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Journal of Natural Medicines

, Volume 70, Issue 3, pp 335–360 | Cite as

Screening of promising chemotherapeutic candidates from plants extracts

  • Junei Kinjo
  • Daisuke Nakano
  • Toshihiro Fujioka
  • Hikaru Okabe
Open Access
Review Biologically Active Natural Products from Microorganisms and Plants

Abstract

Over the course of our studies investigating anti-proliferative properties of compounds originating from plants against human gastric adenocarcinoma (MK-1), human uterine carcinoma (HeLa), murine melanoma (B16F10), and two human T cell lymphotropic virus type 1 (HTLV-1)-infected T-cell lines (MT-1 and MT-2), we have screened 582 extracted samples obtained from a variety of parts from 370 plants. A few extracts showed anti-proliferative activity against all cell lines, but upon further investigation, toxicity toward selected cell lines was recognized. After activity-guided fractionation, isolation of the active principles was achieved. Structure–activity relationship studies identified the components and functionalities responsible for the specific selectivity against each cancer cell line. The effect of polyacetylenes against MK-1 cells was more potent than against HeLa and B16F10 cells. The compound having a 3,4-dihydroxyphenethyl group also showed an anti-proliferative effect against B16F10 cells. Some 6-methoxyflavone derivatives and 8-hydroxy furanocoumarins were good inhibitors of HeLa cell growth. The 17 compounds whose EC50 values were less than 1 nM did not show specific cellular selectivity. Because the cytotoxic effect of 24, 25-dihydrowithanolide D toward control cells was observed at a concentration about 100 times higher than those for the cancer cell lines, withanolide was identified as the most promising chemotherapeutic candidate in our experiments.

Keywords

Cancer cell lines Anti-proliferative activity Activity-guided fractionation Plant extracts Active principles Structure–activity relationship 

Introduction

Development of anti-neoplastic drugs is the focus of numerous research programs around the world. Plants are the richest source of novel chemical compounds and in fact, many natural product-derived compounds have been identified as chemotherapeutic candidates [1]. For instance, vinca alkaloids, podophyllotoxins, taxanes, and camptothecins are four main classes of compounds that are well-known anti-neoplastic drugs originating from plants [2]. It is significant that over 60 % of the currently used anti-neoplastic drugs are derived from natural sources including plants [3].

Over the course of our studies investigating the anti-proliferative characteristics of compounds originating from plants against human gastric adenocarcinoma (MK-1), human uterine carcinoma (HeLa), murine melanoma (B16F10), and two human T-cell lymphotropic virus type 1 (HTLV-1)-infected T-cell lines (MT-1 and MT-2), we have already reported many compounds active against cancer cell lines [4]. Herein, we report not only the screening results against the above cell lines but also the active principles and analysis of their structure–activity relationships.

Screening results

The 582 samples obtained from a variety of plant parts from 370 plants (302 genera, 104 families) were extracted with MeOH under reflux. The anti-proliferative effects of the extracts against the MK-1, HeLa, B16F10, MT-1, and MT-2 cell lines were evaluated (Table 1). The extracts listed in Table 1 are classified in the Angiosperm Phylogeny Group III system. The extracts of the leaves of Annona squamosa (Annonaceae), the aerial parts and roots of Tylophora tanakae (Asclepiadaceae), and the leaves of Thuja occidentalis (Cupressaceae) showed the most potent anti-proliferative activities against all cell lines. The extracts of the leaves of Annona cherimola (Annonaceae), the fresh leaves of Tylophora ovata and T. ovata var. brownii (Asclepiadaceae), twigs of T. ovata, the roots of Saussurea lappa (Asteraceae), the seeds of Luffa acutangula (Cucurbitaceae), the leaves of Juniperus rigida (Cupressaceae), the woods of Haematoxylum brasileto (Fabaceae), the rhizomes of Coptis japonica (Ranunculaceae), the roots of Ruta graveolens (Rutaceae), and the leaves of Cephalotaxus harringtonia (Taxaceae) showed decreasing levels of potency in the order listed. Homoharringtonine (Omacetaxine), a protein translation inhibitor for the treatment of chronic myelogenous leukemia, is found in the leaves of C. harringtonia [5]; therefore, the extract might show potent activity. There were a few extracts that had anti-proliferative activity against all cell lines and upon further investigation, toxicity toward selected cell lines was identified.
Table 1

Anti-proliferative activities of the plants extracts against MK-1, HeLa, B16F10, MT-1, and MT-2 cells

