The Biochemistry of Phytocannabinoids and Metabolic Engineering of Their Production in Heterologous Systems

Engineering cannabinoid production in Saccharomyces cerevisiae

Phytocannabinoids are natural products with highly interesting pharmacological properties mainly produced by plants. The production of cannabinoids in a heterologous host system has gained interest in recent years as a promising alternative to production from plant material. However, the systems reported so far do not achieve industrially relevant titers, highlighting the need for alternative systems. Here, we show the production of the cannabinoids cannabigerolic acid and cannabigerol from glucose and hexanoic acid in a heterologous yeast system using the aromatic prenyltransferase NphB from Streptomyces sp. strain CL190. The production was significantly increased by introducing a fusion protein consisting of ERG20WW and NphB. Furthermore, we improved the production of the precursor olivetolic acid to a titer of 56 mg L-1 . The implementation of the cannabinoid synthase genes enabled the production of Δ9 -tetrahydrocannabinolic acid, cannabidiolic acid as well as cannabichromenic acid, where the heterologous biosynthesis of cannabichromenic acid in a yeast system was demonstrated for the first time. In addition, we found that the product spectrum of the cannabinoid synthases localized to the vacuoles of the yeast cells was highly dependent on extracellular pH, allowing for easy manipulation. Finally, using a fed-batch approach, we showed cannabigerolic acid and olivetolic acid titers of up to 18.2 mg L-1 and 117 mg L-1 , respectively.

Harnessing the advances of genetic engineering in microalgae for the production of cannabinoids

Cannabis is widely recognized as a medicinal plant owing to bioactive cannabinoids. However, it is still considered a narcotic plant, making it hard to be accessed. Since the biosynthetic pathway of cannabinoids is disclosed, biotechnological methods can be employed to produce cannabinoids in heterologous systems. This would pave the way toward biosynthesizing any cannabinoid compound of interest, especially minor substances that are less produced by a plant but have a high medicinal value. In this context, microalgae have attracted increasing scientific interest given their unique potential for biopharmaceutical production. In the present review, the current knowledge on cannabinoid production in different hosts is summarized and the biotechnological potential of microalgae as an emerging platform for synthetic production is put in perspective. A critical survey of genetic requirements and various transformation approaches are also discussed.

Hormonal control of promoter activities of Cannabis sativa prenyltransferase 1 and 4 and salicylic acid mediated regulation of cannabinoid biosynthesis

Cannabis sativa aromatic prenyltransferase 4 (CsPT4) and 1 (CsPT1) have been shown to catalyze cannabigerolic acid (CBGA) biosynthesis, a step that rate-limits the cannabinoid biosynthetic pathway; both genes are highly expressed in flowers. CsPT4 and CsPT1 promoter driven β-glucuronidase (GUS) activities were detected in leaves of cannabis seedlings, and strong CsPT4 promoter activities were associated with glandular trichomes. Hormonal regulation of cannabinoid biosynthetic genes is poorly understood. An in silico analysis of the promoters identified putative hormone responsive elements. Our work examines hormone-responsive elements in the promoters of CsPT4 and CsPT1 in the context of physiological responses of the pathway to the hormone in planta. Dual luciferase assays confirmed the regulation of promoter activities by the hormones. Further studies with salicylic acid (SA) demonstrated that SA pretreatment increased the expression of genes located downstream of the cannabinoid biosynthetic pathway. The results from all aspects of this study demonstrated an interaction between certain hormones and cannabinoid synthesis. The work provides information relevant to plant biology, as we present evidence demonstrating correlations between molecular mechanisms that regulate gene expression and influence plant chemotypes.

Biosynthesis of Phytocannabinoids and Structural Insights: A Review

Cannabis belongs to the family Cannabaceae, and phytocannabinoids are produced by the Cannabis sativa L. plant. A long-standing debate regarding the plant is whether it contains one or more species. Phytocannabinoids are bioactive natural products found in flowers, seeds, and fruits. They can be beneficial for treating human diseases (such as multiple sclerosis, neurodegenerative diseases, epilepsy, and pain), the cellular metabolic process, and regulating biological function systems. In addition, several phytocannabinoids are used in various therapeutic and pharmaceutical applications. This study provides an overview of the different sources of phytocannabinoids; further, the biosynthesis of bioactive compounds involving various pathways is elucidated. The structural classification of phytocannabinoids is based on their decorated resorcinol core and the bioactivities of naturally occurring cannabinoids. Furthermore, phytocannabinoids have been studied in terms of their role in animal models and antimicrobial activity against bacteria and fungi; further, they show potential for therapeutic applications and are used in treating various human diseases. Overall, this review can help deepen the current understanding of the role of biotechnological approaches and the importance of phytocannabinoids in different industrial applications.

