DRUGS FROM MARINE SOURCES

PRINCE1111038Principles of drug design

Why marine sources?

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Competition for survival and environmental pressure

Biodiversity

DefenceAttack

Signalling

Chemical Diversity

Potential new drugs4

Marine natural ProductsMany natural products from these

organisms act as chemical weapons and are highly potent inhibitors of physiological processes in prey, predator or competitor

Several show pharmacological activities and are effective against cancer, AIDS, arthritis

Highly potent6

• α- and αA-conotoxins -competitively inhibited Nicotinic acetylcholine receptors (nAChR)

•ψ-conotoxins noncompetitiveinhibition of this family of receptors.

•σ-conotoxins - antagonize the related 5-HT3 serotonin receptor

•ω-conotoxins - calcium-channelblockers

Harfner et al,2003

•κ-conotoxins - potassium-channelblockers•μ-, as well as μO-conotoxins

sodium channel blockersAnd many other conotoxins…

Conus magus (Cone snail)8

ZiconotidePrialt™, Azur PharmaSynthetic equivalent of naturally occurring ω-conotoxin MVIIAIt is considered medically necessary for

the management of severe chronic pain in those individuals for whom intrathecal (IT) therapy is warranted, and who are intolerant of or refractory to other treatment, such as systemic analgesics, adjunctive therapies or IT morphine.

It is administered by intrathecal infusion

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Intrathecal infusion

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Biology and chemistry of Ziconotide

•Amino acid sequence of -MVIIA, illustrating the characteristic disulphide linkage pattern between the six cysteine residues. The three disulphide bridges serve to stabilize the native conformation of the toxin and cause the peptide to display 4 loops, some of which contain important structural determinants of N-type calcium channel blocking activity, eg, tyrosine-13

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Three-dimensional structure ofthe synthetic ω-conotoxin MVIIA polypeptide. The

cylinderrepresents the amide backbone of ω-conotoxin

VIIAoverlayed against an electrostatic potential

surface.

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Pharmacology• 25-amino acid peptide• Six cysteine residues linked by 3

disulfide bonds Pharmacodynamics : N-type voltage-sensitive calciumchannels (NVSCCs) were subsequently identified asits target site. It potently inhibits the conduction of nerve signals by specifically blocking the NVSCC. In the complex with NVSCC, it forms a compact folded structure with a binding loop between Cys8 and Cys15 that also contains Tyr13, an important amino-acid residue located at the binding site.

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Direct blockade of N-type channel inhibits the activity of a subset of neurons, including pain-sensing primary nociceptors which are controlled by the former

50 times more effective than morphineN-Ca Channel

(Miljanich 2004)17

 PharmacokineticsBioavailability = 50%Rat model : ED50 = 49pM (Morphine

ED50 = 2.1nM)Half life =  1.3 hourExcretion = <1% urineTmax = 5.3 hourOral,Mouse : LD50 = 300 mg/kg Oral, rabbit : LD50 = 3200 mg/kg Oral, rat : LD50 = 980 mg/kg

Yaksh et al,201218

Side effectsMost frequent : Dizziness, nausea, confusional

state and nystagmus (>25%)Meningitis, when infused with an external

catheter Cases of meningitis were not observed when an

internal catheter was surgically implanted.

Side effects are to be weighed against high level of pain management, its degree and length and also lack of dependence and tolerance even after long treatment when most other drugs do not work.

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20 The Caribbean sea-squirt Ecteinascidia turbinata

ecteinascidins

Ecteinascidin-743 (ET-743 / Trabectedine) Yondelis™ by PharmaMar/Johnson & Johnson/OrthoBiotech)

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A significant milestone in development of marine derived drugs.

First marine-derived anticancer drug to reach the market – after 40 years of its discovery and 17 years after publication of its structure.

Extracts of caribbean derived tunicate Ecteinascidia turbinata• the yield for ET-743 from the tunicate is very low (~10 parts per million)

Structure of Ecteinascidin

22 Rinehart and Wright et al,1990

•Three fused tetrahydro- isoquinoline rings•The connection of the third tetrahydroisoquinolinering to the base structure by a thioether bridge completes a 10-membered lactone - a distinctive structuralfeature of ecteinascidins•8 rings, 7 chiral centers

details

Cytotoxic Activity

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ecteinascidins were found to be cytotoxic against L1210 leukaemia cells (IC50 value of 0.5 ng per ml)

strong in vivo antitumour effects in various mice models bearing P388 lymphoma, B16 melanoma, M5076 ovarian sarcoma, lewis and lX-1 human lung carcinoma, and MX-1 human mammary carcinoma xenografts

Synthesis

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the first multistep synthesis of the compound was completed in 1996 (0.75% yield) (Corey et al, JACS)

Large scale semi synthesis developed by PharmaMar that starts with cynosafracin B which can be produced by fermentation of Pseudomonas fluorescens

Mechanism of Action :

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A ring

C ring

Fig. Molecular-dynamics model showing the alkylation of DNA by ET-743 at N2 of guanine in the minor groove. The A Ring and C Ring represent the tetra hydroisoquinoline A and C rings of ET-743

• Ascribed to covalent modification of DNA by guanine-specific alkylation at the N2 position

• Selective for GC-rich sequence and forms an adduct with duplex DNA which induces a bend in the DNA helix directed towards the major grooveZewail-Foote et al,1999,2001,Takebayashi et al.2001

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• Protrusion of ring C of ET-743 into minor groove and interference with DNA binding factors ET-743 also affects transition-coupled nucleotide excision repair and triggers cell death

Actual mechanism is not yet known but it is believed to involve the production of superoxide near the DNA strand resulting in DNA backbone cleavage and cell apoptosis.

There is also some speculation the compound becomes 'activated' into its reactive oxazolidine form.

Success :

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Ewing’s sarcoma and soft-tissue sarcomas, colorectal cancer, pretreated advanced breast cancer, ovarian cancer, and other sarcomas

ET-743 has remarkable antitumour activity against solid tumours, in particular breast cancer and renal carcinoma, and soft-tissue sarcomas (particularly osteosarcomas, mesothelioma, leiomyosarcoma and liposarcoma).

Cells in the G1 phase of the cell cycle, and of these softtissue

sarcoma cells in particular, are extremely sensitive to ET743-induced cell killing

Mode of administration :

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Intravenousthrough a fine plastic tube that is inserted

under the skin and into a vein near the collarbone (central line)

into a fine tube that is inserted into a vein in the crook of arm (PICC line).

To help prevent some of the side effects of trabectedin, you will be given an injection of a steroid drug 30 minutes before the chemotherapy

Pharmacokinetic data

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Protien binding : 94 to 98%Metabolism : Hepatic (mostly CYP3A4-

mediated)Half-life : 180 hours (mean)Oral, Mouse : LD50 = 300 mg/kg;Oral, rabbit: LD50 = 3200 mg/kgOral, rat:LD50  = 980 mg/kgExcretion : Mostly fecal

Possible side effects :

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Varies from person to personRisk of infection as it reduces white blood

cell countBruising and bleeding – it reduces

production of platelatesAnaemiaLoss of appetiteTiredness…

Future of Drugs from marine sources?

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Thank You!