Transient Receptor Potential Cation Channel Subfamily V Member 1 (TRPV1). It is a potent TRPV1 agonist. [1]

Resiniferatoxin promotes inflow and prolongs channel opening, which causes TRPV1 fibers or cell bodies to undergo acute pain-inducing cytotoxicity [1].

---

In live cell microscopic studies using stably transfected cell lines expressing a TRPV1eGFP fusion protein and cultured DRG neurons, resiniferatoxin was shown to bind with nanomolar affinity to TRPV1-positive cells. This binding caused prolonged opening of the TRPV1 ion channel, leading to a rapid and massive increase in intracellular calcium. [1]
Confocal imaging revealed that within 1 minute of resiniferatoxin exposure, vesiculation of mitochondria and the endoplasmic reticulum occurred in nociceptive primary sensory neurons endogenously expressing TRPV1. Nuclear membrane disruption was observed within 5-10 minutes, and cell lysis was documented within 1-2 hours, followed by specific deletion of TRPV1-expressing cells. [1]
The presence of TRPV1 was critical for resiniferatoxin cytotoxicity. At concentrations 1000 times above the dose used to lesion expressing cells, RTX did not appear to produce any negative effects on non-TRPV1-expressing cells at the cellular level. Non-expressing neurons remained intact even when adjacent to TRPV1-expressing neurons undergoing RTX-induced damage. [1]

Resiniferatoxin (2 μg/10 μl; intrathecally into the T2/T3 area; causes cardiomyopathy 4 weeks post-coronary blockage) reduces overactivated CSNA and dramatically and indirectly abolishes marker expression in the dorsal horn (TRPV1 and nortonin-inducible gene-related peptide). Resiniferatoxin decreases the susceptibility of ventricular arrhythmias and dramatically reverses the lengthening of action episode duration (APD) and APD alternation [2].

---

Rodent Corneal Application: In rats, unilateral microinjection of resiniferatoxin (200 ng) into the trigeminal ganglion completely suppressed the eye-wiping response evoked by intraocular capsaicin drops. This antinociceptive effect was permanent, lasting for the duration of the experiments (350 days post-injection). In nonhuman primates, unilateral infusion of resiniferatoxin (20 μL of 0.1 mg/mL solution) into the trigeminal ganglion selectively and significantly reduced the response to capsaicin stimulation for up to 12 weeks. In C57BL/6J mice, intracisternal injection of resiniferatoxin (100 μg) rendered them completely insensitive to corneal capsaicin application. Immunohistochemical analysis confirmed selective elimination of TRPV1-positive neurons in the ganglia. Animals showed no neurological deficits, corneal damage, or alterations in normal behaviors, and the mechanosensitive corneal reflex was preserved. [1]
Rodent Inflammatory Pain: In adult rats, intrathecal administration of resiniferatoxin dramatically decreased pain sensitivity to intraplantar capsaicin injection, as indicated by a reduction in both the duration and number of guarding and licking behaviors. RTX-treated animals also showed no change in paw withdrawal latency to noxious thermal stimulation after carrageenan-induced inflammation, indicating alleviation of inflammatory thermal hypersensitivity. Mechanical sensitivity (tested with von Frey filaments) was unaffected, consistent with the fact that mechanosensitive nociceptors do not express TRPV1. Immunohistochemistry documented a complete loss of TRPV1 labeling in the dorsal horn of the spinal cord localized to the lumbar segments near the injection site. [1]
Canine Noxious Thermal Stimulation: In dogs, intrathecal administration of resiniferatoxin (1.2 and 3.0 μg/kg) into the cisterna magna caused nearly complete loss of sensitivity to noxious thermal stimulation (paw withdrawal latency to a radiant heat source) starting 2 days after treatment and maintained through day 12. All dogs maintained normal locomotor and proprioceptive activities on repeated neurologic examinations. [1]
Murine Operant Orofacial Assay: In mice treated with intracisternal resiniferatoxin, operant testing using a reward-conflict platform with a thermal stimulus showed that RTX-treated animals had significantly higher licks (accessing a reward bottle) compared to vehicle-treated animals when the thermode was in the noxious heat range, indicating reduced pain sensitivity. [1]
Canine Bone Cancer Pain (Companion Dog Model): In a single-blind, controlled study of 72 companion dogs with spontaneously occurring bone cancer pain, dogs randomized to receive intrathecal resiniferatoxin (1.2 μg/kg) plus standard of care required unblinding (due to unacceptable discomfort) significantly later than dogs receiving standard of care alone. 78% of control dogs required unblinding within 6 weeks, compared to 50% of RTX-treated dogs. Blinded orthopedic evaluation of lameness through video analysis showed that 33% of RTX-treated dogs had improved lameness two weeks after randomization, compared to only 7% of control dogs. At necropsy, DRG of treated dogs showed degenerating TRPV1-expressing neurons being replaced by satellite cells, while larger diameter neurons (non-TRPV1) remained unaffected, correlating with the observed analgesic effect and retention of other sensory and proprioceptive functions. [1]