Relationship between Total Antioxidant Capacity, Cannabinoids and Terpenoids in Hops and Cannabis

Efficient determination of antioxidant activity in medicinal plants may provide added value to extracts. The effects of postharvest pre-freezing and drying [microwave-assisted hot air (MAHD) and freeze drying] on hops and cannabis were evaluated to determine the relationship between antioxidant activity and secondary metabolites. The 2,2-diphenyl-1-picrylhydrazine (DPPH) reduction and ferric reducing ability of power (FRAP) assays were assessed for suitability in estimating the antioxidant activity of extracted hops and cannabis inflorescences and correlation with cannabinoid and terpene content. Antioxidant activity in extracts obtained from fresh, undried samples amounted to 3.6 Trolox equivalent antioxidant activity (TEAC) (M) dry matter^-1 and 2.32 FRAP (M) dry matter^-1 for hops, in addition to 2.29 TEAC (M) dry matter^-1 and 0.25 FRAP (M) dry matter^-1 for cannabis. Pre-freezing significantly increased antioxidant values by 13% (DPPH) and 29.9% (FRAP) for hops, and by 7.7% (DPPH) and 19.4% (FRAP) for cannabis. ANOVA analyses showed a significant (p < 0.05) increase in total THC (24.2) and THCA (27.2) concentrations (g 100 g dry matter^-1) in pre-frozen, undried samples compared to fresh, undried samples. Freeze-drying and MAHD significantly (p < 0.05) reduced antioxidant activity in hops by 79% and 80.2% [DPPH], respectively and 70.1% and 70.4% [FRAP], respectively, when compared to antioxidant activity in extracts obtained from pre-frozen, undried hops. DPPH assay showed that both freeze-drying and MAHD significantly (p < 0.05) reduced the antioxidant activity of cannabis by 60.5% compared to the pre-frozen samples although, there was no significant (p < 0.05) reduction in the antioxidant activity using the FRAP method. Greater THC content was measured in MAHD-samples when compared to fresh, undried (64.7%) and pre-frozen, undried (57%), likely because of decarboxylation. Both drying systems showed a significant loss in total terpene concentration, yet freeze-drying has a higher metabolite retention compared to MAHD. These results may prove useful for future experiments investigating antioxidant activity and added value to cannabis and hops.

Biotechnological Fungal Platforms for the Production of Biosynthetic Cannabinoids

Cannabinoids are bioactive meroterpenoids comprising prenylated polyketide molecules that can modulate a wide range of physiological processes. Cannabinoids have been shown to possess various medical/therapeutic effects, such as anti-convulsive, anti-anxiety, anti-psychotic, antinausea, and anti-microbial properties. The increasing interest in their beneficial effects and application as clinically useful drugs has promoted the development of heterologous biosynthetic platforms for the industrial production of these compounds. This approach can help circumvent the drawbacks associated with extraction from naturally occurring plants or chemical synthesis. In this review, we provide an overview of the fungal platforms developed by genetic engineering for the biosynthetic production of cannabinoids. Different yeast species, such as Komagataella phaffii (formerly P. pastoris) and Saccharomyces cerevisiae, have been genetically modified to include the cannabinoid biosynthetic pathway and to improve metabolic fluxes in order to increase cannabinoid titers. In addition, we engineered the filamentous fungus Penicillium chrysogenum for the first time as a host microorganism for the production of Δ⁹-tetrahydrocannabinolic acid from intermediates (cannabigerolic acid and olivetolic acid), thereby showing the potential of filamentous fungi as alternative platforms for cannabinoid biosynthesis upon optimization.

Current status and future prospects in cannabinoid production through in vitro culture and synthetic biology

