The role of cannabinoids in prostate cancer: Basic science perspective and potential clinical applications
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Prostate cancer is a global public health problem, and it is the most common cancer in American men and the second cause for cancer-related death. Experimental evidence shows that prostate tissue possesses cannabinoid receptors and their stimulation results in anti-androgenic effects. To review currently relevant findings related to effects of cannabinoid receptors in prostate cancer. PubMed search utilizing the terms “cannabis,” “cannabinoids,” “prostate cancer,” and “cancer pain management,” giving preference to most recent publications was done. Articles identified were screened for their relevance to the field of prostate cancer and interest to both urologist and pain specialists. Prostate cancer cells possess increased expression of both cannabinoid 1 and 2 receptors, and stimulation of these results in decrease in cell viability, increased apoptosis, and decreased androgen receptor expression and prostate-specific antigen excretion. It would be of interest to conduct clinical studies utilizing cannabinoids for patients with metastatic prostate cancer, taking advantage not only of its beneficial effects on prostate cancer but also of their analgesic properties for bone metastatic cancer pain.
Keywords: Androgen antagonists, cannabis, cannabinoids, investigational therapies, prostatic neoplasms
Prostate cancer is an established public health concern in modern society and has been for decades. It is the most common cancer in men (asides from non-melanoma skin cancer) and the second most common cause of cancer death in the United States. Even with widespread screening with prostate-specific antigen (PSA), still 5% of cases present with metastatic lesions at the time of diagnosis. Because of all this, there is a fundamental necessity to search for and find new and novel treatments to this common pathology. Cannabis and cannabinoids have often been an issue of much polemics in the realm of science, but since the discovery of cannabinoid receptors in rat brain in the late 1980s, there has been a growing interest in the research of these compounds and our knowledge continues to expand. There has been experimental evidence that cannabinoids possess anti-androgenic proprieties; the purpose of this review is to describe in detail the effects, characteristics, and possible role of cannabis and cannabinoids in the subject of prostate cancer.
MATERIALS AND METHODS
A PubMed search was conducted for manuscripts published regardless of publication date, which contained the terms “cannabis,” “cannabinoids,” “prostate cancer,” and “cancer pain management,” giving preference to most recent publications. Articles identified were screened for their relevance to the field of prostate cancer and likely interest to both urologist and pain specialists. This review article focuses on the effects of cannabinoids in the realm of prostate cancer pathophysiology and their potential uses.
Overview: Prostate cancer
Prostate cancer is the most common cancer in American men except for non-melanoma skin cancer. In the United States, an estimated 217,730 cases will be diagnosed in 2010 and 32,050 deaths will occur. Its frequency has increased in part due to the widespread availability of serum PSA testing. Its incidence peaked in 1992, declined between 1992 and 1995, and has been rising about 1% annually since then[1,4] until 2000-2006, since then incidence rates have declined by 2.4% per year, which may reflect recent stabilization of PSA testing.[5–7] Widespread PSA use has led to an increasing proportion of prostate cancer cases that are localized at diagnosis, with fewer patients presenting with metastatic disease. As an example, between 1984 and 1991, 30–40% of men presented with advanced disease, and currently only 5% have distant metastases at the time of diagnosis. Prostate cancer remains the second most common cause of cancer death in American men.
Despite the fact that a higher percentage of men have localized disease at presentation, metastatic prostate cancer remains an important clinical problem, both in terms of the number of affected men and its impact on their quality of life. Hematogenous spread of prostate cancer cells is a common event. For these malignant cells, tumor growth preferentially occurs in bones of the axial skeleton. The most common site of metastasis is bone and frequently is symptomatic, causing pain, debility, and functional impairment. The presence of pain in men with advanced prostate cancer is an immediate indication for aggressive management with analgesics, while adequate treatments that address directly the cause of the pain are pursued.
Numerous treatment options have been established to treat bone metastatic prostate cancer; some focus on treating the underlying pathophysiology, while others focus on pain management and palliative care. Examples of the former are androgen deprivation therapy (ADT), being the initial approach in most cases, it alleviates pain from bone metastases to 80–90%. Second-line hormonal therapy with systemic chemotherapy with docetaxel and mitoxantrone,[11,12] may be beneficial when the initial ADT regimen is no longer effective. More local modalities also considered in today’s medical world are focal external beam radiation therapy, an excellent treatment choice for men with castrate-resistant prostate cancer and bone pain that is limited to one or a few sites, bone-targeted radioisotopes 89-strontium (89Sr) and 153-samarium (153Sm) for multiple blastic bone lesions, and radiofrequency ablation.