Family

Scientific name

Parts

MK-1

HeLa

B16F10

MT-1

MT-2

Acanthaceae

Dicliptera japonica

Aerial parts

+

Justicia procumbens

Whole part

+

+

****

**

Actinidiaceae

Actinidia chinensis

Fruits

+

+

++++

Adoxaceae

Sambucus chinensis

Leaves

Stems

Aizoaceae

Tetragonia expansa

Whole part

+

Amaranthaceae

Achyranthes fauriei

Roots

+++

++++

Celosia argentea

Seeds

Chenopodium ambrosidoides

Aerial parts

Chenopodium ambrosidoides var. anthelminticum

Leaves

+

+

Stems

NT

NT

Chenopodium graveolens

Aerial parts

++

+

+

**

Gomphrena globosa

Whole part

Amaryllidaceae

Allium sativum var. pekinense

Bulbs

+++

+

++++

Anacardiaceae

Mangifera indica

Barks

++++++

++++++

++++++

Leaves

+

+

++++

**

Peels

+

+

+

**

**

Pulp

Seeds

+++

+

++++

**

**

Annonaceae

Annona cherimola

Barks

+

+

****

****

Leaves

++++++

++++++

++++++

**

**

Annona muricata

Leaves

+++

+

++++++

Stems

+++++

+

++++++

**

Annona reticulata

Barks

+

heartwoods

+

NT

NT

Leaves

+++

+

+

********

********

Annona squamosa

Leaves

+++++

++++++

++++++

******

******

Twigs

+++

+++++

+++++

**

Apiaceae

Angelica acutiloba

Fruits

+

NT

NT

Leaves

NT

NT

Roots

Angelica dahurica

Fruits

++

+

**

**

Angelica decursiva

Aerial parts

Leaves

++

NT

NT

Fruits

+

+++

**

**

Roots

+

**

**

Angelica japonica

Fruits

++

++

NT

NT

Leaves

NT

NT

Roots

+++

NT

NT

Angelica keiskei

Aerial parts

+

Leaves

NT

NT

Fruits

+

Roots

+

++

**

**

Angelica kiusiana

Leaves

+

Angelica pubescens

Roots

+

+

+

Anethum graveolens

Fruits

NT

NT

Leaves

+

NT

NT

Roots

+++

NT

NT

Anthriscus cerefolium

Fruits

++

NT

NT

Anthriscus sylvestris

Fruits

++++++

++++++

++++++

NT

NT

Leaves

++++++

++++++

++++++

NT

NT

Roots

++++++

++++++

++++++

NT

NT

Bupleurum falcatum

Leaves

NT

NT

Bupleurum rotundifolium

Fruits

+++++

++

+++

NT

NT

Carum carvi

Fruits

++

+

NT

NT

Leaves

+

NT

NT

Roots

++++

+

NT

NT

Centella asiatica

Leaves

++

++

NT

NT

Aerial parts

+

+++

Cnidium monnieri

Fruits

++

++

+++

Cnidium officinale

Leaves

NT

NT

Rhizomes

+

Coriandrum sativum

Leaves

Fruits

++

++

NT

NT

Cryptotaenia japonica

Leaves

++

+

NT

NT

Foeniculum vulgare

Leaves

+

+

NT

NT

Glehnia littoralis

Fruits

+++++

+++

NT

NT

Heracleum moellendorffii

Leaves

+

NT

NT

Roots

+++

NT

NT

Osmorhiza aristata

Aerial parts

++++++

Roots

**

**

Peucedanum japonicum

Leaves

Stems, Root barks

+

+

**

**

Woods

Peucedanum praeruptorum

Roots

**

**

Torilis japonica

Fruits

++++

++++

NT

NT

Leaves

NT

NT

Roots

+++

+

NT

NT

Apocynaceae

Apocynum venetum

Whole part

+

+

Cerbera manghas

Barks

NT

NT

NT

**

**

Leaves

+++

++++

****

****

Trachelospermum jasminoides

Aerial parts

**

**

Trachelospermum liukiuense

Aerial parts

+

**

Aquifoliaceae

Ilex cornuta

Fruits

+

Leaves

+

+

**

****

Ilex kudingcha

Leaves

NT

NT

NT

Ilex latifolia

Leaves

+

Ilex rotumda

Fruits

**

**

Leaves

+

+

+

**

**

Araceae

Arisaema ringens

Tubers

+

+

Pinellia ternata

Tubers

Araliaceae

Aralia cordata

Roots

Aralia elata

Barks

+

++++

Leaves

+

+

Dendropanax trifidus

Barks

+

Fruits

+

Leaves

+

+

+++

Eleutherococcus senticosus

Root barks

+

**

**

Fatsia japonica

Barks

+

Leaves

+

Roots

+

Hedera rhombea

Fruits

+

Leaves

+

**

Stems

+

**

**

Hydrocotyle nepalensis

Aerial parts

+

Schefflera arboricola

Leaves

+

+

+

Tetrapanax papyriferum

Leaves

+++

++++

+

**

Woods

+

+

+

Araucariaceae

Araucaria heterophylla

Leaves

++++

+++++

++++++

Aristolochiaceae

Aristolochia spp.

Roots

+

+

****

****

Asarum nipponicum

Aerial parts

+

Roots

+

****

****

Asarum sieboldii

Roots

+

+

Asclepiadaceae

Asclepias curassavica

Leaves

+

++++

+

**

**

Roots

+++

++++

**

****

Stems

+++

++++

****

****

Cynanchum caudatum

Leaves

+

Marsdenia cundurango

Roots

Marsdenia tomentosa

Leaves

+

Stems

Asclepiadaceae

Metaplexis japonica

Aerial parts

NT

NT

Roots

Periploca spp.

Root barks

++++

+++

++

**

**

Tylophora ovata

Fresh leaves

++++

+++

++++

****

****

Twigs

+++++

+++++

+++++

****

****

Tylophora ovata var. brownii

Fresh leaves

++++++

++++++

++++++

****

****

Twigs

NT

NT

NT

Tylophora tanakae

Aerial parts

++++++

++++++

++++++

****

******

Roots

++++++

++++++

++++++

******

******

Asparagaceae

Anemarrhena asphodeloides

Roots, Rhizomes

**

**

Dracaena draco

Barks

+++

Leaves

++++

Ophiopogon japonicus

Tubers

Asteraceae

Achillea millefolium

Leaves

+

Stems

+

Adenocaulon himalaicum

Aerial parts

+

+

+

**

Roots

Adenostemma lavenia

Aerial parts

+

+

**

Arctium lappa

Roots

Seeds

+

++

Artemisia absinthium

Aerial parts

+

**

**

Leaves

Roots

+

+

**

**

Stems

Artemisia campestris

Aerial parts

Artemisia capillaris

Aerial parts

+

+

**

Roots

Artemisia ludoviciana var. mexicana

Aerial parts

+++

+

+++

Aster spathulifolius

Leaves

+

+++

**

**

Stems

+

+

**

**

Aster verticillatum

Aerial parts

+

+

Bidens frondosa

Aerial parts

+

+

+

Roots, Rhizomes

++++

++++

+++

**

**

Carthamus tinctorius

Flowers

Centaurea benedictus

Leaves

+

+

NT

NT

Chrysanthemum vulgare

Aerial parts

+

+

+

**

**

Cichorium intybus

Aerial parts

+

+

Roots

+

+

Cosmos bipinnatus

Seeds

Crassocephalum crepidioides

Aerial parts

+

Roots, Rhizomes

+

Crepidiastrum lanceolatum

Aerial parts

Roots

++++

++++++

++++++

Eclipta prostrata

Whole part

+

+

Eupatorium stoechadosmum

Leaves

Roots

+

+++

+

Stems

Euryops pectinatus

Leaves

+

Stems

Helianthus annuus

Aerial parts

**

**

Inula helenium

Roots

+++

+++

+++

NT

NT

Ligularia japonica

Leaves

**

Roots

Neurolaena lobata

Leaves

+

+

NT

NT

Parasenecio tebakoensis

Aerial parts

+

+

Santolina chamaecyparissus

Leaves

+

Stems

+++

Saussurea lappa

Roots

+++++

+++++

+++++

**

****

Senecio vulgaris

Whole part

Siegesbeckia glabrescens

Leaves

+

+

Roots

Sonchus asper

Aerial parts

+

Tagetes patula

Aerial parts

+

**

Roots

+

Tridax procumbens

Leaves

NT

NT

Tussilago farfara

Roots

+

+

Wedelia prostrata

Whole part

+

**

**

Xanthium strumarium

Fruits

Balsaminaceae

Impatiens textori

Aerial parts

+

**

**

Berberidaceae

Berberis japonica

Leaves

+

++

+++

**

Roots

+

+

++++

**

**

Stems

+

+

++++

**

****

Epimedium grandiflorum subsp.

Roots, Rhizomes

Epimedium sagittatum

Aerial parts

+++++

++++

++++

Nandina domestica

Barks

+

+

+++

**

Leaves

++

++++

Bignoniaceae

Pseudocalymma alliaceum

Aerial parts

+

**

Tabebuia spp.

Barks

+

+

+

**

**

Boraginaceae

Lithospermum officinale var. erythrorhizon

Roots

Brassicaceae

Isatis indigotica

Fruits

+

**

**

Leaves

Roots

Lepidium apetalum

Seeds

+++++

++++

**

**

Lepidium virginicum

Whole part

+

Thlapsi arvense

Seeds

Burseraceae

Bursera simaruba

Fruits

+

++

+

Leaves

+++

+

+

**

**

Woods

+

++

+

NT

NT

Campanulaceae

Codonopsis spp.

