Guisen Zhao

Thiadiazole—a Promising Structure in Medicinal Chemistry

Many compounds containing a five‐membered heterocyclic ring display exceptional chemical properties and versatile biological activities. In this Minireview, thiadiazoles are summarized according to their therapeutic potential, highlighting the versatility of this scaffold in medicinal chemistry. The unique properties of thiadiazoles are also discussed in relation to their potential effect on activity. Thiadiazole is a bioisostere of pyrimidine and oxadiazole, and given the prevalence of pyrimidine in nature it is unsurprising that thiadiazoles exhibit significant therapeutic potential. The sulfur atom of the thiadiazole imparts improved liposolubility, and the mesoionic nature of thiadiazoles makes these compounds better able to cross cellular membranes. By summarizing the thiadiazole‐containing compounds reported in recent decades, we aim to give a brief introduction to their synthesis and diverse biological activities, such as anti‐inflammatory, anticancer, antibacterial, antifungal, antiviral, antiparasitic, anticonvulsant, anticoagulant, antidiabetic, and to show the significant utility of the thiadiazole scaffolds in medicinal chemistry.

Ethacrynic Acid Butyl-Ester Induces Apoptosis in Leukemia Cells through a Hydrogen Peroxide–Mediated Pathway Independent of Glutathione S-Transferase P1-1 Inhibition

Ethacrynic acid (EA), a glutathione S-transferase inhibitor and diuretic agent, inhibits cell growth and induces apoptosis in cancer cells. To improve the activities, the structure of EA has been modified, and it has been shown that EA esters had an increased cell growth inhibitory ability compared with nonesterified analogue. EA butyl-ester (EABE) was synthesized, and its apoptosis induction ability was studied. The efficacy of EABE was compared with that of EA, and the mechanisms of action were studied in HL-60 leukemia cells. EABE exhibited greater cell growth inhibitory and apoptosis induction abilities than did EA. EABE-induced apoptosis in HL-60 cells correlated with increased levels of reactive oxygen species, the death receptor 5 (DR5), and caspase activation and decreased levels of the mitochondrial membrane potential. Pretreatment with antioxidants, either N-acetylcysteine or catalase, completely blocked EABE-induced apoptosis, H2O2 accumulation, and up-regulation of DR5 levels. RG19, a subclone of Raji cells stably transfected with a GSTpi expression vector, and K562 cells with high endogenous GSTP1-1 activity were less sensitive to EABE-induced apoptosis. EABE was more rapidly taken up than EA by HL-60 cells as determined by high-performance liquid chromatography (HPLC) measurements of intracellular concentrations. These results suggest that (a) H2O2 production is a mediator of EABE and EA-induced apoptosis; (b) GSTP1-1 plays a negative role in EABE and EA-induced apoptosis; and (c) the activity of EABE is greater than EA due to its more rapid entry into cells.

Novel oxadiazole analogues derived from ethacrynic acid: design, synthesis, and structure-activity relationships in inhibiting the activity of glutathione S-transferase P1-1 and cancer cell proliferation.

Ethacrynic acid (EA) is a glutathione S-transferase P1-1 (GST P1-1) inhibitor with weak antiproliferative ability in tumor cells. By use of the principle of bioisosterism, a series of novel EA oxadiazole analogues were designed and synthesized. The structure-activity relationships of inhibiting GST P1-1 activity and cell proliferation of those EA analogues were investigated in human leukemia HL-60 cells. Our data revealed that those EA oxadiazole analogues had improved antiproliferative activity and most of them had similar or better inhibitory effects on GST P1-1 activity than EA. Compound 6u was one of the potent antiproliferative agents without inhibition of GST P1-1 activity. Compounds 6r and 6s were two potent cell growth inhibitors in several solid tumor cell lines with the concentrations inhibiting half of cell growth of less than 5 microM. Our data suggest that these EA oxadiazole analogues are promising antitumor agents that may act through GST P1-1 inhibition-dependent and/or -independent pathways.

Ethacrynic acid and a derivative enhance apoptosis in arsenic trioxide-treated myeloid leukemia and lymphoma cells: the role of glutathione S-transferase p1-1.

Purpose: Arsenic trioxide (ATO) as a single agent is used for treatment of acute promyelocytic leukemia (APL) with minimal toxicity, but therapeutic effect of ATO in other types of malignancies has not been achieved. We tested whether a combination with ethacrynic acid (EA), a glutathione S-transferase P1-1 (GSTP1-1) inhibitor, and a reactive oxygen species (ROS) inducer will extend the therapeutic effect of ATO beyond APL. Experimental Design: The combined apoptotic effects of ATO plus ethacrynic acid were tested in non-APL leukemia and lymphoma cell lines. The role of ROS, GSTP1-1, glutathione (GSH), and Mcl-1 in apoptosis was determined. The selective response to this combination of cells with and without GSTP1-1 expression was compared. Results: ATO/EA combination synergistically induced apoptosis in myeloid leukemia and lymphoma cells. This treatment produced high ROS levels, activated c-jun-NH2-kinase (JNK), and reduced Mcl-1 protein. This led to the decrease of mitochondrial transmembrane potential, release of cytochrome c, and subsequently, to activation of caspase-3 and -9. Induction of apoptosis in leukemia and lymphoma cells expressing GSTP1-1 required high ethacrynic acid concentrations to be combined with ATO. Silencing of GSTP1 in leukemia cells sensitized them to ATO/EA–induced apoptosis. In a subgroup of B-cell lymphoma, which does not express GSTP1-1, lower concentrations of ethacrynic acid and its more potent derivative, ethacrynic acid butyl-ester (EABE), decreased intracellular GSH levels and synergistically induced apoptosis when combined with ATO. Conclusion: B-cell lymphoma cells lacking GSTP1-1 are more sensitive than myeloid leukemia cells to ATO/EA–induced apoptosis. Clin Cancer Res; 18(24); 6690–701. ©2012 AACR.