Role of cannabinoids in male physiology
Cannabis is a bushy plant with palmate leaves and clusters of small green flowers, and it grows wild in regions of tropical weather and can attain up to 3 m height. The genus Cannabis is complemented by sativa which translates to useful. Cannabis has indeed been used throughout history for a variety of purposes, including the production of fiber for paper and textile manufacture. However, its current popularity lies in its use as a recreational drug with psychoactive properties. The plant contains many chemical compounds that have different pharmacological properties, varying in quantity and quality depending on the strain, culture, and storage conditions.
In 1964, Mechoulam and colleagues found that delta-9-tetrahydrocannabinol (THC) was the major psychoactive ingredient of cannabis. However, the endocannabinoid signaling system has only been the focus of medical research and considered a potential therapeutic target in recent times.[15–17] During the late 1980s Howlett and colleagues identified and characterized a receptor in rat brain that met criteria for a high-affinity, stereoselective, pharmacologically distinct cannabinoid receptor, by means of radiolabelled agonist ligand binding and functional assays for G-protein coupled receptors.
Two different cannabinoid receptors have been described from mammalian tissues: the “central” Cannabinoid 1 (CB1) receptor and the “peripheral” Cannabinoid 2 (CB2) receptor.
In the United States, cannabis has been illegal since 1937, and currently 14 states (Alaska, California, Colorado, Hawaii, Maine, Michigan, Montana, Nevada, New Jersey, New Mexico, Oregon, Rhode Island, Vermont, and Washington) and DC have enacted laws that legalize medical marijuana, requiring it to be prescribed by physicians and being especially used to relieve AIDS patients treatment side effects. The frequently held view of cannabis and its related products as drugs of abuse have slowed progress in the development of studies designed to take advantage of the properties of cannabinoid derivatives for therapeutic purposes.
The antagonizing effect of cannabinoids in the male reproductive system and physiology can be dated to 1974 where experimental models in male rats showed depression of spermatogenesis and decrease in circulating testosterone levels. Chakravarty and colleagues[23,24] in 1980-1981 demonstrated how administration of cannabis reduced levels of fructose and citric acid, and decreased glucuronidase, glycosidase, and acid phosphatase levels in accessory reproductive organs of male rats, most of these which are regulated by circulating levels of testosterone, suggesting at the time a possible anti-androgenic effect of cannabis.
Current basic science research
In recent years, cannabinoids and their derivatives have drawn renewed attention due to the discovery of diverse pharmacologic activities such as cell growth inhibition, anti-inflammatory effects, and tumor regression.[25–30] Focusing on prostate cancer, in 2005, Sarfaraz and colleagues showed that expression of both CB1 and CB2 receptors was significantly higher in cultured prostate cancer cells LNCaP, DUI45, PC3, CWR22Rr1, and CAHPV-10 when compared with normal prostate cells PZ-HPV-7 and PrEC. Data also show that treatment of LNCaP prostate cancer cells with cannabinoid CB1/CB2 agonist WIN-55,212-2 results in a significant dose- and time-dependent decrease in cell viability and increased apoptosis of the former at 24 and 48 hours, with no significant change in apoptosis of the normal prostate epithelial cells at similar doses. When the same cells were pretreated with cannabinoid receptor antagonists SR141716 (CB1 antagonist) or SR144528 (CB2 antagonist), the coadministration of WIN-55,212-2 had no effect on cell viability, exhibiting a significant protective effect. These data suggest that both CB1 and CB2 receptors may be involved in WIN-55,212-2-mediated growth inhibition and apoptosis.
Androgens are involved in the maintenance and progression of prostate cancer, where the androgen receptor is assumed to be the essential mediator for androgen action.[31,32] Sarfaraz’ study also showed that stimulation of cannabinoid receptors resulted in a marked decrease in androgen receptor protein expression and a dose-dependent decrease in PSA expression and secreted PSA (secreted levels of PSA decreased by 30%, 53%, and 62 % at 5.0, 7.5, and 10 Amol/L, respectively) at 24 hours. PSA is considered as the most sensitive biomarker and screening tool for prostate cancer to date; its regulation is androgen-dependent.