Roots

Cannabaceae

Humulus japonicus

Aerial parts

+

**

**

Caprifoliaceae

Lonicera japonica

Flowers

Leaves

+

+

Stems

+

Caricaceae

Carica papaya

Barks

Leaves

+

+

Roots

Caryophyllaceae

Agrostemma githago

Seeds

+

+

Vaccaria segetalis

Seeds

+

+

Celastraceae

Celastrus orbiculatus

Vines

Euonymus alatus

Barks

+++

NT

NT

Euonymus japonicus

Barks

+++

+

++++

**

**

Leaves

++

Maytenus diversifolia

Leaves

+

Stems

+++

+++

+++

NT

NT

Chloranthaceae

Sarcandra glabra

Roots

+++

+

Clusiaceae

Garcinia subelliptica

Barks

+

+

++++++

Heartwoods

Leaves

+

+

Garcinia xanthochymus

Leaves

+

NT

NT

Pulp

+

Seeds

+

+

**

**

Stems

+

+

+

NT

NT

Combretaceae

Terminalia chebula

Fruits

+

+++

++++

**

**

Commelinaceae

Commelina communis

Whole part

+

Cornaceae

Camptotheca acuminata

Fruits

+++++

++++

++++

**

**

Cornus officinalis

Fruits

Crassulaceae

Bryophyllum pinnatum

Aerial parts

+

+

Roots

+++++

+++++

+

**

****

Hylotelephium erythrosticum

Roots

+

+

++

Orostachys japonicus

Whole part

+

Sedum aizoon var. floribundum

Roots

+++

+

+++

Sedum tomentosum

Whole part

+

Cucurbitaceae

Actinostemma lobatum

Aerial parts

+

+

Citrullus colocynthis

Seeds

Gynostemma pentaphyllum

Aerial parts

Lagenaria leucantha var. gourda

Fruits

+++++

++++++

+

****

**

Leaves

+

Roots

+

+++

+

Seeds

++++

+++++

+

Stems

+++

+++

+

Lagenaria leucantha var. microcarpa

Fruits

+++++

+++++

+++

NT

NT

Seeds

++++

+++++

+++

Luffa acutangula

Aerial parts

+

+

+

**

**

Seeds

++

++++++

++++++

**

****

Luffa aegyptiaca

Fruits

Momordica charantia

Aerial parts

Fruits

NT

NT

Roots

Momordica cochinchinensis

Seeds

++++++

++++++

++++++

Sicana odorifera

Fruits

+

+

NT

NT

Trichosanthes kirilowii var. japonica

Roots

+++

++++

+

Cupressaceae

Biota orientalis

Leaves

++

+++

++++

**

**

Stems

+

+

+

Juniperus chinensis var. kaizuka Hort.

Leaves

+

++++

+

**

**

Stems

+

+

+

****

**

Juniperus rigida

Leaves

+++++

++++++

++++++

****

****

Stems

+

++++

++++

**

Thuja occidentalis

Leaves

++++++

++++++

++++++

******

******

Stems

+

++++

+++

******

**

Cycadaceae

Cycas revoluta

Leaves

+

Peels

+

Seed kernels

Daphniphyllaceae

Daphniphyllum macropodum

Barks

+

Leaves

+

Elaeocarpaceae

Elaeocarpus sylvestris var. ellipticus

Barks

+++

+++

++++

**

**

Leaves

+++

+

++++

**

Eucommiaceae

Eucommia ulmoides

Barks

**

**

Euphorbiaceae

Acalypha australis

Roots

++

+

+

Croton spp.

Leaves

+

+

Euphorbia helioscopia

Aerial parts

+

+

**

**

Roots

+

**

Euphorbia jolkini

Aerial parts

+

++

++++

Roots

+

++

++++

Euphorbia supina

Whole part

+++

+

+

Euphorbia tirucalli

Aerial parts

++

+

+

Hura polyandra

Seeds

+++

Fabaceae

Acacia melanoxylon

Barks

+++

+

+++

Leaves

+

+

+

**

Apios americana

Flowers

NT

NT

NT

Astragalus membranaceus

Roots

+

Canavalia gladiata

Roots

+

**

Seeds

+

**

**

Cassia obtusifolia

Seeds

+

+

Crotalaria juncea

Leaves

+

+

**

Seeds

Stems

+

Erythrina variegata var. orientalis

Barks

+

Euchresta japonica

Roots

+

**

Eysenhardtia polystachia

Woods

+

+

+++

Gliricidia sepium

Leaves

+

++

Glycyrrhiza pallidiflora

Underground parts

+

Glycyrrhiza uralensis

Roots

+

Haematoxylum brasileto

Woods

++++

+++

++++

****

****

Lonchocarpus oxacensis

Roots

+

NT

NT

Lonchocarpus unifoliolatus

Roots

+

NT

NT

Medicago polymorpha

Whole part

Melilotus officinalis

Whole part

+

Psoralea corylifolia

Seeds

++

++

++

**

Rhynchosia volubilis

Seeds

+++

++

++++

**

Sophora japonica

Fruits

+

**

**

Trifolium dubium

Aerial parts

+

Zornia spp.

Leaves

+

+

**

Gelsemiaceae

Gelsemium sempervirens

Leaves

+++

Stems

+

Geraniaceae

Pelargonium graveolens

Leaves

+++

+

++++

**

Stems

+++

+

++++

**

Iridaceae

Crocosmia aurea

Bulbs

Jugulandaceae

Juglans mandshurica var. sachalinensis

Barks

++

++

+++

Lamiaceae

Ajuga decumbens

Whole part

Ajuga reptans

Leaves

Roots

Caryopteris incana

Aerial parts

+

Clerodendron thomsonaiae

Leaves

NT

NT

Clerodendrum bungei

Flowers

Leaves

++

Stems

Clerodendrum trichotomum

Barks

+

+++

Flowers

Fruits

+

Leaves

+

+++

Elsholtzia ciliata

Aerial parts

+

+

Glechoma longituba

Whole part

Isodon japonicus

Leaves

+

+

++++

Roots

+

+

+

Stems

+

+

++++

Lamium amplexicaule

Whole part

Leonurus sibiricus

Aerial parts

**

**

Roots

+

Seeds

+

Rosmarinus officinalis

Leaves

+++

+

++++

**

**

Salvia miltiorrhiza

Roots

+

+

Scutellaria baicalensis

Roots

+

+

+

Scutellaria barbata

Whole part

+

**

**

Teucrium japonicum

Leaves

+++

Vitex trifolia

Branches

NT

NT

NT

Leaves

NT

NT

NT

Lauraceae

Cinnamomum cassia

Barks

+

+

+

**

**

Lindera strychnifolia

Roots

+

+

+

Persea americana

Leaves

+++++

++++++

++++++

Pulp

+

+++

+

Seeds

+

+

+

Twigs

+

+

+

Liliaceae

Fritillaria verticillata var. thungergii

Bulbs

+

Lythraceae

Cuphea hyssopifolia

Aerial parts

+

++

+

Roots

++

+

+

Punica granatum

Peels

+++

+

++++

**

**

Magnoliaceae

Magnolia ovata

Barks

+

+

+

Malvaceae

Abelmoschus manihot

Leaves

+

+

Althaea cannabina

Leaves

Chorisia speciosa

Immatured fruits

Corchoropsis tomentosa

Fruits

+

**

**

Leaves

+

+

+++

Stems

+

Gossypium arboreum

Leaves

+

+

++

Roots

+

+

++

Stems

+

+

Gossypium brasiliensis

Leaves

++

++

++

Roots

+

+

Stems

+

+

Malvaviscus arboreus

Leaves

+

Pachira macrocarpa

Barks

+

+

+

**

**

Leaves

+

+

**

Sterculia nobilis

Barks

Heartwoods

Leaves

++

+

+

**

**

Meliaceae

Melia azedarach var. toosendan

Fruits

++++

**

**

Menispermaceae

Cocculs trilobus

Fruits

+

Leaves

+

+

+

Vines

+

Stephania tetrandra

Roots

+

**

**

Tinospora tuberculata

Stems

Moraceae

Ficus carica

Leaves

+

Ficus pumila

Fruits

+

+

Leaves

+

+

+++

Stems

+

Morus alba

Root barks

Myristicaceae

Myristica fragrans

MeOH−oil

++

++

++

NT

NT

MeOH−ppt

+

Muntingiaceae

Muntingia calabura

Fruits

+

+

NT

NT

Leaves

+++

+

++

Myrtaceae

Eugenia javanica

Barks

+++

+++

++++

Leaves

+

+

+++

Eugenia uniflora

Leaves

+

+

+++

Twigs

+++

+

+++

**

Psidium cattleyanum

Branches

+++

+

+

**

Fruits

Leaves

+

+

+

Psidium guajava

Branches

+

+

+++

Leaves

+

+

+

Psidium littorale

Leaves

+

+

+++

Twigs

+++

+++

++++

**

Nyctaginaceae

Mirabilis jalapa

Leaves

+

**

Roots

+

+

+

Oleaceae

Ligustrum japonicum

Immatured fruits

+

+

Leaves

+

+

+++

NT

NT

Ligustrum lucidum

Fruits

+

+

Leaves

++

Ligustrum ovalifolium

Leaves

+

Ligustrum purpurascens

Leaves

+

+

+

Ligustrum salicinum

Leaves

+

+++

Orchidaceae

Dendrobium spp.

