Nordihydroguaiaretic Acid in Therapeutics: Beneficial to Toxicity Profiles and the Search for its Analogs.

Nordihydroguaiaretic acid (NDGA) is a plant lignan obtained from creosote bush, Larrea tridentata and is known to possess antioxidant, anticancer activities and is used in traditional medicine in North America and Mexico. However, its prolonged consumption leads to liver damage and kidney dysfunction. Despite its toxicity and side effects, there is little awareness to forbid its consumption and its use in the treatment of medical ailments has continued over the years. Several reports discuss its therapeutic efficiency and its medical applications have tremendously been on the rise to date. There has been a recent surge of interest in the chemical synthesis of NDGA derivatives for therapeutic applications. NDGA derivatives have been developed as better alternatives to NDGA. Although several NDGA derivatives have been chemically synthesized as evidenced by recent literature, there is a paucity of information on their therapeutic efficacies. This review is to highlight the medicinal applications of NDGA, its toxicity evaluations and discuss the chemical derivatives of NDGA synthesized and studied so far and suggest to continue research interests in the development of NDGA analogs for therapeutic applications. We suggest that NDGA derivatives should be investigated more in terms of chemical synthesis with preferred conformational structures and exploit their biological potentials with future insights to explore in this direction to design and develop structurally modified NDGA derivatives for potential pharmacological properties.

Design, synthesis, and evaluation of NDGA analogues as potential anti-ischemic stroke agents.

Exogenous supplementation of antioxidants with ROS scavenging activity would be a potential therapy to cerebral ischemia-reperfusion injury in stroke. In the present study, a series of NDGA analogues with attenuation oxidative stress by directly scavenging ROS and indirectly through keap1/Nrf2/ARE pathway activation were designed and synthesized. All analogues were found to effectively remove ROS directly by DPPH radical scavenging assay, and compound 3a conferred potent protection from the oxidative injury in PC12 cells via promoting Nrf2 to translocate into nucleus and increasing expression of heme oxygenase-1(HO-1), where strongly reduced intracellular ROS level indirectly. More importantly, 3a significantly reduced brain infarction after cerebral ischemia-reperfusion injury in rats subjected to transient middle cerebral artery occlusion (MCAO). Overall, our findings shown compound 3a could serve as a promising compound for the treatment of stroke.

Ring substitution influences oxidative cyclisation and reactive metabolite formation of nordihydroguaiaretic acid analogues.

Nordihydroguaiaretic acid (NDGA) is a natural polyphenol with a broad spectrum of pharmacological properties. However, its usefulness is hindered by the lack of understanding of its pharmacological and toxicological pathways. Previously we showed that oxidative cyclisation of NDGA at physiological pH forms a dibenzocyclooctadiene that may have therapeutic benefits whilst oxidation to an ortho-quinone likely mediates toxicological properties. NDGA analogues with higher propensity to cyclise under physiologically relevant conditions might have pharmacological implications, which motivated this study. We synthesized a series of NDGA analogues which were designed to investigate the structural features which influence the intramolecular cyclisation process and help to understand the mechanism of NDGA's autoxidative conversion to a dibenzocyclooctadiene lignan. We determined the ability of the NDGA analogues investigated to form dibenzocyclooctadienes and evaluated the oxidative stability at pH 7.4 of the analogues and the stability of any dibenzocyclooctadienes formed from the NDGA analogues. We found among our group of analogues the catechols were less stable than phenols, a single catechol-substituted ring is insufficient to form a dibenzocyclooctadiene lignan, and only compounds possessing a di-catechol could form dibenzocyclooctadienes. This suggests that quinone formation may not be necessary for cyclisation to occur and the intramolecular cyclisation likely involves a radical-mediated rather than an electrophilic substitution process. We also determined that the catechol dibenzocyclooctadienes autoxidised at comparable rates to the parent catechol. This suggests that assigning in vitro biological activity to the NDGA dibenzocyclooctadiene is premature and requires additional study.

Discovery and anti-cancer evaluation of two novel non-ATP-competitive FGFR1 inhibitors in non-small-cell lung cancer.

