2.1. Alkaloids

The bcr-abl oncogene encodes a constitutively activated tyrosine kinase, BCR-ABL. The catalytically activated kinase, in turn, activates multiple cell proliferatory signaling pathways such as RAS, a small GTPase, mitogen activated protein kinase (MAPK), signal transducers and

Figure 1. Schematic representation of NPs and TKIs on BCR-ABL inhibition and downregulation of downstream signaling pathways (NP—natural products, TKI—tyrosine kinase inhibitor, CML—chronic myeloid leukemia, MDR—multi-

Targeting Abl kinase is clearly a proven successful strategy to combat CML. First generation tyrosine kinase inhibitor (TKI), imatinib, also known as Gleevac or STI571 inhibited BCR-ABL and suppressed CML progression [4]. Second generation TKIs such as nilotinib, dasatinib & bosutinib and third generation TKIs (Ponatinib) that are more potent to inhibit BCR-ABL kinase are currently used to treat CML [5, 6]. All these TKIs were approved by the US Food and Drug Administration (FDA). TKIs have changed the clinical course of CML. However, mutations in bcr-abl and multi-drug resistance (MDR) due to efflux of the drug as a result of overexpression of p-glycoprotein (p-gp) make TKIs less effective. Primary or secondary resistance to TKIs therapy still exists; however, there is a constant need for alternative therapeutic

Natural products (NPs) represent a large family of diverse secondary metabolites with profound biological activities. NPs are produced in several organisms like bacteria, fungi, plants

activator of transcription (STAT), and phosphoinositide-3-kinase (PI3K) pathways [3].

strategy (Figure 1) [7].

drug resistance).

4 Anti-cancer Drugs - Nature, Synthesis and Cell

2. Natural products

Alkaloids are naturally occurring organic compounds containing heterocyclic ring with nitrogen atom. Alkaloids, widely distributed in plant kingdom, are bitter secondary metabolites synthesized by plants, microbes and animals. They possess several physiological activities like anti-malarial, anti-asthmatic, anti-cancer, anti-bacterial, antiviral, anti-hyperglycemic and vasodilatory activities [10–13]. Their anti-CML activity is described below.

Berbamine (BBM) is a natural bisbenzylisoquinoline product, isolated from traditional Chinese herbal medicine Berberis amurensis, was tested on imatinib resistant K562 cell line (K562/IR) both in vitro and in vivo. The IC50 value was found to be 17.1 and 11.1 μM at 24 and 48 h. BBM downregulated Bcl-2, Bcl-xL, mdr-1 mRNA, p-gp levels and enhanced Bax & cytochrome C (cyt.C) release. BALB/c or nu/nu mice were injected with K562-r subcutaneously and the tumor-bearing mice, when treated with BBM [60 mg/kg body weight (BW)] intravenously effectively suppressed the xenotransplated tumors in these mice [14]. BBM also induced apoptosis in CML cells via downregulating survivin protein levels [15]. At 8 μg/ml dose of BBM, NFκB nuclear, IKK-α, IKB-α [16], BCR-ABL, p-BCR-ABL level were decreased [17]. Furthermore, BBM-induced differentiation of CML cells into RBC, granulocyte and megakaryocytes [18]. Interestingly, BBM is a heat shock protein 90 (Hsp90) inhibitor [19]. BBM inhibited MDR K562/adriamycin (ADR) [20] and K562/A02 cell lines consequently inducing apoptosis by reducing mdr-1 gene expression and reversing MDR effect [21]. 4-chlorobenzoyl berbamine (BBD9), an analogue of BBM was also tested against K562/IR. BBD9 with IC50 0.5 μg/ml was found to be more effective than BBM (IC50 8 μg/ml), BBD9-lowered BCR-ABL, IKK a, nuclear NF-κB. Furthermore, it increased the cleaved caspases 3,9, Poly(ADP-Ribose) polymerase (PARP) and LC3-phosphatidylethanolamine conjugate (LC3 II) expression levels. In nude mice model bearing K562 tumors, BBD9 was effective in reducing the tumor weight, promoting tumor regression [22]. E6, a derivative of BBM, was tested against MDR K562/doxorubicin (DOX) with 1, 3, 10 and 30 μM concentrations, and it significantly reduced the IC50 of DOX from 79.19 μM to 35.18, 21.86, 6.31 and 1.97 μM. Co-treatment of E6 with DOX arrested K562 cells at G2/M phase [23].

Camptothecin, isolated from Camptotheca acuminate, is documented to display anti-CML activity. Homocampthothecin (hCPT), a synthetic analogue of camptothecin, showed potent activity at IC50 value of 11 nM suggesting its potential use compared to parent compound camptothecin (IC50 57 nM) [24]. BN80927, an analogue of camptothecin, effectively inhibited K562 cell proliferation with IC50 of 8.4 nM [25]. NSC606985, an analogue of camptothecin, inhibited CML cell growth in a dose-dependent manner. The IC50 was found to be 6.25 nM [26]. Combination of imatinib and camptothecin increased Bax, cleavage of PARP-1, DNAdependent protein kinase (DNA–PK) in CML cells [27].

