1
Animal images from Google images
Literature Seminar-Kelsey Mayer



Venom is typically characterized by its ability to impair the vital functions of organisms.
This ability is due to interactions with physiologically important molecular targets.

Venomous species have coevolved with their prey such that venom components are highly efficient and selective in their toxicity.

Venom can be isolated from a variety of animals such as snakes, spiders, scorpions, bees and wasps, marine snails and even mammals.
2
From Google images
Estrada, G., et al. Nat. Prod. Rep. 2007, 24, 145-161.
Nelson, L. Nature, 2004, 429, 798-799.
Sher, E., et al. Biochimie. 2000, 82, 927-936 .

Venom

Venomous species are generally considered to be dangerous and undesirable animals. In fact ~ 20,000 people die from snake bites yearly, ~30 die from cone snail stings and ~20 from spider bites.

However, when the venom components of these animals is isolated and examined they are found to have some remarkable medicinal properties.
3
Severe necrosis from a snake bite
Nelson, L. Nature, 2004, 429, 798-799.
Kasturiratne A., et al. PLoS Med. 2008, 5, 218.

Venom


Venom samples are extremely complex and contain a wide variety of components from organic acids to large proteins.
This makes separation and structure/sequence determination difficult.
This can require extensive purification and characterization through the use of NMR, mass spectrometry and Edman sequencing. In many cases, with small molecule components the stereochemistry can only be determined through the synthesis of analogs.
4
% concentration of acetonitrile
Lucio, A. D., et al. Protein Peptide Lett. 2008, 15, 700-708.

Venom


Because of the difficulties in isolating and characterizing venom components, new active components are being discovered regularly.
Many of these components have remarkable physiological properties and have been examined for their ability to contribute to human health and well-being.
 There are venom components that may be able to:



Treat cancer and interact with platelet aggregation.
Alleviate chronic pain
Treat neurodegenerative disorders.
5
Uemura, D., et al. Pure appl. Chem. 2009, 81, 1093-1111.

6
RGD site



Disintegrins are peptides that are isolated from snake venom
These peptides vary in size from
5000-14,000 Da.
They are disulfide rich.

Can be classified into several catagories,


They are either mono- or dimeric.
They are classified as either RGDcontaining or non-RGD containing.
(Arg-Gly-Asp)
Flavoridin: PDB code 1FVL
Swenson, S., et al. Curr. Pharm. Design. 2007, 13, 2860-2871.


RGD-containing disintegrins are effective antagonists of several of the subtypes of proteins known as Integrins.


Integrins are proteins on the cell surface that mediate attachment between the cell and the tissues around it, such as the extracellular matrix (ECM)
Integrins are heterodimers that contain an α and β subunit that are non-covalently associated.
RGD binding site
Integrin Protein
Cell Membrane
7
Francavilla, C. et al. Semin. Cancer Biol. 2009, 19, 298–309.
Yeh, C. H., et al. Blood. 1998, 92, 3268-3276.



Several integrins bind to extracellular matrix proteins through the RGD sequence that these proteins contain.
RGD-containing disintegrins are able to competitively inhibit binding to these extracellular matrix proteins via the RGD binding site on the α subunit of the integrin protein.
8
Zhou, Q., et al. Breast Cancer Res. Treat. 2000, 61, 249-260.


Disintegrins have been shown to prevent tumor cell growth through inhibition of angiogenesis, prevent tumor metastasis through inhibition of cellular adhesion and inhibit platelet aggregation.

Inhibition of platelet aggregation and cellular adhesion occurs through competitive inhibition at the RGD binding site of integrins.
 The mechanism of angiogenesis inhibition is not fully understood. Though it is known that this occurs through interactions with the α
V
β
3 integrin subtype.
9
Micrograph of rat muscle that shows blood vessels growing toward a sarcoma tumor. www.dfhcc.harvard.edu
Zhou, Q., et al. Breast Cancer Res. Treat. 2000, 61, 249-260.


Angiogenesis is the process through which new blood cells form from pre-existing blood cells.

Angiogenesis is a leading factor in cancer proliferation

Method by which tumor cells are provided with oxygen and nutrients.
10
Francavilla, C. et al. Semin. Cancer Biol. 2009, 19, 298–309.


Within the last 10 years a large group of disintegrins have been found to inhibit angiogenesis as well as prevent adhesion of tumor cells to the extracellular matrix.



The disintegrin accutin has been found to inhibit angiogenesis.
The disintegrin salmosin exhibited anti-metastatic effects in vivo.
The disintegrin contortrostatin inhibits tumor growth and angiogenesis .
11
Swenson, S., et al. Curr. Pharm. Design. 2007, 13, 2860-2871.




