Elsevier

Bioorganic & Medicinal Chemistry

Volume 21, Issue 22, 15 November 2013, Pages 7182-7193
Bioorganic & Medicinal Chemistry

Antiproliferative, antiandrogenic and cytotoxic effects of novel caffeic acid derivatives in LNCaP human androgen-dependent prostate cancer cells

https://doi.org/10.1016/j.bmc.2013.08.057Get rights and content

Abstract

Caffeic acid and its naturally occurring derivative caffeic acid phenethyl ester (CAPE) have antiproliferative and cytotoxic properties in a variety of cancer cell lines without displaying significant toxicity toward healthy cells, and are considered to be potential anticancer agents. However, little is known about their effects on prostate cancer cells. We synthesized and evaluated the effects of caffeic acid, CAPE (2) and 18 synthetic derivatives on cell viability and androgen-dependent cell proliferation, subcellular localisation and expression of androgen receptor (AR) and secretion of prostate-specific antigen (PSA) in LNCaP human hormone-dependent prostate cancer cells. Several synthetic derivatives of CAPE were strong, concentration-dependent cytotoxic agents in LNCaP cells with IC50 values in the 6.8–26.6 μM range, potencies that were up to five-fold greater than that of CAPE (33.7 ± 4.0 μM). A number of caffeic acid derivatives were inhibitors of androgen-stimulated LNCaP cell proliferation with concomitant inhibition of DHT-stimulated PSA secretion. Compound 24 was the most cytotoxic and antiproliferative caffeic acid derivative (IC50 values of 6.8 ± 0.3 and 2.4 ± 0.8 μM, respectively) inhibiting DHT-stimulated cell proliferation and PSA secretion statistically significantly at concentrations as low as 0.3 μM. Exposure to DHT increased cytoplasmic and nuclear AR levels and co-treatment with increasing concentrations of compound 24 or CAPE (2), notably, further increased these levels. In conclusion, a number of synthetic derivatives of caffeic acid are potent inhibitors of androgen-dependent prostate cancer cell proliferation and viability, acting, at least in part, via an antiandrogenic mechanism that involves increased nuclear accumulation of (presumably inactive) AR.

Introduction

The incidence of certain (longevity-corrected) cancers is increasing in the West, including that of various hormone-dependent cancers such as those of the breast, testis and prostate. In Western men, prostate cancer is now the most common malignancy (accounting for 30% of newly diagnosed cancers) and the third leading cause of cancer-related death. The burden of human suffering and cost to society are expected to increase significantly in the coming decades due to increased life-expectancy.1, 2 In the United States alone the number of new cases is expected to grow from 241,740 in 2012, a year that will see 28,170 prostate cancer deaths, to 350,000 by 2025.3 The Canadian Cancer Society predicts 26,500 new cases and 4000 prostate cancer deaths for 2012.4 Poor nutrition has been implicated as an important risk factor in these developments. Epidemiological studies consistently associate a life-time of high plant-derived consumption with reduced risk of developing cancer.5, 6, 7 Unfortunately, a generation of people has been raised on a high fat, carbohydrate and protein diet, low in fibre and plant-derived nutrients. A plant-derived diet contains a large variety of phytochemicals purported to have many health benefits, including protection against cancers such as that of the prostate.8, 9, 10