Aerial parts

+

+

+

Orobanchaceae

Cistanche deserticola

Stems

+

Oxalidaceae

Averrhoa carambola

Barks

+

Leaves

+

Paeoniaceae

Paeonia lactiflora

Roots

Papaveraceae

Corydalis heterocarpa var. japonica

Aerial parts

+

**

**

Roots

+

Corydalis turtschaninovii forma yanhusuo

Tubers

+

+

++

**

Macleaya cordata

Aerial parts

+++

+++

+++

Underground parts

+

+

+

**

**

Phrymaceae

Phryma leptostachya

Aerial parts

+

+

Roots

+

+

+

Phyllanthaceae

Phyllanthus aciduse

Leafstalks, Twigs

Leaves

+

Phyllanthus urinaria

Whole parts

+

+

++++

Phytolaccaceae

Petiveria alliacea

Leaves

+

+

+++

NT

NT

Phytolacca americana

Roots

Rivina humilis

Aerial parts

+

Piperaceae

Piper spp.

Leaves

+

+

**

**

Pittosporaceae

Pittosporum tobira

Barks

Fruits

+

+

+

Leaves

+

+

Peels

+

+

+

**

**

Plantaginaceae

Pentstemon gloxinioides

Leaves

+

Rhizomes

+++

Stems

+

Picrorhiza scrophulariiflora

Rhizomes

+

Russelia equisetiformis

Aerial parts

+

++++

Plumbaginaceae

Plumbago capensis

Whole part

+

+

+

Podocarpaceae

Podocarpus macrophyllus

Leaves

+

+

+++

Stems

+

+

++++

Polygalaceae

Polygala tenuifolia

Roots

Polygonaceae

Fallopia japonica

Roots

+

+

+

Polygonum orientale

Seeds

+

+

+++

Polygonum tinctorium

Whole part

**

**

Rheum palmatum

Rhizomes

+++

+

++++

Rumex acetosa

Roots, Rhizomes

+

**

**

Rumex japonicus

Roots, Rhizomes

++

**

Polypodiaceae

Drynaria fortunei

Rhizomes

+

Phleboidum aureum

Dried roots

+

+

Fresh roots

+

**

Whole part

+

+

Portulacaceae

Portulaca oleracea

Whole part

+

+

**

Primulaceae

Ardisia crenata

Leaves

+++

Roots

++++

+

+++

****

****

Stems

+++

Ardisia japonica

Leaves

+

+

+

Stems, Undergorund parts

+

+

+++

Lysimachia japonbica

Whole part

+

Proteaceae

Macadamia ternifolia

Leaves

+

+

+++

Twigs

+++

++

+++

NT

NT

Pteridaceae

Pteris multifida

Aerial parts

Roots, Rhizomes

+

+

+

Ranunculaceae

Cimicifuga simplex var. ramosa

Aerial parts

+

Underground parts

+

Clematis paniculata

Aerial parts

+

+

Coptis japonica

Rhizomes

+++++

+++++

++++++

**

**

Thalictrum thunbergii

Aerial parts

+

Underground parts

+++

Rhamnaceae

Berchemia racemosa

Leaves

+

Stems

+

Hovenia dulcis

Fruits

+

Zizyphus jujube var. jujuba

Fruits

Zizyphus jujube var. spinosa

Seeds

++

+

Rehmanniaceae

Rehmannia glutinosa var. purpurea

Roots

Rosaceae

Agrimonia pilosa

Whole part

++

Chaenomeles sinensis

Fruits

+

+

+++

Crataegus cuneata

Fruits

+

Eryobotrya japonica

Barks

+

+

+

Leaves

+

Seeds

+

Geum japonicum

Aerial parts

+

+

+

Roots

+

+

+++

Potentilla chrysantha

Whole part

+

Potentilla fragarioides var. major

Aerial parts

+

Underground parts

+

+

+++

**

**

Potentilla indica

Whole part

+

+

Prunus armeniaca

Seeds kernels

+

Rosa multiflora

Fruits

+

Rubus hirsutus

Aerial parts

+

Roots

+

+

Sanguisorba officinalis var. carnea

Roots

++

++

++++

Rubiaceae

Damnacanthus macrophyllus var. macrophyllus

Leaves

++

++

Roots

Stems

Galium pogonanthum

Aerial part

+

**

Hamelia patens

Leaves, Twigs

+

++

Hedyotis diffusa

Whole part

Paederia scandens

Fruits

+

+

Leaves

Stems

Rubia argyi

Roots

++++

++++

++++

**

**

Uncaria rhynchophylla

Hooks

++

Rutaceae

Boenninghausenia japonica

Aerial parts

+

+++

+

**

**

Roots

+++

++++

+

******

**

Citrus grandis

Peels

+

Citrus natsudaidai

Immatured fruits

Evodia rutaecarpa

Barks

+

Fruits

+++

+++

++++

Orixa japonica

Leaves

+

+

+

Stems

+

Phellodendron amurense

Barks

+

++

+++++

**

****

Ruta graveolens

Aerial parts

+

++++

**

**

Leaves

+

+

+

**

****

Roots

++++

+++++

+++

**

****

Zanthoxylum ailanthoides

Barks

+

+

+++

**

**

Fruits

+

**

Leaves

+

**

**

Woods

+

**

Zanthoxylum bungeanum

Peels

+

**

**

Sapindaceae

Aesculus turbinata

Seeds

++

Cardiospermum halicacabum

Seeds

+

Dimocarpus longan

Leaves

+++

+

+++

Twigs

+++

+

+++

Litchi chinensis

Leaves

+

+

+++

Twigs

+++

+

+

Sapindus mukurossi

Peels

+++

+++

+++

****

**

Seeds

+

Sapotaceae

Chrysophyllum cainito

Leaves

+

+

+

NT

NT

Pouteria sapota

Seeds

+

Schisandraceae

Kadsura japonica

Leaves

+

Vines

+

+

**

Schisandra chinensis

Fruits

Scrophlariaceae

Scrophularia buergeriana

Roots

Verbascum thapsus

Leaves

+

Simaroubaceae

Picrasma quassioides

Woods

+

+

+

Smilacaceae

Smilax china

Rhizomes

+

+

+++

Smilax medica

Rhizomes

+

+

+

Solanaceae

Brunfelsia latifolia

Leaves

+

+

Nicandra physalodes

Fruits

Leaves

+

+++

Roots

+++

+++

Stems

Physalis angulata

Aerial parts

++++

+++

+++

Roots

Physalis pruinosa

Aerial parts

++++++

+++

+++

**

**

Roots

+++++

+

+++++

****

****

Solanum mammosum

Aerial parts

+

+

Roots

+

Solanum nigrum

Aerial parts

+

**

Fruits

+

+

+

**

Roots

+

+

+++

**

**

Taxaceae

Cephalotaxus harringtonia

Leaves

++++

++++

++++

****

****

Stems, Twigs

+++++

++++

+++++

Torreya grandis

Seeds

++

+

+++

Theaceae

Camellia sinensis

Leaves

++

NT

NT

NT

NT

Thymelaeaceae

Daphne genkwa

Flowers

+

+

+

**

**

Daphne odora

