Oncogenic B-Raf proto-oncogene, serine/threonine kinase-mediated hedgehog signalling in the pathogenesis and targeted therapy of melanoma

Table 2 Key modulators of hedgehog signaling and their mechanisms of action

Compound	EC50	Mechanism of action	Ref.
Cyclopamine	300 nM	Directly blocks HH signaling by binding to and inhibiting SMO receptors	[138,139]
KAAD-cyclopamine	20 nM	Cyclopamine-KAAD is a potent cell-permeable analog of cyclopamine that specifically inhibits HH signaling (with similar or lower toxicity) by binding to SMOA1 and promoting its exit from the endoplasmic reticulum	[140]
SAG	3 nM	SAG is a chlorobenzothiophene-containing HH pathway agonist that regulates the SMO activity by directly binding to SMO’s heptahelical bundle	[141]
Jervine	500-700 nM	Jervine is a steroidal alkaloid that blocks HH signaling by binding to SMO receptors	[142]
Cyclopamine tartrate	20 nM	CycT is an improved analogue of cyclopamine that inhibits the SMO receptor by binding to it	[139]
Cur-61414	100-200 nM	CUR-61414 (aminoproline, mol. wt. 513Da) is a specific and highly potent antagonist of SMO that can block elevated HH signaling activity arising from oncogenic mutations in PTCH-1	[143]
SANT-1	200 nM	SANT-1 is an SMI of SMO and functions as a potent SHH pathway antagonist	[144]
SANT-2	20 nM	SANT-2, belonging to the benzimidazole class of compounds, is an SMI and a cell-permeable antagonist of the SMO receptor	[145]
SANT-3	30 nM	An SMI of SMO receptor	[127]
SANT-4	100 nM	An SMI of SMO receptor	[127]
Compound 5	200 nM	SMI targeting the SMO receptor	[146]
Compound Z	< 1 nM	Compound Z has an efficacy of less than 1 nM and is classified as a second-generation SMO inhibitor	[147]
Vismodegib	< 20 nM	Vismodegib (GDC-0449) is a first-in-class, SMI of SMO	[135]
Saridegib	-	Saridegib (IPI-926), a semisynthetic analogue of cyclopamine with a seven-membered D-ring, functions as an SMI of SMO with improved potency and improved plasma half life However, saridegib is a substrate of the P-glycoprotein transporter, therefore, its extended use causes drug resistance	[133]
Sonidegib (LDE225)	< 20 nM	Orally bioavailable cyclopamine-derived SMO inhibitor that causes cell cycle arrest and apoptosis in variety of cell lines	[148]
TAK-441	4.6 nM	TK-441 is an SMI of SMO that blocks castration-resistant progression of LNCaP xenografts by obstructing paracrine HH signaling	[149]
2-amino-thiazoles	30 nM	2-Aminothiazole (JK184) is inhibitor of Shh-N-mediated Gli-transcription and retards the growth of cancer cell lines with aberrantly activated HH signaling	[150]
Gant-58	5 μM	SMI that inhibits GLI1-mediated GLI luciferase	[150]
Gant-61	5 μM	SMI that inhibits GLI1-mediated GLI luciferase	[150]
IPI-296	< 20 nM	IPI-926 is a novel, natural product-based SMI of SMO	[151]
BMS-833923 (XL139)	< 20 nM	BMS-833923 is an orally bioavailable SMI of the SMO receptor that dose-dependently affects HH signature gene transcription in vitro	[152]
L4	2.33 nM	L-4 is a potent, orally bioavailable antagonist of the SMO receptor that exhibits potent anti-tumor effects against medulloblastoma, BCC and other cancers	[153]
Robotnikinin	< 10 μM	SMI that interferes with SHH protein function	[154]
Vitamin D3	100 μM	Vitamin D3 is an SMI that binds to SMO and blocks GLI reporter activity in cultured fibroblasts in vitro	[155]
RU-SKI 41	0.66 μM	5-acyl-6,7-dihydrothieno(3,2-c) pyridine 41 (termed RU-SKI43) is an SMI that blocks HHAT	103]
RU-SKI 43	2.38 μM	SMI that inhibits HH acyltransferase	[156]
RU-SKI 101	-	SMI that inhibits HH acyltransferase	[156]
RUSKI-201	0.20 μM	SMI that blocks HH acyltransferase	[157]
CA1	-	SMI of SMO that affects ciliary localization and ciliogenesis	[158]
CA2	-	SMI of SMO that affects ciliary localization and ciliogenesis	[158]
NVP-LEQ506	2-4 nM	Orally bioavailable SMI of SMO with potential antineopastic activity	[159]
PF-04449913	191 nM	PF-04449913 is a novel oral SMI that selectively binds to SMO	[160]
LY2940680 (taladegib)	-	SMI that inhibits SMO	[161]
BRD-6851	0.4 μM	SMI that inhibits SMO	[132]
SEN450	-	SMI that inhibits SMO	[162]
MRT-83	10 nM	A novel, potent SMO antagonist from the acylguanidine family of SMIs	[163]
Arcyriaflavin C	11.3 μM	Attenuate GLI1 activity through PKC/MAPK pathway blockade	[164]
Physalins F	0.66 μM	Attenuate GLI1 activity through PKC/MAPK pathway blockade	[164]
HPI1	1.5 μM	SMI influences the processing, activation, and/or trafficking of GLI1	[165]
HPI2	2 μM	SMI influences the processing, activation, and/or trafficking of GLI1	[165]
HPI3	3 μM	SMI influences the processing, activation, and/or trafficking of GLI1	[165]
HPI4 (Ciliobrevin A)	7 μM	SMI influences the processing, activation, and/or trafficking of GLI1	[165]
Arsenic trioxide	2.7 μM	SMI inhibits GLI transcription factors. ATO directly bound to GLI1 protein	[166]
Glabrescione B	-	Glabrescione B is an SMI that interferes with GLI1/DNA interaction in HH-dependent tumor cells well as the self-renewal of tumor-derived stem cells	[167]
Pyrazolo-imidazole smoothib	157 ± 118 nM	Smoothib functions as an antagonist of SMO by binding to its heptahelical bundle, preventing its localization to the cilia. This subsequently reduces the expression of HH target genes	[168]

