Anticancer Principles from Medicinal Piper (胡椒 Hú Jiāo) Plants

Abstract

The ethnomedical uses of Piper (胡椒 Hú Jiāo) plants as anticancer agents, in vitro cytotoxic activity of both extracts and compounds from Piper plants, and in vivo antitumor activity and mechanism of action of selected compounds are reviewed in the present paper. The genus Piper (Piperaceae) contains approximately 2000 species, of which 10 species have been used in traditional medicines to treat cancer or cancer-like symptoms. Studies have shown that 35 extracts from 24 Piper species and 32 compounds from Piper plants possess cytotoxic activity. Amide alkaloids account for 53% of the major active principles. Among them, piplartine (piperlongumine) shows the most promise, being toxic to dozens of cancer cell lines and having excellent in vivo activity. It is worthwhile to conduct further anticancer studies both in vitro and in vivo on Piper plants and their active principles.

INTRODUCTION

Natural products from plants are important sources of new drugs.[1] The genus Piper (胡椒 Hú Jiāo) (Piperaceae), which contains approximately 2000 plant species distributed mainly in tropical areas,[2] is a potential source of drugs based on the use of some Piper species in traditional medicine. For example, nearly 30 out of 60 indigenous Chinese Piper species are used medically.[3,4,5,6,7,8] Our recent ethnobotanical and medicinal chemistry research focused on Piper plants led to the discovery of cytotoxic amides from Piper boehmeriifolium Wall.,[8,9,10,11] an anticancer medicine used in India.[12] In China, Piper plants are also used in some formulae to treat cancers.[13,14] The present paper reviews the traditional uses and scientific evidence for Piper natural products as anticancer agents. We reviewed the scientific articles that were published between 1970 and 2013 from Web of Science, SciFinder, and Google Scholar. We used the following search terms: Piperaceae, Piper, anticancer, antitumor, cytotoxicity, and ethnobotany. No restrictions regarding the language of publication were imposed, but most of the relevant studies were published in English and Chinese. Both plant extracts and compounds were found to show good in vitro cytotoxic activity with concentration giving 50% inhibition (IC₅₀) values less than 30 μg/ml and 4 μg/ml, respectively, and some compounds showed significant in vivo antitumor activity with 50% inhibition of tumor growth at concentrations less than 15 mg/kg body weight in mice.[15]

PIPER PLANTS WITH TRADITIONAL ANTICANCER APPLICATION

In the literature, 10 Piper (胡椒 Hú Jiāo) species have been reported to treat cancer or cancer-like symptoms, as summarized in Table 1.

Table 1.

List of Piper plants used traditionally against cancer or cancer-like symptoms

In Mexico, Piper aduncum L. is traditionally used to treat urological problems, dermatological conditions, and skin tumors.[15] Dichloromethane extracts of P. aduncum leaf were marginally cytotoxic to glioma (SF-268), human large cell lung carcinoma (H-460), and human breast carcinoma (MCF-7) cell lines with IC₅₀ values of 23, 25, and 27 μg/ml, respectively [Table 2].[16] Piperaduncin A [27 in Figure 1] a dihydrochalcone from this plant, showed growth inhibitory activity against human nasopharynx carcinoma (KB) cells (IC₅₀ = 2.3 μg/ml) [Table 3].[17]

Table 2.

Cytotoxic crude extracts from Piper plants

Figure 1.

Cytotoxic non-alkaloid constituents from Piper plants

Table 3.

Cytotoxic principles from Piper plants

In the Ayurvedic system of Indian medicine, the roots of P. boehmeriifolium Wall. and Piper sylvaticum Roxb. are used for their laxative, anthelmintic, and carminative properties, as well as to treat bronchitis, diseases of the spleen, and tumors.[12] Recently, a cytotoxic amide alkaloid, 1-[(9E)-10-(3,4-methylenedioxyphenyl)- 9-decenoyl] pyrrolidine [7 in Figure 2], was isolated from the whole plant of P. boehmeriifolium. This compound exhibited an IC₅₀ of 2.7 μg/ml against human cervical carcinoma human cervix adenocarcinoma (HeLa) cells [Table 3].[11] The amide alkaloid piplartine [1 in Figure 2, Tables 3 and 4] might be responsible for the anticancer effect of P. sylvaticum.[18]

Figure 2.

Cytotoxic amide alkaloids from Piper plants

Table 4.