Roots

++++

Edgeworthia chrysantha

Roots

+

Urticaceae

Cecropia obtusifolia

Fresh leaves

+

+

Leaves

++

+

+

Urtica dioica

Leaves, Twigs

Urtica thunbergiana

Aerial parts

+

Verbenaceae

Aloysia triphylla

Leaves

+++

+

+

Lantana camara var. aculeata

Leaves

+++

+++

+

Stems

+++

+++

+

Lantana montevidensis

Leaves

++++

+++++

+++++

Lippia canescens

Aerial parts

+

Lippia dulcis

Aerial parts

+

++++

Lippia triphylla

Leaves

+

+++

Stems

+

Verbena brasiliensis

Aerial parts

+

+

Roots

+

++

Verbena officinalis

Aerial parts

+

+

Roots

Vitaceae

Cayratia japonica

Aerial parts

+

Xanthorrhoeaceae

Aloe ferox

Leaves

+

Zingiberaceae

Alpinia japonica

Fruits

Seeds

+

+

**

Curcuma zedoaria

Rhizomes

+

+

**

**

Hedychium coronarium

Rhizomes

+

+

+

**

**

Zingiber officinale

Rhizomes

+

+

++

**

****

The extracts are classified in the Angiosperm Phylogeny Group III system. EC50 values against MK-1, HeLa, and B16F10 cells (<3.13 μg/mL, ++++++; 3.13–6.25 μg/mL, +++++; 6.25–12.5 μg/mL, ++++; 12.5–25 μg/mL, +++; 25–50 μg/mL, ++; 50–100 μg/mL, +; >100 μg/mL, -). EC50 values against MT-1 and MT-2 cells (<0.1 μg/mL, ********; 0.1–1 μg/mL, ******; 1–10 μg/mL, ****; 10–100 μg/mL, **; >100 µg/mL, -)

NT not tested

Table 2 shows a summary of the sensitivity of the plant extracts toward MK-1, HeLa, B16F10, MT-1, and MT-2 cells. The percentage of extracts that were active at concentrations of less than 100 μg/mL against the various cell lines were as follows: B16F10 (70 %), MK-1 (55 %), HeLa (39 %), MT-1 (23 %), and MT-2 (28 %). Adult T-cell leukemia/lymphoma (ATL) is a malignancy of mature peripheral T lymphocytes caused by HTLV-1. Although conventional chemotherapeutic regimens used against other malignant lymphomas have been administered to ATL patients, the therapeutic outcomes remain very poor. Therefore, these results suggest that a few plant extracts were sensitive to the T-cell lymphotropic virus type 1 (HTLV-1)-infected T cells (MT-1 and MT-2).
Table 2

Summary of the sensitivity of the plants extracts against MK-1, HeLa, B16F10, MT-1, and MT-2 cells

Confirmed EC50 activities

MK-1 (%)

HeLa (%)

B16F10 (%)

MT-1 (%)

MT-2 (%)

<100 μg/mL

55

39

70

23

28

<12.5 μg/mL

7.6

7.8

12

<10 μg/mL

4.5

5.3

<3.13 μg/mL

1.9

2.8

3.6

<1 μg/mL

1.1

0.9

The percentages for each cell type represent the percent of the extracts with EC50s within each category of activity

Active principles

Polyacetylenes (Fig. 1)

After activity-guided fractionation against MK-1 cells, two active polyacetylenes, falcarindiol (1) and panaxynol (2), were isolated from the roots of Heracleum moellendorffii (Apiaceae) [6]. Six other polyacetylenes were isolated from the roots of Angelica japonica (Apiaceae) [7] together with 1 and 2 after activity-guided fractionation against MK-1 cells. Among them, four compounds were furanocoumarin ethers of 1. It was evident that the effects of these compounds except for compound 3 against MK-1 cells were more potent than their effects against HeLa and B16F10 cells (Table 3). Because compound 2 showed 16 times greater activity when compared with its 8-hydroxy derivative (1), the presence of a hydroxy group at C-8 was presumed to reduce activity. The most potent compound was panaxynol (2), with an EC50 value of 1.2 μM against MK-1 cells. Bioactive panaxynol-type polyacetylenes in plant-derived foods have attracted attention as health-promoting compounds [8].
Fig. 1

Structures of polyacetylenes identified from a screen of plant extracts

Table 3

Anti-proliferative activities of compounds 1118 (EC50, μM) against MK-1, HeLa, B16F10, MT-1, MT-2, and control PBMNC cells

Compound name

MK-1

HeLa

B16F10

MT-1

MT-2

Normal

Falcarindiol (1)

15

149

89

NT

NT

NT

Panaxynol (2)

1.2

224

80

NT

NT

NT

8-O-Acetylfalcarindiol (3)

274

175

203

NT

NT

NT

(9Z)1,9-Heptadecadiene-4,6-diyne-3,8,1 1-triol (4)

8

106

62

NT

NT

NT

Japoangelol A (5)

15

24

32

NT

NT

NT

Japoangelol B (6)

8.7

26

42

NT

NT

NT

Japoangelol C (7)

20

32

28

NT

NT

NT

Japoangelol D (8)

30

41

53

NT

NT

NT

Deoxypodophyllotoxin (9)

0.055

0.082

0.21

0.006

0.003

NT

(-)-Deoxypodorhizone (10)

1.85

3.2

4

NT

NT

NT

Nemerosin (11)

1.8

1

1.8

NT

NT

NT

Anthriscinol methyl ether (12)

13

11

11

NT

NT

NT

Elemicin (13)

22

9.6

13

NT

NT

NT

Anthriscusin (14)

6.2

5.2

7.5

NT

NT

NT

Morelensin (15)

0.24

0.14

0.23

NT

NT

NT

(-)-Hinokinin (16)

4.8

7.3

7.6

NT

NT

NT

Acteoside (17)

35

50

11

NT

NT

NT

Isoacteoside (18)

40

32

10

NT

NT

NT

Arenarioside (19)

34

34

16

NT

NT

NT

Leucosceptoside A (20)

42

33

28

NT

NT

NT

Ligupurpuroside A (21)

26

69

6.5

NT

NT

NT

Ligupurpuroside C (22)

49

49

11

NT

NT

NT

Ligupurpuroside B (23)

>135

>135

120

NT

NT

NT

Epicatechin (24)

45

NT

NT

NT

NT

NT

Epigallocatechin (25)

14

NT

NT

NT

NT

NT

Epigallocatechin gallate (26)

9

NT

NT

NT

NT

NT

Gallocatechin (27)

14

NT

NT

NT

NT

NT

Epicatechin gallate (28)

14

NT

NT

NT

NT

NT

Gallocatechin gallate (29)

10

NT

NT

NT

NT

NT

7-O-Galloylcatechin (30)

41

38

9

NT

NT

NT

Gallic acid (31)

