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Year : 2018  |  Volume : 50  |  Issue : 4  |  Page : 155--158

Modulation of endocannabinoid system: Success lies in the failures

Subodh Kumar, Phulen Sarma, Harish Kumar, Ajay Prakash, Bikash Medhi 
 Department of Pharmacology, PGIMER, Chandigarh, India

Correspondence Address:
Dr. Bikash Medhi
Department of Pharmacology, PGIMER, Chandigarh - 160 012

How to cite this article:
Kumar S, Sarma P, Kumar H, Prakash A, Medhi B. Modulation of endocannabinoid system: Success lies in the failures.Indian J Pharmacol 2018;50:155-158

How to cite this URL:
Kumar S, Sarma P, Kumar H, Prakash A, Medhi B. Modulation of endocannabinoid system: Success lies in the failures. Indian J Pharmacol [serial online] 2018 [cited 2022 Aug 16 ];50:155-158
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“Cannabis” also known as “marijuana” is a medicinal plant, whose scientific name is Cannabis sativa and belongs to Cannabaceae family. Since many centuries, this plant has been controversial for its medicinal use as well as for the purpose of feeling intoxicated (“high”) due to psychoactive compounds such as tetrahydrocannabinol (cannabinoid). Cannabis contains >100 identified cannabinoids till date, which is the diverse class of chemical compounds that bind to cannabinoid receptors present in the cells and play a crucial role in the alteration of neurotransmitter released in the brain. In the human body, these receptors are the target of internally produced proteins called endocannabinoids. The endocannabinoid system comprises biosynthesis of endocannabinoids, their receptors, and downstream pathways. The receptors involved in the endocannabinoid pathway are mostly G protein-coupled receptors (CB1 and CB2), GPR55 receptors, and many yet unidentified receptors. Endocannabinoids are produced by almost all cell types in the brain and peripheral tissues, and the biological effect of these endogenous agents is similar to marijuana. But safety issues and addictive property were the main issues hindering medical use of Cannabis. Cannabis clinical development history has been controversial throughout as it has been surrounded with ethical, legal, and social challenges; adverse health consequences; and mortality attributed due to Cannabis and Cannabis-based synthetic drugs due to lack of sufficient clinical data. Despite so much failures, even and odds, in June 2018, first cannabinoid-based drug epidiolex got approval from the Food and Drug Administration (FDA) for the treatment of two rare syndromes and opened new horizons for medical and research fraternity around the world.

 History of Cannabinoid-Based Therapeutics

Ancient era

Early 19th century is the beginning of Cannabis as homeopathic medications, but it was O'Shaugnessy who came in the limelight in 1839 after publication of his book “On the preparations of the Indian hemp, or gunjah” after finding success in human experimentations using Cannabis preparations for various diseases in India.[1] Later, in Paris, Moreau used Cannabis for psychiatric patients and summarized in his published book “Du Hachisch et de l'Alienation Mentale: Etudes Psychologiques” describing acute effects of Cannabis.[2] Medical interest for Cannabis remained in limelight worldwide for several years due to its psychoactive effects as well as possible therapeutic use in other domains such as cholera, rabies, and tetanus. Therapeutic use of Cannabis (basically as sedative, hypnotic, analgesic, appetite improvement and sexual atony) came to a log phase in the second half of the 19th century and early 20th century when >100 scientific articles got published worldwide and also summarized in a book Sajous's Analytic Cyclopedia of Practical Medicine (1924).[3],[4] After that, medical use of Cannabis decreased drastically due to lack of replicable effects, development of alternate treatment medications, such as vaccines, analgesics, and hypodermic syringes for injection of morphine, as well as many legal restrictions due to detonation of its utilization for hedonistic purposes.[5]

Post-1950: The modern science/drug era

Modern era for Cannabis started in 1964, with the identification of chemical structure of delta-9-tetrahydrocannabinol (D9-THC) by Gaoni Y et al, 1964,[6] and their work contributed toward its constituents and increased scientific interest in Cannabis. Their work is followed by another research group from Brazil, led by Carlini, gave significant contribution by exploring the D9-THC interaction with other cannabinoids.[7] In the early 1990s, with the isolation of anandamide (endogenous cannabinoid) and successful cloning and characterization of cannabinoid-specific receptors of the nervous system, interest of the scientist community again shifted toward this herb. Today, Cannabis is known to have >100 cannabinoids including major psychoactive ingredients such as D9-THC. Other cannabinoids present in marijuana are D8-THC, cannabinol, and cannabigerol, with small quantities and less psychotropic effects.[8],[9],[10] In 1999, Health Canada and Canadian Institutes of Health Research jointly started a dedicated Cannabis research initiative named as “Medical Marihuana Research Program.” Till date, lots of clinical trials are going on evaluating the therapeutic applications of Cannabis and its derivatives, and recently, FDA approval of drug Epidialox, a purified active component from Cannabis, is one of them.

