Dimers of Melampomagnolide B Exhibit Potent Anticancer Activity against Hematological and Solid Tumor Cells

Novel carbamate (<b>7a</b>–<b>7h</b>) and carbonate (<b>7i</b>, <b>7j</b>, and <b>8</b>) dimers of melampomagnolide B have been synthesized by reaction of the melampomagnolide-B-triazole carbamate synthon <b>6</b> with various terminal diamino- and dihydroxyalkanes. Dimeric carbamate products <b>7b</b>,<b> 7c</b>, and <b>7f</b> exhibited potent growth inhibition (GI₅₀ = 0.16–0.99 μM) against the majority of cell lines in the NCI panel of 60 human hematological and solid tumor cell lines. Compound <b>7f</b> and <b>8</b> exhibited anticancer activity that was 300-fold and 1 × 10⁶-fold more cytotoxic than DMAPT, respectively, at a concentration of 10 μM against rat 9L-SF gliosarcoma cells. Compounds <b>7a</b>–<b>7j</b> and <b>8</b> were also screened against M9-ENL1 and acute myelogenous leukemia (AML) primary cell lines and exhibited 2- to 10-fold more potent antileukemic activity against M9-ENL1 cells (EC₅₀ = 0.57–2.90 μM) when compared to parthenolide (EC₅₀ = 6.0) and showed potent antileukemic activity against five primary AML cell lines (EC₅₀ = 0.76–7.3 μM)

A Small-Molecule Inhibitor of Human DNA Polymerase η Potentiates the Effects of Cisplatin in Tumor Cells

Translesion DNA synthesis (TLS) performed by human DNA polymerase eta (hpol η) allows tolerance of damage from <i>cis</i>-diammine­dichloroplatinum­(II) (CDDP or cisplatin). We have developed hpol η inhibitors derived from N-aryl-substituted indole barbituric acid (IBA), indole thiobarbituric acid (ITBA), and indole quinuclidine scaffolds and identified 5-((5-chloro-1-(naphthalen-2-ylmethyl)-1<i>H</i>-indol-3-yl)­methylene)-2-thioxodihydropyrimidine-4,6­(1<i>H</i>,5<i>H</i>)-dione (PNR-7-02), an ITBA derivative that inhibited hpol η activity with an IC₅₀ value of 8 μM and exhibited 5–10-fold specificity for hpol η over replicative pols. We conclude from kinetic analyses, chemical footprinting assays, and molecular docking that PNR-7-02 binds to a site on the little finger domain and interferes with the proper orientation of template DNA to inhibit hpol η. A synergistic increase in CDDP toxicity was observed in hpol η-proficient cells co-treated with PNR-7-02 (combination index values = 0.4–0.6). Increased γH2AX formation accompanied treatment of hpol η-proficient cells with CDDP and PNR-7-02. Importantly, PNR-7-02 did not impact the effect of CDDP on cell viability or γH2AX in hpol η-deficient cells. In summary, we observed hpol η-dependent effects on DNA damage/replication stress and sensitivity to CDDP in cells treated with PNR-7-02. The ability to employ a small-molecule inhibitor of hpol η to improve the cytotoxic effect of CDDP may aid in the development of more effective chemotherapeutic strategies

DataSheet1_Parthenolide induces rapid thiol oxidation that leads to ferroptosis in hepatocellular carcinoma cells.PDF

Hepatocellular carcinoma (HCC) is both a devastating and common disease. Every year in the United States, about 24,500 men and 10,000 women are diagnosed with HCC, and more than half of those diagnosed patients die from this disease. Thus far, conventional therapeutics have not been successful for patients with HCC due to various underlying comorbidities. Poor survival rate and high incidence of recurrence after therapy indicate that the differences between the redox environments of normal surrounding liver and HCC are valuable targets to improve treatment efficacy. Parthenolide (PTL) is a naturally found therapeutic with anti-cancer and anti-inflammatory properties. PTL can alter HCC’s antioxidant environment through thiol modifications leaving tumor cells sensitive to elevated reactive oxygen species (ROS). Investigating the link between altered thiol mechanism and increased sensitivity to iron-mediated lipid peroxidation will allow for improved treatment of HCC. HepG2 (human) and McARH7777 (rat) HCC cells treated with PTL with increasing concentrations decrease cell viability and clonogenic efficiency in vitro. PTL increases glutathione (GSH) oxidation rescued by the addition of a GSH precursor, N-acetylcysteine (NAC). In addition, this elevation in thiol oxidation results in an overall increase in mitochondrial dysfunction. To elucidate if cell death is through lipid peroxidation, using a lipid peroxidation sensor indicated PTL increases lipid oxidation levels after 6 h. Additionally, western blotting reveals glutathione peroxidase 4 (GPx4) protein levels decrease after treatment with PTL suggesting cells are incapable of preventing lipid peroxidation after exposure to PTL. An elevation in lipid peroxidation will lead to a form of cell death known as ferroptosis. To further establish ferroptosis as a critical mechanism of death for HCC in vitro, the addition of ferrostatin-1 combined with PTL demonstrates a partial recovery in a colony survival assay. This study reveals that PTL can induce tumor cell death through elevations in intracellular oxidation, leaving cells sensitive to ferroptosis.</p