Compounds from Piper plants with antitumor activity in vivo

Piper capense L.f. is reported to treat cancer in Cameroon; however, details about its ethnomedical uses are not included in the literature references.[19,20] Methanolic extracts of the seed are cytotoxic toward many tumor cell lines, including human leukemic lymphoblast (CCRF-CEM; IC₅₀ = 7.03 μg/ml), human acute T-lymphoblastic leukemia (CEM/ADR5000; IC₅₀ = 6.56 μg/ml), human pancreatic adenocarcinoma (Mia PaCa2; IC₅₀ = 8.92 μg/ml), p53-expressing human colon cancer cell (HCT116 p53^+/+; IC₅₀ = 4.64 μg/ml), p53-knockout human colon cancer cell (HCT116 p53⁻/⁻; IC₅₀ = 4.62 μg/ml), human hepatocarcinoma (Hep-G2; IC₅₀ = 16.07 μg/ml), human myeloid leukemia (HL-60; IC₅₀ = 8.16 μg/ml), anthracycline-resistant HL-60 (HL-60AR; IC₅₀ = 11.22 μg/ml), human breast carcinoma (MDA-MB-231; IC₅₀ = 4.17 μg/ml), MDA-MB-231BCRP (IC₅₀ = 19.45 μg/ml), human malignant glioblastoma (U87MG; IC₅₀ = 13.48 μg/ml), EGFRvIII expressing glioma cells (U87MGΔEGFR; IC₅₀ = 7.44 μg/ml), etc.[19,20] Piperine [6 in Figure 2 and Table 3] might be an active constituent.[21,22]

A recent ethnopharmacological study in Morocco calculated the percent importance of 14 plants selected by 100 herbalists for significance against cancer. Piper cubeba (蓽澄茄 Bì Chéng Qié) was one of the most important plants against cancer.[23] Lignans, such as (-)-cubebin, are the major constituents of P. cubeba.[24] Research results show that the P. cubeba extract (P9605) and the synthetic lignan cubebin might have potential therapeutic use against prostate cancer growth by targeting multiple aspects of the androgen-signaling pathway.[25,26]

In Papua New Guinea, a patient with suspected cancer or other internal sores drinks the juice squeezed from heated bark of Piper gibbilimbum C.DC. with traditional ash salt.[27] Gibbilimbols D (IC₅₀ = 2.1 μg/ml) [19 in Table 3] and B (IC₅₀ = 3.9 μg/ml) [20 in Table 3] from this plant are cytotoxic toward KB cells.[28]

The seed of the Nigerian plant Piper guineense Schum and Thonn reportedly possesses anticancer properties.[29] The plant is also reported to treat cancer in Cameroon.[20] A methanolic extract of its seed was cytotoxic against leukemia CEM/ADR5000 cells (IC₅₀ = 8.20 μg/ml).[20] However, the active constituents remain unclear.

Piper longum L. (syn. Piper latifolium Forst.) is a well-known tropical food and medicinal plant. In traditional medical practice in the Cook Islands, 12 leaves of this plant and a similar number of those of Thespesia populnea (L.) Soland (Malvaceae) are pounded in a wooden bowl with little water and the solution is washed on the chest of a person with suspected breast cancer.[30] P. longum is also used to treat tumors in Indian Ayurvedic medicine. Piplartine,[18] cepharadione A (15), and piperolactams A (16) and B (17) are the active principles.[31,32]

In Thailand, the root of Piper nigrum L. (black pepper plant), in the form of ghee, powders, enemas, and balms, is applied to abdominal tumors. The plant can also be used to treat abdominal fullness, adenitis, cancer, cholera, cold, colic, kidney stone, and headache.[33] Black pepper (黑胡椒 Hēi Hú Jiāo) is used in some formulae to treat respiratory or gastric cancers in China.[13,14] Piperine might be the major active principle from P. nigrum.[22,34]

In Bolivia, a reported Piper species known as Tudhar is used to treat uterine cancer.[35] However, the scientific name of the plant was not confirmed.

EXTRACTS FROM PIPER PLANTS WITH CYTOTOXIC ACTIVITY IN VITRO

Many crude extracts from Piper (胡椒 Hú Jiāo) plants have been evaluated for in vitro cytotoxicity based on ethnomedical knowledge, chemotaxonomic information, or random screening. Among them, 35 extracts of 24 Piper species have shown inhibitory activity (IC₅₀ < 30 μg/ml) against at least one tumor cell line [Table 2]. Extracts from P. aduncum L., Piper barbatum Kunth, Piper fragile Benth., Piper jacquemontianum Kunth, and Piper pellucidum L. showed the highest potential against at least one tumor cell line, with an IC₅₀ value less than 4 μg/ml.[16,36]

