSA combination modulated levels of apolipoprotein E, selenoprotein P and Nrf2 in a fashion that favors anti-proliferative responses in PCa. Interestingly, we found that the combination using a lower dose of γT was much more effective than the higher dose, in most of the parameters evaluated. In the most effective treatment group, the approximate daily human equivalent dose for γT was 72 mg/day (corresponding to 20.8 mg/kg in mouse) and for MSA is 142 μg/day (corresponding to 41 μg/kg in mouse), which is significantly lower than the doses used in SELECT. Overall, our study suggests that γT and MSA, at the lower dose regimen, could be useful in PCa management. However, further studies with additional formulations and doses in more relevant animal model(s) are needed to confirm our findings.

Citation Format: Chandra K. Singh, Mary A. Ndiaye, Imtiaz A. Siddiqui, Minakshi Nihal, Thomas Havighurst, Weixiong Zhong, Hasan Mukhtar, Nihal Ahmad. Methaneseleninic acid and γ-tocopherol combination inhibits prostate tumor growth in a xenograft model . [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3693. doi:10.1158/1538-7445.AM2013-3693

Inactivation of glycogen synthase kinase-3β, a downstream target of the raf-1 pathway, is associated with growth suppression in medullary thyroid cancer cells

Glycogen synthase kinase-3beta (GSK-3beta) is an important regulator of cell proliferation and survival. Conflicting observations have been reported regarding the regulation of GSK-3beta and extracellular signal-regulated kinase (ERK1/2) in cancer cells. In this study, we found that raf-1 activation in human medullary thyroid cancer cells, TT cells, resulted in phosphorylation of GSK-3beta. Inactivation of GSK-3beta in TT cells with well-known GSK-3beta inhibitors such as lithium chloride (LiCl) and SB216763 is associated with both growth suppression and a significant decrease in neuroendocrine markers such as human achaete-scute complex-like 1 and chromogranin A. Growth inhibition by GSK-3beta inactivation was found to be associated with cell cycle arrest due to an increase in the levels of cyclin-dependent kinase inhibitors such as p21, p27, and p15. Additionally, LiCl-treated TT xenograft mice had a significant reduction in tumor volume compared with those treated with control. For the first time, we show that GSK-3beta is a key downstream target of the raf-1 pathway in TT cells. Also, our results show that inactivation of GSK-3beta alone is sufficient to inhibit the growth of TT cells both in vitro and in vivo.

Overexpression of the NOTCH1 intracellular domain inhibits cell proliferation and alters the neuroendocrine phenotype of medullary thyroid cancer cells

The role of NOTCH1 as an oncogene or tumor suppressor appears to be cell type-specific. Medullary thyroid cancer (MTC) cells characteristically express the transcription factor ASCL1 (achaete-scute complex-like 1) as well as high levels of the neuroendocrine (NE) markers calcitonin and chromogranin A (CgA). In this study, we show that the active NOTCH1 intracellular domain is absent in human MTC tumor tissue samples and MTC-TT cells. To determine the effects of NOTCH1 expression, we created a doxycycline-inducible NOTCH1 intracellular domain in MTC cells (TT-NOTCH cells). Treatment of TT-NOTCH cells with doxycycline led to dose-dependent induction of NOTCH1 protein with corresponding decreases in ASCL1 protein and NE hormones. ASCL1 promoter-reporter assay and Northern analysis revealed that ASCL1 reduction by NOTCH1 activation is predominantly via silencing of ASCL1 gene transcription. Overexpression of ASCL1 in MTC cells indicated that CgA expression is highly dependent on the levels of ASCL1. This was further confirmed by experiments using small interfering RNA against ASCL1, in which reduction in ASCL1 led to reduction in both CgA and calcitonin. Furthermore, we demonstrate that NOTCH1 signaling activation leads to ERK1/2 phosphorylation, but that reduction in NE markers is independent of ERK1/2 activation. Activation of NOTCH1 resulted in significant MTC cell growth inhibition. Notably, reduction in MTC cell growth was dependent on the level of NOTCH1 protein present. Moreover, no increase in growth upon expression of ASCL1 in NOTCH1-activated cells was observed, indicating that the growth suppression observed upon NOTCH1 activation is independent of ASCL1 reduction. Mechanistically, we show that MTC cell growth inhibition by NOTCH1 is mediated by cell cycle arrest associated with up-regulation of p21.