A novel combination therapy with histone deacetylase inhibitor and Aurora kinase inhibitor for “triple negative” breast cancers.

Abstract

Abstract Abstract #401 Background: Aurora A and B are essential for normal mitosis. Aurora A (AA) is amplified and/or co-overexpressed with Aurora B (AB) in over 50% of breast cancers, including the basaloid variety, “Triple Negative” breast cancers. MK-0457 (M) is a pan-Aurora kinase inhibitor that inhibits in vitro and in vivo tumor growth, as well as induces apoptosis of cancer cells. Aurora kinases are chaperoned by hsp90, and their down regulation is known to sensitize transformed cells to paclitaxel. Vorinostat (V) is a pan-histone deacetylase inhibitor (HA-HDI) that induces in vitro growth arrest, differentiation and apoptosis of human breast cancer cells. By inhibiting HDAC6 and inducing hyper-acetylation and inhibition of hsp90, V depletes the levels of hsp90 chaperoned proteins, including AA and AB kinase. Methods: AA amplification in MB-231 (“Triple Negative”) and BT-474 (HER-2 amplified) cells were determined by FISH and array-CGH. The cells were treated with M (50 to 250 nM) and/or V (0.5 to 2.0 μM) for 24 to 48 hours. Cell cycle status, DNA endoreduplication (PI staining) and apoptosis (Annexin V/PI staining) were determined by flow cytometry. Intracellular protein levels of p-AA or p-AB, AA and AB, p-survivin, survivin, were determined by immunoblot analyses. Results: Treatment with M or V induces cell cycle G2/M phase accumulation and apoptosis of the breast cancer cells. Dose-dependently, treatment with M depleted phosphorylated (p)-AA, -survivin, and -Ser10 H3 levels. V induced hsp90 acetylation and depleted the levels of AA, AB and survivin. Both M and V induced formation of multi-polar aberrant mitotic spindles. Co-treatment with M and V mediated more depletion of p-survivin, AA and AB levels, as well as synergistically induced apoptosis of MB-231 and BT-474 cells. In the orthotopic MB-231 xenograft breast cancer model, co-treatment with M and V caused significantly more tumor growth delay, lung metastases and survival than treatment with either agent alone. Treatment with V induced in vivo hsp90 hyper-acetylation in the mouse xenografts, as well as in the accessible tumors from patients with breast cancer. This was determined by immunoblot analysis of post-treatment versus pre-treatment tumors with the anti-acetylated-K69-hsp90 antibody, which was developed for these studies. Hsp90 hyper-acetylation was associated with in vivo depletion of AA and AB levels in the mouse xenografts. Co-treatment with M and V, versus treatment with either M or V, also led to greater in vivo attenuation of AA, AB and p-survivin. Conclusion: These studies support the rationale to evaluate the safety and efficacy of the combination of M and V, without or with paclitaxel, against breast cancers with AA amplification and/or overexpression. Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 401.