 Adverse Effects

As per reports, Cannabis-based adverse reactions are diverse and at the same time are dose and duration dependent. Short-term, high-dose use of Cannabis is associated with impairment in memory, motor coordination difficulties, distorted judgment, and phobia. Long-term or heavy use, especially in youngsters, causes addiction, distorted brain development, chronic bronchitis, myocardial infarction, stroke, schizophrenia, depression, and poor social as well as educational outcomes, which ultimately lead to compromised life.[11],[12],[13] In a systematic review by Wang T et al, 2008, a total of 31 studies evaluating 23 randomized controlled trials and eight observational studies showed a total of approximate 4779 reported adverse effects (96.6% of these were of non-serious category) and dizziness being the most common (15.5%).[14]

 Issues with Cannabinoid System Modulation

The journey of medicinal Cannabis from Schedule I controlled substance from a substance for addiction to bedside as a new drug has been very eventful and controversial. Despite numerous compounds and complex interactions of various cannabinoids present in this herb and complexities of regulating this plant-based therapy, the “U.S. Pharmacopoeia”and the FDA have considered its medicinal value and shown faith in its therapeutic potential to get fit in framework of drug in the United States.[15],[16],[17] Despite associated health risks with its use, there have been considerable arguments in favor of the existence of beneficial cannabinoids, such as cannabidiol (CBD), present in medicinal Cannabis, for conditions especially where no other therapies are effective. Cannabis also contained compounds such as THC due to which this herb is kept under Schedule I. Here came the importance of synthetic cannabinoids with less adverse drug reactions and less addictive properties and some of them have shown that great therapeutic potential is in clinical trials with minimal adverse effects except BIA-10-2474 trial. Many synthetic cannabinoids have shown promising therapeutic potential in many disease conditions including emergency care.

 Modulation of Endocannabinoid System: BIA-10-2474 Trial

Endocannabinoids are hydrolyzed by fatty acid amide hydrolase (FAAH), and thus, inhibition of FAAH should have the potential to increased availability of endocannabinoids at target tissue level and is a therapeutic target in many disorders including pain.[18] Several FAAH inhibitors have been tested already, but all failed due to lack of efficacy. BIA-10-2474 is a FAAH inhibitor. Toxicity testing of BIA-10-2474 was conducted in four different species, and only pulmonary toxicity was seen in dogs when tested in very high doses. The Phase 1 trial of the compound was conducted by “Biotrial,” a French CRO, in Rennes, France. The Phase 1 had four substudies single ascending dose (SAD), multiple ascending dose (MAD), food interaction, and pharmacodynamic studies to look for possible indications. The dose escalation was based on previous kinetic data generated in animals. A total of 128 healthy volunteers were recruited and 90 participants received either placebo or different dosage of the drug.[19] Uneventful SAD studies were conducted up to a maximum dose of 100 mg.[20] In MAD studies, in the first four dose increments (up to 20 mg/day), there was no problem. In the 50 mg/day group of MAD studies, one patient developed neurological problem and had to be admitted to hospital. Other patients were given the same dose on the next day, without knowing the status of the first patient. Other five participants also showed sign of similar involvement. The first patient died and the medulla oblongata showed a very unusual magnetic resonance imaging pattern in the thalamus and medulla.[19] The patients who showed signs of toxicity received were receiving repeat higher doses as a part of MAD study.[20] The end result was death of one participant and three participants recovered with residual serious neurological damage.[19]