On a future study, Sarfaraz and colleagues revealed the molecular bases for increased apoptosis and cell inhibition in prostate cancer cells treated with cannabinoid agonists, showing that treatment with WIN-55,212-2 resulted in arrest of the cells in the G0/G1 phase of the cell cycle; induction of p53 and p27/KIP1 genes; down-regulation of cyclins D1, D2, E; decrease in the expression of cdk-2, -4, and -6; and decrease in the protein expression of DP1and DP2. Curiously enough it was determined that high cannabinoid CB1 receptor immunoreactivity is associated with greater disease severity and poorer outcome in prostate cancer patients. In this study, 42% of the high CB1 receptor immunoreactivity group on prostate biopsy presented with Gleason scores of 8–10 when compared with 12% in the low CB1 receptor immunoreactivity. The incidence of metastases at diagnosis was also higher in the high CB1 receptor immunoreactivity (17%) than in the low group (5%). Patients with high CB1 receptor immunoreactivity showed a significantly worse survival rate than those with low CB1 receptor immunoreactivity (hazard ratio 2.51, with 95% confidence limits of 1.43–4.43; P < 0.05). A possible explanation for these results that is in synch with the cell line data is that the expression of CB1 receptors is regulated by the local endocannabinoid release. The author's conclusion in this scenario was that a low endocannabinoid tone would allow for an increased rate of proliferation, resulting in a compensatory increase in surface expression of CB1 receptors.
Cannabinoids in cancer pain management
Cannabinoid CB1 receptors are found mainly in the central nervous system and, in less abundance, in certain peripheral tissues. At the peripheral level, they are localized in the adrenal gland, adipose tissue, heart, liver, lung, prostate, uterus, ovary, testis, bone marrow, thymus, tonsils, and presynaptic nerve terminals.[37–42] More significantly for the purposes of the present review, they are found at central and peripheral levels of the pain pathways.[39–47] The distribution of cannabinoid receptors provides an anatomical explanation for the analgesic effects of the cannabinoids. Activation of presynaptic CB1 receptors in different brain regions or on primary afferents inhibits the release of neurotransmitters by decreasing calcium conductance and by increasing the conductance of potassium. Neurophysiological studies by Walker’s laboratory first documented that cannabinoids suppress nociceptive processing.[48–50] Cannabinoids, administered systemically, suppress activity of nociceptive neurons in the spinal dorsal horn and ventralposterior lateral nucleus of the thalamus, without altering the activity of purely non-nociceptive neurons. Stimulation-produced analgesia was blocked by the CB1 antagonist SR141716A, demonstrating mediation by the CB1 receptor.
Delta-9-THC is the substance with the greatest psychoactive potency of the natural cannabinoids and exhibits the greatest analgesic activity. Cannabidiol (CBD), another major constituent of the Cannabis sativa plant, has the same therapeutic effects of THC (analgesic, anti-inflammatory, and others), but with a different pharmacologic profile. Studies with CBD derivatives developed to inhibit peripheral pain responses and inflammation after binding to cannabinoid receptors have been described. Interestingly, some of these CBD derivatives did not have central nervous system effects, but maintained their antinociceptive and anti-inflammatory properties. This means that centrally inactive synthetic CBD analogues may be candidates for the development of analgesic and anti-inflammatory drugs for peripheral conditions without major central nervous system alterations of the sensorium.
In animal models of cancer bone pain, synthetic cannabinoids reduced hyperalgesia by a CB1 receptor-mediated effect and possibly at the peripheral CB2 receptor. In some models, cannabinoids were superiorly effective in cancer pain when compared with other pain types.[54–58]
Clinical trials have shown that nonselective cannabinoid receptor agonists are relatively safe and therapeutically efficacious, however, inducing also psychotropic side effects.
Cannabinoid efficacy has also been studied clinically in cancer pain. Initial studies quantified the modest efficacy of oral 20 mg D9-THC equivalent to 120 mg codeine with some sedation, dizziness, and confusion.[54,60,61] Recently in an observational study of patients with advanced cancer pain, nabilone reduced pain scores, total opioid requirements, and nausea. Nabilone did not significantly increase adverse effects compared with the control group, and this fact could be attributed to the concurrent decrease in opioid dose.