Live Cell Calcium Imaging and Confocal Microscopy: Ratiometric imaging of intracellular free calcium and confocal imaging of TRPV1-green fluorescent fusion protein were used in stably transfected cell lines and cultured DRG neurons. Cells were exposed to resiniferatoxin, and changes in intracellular calcium levels and organelle morphology (mitochondria, endoplasmic reticulum, nuclear membrane) were monitored over time. This allowed for the visualization of RTX-induced calcium influx and subsequent cytotoxicity leading to specific deletion of TRPV1-expressing cells. [1]
Electrophysiology: RTX application to DRG cells known to express TRPV1 induced large inward currents, which were not induced in DRG cells that do not express the receptor. [1]

Rodent Trigeminal Ganglion Injection (Rat):** Resiniferatoxin was microinjected unilaterally into the trigeminal ganglia using a transcranial stereotaxic approach or a percutaneous approach via an electrical-stimulation needle inserted through the infraorbital foramen. A dose of 200 ng was used. [1]
* **Nonhuman Primate Trigeminal Ganglion Infusion:** Resiniferatoxin solution (20 μL of 0.1 mg/mL concentration) was infused unilaterally into the trigeminal ganglia. [1]
* **Rodent Intracisternal Injection (Mouse):** Resiniferatoxin (100 μg) or vehicle was injected into the cerebrospinal fluid at the cisterna magna. [1]
* **Rodent Intrathecal Injection (Rat):** Resiniferatoxin was administered intrathecally to target the ganglionic nerve roots. Inflammation was induced by intraplantar injection of 100 μL of 2% carrageenan. Pain sensitivity was tested with intraplantar capsaicin injection and thermal paw withdrawal latency. [1]
* **Canine Intrathecal Injection:** Under general anesthesia, resiniferatoxin was administered intrathecally into the cisterna magna at doses of 0.1, 1.2, or 3.0 μg/kg. For the bone cancer study, dogs were randomized to standard of care alone or standard of care plus a single intrathecal injection of resiniferatoxin (1.2 μg/kg). All dogs in the RTX group were anesthetized for the procedure and hospitalized overnight. [1]
* **Behavioral Testing (Canine):** Paw withdrawal latency to a radiant thermal stimulus was measured in unrestrained dogs placed on a glass-top table. The heat source was positioned under a paw and terminated when the dog lifted its limb, with a maximum exposure of 20 seconds. Lameness was evaluated by a blinded orthopedist through video analysis. Owner pain assessments and activity monitoring via collar-worn accelerometers were also used. [1]
* **Human Clinical Trial Protocol:** In a Phase I clinical trial for patients with advanced cancer, an intrathecal catheter is placed, and resiniferatoxin (3 to 26 μg) is injected under general anesthesia to prevent the acute pain associated with TRPV1 activation. Serial electrocardiograms, brain and spine MRIs, eye exams, blood analyses, and neurological exams are performed pre- and post-injection. Pain, quality of life, activity, and mental status are assessed using standardized tools. [1]