BACKGROUND: Fibroblast growth factor receptor 1 (FGFR1) is correlated closely with the occurrence and development of lung cancer. FGFR1 kinase inhibitors have exhibited significant therapeutic effects against non-small-cell lung cancer. Recently, non-ATP competitive FGFR1 inhibitors have attracted extensive attention due to their low side effects. METHODS: Caliper Mobility Shift Assay was used for FGFR1 inhibition test and kinase inhibitory mode study. Hoechst staining and Annexin V/PI staining were used to evaluate the cell apoptosis induction. Western blot were then performed to confirm the intracellular FGFR1 inhibition and apoptotic protein expression. Finally, the anti-tumor effect and mechanism of Af23 and Ad23 was evaluated in vivo. RESULTS: In this study, we designed, synthesized and discovered two novel non-ATP competitive FGFR1 inhibitors, Af23 and Ad23, using NDGA as a leading compound. They had IC50 values of 0.6 µM and 1.4 µM against FGFR1 kinase, respectively. The kinase inhibitory assay carried at different ATP concentrations showed that the FGFR1 inhibition mode of both Ad23 and Af23 was non-ATP-competitive. Further, Af23 and Ad23 significantly suppressed FGFR1 phosphorylation and cell proliferation in non-small-cell lung cancer (NSLCLC) H460 cells and induced cell apoptosis. Af23 and Ad23 also showed significant anti-tumor activity in the H460 xenograft mouse model, accompanied with the inhibition of FGFR1, ERK, and AKT phosphorylation without exhibiting toxicity. CONCLUSIONS: These results indicate that Ad23 and Af23 are potential agents for the treatment of non-small-cell lung cancer. This work also provides a structural lead for the design of new non-ATP-competitive FGFR1 inhibitors.

Hepatocellular carcinoma targeting agents: conjugates of nitroimidazoles with trimethyl nordihydroguaiaretic acid.

Cancer has been a primary global health issue for decades, with hepatocellular carcinoma (HCC) resulting in more than half a million new cases annually. With survival rates as low as <5% after five years, it remains a poorly treated cancer. Nordihydroguaiaretic acid (NDGA), an antioxidant, was previously proven effective against cancer cells. Nitroimidazole derivatives convert into reactive compounds under hypoxic conditions. In this study, eight methylated NDGAs containing a 2- or 4-nitroimidazole moiety were synthesized as leads against HCC. Four of these conjugates, possessing a poly(ethylene glycol) tether, had superior aqueous solubility. These four NDGA-nitroimidazole conjugates were found to inhibit the proliferation HCC Hep3B cells with IC50 values between 10 and 15 µM. Furthermore, nitroimidazole-conjugated NDGA derivatives exhibit better antiproliferative activity under hypoxic conditions.

Synthesis of nordihydroguaiaretic acid derivatives and their bioactivities on S. pombe and K562 cell lines.

Nordihydroguaiaretic acid (NDGA) and its synthetic analogues are potentially useful in treating diseases related to cancers, diabetes, viral and bacterial infections, and inflammation. In this paper, we report the optimal synthetic methods and the bioactivity study of terameprocol 2, NDGA derivative 3, and its cyclized analogue 4. The IC50 of these three compounds 2, 3 and 4 on the growth metabolism of Schizosacchromyces pombe and K562 cell lines were determined by microcalorimetry. The preliminary results showed that the compounds 2, 3 and 4 possessed good inhibition activities on S. pombe and K562 cell lines, and exhibited bidirectional biological effect and Hormesis effect. In particular, terameprocol 2 was found to possess the most potent inhibitory effect on K562 cell lines.

Discovery of a small molecule PDI inhibitor that inhibits reduction of HIV-1 envelope glycoprotein gp120.

Protein disulfide isomerase (PDI) is a promiscuous protein with multifunctional properties. PDI mediates proper protein folding by oxidation or isomerization and disrupts disulfide bonds by reduction. The entry of HIV-1 into cells is facilitated by the PDI-catalyzed reductive cleavage of disulfide bonds in gp120. PDI is regarded as a potential drug target because of its reduction activity. We screened a chemical library of natural products for PDI-specific inhibitors in a high-throughput fashion and identified the natural compound juniferdin as the most potent inhibitor of PDI. Derivatives of juniferdin were synthesized, with compound 13 showing inhibitory activities comparable to those of juniferdin but reduced cytotoxicity. Both juniferdin and compound 13 inhibited PDI reductase activity in a dose-dependent manner, with IC(50) values of 156 and 167 nM, respectively. Our results also indicated that juniferdin and compound 13 exert their inhibitory activities specifically on PDI but do not significantly inhibit homologues of this protein family. Moreover, we found that both compounds can inhibit PDI-mediated reduction of HIV-1 envelope glycoprotein gp120.

