Calanolide A is an experimental

non-nucleoside reverse transcriptase inhibitor Reverse-transcriptase inhibitors (RTIs) are a class of antiretroviral drugs used to treat HIV infection or AIDS, and in some cases hepatitis B. RTIs inhibit activity of reverse transcriptase, a viral DNA polymerase that is required for replicatio ...

(NNRTI). This compound was extracted from the tree ''

Calophyllum ''Calophyllum'' is a genus of tropical flowering plants in the family Calophyllaceae. They are mainly distributed in Asia, with some species in Africa, the Americas, Australasia, and the Pacific Islands. History Members of the genus ''Calophyll ...

lanigerum,'' of variety ''austrocoriaceum,'' in Lundu,

Malaysia Malaysia is a country in Southeast Asia. Featuring the Tanjung Piai, southernmost point of continental Eurasia, it is a federation, federal constitutional monarchy consisting of States and federal territories of Malaysia, 13 states and thre ...

n state of

Sarawak Sarawak ( , ) is a States and federal territories of Malaysia, state of Malaysia. It is the largest among the 13 states, with an area almost equal to that of Peninsular Malaysia. Sarawak is located in East Malaysia in northwest Borneo, and is ...

in 1992 by United States

National Cancer Institute The National Cancer Institute (NCI) coordinates the United States National Cancer Program and is part of the National Institutes of Health (NIH), which is one of eleven agencies that are part of the U.S. Department of Health and Human Services. ...

(NCI). Due to rarity of the raw materials and low yield of the active ingredient,

total synthesis Total synthesis, a specialized area within organic chemistry, focuses on constructing complex organic compounds, especially those found in nature, using laboratory methods. It often involves synthesizing natural products from basic, commercially ...

of the compound was devised in 1996. For the same reason, its sister compound (-)-Calanolide B (also known as Costatolide) have been touted as replacement. As a result of the discovery of Calanolide A, Sarawak Medichem pharmaceuticals company was established as a joint venture between US-based MediChem Research Inc and Craun Research Sdn Bhd, a company owned by the Sarawak state government. In 2006, Craun Research acquired Sarawak MediChem. In 2016, Craun Research announced the completion of Phase I clinical trials for Calanolide A.

History

In December 1986, Arnold Arboretum of the

Harvard University Harvard University is a Private university, private Ivy League research university in Cambridge, Massachusetts, United States. Founded in 1636 and named for its first benefactor, the History of the Puritans in North America, Puritan clergyma ...

in Massachusetts, requested permission from

government of Sarawak The Sarawak Government is an authority governing Sarawak, one of the States and federal territories of Malaysia, Borneo states of Malaysia, and is based in Kuching, the state capital. The state government adheres to and is created by both the C ...

to collaborate with Sarawak forest department to collect plants from Sarawak for phytochemical analysis. Permission was granted in May 1987. The plants collection project was part of the many expeditions launched by United States

(NCI), to find new natural substances to treat cancer and AIDS infection. In September 1987, a botanist named John Burley went on a mission to collect plant samples from a swamp forest at Lundu, Sarawak, Malaysia. He and his team routinely collected a kilogram of fruits, leaves, and twigs from each type of plant they encountered. Part of the samples were sent to NCI for analysis and the other part was sent to

Harvard University Herbaria The Harvard University Herbaria and Botanical Museum are institutions located on the grounds of Harvard University at 22 Divinity Avenue, Cambridge, Massachusetts. The Botanical Museum is one of three which comprise the Harvard Museum of Natura ...

for safekeeping for future research. A sample which was labelled "Burley-and-Lee-351" although showing no effect when tested against cancer cells in cultures, was able to stop

viral replication Viral replication is the formation of biological viruses during the infection process in the target host cells. Viruses must first get into the cell before viral replication can occur. Through the generation of abundant copies of its genome ...

when tested against

HIV The human immunodeficiency viruses (HIV) are two species of '' Lentivirus'' (a subgroup of retrovirus) that infect humans. Over time, they cause acquired immunodeficiency syndrome (AIDS), a condition in which progressive failure of the im ...