Capsaicin, an active component of capsicum genus, is a homovanillic acid derivative experimentally is shown to exhibit anti-mutagenic activity [28]. Capsaicin treatment of K562 cells decreased microRNA (miRNA) expression such as miR-520a-5p, a putative target of STAT3. Hence, capsaicin induced apoptosis via reducing mRNA involved in JNK/STAT pathway [29]. Capsaicin also stimulated GATA-1 promoter in CML cells which is an essential transcriptional factor for the development of erythroid cells [30].

Homoharringtonine (HHT), isolated from Cephalotaxus harringtona, has been documented to inhibit CML cell proliferation in a dose-dependent manner. The IC50 was found to be 43.89 ng/ ml. HHT arrested K562 cells at G0/G1 phase and, in addition, downregulated Bcl-2, NF-κB, p-JAK2, p-STAT5, p-Akt, p-BCR-ABL levels [31, 32].

Sanguinarine, a benzophenanthridine alkaloid, isolated from blood root plant Sanguinaria canadensis, belonging to the Papaveraceae family inhibited CML cell growth in a dose-dependent manner. At 1.5 μg/ml, sanguinarine induced apoptosis in CML cells. At higher concentration (12.5 μg/ml), sanguinarine caused blister formation in CML cells [33].

Staurosporine, an alkaloid isolated from the bacterium Streptomyces staurosporeus, not only inhibited CML cell growth but also induced differentiation of myeloid cell lineage to megakaryocytic lineage resulting in polypoidy formation. Staurosporine treatment resulted in upregulation and activation of JAK/STAT3, p-STAT3 nuclear translocation and downregulation of c-myc [34, 35]. Staurosporine also induced differentiation of CML cells into erythroid cells via increased CD61 and CD42b levels [36]. 7-Hydroxy staurosporine (UCN-01), a potent PKC inhibitor is effective in inhibiting CML cell proliferation at a concentration of 3 μM for 24 h [37, 38].

Tetrandrine is a bis-benzylisoquinoline alkaloid that is isolated from Chinese herb Stephania tetrandra. Combination of tetrandine and imatinib showed syngerisitic effect significantly inhibited CML cell growth. The combination treatment arrested CML cells at G1/S phase, enhanced caspase 3 mRNA, protein levels and decreased Bcl-2 mRNA, protein levels [39]. Combination of nilotinib and tetrandrine also effectively decreased the IC50 of daunorubicin (DNR) on K562/A02 to 3.12 ± 0.13 μg/ml. This combinational effect not only increased Bax mRNA and protein levels but also decreased the survivin mRNA and protein levels [40]. Tetrandrine citrate, a novel tetrandrine salt which is highly soluble in water, Inhibited the growth of K562/IR, primary leukemic cells and primitive CD34 (+) leukemic cells with IC50 ranging from 1.2 to 2.97 μg/ml. Tetrandrine citrate lowered BCR-ABL mRNA and β-catenin protein levels. Nude mice bearing CML tumors when orally administered with tetrandrine citrate (100 mg/kg BW), reduced the tumor growth [41]. Combination of 5-bromotetrandrine (analogue of tetrandrine) and DNR decreased p-JNK 11,2 and MDR/p-gp levels in ADR resistant K562 cells [42].

Alkaloids from plant and microbial source inhibited CML cell proliferation in micromole (μM)/ microgram (μg) concentration (Table 1) (Figure 2) [43–66]. Alkaloids are well documented to


[26]. Combination of imatinib and camptothecin increased Bax, cleavage of PARP-1, DNA-

Capsaicin, an active component of capsicum genus, is a homovanillic acid derivative experimentally is shown to exhibit anti-mutagenic activity [28]. Capsaicin treatment of K562 cells decreased microRNA (miRNA) expression such as miR-520a-5p, a putative target of STAT3. Hence, capsaicin induced apoptosis via reducing mRNA involved in JNK/STAT pathway [29]. Capsaicin also stimulated GATA-1 promoter in CML cells which is an essential transcriptional

Homoharringtonine (HHT), isolated from Cephalotaxus harringtona, has been documented to inhibit CML cell proliferation in a dose-dependent manner. The IC50 was found to be 43.89 ng/ ml. HHT arrested K562 cells at G0/G1 phase and, in addition, downregulated Bcl-2, NF-κB, p-

Sanguinarine, a benzophenanthridine alkaloid, isolated from blood root plant Sanguinaria canadensis, belonging to the Papaveraceae family inhibited CML cell growth in a dose-dependent manner. At 1.5 μg/ml, sanguinarine induced apoptosis in CML cells. At higher concen-

Staurosporine, an alkaloid isolated from the bacterium Streptomyces staurosporeus, not only inhibited CML cell growth but also induced differentiation of myeloid cell lineage to megakaryocytic lineage resulting in polypoidy formation. Staurosporine treatment resulted in upregulation and activation of JAK/STAT3, p-STAT3 nuclear translocation and downregulation of c-myc [34, 35]. Staurosporine also induced differentiation of CML cells into erythroid cells via increased CD61 and CD42b levels [36]. 7-Hydroxy staurosporine (UCN-01), a potent PKC inhibitor is effective in inhibiting CML cell proliferation at a concentration of 3 μM for