Glycosylated nordihydroguaiaretic acids as anti-cancer agents.

Three perglycosylated nordihydroguaiaretic acids (NDGA) were synthesized through the Huiseng 1,3-dipolar cycloaddition reaction. These sugar-NDGA conjugates containing triazole-linkages possessed good solubility in water. NDGA-(triazol-galactose)(4) (12b) and NDGA-(triazol-glucose)(4) (12c) were found to act as inhibitors against human hepatocellular carcinoma Hep3B cells in culture.

Nordihydroguaiaretic acid analogues: their chemical synthesis and biological activities.

Nordihydroguaiaretic acid is a natural occurring lignan mainly isolated and commercially produced from desert plant, creosote bush (Larrea divaricata Cav. Or Corillea tridentate), which can be widely found in the border zone of southern of USA and northern of Mexico. During past 100 years, extensive research has demonstrated that nordihydroguaiaretic acid and its synthetic analogues are potentially useful in treating diseases related to cancers, diabetes, viral, bacterial infections, and inflammation. Remarkably, terameprocol, a tetra-O-methyl derivative of nordihydroguaiaretic acid, is currently in Phase I/II clinical trials as an anticancer agent. This review deals with the chemical synthesis and bioactivities of nordihydroguaiaretic acid and its structurally-related derivatives, which possess anticancer, antioxidant, antimicrobial, anti-inflammatory and immunosuppressive activities. The review consists of the data reported in over 100 publications.

Synthesis, characterization, and anti-melanoma activity of tetra-O-substituted analogs of nordihydroguaiaretic acid.

Synthesis of seven semi-synthetic analogs of NDGA is described. An approach to NDGA derivatization is described in which the ortho-phenolic groups are tethered together by one atom, forming a 5-membered heterocyclic ring. The analogs were evaluated for cytotoxicity in four cancer cell lines and compared to NDGA and tetra-O-methyl-NDGA (M4N) (1a). NDGA bis-cyclic sulfate (2a), NDGA bis-cyclic carbonate (2b), and methylenedioxyphenyl-NDGA (2d) and NDGA tetra acetate (1b) showed anti-cancer activity in vitro. Two compounds, (1b) and (2b), were evaluated for anticancer activity in a mouse xenograft model of human melanoma and showed dose-dependent activity.

New nordihydroguaiaretic acid derivatives as anti-HIV agents.

Reaction of nordihydroguaiaretic acid with various alkyl chloride, 1-piperidinecarbonyl chloride, methyl chloroformate, or 1,1'-carbonyldiimidazole under alkaline conditions produced the corresponding phenol ethers, carbamates and carbonates, respectively, in 67-83% yields. Among these derivatives, the nitrogen-containing compounds were converted to the corresponding hydrochloride salts. Having good solubility, these NDGA derivatives were found stable in aqueous solution. These new compounds exerted appealing activity against HIV Tat-regulated transactivation in human epithelial cells. The most potent compound meso-2,3-dimethyl-1,4-bis(3,4-[2-(piperdino)ethoxyphenyl])butane tetrakishydrochloride salt (5b) showed IC(50) value of 0.88 microM.

Novel antiviral agent tetraglycylated nordihydroguaiaretic acid hydrochloride as a host-dependent viral inhibitor.

A water soluble derivative of nordihydroguaiaretic acid (NDGA), G(4)N (2), synthesized by reaction of NDGA (1) with N,N-dimethylglycine in the presence of dicyclohexylcarbodiimide and dimethylaminopyridine and then with HCl(g) (Scheme 1), competes effectively with the DNA binding domain of recombinant Sp1 protein for binding to the human immunodeficiency virus (HIV) LTR as demonstrated by an electrophoretic mobility-shift assay (EMSA). By blocking Sp1 binding to the HIV LTR, G(4)N suppresses Sp1-regulated HIV Tat transactivation and replication in cultured cells with an IC(50) of 12 microM similar to that of 3'-O-methyl-NDGA as we have previously reported. In addition simian immunodeficiency virus (SIV) replication was completely inhibited by G(4)N at 5.0 microM. G(4)N showed no toxic effect to 174 x CEM cells and H9 cells at 100 microM.