Uncontrolled pain can cause unnecessary suffering, decreased ability to cope with illness, interference with daily activities and extended hospital admissions, and decreasing overall quality of life.[63,64] The usual approach to cancer pain management differs from physician to physician, but a well-known guideline is described in the World Health Organization’s analgesic ladder:[65,66]
Step 1 of the ladder is for patients with mild to moderate cancer-related pain. These should first be treated with acetaminophen or a nonsteroidal antiinflammatory agent (NSAID), possibly combined with an adjuvant drug that provides additional analgesia (i.e., an analgesic antidepressant drug for neuropathic pain), treats a side effect, or manages a coexisting symptom.
Step 2 describes patients with moderate or severe pain, including those who do not achieve adequate relief after a trial of an NSAID alone; these should be treated with an opioid.
The analgesic ladder promoted the doctrine of using an opioid of inferior analgesic properties (i.e., codeine as the prototype) to treat pain of moderate intensity on step 2 and strong opiates as morphine or hydromorphone for severe pain on step 3.
On both steps 2 and 3, combination therapy that includes an NSAID or other drugs to enhance analgesia or treat side effects is advocated.
The combination of two antinociceptive drugs acting through different specific receptor systems provides major benefits. When synergistic substances are given in combination, the required dose of each agent can be reduced to less than would be explained by mere addition of individual effects. The clinical benefit of this property is fundamental in analgesic treatments because effective pain relief can be achieved with minor, fewer, or no side effects.
Chronic pain is a difficult subject to approach both for the patient and the treating physician and, not uncommonly, leads to chronic opiate consumption and dependence. Physician and the patients both are left with less and less options, and eventually to resort to alternative modes of therapy. Cannabis has been documented to be one of such measures.
As with any therapeutic modality, adverse effects must be taken into account. A number of patients will suffer from these, although most of them will be present within the first days of treatment and attenuate as they adjust to the drug. Some effects described with cannabis use are short-term unsteadiness, dizziness, difficulty concentrating, drowsiness, dryness of the mouth, and/or headache. Chronic cannabis use does not produce serious cognitive disorders, as occurs with other substances such as alcohol, but it can aggravate preexisting mental disease. Therefore, treatment with cannabinoid receptor agonist with central actions may be contraindicated, in individuals predisposed to or with current psychiatric disorders. No human deaths associated to cannabis use have been reported.
Prostate cancer is a grave public health problem worldwide. Despite the fact that most cases currently present with localized disease at the time of diagnosis, about 5% of men still present with metastatic disease. The most common site of spread is bone, and these lesions are frequently symptomatic, causing pain, debility, and functional impairment. Many of these men do not have curative treatment options, and this remains a crucial clinical problem, both in terms of the number of men affected and its impact on their quality of life. For these reasons, it is fundamental to invest time and intellectual resources into finding new and novel targets for the treatment of prostate cancer.
It seems that the studies of Sarfaraz and colleagues lead to the direction that cannabinoids should be considered as agents for the management of prostate cancer, pending support from in vivo experiments. This would not only make sense from an anti-androgenic point of view but also for men with bone metastatic prostate cancer, perhaps from a pain management or palliative point of view. Among the patients suffering with chronic pain and receiving opioids, one in five abuse prescription controlled substances,[69,70] and it is not difficult to see that opioid dependence and abuse is becoming a public health problem. Different methods of managing pain should be addressed to avoid these scenarios.
The presence of pain in men with advanced prostate cancer is an immediate indication for aggressive management with analgesics, while adequate treatments that address directly the cause of the pain are pursued. Cannabinoids possess attributes that have impact in both cancer pain and prostate cancer pathophysiology. These compounds harbor analgesic properties that aid bone cancer pain, reduce opioid consumption, side effects, and dependence, as well as exhibiting anti-androgenic effects on experimental prostate cancer cells.