COMPOUNDS FROM PIPER PLANTS WITH CYTOTOXIC ACTIVITY IN VITRO

Chemical constituents of Piper (胡椒 Hú Jiāo) plants mainly include amide alkaloids, phenylpropanoids, lignans, neolignans, terpenes, steroids, kawapyrones, piperolides, flavonoids, and alkenylphenols.[9,45,46,47] Thirty-two compounds (1-32) have been reported to exhibit cytotoxic activity toward at least one tumor cell line with an IC₅₀ value less than 4 μg/ml [Table 3]. These compounds include amide alkaloids (1-17), a lignan (18), alkenylphenols (19-22), chalcones and dihydrochalcones (25-27), piperolides (28-31), and other chemical classifications. The amide alkaloids account for 53% of the total active principles. Chabamide G [13 in Figure 2 and Table 3] and sintenpyridone [5 in Figure 2 and Table 3] exhibited the most potent activity against human colon adenocarcinoma (COLO-205; IC₅₀ = 0.018 μg/ml) and HT-29 (IC₅₀ = 0.025 μg/ml) cell lines, respectively.[48] Piplartine is the most promising compound showing toxicity against dozens of cell lines along with significant in vivo activity [Tables 3 and 4].[18,49,50,51,52,53]

COMPOUNDS FROM PIPER PLANTS WITH ANTITUMOR ACTIVITY IN VIVO

A few Piper (胡椒 Hú Jiāo) compounds have been studied for in vivo antitumor activity. Piplartine (1) and flavokawain B [26 in Figure 1] exhibited significant inhibitory effects on the growth of at least one tumor cell line in vivo at concentrations less than 15 mg/kg body weight [Table 4]. Piplartine was tested against xenograft models of human bladder carcinoma (EJ), human breast carcinoma (MDA-MB436), human alveolar carcinoma epithelial (A549), murine melanoma (B16-F10), and MMTV-polyomavirus middle T antigen transgenic mice model (MMTV-PyVT). Animals were treated for 13 or 21 days at a dose of 1.5 or 2.4 mg/kg/day. Marked antitumor effects were observed in the treated tumor-bearing mice with inhibition rates near those with positive controls, paclitaxel (10 mg/kg/day) and cisplatin (1 mg/kg/day).[67] In addition, flavokawain B treatment (0.75 mg/kg/day) significantly inhibited in vivo growth of human KB cell-derived tumor xenografts in nude mice.[68]

ANTICANCER MECHANISMS OF ACTION OF PIPER COMPOUNDS

Piplartine

Piplartine, also known as piperlongumine, comprises approximately 0.11% content in the fruit of P. longum.[18,69] The compound kills cancer cells by targeting the stress response to reactive oxygen species (ROS). Piplartine induces apoptosis selectively in cells that have a cancer genotype by targeting a non-oncogene co-dependency acquired through expression of the cancer genotype in response to transformation-induced oxidative stress.[67] Structure-activity relationships suggest that the electrophilicity of the C2-C3 olefin is critical for the observed effects on cancer cells.[70] The latest studies suggest that cancer cell lines are more resilient to chemically induced increases in ROS levels than previously thought and highlight that electrophilicity may be more closely associated with cancer-selective cell death than ROS elevation.[71]

Piplartine may target p38 signaling to cause selective killing of cancer cells and autophagy.[72,73] Research results suggest that the anticancer activity of piplartine involves inhibition of the ubiquitin-proteasome system at a pre-proteasomal step, prior to de-ubiquitination of malfolded protein substrates at the proteasome, and that the previously reported induction of ROS is a consequence of this inhibition.[74]

Piplartine can down-regulate Epstein–Barr virus encoded latent membrane protein 1 (EBV-encoded LMP1), cellular myelocytomatosis oncogene (Myc), constitutive nuclear factor kappa B (NF-κB) activity, and a host of LMP1-Myc-NF-κB-regulated target genes, while the LMP1-NF-κB-Myc axis plays the central role in B-lineage neoplasia.[51] Piplartine-dependent cytotoxicity is affected in part by reduced NF-κB and Myc activity.[50]

Piplartine induces rapid depletion of the androgen receptor in prostate cancer cells. Consequently, piplartine may afford novel opportunities for both prevention and treatment of prostatic malignancy.[75] Piplartine may act, at least in part, on the mitogen-activated protein kinase (MEK)/extracellular signal-regulated kinase (ERK) pathway to cause colon cancer cell death.[76]