Tetrandrine is a bis-benzylisoquinoline alkaloid that is isolated from Chinese herb Stephania tetrandra. Combination of tetrandine and imatinib showed syngerisitic effect significantly inhibited CML cell growth. The combination treatment arrested CML cells at G1/S phase, enhanced caspase 3 mRNA, protein levels and decreased Bcl-2 mRNA, protein levels [39]. Combination of nilotinib and tetrandrine also effectively decreased the IC50 of daunorubicin (DNR) on K562/A02 to 3.12 ± 0.13 μg/ml. This combinational effect not only increased Bax mRNA and protein levels but also decreased the survivin mRNA and protein levels [40]. Tetrandrine citrate, a novel tetrandrine salt which is highly soluble in water, Inhibited the growth of K562/IR, primary leukemic cells and primitive CD34 (+) leukemic cells with IC50 ranging from 1.2 to 2.97 μg/ml. Tetrandrine citrate lowered BCR-ABL mRNA and β-catenin protein levels. Nude mice bearing CML tumors when orally administered with tetrandrine citrate (100 mg/kg BW), reduced the tumor growth [41]. Combination of 5-bromotetrandrine (analogue of tetrandrine) and DNR decreased p-JNK 11,2 and MDR/p-gp levels in ADR

Alkaloids from plant and microbial source inhibited CML cell proliferation in micromole (μM)/ microgram (μg) concentration (Table 1) (Figure 2) [43–66]. Alkaloids are well documented to

tration (12.5 μg/ml), sanguinarine caused blister formation in CML cells [33].

dependent protein kinase (DNA–PK) in CML cells [27].

6 Anti-cancer Drugs - Nature, Synthesis and Cell

factor for the development of erythroid cells [30].

JAK2, p-STAT5, p-Akt, p-BCR-ABL levels [31, 32].

24 h [37, 38].

resistant K562 cells [42].


↑ – upregulation, ↓ – downregulation, ⊥ – cell cycle arrest & \* – Inhibition rate (IR) at 100 μg/ml.

Table 1. Anti-CML activity of alkaloids.

potently reduce tumor growth in in vivo models (Table 2). Besides, some alkaloids such as capasaicin, staurosporine induces differentiation of CML cells (Table 3).

#### 2.2. Flavonoids

Flavonoids belong to polyphenolic compounds which are prevalent in plants. They contain two phenyl rings A, B and a heterocyclic ring C (commonly referred as C6-C3-C6 skeleton) and are classified into many major classes like flavones, flavonols, flavanones, flavanonols and isoflavonoids (Figure 3). They exhibit antioxidant, anti-inflammatory, anti-bacterial, antiviral and anti-cancer activities and play a significant role in human health [67–74].

Oroxylin A, an O-methylated flavone, found in the medicinal plant Scutellaria baicalensis, was tested against MDR K562/ADR cells. Oroxylin A specifically enhanced the sensitivity of K562/ ADR to ADR by selectively inducing apoptosis. The treatment downregulated CXCR4 expression and inhibited PI3K/Akt/NF-κB pathways [75]. NOD/SCID mice-bearing K562 xenograft, treated with oroxylin A (30 mg/kg BW) alone or in combination with imatinib enhanced the sensitivity of imatinib to K562 cells through suppression of STAT3 pathway, decreasing p-gp levels thus reversing MDR in CML cells [76].

Quercetin (Q), a major flavonol, found in the kingdom Plantae, exhibits many biological effects including Antioxidant, anti-inflammatory, anti-cancer and anti-diabetic activities [77]. While evaluating the anti-proliferative effect of pytoestrogens, it was found that Q specifically inhibits K562 and MDR K562/A cell growth [78]. When K562 cells were treated with Q at a Natural Products for Treatment of Chronic Myeloid Leukemia http://dx.doi.org/10.5772/66175 9

potently reduce tumor growth in in vivo models (Table 2). Besides, some alkaloids such as

on K562 cells

18.97 and 10.95 μg/ml

and 5.78%

μM

Mechanism of action References

– [62]

– [64]

– [65]

[66]

BCR-ABL, and ⊥G1/S phase

0.24—45 μM – [63]

Flavonoids belong to polyphenolic compounds which are prevalent in plants. They contain two phenyl rings A, B and a heterocyclic ring C (commonly referred as C6-C3-C6 skeleton) and are classified into many major classes like flavones, flavonols, flavanones, flavanonols and isoflavonoids (Figure 3). They exhibit antioxidant, anti-inflammatory, anti-bacterial, antiviral

Oroxylin A, an O-methylated flavone, found in the medicinal plant Scutellaria baicalensis, was tested against MDR K562/ADR cells. Oroxylin A specifically enhanced the sensitivity of K562/ ADR to ADR by selectively inducing apoptosis. The treatment downregulated CXCR4 expression and inhibited PI3K/Akt/NF-κB pathways [75]. NOD/SCID mice-bearing K562 xenograft, treated with oroxylin A (30 mg/kg BW) alone or in combination with imatinib enhanced the sensitivity of imatinib to K562 cells through suppression of STAT3 pathway, decreasing p-gp

Quercetin (Q), a major flavonol, found in the kingdom Plantae, exhibits many biological effects including Antioxidant, anti-inflammatory, anti-cancer and anti-diabetic activities [77]. While evaluating the anti-proliferative effect of pytoestrogens, it was found that Q specifically inhibits K562 and MDR K562/A cell growth [78]. When K562 cells were treated with Q at a

capasaicin, staurosporine induces differentiation of CML cells (Table 3).

