Designing Treatment Strategies for Prostate Cancer Using Cannabinoids

Cannabis sativa (C. sativa) has been known by numerous names such as hemp, hashish, bhang, weed, etc. C. sativa is one of mother nature’s toughest and oldest cultivated plants, christened formally in 1753 by Carl Linnaeus. It has been used for thousands of years for its food content, medicinal properties and textile uses. Shen-nung pen-ts’ao ching mentioned C. sativa in the world’s oldest pharmacopoeia. The applications of C. sativa include analgesic-hypnotic, anti-epileptic and anti-spasmodic, appetite stimulant, prophylactic and treatment of neuralgias (migraine), anti-depressant and tranquilizer, anti-asthmatic, oxytocic (stimulant of uterine contraction during childbirth), topical anesthetic and antibiotic. Most recently, C. sativa has been used as a part of palliative care to relieve nausea, alleviate pain and stimulate appetite in cancer patients. Treatment options are associated with adverse side effects that reduce an individual’s quality of life. Thus, novel treatment options are required to target malignant cells instead of non-malignant ones. Over 500 compounds, including phytocannabinoids and terpenes, have been identified in C. sativa. Most of these compounds are yet unexplored, and their anti-cancer properties remain unknown. Additionally, many in vitro and a few animal studies have implicated the anti-tumor effects of cannabinoids in various cancer types such as prostate, breast and colon. However, very few studies have investigated its effect on prostate cancer. This thesis reveals the therapeutic potential of cannabis extract in prostate cancer. Prostate cancer is the second most frequently occurring cancer diagnosed among males. Recent preclinical evidence implicates cannabinoids as potent regulators of cell growth and differentiation. Besides the palliative effects of cannabinoids, research from the past two decades has demonstrated their promising potential as anti-tumor agents in various cancers. Chapter 1 consisted of a comprehensive review of the literature on the therapeutic potential of cannabinoids in the treatment of prostate cancer. The overarching aim of undertaking these studies was to seek a deeper understanding of the activity of cannabis extract in prostate cancer cells and explore the possible mechanism of action. This analysis may provide pharmacological insights into the selection of specific cannabinoids for developing anti-tumor drugs for the treatment of prostate cancer. Chapter 2 evaluated the effect of cannabinoids on in vivo prostate cancer models. The databases searched included PubMed, Embase, Scopus and Web of Science from inception to August 2020. Articles reporting on the effect of cannabinoids on prostate cancer were deemed eligible. The six identified studies were all found to be based on in vivo/xenograft animal models. WIN55,212-2 reduced cell proliferation dose-dependently in PC3 and DU145 xenografts. Furthermore, in LNCaP xenografts, WIN55,212-2 reduced cell proliferation by 66–69%. PM49, a synthetic cannabinoid quinone, was also found to significantly inhibit tumor growth of up to 90% and 40% in xenograft models of LNCaP and PC3 cells, respectively. All studies reported that the treatment of prostate cancers in in vivo/xenograft models with various cannabinoids decreased the tumor size, depending on the dose and length of treatment. Within these identified studies’ limitations, cannabinoids were shown to reduce the size of prostate cancer tumors in animal models. Given the therapeutic potential that has been demonstrated for cannabis extracts in pre-clinical models, it has been further studied by us to confirm its’ anti-cancer properties in prostate cancer cells. Chapter 3 provides evidence for the use of cannabis extract as a therapeutic treatment for prostate cancer. It has been investigated that extract selectively reduces the percentage of viable cancer cells, reduces their colony formation ability and migration capacity. This study examined the in vitro effects of the cannabis extract on the human prostate cancer cell lines 22RV1, PC3, DU145 and LNCaP. We found that this extract significantly inhibited the proliferation and colony formation of these tumor cells, as well as the growth of 3D tumor spheroids. These results indicated that the extract might have therapeutic effects on prostate cancer cells. In Chapter 4, the possible mechanism of action of cannabis extract treatment on PC3 and LNCaP prostate cancer cells was studied. This has been demonstrated by various methods such as blocking the cannabinoid receptors with their respective antagonists, analyzing the effect on cell cycle distribution and assessing the percentage of cells undergoing apoptosis post the extracts’ treatment. Fluorescence-activated cell sorting was used to determine apoptosis and cell cycle distribution. Additionally, the gene expression of various genes of interest, such as CNR1, CNR2, GPR55 and TRPV1 has also been studied after the treatment of cannabis extract. Finally, in Chapter 5, combination studies were performed to study the possible synergistic activity between two drugs. Therapeutic synergy is an interaction between two or more drugs whose combined effect is more significant than their individual effects. Some of the multi-components in the medicinal cannabis plant, such as phytocannabinoids, terpenoids and flavonoids, may act together synergistically and with other conventional cancer drugs. Due to the lack of reliable in vitro evidence, comprehensive studies are required to fully understand the synergistic effect and the molecular pathways that lead to the anti-cancer impacts of combinatorial therapy, such as cannabidiol and DNA-damaging agents. Although cannabinoids may well be able to help manage prostate cancer, there is still an urgent need to identify the best and the most effective combination(s) of such for treating these and other cancers. Therefore, the effect of the combination of auranofin, cisplatin and docetaxel with cannabis extract on healthy cells of the prostate and cancerous cells prostate cell viability to identify whether this cannabis extract showed improved anti-cancer activity when combined with other cancer-chemotherapeutics drugs. The novel work presented in this thesis will add additional information and improve the understanding of the therapeutic benefits of cannabis extract in prostate cancer. This evidence will provide a basis for future in vitro and in vivo experimental research and clinical trials. Additionally, this data will help in understanding the potential role of cannabis extract in prostate cancer and help in designing future treatment strategies for managing and treating this disease.<p></p>