Xiajuan Huan

Design, Synthesis, and Biological Evaluation of a Series of Benzo(de)(1,7)naphthyridin-7(8H)‑ones Bearing a Functionalized Longer Chain Appendage as Novel PARP1 Inhibitors

A series of benzo[de][1,7]naphthyridin-7(8H)-ones possessing a functionalized long-chain appendage have been designed and evaluated as novel PARP1 inhibitors. The initial effort led to the first-generation PARP1 inhibitor 26 bearing a terminal phthalazin-1(2H)-one framework and showing remarkably high PARP1 inhibitory activity (0.31 nM) but only moderate potency in the cell. Further effort generated the second-generation lead 41, showing high potency against both the PARP1 enzyme and BRCA-deficient cells, especially for the BRCA1-deficient MDA-MB-436 cells (CC50 < 0.26 nM). Mechanistic studies revealed that the new PARP1 inhibitors significantly inhibited H2O2-triggered PARylation in SKOV3 cells, induced cellular accumulation of DNA double-strand breaks, and impaired cell-cycle progression in BRCA2-deficient cells. Significant potentiation on the cytotoxicity of Temozolomide was also observed. The unique structural character and exceptionally high potency of 41 made it stand out as a promising drug candidate worthy for further evaluation.

MCL-1 Degradation Mediated by JNK Activation via MEKK1/TAK1-MKK4 Contributes to Anticancer Activity of New Tubulin Inhibitor MT189

Colchicine site–targeted tubulin inhibitors are a promising type of anticancer drugs. MT189 is a new derivative of MT119, a previously reported colchicine site–binding antitubulin agent. In this study, MT189 was demonstrated to retain the property of MT119 in disrupting microtubulin via binding to the colchicine site, causing mitotic arrest and inducing apoptosis, and to display 8.7-fold enhanced proliferative inhibition in a panel of cancer cells. MT189 was shown to elicit in vivo anticancer effects on MDA-MB-231 xenografts in nude mice, and the tumor growth was suppressed by 35.9% over 14 days. MT189 led to degradation of MCL-1, a member of the antiapoptotic BCL-2 protein family. Its overexpression reduced but its silenced expression increased the apoptotic induction followed by the treatment with MT189. Moreover, the treatment with MT189 caused activation of the MEKK1/TAK1–MKK4–JNK signaling pathway. The activated JNK resulted in phosphorylation of MCL-1, which facilitated its ubiquitination-mediated degradation. Our results show that MT189 inhibits microtubulin polymerization by binding to the colchicine site. Relief of apoptotic suppression by MCL-1 degradation together with mitotic arrest contributes to the anticancer activity of MT189. Mol Cancer Ther; 13(6); 1480–91. ©2014 AACR.

Synthesis of isoquinolinone-based tricycles as novel poly(ADP-ribose) polymerase-1 (PARP-1) inhibitors.

The isoquinolinone-based tricyclic compounds were designed and synthesized. Preliminary biological study of these compounds provided potent compounds 17a, 33b, 33c, 33d, and 33g with low nanomolar IC50s against PARP-1 enzyme.

Triptolide Induces Cell Killing in Multidrug-Resistant Tumor Cells via CDK7/RPB1 Rather than XPB or p44

Multidrug resistance (MDR) is a major cause of tumor treatment failure; therefore, drugs that can avoid this outcome are urgently needed. We studied triptolide, which directly kills MDR tumor cells with a high potency and a broad spectrum of cell death. Triptolide did not inhibit P-glycoprotein (P-gp) drug efflux and reduced P-gp and MDR1 mRNA resulting from transcription inhibition. Transcription factors including c-MYC, SOX-2, OCT-4, and NANOG were not correlated with triptolide-induced cell killing, but RPB1, the largest subunit of RNA polymerase II, was critical in mediating triptolides inhibition of MDR cells. Triptolide elicited antitumor and anti-MDR activity through a universal mechanism: by activating CDK7 by phosphorylating Thr170 in both parental and MDR cell lines and in SK-OV-3 cells. The CDK7-selective inhibitor BS-181 partially rescued cell killing induced by 72-hour treatment of triptolide, which may be due to partial rescue of RPB1 degradation. We suggest that a precise phosphorylation site on RPB1 (Ser1878) was phosphorylated by CDK7 in response to triptolide. In addition, XPB and p44, two transcription factor TFIIH subunits, did not contribute to triptolide-driven RPB1 degradation and cell killing, although XPB was reported to covalently bind to triptolide. Several clinical trials are underway to test triptolide and its analogues for treating cancer and other diseases, so our data may help expand potential clinical uses of triptolide, as well as offer a compound that overcomes tumor MDR. Future investigations into the primary molecular target(s) of triptolide responsible for RPB1 degradation may suggest novel anti-MDR target(s) for therapeutic development. Mol Cancer Ther; 15(7); 1495–503. ©2016 AACR.

