Potent inhibition of tumor survivalin vivoby β-lapachone plus taxol: Combining drugs imposes different artificial checkpoints

Abstract

Ablation of tumor colonies was seen in a wide spectrum of human carcinoma cells in culture after treatment with the combination of ␤-lapachone and taxol, two low molecular mass compounds. They synergistically induced death of cultured ovarian, breast, prostate, melanoma, lung, colon, and pancreatic cancer cells. This synergism is schedule dependent; namely, taxol must be added either simultaneously or after ␤-lapachone. This combination therapy has unusually potent antitumor activity against human ovarian and prostate tumor prexenografted in mice. There is little host toxicity. Cells can commit to apoptosis at cell-cycle checkpoints, a mechanism that eliminates defective cells to ensure the integrity of the genome. We hypothesize that when cells are treated simultaneously with drugs activating more than one different cell-cycle checkpoint, the production of conflicting regulatory signaling molecules induces apoptosis in cancer cells. ␤-Lapachone causes cell-cycle delays in late G1 and S phase, and taxol arrests cells at G 2/M. Cells treated with both drugs were delayed at multiple checkpoints before committing to apoptosis. Our findings suggest an avenue for developing anticancer therapy by exploiting apoptosis-prone ''collisions'' at cell-cycle checkpoints.A variety of cancer chemotherapeutic drugs has been discovered, but treatment of most human solid tumors remains largely palliative. One way to improve the efficacy of anticancer therapy is to develop optimal combination regimens of chemotherapeutic drugs. In this study, we demonstrate a treatment synergism by combining ␤-lapachone and taxol. This combination resulted in simultaneous cell-cycle checkpoint delays at the G 1 /S and G 2 /M transitions, setting up for apoptosis-prone ''collisions'' (1). We observed very extensive death of various human tumor cells in culture. Importantly, growth of human ovarian tumor cells implanted into immunosuppressed mice was decreased dramatically, without signs of deleterious effects to the mice. Our preliminary experiments also produced dramatic antitumor activity against xenografted human prostate cancer. This study suggests a combination chemotherapy of very great effectiveness as well as a potential avenue for developing anticancer therapies.Cell-cycle checkpoints can be targeted for cancer therapy either by activating checkpoint-mediated apoptosis pathways or by exploiting chemical sensitivity because of loss of checkpoint function (2, 3). Cells arrest in G 2 /M after treatment with DNA-damaging agents, such as chemotherapeutic agents and x-rays (2, 4). Taxol is an anticancer agent with a wide spectrum of activity that blocks cell proliferation in mitosis presumably by interfering with microtubule function (5). Taxol induces a p53-independent G 2 /M arrest (prophase) that triggers the rapid onset of apoptosis (5-8).Drugs that induce G 1 /S checkpoint delays are rarely used. ␤-Lapachone (3,4-dihydro-2,2-dimethyl-2H-naphthol[1,2-b] pyran-5,6-dione) is a plant product (9, 10). It induces a cell-cycle delay in G 1 and/or ...

Beta-lapachone inhibits proliferation and induces apoptosis in retinoblastoma cell lines

“…[17][18][19][20][21][22] We subsequently confirmed that growth inhibition was mediated, at least in part, by induction of apoptosis, as indicated by increased caspase 3/7 activity and intranucleosomal fragmentation. In addition, beta-lapachone-treated Y79 RB cells displayed cellular morphology characteristic of apoptosis, including chromatin condensation, nuclear fragmentation with bleb formation, and pyknotic bodies 28 (http:// www.cyto.purdue.edu/cdroms/flow/vol4/index.htm).…”

“…27,34,35 Although our experiments were limited to evaluating the cytotoxic effects of beta-lapachone alone in RB cells, a number of studies have found significant synergistic effects of beta-lapachone with other chemotherapeutic agents. 18,[35][36][37] Beta-lapachone induces G1/S checkpoint delay before inducing cell death, and remarkable in vitro and in vivo synergistic effects have been observed when this agent is administered in combination with taxol, which arrests cells in G2/M. 18 Beta-lapachone has also been reported to enhance the cytotoxicity of alkylating agents in vitro, possibly owing to beta-lapachone-induced inhibition of DNA repair.…”

“…18,[35][36][37] Beta-lapachone induces G1/S checkpoint delay before inducing cell death, and remarkable in vitro and in vivo synergistic effects have been observed when this agent is administered in combination with taxol, which arrests cells in G2/M. 18 Beta-lapachone has also been reported to enhance the cytotoxicity of alkylating agents in vitro, possibly owing to beta-lapachone-induced inhibition of DNA repair. 37 Other studies have demonstrated that beta-lapachone can be effective as a single agent in cross-resistant cell lines.…”

“…This agent induces potent cytotoxic effects in a wide variety of malignant human cell types, including colon, lung, prostate, breast, pancreatic, ovarian, and bone cancers, as well as leukaemia, melanoma, and malignant glioma. [17][18][19][20][21][22] Beta-lapachone appears to exert a spectrum of anticancer effects, resulting in both apoptotic 20,23,24 and necrotic 17,19 cell death. Beta-lapachone can directly inhibit DNA topoisomerases I and II, 25,26 and induce G1-and/or S-phase cell-cycle delay followed by apoptosis or necrosis.…”

“…Beta-lapachone can directly inhibit DNA topoisomerases I and II, 25,26 and induce G1-and/or S-phase cell-cycle delay followed by apoptosis or necrosis. 17,18,23 Beta-lapachone cytotoxicity may also be mediated by the activity of the NAD(P)H:quinone oxidoreductase enzyme NQO1. 27 This agent has also been shown to selectively induce apoptosis in breast and prostate cancer cells but not in untransformed cells through a mechanism that appears to involve selective induction of the transcription factor E2F1, a regulator of both S-phase progression and apoptosis.…”