---

Rodent Trigeminal Ganglion Injection (Rat): Resiniferatoxin was microinjected unilaterally into the trigeminal ganglia using a transcranial stereotaxic approach or a percutaneous approach via an electrical-stimulation needle inserted through the infraorbital foramen. A dose of 200 ng was used. [1]
Nonhuman Primate Trigeminal Ganglion Infusion: Resiniferatoxin solution (20 μL of 0.1 mg/mL concentration) was infused unilaterally into the trigeminal ganglia. [1]
Rodent Intracisternal Injection (Mouse): Resiniferatoxin (100 μg) or vehicle was injected into the cerebrospinal fluid at the cisterna magna. [1]
Rodent Intrathecal Injection (Rat): Resiniferatoxin was administered intrathecally to target the ganglionic nerve roots. Inflammation was induced by intraplantar injection of 100 μL of 2% carrageenan. Pain sensitivity was tested with intraplantar capsaicin injection and thermal paw withdrawal latency. [1]
Canine Intrathecal Injection: Under general anesthesia, resiniferatoxin was administered intrathecally into the cisterna magna at doses of 0.1, 1.2, or 3.0 μg/kg. For the bone cancer study, dogs were randomized to standard of care alone or standard of care plus a single intrathecal injection of resiniferatoxin (1.2 μg/kg). All dogs in the RTX group were anesthetized for the procedure and hospitalized overnight. [1]
Behavioral Testing (Canine): Paw withdrawal latency to a radiant thermal stimulus was measured in unrestrained dogs placed on a glass-top table. The heat source was positioned under a paw and terminated when the dog lifted its limb, with a maximum exposure of 20 seconds. Lameness was evaluated by a blinded orthopedist through video analysis. Owner pain assessments and activity monitoring via collar-worn accelerometers were also used. [1]
Human Clinical Trial Protocol: In a Phase I clinical trial for patients with advanced cancer, an intrathecal catheter is placed, and resiniferatoxin (3 to 26 μg) is injected under general anesthesia to prevent the acute pain associated with TRPV1 activation. Serial electrocardiograms, brain and spine MRIs, eye exams, blood analyses, and neurological exams are performed pre- and post-injection. Pain, quality of life, activity, and mental status are assessed using standardized tools. [1]

Cardiovascular Effects (Canine): Significant increases in blood pressure and heart rate can occur after intrathecal resiniferatoxin injection in dogs. These effects peak within minutes of injection and return to baseline over the hour that the dog remains anesthetized through the period of TRPV1 activation. [1]
Respiratory and Temperature Effects (Canine): Immediately after extubation, many dogs pant for several hours, during which they develop hypothermia that plateaus 3 to 4 hours after extubation. Even the most hypothermic animals (core body temperature drop >4°C) otherwise make an uneventful recovery and regain normothermia in 12 to 18 hours. [1]
Deafferentation Pain: Behaviors consistent with deafferentation pain syndromes (e.g., self-mutilation) did not occur in any dogs treated with resiniferatoxin. [1]
Neurological and Sensory Function (Multiple Species): Treated animals showed no neurological deficits, alterations in eating/grooming habits, or loss of mechanosensitive reflexes (e.g., corneal blink reflex). In the canine bone cancer study, there was no evidence of development of neurologic abnormalities typically seen with neurolytic therapies. In the human Phase I trial, no changes in EKG, MRI, or eye examination were noted. Thermal perception reduction was consistent with TRPV1 neuron deletion, but there were no other sensory or motor changes post-treatment. [1]
Hematology/Biochemistry (Canine): Blood and urine collected before and one and two weeks after resiniferatoxin administration revealed no significant increases or decreases of parameters out of the normal range. [1]
Toxicity Doses: In canine studies, toxicity was not explicitly defined for RTX alone, but adverse effects were documented as above. In the bone cancer study, seven dogs in the treated group underwent euthanasia prior to the two-week endpoint, though this was not specifically attributed to drug toxicity. [1]

[1]. Brown DC. Resiniferatoxin: The Evolution of the "Molecular Scalpel" for Chronic Pain Relief. Pharmaceuticals (Basel). 2016;9(3):47. Published 2016 Aug 11.

[2]. Resiniferatoxin reduces ventricular arrhythmias in heart failure via selectively blunting cardiac sympathetic afferent projection into spinal cord in rats. Eur J Pharmacol. 2020;867:172836.

Resiniferatoxin is a heteropentacyclic compound with the molecular formula C37H40O9 found in plants of the genus Euphorbia. It is an agonist of transient receptor potential cation channel subfamily V member 1 (TRPV1). It possesses multiple functions, including TRPV1 agonist, plant metabolite, neurotoxin, and analgesic. It is a diterpenoid, orthoester, tertiary α-hydroxy ketone, phenolic compound, monomethoxybenzene, organic heteropentacyclic compound, carboxylic acid ester, and enone. Resiniferatoxin (RTX) is a naturally occurring, highly potent capsaicin analog that activates vanillin receptors in primary afferent sensory neuron subsets involved in nociception (the transmission of physiological pain). Resiniferatoxin has been reported to exist in Euphorbia unispina and Euphorbia resinifera, with relevant data available. Resiniferatoxin is a naturally occurring capsaicin analog found in the latex of Euphorbia resinifera and possesses analgesic activity. Resiniferatoxin (RTX) binds to and activates transient receptor potential (TRP) vanillin receptor 1 (TRPV1), a non-selective cation channel on the plasma membrane of primary afferent sensory neurons. This increases cation permeability, leading to an influx of calcium and sodium ions. This causes membrane depolarization, producing a stimulatory effect, followed by desensitization of the sensory neuron, thereby inhibiting signal transduction in the afferent pain pathway and producing an analgesic effect. TRPV1 is a member of the transient receptor potential (TRP) superfamily and is a heat- and chemically sensitive calcium/sodium ion channel selectively expressed in a subset of primary pain-sensing afferent neurons.

