Small Interfering RNA Targeted to IGF-IR Delays Tumor Growth and Induces Proinflammatory Cytokines in a Mouse Breast Cancer Model

Abstract

Insulin-like growth factor I (IGF-I) and its type I receptor (IGF-IR) play significant roles in tumorigenesis and in immune response. Here, we wanted to know whether an RNA interference approach targeted to IGF-IR could be used for specific antitumor immunostimulation in a breast cancer model. For that, we evaluated short interfering RNA (siRNAs) for inhibition of in vivo tumor growth and immunological stimulation in immunocompetent mice. We designed 2′-O-methyl-modified siRNAs to inhibit expression of IGF-IR in two murine breast cancer cell lines (EMT6, C4HD). Cell transfection of IGF-IR siRNAs decreased proliferation, diminished phosphorylation of downstream signaling pathway proteins, AKT and ERK, and caused a G0/G1 cell cycle block. The IGF-IR silencing also induced secretion of two proinflammatory cytokines, TNF- α and IFN-γ. When we transfected C4HD cells with siRNAs targeting IGF-IR, mammary tumor growth was strongly delayed in syngenic mice. Histology of developing tumors in mice grafted with IGF-IR siRNA treated C4HD cells revealed a low mitotic index, and infiltration of lymphocytes and polymorphonuclear neutrophils, suggesting activation of an antitumor immune response. When we used C4HD cells treated with siRNA as an immunogen, we observed an increase in delayed-type hypersensitivity and the presence of cytotoxic splenocytes against wild-type C4HD cells, indicative of evolving immune response. Our findings show that silencing IGF-IR using synthetic siRNA bearing 2′-O-methyl nucleotides may offer a new clinical approach for treatment of mammary tumors expressing IGF-IR. Interestingly, our work also suggests that crosstalk between IGF-I axis and antitumor immune response can mobilize proinflammatory cytokines.

Citrate Suppresses Tumor Growth in Multiple Models through Inhibition of Glycolysis, the Tricarboxylic Acid Cycle and the IGF-1R Pathway

“…Durfort et al . reported that knockdown of IGF-1R increased the infiltration of lymphocytes and polymorphonuclear neutrophils, and induced secretion of two pro-inflammatory cytokines, TNF-α and IFN-γ 23 . Therefore, we hypothesized that citrate treatment may suppress tumor growth via inhibition of IGF-1R phosphorylation (and activity), which might increase tumor-infiltrating T lymphocytes and pro-inflammatory cytokines.

Figure 5Citrate treatment impacts IGF-1R-AKT pathway.

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Targeting Insulin and Insulin-Like Growth Factor Signaling in Breast Cancer

“…The compound reportedly possesses both signal inhibitory properties and downregulates IGF-IR in vitro [51]. A phase I trial of this drug has been completed showing favorable safety and pharmacokinetics profiles of PPP in patients with advanced cancer (NCT01062620).…”

“…Recently, an interesting preclinical study showed that 2’-O-methyl modified IGF-IR specific siRNA are able to downregulate IGF-IR expression, block IGF-IR signaling, and suppress tumor growth in vivo by triggering antitumor immune responses [51]. siRNA-based therapies face two major barriers: the delivery of the large and highly charged molecules to the targets [52] and the transient effects of the downregulation of the target gene.…”

IGF1 dependence of dietary energy balance effects on murine Met1 mammary tumor progression, epithelial-to-mesenchymal transition, and chemokine expression

“…The current study is the first, to our knowledge, to show that reduction in circulating IGF1 levels (either genetically or by CR), despite elevated circulating levels of insulin, decreases ERa low luminal mammary tumor growth. We also demonstrate in the Met1 ERa low luminal B breast cancer model that, despite enhanced serum insulin levels, reduced circulating levels of IGF1 decrease Akt signaling (pAkt and cyclin D1) and EMT and chemokine gene expression, all of which regulate tumor growth, progression, and/or metastatic potential in other cancer models (Ahmad et al 1999, Mira et al 1999, 2001, Akekawatchai et al 2005, Singh et al 2009, Wu et al 2010, Durfort et al 2012. Pharmacological inhibitors of the IGF1 pathway effectively diminish breast tumor growth in several preclinical models of breast cancer (Maloney et al 2003, Haluska et al 2006, Gualberto & Pollak 2009, Sabbatini et al 2009, Sun et al 2011.…”