Novel PARP1/2 inhibitor mefuparib hydrochloride elicits potent in vitro and in vivo anticancer activity, characteristic of high tissue distribution.

The approval of poly(ADP-ribose) polymerase (PARP) inhibitor AZD2281 in 2014 marked the successful establishment of the therapeutic strategy targeting homologous recombination repair defects of cancers in the clinic. However, AZD2281 has poor water solubility, low tissue distribution and relatively weak in vivo anticancer activity, which appears to become limiting factors for its clinical use. In this study, we found that mefuparib hydrochloride (MPH) was a potent PARP inhibitor, possessing prominent in vitro and in vivo anticancer activity. Notably, MPH displayed high water solubility (> 35 mg/ml) and potent PARP1/2 inhibition in a substrate-competitive manner. It reduced poly(ADP-ribose) (PAR) formation, enhanced γH2AX levels, induced G2/M arrest and subsequent apoptosis in homologous recombination repair (HR)-deficient cells. Proof-of-concept studies confirmed the MPH-caused synthetic lethality. MPH showed potent in vitro and in vivo proliferation and growth inhibition against HR-deficient cancer cells and synergistic sensitization of HR-proficient xenografts to the anticancer drug temozolomide. A good relationship between the anticancer activity and the PARP inhibition of MPH suggested that PAR formation and γH2AX accumulation could serve as its pharmacodynamic biomarkers. Its high bioavailability (40%~100%) and high tissue distribution in both monkeys and rats were its most important pharmacokinetic features. Its average concentrations were 33-fold higher in the tissues than in the plasma in rats. Our work supports the further clinical development of MPH as a novel PARP1/2 inhibitor for cancer therapy.

Differential sensitivity of RIP3-proficient and deficient murine fibroblasts to camptothecin anticancer drugs

Differential sensitivity of RIP3-proficient and deficient murine fibroblasts to camptothecin anticancer drugs

Discovery of potent 2,4-difluoro-linker poly(ADP-ribose) polymerase 1 inhibitors with enhanced water solubility and in vivo anticancer efficacy

Poly (ADP-ribose) polymerase 1 (PARP1) is overexpressed in a variety of cancers, especially in breast and ovarian cancers; tumor cells that are deficient in breast cancer gene 1/2 (BRCA1/2) are highly sensitive to PARP1 inhibition. In this study, we identified a series of 2,4-difluorophenyl-linker analogs (15–55) derived from olaparib as novel PARP1 inhibitors. Four potent analogs 17, 43, 47, and 50 (IC50=2.2–4.4 nmol/L) effectively inhibited the proliferation of Chinese hamster lung fibroblast V-C8 cells (IC50=3.2–37.6 nmol/L) in vitro, and showed specificity toward BRCA-deficient cells (SI=40–510). The corresponding hydrochloride salts 56 and 57 (based on 43 and 47) were highly water soluble in pH=1.0 buffered salt solutions (1628.2 μg/mL, 2652.5 μg/mL). In a BRCA1-mutated xenograft model, oral administration of compound 56 (30 mg·kg-1·d-1, for 21 d) exhibited more prominent tumor growth inhibition (96.6%) compared with the same dose of olaparib (56.3%); in a BRCA2-mutated xenograft model, oral administration of analog 43 (10 mg·kg-1·d-1, for 28 d) significantly inhibited tumor growth (69.0%) and had no negative effects on the body weights. Additionally, compound 56 exhibited good oral bioavailability (F=32.2%), similar to that of olaparib (F=45.4%). Furthermore, the free base 43 of the hydrochloride salt 56 exhibited minimal hERG inhibition activity (IC50=6.64 μmol/L). Collectively, these data demonstrate that compound 56 may be an excellent drug candidate for the treatment of cancer, particularly BRCA-deficient tumors.