Developments in Selective Small Molecule ATP-Targeting the Serine/Threonine Kinase Akt/PKB

The serine/threonine kinase Akt, also known as protein kinase B (PKB), plays a key role in cell survival and proliferation through a number of downstream effectors. Recent studies indicate that unregulated activation of the Phosphatidylinositol 3-kinase (PI3K)/Akt pathway is a prominent feature of many human cancers and Akt is overexpressed or activated in all major cancers. For these reasons, Akt is considered as an attractive target for cancer therapy. In the past few years, several series of compounds with diverse structural features have been reported as Akt inhibitors, such as, ATP-competitive inhibitors, Phosphatidylinositol (PI) analogs, and allosteric inhibitors. Although most of the inhibitors exhibited potent inhibitory activities at nanomolar concentrations against Akt, some of them have shown unfavorable selectivity against other protein kinases especially PKA and PKC. This review will focus on the recent advances in the development and biological evaluation of selective ATP-competitive inhibitors for Akt. We will summarize the novel approaches toward the developments of selective ATP-competitive inhibitors, expecting to give information to design new ATP-competitive inhibitors with high selectivity, bioavailability, and potency.

New developments in diketo-containing inhibitors of HIV-1 integrase.

HIV-1 integrase is one of the three enzymes, which are critical for viral replication. It catalyzes the integration of the HIV genome into the cellular chromosome. Since there is no known human homolog to integrase, its inhibition is one of the most promising novel drug targets for anti-retroviral therapy with potential advantage over existing therapies. To date, numerous compounds with diverse structural features have been reported as integrase inhibitors, among which the diketo-containing inhibitors of HIV-1 integrase represent a major lead for anti-HIV drug development. The discovery of diketo acids plays an important role in validating integrase as a legitimate target for treatment of AIDS. In this review, we summarize several drug candidates in clinical trials and new diketo-containing inhibitors of HIV-1 integrase discovered recently.

Amide-containing diketoacids as HIV-1 integrase inhibitors: Synthesis, structure–activity relationship analysis, and biological activity

HIV-1 integrase, which catalyzes the integration of the viral genome into the cellular chromosome, is an essential enzyme for retroviral replication, and represents an attractive and validated target in the development of therapeutics against AIDS. In this paper, 17 amide-containing novel diketoacids were designed and synthesized, and their ability to inhibit HIV-1 integrase was tested. The structure-activity relationships were also analyzed.

The synthesis of ethacrynic acid thiazole derivatives as glutathione S-transferase pi inhibitors.

Glutathione S-transferase pi (GSTpi) is a phase II enzyme which protects cells from death and detoxifies chemotherapeutic agents in cancer cells. Ethacrynic acid (EA) is a weak GSTpi inhibitor. Structure modifications were done to improve the ability of EA to inhibit GSTpi activity. Eighteen EA thiazole derivatives were designed and synthesized. Compounds 9a, 9b and 9c with a replacement of carboxyl group of EA by a heterocyclic thiazole exhibited improvement over EA to inhibit GSTpi activity.

Developments in Nonsteroidal Antiandrogens Targeting the Androgen Receptor

The burden of prostate cancer (PCa) in the world is significant; PCa remains the most frequently diagnosed noncutaneous malignancy and remains the second leading cause of cancer-related deaths among men in Western countries. In 2009, approximately 192 280 men were diagnosed with PCa, and 27 360 men were estimated to die from the disease. The risk factor in PCa includes, but is not limited to, race, geography, age and gene rearrangements. Though patients with PCa initially respond to androgen-deprivation therapy, they inevitably relapse to castration-resistant prostate cancer (CRPC) within 18–24 months. CRPC is incurable, and it is acknowledged that androgen and androgen signaling still play the most influential role in the development of PCa. Thus, the treatment of PCa by inhibiting the function of the androgen receptor (AR) remains a standard strategy. Although drugs such as R-bicalutamide and flutamide have been used in the past to inhibit the growth of PCa tumors, eventually the cancer becomes refractory to available AR antagonists. Therefore, new rational approaches and new drugs for the treatment of PCa are needed. This review will focus primarily on the new nonsteroidal compounds that have evolved from classical drugs. These new drugs include bicalutamide derivatives, isoxazolones, pyrrole carboxamides, pyridines and N-arylpiperazine derivatives, imide-based analogues, hydantoin derivatives, carborane-containing derivatives, and organometallic-containing derivatives. We will provide research-related reference materials for the design of new antiprostate cancer drugs.

Caffeoyl naphthalenesulfonamide derivatives as HIV integrase inhibitors

HIV-1 integrase (IN) is an essential enzyme for retroviral replication and a rational target for the design of anti-AIDS drugs. In the present study, we have designed, synthesized and tested a series of caffeoyl naphthalenesulfonamide derivatives as HIV integrase inhibitors. Among these compounds, we found that HIV integrase inhibitory activities of compounds III-3 and III-4 were more potent than L-chicoric acid (IC(50)=11.8 microg/mL) and others were comparable to L-chicoric acid. Furthermore, the structure-activity relationships of these compounds were studied. The information gathered from this paper will be useful in the development and design of HIV-1 integrase inhibitors in the future.