Synthesis and evaluation of sulfonylethyl-containing phosphotriesters of 3'-azido-3'-deoxythymidine as anticancer prodrugs.

A series of bis(sulfonylethyl) and mono(sulfonylethyl) phenyl phosphotriesters of zidovudine (3'-azido-3'-deoxythymidine, AZT) were synthesized as potential anticancer prodrugs that liberate AZT monophosphate via nonenzymatic ß-elimination mechanism. Stability studies demonstrated that all the synthesized prodrugs spontaneously liberate AZT monophosphate with half-lives in the range of 0.07-278.8h under model physiological conditions in 0.1M phosphate buffer at pH 7.4 and 37 °C. Analogous to aldophosphamide, the elimination rates were accelerated in the presence of reconstituted human plasma under the same conditions. Among the compounds, 3, 4, 8, and 10 were comparable or superior to AZT against five established human cancerous cell lines in vitro. Moreover, the selected compounds were equally sensitive to both the wild-type osteosarcoma 143 B and the thymidine kinase-deficient 143 B/TK(-) cell lines. The findings are consistent with that these compounds deliver AZT monophosphate intracellularly.

Synthesis and Anticancer Evaluation of Sulfur Containing 9-anilinoacridines.

BACKGROUND: DNA topoisomerases are a class of enzymes that play a critical role in fundamental biological processes of replication, transcription, recombination, repair and chromatin remodeling. Amsacrine (m-AMSA), the best-known compound of 9-anilinoacridines series, was one of the first DNA-intercalating agents to be considered a Topoisomerase II inhibitor. OBJECTIVES: A series of sulfur-containing 9-anilinoacridines related to amsacrine were synthesized and evaluated for their anticancer activity. METHODS: Cell viability was assessed by the MTT assay. The topoisomerase II inhibitory assay was performed using the Human topoisomerase II Assay kit, and flow cytometry was used to evaluate the effects on the cell cycle of K562 cells. Molecular docking was performed using the Schrödinger Maestro program. RESULTS: Compound 36 was found to be the most cytotoxic of the sulfide series against SW620, K562, and MCF-7. The limited SAR suggested the importance of the methansulfonamidoacetamide side chain functionality, the lipophilicity, and the relative metabolic stability of 36 in contributing to the cytotoxicity. Topoisomerase II α inhibitory activity appeared to be involved in the cytotoxicity of 36 through the inhibition of decatenation of kinetoplast DNA (kDNA) in a concentration- dependent manner. Cell cycle analysis further showed Topo II inhibition through the accumulation of K562 cells in the G2/M phase of the cell cycle. The docking of 36 into the Topo II α-DNA complex suggested that it may be an allosteric inhibitor of Topo II α. CONCLUSION: Compound 36 exhibits anticancer activity by inhibiting topoisomerase II, and it could further be evaluated in in vivo models.

CK0403, a 9­aminoacridine, is a potent anti­cancer agent in human breast cancer cells.

3­({4­[4­(Acridin­9­ylamino)phenylthio]phenyl}(3­hydroxypropyl)amino)propan­1­ol (CK0403) is a sulfur­containing 9­anilinoacridine analogue of amsacrine and was found to be more potent than its analogue 2-({4-[4-(acridin-9-ylamino)phenylthio]phenyl}(2­hydroxyethyl)amino)ethan­1­ol (CK0402) and amsacrine in the inhibition of the topoisomerase II­catalyzed decatenation reaction. A previous study by our group reported that CK0402 was effective against numerous breast cancer cell lines, and the combination of CK0402 with herceptin enhanced its activity in HER2(+) SKBR­3 cells. In order to identify novel chemotherapeutic agents with enhanced potency, the present study explored the potential of CK0403 in the treatment of breast cancer. First, the growth inhibitory activity of CK0403 in the breast cancer cell lines MCF­7, MDA­MB­231, BT474 and SKBR­3, as well as in the non­cancerous MCF­10A cell line, was examined using a sulforhodamine B assay. The results showed that CK0403 exerted more potent growth inhibitory activity than CK0402 in all of the breast cancer cell lines except MCF­7. SKBR­3 and MDA­MB­231 were the most sensitive cell lines tested, and the combination of CK0403 with herceptin in HER2(+) SKBR­3 cells enhanced the growth inhibitory activity of CK0403. Analysis of cell cycle alterations induced by CK0403 in SKBR­3 cells revealed that, similarly to CK0402, CK0403 induced G2/M­phase arrest with a decreased S- and G0/G1-phase ratio. In addition, it was shown that CK0403 induced apoptosis more effectively than CK0402 in SKBR­3 cells. Further analysis of autophagy protein 5 (Atg5) indicated that CK0403 induced more cleaved Atg5 than CK0402 and other chemotherapeutic agents tested. Of note, although still relatively potent, CK0403 exhibited reduced growth inhibitory activity under hypoxic conditions, which can induce autophagy. Collectively, the present results supported that CK0403 is highly potent and more effective than CK0402 against estrogen receptor-negative and HER2­overexpressing breast cancer cell lines, suggesting its future application for chemotherapy in breast cancer.

