Noscapine is a phthalideisoquinoline alkaloid constituting 1-10% of the alkaloid content of opium, has been used as a cough suppressant. The mechanisms for its antitussive action are unknown, although animal studies have suggested central nervous system as a site of action.
Some studies have demonstrated high-affinity, saturable, and stereo-specific binding sites for noscapine in Guinea pig brain homogenates ( [3H]Noscapine binding sites in brain: Relationship to Indoleamines and the phosphoinositide and adenylyl cyclase messenger system. 1992). Other clinical applications of this drug are based on its anti-cancer activities.
The lactone ring is unstable and opens in basic media. The opposite reaction is presented in acidic media. The bond C1-C3' is also unstable. This is the bond connecting the two optically active carbon atoms. In aqueous solution of sulfuric acid and heating it dissociates into cotarnine and opic acid.
When noscapine is reduced with zinc/HCl, the bond C1-C3' saturates and the molecule dissociates into hydrocotarnine (2-hydroxycotarnine) and meconine (6,7-dimethoxyisobenzofuran-1(3H)-one)
We reported the Noscapine’structure because superficially this drug shares similar chemical groups with colchicine and podophyllotoxin but the stereo structure of Noscapine, colchicine and podophyllotoxin differ.
Noscapine is a drug with low toxicity and good tolerance, as acute and chronic toxicity studies in animals shows a large margin of safety for noscapine (Toxicity studies on noscapine,2004. Toxicol).
Noscapine has a history of over-the-counter drug abuse in several countries, being readily available from local pharmacies without a prescription. The effects, beginning around 45 to 120 mins after consumption, are similar to dextromethorphan and alcohol intoxication. Unlike dextromethorphan, noscapine is not an NMDA receptor antagonist.
Noscapine, currently, is also a substance of abuse. It can induce the appearance of some possible side effects such as: Loss of coordination, Hallucinations (auditory and visual), loss of sexual drive, Swelling of prostate, loss of appetite, Dilated pupils, Increased heart rate, shaking and muscle spasms, chest pains, increased alertness, loss of any sleepiness and loss of stereoscopic vision.
These effects are not permanent, dose and time dependent.
Noscapine is rapidly absorbed after oral administration and gives a maximum plasma concentration after one hour. Its pharmacokinetics, also, shows a bi-exponential kinetics in human healthy volunteers (either sex); moreover, its water solubility and feasibility for oral administration are valuable advantage over many other drugs for cancer therapy. Nor-noscapine as a metabolite of noscapine has been detected in serum from all tested subjects. Nor-noscapine shows its maximal concentration at the same time as that for noscapine and the plasma concentration declines with a half-life of 13 minutes for distribution and 156 minutes for elimination phases. After oral administration, noscapine shows dose-dependent availability which shows extensive first-pass lossPharmacokinetics of oral noscapine (Pharmacokinetic of oral Noscapine, 1990.).
For evaluation of pharmacokinetic parameters of noscapine, it is required to measure its concentration in serum. The lowest concentration that could be determined was 2.5 and 3ng/ml for noscapine and nor-noscapine respectively.
Other noscapine metabolites, cotarnine and narcotoline could be determined at about similar concentrations, but they were not detected in the serum samples. Pharmacokinetic studies of noscapine were performed in mice following intravenous bolus of 10 mg/kg and oral administration of 75, 150 and 300mg/kg. Oral bioavailability of noscapine was 31.5%, which offers a feasible administration of drug with precluding hypersensitivity reactions encountered drug infusion of chemotherapeutic agents (Preclinical pharmacokinetics and bioavailability of noscapine, a tubulin-binding agent,2007.).
ANTICANCER ACTIVITY OF NOSCAPINE: interaction with microtubule
Composed of α/β-tubulin heterodimers, microtubules are ubiquitous dynamic cytoskeletal polymers that have been long recognized as a validated pharmaceutical target in cancer chemotherapy.
