A phosphodiesterase inhibitor is a drug that blocks one or more of the five subtypes of the enzyme phosphodiesterase (PDE), thereby preventing the inactivation of the intracellular second messengers, cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) by the respective PDE subtype(s). The ubiquitous presence of this enzyme means that non-specific inhibitors have a wide range of actions, the actions in the heart, and lungs being some of the first to find a therapeutic use.
Prostaglandin analogues are a class of drugs that bind to a prostaglandin receptor.
Nabilone, sold under the brand name Cesamet among others, is a synthetic cannabinoid with therapeutic use as an antiemetic and as an adjunct analgesic for neuropathic pain. It mimics tetrahydrocannabinol (THC), the primary psychoactive compound found naturally occurring in Cannabis.
NMDA receptor antagonists are a class of drugs that work to antagonize, or inhibit the action of, the N-Methyl-D-aspartate receptor (NMDAR). They are commonly used as anesthetics for animals and humans; the state of anesthesia they induce is referred to as dissociative anesthesia.
Fenobam is an imidazole derivative developed by McNeil Laboratories in the late 1970s as a novel anxiolytic drug with an at-the-time-unidentified molecular target in the brain. Subsequently, it was determined that fenobam acts as a potent and selective negative allosteric modulator of the metabotropic glutamate receptor subtype mGluR5, and it has been used as a lead compound for the development of a range of newer mGluR5 antagonists.
(+)-CPCA is a stimulant drug similar in structure to pethidine and to RTI-31, but nocaine is lacking the two-carbon bridge of RTI-31's tropane skeleton. This compound was first developed as a substitute agent for cocaine.
Naphthylaminopropane (PAL-287) is an experimental drug under investigation as of 2007 for the treatment of alcohol and stimulant addiction.
Nefopam, sold under the brand name Acupan among others, is a centrally acting, non-opioid painkilling medication, that is primarily used to treat moderate to severe pain.
MDAI (5,6-methylenedioxy-2-aminoindane) is a drug developed in the 1990s by a team led by David E. Nichols at Purdue University. It acts as a non-neurotoxic and highly selective serotonin releasing agent (SSRA) in vitro and produces entactogen effects in humans.
Dexanabinol is a synthetic cannabinoid derivative in development by e-Therapeutics plc. It is the "unnatural" enantiomer of the potent cannabinoid agonist HU-210. Unlike other cannabinoid derivatives, HU-211 does not act as a cannabinoid receptor agonist, but instead has NMDA antagonist effects. It therefore does not produce cannabis-like effects, but is anticonvulsant and neuroprotective, and is widely used in scientific research as well as currently being studied for applications such as treating head injury, stroke, or cancer. It was shown to be safe in clinical trials and is currently undergoing Phase I trials for the treatment of brain cancer and advanced solid tumors.
AR-R17779 is a drug that acts as a potent and selective full agonist for the α7 subtype of neural nicotinic acetylcholine receptors. It has nootropic effects in animal studies, but its effects do not substitute for those of nicotine. It has also been studied as a potential novel treatment for arthritis.
3,4-Dichloromethylphenidate is a stimulant drug related to methylphenidate. Dichloromethylphenidate is a potent psychostimulant that acts as both a dopamine reuptake inhibitor and norepinephrine reuptake inhibitor, meaning it effectively boosts the levels of the norepinephrine and dopamine neurotransmitters in the brain, by binding to, and partially blocking the transporter proteins that normally remove those monoamines from the synaptic cleft.
Rivastigmine is a cholinesterase inhibitor used for the treatment of mild to moderate Alzheimer's disease. The drug can be administered orally or via a transdermal patch; the latter form reduces the prevalence of side effects, which typically include nausea and vomiting.