Accutin is a RGD-containing disintegrin isolated from the snake Agkistrodon acutus.
It has been shown to inhibit endothelial cell adhesion in vitro and in vivo.
Research indicates that this occurs primarily through an antagonistic interaction with the integrin subtype α v
β
3.
12 From Google images
Yeh, C. H., et al. Blood. 1998, 92, 3268-3276.


Accutin was shown to effectively inhibit angiogenesis in vivo through the use of a chick embryo model.
Control


In the control case the chick embryo was dissected and observed by microscope indicating large amounts of angiogenesis.
In the accutin example the chick embryo was coated with a 10 μM solution of accutin and observed after 48 hours of incubation.
Accutin at 10 μM
13
Yeh, C. H., et al. Blood. 1998, 92, 3268-3276.



Contortrostatin is an RGD-containing disintegrin isolated from the venom of the southern copperhead snake
(Agkistrodon contortrix contortrix).
It is homodimeric, each monomeric unit is made up of 65 amino acid residues and each contains one RGD site which are placed at the tip of a flexible loop.
From Google images
14
Swenson, S., et al. Mol. Cancer Ther. 2004, 3, 499-511.


Analysis of contortrostatin has indicated that it has significant affects on inhibition of tumor growth and metastasis.

Injection of contortrostatin daily into a tumor mass of human breast cancer cells in a mouse model indicated that it significantly inhibited tumor growth and reduced metastasis by
65%.

Contortrostatin inhibits angiogenesis through interaction with the integrins α
5
β
3
, α v
β
3 and α v
β
5
.
15
Swenson, S., et al. Mol. Cancer Ther. 2004, 3, 499-511.



Researchers studied the efficacy of contortrostatin encapsulated within a liposome.
Liposome encapsulation allows contortrostatin to be delivered intravenously by IV and delivered effectively to the tumor site.

The encapsulated contortrostatin does not elicit an immune response and increases the in vivo half life of contortrostatin from 0.5 hours to 19 hours.
16
From Google images Swenson, S., et al. Mol. Cancer Ther. 2004, 3, 499-511.



Intravenously administered LCN was compared to CN that had been directly injected into the tumor.
Found that the LCN was an effective inhibiter of tumor cell growth when injected intravenously.
17
Swenson, S., et al. Mol. Cancer Ther. 2004, 3, 499-511.


While the absolute structure of contortrostatin is not known it is believed to be similar to the heterodimeric
RGD-containing disintegrin acostatin.

Acostatin is also isolated from Agkistrodon contortrix contortrix, similar to contortrostatin it has ~ 65 amino acid residues and one RGD sequence per monomeric unit.
18
Moiseeva, N. et al. Acta Cryst . 2008, D64, 466–470.




In acostatin and most disintegrin dimers the two units orient such that the RGD sequences are opposite each other. This occurs through the disulfide linkage at the n-terminus.
The loop containing the RGD sequence is flexible.
The secondary structure of disintegrins is observed in large part because of the highly conserved cysteine residues which form the disulfides bond that yield the disintegrin’s secondary structure.
Acostatin: PDB code 3C05
19
Moiseeva, N. et al. Acta Cryst . 2008, D64, 466–470.

Flexible Loop
RGD site
Acostatin: PDB code 3C05
20
Moiseeva, N. et al. Acta Cryst . 2008, D64, 466–470.




Conotoxins are small peptides that are isolated form marine cone snails.
Each cone snail species produces ~100 different conotoxins and there are over 500 different species of cone snails.
The spectrum of ion channels and receptors that are targeted by conotoxins is vast.
21
ω-MVIIA: PDB code 1TT3
Han, T. S., et al. Curr. Pharm. Design. 2008, 14, 2462-2479.



Conotoxins share few distinct features.
They are rich in disulfide bonds as well as post-translation modifications. The placement of the disulfide bonds is conserved across a family of conotoxins but there are few similarities in the rest of the primary sequence or the post-translational modifications.
22
Red = 4 residues
Purple = 7 residues
Han, T. S., et al. Curr. Pharm. Design. 2008, 14, 2462-2479.


Out of the few hundred identified conotoxins, 1 is currently on the market for the treatment of chronic pain,
6 have made it to clinical trials, and 4 are in pre-clinical trials.
Conopeptide
ω-MVIIA
Conantokin-G
Α-Vc1.1
CGX-1204
Indication Molecular target
Intractable pain N-type calcium channels/antagonist
Intractable epilepsy
NMDA receptor/antagonist
Neuropathic pain nAChR/antagonist
Muscle relaxer nAChR/antagonist
Clinical stage
Phase IV
(market, Elan)
Phase I
Phase II
Pre-clinical
23
Han, T. S., et al. Curr. Pharm. Design. 2008, 14, 2462-2479.