Cannabis sativa and its main active component delta-9-THC have long been used for numerous purposes throughout history including medicinal, textile, and recreational. Since its legal banning in the United States in 1937, it has become an issue of taboo and controversy, frowned upon for its recreational uses and psychotropic effects. Nonetheless, the endocannabinoid signaling system has recently been the focus of medical research and considered a potential therapeutic target[15–17] since the late 1980s when Howlett and colleagues identified and characterized the distinct cannabinoid receptor in rat brain. The antagonizing effect of cannabinoids in the male reproductive system and physiology can be dated to 1974 where experimental models in male rats showed depression of spermatogenesis and decrease in circulating testosterone levels. In 2005, Sarfaraz and colleagues showed increased expression of both CB1 and CB2 receptors in cultured prostate cancer cells when compared with normal prostate cells, treatment of prostate cancer cells with cannabinoid CB1/CB2 agonist WIN-55,212-2 results in a dose and time dependent decrease in cell viability ,and increased apoptosis along with decrease in androgen receptor protein expression, PSA expression, and secreted PSA, suggesting that cannabinoids should be considered as agents for the management of prostate cancer. If the hypothesis is supported by in vivo experiments. It is our conclusion that it would be of interest to conduct clinical trials involving medicinal cannabis or other cannabinoid agonists, comparing clinical markers such as PSA with controls, especially in men with bone metastatic prostate cancer, whom would not only benefit from the possible anti-androgenic effects of cannabinoids but also from analgesia of bone pain, improving quality of life, while reducing narcotic consumption and preventing opioid dependence.
Using cannabis in prostate cancer patients
In our hospital’s daily practice we notice the popular use of cannabis oil in prostate cancer (PCa) patients. As a nursing specialist for urology, I have even met patients who are so convinced of the curative benefits of cannabis oil in treating prostate cancer that they replace standard treatment with the use of cannabis oil.
These patients include those who have localised prostate cancer where active surveillance is followed, those with biochemical recurrence after treatment, and patients with metastatic PCa. I have always wondered whether cannabis oil could indeed be a cure for prostate cancer. Unfortunately, I do not see in practice the desired beneficial effect and the PSA values continue to rise. To find some answers, I did a search in scientific literature.
Cannabis, a very easy plant to grow, has been used for centuries for its medicinal properties. The oldest known document about cannabis use originates from the Chinese emperor Shen Nung in 2727 B.C. It suggested that cannabis has a neuron-protective effect. The Egyptians used cannabis to treat glaucoma and as an anti-inflammatory agent (inflammation of the eyes, fever). Cannabis was even used in obstetrics (mixed with honey) and the mixture was applied in the vagina to “cool” the uterus. In the Old Testament, there is also an account of God instructing Moses to make a holy anointing olive oil-based “Kaneh Bosm.”
Cannabis contains more than 400 chemical components 80 of which contain cannabinoid components and 200 non-cannabinoids components. For medical purposes, cannabinoid substances such as THC (Delta-9-tertrahydrocannabinol), CBD (cannabidiol) and non-cannabinoid substances such as terpenoids and flavonoids are relevant.
Medicinal cannabis must be distinguished from recreational cannabis which is used to achieve a psychotomimetic state of ‘high’. Cannabis strains used for recreational purposes contain a higher THC and lower CBD ratio than cannabis for medicinal use. Usually two cannabis plants are used: cannabis sativa which has a higher THC concentration and cannabis indica which has a higher CBD concentrate. The flavonoids are known for their antioxidant and anti-inflammatory effects. The terpenoids are resins (oil) with a strong odour.
In the 1990s, the endocannabinoid system (ESC) of the body was discovered by Raphael Mechoulam, an Israeli professor of medical chemistry. The endocannabinoid system, a central regulatory system, is the body’s largest receptor system and is important to maintain the homeostasis of the body.
Human beings produce their own cannabinoids (endocannabinoids) according to need and are not stored in the body. Like endorphins, the human body produces endocannabinoids in response to activities such as physical exercise (the high of runners might be due to endocannabinoids, not endorphins!).
Cannabinoid receptor type 1 (CB1) is mainly found in the brain, and also in the lungs, the reproductive organs, etc. Cannabinoid receptor type 2 (CB2) is usually located in the immune system and in the bones. THC mainly works on CB1 receptors, CBD on CB2 receptors.
In vitro studies with THC have shown that cannabinoids affect migration, angiogenesis and apoptosis (programmed cell death) of cancer cells, but each type of cancer appears to respond differently to the effect of exogenous cannabinoids. Many types of cancer cells have a higher concentration of CB1 and CB2 receptors.