8-Carboxamidocyclazocine (8-CAC) is an opioid analgesic drug related to cyclazocine, discovered by medicinal chemist Mark P. Wentland and co-workers in Cogswell Laboratory at Rensselaer Polytechnic Institute. Similarly to cyclazocine, 8-CAC acts as an agonist at both the μ and κ opioid receptors, but has a much longer duration of action than cyclazocine, and does not have μ antagonist activity. Unexpectedly it was discovered that the phenolic hydroxyl group of cyclazocine could be replaced by a carboxamido group with only slight loss of potency at opioid receptors, and this discovery has subsequently been used to develop many novel opioid derivatives where the phenolic hydroxy group has been replaced by either carboxamide or a variety of larger groups. Due to their strong κ-opioid agonist activity, these drugs are not suited for use as analgesics in humans, but have instead been researched as potential drugs for the treatment of cocaine addiction.
UWA-101 is a phenethylamine derivative invented by Dr Matthew Piggott at the University of Western Australia, and researched as a potential treatment for Parkinson's disease. Its chemical structure is very similar to that of the illegal drug MDMA, the only difference being the replacement of the α-methyl group with an α-cyclopropyl group. MDMA has been found in animal studies and reported in unauthorised human self-experiments to be effective in the short-term relief of side-effects of Parkinson's disease therapy, most notably levodopa-induced dyskinesia. However the illegal status of MDMA and concerns about its potential for recreational use, neurotoxicity and potentially dangerous side effects mean that it is unlikely to be investigated for medical use in this application, and so alternative analogues were investigated.
KM-233 is a synthetic cannabinoid drug which is a structural analog of Δ8-tetrahydrocannabinol (THC), the less active but more stable isomer of the active component of Cannabis. KM-233 differs from Δ8-THC by the pentyl side chain being replaced by a 1,1-dimethylbenzyl group. It has high binding affinity in vitro for both the CB1 and CB2 receptors, with a CB2 affinity of 0.91 nM and 13-fold selectivity over the CB1 receptor. In animal studies, it has been found to be a potential treatment for glioma, a form of brain tumor. Many related analogues are known where the 1,1-dimethylbenzyl group is substituted or replaced by other groups, with a fairly well established structure-activity relationship.
Gabapentinoids, also known as α2δ ligands, are a class of drugs that are derivatives of the inhibitory neurotransmitter gamma-Aminobutyric acid (GABA) which block α2δ subunit-containing voltage-dependent calcium channels (VDCCs). This site has been referred to as the gabapentin receptor, as it is the target of the drugs gabapentin and pregabalin.
5-Chloro-α-methyltryptamine (5-Chloro-αMT), also known as PAL-542, is a tryptamine derivative related to α-methyltryptamine (αMT) and one of only a few known specific serotonin-dopamine releasing agents (SDRAs). It has been investigated in animals as a potential treatment for cocaine dependence. The EC50 values of 5-chloro-αMT in evoking the in vitro release of serotonin (5-HT), dopamine (DA), and norepinephrine (NE) in rat synaptosomes were reported as 16 nM, 54 nM, and 3434 nM, with an NE/DA ratio of 63.6 and a DA/5-HT ratio of 3.38, indicating that it is a highly specific and well-balanced SDRA. However, 5-chloro-αMT has also been found to act as a potent full agonist of the 5-HT2A receptor, with an EC50 value of 6.27 nM and an efficacy of 105%, and almost assuredly acts as a potent agonist of other serotonin receptors as well.
GS-6620 is an antiviral drug which is a nucleotide analogue. It was developed for the treatment of Hepatitis C but while it showed potent antiviral effects in early testing, it could not be successfully formulated into an oral dosage form due to low and variable absorption in the intestines which made blood levels unpredictable. It has however continued to be researched as a potential treatment for other viral diseases such as Ebola virus disease.
EICAR is a drug which acts as an inhibitor of the enzyme IMP dehydrogenase. It is a nucleoside derivative which has both anti-cancer and antiviral effects, and was originally developed for the treatment of leukemia, but was unsuccessful in human clinical trials. It has broad spectrum antiviral effects with activity against pox viruses, Semliki forest virus, Junin virus, reovirus, influenza, measles virus and respiratory syncytial virus among others, although it is not active against coronaviridae such as SARS-CoV-1. This useful spectrum of activity means that EICAR and related derivatives continue to be investigated for the treatment of viral diseases.
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