Alkaloid Source of isolation IC50 value

DFFSCS013

F3

Auranomides A, B and C Penicillium aurantiogriseum \*20.48, 76.36

Aspergillus westerdijkiae

Anaxagorea dolichocarpa Sprague and sandwith

Arthrinium arundinis ZSDS1-

Euplexauria robusta 0.35—10.82

Virosecurinine Securinega suffruticosa 32.984 μM ↑PTEN & ↓mTOR, SHIP-2

↑ – upregulation, ↓ – downregulation, ⊥ – cell cycle arrest & \* – Inhibition rate (IR) at 100 μg/ml.

and anti-cancer activities and play a significant role in human health [67–74].

levels thus reversing MDR in CML cells [76].

2.2. Flavonoids

5-Chlorosclerotiamide and 10-episclerotiamide (prenylated indole alkaloids)

8 Anti-cancer Drugs - Nature, Synthesis and Cell

(azaphenanthrene alkaloids)

Arthpyrones A, B and C (4 hydroxy-2-pyridone alkaloids)

Eupolauramine and sampangine

Malonganenones 1–3 (tetraprenylated alkaloids)

Table 1. Anti-CML activity of alkaloids.

Figure 2. List of anti-CML alkaloids as 1—Ancistrotectorine E, 2—Berbamine, 3—BBD9, 4—Camptothecin, 5—BN80927, 6—NSC606985, 7—Homocamptothecin, 8—Capsaicin, 9—Cathachunine, 10—Cephranathine, 11—Crambescidin 800, 12 —Crebanine, 13—Curine, 14—Cyanogramide, 15—9-deacetoxyfumigaclavine C, 16—d-Dicentrine, 17—Evodiamine, 18 —Homoharringtonine, 19—Naamidine J, 20—Piperine, 21—Salvicine, 22—Staurosporine, 23—UCN-01, 24—Tetrandrine, 25—5-bromotetrandrine, 26—α-tomatine, 27—tylophorine, 28—tylophorinine, 29—5-chlorosclerotiamide, 30—10 episclerotiamide, 31—Eupolauramine, 32—Sampangine, 33, 34, 35—Arthpyrones A, B and C, 36–38—Auranomides A, B and C and 39—Virosecurinine.


Table 2. In vivo results of anti-CML NPs.

concentration of 9.2 mg/ml for 72 h, it induced apoptosis and reduced the BCR-ABL levels in CML cells [79]. Combination of Q and ADR was tested on MDR K562/ADR cells. Combined treatment enhanced activation of caspases 3,8 and loss of mitochondrial membrane potential (MMP). Furthermore, it lowered Bcl-2, Bcl-xl and enhanced the p-c-Jun-N terminal kinase and p-p38 mitogen-activated protein kinase (p-p38-MAPK). Q also significantly decreased the p-gp levels [80] and sensitized MDR K562/ADM to DNR and reversed MDR in CML cells [81]. Q inhibited K562 and MDR K562/A in the range of 5–160 μM. Q treatment of K562/ADR cells (5 μM) enhanced accumulation of ADR and, in addition, decreased the expression of MDRcausing proteins like ABC, solute carrier (SLC). Moreover, it reduced Bcl-2, TNF expression reversing MDR in CML cells [82]. Moreover, Q arrested CML cells at G2/M phase [83]. IC50 of Q on K562 and K562/ADR was found to be 11 ± 2 μM and 5 ± 0.4 μM [84]. It also inhibited the


Table 3. List of some NPs and its differentiation capacity.

Hsp70 levels in CML cells [85]. Q induced apoptosis via inhibiting the telomerase enzyme by enhancing human telomerase reverse transcriptase (hTERT) enzymes in CML cells [86].

In sum, flavonoids not only inhibit the growth of CML cells (Table 4) but also induce their differentiation into erythroid or monocyte lineage (Table 3). Flavonoid fractions of plant extracts also inhibit CML cell proliferation and induced apoptosis [87–109].

#### 2.3. Terpenoids

concentration of 9.2 mg/ml for 72 h, it induced apoptosis and reduced the BCR-ABL levels in CML cells [79]. Combination of Q and ADR was tested on MDR K562/ADR cells. Combined treatment enhanced activation of caspases 3,8 and loss of mitochondrial membrane potential (MMP). Furthermore, it lowered Bcl-2, Bcl-xl and enhanced the p-c-Jun-N terminal kinase and p-p38 mitogen-activated protein kinase (p-p38-MAPK). Q also significantly decreased the p-gp levels [80] and sensitized MDR K562/ADM to DNR and reversed MDR in CML cells [81]. Q inhibited K562 and MDR K562/A in the range of 5–160 μM. Q treatment of K562/ADR cells (5 μM) enhanced accumulation of ADR and, in addition, decreased the expression of MDRcausing proteins like ABC, solute carrier (SLC). Moreover, it reduced Bcl-2, TNF expression reversing MDR in CML cells [82]. Moreover, Q arrested CML cells at G2/M phase [83]. IC50 of Q on K562 and K562/ADR was found to be 11 ± 2 μM and 5 ± 0.4 μM [84]. It also inhibited the

Name of

Tetrandrine citrate

Gambogic acid

d-Dicentrine

NP Type of NP

10 Anti-cancer Drugs - Nature, Synthesis and Cell

Mice strain

BBM Alkaloid Balb/c K562-r 60 mg/

BBD9 Analogue of BBM nu−/− K562/IR 15 and

Oroxylin A Flavonoid SCID K562 80 mg/

mice

mice

NPB001–05 Piper betle extract – T315I 500 mg/

Garcinia hanburyi Balb/c KBM5-T315I 3 mg/kg/

Balb/c K562 50 mg/

Nobiletin Flavonoid Nude

dEpoF Polyketide Nude

from Tegillarca granosa

Eurycoma longifolia MeOH extract

Table 2. In vivo results of anti-CML NPs.

