Phosphorylated insulin-like growth factor-i/insulin receptor is present in all breast cancer subtypes and is related to poor survival.

Drugs that target the insulin-like growth factor-I receptor (IGF-IR) and/or insulin receptor (IR) are currently under investigation for a variety of malignancies including breast cancer. Although we have previously reported that IGF-IR expression in primary breast tumors is common, the activation status of this receptor has not been examined in relation to survival. Phosphorylated IGF-IR/IR (P-IGF-IR/IR) and its downstream signaling partner phospho-S6 (P-S6) were evaluated immunohistochemically in tumor tissue microarrays representing 438 cases of invasive breast cancer. P-IGF-IR/IR (n = 114; P = 0.046) and total levels of IR (n = 122; P = 0.009) were indicative of poor survival, whereas total IGF-IR (n = 112; P = 0.304) was not. P-IGF-IR/IR and P-S6 were coordinately expressed in primary breast tumors (likelihood ratio, 11.57; P = 6.70 x 10(-4)). Importantly, P-IGF-IR/IR was detected in all breast cancer subtypes (luminal, 48.1%; triple negative, 41.9%; and HER2, 64.3%). In vitro, the IGF-IR/IR inhibitor BMS-536924 decreased phospho-RSK and P-S6, and significantly suppressed the growth of breast cancer cell lines MCF-7, SUM149, and AU565 representing the luminal, triple negative, and HER2 subtypes, respectively, in monolayer and soft agar. BMS-536924 also inhibited growth in tamoxifen resistant MCF-7 Tam-R cells while having little effect on immortalized normal breast epithelial cells. Thus, we can determine which patients have the activated receptor and provide evidence that P-IGF-IR/IR is a prognostic factor for breast cancer. Beyond this, P-IGF-IR/IR could be a predictive marker for response to IGF-IR and/or IR-targeted therapies, as these inhibitors may be of benefit in all breast cancer subtypes including those with acquired resistance to tamoxifen.

Targeting YB-1 in HER-2 overexpressing breast cancer cells induces apoptosis via the mTOR/STAT3 pathway and suppresses tumor growth in mice.

The Y-box binding protein-1 (YB-1) is a transcription/translation factor that is highly expressed in primary breast tumors where it is consistently associated with poor survival. It induces human epidermal growth factor receptor (her-2) along with its dimerization partner egfr by directly binding to their promoters. In addition to promoting growth by inducing receptor tyrosine kinases, YB-1 also protects cells against apoptosis through mechanisms that have not been fully revealed. Given this, we addressed whether YB-1 might be an eventual therapeutic target for breast cancer by inhibiting it with small interfering RNAs in vitro and in vivo. Inhibiting YB-1 suppressed the growth of six of seven breast cancer cell lines that had amplified her-2 or were triple negative. Importantly, targeting YB-1 induced apoptosis in BT474-m1 and Au565 breast cancer cells known to have her-2 amplifications. The potential role of signal transducers and activators of transcription 3 (STAT3) was pursued to address the underlying mechanism for YB-1-mediated survival. Inhibition of YB-1 decreased P-STAT3(S727) but not P-STAT3(Y705) or total STAT3. This was accompanied by decreased P-ERK1/2(T202/Y204), P-mTOR(S2448), and total mammalian target of rapamycin mTOR. Furthering the role of STAT3 in these cells, we show that knocking it down recapitulated the induction of apoptosis. Alternatively, constitutively active P-STAT3 rescued YB-1-induced apoptosis. Finally, targeting YB-1 with 2 different siRNAs remarkably suppressed tumor cell growth in soft agar by >90% and delayed tumorigenesis in nude mice. We conclude that HER-2 overexpressing as well as triple-negative breast cancer cells are YB-1 dependent, suggesting it may be a good therapeutic target for these exceptionally aggressive tumors.