-1 virus. The sample was later determined to have come from a tree identified as ''Calophyllum lanigerum'' (locally known as Bintangor tree) of variety ''austrocoriaceum''. Sarawak Forest Department was informed of the result in late 1991. On return trip to Sarawak in March 1992, it was found that the tree had been cut down by local people most likely for fuel and building material. There was no other trees of the same variety existed in the Lundu region. The collectors then returned home with samples from other varieties of the ''Calophyllum lanigerum'' species, most of which failed to show any anti-HIV properties. Then, a few existing species were eventually located in the

Singapore Botanic Gardens The Singapore Botanic Gardens is a -year-old tropical garden located at the fringe of the Orchard Road shopping district in Singapore. It is one of three gardens, and the only tropical garden, to be honoured as a UNESCO World Heritage Site. Th ...

. With sufficient raw materials, the scientists were able to isolate the active ingredient as (+)-Calanolide A. Since the plant source is relatively rare, a method of

was developed in 1996 which showed same effectiveness against HIV virus when compared to the original compound. In addition, the samples collected from the trip in March 1992 yielded another positive result. A sister compound (-)-Calanolide B (also known as Costatolide) was isolated from the latex of ''Calophyllum teysmannii'' var. ''innophylloide'' trees. Sarawak Forestry Department was in collaboration with

University of Illinois at Chicago The University of Illinois Chicago (UIC) is a public research university in Chicago, Illinois, United States. Its campus is in the Near West Side community area, adjacent to the Chicago Loop. The second campus established under the Universi ...

(UIC) for sustainable harvest of (-)-Calanolide B. Although Costatolide is less potent than Calanolide A, the yield from raw materials is much higher (20 to 25%) when compared to Calanolide A (0.05%). Therefore, Costatolide had been accepted as replacement for Calanolide A. In June 1993, The Calophyllum Species (Prohibition of Felling and Restriction of Export) Order was issued by the Sarawak state government to ensure adequate supply of the trees for medicinal purposes. In the same year, International

Convention on Biological Diversity The Convention on Biological Diversity (CBD), known informally as the Biodiversity Convention, is a multilateral treaty. The Convention has three main goals: the conservation of biological diversity (or biodiversity); the sustainable use of its ...

(CBD) treaty came into effect with 179 countries as its signatories. However, the United States did not sign the treaty. Therefore, the Sarawak state government set up Sarawak Biodiversity Centre (SBC) in 1997 to regulate

bioprospecting Bioprospecting (also known as biodiversity prospecting) is the exploration of natural sources for small molecules, macromolecules and biochemical and genetic information that could be developed into commercialization, commercially valuable prod ...

activities in the state. In 1994, NCI signed a "letter of collection" with Sarawak state government. NCI also partnered with a small American pharmaceutical company named MediChem Research Inc based in

Lemont, Illinois Lemont is a village located in Cook, DuPage, and Will counties in the U.S. state of Illinois, and is a south-west suburb of Chicago. The population was 17,629 as of the 2020 census. The village is situated on a hillside along the south banks ...

to develop the Calanolide compound. In 1995, NCI granted MediChem all rights to develop the compound. Due to lack of funds, Medichem entered a joint venture with Sarawak state government in 1996 where the former provided technical expertise and facilities for Sarawak scientists. Meanwhile, the state government provided further funding for the development of the compound. Sarawak MediChem pharmaceuticals company was then created as a result of the joint venture. Both partners have 50:50 percent stake in all intellectual property rights of the venture. The Sarawak government entered the joint venture through its wholly owned company named Craun Research Sdn Bhd. The company was established in 1993 for research into commercialisation of

sago Sago () is a starch extracted from the pith, or spongy core tissue, of various tropical palm stems, especially those of ''Metroxylon sagu''. It is a major staple food for the lowland peoples of New Guinea and the Maluku Islands, where it is c ...

. In December 2006, Craun Research acquired Sarawak MediChem Pharmaceuticals. Craun Research collaborates with various

contract research organizations In the life sciences, a contract research organization (CRO) is a company that provides support to the pharmaceutical, biotechnology, and medical device industries in the form of research services outsourced on a contract basis. A CRO may provid ...

in the drug development, such as Nova Laboratories (under Nova Wellness Group). In 2016, Craun Research announced the successful completion of

Phase I trial The phases of clinical research are the stages in which scientists conduct experiments with a health intervention to obtain sufficient evidence for a process considered effective as a medical treatment. For drug development, the clinical phases ...

of the drug. In 2019, Dr Annuar Rapaee, Sarawak Assistant Minister for Education, Science and Technological Research admitted the slow progress in developing and commercialising the drug.