For centuries, cannabis has been a rich source of fibrous, pharmaceutical, and recreational ingredients. Phytocannabinoids are the most important and well-known class of cannabis-derived secondary metabolites and display a broad range of health-promoting and psychoactive effects. The unique characteristics of phytocannabinoids (e.g., metabolite likeness, multi-target spectrum, and safety profile) have resulted in the development and approval of several cannabis-derived drugs. While most work has focused on the two main cannabinoids produced in the plant, over 150 unique cannabinoids have been identified. To meet the rapidly growing phytocannabinoid demand, particularly many of the minor cannabinoids found in low amounts in planta, biotechnology offers promising alternatives for biosynthesis through in vitro culture and heterologous systems. In recent years, the engineered production of phytocannabinoids has been obtained through synthetic biology both in vitro (cell suspension culture and hairy root culture) and heterologous systems. However, there are still several bottlenecks (e.g., the complexity of the cannabinoid biosynthetic pathway and optimizing the bioprocess), hampering biosynthesis and scaling up the biotechnological process. The current study reviews recent advances related to in vitro culture-mediated cannabinoid production. Additionally, an integrated overview of promising conventional approaches to cannabinoid production is presented. Progress toward cannabinoid production in heterologous systems and possible avenues for avoiding autotoxicity are also reviewed and highlighted. Machine learning is then introduced as a powerful tool to model, and optimize bioprocesses related to cannabinoid production. Finally, regulation and manipulation of the cannabinoid biosynthetic pathway using CRISPR- mediated metabolic engineering is discussed.

Biosynthetic origins of unusual cannabimimetic phytocannabinoids in Cannabis sativa L: A review

Plants of Cannabis sativa L. (Cannabaceae) produce an array of more than 160 isoprenylated resorcinyl polyketides, commonly referred to as phytocannabinoids. These compounds represent molecules of therapeutic importance due to their modulation of the human endocannabinoid system (ECS). While understanding of the biosynthesis of the major phytocannabinoids Δ⁹-tetrahydrocannabinol (Δ⁹-THC) and cannabidiol (CBD) has grown rapidly in recent years, the biosynthetic origin and genetic regulation of many potentially therapeutically relevant minor phytocannabinoids remain unknown, which limits the development of chemotypically elite varieties of C. sativa. This review provides an up-to-date inventory of unusual phytocannabinoids which exhibit cannabimimetic-like activities and proposes putative metabolic origins. Metabolic branch points exploitable for combinatorial biosynthesis and engineering of phytocannabinoids with augmented therapeutic activities are also described, as is the role of phytocannabinoid remodelling to accelerate the therapeutic portfolio expansion in C. sativa.

A polarized supercell produces specialized metabolites in cannabis trichomes

For centuries, humans have cultivated cannabis for the pharmacological properties that result from consuming its specialized metabolites, primarily cannabinoids and terpenoids. Today, cannabis is a multi-billion-dollar industry whose existence rests on the biological activity of tiny cell clusters, called glandular trichomes, found mainly on flowers. Cannabinoids are toxic to cannabis cells,¹ and how the trichome cells can produce and secrete massive quantities of lipophilic metabolites is not known.¹ To address this gap in knowledge, we investigated cannabis glandular trichomes using ultra-rapid cryofixation, quantitative electron microscopy, and immuno-gold labeling of cannabinoid pathway enzymes. We demonstrate that the metabolically active cells in cannabis form a "supercell," with extensive cytoplasmic bridges across the cell walls and a polar distribution of organelles adjacent to the apical surface where metabolites are secreted. The predicted metabolic role of the non-photosynthetic plastids is supported by unusual membrane arrays in the plastids and the localization of the start of the cannabinoid/terpene pathway in the stroma of the plastids. Abundant membrane contact sites connected plastid paracrystalline cores with the plastid envelope, plastid with endoplasmic reticulum (ER), and ER with plasma membrane. The final step of cannabinoid biosynthesis, catalyzed by tetrahydrocannabinolic acid synthase (THCAS), was localized in the cell-surface wall facing the extracellular storage cavity. We propose a new model of how the cannabis cells can support abundant metabolite production, with emphasis on the key role of membrane contact sites and extracellular THCA biosynthesis. This new model can inform synthetic biology approaches for cannabinoid production in yeast or cell cultures.

Delineating genetic regulation of cannabinoid biosynthesis during female flower development in Cannabis sativa

Cannabinoids are predominantly produced in the glandular trichomes on cannabis female flowers. There is little known on how cannabinoid biosynthesis is regulated during female flower development. We aim to understand the rate-limiting step(s) in the cannabinoid biosynthetic pathway. We investigated the transcript levels of cannabinoid biosynthetic genes together with cannabinoid contents during 7 weeks of female flower development. We demonstrated that the enzymatic steps for producing cannabigerol (CBG), which involve genes GPPS, PT, TKS, and OAC, could rate limit cannabinoid biosynthesis. Our findings further suggest that upregulation of cannabinoid synthases, CBDAS and THCAS in a commercial hemp and medical marijuana variety, respectively, is not critical for cannabinoid biosynthesis. The cannabinoid biosynthetic genes are generally upregulated during flower maturation; increased expression occurs coincident with glandular trichome development and cannabinoid production in the maturing flower. The results also suggest that different cannabis varieties may experience discrete transcriptional regulation of cannabinoid biosynthetic genes. In addition, we showed that methyl jasmonate (MeJA) can potentially increase cannabinoid production. We propose that biweekly applications of 100 μM MeJA starting from flower initiation would be efficacious for promoting cannabinoid biosynthesis. Our findings provide important genetic information for cannabis breeding to generate new varieties with favorable traits.

