Jornal de Distúrbios Nutricionais e Terapia

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Congresso de Nutrição 2015: Efeito quimiopreventivo aprimorado pela combinação de quercetina e chá verde no câncer de próstata - Piwen Wang - Charles R Drew University of Medicine and Science

Piwen Wang

A ação quimiopreventiva dos polifenóis do chá verde (GT) no câncer de próstata foi bem demonstrada em cultura de células pré-clínicas e modelos animais. No entanto, os resultados de estudos em humanos são inconsistentes. A baixa biodisponibilidade e o extenso metabolismo dos polifenóis GT (GTPs) in vivo limitam a atividade anticâncer do GT. Determinamos se um inibidor de metilação quercetina (Q) aumentará a quimioprevenção do adenocarcinoma prostático in vivo. Descobrimos em tecidos de próstata humana e em tecidos de tumor de próstata xenoenxerto de camundongo que cerca de 50% dos GTPs estavam na forma metilada após o consumo de GT e, portanto, a metilação diminuiu a atividade anticâncer dos GTPs. Determinamos que a mistura de um inibidor natural de metilação quercetina (Q) com GT aumenta as concentrações celulares de GTPs de 4 a 10 vezes em células LNCaP e PC-3 de adenocarcinoma prostático e diminui a metilação de GTPs. Este tratamento de mistura aumentou a inibição da proliferação celular e a indução de apoptose em ambas as linhagens celulares. Então, realizamos um estudo animal para verificar o efeito combinado de GT e Q in vivo. Camundongos com deficiência imunológica combinada grave (SCID) foram implantados com células de adenocarcinoma prostático LAPC-4 sensíveis a andrógenos e tratados com GT, Q, GT+Q ou controle. Células de adenocarcinoma prostático LAPC-4 sensíveis a andrógenos foram injetadas subcutaneamente em camundongos com imunodeficiência combinada grave (SCID) uma semana antes da intervenção. A concentração de GTPs no chá preparado administrado como bebida foi de 0,07% e Q foi suplementado na dieta a 0,2% ou 0,4%. Após 6 semanas de intervenção, o crescimento do tumor foi inibido em 16% (Q), 21% (GT) e 45% (GT+Q) em comparação ao regulamento. As concentrações teciduais de GTPs não metilados foram significativamente aumentadas no grupo de combinação e foram associadas a uma expressão proteica diminuída de transferência de catecol-O-metil e proteína associada à resistência a múltiplos fármacos (MRP)-1. O tratamento de combinação também foi associado a um aumento significativo na inibição da proliferação, sinalização do receptor de andrógeno (AR) e fosfatidilinositol 3-quinases (PI3K)/Akt e estimulação da apoptose. O efeito combinado de GT+0,4% Q na inibição do tumor foi confirmado ainda mais em outro experimento onde a intervenção começou antes da inoculação do tumor. A combinação aumentou a inibição da expressão proteica do receptor de andrógeno, antígeno prostático específico e fator de crescimento endotelial vascular.

Quercetin (Q) is a flavonoid that is found in most vegetables and fruits that are edible, particularly in onions, apples, and red wine. The inhibitory effect of Q on the actions of MRPs and COMT has been documented well. Q itself has been shown to exhibit chemo preventive activities specially in prostate cancer. We were able to demonstrate in vitro that the combined use of Q with GT significantly increased the cellular concentrations of non-methylated EGCG in prostate cancer LNCaP and PC-3 cells, leading to enhanced anti-proliferative effects. The present study was designed to test the hypothesis that the combined effect of Q and GT in vivo leads to an increased anticarcinogenic effect in a xenograft prostate tumor mouse model using severe combined immune deficiency (SCID) mice and to elucidate the mechanisms of the increased anticarcinogenic effect of the combination treatment.

The effect of the combination treatment was related to the concentration of GTPs in tumor tissue, which in turn was dependent on the Q dose. The dose of GT used in this study is equivalent to the consumption of 5-6 cups of green tea per day for an adult human. This estimate is based on the observation that the consumption of 5-6 cups of tea daily achieved similar tissue concentrations in human prostate compared to tissue in mice consuming the same brewed GT. Q dose would be equivalent to 1.0g (low dose) and 2.0g (high dose) per day for an adult based on blood concentrations of Q and its metabolites as observed in the present study (data not shown) relative to that from a human study. The consumption of 1000 mg of Q per day was not associated with any adverse effects in humans. A pilot clinical trial is on-going to determine the Q concentration necessary in humans to increase the bioavailability of EGCG. Our results showed that the combination treatment decreased the protein expression of MRP1 in tumor tissues. However, no changes of mRNA expression of MRP1 were observed, indicating that post-transcriptional regulation such as microRNA (miRNA) may be responsible. Many polyphenols including GT and Q have been shown to modulate the expression of miRNA, a class of small non-coding RNAs that interact with mRNA to regulate the gene expression post-transcriptionally. Several other investigators demonstrated the inhibitory effects of Q on the activities of transport-regulating proteins such as p-glycoprotein and MRPs, leading to an increased absorption of GTPs from the intestinal tract and retention in the tissues. Although Q is extensively methylated, sulfated, or glucuronidated upon uptake it has been demonstrated that these Q metabolites, such as isorhamnetin and 7-O-glucuronosyl quercetin exhibited equal or stronger inhibition on the activities of MRPs compared to Q. Considering the importance of MRPs in the development of chemo resistance during chemotherapy, GT and Q may also be good candidates to be combined with chemotherapy drugs to reduce drug resistance and enhance therapeutic efficacy.