HSS Protein extract

TAF273 Fraction of

Alkaloid nu−/− K562/IR 100 mg/

Alkaloid SCID K562 100 mg/

Type of CML cells used to

induce tumors Dosage

K562 12.5, 25,

kg BW

30 mg/ kg BW

kg BW

kg BW

kg BW

50 mg/ kg BW

2 days

kg

kg

– K562/ADM – – ↓mdr1, BCR-

K562 6 mg/kg Intravenously Complete tumor

Mode of administration Mechanism of

p-gp protein

IKKa, NF-κBp65

Intravenously ↓mdr-1 mRNA,

– ↓p-BCR-ABL,

Orally ↓BCR-ABL, βcatenin

Intravenously ↓STAT3

Intraperitoneal ↓tumor size [52]

pathway

regression

Intraperitoneal ↓Bcr-Abl, Akt,

Intraperitoneal ↑apoptosis and

Orally ↓PI3K/AKT,

ABL and sorcin

Erk1/2, and STAT5

↓blood vessel formation

MAPK pathways

– ↓VEGF [99]

action References

[14]

[22]

[41]

[76]

[147]

[177]

[229]

[258]

[275]

Terpenoids are naturally occurring products representing the largest secondary metabolites. Approximately 60% of NPs are terpenoids. They are basically made up of five carbon isoprene units (IU). Depending upon the number of isoprene units present, terpenoids has been classified into hemiterpenoids (1 IU), monoterpenoids (2 IU), sesquiterpenoids (3 IU), diterpenoids (4 IU), sesterterpenoids (5 IU), triterpenoids (6 IU), tetraterpenoids (8 IU) and polyterpenoid (n IU). They have been documented to possess antioxidant, anti-inflammatory, anti-helminitic and anti-cancer activities [110–115].

Sesquiterpenoids, diterpenoids, sesterterpenoids and triterpenoidshas been shown to potently inhibit CML cell proliferation and induce apoptosis (Figure 3) (Table 5) [116–144]. Other diterpenoids such as scapaundulin C (from Scapania undulate (L.) Dum.,) [120], parvifoline Z, parvifoline AA (from Isodon parvifolius) [121], labdane-type diterpenes (from Chloranthus henryi Hemsl.) [124] and sesterterpenoid compounds 3, 11 and 12 (from Sarcotragus sp.) [133] and triterpenoid compounds 1, 2, 5, 7 and 9 (from Ganoderma hainanense) [135], (24R/S)-24-hydroxy-

Figure 3. Anti-CML activity of some NPs which include – flavonoids: 1—Apigenin, 2—Baicalein, 3—Fistein, 4— Galangin, 5—Genistein, 6—Kaempferol, 7—Myricetin, 8—Naringenin, 9—Nobiletin, 10—Oroxylin A and 11— Tamarixetin. Terpenoids: 1—Gukulenin A, 2–4—Hebeiabinin A, D & E, 5—Parvifolines C, 6—3-hydrogenwadaphnin, 7 —Tanshinone I, 8—EM23, 9, 10—Felixins F & G, 11—Kadlongilactone D. Polyketides: 1—Epiaspinonediol, 2—aza-EpoB, 3—dEpoF, 4—Heveadride, 5—Gilvocarin HE, 6—Rhizoxin, 7—Salarin C, 8—Tausalarin C, 9—Trineurone E. Lignans: 1— Arctigenin, 2—Cleistanthin A, 3—Honokiol, 4—6-hydroxyjusticidin C, 5—(+) –lariciresinol 9'-p-coumarate, 6—4 methoxy magndialdehyde. Peptides: 1, 2—chujamide A, B, 3—gombamide A.


Table 4. Anti-CML activity of flavonoids.

3α 10α-epoxy-9-eip-cucurbita-25-ene (1a, b) (from Fructus Viticis Negundo) [136] are also shown to efficiently inhibit CML cell proliferation.

#### 2.4. Polyketides

Figure 3. Anti-CML activity of some NPs which include – flavonoids: 1—Apigenin, 2—Baicalein, 3—Fistein, 4— Galangin, 5—Genistein, 6—Kaempferol, 7—Myricetin, 8—Naringenin, 9—Nobiletin, 10—Oroxylin A and 11— Tamarixetin. Terpenoids: 1—Gukulenin A, 2–4—Hebeiabinin A, D & E, 5—Parvifolines C, 6—3-hydrogenwadaphnin, 7 —Tanshinone I, 8—EM23, 9, 10—Felixins F & G, 11—Kadlongilactone D. Polyketides: 1—Epiaspinonediol, 2—aza-EpoB, 3—dEpoF, 4—Heveadride, 5—Gilvocarin HE, 6—Rhizoxin, 7—Salarin C, 8—Tausalarin C, 9—Trineurone E. Lignans: 1— Arctigenin, 2—Cleistanthin A, 3—Honokiol, 4—6-hydroxyjusticidin C, 5—(+) –lariciresinol 9'-p-coumarate, 6—4-

methoxy magndialdehyde. Peptides: 1, 2—chujamide A, B, 3—gombamide A.