Use of cannabis in cancer
– Pain: Cannabinoids have been used for centuries to lessen pain. Historical texts and old pharmacopoeia noted the use of cannabis for menstrual cramps, pain during childbirth, and headaches. Studies have shown that the cannabinoids have no effect on acute pain and post- operative pain. Two placebo-controlled studies with a cannabis extract showed modest benefits when using cannabinoids in addition to opioids and other adjuvant pain-killers in cancer patients with chronic pain. However, the effect of cannabinoids in chronic neuropathic pain was clearly demonstrated in 29 randomized studies.
– Nausea and vomiting: An initial study in 1975 showed a beneficial effect of THC on nausea induced by chemotherapy. Subsequently, two systematic reviews showed benefits of cannabinoids in nausea and vomiting due to chemotherapy, but most studies were observational or uncontrolled.
– Stimulation of appetite: Cannabinoids seem to have only a modest effect in cancer patients with cachexia. More promising results were seen in studies in the population without cancer.
– Pre-clinical studies (in vitro = cells in laboratory and in vivo = in mouse model) have shown the antiproliferative, anti-metastatic, anti-angiogenic and pro-apoptotic effects of cannabinoids in various malignancies (lung, glioma, thyroid, lymphoma, skin, pancreas, endometrium, breast and prostate). Even if an identified substance in vitro / in vivo appears to have a beneficial effect on a disease, it is important to realise that only one in 5,000-500,000 substances obtain a registration and becomes available to the patient (after 10-16 years of different study phases). Cannabis has never been clinically studied as a treatment for malignancy.
On the Internet, patients can get a lot of information about the curative effect of cannabis oil on prostate cancer but this information extrapolate the results of pre-clinical work to possible effects in people without any factual evidence. I often see patients in the doctor’s office showing me a website where it has been proven that cannabis oil can cure prostate cancer, which is obviously their own interpretation. In my view this can be a misleading message even though the website does not explicitly provide false information. The website [See figure below] shows information which is based on a study published in the British Journal of Cancer. This is correct, but the website “neglects” to mention that this is a publication of an in vitro study. The patient might not even know what an in vitro study is and is not aware that there are no studies on humans yet to prove this.
A challenge for the caregiver can be that the patient is convinced that we as healthcare practitioners work together with the pharmacists, and that we do not wish to carry out clinical trials (unfortunately, I hear that very often). We can hardly persuade patients that this is not true.
It is also important that we inform the patient about the possible interactions of cannabis oil with certain regular medications such as Coumarin (this blood thinner interacts with cannabis oil, leading to an increase of the INR and a greater risk of bleeding!). There are different types of cannabis oil available, such as CBD and THC oils with different concentrations which makes it difficult for patients to make a choice.
• There is no proof of cannabis oil as cure for prostate cancer;
• It is important not to be prejudiced or judgmental against patients who use cannabis oil;
• Listening to the patient’s view can be helpful since the patient often confides to the nurse rather than to their physicians;
• Avoid persuading patients not to use cannabis oil, but try to convince them of the need to follow a regular treatment combined with cannabis oil;
• Consider adverse interactions between cannabis oil and certain medications and inform your patient about these.
- Abrams, D.I. Integrating cannabis into clinical cancer care. Current Oncology, 23, S8-S14 (2016).
- Benzi Kluger, Piera Triolo, Wallace Jones, Joseph Jankovic. The Therapeutic Potential of Cannabinoids for Movement Disorders. Mov Disord. 2015 Mar; 30(3):313–327.
- Bowles, D.W, O’Brien, C.L, Camidge D.R, Jimeno A. The intersection between cannabis and cancer in the U.S. Critical Reviews in Oncology/Hematology, 83, 1-10 (2012).
- Bridgeman M.B and Abazia D. T. Medicinal Cannabis: History, Pharmacology, And Implications for the Acute Care Setting. P T. 2017 Mar; 42(3): 180–188.
- De Petrocellis L. et al. Non-THC cannabinoids inhibit prostate carcinoma growth in vitro and in vivo:pro-apoptotic effects and underlying mechanisms. Br J Pharmacol. 2013 Jan; 168(1): 79–102.