Structure-activity relationship studies of nordihydroguaiaretic acid inhibitors toward soybean, 12-human, and 15-human lipoxygenase.

Lipoxygenase (LO) is a biological target for many diseases such as asthma, atherosclerosis, and cancer. Our labs have synthesized and investigated nordihydroguaiaretic acid (NDGA) derivatives and have established that the reductive inhibition of soybean and 15-human LO can be affected by the strength of the electron-withdrawing substituents on the phenyl rings of NDGA. In addition, we have determined that hydrophobic NDGA derivatives activate 15-HLO, suggesting a hydrophobic allosteric site.

Synthesis and anticancer activity of nordihydroguaiaretic acid (NDGA) and analogues.

Nordihydroguaiaretic acid (NDGA) 1 is a constituent of the creosote bush Larrea divaricata and is well known to be a selective inhibitor of lipoxygenases. NDGA can also inhibit the platelet derived growth factor receptor and the protein kinase C intracellular signalling family, which both play an important role in proliferation and survival of cancers. Moreover, NDGA induces apoptosis in tumour xenografts. Although it is likely to have several targets of action, NDGA is well tolerated in animals. These encouraging results have prompted interest in the compound for clinical study. However, high concentrations of NDGA are required for efficacy and more potent analogues are required. We have synthesized five analogues of NDGA with different lengths of carbon bridge between the two catechol moieties in order to establish the spacing required for optimum anticancer effect and to compare their activities with NDGA. In order to ascertain if the catechol moieties are essential for anticancer activity, we prepared five analogues of NDGA containing only one hydroxyl group on each aromatic ring. NDGA 1, its racemic form 2, the catechol derivatives 5, 6 with five or six carbon atom bridges and the phenol analogues 8-11 with bridges of three to six carbon atoms all showed similar activity, with IC50 values of approximately 3-5 microM against the H-69 small cell lung cancer cell line. Analogues with shorter (3) or longer bridges (7, 12) were much less active. The most potent analogue was the biscatechol with a four-carbon bridge 4 which was > 10 times more active than NDGA and therefore represents a new lead compound in this area. Surprisingly, the tetramethyl ether 14 of this compound was slightly more active than NDGA, but the trihydroxy analogue 13 was less active than NDGA. The conformationally restricted analogue 15 was also less active than NDGA. In summary, simplification of the structure of NDGA by removal of the methyl groups has produced a new lead compound 4, which is >10 times more potent than NDGA as a proliferative inhibitor of H-69 small cell lung cancer cells.

Antiviral activities of methylated nordihydroguaiaretic acids. 1. Synthesis, structure identification, and inhibition of tat-regulated HIV transactivation.

Nordihydroguaiaretic acid (NDGA, meso-1) possesses four phenolic hydroxyl groups. Treatment of NDGA with 0.50-4.1 equiv of dimethyl sulfate and 3.0-6.0 equiv of potassium carbonate in acetone at 56 degrees C gave nine methylated products. Eight of those mono-, di-, tri-, and tetra-O-methylated NDGAs were isolated in pure form, and their structures were identified unambiguously by spectroscopic methods. A preparative amount of tetramethyl NDGA M4N (10) was obtained in 99% yield from NDGA by use of 4.1 equiv of dimethyl sulfate for the methylation. Among the eight different methylated NDGAs (2-6 and 8-10), tetra-O-methyl-NDGA (10) showed the strongest anti-HIV activity (IC50 11 microM). Chemically synthesized 3'-O-methyl-NDGA ((+/-)-2) showed identical anti-HIV activity (IC50 25 microM) to the lignan isolated from Creosote Bush. Lignans with methylated catecholic hydroxyl groups can be produced in large quantities with low cost. At drug concentrations below 30 microM tetramethyl NDGA (10) was a stronger anti-HIV agent than mono- and dimethylated NDGAs.

[Total synthesis of nordihydroguaiaretic acid].

beta-Keto ester(5) was obtained from vanilin through etherification, oxidation and condensation with acetoacetic ester, (5) on oxidative coupling reaction by NaOEt/I2 produced dimer (6) in high yield. Acid catalyzed cyclodehydration of (6) gave the furan derivative(7), and by a series of selective hydrogenation nordihydroguaiaretic acid, furoguaiacin dimethyl ether and dihydroguaiaretic acid dimethyl ether were synthesized.