12 Anti-cancer Drugs - Nature, Synthesis and Cell

Polyketides represent a large group of natural products that are produced by microorganisms and plants. These are secondary metabolites, derived by the repetitive condensation of acetate



\*LC50, lethal concentation.

Terpenoid class Name of terpenoid Source of isolation IC50 value on

Diterpenoids Caesalminaxin D and H Caesalpinia minax 9.9 ± 1.7 and

Hebeiabinin A, D and E Isodon rubescens

3-Hydrogenwadaphnin Dendrostellera

Ludongnin J Isodon rubescens

Tanshinone I Salvia miltiorrhiza

Sesterterpenoids Felixins F and G Ircinia felix 1.27 and 19.9

Compounds 8, 9 Smenospongia sp. \*0.11 and

Gukulenin A and diterpenoid pseudodimers (2–5)

Diterpene compounds 11, 12,

7β,11β,14β-Trihydroxy-entkaur-20-al-6,15-dioxo-16-ene

Enanderianins K—P, Rabdocoetsin B and D

ent-Kaurane diterpenoids 11,

L-Arabinopyranosyloleanolic

16, 17 and 20

Two linear furanosesterterpenes

Triterpenoids 3β,21β,24-Trihydroxyserrat-14-en-24-(4′ hydroxybenzoate)

acid

13, 14 and 15

14 Anti-cancer Drugs - Nature, Synthesis and Cell

Sesquiterpenoids EM23 Elephantopus mollis 10.8 μM ↟ caspases, PARP

K562 cells

9.2 ± 0.9 μM

0.12 ± 0.01, 0.44 ± 0.01, 0.32 ± 0.05 and 0.04 ± 0.09 μM

86.4, 66.3, 91, 45.1 and 58.6 μM

Isodon xerophilus 0.04 μM – [122]

53.21, 5.05 and 0.91 μM

15 nM con. caused 45% apoptosis

and 1.55 μM

μM

0.97μ/ml

Palhinhaea cernua 56.1 μg/ml – [137]

Phorbas gukhulensis \*0.26 ± 0.03,

petroleum ether soluble fraction of the aerial parts of Tirpitzia ovoidea ethanol extract

var. rubescens

var. lushiensis

5-Episinuleptolideacetate Sinularia species 4.09 μg/ml ↓c-ABL, Akt,

Garcinia hanburyi

resin

Bunge.

lessertii

Parvifolines C Isodon parvifolius 13.8 μM – [125]

Isodon enanderianus 0.13–0.87 μg/ ml

Isodon nervosus 2.39, 4.11, 1.05

Smenospongia sp. 3 and 31.6 μg/ ml

Mechanism of action

cleavage and ↓ NFκB. Loss of MMP

– [117]

– [118]

– [119]

– [123]

– [126]

– [127]

– [131]

– [132]

– [134]

[129]

[130]

[144]

0.18 μg/ml – [128]

NFκB

4.15 μM – [138]

and ↓Survivin

38 ± 5.2 μM ↟ Bax, caspase 3

References

[116]

Table 5. Anti-CML activity of terpenoids.

units or other short carboxylic acids catalyzed by multi-functional enzymes called polyketide synthases (PKSs) which is similar to fatty acid synthases [145]. Many polyketides suppress CML cell proliferation and induce apoptosis (Figure 3) (Table 6) [146–155].

## 2.5. Lignans

Lignans, natural compounds that are exclusively found in plants, are derived from amino acid phenyl alanine. They possess anti-oxidant and anti-cancer activities [156]. Various lignans effectively inhibit CML cell proliferation and induced apoptosis (Figure 3) (Table 6) [157–163].

## 2.6. Saponins

Saponins are a diverse group of secondary metabolites widely distributed in the plant kingdom. They produce soap-like foam when shaken in aqueous solutions. Their structure comprise of triterpene or steroid aglycone and one or more sugar chains. They exhibit anti-cancer and anti-cholesterol activities [164, 165]. Various saponins inhibited CML cell proliferation (Table 6) [166–174].

#### 2.7. Peptides

Two peptides, chujamides A (1) and B (2), isolated from the marine sponge Suberites waedoensis inhibited K562 cell growth with LC50 values of 37 and 55.6 μM [175]. Another peptide, gombamide A (1), isolated from the marine sponge Clathria gombawuiensis inhibited CML cell proliferation with LC50 of 6.9 μM [176]. Haishengsu (HSS), a protein extract from



Table 6. Anti-CML activities of polyketides, lignans, saponins and peptides.

Tegillarca granosa, when administered in mice-bearing MDR K562/ADM cell tumors inhibited tumor growth and downregulated mdr1 gene, BCR-ABL and sorcin [177]. HSS was also tested against MDR K562/ADR cells, and it induced apoptosis at 20 mg/l [178]. HSS also inhibited K562 cells at G0/G1 and S phase and lowered Bcl-2 and enhanced Bax levels (Figure 2) (Table 6) [179].