1,2-benzisoxazole phosphorodiamidates as novel anticancer prodrugs requiring bioreductive activation.

Several 1,2-benzisoxazole phosphorodiamidates have been designed as prodrugs of phosphoramide mustard requiring bioreductive activation. Enzymatic reduction of 1,2-benziosoxazole moiety is expected to result in the formation of imine intermediate due to the cleavage of the N-O bond. The imine should then be spontaneously hydrolyzed to a ketone metabolite, thereby facilitating base-catalyzed beta-elimination of cytotoxic phosphoramide mustard. As expected, the proposed prodrugs 4, 9, and 12 were at least 3-5-fold more potent cytotoxins than control compounds 5 and 15, which lack in the phosphoramide mustard group. Upon incubation with phenobarb-induced rat liver S-9 fraction, compounds 4, 9, and 12 underwent extensive NADPH-dependent metabolism with concomitant generation of alkylating activity under both hypoxic and oxic conditions. Corresponding ketone metabolites were detected for 9 and 15. NADPH-dependent bioreduction of 15 to its ketone metabolite 16 was located in the microsomal fraction and inhibited by SKF-525A and pCMBA. Compared with phenobarb-induced rat liver microsomal fraction, incubation of 15 with rat or human p450 reductase microsomes showed moderate generation of 16. Microsomal cytochrome p450 and/or p450 reductase appear to be involved in the reductive metabolism of 1,2-benzisoxazole moiety under hypoxic as well as oxic conditions.

Sulfonyl-containing aldophosphamide analogues as novel anticancer prodrugs targeted against cyclophosphamide-resistant tumor cell lines.

A series of sulfonyl-group containing analogues of aldophosphamide (Aldo) were synthesized as potential anticancer prodrugs that liberate the cytotoxic phosphoramide mustards (PM, IPM, and tetrakis-PM) via beta-elimination, a nonenzymatic activation mechanism. Kinetic studies demonstrated that all these compounds spontaneously liberate phosphoramide mustards with half-lives in the range of 0.08-15.2 h under model physiological conditions in 0.08 M phosphate buffer at pH 7.4 and 37 degrees C. Analogous to Aldo, the rates of beta-elimination in all compounds was enhanced in reconstituted human plasma under same conditions. The compounds were more potent than the corresponding phosphoramide mustards against V-79 Chinese hamster lung fibroblasts in vitro (IC(50) = 1.8-69.1 microM). Several compounds showed excellent in vivo antitumor activity in CD2F1 mice against both P388/0 (Wild) and P388/CPA (CP-resistant) tumor cell lines.

Potentiation of the growth inhibition activity of 2-({4-[4-(acridin-9-ylamino)phenylthio]phenyl}(2-hydroxyethyl)amino)ethan-1-ol (CK0402) by Herceptin in SKBR-3 human breast cancer cells.

The 9-aminoacridine derivative, 2-({4-[4-(acridin-9-ylamino)phenylthio]phenyl}(2-hydroxyethyl) amino)ethan-1-ol (CK0402) was selected as a potential anticancer agent among a series of sulfur-containing 9-aminoacridine analogues. CK0402 is a topoisomerase II inhibitor and has been shown to exert impressive anticancer activities in both in vitro and in vivo assays. In the present study, we tested the effects of CK0402 in a panel of established human breast cancer cells with varying ER and HER2/neu status. The ER(-) and HER2-overexpressing SKBR-3 cells were the most sensitive cells tested in growth inhibition to CK0402 treatment, and the growth inhibition was in a time-and concentration-dependent manner. In addition, CK0402 also induced stronger G(2)/M arrest, apoptosis and autophagy in SKBR-3 cells than in ER(+) and HER2(-) MCF-7 cells. To the best of our knowledge, CK0402 is the first 9-aminoacridine analogue to induce autophagy. These findings suggest that CK0402 may be effective against the more aggressive and malignant ER(-) and HER2-overexpressing breast cancer. Towards this end, we further demonstrated that the combination of CK0402 and Herceptin exhibited synergistic/additive cytotoxic effects in SKBR-3 cells using the median-effect/combination-index isobologram methodology (CI value). Our results indicate that the combination of CK0402 and Herceptin may be a potential therapeutic option against the more aggressive ER(-) and HER2-overexpressing breast cancer.

