The majority of breast cancer patients who achieve an initial therapeutic response to the human epidermal growth factor receptor 2 (HER-2)-targeted antibody trastuzumab will show disease progression within 1 year. We previously reported the characterization of SKBR3-derived trastuzumabresistant pools. In the current study, we show that HER-2 interacts with insulin-like growth factor

The majority of breast cancer patients who achieve an initial therapeutic response to the HER2-targeted antibody trastuzumab will show disease progression within 1 year. Thus, the identification of novel agents that effectively inhibit survival of cancer cells that have progressed on trastuzumab is critical. In the current study, we show that the dual epidermal growth factor receptor (EGFR)/human EGFR-2 (HER2) kinase inhibitor lapatinib induces apoptosis in trastuzumab-resistant cells derived from the HER2-overexpressing SKBR3 breast cancer line. Lapatinib inhibited EGFR and HER2 signaling in resistant cells, blocking activation of downstream Akt, mitogen-activated protein kinase, and S6 kinases and inducing expression of p27kip1. Importantly, lapatinib also inhibited insulin-like growth factor I (IGF-I) signaling and growth-promoting effects in parental and resistant cells, and the cytotoxic effects of lapatinib were further enhanced by the IGF-I receptor -blocking antibody AIR3. As increased IGF-I receptor signaling has been implicated in trastuzumab resistance, our data strongly support further study of lapatinib as a potential therapeutic in breast cancers that have progressed on trastuzumab. [Mol Cancer Ther 2007;6(2):667 -74]

IntroductionThe human epidermal growth factor receptor 2 (HER2) is a validated therapeutic target in breast cancer. Heterodimerization of HER2 with other HER family members results in enhanced tyrosine phosphorylation and activation of signal transduction pathways. HER2 overexpression increases the translation of fatty acid synthase (FASN), and FASN overexpression markedly increases HER2 signaling, which results in enhanced cell growth. However, the molecular mechanism and regulation of HER2 and FASN interaction are not well defined. Lapatinib is a small-molecule tyrosine kinase inhibitor that blocks phosphorylation of the epidermal growth factor receptor and HER2 in breast cancer cells, resulting in apoptosis. We hypothesized that FASN is directly phosphorylated by HER2, resulting in enhanced signaling and tumor progression in breast cancer cells.MethodsUsing mass spectrometry, we identified FASN as one of the proteins that is dephosphorylated by lapatinib in SKBR3 breast cancer cells. Immunofluorescence, immunoprecipitation, Western blotting, a kinase assay, a FASN enzymatic activity assay, an invasion assay, a cell viability assay and zymography were used to determine the role of FASN phosphorylation in invasion of SKBR3 and BT474 cells. The FASN inhibitor C75 and small interfering RNA were used to downregulate FASN expression and/or activity.ResultsOur data demonstrated that FASN is phosphorylated when it is in complex with HER2. FASN phosphorylation was induced by heregulin in HER2-overexpressing SKBR3 and BT474 breast cancer cells. Heregulin-induced FASN phosphorylation resulted in increased FASN enzymatic activity, which was inhibited by lapatinib. The FASN inhibitor C75 suppressed FASN activity by directly inhibiting HER2 and FASN phosphorylation. Blocking FASN phosphorylation and activity by lapatinib or C75 suppressed the activity of matrix metallopeptidase 9 and inhibited invasion of SKBR3 and BT474 cells.ConclusionsFASN phosphorylation by HER2 plays an important role in breast cancer progression and may be a novel therapeutic target in HER2-overexpressing breast cancer cells.