#### 2.8. Others natural products

Type of NP Name of compound Source of isolation IC50 value

Polyketides Epiaspinonediol Aspergillus sp. 16–02–1 44.3 μg/

Hygroscopicus

QD01–2

Rhizoxin Burkholderia rhizoxina 5×10−<sup>7</sup> μg/

Dichotomyces cejpii

chlamydosporia and Monosporium bonorden

Salarin C Fascaplysinopis sp. 0.1 μM ↟ caspase 3 and 9

Lignans Arctigenin Asteraceae family – ↑Bax and ↓ Bcl-2 [157]

(Rox B)

6-Hydroxyjusticidin C Justica procumbens 43.9 ± 2.9

Rend. Et wils.

koreana.

Tausalarin C Fascaplysinopis sp. 1 μM – [154] Trineurone E Peperomia trineura 26 μM – [155]

4-Methoxy magndialdehyde Magnolia officinalis 3.9 μg/ml – [163]

Astrogor dumbea 26.8—45.6

Tupistra wattii Hook.F. 35.67,

Cynanchum wilfordii

Total saponin content Aralia Taibaiensis – Loss of MMP. ↑ Bax

roots

Geldanamycin Streptomyces

16 Anti-cancer Drugs - Nature, Synthesis and Cell

Heveadride Ascomycota

Gilvocarin HE Streptomyces sp.

Cleistanthin A Cleistanthus collinus

Honokiol Magnolia officinalis

(+)-Lariciresinol 9′-p-coumarate Larix olgensis var.

5,5′-Dimethoxylariciresinol-4′- O-β-D-glucoside (DMAG)

Saponins Astrgorgiosides A, B, C (19-

saponins)

saponins)

norand aromatized B ring bearing steroid aglycone)

Tenacissoside C (steroidal

Compounds 14 and 15 (C21 steroidal pregnane sapogenins)

Wattoside G, H, and I (steroidal

Radicicol Diheterospora

on K562

82.7 ± 11.3 μM

mL

ml

Mahonia – ↓IC50 of DOX from

μM

μM

76.16 and 76.96 μM

Marsdenia tenacissima 31.4 μM ↓ cyclin D, Bcl-2, Bcl-

Mechanism of action References

– [146]

↟ TNFα [149]

– [152]

[153]

[159]

[161]

[170]

[172]

– ↓c-Raf, Akt, BCR-ABL [148]

45 μM – [150]

– ↓p-Raf1, p-BCR-ABL [151]

cleavage

0.4 μM – [158]

34.93 to 12.51 μM

28.4 μM – [160]

2.9 μg/ml – [162]

3

↟ROS levels, casapase

– [168]

– [169]

xL and ↑caspases 3, 9, Bax and Bak

6.72 μM – [171]

and ↓ Bcl-2

Other natural products such as acetylenic metabolites, betanin, bufadienolide, mamea a/ba, cryptotanshinone, bavachalcone, polyanthumin, cubebin, denbinobin, digallic acid, perforanoid A, β- and α-mangostin, parthenolide, perezone, polyphyllin D, squamocin, toxicarioside H, tripolide, woodfordin I and rhodexin A inhibited CML cell proliferation (Table 7) [180–230]. Moreover, many plant crude extracts enriched with NPs inhibited the CML cell proliferation and induced apoptosis (Table 8) [231–280].

#### 2.9. Natural products in clinical trials

Of the several natural products, Homoharringtonine (alkaloid) (NCT00114959) is currently under phase II study sponsored by Chem Genex pharmaceuticals to reverse the Gleevac resistance in CML patients [281]. 17-AAG (analogue of glendamycin–polyketide) (NCT00100997) is currently under phase I clinical trial sponsored by Jonsson Comprehensive Cancer Center collaborated with National Cancer Institute (NCI). Efforts are underway to determine the side effects and optimal dose of 17-AAG for treating patients with CML in chronic phase who did not respond to imatinib-mesylate [282]. Paclitaxel (diterpenoid) (NCT00003230) is currently under Phase I/II trials to study the effectiveness in treating patients with refractory or recurrent acute leukemia or CML. This work is sponsored by Swiss Group for Clinical Cancer Research [283].



Name of NP Source of isolation IC50 value on

Acetylenic metabolites Stelletta sp. 43.5, 51.3 and

Bufalin 3β-acrylic ester (Bufadienolide)

methylcarbazole-3-carboxylate and 2-methoxy-1-(3-methyl-buten-1-yl)- 9H-carbazole-3-carbaldehyde

18 Anti-cancer Drugs - Nature, Synthesis and Cell

Pangelin and oxypeucedanin

Cryptotanshinone (lipid soluble

Polyanthumin (novel chalcone trimmer) and sulfuretin

1,4,5-Trihydroxy-7-methoxy-9Hfluoren-9-one, dendroflorin and denchrysan (fluorenones)

9α-Acetoxyartecanin, apressin, inducumenone and centaureidin

hydrate acetonide

active compound)

