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- TRPV1 agonistsa) Preclinical research
b) Clinical trial in cancer pain
c) Osteoarthritis
- TRPV1 positive allosteric modulators
Multiple Pathways for Pain Control Using TRPV1
Ion Channel Agonists and Positive Allosteric
Modulators
Michael Iadarola, Ph.D.
Neurobiology and Pain Therapeutics Section (NPTS)
Laboratory of Sensory Biology, NIDCR
National Institutes of Health, USA
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Neuronal Pathways & Analgesic Targets
Central or Peripheral nervous system?
PeripheralNo CNS side
effects,
Can produce
insensitivity
to pain
CentralPossible CNS side
effects
Level of relief from
severe pain
Neurosurgical Lesions for Pain Relief: Antero-lateral Quadrant Cordotomy (ALQ)
Cut here
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TRPV1 Agonists ?If agonists activatethe ion channel, wont that cause pain?
Yes: a) 8%capsaicin patch: pretreat with 4% lidocaine patch and oxycodone after.
Backonja et al., Lancet Neurol 7:110612, 2008.b) Iadarola et al., Neural activation during acute capsaicin-evoked pain and allodynia
assessed with positron emission tomography. Brain 121:931-947, 1998.
Literally cut the connection
between the body and the
spinal cord: Permanent
intervention
Can we use this
Therapeutically?
Yes: agonist activation leads
to a calcium overload. This
produces a highly selective
Lesion of pain fibers or neurons
Ca++
TRPV1 Model constructed by Krisztian Kaszas, NPTS, NIDCR
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Molecular Targeting of TPRV1
Using Agonists
Capsaicin Resiniferatoxin (RTX)
Karai L, Russell JT, Iadarola MJ, Olah Z: J Biol Chem. 279:16377-16387, 2004.
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Con 0.5
5 15
RTX-induced Fragmentation of ER and Mitochondria
Laser confocal microscopy at 24 hrs after transfection; TRPV1eGFP: Green fusion protein labels ER and
plasma membrane; Mitochondria: MitoTracker Red dye.
No bystander effect: cells without the receptor (red only) are unaffected
Olah Z, Karai L and Iadarola MJ: J Biol Chem 276: 31163-31170, 2001.
eGFP
TRPV1-eGFP fusion
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Agonist Selectivity
TRPV1: ENRICHED EXPRESSION IN SENSORY GANGLIA
1 Cerebellum2 Cortex
3 Dorsal Root Ganglion
4 Hippocampus
5 Hypothalamus
6 Substantia Nigra7 Spinal Cord
8 Striatum
9 Trigeminal Ganglion
10 Blank
TRPV1
GAPDH
1 2 3 4 5 6 7 8 9 10
RT-PCR (30 cycles) Rat Brain and Sensory Ganglia
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Animal studies of RTX
Non-clinical rodent studies: Established specificity, dose range,
duration of action and route of administration
Canine modelthat closely resembles human situation.- UPenn School of Veterinary Medicine, Dr. Dorothy Cimino Brown.
- Client dogs with naturally occurring osteosarcoma
- Candidates for euthanasia. Why? Poor pain control
- Owner can assess higher order function
Profound analgesia, durable, resistant to disease progression, no personality change,
no impact on bladder or bowel function, no impact on motor function.
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Long term pain control in bone cancer
Brown DC, Iadarola MJ, et al., Anesthesiology 103:1052-1059, 2005.
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Analgesic & Anti-inflammatory Medication Administered to Dogs with Bone Cancer
Dog Prior to RTX Administration 2 Weeks Following RTX Administration
1 Carprofen 100mg every 12 hours
Prednisone 10 mg every 12 hours
Prednisone 2.5 mg every 12 hours
Dose decreased
2 Piroxicam 10 mg every 24 hours Piroxicam 10 mg every 48 hours3 Codeine 90 mg every 8 hours
Piroxicam 10 mg every 24 hours
None
4 Prednisone 20 mg every 12 hours Prednisone 20 mg every 12 hours
5 Etodolac 450 mg every 12 hours Etodolac 450 mg every 12 hours
6 Carprofen 75 mg every 12 hoursButorphanol 5 mg every 12 hours
None
7 Piroxicam 20 mg every 24 hours None
8 Carprofen 100mg every 12 hours None
9 Deracoxib 100 mg every 24 hours Deracoxib 100 mg every 24 hours
10 Codeine 120 mg every 8 hours None
11 Deracoxib 100 mg every 24 hours None
14 Deracoxib 100 mg every 24 hours
Codeine 30mg every 6 hours
Deracoxib 50 mg every 24 hours
Dose Decreased
67%of the
dogs either
discontinued
or decreasedstandard
analgesic
drugs
Brown DC, Iadarola MJ, et al., Anesthesiology 103:1052-1059, 2005.
