The role of a KRAS 3’UTR Mutation in Cellular Transformation and Drug Response

The identification of new diagnostic biomarkers is needed to advance the scope of personalized cancer therapies. In 2008, our laboratory identified a first-in-its-class, germ-line mutation located in the 3’UTR of the KRAS oncogene. The T>G mutation (rs61764370) disrupts a let-7 microRNA-target site causing over-expression of KRAS, altered down-stream signaling, and unique overall tumor biology. We established that rs6174370 associates with an increased risk of developing non-small cell lung cancer[1], ovarian cancer[2], and triple negative breast cancer[3]. Furthermore, the rs61764370 associates with poor outcome in head and neck[4] and ovarian cancer[5]. Concomitantly ovarian cancer patients harboring the rs61764370 mutation display resistance to platinum-based therapies[5], whereas patients with metastatic colorectal cancer display resistance to cetuximab-irinotecan combination therapy[6].

Since there are two clear clinico-pathologic phenotypes associated with this mutation, the overall goal of this project is to (1) understand the mechanism by which the rs61764370 mutation plays a role in cellular transformation; and (2) identify FDA-approved drugs capable of specifically targeting the rs61764370 mutation.

To address these goals we generated isogenic breast cell lines harboring either the wild-type (T/T) or mutant (T/G) KRAS 3’UTR.  Here we show that cells harboring the rs61764370 mutation senesced in the absence of serum. The addition of serum counteracted this phenotype and lead to enhanced cell growth and a mesenchymal-like morphology when compared to the wild-type epithelial breast cell lines. Additionally, cells harboring the rs61764370 mutation displayed differential sensitivity to EGFR pathway inhibitors. Together this data indicates that the rs61764370 mutation may serve as a predictive clinical biomarker.

1.    Chin, L.J., et al., A SNP in a let-7 microRNA complementary site in the KRAS 3’ untranslated region increases non-small cell lung cancer risk. Cancer Res, 2008. 68(20): p. 8535-40.
2.    Ratner, E., et al., A KRAS-variant in ovarian cancer acts as a genetic marker of cancer risk. Cancer Res, 2010. 70(16): p. 6509-15.
3.    Paranjape, T., et al., A 3’-untranslated region KRAS variant and triple-negative breast cancer: a case-control and genetic analysis. Lancet Oncol, 2011. 12(4): p. 377-86.
4.    Christensen, B.C., et al., A let-7 microRNA-binding site polymorphism in the KRAS 3’ UTR is associated with reduced survival in oral cancers. Carcinogenesis, 2009. 30(6): p. 1003-7.
5.    Ratner, E.S., et al., A KRAS variant is a biomarker of poor outcome, platinum chemotherapy resistance and a potential target for therapy in ovarian cancer. Oncogene, 2012. 31(42): p. 4559-66.
6.    Graziano, F., et al., Genetic modulation of the Let-7 microRNA binding to KRAS 3’-untranslated region and survival of metastatic colorectal cancer patients treated with salvage cetuximab-irinotecan. Pharmacogenomics J, 2010. 10(5): p. 458-64.