Piperine

Piperine (6) is a major component of black (P. nigrum) and long (P. longum) pepper. The content of piperine in black pepper varies between 5% and 9%.[77] Piperine can inhibit human fibrosarcoma (HT-1080) cell expression of matrix metalloproteinase (MMP)-9, thereby interfering with tumor cell migration and invasion.[78] Piperine inhibits HER2 gene expression at the transcriptional level implying that it may be a potential agent for the prevention and treatment of human breast cancer with HER2 overexpression.[79] Piperine-induced cytotoxicity against human rectal tumor (HRT)-18 cells may be mediated at least in part by ROS.[80] Piperine also exhibits an antiproliferative effect on human prostate cancer cells by inducing cell cycle arrest and autophagy.[81]

Flavokawain B

Kava (Piper methysticum Forst.) is a perennial plant indigenous to the Pacific Islands. Some data indicate that the more kava consumed by a population, the lower the cancer incidence in that population.[82] Flavokawain B, constituting about 0.015% of kava extracts, appears to be a potent antiproliferative agent against a wide variety of cancer cells.[83,84] Flavokawain B–induced apoptosis, at least in part, requires Bim expression.[66] In KB cells, the induction of apoptosis by flavokawain B may involve both the death receptor and mitochondrial pathway.[68] Flavokawain B also has a pro-apoptotic effect on synovial sarcomas cell lines.[85] Flavokawain B induces apoptosis of non-small cell lung cancer H-460 cells via Bax-initiated mitochondrial and c-Jun N-terminal kinase (JNK) pathways.[86] In osteosarcoma cell lines, apoptotic induction by flavokawain B involves both extrinsic and intrinsic pathways. Flavokawain B also causes G2/M phase cell cycle arrest.[64]

CONCLUSION

Piper (胡椒 Hú Jiāo) plants are important sources for research on and development of new anticancer agents. Ten Piper plants have been used as traditional medicines to treat cancer or cancer-like symptoms. In various studies, 35 extracts from 24 Piper species and 32 compounds from Piper plants were found to possess in vitro cytotoxic activity. Among them, the amide alkaloid piplartine (1) represents the most promising candidate showing cytotoxicity against dozens of cell lines, together with excellent in vivo activity. Piper plants comprise about 2000 species, most of which have not been studied for their chemical constituents and anticancer effects. Thus, further in vitro and in vivo anticancer research studies on Piper plants and their isolates are worthwhile.

ABBREVIATIONS USED

143B, human osteosarcoma; 4T1, murine mammary carcinoma; A549, human alveolar carcinoma epithelial; A2780, human ovarian carcinoma; B-16, murine melanoma; B16-F10, murine melanoma; BCRP, breast cancer resistance protein; C4-2B, human prostate cancer; CCRF-CEM, human leukemic lymphoblast; CEM, human lymphoblastic leukemia; CEM/ADR5000, human acute T-lymphoblastic leukemia; CHCl₃, chloroform; CH₂Cl₂, dichloromethane; COLO-205, human colon adenocarcinoma; DU-145, human prostate carcinoma; EAT, Ehrlich ascites tumor; EBV, Epstein Barr virus; EJ, human bladder carcinoma; ERK, extracellular signal-regulated kinase; EtOH, ethanol; MCF-7, human breast carcinoma; H-460, human large cell lung carcinoma; HCT116 p53^+/+, p53-expressing human colon cancer cell; HCT116 p53^−/−, p53-knockout human colon cancer cell; HeLa, human cervix adenocarcinoma; HEp-2, human laryngeal carcinoma; Hep-G2, human hepatocarcinoma; IC₅₀, concentration giving 50% inhibition; HL-60, human myeloid leukemia; human promyelocytic leukemia; HL-60AR, anthracycline-resistant HL-60; HRT-18, human rectal tumor; HT-1080, human fibrosarcoma; K562, human erythromyeloblastoid leukemia; KB, human nasopharynx carcinoma; LNCaP, human prostate carcinoma; MCF-7, human breast carcinoma; MDA-MB-231, human breast carcinoma; MDA-MB436, human breast carcinoma; MEK, mitogen-activated protein kinase; MeOH, methanol; Mia PaCa2, human pancreatic adenocarcinoma; MMTV-PyVT, MMTV-polyomavirus middle T antigen transgenic mice model; Molt-4, human lymphocytic leukemia; NCI-H460, human non-small cell lung cancer; NF-κB, nuclear factor kappa B; P-388, mouse lymphocytic leukemia; PC-3, human prostate adenocarcinoma; PE, petroleum ether; ROS, reactive oxygen species; SF-268, glioma; SK-LMS-1, human leiomyosarcoma; SK-MEL-2, human skin melanoma; U87MG, human malignant glioblastoma; U87MGΔEGFR, EGFRvIII expressing glioma cells; WPMY-1, human prostatic stromal myofibroblast.