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1) Raw Material: Latex from
Euphorbia resinifera a
cactus-like succulentfrom Morocco
3) RTX Toxicology
Two species: CompleteNIDA Collaboration
4) Clinical protocol: Single administration of intrathecal
resiniferatoxin for treating severe refractory pain
associated with advanced disease.
2a) Large scale cGMP production
of RTX NIDA Collaboration
2b) Formulation of RTX for injectionNIH Pharmacy
5) IND to FDAAnimal and cellular
toxicology data,
Drug master file,Stability, etc
NIDA Collaboration
6)Phase IClinical trial
at NIH
Recruiting
NOW
Steps to Human Clinical Trial of RTX for Cancer Pain
http://clinicaltrials.gov/ct2/show/NCT00804154
Iadarola MJ and Mannes AJ: Curr Top Med Chem. 11(17):2171-2179, 2011
Protocol 09-D-0039:
A Phase I Study of the Intrathecal
Administration of Resiniferatoxin
for Treating Severe Refractory Pain
Associated With Advanced Cancer
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Eligibility Criteria:Pain in lower half of body
Cauda
Equina:
site of
lumbar
punctureand
catheter
insertion
RTX injection procedure: lumbar puncture
Dermatome map of body
L5
L4
L3
L2
L1
T12
Affecteddermatomes
http://clinicaltrials.gov/ct2/show/NCT00804154
Protocol 09-D-0039: A Phase I Study of the Intrathecal Administration of Resiniferatoxin
for Treating Severe Refractory Pain Associated With Advanced Cancer
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Peripheral RTX Administration
Central Administration
PERMANENTcuts the axon or kills the cell
Peripheral Administration
TRANSIENTNerve terminals die back and re-grow
Routes:Topical (cornea)
Intra-joint
Perineural
Subcutaneous
Primary
afferent
neuron
Terminal in
spinal cordTerminal
In body
Indications:
Corneal pain
Osteoarthritis
Post-injury neuropathic pain with
A localized site of origin or trigger zone
Certain types of low back pain
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TRPV1 Allosteric Modulators
Objective: new approach to TRPV1 based analgesic agents
Roadmap Grant R03 MH089480, HTS for Identifying Allosteric
Modulators of the TRPV1 receptor.
Positive allosteric modulators. Concept: impose an activity-
dependent mode of action to enhance process of nerve terminal
inactivationLead compounds
TRPV1 PAMs should be selective for areas actively experiencing tissue damage or inflammation
peripheral generators that would be sites of endovanilloid production and low pH.
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MRS-1477: a TRPV1 positive allosteric modulator
- capsaicin + capsasicin
Calcium imaging in primary DRG neurons
Roh EJ, Keller JM, Zoltan Olah Z,Iadarola MJ, Jacobson KA: Bioorganic & Medicinal Chemistry 16:93499358, 2008
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Positive Allosteric Modulation of TRPV1 with MRS1477Positive modulator effects on orthosteric agonist and H+ ion
Ca++Ca++
Kaszas K, Keller JM, Coddu C, Mishra S, Hoon M, Stojilkovic S,Jacobson KA, Iadarola MJ:
J Pharmacol Exp Ther 340: 152-160, 2012
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1477 produces a long-term nerve terminal inactivation
Thermal testing of the paw for A-delta or C-fiber integrity following combination
Injectnion of capsaicin (the TRPV1 agonist) and MRS1477 (the TRPV1 PAM)
A-delta stimulation
Lebovitz E, et al., Molecular Pain, in press
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SummaryA. TRPV1 agonists can be used in many different ways.
Two examples are:
- Intrathecal administration of RTX to treat pain from advanced cancer
- Peripheral administration into areas of inflammation or nerve damage.
B. TRPV1 PAMs may also be versatile analgesic agents.
- The duration of action occurs over several days in our experimental model
- It may be possible to administer them systemically or by local injection
- They have an activity-dependent component to their action
- The role of endovanilloids requires further investigation.
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Acknowledgements
Many of my colleagues were, and still are, involved in bringing the work with RTXfrom the bench to the bedside. The development of the PAMs is part of the next
phase of TRPV1-based drugs.
RTX
NIDCR: Zoltan Olah, Laszlo Karai, Ofer Wellisch, Andrew Mannes, Jason Keller
University of Pennsylvania: Dorothy Cimino Brown
NIH Pharmaceutical Development Section: George Grimes
NIDA: Nate Appel, Robert Walsh, Nora Chiang, Moo Park, Marta DeSantis, Jim Terrill
PAMs
NIDCR: Krisztian Kaszas, Jason Keller, Evan Lebovitz, Zoltan Olah, Ken Jacobson,NCATS, NCGC: Noel Southall, Erika Englund, Juan Marugen, Steve Titus
This work was supported by the Intramural Research Program NIH, NIDCR and
Molecular Libraries Screening Grant, 1 R03 MH089480, HTS for Identifying
Allosteric Modulators of the TRPV1 receptor.
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