Purpose: To determine the role of PEA-15 in breast cancer. Experimental Design: A reverse-phase protein array was used to measure PEA-15 expression levels in 320 human breast cancers; these levels were correlated with clinical and tumor characteristics. PEA-15 was overexpressed by an adenovirus vector or by stably expressing PEA-15 in different breast cancer cell lines. The effects on breast cancer cell survival and on the downstream apoptotic signaling pathway were measured in terms of cell proliferation (trypan blue for cell viability, bromodeoxyuridine incorporation for DNA synthesis), anchorage-independent growth (soft agar colony formation), and apoptosis (fluorescence-activated cell sorter analysis). The preclinical efficacy of Ad.PEA-15 given intratumorally was evaluated in nude mice bearing tumors from s.c. implanted human MDA-MB-468 triple-negative breast cancer cells.Results: In human breast cancers, low levels of PEA-15 expression correlated with high nuclear grade (P < 0.0001) and with negative hormone receptor status (P = 0.0004). Overexpression of PEA-15 in breast cancer cells resulted in growth inhibition, reduction in DNA synthesis, and onset of caspase-8-dependent apoptosis. In athymic nude mice bearing MDA-MB-468 xenografts, tumor volumes were significantly smaller in mice treated intratumorally with Ad.PEA-15 than in control mice (P < 0.0001). Tumors from mice treated with Ad.PEA-15 had increased levels of activated (phosphorylated) extracellular signal-regulated kinase and reduced levels of Ki-67 compared with tumors from nontreated or control-adenovirustreated mice.Conclusion: PEA-15 has therapeutic potential in breast cancer. Further preclinical and clinical exploration of PEA-15 as a druggable target is warranted. Clin Cancer Res; 16(6); 1802-11. ©2010 AACR.Breast cancer is the most common cancer in women in the United States and most of the Western world (1). In 2008, 182,460 cases are expected to be diagnosed (26% of all cancers in women), and 40,480 women are expected to die of the disease (accounting for 15% of all cancer deaths in women, making this disease the second most common cause of cancer death among women). Breast cancer that is negative for estrogen receptor, progesterone receptor, and HER-2 is known as triple receptor-negative breast cancer. It is the only major type of breast cancer for which no specific targeted therapy is available to improve patient outcomes (2). A deeper understanding of the molecular mechanisms responsible for breast cancer is imperative if more effective treatments are to be discovered.PEA-15 (also called PED) is an acidic, serine-phosphorylated, 15-kDa phosphoprotein that contains a death effector domain and is associated with microtubules (3). In primary astrocytes (the first cells in which this protein was identified), PEA-15 was shown to regulate the nuclear localization of extracellular signal-regulated kinase (ERK) and consequently affect the transcription of ERK-dependent targets such as transcription factor Elk. This function was shown...

Purpose Preclinical data showed enhancement of breast cancer cell death when G3139 was combined with anthracyclines and taxanes. We evaluated the efficacy and safety of a Bcl-2 antisense oligonucleotide, G3139, in combination with doxorubicin (A) and docetaxel (T) in patients with locally advanced breast cancer (LABC). Experimental Design Following a brief phase I to determine the phase II dose, patients with locally advanced breast cancer received G3139 administered by continuous i.v. infusion for 5 to 7 days with bolus A (50mg/m2) and T (75 mg/m2) administered on either day 3 or 6 of therapy with G3139. Cycles were repeated every 21 days × 6 in the neoadjuvant setting. Serial plasma samples were obtained for pharmacokinetic analysis. Tissue samples were obtained before and after therapy for pharmacodynamic analysis of Bcl-2 expression. Results Thirty patients (median age, 49 years; range, 24–71years) received 160 cycles. During the phase I portion of the trial, the dose of G3139 was escalated from 3 to 7 mg/kg/d (i.v. for 5 days) in combination with AT. During the phase II portion of the trial, several doses and schedules of G3139 were evaluated. There were no pathologic complete responses. Pharmacodynamic studies showed limited Bcl-2 down-regulation in the primary tumors. Conclusions G3139 in combination with doxorubicin and docetaxel is well tolerated. No pathologic complete response was seen and pharmacodynamic studies showed very little down-regulation of Bcl-2 in primary tumors, perhaps related to issues with insufficient drug delivery to the intact tumor.