19

22

7.1

NT

NT

NT

Gallic acid methylester (32)

65

43

18

NT

NT

NT

Trigalloylgallic acid (33)

10

9.3

2.9

NT

NT

NT

1-O-Galloylglucose (34)

60

45

15

NT

NT

NT

1,6-Di-O-galloylglucose (35)

39

29

8.1

NT

NT

NT

Corilagin (36)

13

30

4.7

NT

NT

NT

Prodelphidin B1 (37)

13

15

3.3

NT

NT

NT

Prodelphidin B2 (38)

15

15

3.3

NT

NT

NT

Apigenin (39)

22

15

26

NT

NT

NT

Hispidulin (40)

83

17

67

NT

NT

NT

Eupafolin (41)

29

6

16

NT

NT

NT

Compound 42

55

55

18

NT

NT

NT

Compound 43

73

73

29

NT

NT

NT

Compound 44

33

44

39

NT

NT

NT

Cirsiliol (45)

18

21

9

NT

NT

NT

Eupatorin (46)

58

15

44

NT

NT

NT

Cirsilineol (47)

17

203

73

NT

NT

NT

Compound 48

22

14

14

NT

NT

NT

Compound 49

>267

>267

241

NT

NT

NT

Chrysin (50)

63

8

51

NT

NT

NT

Luteolin(51)

31

10

21

NT

NT

NT

Baicalein (52)

26

30

11

NT

NT

NT

6-Hydroxyluteolin (53)

26

30

13

NT

NT

NT

Pectolinarigenin (54)

115

10

64

NT

NT

NT

Desmethoxylcentaureidin (55)

24

9

64

NT

NT

NT

Jaceosidin (56)

27

33

27

NT

NT

NT

Eupatilin (57)

55

35

58

NT

NT

NT

7-Methoxyflavone (58)

119

87

119

NT

NT

NT

6-Methoxyflavone (59)

398

8

398

NT

NT

NT

1,3,11(13)-Elematrien-8β, 12-olide (60)

6.9

13

4.3

NT

NT

NT

5α-Epoxyalantolactone (61)

6.9

6.5

3.6

NT

NT

NT

4β,5α-epoxy-1(10),11(13)-germacradiene-8,12-olide (62)

12

33

14

NT

NT

NT

Alantolactone (63)

6.9

6.9

4.7

NT

NT

NT

Isoalantolactone (64)

44

41

29

NT

NT

NT

11α,13-Dihydroalantolactone (65)

>427

>427

>427

NT

NT

NT

11α,13-Dihydroisoalantolactone (66)

>427

>427

44

NT

NT

NT

Rotundifolioside I (67)

20

37

18

NT

NT

NT

Rotundifolioside J (68)

16

21

11

NT

NT

NT

Rotundifolioside A (69)

48

71

31

NT

NT

NT

Rotundifolioside H (70)

18

31

18

NT

NT

NT

Rotundifolioside G (71)

84

>108

46

NT

NT

NT

Rotundifolioside E (72)

>110

>110

>110

NT

NT

NT

Rotundifolioside F (73)

>108

>108

>108

NT

NT

NT

Rotundioside F (74)

17

19

6.6

NT

NT

NT

Rotundioside G (75)

7.8

15

17

NT

NT

NT

Rotundioside T (76)

13

12

7.7

NT

NT

NT

Rotundioside Q (77)

34

37

12

NT

NT

NT

Rotundioside S (78)

19

34

8.9

NT

NT

NT

Ursolic acid lactone (79)

90

88

194

NT

NT

NT

Ursolic acid (80)

19

65

14

NT

NT

NT

Pomolic acid (81)

55

59

29

NT

NT

NT

Corosolic acid (82)

59

69

44

NT

NT

NT

2α,3α-Dihydoxy-urs-12-en-28-oic acid (83)

55

38

36

NT

NT

NT

3-Epimaslinic acid (84)

21

21

19

NT

NT

NT

Psoralen (85)

403

40

376

345

177

NT

Bergapten (86)

167

37

167

189

214

NT

Xanthotoxol (87)

>431

16

289

NT

NT

NT

8-Hydroxybergapten (88)

139

8.9

104

NT

NT

NT

Xanthotoxin (89)

139

74

181

73

48

NT

Isopimpinellin (90)

151

53

159

85

231

NT

1,3-Dihydroxy-4-(2’-hydroxy-3’-hydroxymethyl-3’,4’-epoxybutyl)-N-methylacridone (91)

0.056

0.056

1.76

NT

NT

NT

1,3-Dihydroxy-4-[(Z)-3’-hydroxy-3’-methylbuten-1’-yl]-N-methylacridone (92)

308

68

13

NT

NT

NT

4β-Hydroxywithanolide E (93)

NT

NT

NT

0.2

0.2

1.6

withanolide S (94)

NT

NT

NT

196

81

NT

5α-O-Methylwithanolide S (95)

NT

NT

NT

21

3.6

NT

5α-O-Butylwithanolide S (96)

NT

NT

NT

2.4

0.8

NT

2-Hydro-3β-methoxy-4β-hydroxywithanolide E (97)

NT

NT

NT

1.9

1.7

NT

Sitoindoside IX (98)

NT

NT

NT

0.83

6.1

NT

Withaferine A (99)

NT

NT

NT

0.16

1.3

NT

2,3-Dihydrowithaferine A (100)

NT

NT

NT

0.022

0.51

NT

24,25-Dihydrowithanolide D (101)

NT

NT

NT

0.008

0.008

860

Physapruin A (102)

NT

NT

NT

0.05

0.28

NT

Withanolide F (103)

NT

NT

NT

1.4

1.6

NT

Nivaphysalin A (104)

NT

NT

NT

>100

>100

NT

Nivaphysalin B (105)

NT

NT

NT

>100

>100

NT

Nivaphysalin C (106)

NT

NT

NT

59

58

NT

Liriodenine (107)

NT

NT

NT

3.1

3.6

NT

Lysicamne (108)

NT

NT

NT

32

16

NT

Lanuginosine (109)

NT

NT

NT

1.3

4.5

NT

14β-Hydroxytylophorine N-oxide (110)

NT

NT

NT

0.07

0.027

NT

Tylophorinine N -oxide (111)

NT

NT

NT

0.029

0.0048

NT

3-Demethyl- 14α-hydroxyisotylocrebrine N -oxide (112)

NT

NT

NT

0.0083

0.0071

0.04

Tylophorine N -oxide (113)

NT

NT

NT

1.6

1.5

NT

Isotylocrebrine N -oxide (114)

NT

NT

NT

0.38

0.25

NT

3-Demethyl-14β-hydroxyisotylocrebrine (115)

NT

NT

NT

0.0028

0.0026

NT

Tylophorine (116)

NT

NT

NT

0.076

0.051

NT

Isotylocrebrine (117)

NT

NT

NT

0.048

0.025

NT

7-Demethyltylophorine (118)

NT

NT

NT

0.019

0.029

NT

5-FU

21

13

1.1

NT

NT

NT

DOX

NT

NT

NT

0.015

0.013

NT

Dox doxorubicin, 5-FU 5-fluorouracil (positive controls), NT not tested

Lignans (Fig. 2)

