Treatment of hormone-refractory breast cancer: apoptosis and regression of human tumors implanted in mice

Abstract

Following surgery, the hormone dependence of breast tumors is exploited for therapy using antagonists such as tamoxifen, although occasional hormone-resistant clones do appear. Another chemotherapeutic strategy uses microtubule inhibitors such as taxanes. Unfortunately, these agents elicit toxicities such as leukocytopenia, diarrhea, alopecia, and peripheral neuropathies and are also associated with the emergence of drug resistance. We have previously described a tubulin-binding, natural compound, noscapine, that was nontoxic and triggered apoptosis in many cancer types albeit at 10 Mmol/L or higher concentrations depending on the cell type. We now show that a synthetic analogue of noscapine, 9-bromonoscapine, is f10-fold to 15-fold more potent than noscapine in inhibiting cell proliferation and induces apoptosis following G 2 -M arrest in hormone-insensitive human breast cancers (MDA-MB-231). Furthermore, a clear loss of mitochondrial membrane potential, release of cytochrome c, activation of the terminal caspase-3, and the cleavage of its substrates such as poly(ADP-ribose) polymerase, suggest an intrinsic apoptotic mechanism. Taken together, these data point to a mitochondrially mediated apoptosis of hormone-insensitive breast cancer cells. Human tumor xenografts in nude mice showed significant tumor volume reduction and a surprising increase in longevity without signs of obvious toxicity. Thus, our data provide compelling evidence that 9-bromonoscapine can be useful for the therapy of hormone-refractory breast cancer. [Mol Cancer Ther 2006;5(9):2366 -77]

Nonimmunosuppressive chemotherapy: EM011-treated mice mount normal T-cell responses to an acute lymphocytic choriomeningitis virus infection

“…The prototypic member of this gene family is Bcl-2, whose overexpression provides protection against cell death by preventing release of cytochrome c after mitochondrial damage. Because EM011-induced mitochondrially driven apoptotic cell death in cancer cells is through the decrease of the proapoptotic/antiapoptotic ratio (15,17), we were inquisitive to learn if EM011 altered the expression levels of Bcl-2 in CD8 + T cells. The expression of Bcl-2 in splenic CD8 + T cells from vehicleand EM011-treated mice was determined on day 8 postinfection, a time point that precedes the onset of the contraction phase of the CD8 + T-cell response.…”

“…We have also shown earlier that noscapinoids arrest normal cells too at mitoses but they resume normal cell cycle after the drug is removed or cleared from the system (16). Furthermore, EM011 inhibits the growth of several human neoplasms including lymphomas and breast carcinomas, without causing any gross changes in the microtubule arrays of postmitotic cells (15,17). More importantly, we have thus far failed to detect any toxicity in tissues such as hematopoietic, gut, spleen, and long nerves that are common targets of currently used antimicrotubule drugs (15,17).…”

“…Furthermore, EM011 inhibits the growth of several human neoplasms including lymphomas and breast carcinomas, without causing any gross changes in the microtubule arrays of postmitotic cells (15,17). More importantly, we have thus far failed to detect any toxicity in tissues such as hematopoietic, gut, spleen, and long nerves that are common targets of currently used antimicrotubule drugs (15,17). Because our animal studies to investigate the inhibition and regression of tumor growth used immunodeficient (nu/nu) mice to grow human tumor xenografts, we had been thus far restricted to determine the immunosuppressive nature of EM011.…”

“…Although we have previously reported the absence of alterations in immune cell counts on EM011 treatment (despite the fact that these nude mice have very low T-cell counts; refs. 15,17), those data may not have represented a true scenario of the drug effects on the immune surveillance system. Therefore, to rigorously investigate the effects of EM011 therapy on the immune system, we chose to use the wellestablished model of murine infection with lymphocytic choriomeningitis virus (LCMV).…”

Multidrug Resistance-Associated Protein–Overexpressing Teniposide-Resistant Human Lymphomas Undergo Apoptosis by a Tubulin-Binding Agent

“…1Ai). Because EM011 is a tubulin-binding agent that blocks mitosis (22,26), our next aim was to follow the cell cycle progression of CEM/VM-1-5 cells upon drug treatment over time. EM011 treatment resulted in a timedependent accumulation of cells in the G 2 -M phase as revealed by an increasing population of cells with 4N DNA with concomitant losses from G 0 -G 1 phases (Table 1).…”