To form microtubules, the dimers of α- and β-tubulin bind to GTP and assemble onto the ends of microtubules while in the GTP-bound state. After the dimer is incorporated into the microtubule, the molecule of GTP bound to the β-tubulin subunit eventually hydrolyzes into GDP through inter-dimer contacts along the microtubule protofilament.
Whether the β-tubulin member of the tubulin dimer is bound to GTP or GDP influences the stability of the dimer in the microtubule. β-tubulin faces the plus end of the microtubule while α-tubulin faces the minus end. That is, the β side of added dimers connect to the plus end whereas the α sides point outwards and connect to incoming minus ends.
Dimers bound to GTP tend to assemble into microtubules, while dimers bound to GDP tend to fall apart; thus, this GTP cycle is essential for the dynamic instability of the microtubule.
Drugs that interfere with microtubule dynamic stability are widely employed in the clinic to treat a wide variety of tumors or are exploited as probes to gain insights into microtubule structure and function.
Three major classes of drugs namely, taxanes, vinca alkaloids and colchicine analogs are well recognized and the positions they occupy on the cellular target, tubulin, have been identified (Microtubules as a target for anticancer drugs;2004.). Traditionally, these three drug’s classes are categorized into stabilizers and destabilizers; the stabilizers predominantly causing overpolymerization of microtubules into bundles and sheets wile the destabilizers resulting in depolymerization of microtubules into soluble tubulin. Finally, yet another emerging class of microtubule-modulating agents is based upon noscapine and they are Vinblastine and Taxol.
Noscapine binds tubulin subunits, alters tubulin assembly, arrests a variety of mammalian cells in mitosis and causes apoptosis in cycling cells .This may also be true for previously used agents known to cause mitotic arrest. For example, taxol promotes tubulin assembly and inhibits microtubule depolymerization (Taxol stabilizes microtubules in mouse fibroblast,1980). It blocks mitosis, induces extensive formation of microtubule bundles in cells and induces the formation of multinucleated cells.
The other agents are colchicine analogs and vinblastine, which arrest cells in mitosis. However, the nanomolar concentrations at which these agents can cause mitotic arrest are well below their ability to depolymerize microtubules (Mycrotubule Dynamics: Taking aim at a moving target;1995). It has thus been suggested that these drugs act by a mechanism of kinetic stabilization.
Noscapine bound tubulin subunits can assemble into microtubules and that stoichiometric micromolar concentrations are required to elicit these effects. Although noscapine has chemical moieties that similar to those of colchicine and podophyllotoxin, the [3H]colchiciney noscapine binding competition experiment and the effects of noscapine on the fluorescence time course of colchicine binding to tubulin suggest that noscapine and colchicine probably bind to different sites on tubulin.
We have said that superficially, noscapine shares similar chemical groups with colchicine and Podophyllotoxin but the stereostructure of noscapine, colchicine, and podophyllotoxin differ. Therefore, it is possible that noscapine may form other contacts on the surface of tubulin.
Although at a lower dose (20 mg/kg), noscapine also showed promising results, at a higher dose (120 mg/kg), the antitumor activity was better. The significant in vivo antitumor activity coupled with its minimal toxicity is probably derived from the weak interaction between noscapine and tubulin.
Noscapine does not bind to tubulin as strongly as colchicine, but its interaction is adeguate to arrest mitosis. As a consequence, it may be that the mechanism by which noscapine kills cancer cells is a result of this kinetics stabilization of the microtubules and not the action of the drug on the assembly and disassembly of the polymer. Perhaps it is this relatively unique combination of properties that makes noscapine so special. Collectively, these data argue strongly that noscapine and its analogs may be good chemotherapeutic agents for the treatment or clinical management of some types of human cancers. (Opium alkaloid noscapine is an antitumor agent that arrests metaphase and induces apoptosis in dividing cells, 1998).