Toxicarioside F and G Latex of Antaris

Mamea A/BA Calophyllum

Denbinobin 5-Hydroxy-3,7-

C27-Steroidal glycoside Liriope graminifolia

Linoleic acid Methanol extracts

3-Formylcarbazole,

K562 cells

62.5 μg/ml

20.48 ± 1.78, 26.5 ± 2.12 and 23.49 ± 1.85 μg/

ml

Bavachalcone (Chalcones) – 2.7 μM – [191]

(−)-Cubebin Piper cubeba 8.66 ± 0.43 μM – [193]

Digallic acid Pistascia lentiscus – Induced DNA fragmentation

Achillea clavennae 9.84 ± 2.52, 4.44

Perforanoid A (limonoid) – 4.24 μM – [200]

β- and α-Mangostin Garcinia malaccensis – [202, 203]

Betanin (betacyanin pigment) Opuntia ficus-indica 40 μM ↟ PARP cleavage, release of

Clausena lansium (Lour.) Skeels

toxicaria (Pers.) Lasch

brasiliense

Memecylon polyanthum H.L. Li.

dimethoxy-1,4 phenanthraquinone

Dendrobium chrysotoxum

(Linn.) Baker

of proso and Japanese millet Mechanism of action References

[182]

[189, 190]

[194]

[195]

– [180]

– [184]

Cyt C and ↓ BCl-2. Loss of

– – [185]

0.04–0.59 μM – [187, 188]

cleavage and ↓BCR-ABL, STAT3, mTOR & eIF4E

and pro-apoptotic effect in

– [196]

– [199]

1.84 μM ↓ BCR-ABL, CrkL and⊥G2/M phase

CML cells

18.6 μg/ml – [198]

68 μM – [201]

– [192]

MMP

"Ch'an Su" 6.83 nM – [183]

Angelica dahurica 8.6–14.6 μg/ml – [186]

Salvia miltiorrhiza – induced apoptosis ↑ PARP

45.4 and 30.5 μg/ml

32.18, 26.65 and 52.28 μg/ml

± 0.76, 52.53 ± 8.43 and 5.37 ± 0.8 μM


\*LC50–lethal concentation.

Table 7. Anti-CML activity of other natural products.



Name of NP Source of isolation IC50 value on

Datura metel flowers

Garcinia hanburyi

Isodon rubescens var. rubescens

Hypericum beanie

Rhodexin A Rhodea japonica 19 nM ⊥G2/M phase induced

Gambogic acid Garcinia hanburyi 0.62 μM ↓p-BCR-ABL, pSTAT5, p-

At 500 μg/ml the cell viability of CML cells was found to be 60.1 ± 8.5 and 47.5 ± 11.9%

AQE extract of Rhodiola imbricate – ↓CML cell proliferation at 100 and

DCM) extract of Psidium guajava L. 32 μg/ml – [238]

resin

Withametelins I, J, K, L and N MeOH extract of

Hyperbeanols B and D MeOH extract of

Table 7. Anti-CML activity of other natural products.

Woodfordin I (macrocyclic ellagitannin dimer)

Xindongnins C–D, A, B, melissoidesin G, dawoensin A and

\*LC50–lethal concentation.

Acetone extract of Peucedanum nebrodense (Guss.) Strohl.,

AQE extract of Cornus officinalis

AQE extracts of the husk fiber of the typical A and common varieties of Cocos nucifera (Palmae)

Abnobaviscum F® (standardized AQE extract of European mistletoe from the host tree Fraxinus)

Chloroform extract of Polyalthia

Chloroform extract of Tecomella

Sieb. et Zuce

rumphii stem

undulata bark

(xanthones)

glabcensin V

Gaudichaudic acid, isogambogenic acid and deoxygaudichaudione A

20 Anti-cancer Drugs - Nature, Synthesis and Cell

K562 cells

0.05, 2.5, 0.12, 0.55 and 0.46 μM

0.41 ± 0.03, 2.1 ± 0.14 and 1.74 ± 0.22 μg/ml

16.9 and 20.7 μM

Curcumin Curcumina longa 20 μg/ml ↓BCR-ABL, Hsp90, WT1 [227, 228]

Plant extract IC50 value on K562 cells Mechanism of action References

– – ↓ Bcl-2, Bcl-xL, Bax, c-Abl &

Mechanism of action References

[222]

[226]

[229, 230]

[234]

[235]

[237]

– [221]

– [223]

– [225]

BCR-ABL and Loss of MMP

0.3–7.3 μg/ml – [224]

CRKL, pERK1/2, p-Akt

– [233]

200 μg/ml for 72 hrs. induced ROS & apoptosis and ⊥G2/M phase

↓ Bcl-1, Erk-1/2 & PKB phosphorylation

Induced DNA fragmentation &

apoptosis

14–10.27 μg/ml – [231]

100 μg/ml – [232]

– ↟ caspase 9, JNK-1,2, p38 MAPK and

30 μg/ml ↟ FAS, FADD, & caspase 8, 3/7.

40–60μ/ml – [236]

apoptosis


AQE, aqueous, DCM, dichloromethane, HEX, hexane, EtOH, ethanol, EtoAc, ethyl acetate, MeOH, methanol, ^TGI, tumor growth inhibition,\*ED50, –effective concentration; # GI50, growth inhibition.

Table 8. Anti-CML activity of plant extracts.