A Case Report of Subcutaneously Injected Liposomal Cannabidiol Formulation Used as a Compassion Therapy for Pain Management in a Dog

A 14-year-old intact mixed breed dog (26 kg) was submitted for a novel cannabidiol (CBD) analgesic treatment. The dog was cachectic and had a testicular neoplasia, hip and elbow osteoarthritis and severe cervical pain. Analgesic treatment included canine osteoarthritic supplement, robencoxib and gabapentin. An additional liposomal CBD injectable formulation at 5 mg/kg was administered subcutaneously between the shoulder blades. The dog was monitored using an activity monitoring collar (PetPace), owner wellbeing questionnaire (Canine Brief Pain Inventory; CBPI), pain interactive visual analog scale (iVAS), blood work and CBD plasma concentrations. A week from the injection and up to 3 weeks afterwards the dog had improved CBPI and iVAS pain scores, and increased collar activity scores. CBD was quantified in plasma for 28 days. Due to disease progression, further difficulty to rise and walk, and relapse to pain after 3 weeks, the owners requested a second liposomal CBD injection, which was performed 4 weeks following the first injection using 3 mg/kg dose. Two days later, the dog was found dead in the yard under direct sun, while environmental temperature was 37°C. Major findings on necropsy revealed evidence of heat stroke and severe cervical disc protrusion with spinal hematoma, none related to liposomal CBD. In conclusion, subcutaneous liposomal CBD produced quantifiable CBD plasma concentrations for 28 days and may be an effective additional treatment as part of multimodal pain management in dogs.

Elusive partners: a review of the auxiliary proteins guiding metabolic flux in flavonoid biosynthesis

Flavonoids are specialized metabolites widely distributed across the plant kingdom. They are involved in the growth and survival of plants, conferring the ability to filter ultra-violet rays, conduct symbiotic partnerships, and respond to stress. While many branches of flavonoid biosynthesis have been resolved, recent discoveries suggest missing auxiliary components. These overlooked elements can guide metabolic flux, enhance production, mediate stereoselectivity, transport intermediates, and exert regulatory functions. This review describes several families of auxiliary proteins from across the plant kingdom, including examples from specialized metabolism. In flavonoid biosynthesis, we discuss the example of chalcone isomerase-like (CHIL) proteins and their non-catalytic role. CHILs mediate the cyclization of tetraketides, forming the chalcone scaffold by interacting with chalcone synthase (CHS). Loss of CHIL activity leads to derailment of the CHS-catalyzed reaction and a loss of pigmentation in fruits and flowers. Similarly, members of the pathogenesis-related 10 (PR10) protein family have been found to differentially bind flavonoid intermediates, guiding the composition of anthocyanins. This role comes within a larger body of PR10 involvement in specialized metabolism, from outright catalysis (e.g., (S)-norcoclaurine synthesis) to controlling stereochemistry (e.g., enhancing cis-trans cyclization in catnip). Both CHILs and PR10s hail from larger families of ligand-binding proteins with a spectrum of activity, complicating the characterization of their enigmatic roles. Strategies for the discovery of auxiliary proteins are discussed, as well as mechanistic models for their function. Targeting such unanticipated components will be crucial in manipulating plants or engineering microbial systems for natural product synthesis.

High-Titer Production of Olivetolic Acid and Analogs in Engineered Fungal Host Using a Nonplant Biosynthetic Pathway

The microbial synthesis of cannabinoids and related molecules requires access to the intermediate olivetolic acid (OA). Whereas plant enzymes have been explored for E. coli and yeast biosynthesis, moderate yields and shunt product formation are major hurdles. Here, based on the chemical logic to form 2,4-dihydroxybenzoate-containing natural products, we discovered a set of fungal tandem polyketide synthases that can produce OA and the related octanoyl-primed derivative sphaerophorolcarboxylic acid in high titers using the model organism Aspergillus nidulans. This new set of enzymes will enable new synthetic biology strategies to access microbial cannabinoids.