- Guindon, J. Hohmann, A.J. The Endocannabinoid System and Cancer.: Therapeutic Implication. British Journal of Pharmacology. 163, 14447-1463 (2011) – Johnson J.R et al. Multicenter, dubbel blind, randomized, placebo-controlled, parallel-group study of the efficacy, safety and tolerability of THC: CBD extract and THC extract in patients with intractable cancerrelated pain. J.Pain Symptom Manage 2010;39:167-79.
- Machado Rocha F.C. et al. Therapeutic use of Cannabis Sativa on chemotherapy-induced nausea and vomiting among cancer patients: systematic review and meta-analysis. Eur. J. Cancer Care 2008;17:431-43.
- Olea-Herrero N. et al. Inhibition of human tumour prostate PC-3 cell growth by cannabinoids R(+)-Methanandamide and JWH-015: Involvement of CB2. British Journal of Cancer volume 101, pages 940–950 (15 September 2009).
- Portenoy R.K et al. Nabiximols for opioid-treated cancer patients with poorly-controlled chronic pain: a randomized, placebo-controlled, graded dose trial. J. Pain 2012;13:438-49.
- Ramos J.A. et al. The role of cannabinoids in prostate cancer: Basic science perspective and potential clinical applications. Indian J Urol. 2012 Jan-Mar; 28(1): 9–14.
- Tramer M.R. et al. Cannabinoids for control of chemotherapy induced nausea and vomiting: quantitative systematic review. BMJ 2001;323:16-21.
Corinne Tillier, Nurse Practitioner Urology, Antoni van Leeuwenhoek Hospital, Amsterdam (NL), [email protected]
Update on Cannabis and Prostate Cancer
Research since the March 2018 posting of the blog below supports the anti-tumor effect of non-psychoactive CBD (cannabidiol), one of 100+ identified plant-derived cannabinoid compounds. For example, Kis et al. note that lab studies have shown a chemopreventive effect of cannabidiol in prostate cancer (PCa) as well as stimulating PCa cancer cell death pathways and boosting genomic antitumor activity. [i] Furthermore, CBD is a “potent inhibitor” of the release of exosomes from PCa cells; exosomes are very tiny particles containing molecular messages that can change the behavior of healthy cells that receive them, and are thus a biogenetic pathway for the spread of PCa. A cell study by Kosgodade et al. revealed that CBD’s ability to regulate the release of PCa exosomes is one of its mechanisms for anti-cancer activity, though such dose-dependent activity appears more powerful in some types of cells others. [ii]
Thus, there is clear evidence that CBD has properties that inhibit PCa cell growth and division, encouraging cancer cell death, and block cancer cells from transforming normal cells into PCa. However, all research thus far has been conducted either in lab animals or using lab-cultured PCa cell lines. The only human clinical trials of CBD are with advanced PCa patients for management of pain and chemotherapy side effects. Thus, the potential use of CBD as a PCa prevention or a treatment for localized PCa is promising but remains hypothetical.
Cannabis (marijuana, pot, weed, grass etc.) is a widely used recreational and medicinal drug. In fact, cannabis use dates far back in ancient times, probably for the same two purposes. Today, state laws in the U.S. are rapidly becoming more permissive less than a century after it was made illegal in 1937.
According to Ramos & Bianco (1912), “The plant contains many chemical compounds that have different pharmacological properties, varying in quantity and quality depending on the strain, culture, and storage conditions. In 1964, Mechoulam and colleagues found that delta-9-tetrahydrocannabinol (THC) was the major psychoactive ingredient of cannabis.”[iii] These compounds, including THC, are called cannabinoids, and 66 separate cannabinoids have been identified.
Cannabinoids produce their physical and psychological effects by interacting with specific receptors on cell surfaces that have an affinity for these compounds. There are two types of receptors:
- Cannabinoid receptor type 1 (CB1) are mostly found in the brain, and also in the male and female reproductive systems. To a lesser extent, they exist in central and peripheral pain pathways (nerves) which may explain why pain relief is a benefit of cannabinoids, particularly THC.
- Cannabinoid receptor type 2 (CB2) are primarily found in the immune system, and may be associated with anti-inflammatory and other therapeutic effects of cannabis.
Cannabis and prostate cancer
There has been both enthusiasm and caution about cannabis use and cancer. By mid-2015, 23 states had legalized medical marijuana, one of the primary uses being to ease the side effects of chemotherapy and radiation in cancer treatment. As described above, CB1 receptors play a key role in cancer pain relief.