EC50: Half maximal effective concentration; KAAD: Keto-N-aminoethylaminocaproyldihydrocinnamoyl cyclopamine; HH: Hedgehog; SMOA1: SmoothenedA1; SAG: Smoothened agonist; SMO: Smoothened; CycT: Cyclopamine tartrate; CUR: N-((3S,5S)-1-(Benzo[d][1,3]dioxol-5-ylmethyl)-5-(piperazine-1-carbonyl)pyrrolidin-3-yl)-N-(3-methoxybenzyl)-3,3-dimethylbutanamide; SMI: Small molecule inhibitor; SANT: Series of smoothened antagonist; GDC-0449: 2-chloro-N-(4-chloro-3-(pyridin-2-yl)phenyl)-4-(methylsulfonyl)benzamide; IPI926: N-[(5βH)-5,6-Dihydro-17,23β-epoxy-16a-homoveratraman-3α-yl] methanesulfonamide; TAK: 6-ethyl-N-[1-(2-hydroxyacetyl)piperidin-4-yl]-1-methyl-4-oxo-5-phenacyl-3-(2,2,2-trifluoroethoxy)-4,5-dihydro-1H-pyrrolo[3,2-c]pyridine-2-carboxamide; GLI: Glioma associated oncogene homolog; BCC: Basal cell carcinoma; HHAT: Hedgehog acyltransferase; RU-SKI: Rutgers University Small-molecule Kinase Inhibitor - naming originates from the lab’s kinase inhibitor program; CA: Cyclopamine; NVP-LEQ506: 2-{5-[(2R)-4-(6-benzyl-4,5-dimethylpyridazin-3-yl)-2-methylpiperazin-1-yl]pyrazin-2-yl}propan-2-ol; BRD-6851: N-(4-chlorobenzyl)-2-[((3R,11S,E)-3-(4-chlorophenyl)-5,12-dioxo-1-oxa-4-azacyclododec-8-en-11-yl)acetamide]; SEN450: N-[3-(1H-benzimidazol-2-yl)-4-chlorophenyl]-3,5-dimethoxybenzamide; MRT83: N-(2-methyl-5-(3-(3,4,5-trimethoxybenzoyl)guanidino)phenyl)-[1,1′-biphenyl]-4-carboxamide hydrochloride; PKC: Protein kinase C; MAPK: Mitogen activated protein kinase; HPI: Hedgehog pathway inhibitor.