 Problems in the Trial

All six participants in 50 mg/day MAD study received the drug doses simultaneously, not sequentially. Such similar simultaneous administration is also seen in the catastrophic TGN1414 case. Sequential administration has some advantage in this case. In the BIA-10-2474 case, when the first participant has shown definite signs of toxicity, the study should have been temporarily suspended, to ensure safety of the other participants[20]Another postulated hypothesis is loss of selectivity of BIA-10-2474 at higher dosage and leading to off-target actions.[21] A threshold effect on other enzymatic pathways seems the most plausible.[19] To overcome these, they could have taken help of radiolabeled studies on cadaveric brain to find out its binding targets.[20] Later, confirmatory activity-based proteomic methods to determine the protein interaction landscape of BIA 10-2474 in the human cells and tissues confirmed that off-target activities of BIA 10-2474.[21] These analyses revealed that the drug might have inhibited several lipases and worsen the lipid networks of human cortical neurons, suggesting that lipase inhibitors can cause potential metabolic dysregulation in the nervous system[21]Kinetics of the drug was not showing linear pattern and increasing half-life was seen, which were indicative of cumulation, which was overlookedAnother possibility is steeper dose increment in MAD studies (20 mg on day 4 to 50 mg on day 5)[19]Another query is why such a higher dose was evaluated? Such a higher dose seems scientifically irrelevant as 3 mg/day of BIA-10-2474 was sufficient enough for causing maximal FAAH inhibition[19]The incident was not reported to the French National Agency for Medicines and Health Products Safety even for 3 days after the incidence (doi: 10.1126/science.aaf4017)The subsequent volunteers, who were to be given the test drug, were not informed about the toxicity features of the first patient (doi: 10.1126/science.aaf4017).

 Approval of Schedule I Category-Based Active Cannabinoid as Drug: Road to Success

After this trial, it was thought that Cannabis-based drug trials will come to a halt, but subsequently, Cannabis-based research went on and the outcome of this came in a more fruitful way. Recently, the U.S. FDA approved Epidiolex (CBD) an active product of Cannabis, for the treatment of Lennox-Gastaut syndrome and Dravet syndrome of children. Epidiolex is the first FDA-approved drug that contains a purified drug substance derived from marijuana.[22] CBD is not psychoactive component of marijuana, and it is THC that causes intoxication or euphoria (the “high”) evident from preclinical and clinical studies.

Efficacy of Epidiolex was evaluated in three randomized, double-blind, placebo-controlled clinical trials (n = a total of 516 patients suffering from either Lennox-Gastaut syndrome or Dravet syndrome). In combination with other medications, Epidiolex showed its effectiveness for seizures control when compared with placebo.[22] This approval is the perfect example of success around dark when proper evaluation is done and opened the doors for medical research fraternity working on marijuana or in similar direction. The approval of Epidiolex was not so easy and the FDA carefully evaluated all the trials in very appropriate way. Adequate number of patients and well-controlled clinical trials gave sufficient evidence for its approval and gave confidence to prescribers to prescribe this drug for such serious epilepsy syndromes.

 Clinical Pharmacology Lessons from Cannabinoid Approval as a Drug

Despite problems like risks of addiction, controversial clinical evaluation path, the approval of epidiolex (endocannabinoid modulator) opened up a new era of cannabis based therapeutics and this evolution path teaches us many lesson's which can be incorporated in designing/conducting clinical trials of similar agents

Preclinical data to be considered critically while making a clinical trial protocolImportance of data generation in higher and genetically closer animals at preclinical levelIf required, human microdosing may be of help to evaluate aberrant kineticsImportance of organ on a chip study to predict human kinetics and other dataDuring trials, before exploring a higher dose, we should have data on the same dose range from animal studies. Human dose range or regimen to be evaluated should have enough evaluation in animal studiesAn equipped, well-informed clinical trial team and rapid communication (in case of any mishaps) is the heart of a successful clinical trial teamDo not expose trial participants to unnecessary and unevaluated high doseDose-dependent changes in kinetics to be evaluated properly.It is unscientific to expose trial participants to drugs that lack an identified therapeutic potentialIdentify the targets. Off-targeting to be considered and evaluated properlyMedia hype should be justified scientificallyComplete assessment of volunteersEnough time between two dose escalations. Any sign of a probable wrong going; stop others from dosing and observe the patientLess steep dose escalationTake adequate precautions in apparently safe drugs alsoDo not get disheartened easily; go forward with strong scientific justifications.

The US-FDA approval of Epidiolex oral solution for the treatment of seizures highlights the importance of critical risk–benefit analysis and careful evaluation in drug development process. Safety of research participants is of utmost importance; however, at the same time, development of new drugs for patient benefit is also important, and inclusion of above-mentioned points in inclusion criteria may give us additional advantage. A delicate balance between these two can serve the interest of the society as well as for science; therefore, we should be more vigilant and attentive in the development of natural product drug developments in all means, i.e., efficacy as well as safety, while taking care of its addictive nature.


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