Caspase-dependent cell death mediates potent cytotoxicity of sulfide derivatives of 9-anilinoacridine.

9-anilinoacridine contains a tricyclic and planar aromatic structure that enables DNA intercalation and inhibition of topoisomerase II. Two recently developed sulfide derivatives of 9-anilinoacridines, 2-({4-[4-(acridin-9-ylamino)phenylthio]phenyl}(2-hydroxyethyl)amino)ethan-1-ol (CK0402) and 3-({4-[4-(acridin-9-ylamino)phenylthio]phenyl}(3-hydroxypropyl)amino)propan-1-ol (CK0403), displayed potent cytotoxic activity in multiple cancer cell lines. In-vitro enzymatic assay demonstrated that CK0402 and CK0403 directly inhibit decatenation reaction of topoisomerase IIalpha. Cells exposed to CK0403 showed DNA fragmentation, and activation of caspase-3 and caspase-2, indicating that it triggers caspase-dependent apoptosis. This was further supported by the fact that cytotoxicity of these drugs is attenuated by pharmacological inhibition of caspases with z-VAD-FMK. Studies with wild-type and p53 primary mouse embryonic fibroblasts demonstrated that p53 does not play a significant role in cell death process initiated by this kind of drug. In addition, pharmacological inhibition of poly(ADP-ribose) polymerase-1activity moderately enhanced cytotoxic activity of sulfide 9-anilinoacridine, suggesting that poly(ADP-ribose) polymerase-1 may have a protective function against 9-anilinoacridine-induced cell death process.

Sulfonyl-containing nucleoside phosphotriesters and phosphoramidates as novel anticancer prodrugs of 5-fluoro-2'-deoxyuridine 5'-monophosphate (FdUMP).

A series of sulfonyl-containing 5-fluoro-2'-deoxyuridine (FdU) phosphotriester and phosphoramidate analogues were designed and synthesized as anticancer prodrugs of FdUMP. Stability studies have demonstrated that these compounds underwent pH dependent beta-elimination to liberate the corresponding nucleotide species with half-lives in the range of 0.33-12.23 h under model physiological conditions in 0.1 M phosphate buffer at pH 7.4 and 37 degrees C. Acceleration of the elimination was observed in the presence of human plasma. Compounds with an FdUMP moiety (4-9) were considerably more potent than those without (1-3) as well as 5-fluorouracil (5-FU) against Chinese hamster lung fibroblasts (V-79 cells) in vitro. Addition of thymidine (10 microM) reversed the growth inhibition activities of only 5-FU and the compounds with an FdUMP moiety, but had no effect on those without. These results are consistent with thymidylate synthase as the target of the prodrugs.

Synthesis and antitumor activity of sulfur-containing 9-anilinoacridines.

A series of sulfur-containing 9-anilinoacridines related to amsacrine were synthesized and evaluated for their anticancer potential. Among the compounds, both diol-containing compounds, 2a and 3, were the most cytotoxic of the sulfide series against V-79 cells in vitro (IC(90) = 2.1 microM and 1.9 microM, respectively). Among the non-alkyl-substituted compounds (7-9), compounds with electron-donating substitution para to the sulfide (7 and 9) were more cytotoxic than the electron-withdrawing nitro-substituted compound 8. The limited SAR suggested the importance of hydroxyl functionality along with its location for the cytotoxicity in the series. A preliminary anticancer screening against P388 leukemia showed that 2a is highly active in vivo as well. Topoisomerase II inhibitory activity appeared to be involved in the cytotoxicity of compound 2a. Sulfoxide compound 2b, which is 6-7-fold less cytotoxic than its sulfide 2a, appears to be a potential bioreductive anticancer prodrug on the basis of its bioreductive metabolism findings.