After activity-guided fractionation against MK-1, HeLa, and B16F10 cells, seven lignans including deoxypodophyllotoxin (9), (-)-deoxypodorhizone (10), and related compounds were isolated from the roots of Anthriscus sylvestris (Apiaceae) [9]. From the fruits of the same plant, two other lignans (14 and 15) were isolated together with 9 and 10 after activity-guided fractionation against MK-1, HeLa, and B16F10 cells [10]. Deoxypodophyllotoxin (9) showed higher activity than polyacetylenes against these cell lines. Etoposide, a clinically used chemotherapeutic agent against small-cell lung cancer, malignant lymphoma, and acute leukemia is a derivative of a podophyllotoxin isolated from Podophyllum peltatum (Berberidaceae) [11]. Of note is that the EC50 value of deoxypodophyllotoxin (9) was in the nanomolar range across all cell lines tested including MT-1 and MT-2 cells (Table 3). Topoisomerase II-inhibited DNA breakage was recognized as the mechanism of action of Etoposide. The structural features that are crucial for the anti-topoisomerase II activity of podophyllotoxin derivatives have been roughly identified as: bulky 7β-bulky substituent, trans-lactone in ring D, dioxolane ring in ring A, quasi-axial configuration of ring E, and 4′-hydroxy group [12].
Fig. 2

Structures of lignans identified from a screen of plant extracts

Phenylethanoids (Fig. 3)

After activity-guided fractionation against B16F10 cells, two active phenylethanoids, acteoside (17) and isoacteoside (18), were isolated from the leaves of Clerodendrum bungei and the bark of C. trichotomum (Laminaceae) [13]. Four other phenylethanoids including arenarioside (19) and leucosceptoside A (20) were isolated from the aerial parts of Lippia dulcis and L. canescens (Verbenaceae) together with some miscellaneous compounds after activity-guided fractionation against MK-1, HeLa, and B16F10 cells [14]. Furthermore, three other phenylethanoids (2123) isolated from the leaves of Ligustrum purpurascens (Oleaceae) were also evaluated [15]. It was remarkable that the effect of phenylethanoids (1723) against B16F10 cells was more potent than their effects against HeLa and MK-1 cells. Because the effects of compound 23 were extremely weak, this suggested the 3,4-dihydroxyphenethyl group is essential for the observed strong anti-proliferative activity. Furthermore, 3,4-dihydroxyphenethyl alcohol itself showed potent activity [13]. It is also known that treatment of phenylethanoids resulted in apoptotic cell death [16].
Fig. 3

Structures of phenylethanoides identified from a screen of plant extracts

Polyphenols (Fig. 4)

Epidemiological studies have suggested that the consumption of green tea [Camellia sinensis (Theaceae)] provides protection against stomach cancer. In a rural area of northern Kyushu, Japan, a decreased risk of stomach cancer was also noted among people reporting a high consumption of green tea [17]. Fractionation of green tea extract, guided by the anti-proliferative activity against MK-1 cells, resulted in the isolation of six flavan-3-ols (2429) together with the inactive glycosides of kaempferol and quercetin [18]. A study of their structure–activity relationships suggested that the presence of the three adjacent hydroxyl groups (pyrogallol or galloyl group) in the molecule is a key factor for enhancing the compound’s activity. Six active polyphenols (3035) were isolated from the seeds of Rhynchosia volubilis (Fabaceae) after activity-guided fractionation against MK-1, HeLa, and B16F10 cells [19]. These compounds all showed much stronger inhibition against B16F10 cell growth than against HeLa and MK-1 cell growth. Gallic acid (31) with a free carboxyl group showed higher activity than its methyl ester (32). A hydrolysable tannin (36) and two condensed tannins (37, 38) isolated from Phyllanthus emblica (Phyllanthaceae) also showed potent activity [20] against three cell lines. It was proposed that the anti-cancer properties of polyphenols may be related to their ability to participate in a copper-dependent prooxidant mechanism [21].
Fig. 4

Structures of polyphenols identified from a screen of plant extracts

Flavones (Fig. 5)

After activity-guided fractionation against MK-1, HeLa, and B16F10 cells, 11 active flavones (3949) were isolated from the leaves of Lantana montevidensis (Verbenaceae) [22]. Concurrently, several related flavones (5057) isolated from other plant materials and two synthetic ones (58, 59) were also evaluated. 5,7-Dihydroxy flavones (39, 50, 51), 5,7-dihydroxy-6-methoxy flavones (40, 41, 54, 55), and 6-methoxy flavone (59) were much stronger inhibitors of HeLa cell growth than B16F10 and MK-1 cell growth. In particular, compound 59 was a potent inhibitor of HeLa cell growth. Therefore, the 6-methoxy group is likely important for enhancing the anti-proliferative activity of flavones against HeLa cells. A synthetic flavone derivative, flavopiridol (Alvocidib), is being evaluated in clinical trials of ovarian and primary peritoneal cancers [23].
Fig. 5

Structures of flavones identified from a screen of plant extracts as well as those derived synthetically

Sesquiterpenes (Fig. 6)

After activity-guided fractionation against MK-1, HeLa, and B16F10 cells, five active sesquiterpenes (6064) were isolated from the roots of Inula helenium (Asteraceae) together with an inactive sesquiterpene (65) and a weak one (66) [24]. A structure–activity study suggested that the presence of an α-methylene-γ-lactone group is a key component required for the anti-proliferative activity. The thiol reactivity of the α-methylene-γ-lactone group may be responsible for the observed anti-proliferative activity [25]. Two norsesquiterpene glycosides from the roots of Phyllanthus emblica (Phyllanthaceae) exhibited potent activity (data not shown) although their aglycone and monoglucoside showed no inhibitory activity [20].
Fig. 6

Structures of sesquiterpenes identified from a screen of plant extracts

Triterpene glycosides (Fig. 7) and triterpenes (Fig. 8)

From the bioactive fraction of the fruits of Bupleurum rotundifolium (Apiaceae), ten ursane-type triterpene glycosides were isolated and their anti-proliferative activities against MK-1, HeLa, and B16F10 cells were estimated [26]. All active glycosides (6771) have a 13β, 28-epoxy ring system in the molecule except for 72 and 73, which have a 21β-hydroxy group. The glycosides of the other aglycones are almost inactive. Among the active glycosides, 69 and 71, which have a glucosyl group directly linked to the aglycone instead of a fucosyl group, were less potent. It is possible that the fucosyl group plays some role in the anti-proliferative activity. From the same fraction, 19 oleanane-type triterpene glycosides were also isolated and their anti-proliferative activities were evaluated [27]. Similar to the ursane-type triterpene glycosides, all active glycosides (7478) have a 13β, 28-epoxy ring system in the molecule. In contrast to the ursane-type triterpene glycosides, compounds 77 and 78, which have a 21α-hydroxy group, had potent anti-proliferative activities. The configuration at the C-21 hydroxy group might influence the anti-proliferative activity.
Fig. 7

Structures of triterpene glycosides identified from a screen of plant extracts

Fig. 8

Structures of triterpenes identified from a screen of plant extracts

After activity-guided fractionation against MK-1, HeLa and B16F10 cells, ten triterpenes were isolated from the aerial parts of Centella asiatica (Apiaceae) [28]. Some (7984) of these triterpenes showed potent anti-proliferative activities. Similar to the results of the polyphenols, ursolic acid (80) with a free carboxyl group showed higher activity than its lactone (79). Ursolic acid (80) was previously reported to induce apoptoic cell death [29].