---

Pharmacological Indications
It has been studied for the treatment of interstitial cystitis and urinary incontinence.

---

Resiniferatoxin is a potent TRPV1 agonist derived from the Euphorbia resinifera plant. It is the most potent among all known endogenous and synthetic TRPV1 agonists. [1]
The mechanism of action involves extremely prolonged TRPV1 channel opening, leading to a massive calcium influx that causes cytotoxicity specifically in TRPV1-expressing neurons (nociceptive Aδ and C-fibers). This selective neuroablation has been termed "molecular neurosurgery" or a "molecular scalpel" as it spares motor, proprioceptive, and other somatosensory functions. [1]
The compound is being developed for the management of intractable chronic pain states, particularly for patients with advanced cancer experiencing significant cancer-induced pain. [1]
The development of resiniferatoxin for clinical use was significantly advanced by studies in companion dogs with spontaneously occurring bone cancer pain, which provided translational data on efficacy and safety that informed human clinical trial design. [1]
As of this review, intrathecal resiniferatoxin was undergoing a Phase I clinical trial in patients with advanced cancer. Initial findings in patients receiving 13 or 26 μg injections showed clinically meaningful improvement in quality of life, with consistent reports of less pain and improved mobility, without changes in EKG, MRI, or eye exams. [1]

628.267

57444-62-9

5702546

White to off-white solid powder

1.35g/cm3

768.7ºC at 760mmHg

240.3ºC

1.643

4.744

2

9

9

46

1330

8

O1C2(C([H])([H])C3C([H])=C([H])C([H])=C([H])C=3[H])O[C@@]3(C(=C([H])[H])C([H])([H])[H])C([H])([H])[C@@]([H])(C([H])([H])[H])[C@]41[C@]1([H])C([H])=C(C([H])([H])[H])C([C@]1(C([H])([H])C(C([H])([H])OC(C([H])([H])C1C([H])=C([H])C(=C(C=1[H])OC([H])([H])[H])O[H])=O)=C([H])[C@@]4([H])[C@@]3([H])O2)O[H])=O

DSDNAKHZNJAGHN-MXTYGGKSSA-N

InChI=1S/C37H40O9/c1-21(2)35-17-23(4)37-27(33(35)44-36(45-35,46-37)19-24-9-7-6-8-10-24)14-26(18-34(41)30(37)13-22(3)32(34)40)20-43-31(39)16-25-11-12-28(38)29(15-25)42-5/h6-15,23,27,30,33,38,41H,1,16-20H2,2-5H3/t23-,27+,30-,33-,34-,35-,36-,37-/m1/s1

[(1R,2R,6R,10S,11R,13S,15R,17R)-13-benzyl-6-hydroxy-4,17-dimethyl-5-oxo-15-prop-1-en-2-yl-12,14,18-trioxapentacyclo[11.4.1.01,10.02,6.011,15]octadeca-3,8-dien-8-yl]methyl 2-(4-hydroxy-3-methoxyphenyl)acetate

2934.99.9001

Powder      -20°C    3 years

                     4°C     2 years

In solvent   -80°C    6 months

                  -20°C    1 month

Note: This product requires protection from light (avoid light exposure) during transportation and storage.

Room temperature (This product is stable at ambient temperature for a few days during ordinary shipping and time spent in Customs)

DMSO : ~50 mg/mL (~79.53 mM)

Solubility in Formulation 1: ≥ 1.25 mg/mL (1.99 mM) (saturation unknown) in 10% DMSO + 40% PEG300 + 5% Tween80 + 45% Saline (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 12.5 mg/mL clear DMSO stock solution to 400 μL PEG300 and mix evenly; then add 50 μL Tween-80 to the above solution and mix evenly; then add 450 μL normal saline to adjust the volume to 1 mL.
Preparation of saline: Dissolve 0.9 g of sodium chloride in 100 mL ddH₂ O to obtain a clear solution.

---

Solubility in Formulation 2: ≥ 1.25 mg/mL (1.99 mM) (saturation unknown) in 10% DMSO + 90% Corn Oil (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 12.5 mg/mL clear DMSO stock solution to 900 μL of corn oil and mix evenly.

---

 (Please use freshly prepared in vivo formulations for optimal results.)