Overexpression of the transmembrane tyrosine kinase insulin-like growth factor 1 receptor (IGF-IR) or its ligands (e.g. IGF1) correlate with cancer development and progression. For example, activation of the IGF-IR signaling pathway in estrogen receptor (ER) positive breast cancer has anti-apoptotic effects and targeting IGF-IR in ER-negative breast cancer cells decreases metastasis. The mechanism of action of IGF-1R in breast cancer still needs to be elucidated in order to better develop effective and efficient cancer therapies by targeting this pathway. We propose a novel mechanism of action for IGF-IR in breast cancer progression by which cytochrome P450 1A1 (CYP1A1) metabolizes dietary essential omega-3 fatty acids into the eicosanoid 17(18)-epoxyeicosatetraenoic acid (17,18-EpETE). Specifically we hypothesize that IGF-IR/IGF1 induces expression of CYP1A1 which will produce 17,18-EpETE, thereby promoting breast cancer proliferation and survival. CYP1A1 has previously been of particular interest due to its roles metabolizing exogenous compounds (e.g. polycyclic aromatic hydrocarbons) into carcinogenic compounds and metabolizing endogenous compounds such as estrogen. CYP1A1 is also responsible of selectively oxygenating eicosapentaenoic acid (EPA, an omega-3 essential fatty acid commonly found in fish oil) into 17,18-EpETE. Methods: siRNA was utilized to knock down CYP1A1 in breast cancer lines. A liquid chromatography electrospray ionization tandem mass spectrometric (LC-ESI-MS/MS) method was developed to measure 17,18-EpETE levels. Results: CYP1A1 knockdown suggested a role for this CYP in breast cancer cell proliferation. Measurement of IGF1 effects on gene expression in the T47D breast cancer line indicates that IGF1 induces CYP1A1 expression by more than 10-fold. In vitro incubation of EPA with human CYP1A1 expressed in baculovirus extracts results in NADPH-dependent synthesis of 17,18-EpETE. Furthermore, MCF7 and MDA-MB-231 cells contain endogenous 17,18-EpETE, as assayed by the novel LC-ESI-MS/MS method. An MTT proliferation assay demonstrated that exogenous 17,18-EpETE significantly promotes MCF7, T47D, and MDA-MB-231 cell proliferation under serum starvation conditions (P-value < 0.05), exhibiting a threshold for inducing proliferation between 100 nM and 1 microM concentration. Conclusions: Taken together, our results suggest that IGF-IR plays a role in breast cancer progression, in part, by inducing CYP1A1 and associated 17,18-EpETE production, a potential mitogenic and pro-survival eicosanoid.

Citation Information: In: Proc Am Assoc Cancer Res; 2009 Apr 18-22; Denver, CO. Philadelphia (PA): AACR; 2009. Abstract nr 4404.

100th AACR Annual Meeting-- Apr 18-22, 2009; Denver, CO

American Association for Cancer Research
2009