Coumarins and acridone alkaloids (Fig. 9)

After activity-guided fractionation against MK-1, HeLa, and B16F10 cells, 16 compounds were isolated from the aerial parts and roots of Boenninghausenia japonica (Rutaceae) [30]. Among them, an acridone alkaloid (91) showed very strong anti-proliferative activity against these three cell lines. The EC50 value of 91 was in the nanomolar range except for against B16F10 cells. Therefore, a 3′, 4′-epoxy group might be important for enhancing the anti-proliferative activity of acridone alkaloids. Furthermore, some furanocoumarins (8590) showed potent anti-proliferative activities against HeLa cells. The furanocoumarins (87, 88) having an 8-hydroxy group showed more potent activity than those without the substituent (85, 86) and those with an 8-methoxy group (89, 90) against HeLa cells. Therefore, an 8-hydroxy group may be important for enhancing the anti-proliferative activity of these compounds against HeLa cells. Some furanocoumarins (85, 86, 89, 90) also showed moderate anti-proliferative activity against MT-1 and MT-2 cells (Table 3). A recent review reports that natural and synthetic coumarins have anticancer activity toward various cell lines [31].
Fig. 9

Structures of coumarins and acridone alkaloids identified from a screen of plant extracts

Withanolides (Fig. 10)

After activity-guided fractionation against MT-1 and MT-2 cells, five active withanolides (9397) were isolated from the aerial parts of Physalis pruinosa (Solanaceae) [32]. Structure–activity relationships suggested that the presence of a 5β, 6β epoxy group in the B-ring and a 4β-hydroxy group in the A-ring were important for the observed activities. The aliphatic ether side chain at C-5 also seems to increase the activity because as the side chain is lengthened, the activity increases. Because the EC50 value for 4β-hydroxywithanolide E (93) was in the nanomolar range against both MT-1 and MT-2 cells, 31 other withanolides were also evaluated [33]. Except for compound 98, none of the glycosides showed any activity against the ATL cell lines. Because compound 98 has a 5β, 6β-epoxy group as well as a 4β-hydroxy group, we predicted it might show potent activity. However, the activity of the corresponding deglycosylated compound (99) was approximately four times greater than that of its glucoside (98). These results indicated that the presence of a sugar moiety should reduce the anti-proliferative effects. The importance of the 5β, 6β-epoxy group, and 4β-hydroxy group was further supported by the analysis of compound 100 because it showed the second strongest anti-proliferative activity. The activities of 99, having a double bond between C-2 and C-3, were weaker than those for 100, suggesting the double bond between C-2 and C-3 might reduce the activity. Because compound 102 showed greater activity when compared with compound 103, the importance of a 4β-hydroxy group was further supported. Compared with the compounds having the 5β, 6β-epoxy group, the activities of the compounds (104106) having other types of epoxy groups (6α, 7α-epoxy group in the B-ring and/or 24α, 25α-epoxy group in the E-ring) were significantly lower. The position of the epoxy group and/or the configuration of the epoxy group seem to be important for the activity. Compound 106 containing a 15β-hydroxy group showed moderate activity while compound 105 containing a 15α-hydroxy group did not show any activity. This indicated that the configuration of the hydroxy group at C-15 may influence a compound’s activity. Finally, the EC50 value of 24, 25-dihydrowithanolide D (101), the most potent withanolide-type inhibitor, was 8 nM against both cells. In contrast, the cytotoxic effect (860 nM) of 101 toward normal cells was observed at a concentration about 100 times higher than those observed for the ATL cell lines. Furthermore, compound 101 was confirmed to induce dose-dependent apoptosis against MT-1, MT-2, and fresh ATL cells [33]. Therefore, 24, 25-dihydrowithanolide D (101) may be a promising chemotherapeutic candidate.
Fig. 10

Structures of withanolides identified from a screen of plant extracts

Recently inhibition of the growth of human lung cancer cells through DNA damage, apoptosis and G2/M arrest by 4β-hydroxywithanolide E (93) have been reported [34]. Further, induction of apoptosis in leukemia cells by targeting the activation of a neutral sphingomyelinase-ceramide cascade mediated by synergistic activation of c-Jun N-terminal kinase and p38 mitogen-activated protein kinase by withanolide D have been also reported [35]. Wang et al. suggested that Hsp90 inhibition by the withanolides is correlated with their ability to induce cancer cell death [36].

Aporphine and phenanthroindolizidine alkaloids (Fig. 11)

After activity-guided fractionation against MT-1 and MT-2 cells, three active aporphine alkaloids (107109) were isolated from the leaves of Annona reticulata and A. squamosa (Annonaceae) [37]. Liriodenine (107) showed accumulation of Sub-G1 stage cells in the MT-1 and MT-2 cell population, suggesting induction of apoptosis. A structure–activity relationship analysis suggested that the presence of a 1, 2-methylenedioxy group seemed to enhance activity. A similar conclusion on the structure–activity relationship was also obtained by Liu et al. [38].
Fig. 11

Structures of aporphine and phenanthroindolizidine alkaloids identified from a screen of plant extracts

Six phenanthroindolizidine alkaloids (110115) were isolated from the aerial parts of Tylophora tanakae (Asclepiadaceae) by activity-guided fractionation [39]. In addition to 110115, three phenanthroindolizidine alkaloids (116118) obtained from other plants were examined for their anti-proliferative activity against MT-1 and MT-2 cells. The EC50 values of all alkaloids except for compound 113 were in the low nanomolar range. The results suggested that the presence of a 2-methoxy functionality, the methyl group of a 7-methoxy functionality, and an N-oxide moiety appear to reduce the potency of the anti-proliferative activity [39]. Phenanthroindolizidine alkaloids are cytotoxic to multidrug-resistant cells [40], inhibiting the enzyme dihydrofolate reductase [41]. The in vivo efficacy of a new phenanthroindolizidine alkaloid derivative (YPC-10157) was recently evaluated [42].

Conclusions

Cytotoxicity against selected cancer cell lines was characterized and could be explained by identifying the active principles responsible for the observed effects. The polyacetylenes was more potent against MK-1 cells than against HeLa and B16F10 cells. The EC50 value of the most potent polyacetylene (2) against MK-1 cells was 1.2 μM (Fig. 12). The compounds (1722) having a 3, 4-dihydroxyphenethyl group also showed remarkable anti-proliferative effects against B16F10 cells (Fig. 12). Interestingly, some 6-methoxyflavone derivatives (40, 41, 54, 55, 59) and 8-hydroxy furanocoumarins (87, 88) showed strong inhibition against HeLa cell growth (Fig. 12).
Fig. 12

Differences in the specific selectivity of selected compounds against various cancer cell lines

The compounds whose EC50 values were less than one nanomolar (<1 nM) were not selective for specific cell types. This group included two lignans (9, 15), one acridone alkaloid (91), six withanolides (93, 98102), and eight phenanthroindolizidine alkaloids (110112, 114118). Because the cytotoxic effect of 24, 25-dihydrowithanolide D (101) toward normal cells was observed at a concentration about 100 times higher than against the ATL cell lines, withanolide was concluded to be the most promising chemotherapeutic candidate from our experiments.

Notes

Acknowledgments

We thank Drs. Tsuneatsu Nagao, Fumiko Abe, Kunihide Mihashi, Hisashi Matsunaga, Ryuji Ikeda, Takashi Tanaka, Tenji Konishi, Kenji Ishitsuka, Ryota Tsuchihashi, and Masafumi Okawa for supporting our work.

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Copyright information

© The Japanese Society of Pharmacognosy and Springer Japan 2016

Authors and Affiliations

  • Junei Kinjo
    • 1
  • Daisuke Nakano
    • 1
  • Toshihiro Fujioka
    • 1
  • Hikaru Okabe
    • 1
  1. 1.Faculty of Pharmaceutical SciencesFukuoka UniversityFukuokaJapan

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