Additive effects of tamoxifen and the farnesyl transferase inhibitor FTI‐277 on inhibition of MCF‐7 breast cancer cell‐cycle progression

Abstract

The efficacy of tamoxifen in the hormonal therapy of breast cancer is well established, but therapeutic resistance is inevitable. FTIs are a new class of anticancer drugs that are in phase III clinical evaluation. Since the mechanisms of action of these 2 classes of drugs are different, we tested the combination of tamoxifen and FTI-277 on inhibiting proliferation of hormone-dependent MCF-7 human breast cancer cells. An additive effect on cell proliferation was demonstrated, accompanied by an additive G 0 /G 1 arrest. The major effect of the combination of the 2 drugs was to maintain p21 waf/cip1 at an intermediate level, higher than that observed in the presence of tamoxifen alone. This was associated with an additive effect on inactivation of cyclin E-Cdk2 complexes and decreased phosphorylation of pRb and p130 pocket proteins. These effects were accompanied by increased association of 2 CDIs, p27 kip1 and p21 waf/cip1 , with cyclin E-Cdk2 complexes. These data demonstrate that the additive effect is likely predominantly due to the recruitment of p27 kip1 and, to a lesser extent, p21 waf/cip1 into the cyclin E-Cdk2 complexes. E 2 action on mammary gland development is mediated through its nuclear receptors (ER), but in cancer development, growth factors act synergistically with E 2 to promote cell proliferation. 1 New data highlight evidence for crosstalk between E 2 and growth factor-induced cytoplasmic signaling. [2][3][4][5] Many of the components of these signaling pathways are low m.w. GTPases, such as Ras, that require prenylation for function. Ras belongs to the Ras superfamily of low m.w. proteins, whose activity is controlled by a GDP/GTP cycle. This superfamily also includes the Rho and Rab subfamilies. Ras and Rho proteins are posttranslationally modified by isoprenoid lipids. For this, farnesyltransferase and geranylgeranyltransferase I catalyze the covalent attachment of the farnesyl (C 15 ) and geranylgeranyl (C 20 ) groups, respectively, to the carboxyl-terminal cysteine of prenylated proteins. Prenylation is essential not only for membrane association but also for biologic activity. 6,7 Several lines of evidence suggest crosstalk between E 2 action and prenylated proteins. In human breast cancer cells, Ras mutation has been observed in only 5% of cases. 8 However, overexpression of Ras protein has been associated with a more aggressive type of breast cancer. 9 Furthermore, a marked increase of RhoB mRNA was observed in breast cancer cell lines, inversely correlated to the amounts of EGF receptor. 10 Endogenous, hyperactive Rac3 is present in highly proliferative human breast cancer cell lines and tumor tissues. 11 Study of Rho GTPase expression in human breast cancer cells showed that Rac, Cdc42 and in particular RhoA are overexpressed compared to corresponding normal tissues originating from the same patient. 12 Finally, RhoC was overexpressed in inflammatory breast cancers, 13,14 and RhoC expression is now proposed as a potential marker for small breast carcinoma with metastatic ability. 15 T...

Fractionation and Characterization of Bioactive Components in Kefir Mother Culture that Inhibit Proliferation of Cultured MCF-7 Human Breast-Cancer Cells

“…In this study, only the dosage above 0.2 µM/l showed antiproliferative effects on MCF-7 cells. The effective dose reported here was higher than the value reported by Doisneau-Sixou et al (2003). RP-HPLC Fraction 30 of kefir mother culture extract significantly increased MCF-7 cell susceptibility to tamoxifen (Figure 10).…”

Clinical trials of intracellular signal transductions inhibitors for breast cancer — a strategy to overcome endocrine resistance

“…Three other groups have since reported a similar interaction for FTIs with tamoxifen or aromatase inhibitors, and have suggested either a synergistic or an additive antitumor effect (Long et al 2004). One recent study implied an additive effect on G0/G1 cell-cycle arrest, and that the FTI-277, when combined with tamoxifen, maintained higher levels of the cdk inhibitor p21 waf/cip1 , resulting in an additive effect on inactivation of cyclin E/Cdk2 complexes and decreased phosphorylation of pRb (Doisneau-Sixou et al 2003).…”

Tipifarnib Plus Tamoxifen in Tamoxifen-Resistant Metastatic Breast Cancer: A Negative Phase II and Screening of Potential Therapeutic Markers by Proteomic Analysis

“…Moreover, we are in the situation of patients who are in progression on tamoxifen therapy at the initiation of the combination treatment, whereas the patients of the former study already showed resistance to tamoxifen but could respond to letrozole alone. We and others previously showed the additive or synergistic action of a combination of tamoxifen with a FTI to inhibit proliferation and promote apoptosis in vitro and in vivo (9,(13)(14)(15).…”

“…This trial showed good tolerability and objective response (OR) rates of 10% and 14%, respectively, with an additional 15% and 9% clinical benefit (CB) rate in 41 and 35 patients, respectively (12). We (13,14) and other (9) showed that FTIs combined with endocrine therapy have additive or synergistic effects on the antiproliferative effects on MCF-7 cells and in xenografts (15). We then hypothesized that the combination of tamoxifen and tipifarnib may benefit metastatic breast cancer patients.…”