 Research indicates that α-Conotoxins are effective antagonists of nicotinic acetylcholine receptors
(nAChRs).
 There are several native ligands for nAChRs, including nicotine and acetylcholine. These bind at the interfaces of two subunits of the receptor.
24 acetylcholine nicotine
Han, T. S., et al. Curr. Pharm. Design. 2008, 14, 2462-2479.

α-
α-CTx Primary sequence
1 23 5 8 12 16
PIA RDP CC S N P V C TVH N PQI C
MII G CC S N P A C HLE H SNL C
GIC G CC S H P A C AGN N QHI C
OmIA G CC S H P A C NVN N PHI C G
PnIA G CC SL P P C ALN N PKY C
IC
50
(nM) α
3
β
2
74.20
2.20
1.10
11.00
9.56
OmIA: PDB code 2GCZ
25
Luo, S., et al. Biochemistry. 1999, 38, 14542-14548.
Talley, T. T., et al. J. Biol. Chem. 2006, 281, 24678-24686.
Turner, M., et al. Bioorgan. Med. Chem. 2009, 17, 5894-5899.

α-


The common hydrophobic and hydrophilic strips are responsible for the binding affinity with the pertinent subtypes of nAChRs.
It is believed that hydrophobic interactions are the predominant factor for ligand binding to
NAChRs
26
OmIA: PDB code 2GCZ
Talley, T. T., et al. J. Biol. Chem. 2006, 281, 24678-24686.
Turner, M., et al. Bioorgan. Med. Chem. 2009, 17, 5894-5899.

α-

The amphiphilic α -helix, His and Asn residues at positions
5 and 12 and the disulfides bonds are all significant contributors to the binding selectivity for the αconotoxins.
Blue = subunits of receptor
Green = bound conotoxin
27
Acetylcholine binding proteins, a homopentamer homolog of nAChR, used to model conotoxin binding to nAChR: PDB code 2C9T
Celie, P. H. N., et al. Nat. Struct. Mol. Biol. 2005, 12, 582-588 .
Tomizawa, M., et al. Biochemistry. 2007, 46, 8798-8806.
Turner, M., et al. Bioorgan. Med. Chem. 2009, 17, 5894-5899.

α-
PDB code 2C9T
28
Celie, P. H. N., et al. Nat. Struct. Mol. Biol. 2005, 12, 582-588 .

α-
PDB code 2C9T
29
Celie, P. H. N., et al. Nat. Struct. Mol. Biol. 2005, 12, 582-588 .



Types of polyamines are commonly found in almost every prokaryotic and eukaryotic cell type.
Acylpolyamines have been shown to interact with ionotropic glutamate receptors, nicotinic acetylcholine receptors and other types of ligand gated ion channels.
 These acylpolyamines are largely responsible for the spider’s ability to paralyze prey.

The first structure of an acylpolyamine isolated from spider venom was determined in 1986 from argiope lobata.
30
From Google images
Estrada, G., et al. Nat. Prod. Rep. 2007, 24, 145-161.



Ionotropic glutamate receptors (iGluRs) are ligand-gated ion channels that mediate excitatory synaptic transmission for vertebrates and are crucial for normal brain function.
Problems with iGluRs leads to disorders such as Ischemia related to stroke, and neurodegenerative disorders. iGluRs are considered important drug targets for these disorders.

One example of an iGluR inhibitor that has made it through clinical trials is memantine, which is used in the treatment of Alzheimer's.
31
Estrada, G., et al. Nat. Prod. Rep. 2007, 24, 145-161.
Mayer, M. L. et al. Annu. Rev. Physiol. 2004, 66, 161-181.





There are 3 subtypes of iGluRs.
N-methyl-D-aspartate, (NMDA)
αAmino-3-hydroxy-5-methylisoxazole-
4-propionic acid hydrate (AMPA)
Kainate
NMD
A
AMPA



Acylpolyamines are antagonists of iGluRs
Acylpolyamines have a high affinity and are highly selective for iGluRs.
However, they are not as selective for the subtypes of iGluRs.
Kainate
32
Estrada, G., et al. Nat. Prod. Rep. 2007, 24, 145-161.
Mayer, M. L. et al. Annu. Rev. Physiol. 2004, 66, 161-181.

