Abstract 3195: Genomic amplification of IGF-1R in osteosarcoma
Authors: Piperdi Sajida , Levin Jonathan , Chung So-Hak , Gorlick Richard 
Published: February 2011

Osteosarcoma (OS) is the most common primary malignant bone tumor in children and young adults. Even though the current treatment regimen has increased event-free survival to 70%, there still exists a poor prognosis for patients with unresectable primary tumors and those with clinically evident metastases. Insulin like growth factor-1 (IGF-1) and its receptor are thought to have a role in the pathogenesis, invasion, and distant metastasis of many human solid tumors. Our previous preclinical data using an IGF-1R antibody against xenograft models of OS demonstrated responses in four out of six OS xenografts suggesting this as a potential therapeutic target. It may be hypothesized that IGF-1R is selected for genomic amplification in some OS due to its proliferative and anti-apoptotic effects. Real time RT-PCR was performed on the primary patient samples, xenografts, and 143B, a standard cell line, to see the expression of IGF-1R. Only 3 of 20 patient samples, and 1 of 4 xenografts have shown higher level of expression of IGF-1R in reference to GAPDH. Genomic DNA was isolated from the same samples, and quantitative PCR was performed to detect gene copy numbers. 11 of 19 (58%)samples were shown to have more than 2 copies of IGF-1R (2 samples have &gt;10 copies, 1 has 7, 2 have 5, 6 have 33), whereas 37% have 2 copies. Two OS xenografts, which respond to IGF-1R antibody in preclinical testing, showed increases in the copy number of IGF-1R. Fluorescence in situ hybridization (FISH) was used to detect the amplification of IGF-1R gene in both patient derived and xenograft OS cell lines. FISH was performed on metaphase slides of fixed cultured cells. Three BAC probes spanning the IGF-1R gene locus in 15q26.3 were produced by isolating BAC DNA, and labeling with AlexaFluor 488 by nick translation. Metaphase prep slides were then hybridized with IGF-1R probes and Texas Red-labeled chromosome 15 centromere probes, counter stained with DAPI, and viewed under fluorescence microscope. Copy number was counted in cells showing a full metaphase spread. Based on initial FISH results, it seems that in the majority of OS the IGF-1R gene is not amplified. This does not imply that IGF1R overamplification does not play a role in IGF-IR overexpression in OS: given the heterogeneity of these tumors and the limited sample size of the experiments thus far IGF-1R amplification may be a rare phenomenon in OS. As responses to IGF-1R are not observed in the majority, it remains possible that amplification correlates with therapeutic response to IGF-1R antibody. FISH on more patient cell lines and xenografts are underway, and even if no amplification is demonstrated, increased IGF-IR activity could still be explained by GOF mutation, or other mechanisms. Additional experiments including FISH in a larger pool of samples, comparing amplification results to clinical data and responsiveness of the cell lines to anti-IGF-IR therapy, and looking for other abnormalities in the IGF-I system, among others are underway.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3195.