ANTICANCER ACTIVITY OF NOSCAPINE: Apoptosis
Study indicate that noscapine induces apoptosis on two myeloid cell lines, apoptosis-proficient HL60 cells and apoptosis-resistant K562 cells (Apoptotic Pathway induced by noscapine in human myelogenous leukemic cells;2007). An increase in the activities of caspase-2, -3, - 6, -8 and -9, along with increased poly (ADP ribose) polymerase cleavage, detection of phosphatidylserine on the outer layer of the cell membrane, nucleation of chromatin, and DNA fragmentation suggested the induction of apoptosis.
Noscapine increased the Bax/Bcl-2 ratio with a significant decrease of Bcl-2 expression accompanied with Bcl-2 phosphorylation. The Induction of apoptosis was associated with activation of the JNK signaling pathway concomitant with inactivation of the ERK signaling pathway and phosphorylation of the antiapoptotic protein Bcl-2. Noscapine-induced apoptosis was associated with the release of mitochondrial protein AIF and/or cytochrome C. In some glioma cell lines, only AIF release occurred without cytochrome C release or PARP cleavage; while in others, AIF release occurred together with cytochrome C release and was associated with PARP cleavage. That suggest the potential importance of noscapine as a novel agent for use in patients with glioblastoma multiform due to its low toxicity profile and its potent anticancer activity.
Noscapine effectively inhibits the progression of various cancer types both in vitro and in vivo with no obvious side effects even if this drug was initially used as a cough suppressant. Noscapine's antitussive effects appear to be primarily mediated by its sigma receptor agonist activity.
The type of cancer are:
- Breast Cancer: It has been shown that noscapine can arrest mammalian cells at mitosis stage; Noscapine causes apoptosis by binding to microtubule assembly, and arrests cells in mitosis.
- Colon Cancer: Although colorectal cancer is relatively resistant to many chemotherapeutic agents, noscapine induces apoptosis in a p53-dependent manner, which needs p21 induction. Therefore, noscapine can cause cell death in colon adenocarcinoma cells expressing both p53 and p21.
Drug metabolism plays a key role in determining the efficiency and safety of drugs.
On one hand, drugs undergo extensive first-pass metabolism elimination to form numerous stable metabolites, most of which are pharmacologically inactive, which may result in significant alteration of drugs’ therapeutic potential. On the other hand, in some cases, metabolism can catalyze the transformation of drugs to reactive metabolites that can induce adverse effects. Additionally, compared with low antitussive doses, relatively high anti-tumor doses of noscapine might have unfavorable pharmacokinetic and metabolic behavior.
The pharmacokinetics and bioavailability of noscapine in mice was carried out to determine antitumor potential (Preclinical pharmacokinetics and bioavailability of noscapine, a tubulin-binding agent;2007).Therefore, was analized the metabolism of noscapine at a standard anti-tumor dose (300 mg/kg body weight) in mice (Noscapine Crosses the bloodbrain and inhibits glioblastoma growth;2004.), in order to facilitate a mechanistic bridge between the metabolism and pharmacological activity of the drug.
Identification of the enzymes involved in noscapine metabolism is an important task for deciphering the metabolic pathway, which facilitates the understanding of individual response to drugs and drug-drug interactions. Some studies demonstrated that noscapine exhibits competitive and non-competitive inhibition towards CYP3A4/5 and CYP2C9, (Time-dependent inhibition (TDI) of CYP3A4 and CYP2C9 by noscapine potentially explains clinical noscapine-warfarin interaction; 2010), indicating the potential importance of these two P450s in noscapine's metabolism; moreover some studies showed that CYP3A4/5 and CYP2C9 exhibited high catalytic activity towards the formation of many noscapine's metabolites.CYP3A7, the predominant P450 expressed in the human fetal liver, accounts for 87-100% of total fetal hepatic CYP3A content.Gender and age differences should be considered in the metabolism and pharmacokinetic behavior of noscapine. It is generally regarded that women exhibit higher CYP3A activity.These factors might result in individual difference in noscapine’s metabolism.