33

In NMDA receptors Mg 2+ prevents influx of Ca 2+ unless cell voltage increases resulting in release of Mg 2+
NMDA receptor Non-NMDA receptor

In non-NMDA receptors binding of an agonist results in the influx of Ca 2+
Images from www.standford.edu
Mayer, M. L. et al. Annu. Rev. Physiol. 2004, 66, 161-181.




All polyamines isolated from spider venom share certain structural similarities.
An aromatic moiety at one end with a primary amino or guanidine group at the other end.
A lipophilic core that attaches directly to the aromatic moiety through an amide or amino acid linker.
34
Estrada, G., et al. Nat. Prod. Rep. 2007, 24, 145-161.

35
Wang, F., et al. Org. Lett. 2000, 2, 1581-1583.


Derivatives of
one type of iGluRs.
 In the series of analogs the polyamine core length was varied while the total length of the acylpolyamine constant.
36
Kromann, H., et al. J. Med. Chem. 2002, 45, 5745-5754.
Mellor, I. R., et al. Neuropharmacology. 2003, 44, 70-80.



Derivatives of PhTX-433 were made that are able to selectively inhibit one type of iGluRs.
In the series of analogs the polyamine core length was varied while the total length of the acylpolyamine constant.







PhTX-38 (m = 3, n = 8)
PhTX-47 (m = 4, n = 7)
PhTX-56 (m = 5, n = 6)
PhTX-65 (m = 6, n = 5)
PhTX-74 (m = 7, n = 4)
PhTX-83 (m = 8, n = 3)
PhTX-92 (m = 9, n = 2)
37
Kromann, H., et al. J. Med. Chem. 2002, 45, 5745-5754.


The PhTX-433 derivatives were tested using two electrode voltage clamped mammalian cells expressing one of three subunits of non-NMDA receptors
Antagonist effect on AMPA and Kainate receptors, -80 mV
K i
(
μ
M)
AMPA subtype 2
Kainate
PhTX-433 0.022 ± 0.003
> 5 0.015 ± 0.004
PhTX-56 (m = 5, n = 6) 0.0033 ± 0.0008
5 ± 3 2 ± 1
PhTX-83 (m = 8, n = 3) 0.07 ± 0.02
> 10 0.25 ± 0.02
38
Kromann, H., et al. J. Med. Chem. 2002, 45, 5745-5754.

Argiotoxin-636 derivatives X = NH or CH
2
Y = NH or CH
2
W = NH
2 or CH
Z = NH or O
3

All possible variations were synthesized and tested for potency and selectivity.
 Evaluated by measuring the inhibitory activity on mammalian cells expressing either the AMPA receptor GluR1 or the NMDA receptor subunits NR1 and NR2A.
39
Nelson, J. K., et al. Angew. Chem. In. Ed. 2009, 48, 3087-3091.

IC
50
[nm]
Compound X Y W Z AMPA NMDA Selectivity (IC
50
AMPA / IC
50
NMDA)
1
4
7
NH NH NH
2
NH 77 ± 14 10 ± 1
NH CH
2
NH
2
NH 78 ± 12 842 ± 117
CH
2
NH NH
2
NH 454 ± 27 14 ± 1
8
0.09
32
All data collected in triplicate
40
Nelson, J. K., et al. Angew. Chem. In. Ed. 2009, 48, 3087-3091.



Venom components contain a wide variety of compounds from small molecules to proteins and many of these can be utilized for their physiological properties.
In many cases, acquiring the desired venom component can be difficult as synthesis can be complex and only small quantities can be isolated from the animal.



Despite these difficulties there are a multitude of benefits that can result from venom components.
Components have been identified that interact with a multitude of receptors and ion channels.
These components have been examined for their ability to treat cancer, chronic pain and neurodegenerative disorders.
41



There are still components of venom being identified.
Recently several different types of sulfated nucleosides were identified in spider venom.

Studies indicate that these components
Block kainate receptors and weakly block
L-type calcium channels
42

Many venom components have not been structurally and physiologically characterized.

There are still a huge number of discoveries to be made within this field.
Taggi, A. E., et al. J. Am. Chem. Soc. 2004, 126, 10364-10369.

Professor Samuel Gellman
Dr. Pil Seok Chae
Dr. Brendan Mowery
Dr. Kim Kaufman
Li Guo
Matt Windsor
Jonathan Zhang
Mike Giuliano
Holly Haase
Brooke Richardson
Jay Steinkruger
Aaron Almeida
Lisa Johnson
Brain Parker
Stacy Maynard
David Mortenson
Younghee Shin
Teresa Beary
Joe Grim
Aaron McCoy
43