Caffeic acid (1, Fig. 1) is found in relatively high concentrations in many plants as a key intermediate in the biosynthesis of lignins. Caffeic acid and its naturally occurring derivative caffeic acid phenethyl ester (CAPE) (2, Fig. 1), which is found in high concentrations in propolis of the honeybee hive have anticancer properties, as well as immunomodulatory, anti-inflammatory and antioxidant effects. Caffeic acid (1) and CAPE (2) have been found to have antiproliferative and cytotoxic properties in a variety of (nonprostate) cancer cell lines11, 12 without displaying significant toxicity toward healthy cells. Only sporadically have the effects of CAPE been evaluated in prostate cancer cells. CAPE (2) has inhibitory effects on steroid 5 alpha-reductase (SRD5A)13 and the transcription factor NF-κβ,14 which is involved in the activation of many cellular processes including cell proliferation and survival. Although either of these targets may contribute to the antiprostate cancer activity of CAPE (2), the relatively high concentrations required for inhibition suggest that other not yet established targets are likely of greater importance in explaining the growth inhibitory effects of CAPE (2), which we have found to be evident at lower concentrations. Recently, a study showed that a number of transcription factors involved in cell survival were inhibited and that the tumor suppressor gene KLF6 and cyclin-dependent kinase inhibitor p21 were upregulated in PC-3 androgen-independent prostate cancer cells treated with 20 μM of CAPE (2).15 However, no studies to date have systematically evaluated synthetic analogs of caffeic acid or CAPE (2) to search for molecules with improved biological potencies against prostate cancer cell growth. Also, neither CAPE (2) nor other caffeic acid derivatives have been studied in detail in hormone-dependent prostate cancer cells, which generally represents an early stage of the disease. The potential for synthetic variations on the caffeic acid pharmacophore with potent anticancer activities was emphasised recently in a review by one of our laboratories.16 Given the biological significance of the caffeic acid pharmacophore, we hypothesised that certain derivatives of caffeic acid will have potent anticancer activities against human prostate tumor cells, and may be suitable for the development of chemotherapeutic agents effective against hormone-dependent as well as -independent prostate cancer. To test part of this hypothesis the objective of the present study was to synthesize a series of caffeic acid alkyl- and aryl ester-derivatives and determine their antiproliferative, antiandrogenic and cytotoxic potencies in androgen-dependent LNCaP prostate cancer cells. Also, because of the presence of a redox-active catechol group in each molecule, the radical scavenging activity of the newly synthesized caffeic acid derivatives was evaluated.

Section snippets

Synthesis strategy

The strategy for synthesis of the alkyl esters is outlined in Scheme 1. Compounds 38 were prepared by esterification with selected alcohol and commercially available caffeic acid (1) in the presence of sulfuric acid; the overall yield was about 80–90%.

The synthesis of the aryl esters of caffeic acid is depicted in Scheme 2. First, the two hydroxyl groups of caffeic acid (1) were protected by acetate groups in acetic anhydride in the presence of sodium hydroxide. Esters 1021 and an amide 22

Discussion

Our study is the first to describe the synthesis of a series of novel caffeic acid derivatives and to evaluate their cytotoxic effects on androgen-dependent prostate cancer cells. We further provide the first evidence that caffeic acid derivatives including CAPE (2) are capable of inhibiting androgen-dependent LNCaP prostate cancer cell proliferation with certain caffeic acid derivatives having potencies up to five-fold greater than that of naturally occurring CAPE (2). Structure–activity

Conclusion and perspectives

Our present study points at the androgen receptor and its signaling pathway as one of the targets for inhibition of cell proliferation of human androgen-dependent prostate cancer cells by certain derivatives of caffeic acid, including CAPE (2). We have also demonstrated that certain caffeic acid derivatives and, in particular, compound 24, a cyclohexyl-substituted analog of CAPE (2), has potent cytotoxic effects in LNCaP cells. These findings suggest that caffeic acid derivatives with potent

General

All chemicals for the syntheses were purchased from Aldrich. Purification of compounds was carried out by silica gel circular chromatography (Chromatotron®, model 7924, Harrison Research, Palo Alto, CA, USA). Thin layer chromatography (TLC) was performed on silica gel coated aluminum sheets (SiliaPlate TLC, Silicycle®) with detection by UV light (254 nm, UVS-11, Mineralight® shortwave UV lamp). Melting points were obtained using a MEL-TEMP® (model 1001D) melting point apparatus. FTIR spectra

Acknowledgements

This work was funded by the Natural Sciences and Engineering Research Council of Canada (J.T.S.; Grant No. 313313-2012) for the development of structure–activity relationships of endocrine-active molecules as well as by the New Brunswick Health Research Foundation and the New Brunswick Innovation Foundation (M.T.) in support of the synthesis of bioactive molecules. C.P. was supported by an undergraduate bursary from the Fondation Armand-Frappier, and A.F.P. and M.J.G.H. by fellowships from the

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  • Cited by (0)

    Correspondence regarding the synthesis of caffeic acid derivatives to M.T.

    Correspondence regarding the biological activities of caffeic acid derivatives to J.T.S.

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