The important role of catechol O-methylation of GTPs in cancer prevention has been demonstrated in several studies. Due to a common polymorphism of COMT its activity can vary by 3 to 4-fold. A case control study in Asian-American women provided evidence that the risk of breast cancer was significantly reduced only among tea drinkers possessing at least one low-activity COMT allele. We found earlier that EGCG was extensively methylated in human prostate tissues obtained from prostatectomy and in mouse tissues after GT consumption. In cell culture experiments methylation significantly decreased the anticancer activities of EGCG as shown by our laboratory and other investigators. Previously we demonstrated in vitro that the combination of GT and Q significantly decreased the activity and protein expression of COMT in various cancer cell lines. This inhibition of COMT was associated with a decrease in EGCG methylation and increase in the anti proliferative activity. Similarly, Landis-Piwowar et al. demonstrated that EGCG treatment in breast cancer cells of lower COMT activity led to stronger proteasome inhibition and apoptosis induction. The present study confirmed the inhibition of COMT in vivo both in mRNA and protein expression by the combination treatment of GT and Q, which may contribute to the increased concentrations of non-methylated EGCG in tumor tissues and supports the important role of COMT in GT chemoprevention.

Cancer results from a multistage process with distinct molecular and cellular alterations. Therefore, treatments targeting many concerted processes may be advantageous in cancer prevention, therapy and reducing resistance to the treatment. Natural compounds such as GT and Q target multiple events and signaling pathways throughout the stages of carcinogenesis. In combination these compounds may increase the anticarcinogenic activity by expanding the coverage of molecular targets. The androgen receptor (AR) signaling pathway plays a critical role in prostate tumor growth and progression, thus it is an important target in prostate cancer prevention and treatment. Nevertheless, there are other signaling pathways particularly the phosphatidylinositol 3-kinases/Akt/ mammalian target of rapamycin (PI3K/Akt/mTOR) pathway that crosstalk with AR signaling and may directly regulate the expression and activation of AR. The upregulation and activation of PI3K/Akt/mTOR pathway is thought to play an important role in prostate cancer due to the decreased expression or loss of the negative regulator, tumor suppressor phosphatase and tensin homolog (PTEN). Akt is activated after phosphorylation by phosphorylated PI3K and in turn activates its substrates, one being mTOR, which leads to increased cell proliferation and survival. Therefore, an effective intervention strategy in prostate cancer may need to target both AR and PI3K/Akt/mTOR signaling pathways. Both GT and Q inhibit AR signaling through multiple mechanisms including the decrease of AR expression and its nuclear translocation. The combined use of GT and Q in the present study demonstrated an increasing ability to inhibit AR expression compared to individual treatments. In addition, the phosphorylation of Akt was significantly inhibited by the combination treatment while only a slight but non-significant decrease by the individual treatments. Further evidence of a stronger inhibition of AR and PI3K/Akt signaling was also provided through increased inhibition of AR-mediated PSA expression in tumor tissues from mice treated with GT+Q. Similar effects were demonstrated by a recent study that combined mTOR inhibition (everolimus) with an anti-androgen (bicalutamide) to block both pathways, resulting in tumor growth was statistically significantly reduced. In addition to their applications in cancer prevention, GT and Q may be ideal candidates to be combined with anti-androgens to enhance the therapeutic efficacy in a less-toxic manner in the treatment of advanced prostate cancer.

This study provides a novel regimen by combining GT and Q to enhance the chemoprevention of prostate cancer in a non-toxic manner. This was associated with an increased bioavailability of non-methylated GTPs and enhanced anti proliferative and proapoptotic effect. These results warrant future human intervention studies to confirm the combined effect of GT and Q in prostate cancer prevention and treatment.

Biography

Piwen Wang recebeu seu diploma de MD em 2000 e seu diploma de MS em 2003 pela Shandong Medical University, China. Ele concluiu seu doutorado em 2008 pela Texas Tech University e estudos de pós-doutorado no UCLA Center for Human Nutrition. Atualmente, ele é professor assistente no Departamento de Medicina Interna, Divisão de Pesquisa e Treinamento em Câncer na Charles R Drew University of Medicine and Science. Ele publicou mais de 20 artigos em periódicos de renome e tem atuado como revisor de pares para vários periódicos científicos.

NOTA: Este trabalho foi parcialmente apresentado na 4ª Conferência e Exposição Internacional sobre Nutrição, realizada de 26 a 28 de outubro de 2015 em Chicago, Illinois, EUA.