Now, as scientific research into the two types of cannabinoid receptors has progressed, understanding how cannabinoids interact with prostate cancer cells opens the possibility of using these compounds to restrict the activity, including the growth and spread, of prostate cancer itself.
How cannabis affects prostate cancer cells
Research shows that prostate cancer cells have higher levels of expression of both CB1 and CB2 receptors than normal cells. To put it another way, the cancer cells have a greater affinity for cannabinoids than normal cells. Laboratory studies[iv] have demonstrated that when the cells are treated with a specific cannabinoids, three consequences occur:
- In general, the cells became less viable and more prone to apoptosis (programmed cell death), and
- Androgen receptor activity on the cancer cell surfaces decreased (prostate cancer appears to be “fueled” by androgens, or male hormones)
- Two cannabinoids, THC and CBD, discourage the formation of tumor blood vessels (angiogenesis) needed by prostate cancer tumors to nourish themselves.[v]
A very extensive study was conducted by De Petrocellis et al. (2012)[vi] using both prostate cancer cells in lab containers and prostate cancer tumor cells implanted in mice. Non-THC cannabinoids were thus tested for their biochemical effects on individual cells as well as actual tumor behavior in live animals. The overall results were encouraging, with the authors suggesting that “non-THC cannabinoids, and CBD in particular, retard proliferation and cause apoptosis of PCC [prostate cancer cells] via a combination of cannabinoid receptor-independent, cellular and molecular mechanisms.”
The current state of cannabinoids and prostate cancer
With such promising research evidence that cannabinoids are destructive to prostate cancer cells, what is happening with actual prostate cancer patients? Not much, according to a prostate.net blog:
There are many stories of people who have used cannabis oil to shrink prostate cancer tumors, and many of the people had success combining the oil with traditional therapies to fight their cancer. The problem with getting hard data and studies is that United States laws make it challenging for clinical studies on the marijuana plant to take place. Plus, there seems to be a lack of funding for the research. The studies that have taken place tend to focus on symptoms (such as pain relief and nausea) rather than the efficacy of the cannabis oil to shrink cancer tumors.
Yet the research teams who have published their results with laboratory experiments, both in lab containers and animal studies, are clearly calling for clinical trials with patients. They point out that non-THC cannabinoids demonstrate properties that keep the cells from proliferating, spreading, building their own blood supply, and taking up androgens (male hormones). In addition, the De Petrocellis study found that under certain conditions, cannabinoids had a synergistic effect with chemotherapy (docetaxel) or hormone therapy (bicalutamide). Such features conjure visions of creative directions in prostate cancer treatment.
Ramos & Bianco explicitly describe a constructive scenario for prostate cancer patients with painful metastasis to the bone. As they state, cannabinoids “harbor analgesic properties that aid bone cancer pain, reduce opioid consumption, side effects, and dependence, as well as exhibiting anti-androgenic effects on experimental prostate cancer cells.”
Perhaps today’s trend of relaxing cannabis restrictions will open the path to human clinical trials, and the real value of cannabinoids in the treatment of prostate cancer will be revealed.
[i] Kis B, Ifrim FC, Buda V, Avram S et al. Cannabidiol-from Plant to Human Body: A Promising Bioactive Molecule with Multi-Target Effects in Cancer. 2019 Nov 25;20(23):5905
[ii] Kosgodage US, Mould R, Henley AB, AV et al. Cannabidiol (CBD) Is a Novel Inhibitor for Exosome and Microvesicle (EMV) Release in Cancer. Front Pharmacol. 2018 Aug 13;9:889.
[iii] Ramos J, Bianco F. The role of cannabinoids in prostate cancer: basic science perspective and potential clinical applications. Indian J Urol. 2012 Jan-Mar;28(1):9-14.
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About Dr. Dan Sperling
Dan Sperling, MD, DABR, is a board certified radiologist who is globally recognized as a leader in multiparametric MRI for the detection and diagnosis of a range of disease conditions. As Medical Director of the Sperling Prostate Center, Sperling Medical Group and Sperling Neurosurgery Associates, he and his team are on the leading edge of significant change in medical practice. He is the co-author of the new patient book Redefining Prostate Cancer, and is a contributing author on over 25 published studies. For more information, contact the Sperling Prostate Center.