Types and derivatives

Since the discovery of Calanolide A, other similar calanolides have been described (from Calanolide B to Calanolide F). All these compounds are derived naturally from the

species of plants. Besides, other plants are found to produce Calanolide A other than ''Calophyllum lanigerum var. austrocoriaceum''. These are: ''Calophyllum brasiliense'', ''Calophyllum inophyllum'', ''Calophyllum teysmannii'', and ''Clausena excavata''. Calanolide A exists in the form of oil in its natural physical state. There are several

structure–activity relationship The structure–activity relationship (SAR) is the relationship between the chemical structure of a molecule and its biological activity. This idea was first presented by Alexander Crum Brown and Thomas Richard Fraser at least as early as 1868. Th ...

s that give Calanolide A its desired anti-HIV activity. A very specific

stereochemistry Stereochemistry, a subdiscipline of chemistry, studies the spatial arrangement of atoms that form the structure of molecules and their manipulation. The study of stereochemistry focuses on the relationships between stereoisomers, which are defined ...

and

optical rotation Optical rotation, also known as polarization rotation or circular birefringence, is the rotation of the orientation of the plane of polarization about the optical axis of linearly polarized light as it travels through certain materials. Circul ...

is required for its anti-HIV activity. Besides,

racemic mixture In chemistry, a racemic mixture or racemate () is a mixture that has equal amounts (50:50) of left- and right-handed enantiomers of a chiral molecule or salt. Racemic mixtures are rare in nature, but many compounds are produced industrially as r ...

of Calanolide A with its

enantiomer In chemistry, an enantiomer (Help:IPA/English, /ɪˈnænti.əmər, ɛ-, -oʊ-/ Help:Pronunciation respelling key, ''ih-NAN-tee-ə-mər''), also known as an optical isomer, antipode, or optical antipode, is one of a pair of molecular entities whi ...

(±)-12-oxocalanolide A is more active than Calanolide A alone. A C-12

heteroatom In chemistry, a heteroatom () is, strictly, any atom that is not carbon or hydrogen. Organic chemistry In practice, the term is mainly used more specifically to indicate that non-carbon atoms have replaced carbon in the backbone of the molecular ...

is also needed for the activity while medication of C-4 can affect its anti-HIV properties.

Hydrogenation Hydrogenation is a chemical reaction between molecular hydrogen (H2) and another compound or element, usually in the presence of a catalyst such as nickel, palladium or platinum. The process is commonly employed to redox, reduce or Saturated ...

of C-7 and C-8 has little effect on its activity. In 2017, F18, a

structural analog A structural analog, also known as a chemical analog or simply an analog, is a chemical compound, compound having a chemical structure, structure similar to that of another compound, but differing from it in respect to a certain component. It can ...

of Calanolide A could have more potent anti-HIV activity than original molecule.

Biosynthesis

The biosynthesis of Calanolide A in plants is not completely understood. The Calanolide A is synthesised from a precursor molecule

L-phenylalanine Phenylalanine (symbol Phe or F) is an essential α-amino acid with the formula . It can be viewed as a benzyl group substituted for the methyl group of alanine, or a phenyl group in place of a terminal hydrogen of alanine. This essential amin ...

. The precursor molecule then is converted into

umbelliferone Umbelliferone, also known as 7-hydroxycoumarin, hydrangine, skimmetine, and ''beta''-umbelliferone, is a natural product of the coumarin family. It absorbs ultraviolet light strongly at several wavelengths. There are some indications that this c ...

. After that, the umbelliferone molecule go through two pathways: either being converted into 5,7-dihydroxycoumarin or osthenol before being converted into dipetalolactone (a pyranocoumarin). Dipetalolactone is then converted into 3-propyl-intermediate. Through

Wagner–Meerwein rearrangement A Wagner–Meerwein rearrangement is a class of carbocation 1,2-rearrangement rearrangement reaction, reactions in which a hydrogen, alkyl or aryl group migrates from one carbon to a neighboring carbon. They can be described as cationic ,2sig ...

reaction, the propyl intermediate is converted into Calanolide A, B, or C with the help of p450 monooxygenase enzyme.

Pharmacodynamics

The drug has half-life of 20 hours. The drug is metabolised by cytochrome P450 CYP3A.

