Gagan Chhabra

Melanoma Chemoprevention: Current Status and Future Prospects†

The incidence of skin cancers, both nonmelanoma and melanoma, is increasing in the United States. The ultraviolet radiation, mainly from sun, is considered the major cause for these neoplasms. While nonmelanoma skin cancers are far more numerous, melanoma remains the most challenging. This is because melanoma can become extremely aggressive and its incidence is increasing worldwide due to lack of effective early detection, as well as disease recurrence, following both surgery and chemotherapy. Therefore, in addition to better treatment options, newer means are required to prevent melanomas from developing. Chemoprevention is a reasonable cost‐effective approach to prevent carcinogenesis by inhibiting the processes of tumor initiation, promotion and progression. Melanoma is a progressive disease, which makes it very suitable for chemopreventive interventions, by targeting the processes and molecular pathways involved in the progression of melanoma. This review discusses the roles of various chemopreventive agents such as NSAIDs, statins, vitamins and dietary agents in melanoma and highlights current advancements and our perspective on future of melanoma chemoprevention. Although considerable preclinical data suggest that melanoma may be prevented or delayed by a numerous chemopreventive agents, we realize there are insufficient clinical studies evaluating their efficacy and long‐term safety for human use.

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

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

Chemoprotective effects of dietary grape powder on ultraviolet B 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.

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

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

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

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

Abstract 4128: Mechanism of action of G-quadruplex forming oligonucleotide homologous to the telomere overhang in melanoma

T-oligo, a guanine-rich oligonucleotide (GRO) homologous to the 39-telomeric overhang of telomeres, elicits potent DNA-damage responses (DDRs) in cancer cells. However, the detailed molecular mechanism of action of T-oligo in cancer cells is largely unknown. Recent studies suggest that GROs can form G-quadruplexes (G4) which are stabilized by the hydrogen-bonding of guanine residues. This study aims to examine the G4-forming capabilities of T-oligo in vitro and investigates the molecular mechanism of single-stranded (SS) and G4-T-oligo induced DDRs in melanoma cells (MM-AN). G4-formation by T-oligo was confirmed using the SS-T-oligo and G4-T-oligo on a polyacrylamide gel under non-denaturing conditions. NMR studies for T-oligo in KCl confirmed that T-oligo forms G4 structures. Immunofluorescence studies conducted with an anti-G-quadruplex antibody (BG4), a G4 detecting antibody, showed 88.4% co-localization of T-oligo and BG4 in the nuclei of melanoma cells confirming the ability of T-oligo to form G-quadruplexes inside melanoma cells. While G4-T-oligo was found more stable in nuclease degradation assay by DNase I, it had a decreased anti-proliferative effects compared to SS-T-oligo. However, G4-T-oligo had similar cellular uptake as SS-T-oligo. Further, two shelterin complex proteins TRF2 and POT1 which are mainly found at the telomere ends were found to be upregulated (2.0 fold) by T-oligo suggesting TRF2 and POT1 mediated telomere overhang dissociation. We also found that T-oligo can co-localize with telomere binding proteins TRF2 and POT1 by 88.4±4.5% (n=12) and 84.5±8% (n=10) respectively. Western blot analysis results also showed upregulation of both p-JNK and total JNK by 4.0- and 2.0-fold respectively. To further confirm the involvement of p-JNK in T-oligo mediated apoptosis we used a specific JNK inhibitor SP600125. Western blot analysis showed that T-oligo mediated upregulation of p-JNK was reversed in presence of SP600125. Results from an MTT assay showed a 73.8% decrease in cell viability after T-oligo treatment alone; however, cell viability was decreased to 45.8%, and 25.3% when SP600125 was present at concentrations of 10 μM, and 12 μM respectively, in comparison to diluent. T-oligo also inhibited mRNA expression of hTERT; a catalytic subunit of telomerase by 50% .We further investigated the effect of the JNK inhibitor SP600125 on hTERT expression and found that treatment with SP600125 in presence of T-oligo partially reversed the downregulation of hTERT. We found a 16% decrease in hTERT expression in comparison to 50% reduction by T-oligo treatment alone. In conclusion, these studies demonstrate that T-oligo can form G-quadruplexes and the anti-proliferative mechanism of T-oligo may be mediated through POT1 and TRF2 as well as via JNK-activation inducing hTERT-inhibition in melanoma cells. Citation Format: Gagan Chhabra, Luke Wojdyla, Ankita Sanjali, Mark Frakes, Marko Ivancich, Pooja Vinay, Zachary Schrank, Benjamin E. Ramirez, Neelu Puri. Mechanism of action of G-quadruplex forming oligonucleotide homologous to the telomere overhang 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 4128. doi:10.1158/1538-7445.AM2017-4128