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Signaling Cross-Talk Converging On Survivin During Anti-Tumor Drug Action: A Potential New Concept For Breast Cancer Treatment
Survivin, a novel member of the inhibitor of apoptosis (IAP) protein family, is overexpressed in cancer but is undetectable in most normal adult tissues. We initially as well as others later on demonstrated that inhibition of the expression or function of survivin in cancer cells triggers programmed cell death (apoptosis) and a cell division (cytokinesis) defect. Current studies indicate that survivin expression in cancer is associated with cancer progression, poor prognosis, shorter patient survival and drug resistance. Our laboratory recently discovered that treatment of MCF-7 breast cancer cells with T138067, a novel antitumor drug currently in Phase II clinical trial, significantly increased survivin expression. This appears to attenuate drug effectiveness and leads to inherent drug resistance. Conversely, we found that a sub-therapeutic concentration of CPT11/SN-38, a topoisomerase I inhibitor currently used in cancer chemotherapy, effectively decreases survivin expression in MCF-7 breast cancer cells. We found that treatment of MCF-7 cells with T138067 in the presence of a low concentration of SN-38 strikingly enhanced T138067 effectiveness to induce MCF-7 cell death in comparison with results obtained from either drug alone. Moreover, direct inhibition of T138067-mediated survivin induction by survivin mRNA-specific small interfering RNA (siRNA) obtained similar results, which provided direct evidence that T138067-mediated survivin induction is an essential drug resistant factor. The findings described above provide an attractive possibility/hypothesis that utilization of a sub-therapeutic level of CPT11/SN-38 as a survivin modulator to counteract T138067-induced upregulation of survivin may effectively eliminate cancer cells. The goal of this project is to test this chemotherapeutic regimen in the defined model system for killing breast cancer cells, which is based on the signaling cross-talk converging to survivin. In this project, we will: 1) delineate the signal pathways responsible for the opposite effect of T138067 and SN-38 on survivin expression. We will compare the activation of Akt, Erk1/2 and p38 pathways during drug treatment of breast cancer cells with and without kinase-specific inhibitors or by exogenous expression of the corresponding dominant-negative mutants; 2) examine the effect of T138067 on breast cancer cell death in the presence and absence of a sub-therapeutic concentration of SN-38. We will measure colony formation and the sub-G1 DNA content increase during T138067 treatment with and without a low concentration of SN-38 as a survivin modulator. We will also use survivin siRNA to inhibit the effect of T138067 on survivin induction to confirm the role of survivin in cell survival and drug resistance; and 3) investigate the effect of T138067 on breast tumor regression with and without a sub-therapeutic dose of CPT11/SN-38 as a survivin modulator in pre-clinical xenograft models. The studies proposed in this project may lead to a new chemotherapeutic regimen/concept based on the signaling cross-talk and opposing survivin modulation by different antitumor agents in breast cancer cells. Demonstration of this novel concept may expand our vision on drug resistance and action mechanisms, and lead to the development of novel approaches for cancer chemotherapy.
A novel protein that is highly expressed in cancer, but is undetectable in most normal adult tissues has been recently characterized. Expression of this protein in cancer appears to be a universal drug resistant factor and promote cancer cell survival. Therefore, this anti-cancer cell death protein was designated “survivin”. Inhibition of the expression or function of survivin induces cancer cell death and increases drug effectiveness to kill cancer cells. Accumulated data indicate that survivin expression in cancer is involved in cancer progression, poor prognosis, shorter patient survival and drug resistance. Survivin is currently considered as an exciting novel target for cancer diagnosis, prognosis and treatment. Our laboratory recently discovered that treatment of MCF-7 breast cancer cells with T138067 (a novel anti-tumor drug currently in Phase II clinical trials) significantly enhances survivin expression and leads to drug resistance to treatment. Intriguingly, we also found that a sub-therapeutic concentration of CPT11/SN-38 (a clinically used antitumor drug) inhibits survivin expression. We found that sequential treatment of MCF-7 breast cancer cells by T138067 in combination with sub-therapeutic concentrations of SN-38 16 hours prior to T138067 treatment strikingly enhanced cancer cell death in comparison with the result obtained by either drug alone. Moreover, direct inhibition of T138067-mediated survivin induction by a technology called RNA interference (RNAi) obtained similar results, which provided direct evidence that survivin upregulation is an essential drug-resistant factor. Our goal in this project is to test a new concept for anti-cancer drug combination on the basis of modulation of survivin expression. We hypothesize that neutralization of the T138067-mediated survivin induction by a sub-therapeutic dose of CPT11/SN-38 will significantly increase the effectiveness of T138067 in cancer chemotherapy. If this hypothesis would be verified in this project, novel anti-cancer drug combination may be rationally designed for treatment of cancer. We will delineate the signaling pathways responsible for the differential modulation of survivin expression by T138067 and SN-38 as a model system. We will then examine the effects of T138067 and CPT11/SN-38, alone and in combination, on the induction of breast cancer cell death in cell culture systems. Finally, we will investigate the sequential effects of T138067 with or without a sub-therapeutic dose of /CPT11/SN-38 on breast tumor regression in mouse xenograft models. While anti-tumor drugs can inhibit tumor growth during treatment in pre-clinic xenograft models, tumors often acquire drug resistance and begin to re-grow. Similarly, approximate half of the patients with breast cancer relapse after chemotherapy and radiation treatments. The basis for acquisition of drug resistance and cancer relapse is not well understood. Survivin appears to be an essential anti-cancer cell death and drug resistant factor. This project provides a novel model system to test a new concept for anti-cancer drug combination. The studies may expand our vision on drug resistance and action mechanisms, and lead to the development of novel approaches for treatment of cancer.