Mechanism of action

Calanolide A is unique among

(NNRTIs) in that it can bind to two distinct sites on HIV

reverse transcriptase A reverse transcriptase (RT) is an enzyme used to convert RNA genome to DNA, a process termed reverse transcription. Reverse transcriptases are used by viruses such as HIV and hepatitis B to replicate their genomes, by retrotransposon mobi ...

enzyme. It may either bind to one or another site in the

, but not both sites at the same time. The two sites are active site (binding site for 1-ethoxymethyl-5-ethyl-6-phenylthio-2-thiouracil) and

Foscarnet Foscarnet (phosphonomethanoic acid), known by its brand name Foscavir, is an antiviral medication which is primarily used to treat viral infections involving the Herpesviridae family. It is classified as a pyrophosphate Structural analog, analog ...

(also known as phosphonoformic acid) binding site of the reverse transcriptase enzyme. The drug also acts synergistically with

nevirapine Nevirapine (NVP), sold under the brand name Viramune among others, is a medication used to treat and prevent HIV/AIDS, specifically HIV-1. It is generally recommended for use with other antiretroviral medications. It may be used to prevent mo ...

in inhibiting HIV-1 virus. Besides, Calanolide A is also a partially

competitive inhibitor Competitive inhibition is interruption of a chemical pathway owing to one chemical substance inhibiting the effect of another by competing with it for binding or bonding. Any metabolic or chemical messenger system can potentially be affected b ...

of dNTP (deoxyribonucleotide triphosphate) binding site of the enzyme. However, mutated T139I reverse transcriptase is resistant to Calanolide A action.

Therapeutic potential

Calanolide A is active against HIV-1 virus but ineffective against HIV-2. It is also active against resistant strains of HIV such as eAZT-resistant G-9106 strain of HIV-1 and pyridinone-resistant A17 strain. It is also active against NNRTI-related mutations of K103N and Y181C. Calanolide A, Costatolide, and dihydrocostatolide can be used together with azidothymidine (AZT), indinavir, nelfinavir, and saquinavir for enhanced activity against the HIV-1 virus. Although initially, Calanolide A did not show any activity against cancer cell lines in the 1980s, later experimentation in 2003 showed antiproliferative and antitumor-promoting property through inhibition of TPA-induced EBV-EA activation in Raji cell lines. TPA (

12-O-Tetradecanoylphorbol-13-acetate 12-''O''-Tetradecanoylphorbol-13-acetate (TPA), also commonly known as tetradecanoylphorbol acetate, tetradecanoyl phorbol acetate, and phorbol 12-myristate 13-acetate (PMA) is a diester of phorbol. It is a potent Tumor promotion, tumor promoter ...

) is a tumour promoter used in biomedical research. EBV-EA is

Epstein–Barr virus The Epstein–Barr virus (EBV), also known as human herpesvirus 4 (HHV-4), is one of the nine known Herpesviridae#Human herpesvirus types, human herpesvirus types in the Herpesviridae, herpes family, and is one of the most common viruses in ...

early antigen. In 2003, the Calanolide A compound was found to have anti-

tuberculosis Tuberculosis (TB), also known colloquially as the "white death", or historically as consumption, is a contagious disease usually caused by ''Mycobacterium tuberculosis'' (MTB) bacteria. Tuberculosis generally affects the lungs, but it can al ...

activity. It is active against both drug-susceptible and drug resistant strains of mycobacteria such as H37Ra and H37Rv strains. The antitubercular activities of Calanolide A is comparable to

isoniazid Isoniazid, also known as isonicotinic acid hydrazide (INH), is an antibiotic used for the treatment of tuberculosis. For active tuberculosis, it is often used together with rifampicin, pyrazinamide, and either streptomycin or ethambutol. F ...

and is active against

rifampicin Rifampicin, also known as rifampin, is an ansamycin antibiotic used to treat several types of bacterial infections, including tuberculosis (TB), ''Mycobacterium avium'' complex, leprosy, and Legionnaires' disease. It is almost always used tog ...

and

streptomycin Streptomycin is an antibiotic medication used to treat a number of bacterial infections, including tuberculosis, Mycobacterium avium complex, ''Mycobacterium avium'' complex, endocarditis, brucellosis, Burkholderia infection, ''Burkholderia'' i ...

resistant ''M. tuberculosis'' strains.

Side effects

Calanolide A has a relatively good safety profile. A Phase I clinical trial done in 2001 on 47 healthy subjects showed that the side effects were taste alteration, headache, belching, and nausea.

References

{{HIVpharm Antiretroviral drugs Lactones Secondary alcohols Enones Heterocyclic compounds with 4 rings Oxygen heterocycles