Abstract B55: Hypoxanthine Wobble Base Multimutant KRAS2 Mrna PET Imaging Agent in G12D Mice

Activating mutations in KRAS2 oncogene lead to constitutive K-Ras-GTP signals regardless of EGFR signaling, enabling resistance to EGFR-targeted therapies. Some cancers are activated by mutation of the KRAS2 12th codon from the wild type GGU that encodes glycine (G) to a mutant GAU that encodes aspartate (D) or a mutant GUU that encodes valine (V). For this reason, we hypothesize that determining multiple KRAS2 mutations in vivo by external mRNA PET imaging will enable physicians to decide on alternatives to EGFR-directed therapy. We previously pioneered tumor mRNA PET imaging in pancreatic cancer and breast cancer xenografts [Paudyal, et al. (2013) Nuclear Medicine and Biology40(8):994-9] with peptide nucleic acid (PNA) 12-mers coupled to receptor-targeting peptides and imaging reporter moieties, showing single mismatch specificity. Thus, we designed and synthesized a 12-mer PNA hybridization agent with a hypoxanthine wobble base opposite the middle base of the KRAS2 mRNA 12th codon. At the C-terminus, we included a cyclized tetrapeptide based on insulin-like growth factor 1 (IGF1) to enable IGF1R-mediated cellular uptake. We included an N-terminal N2S2 chelator in order to bind 64Cu. Molecular dynamics and circular dichroism analysis of the wobble base PNA H-bonded to KRAS2 RNA showed preference for mutant A or U over wild type G [Sanders, et al. (2013) Journal of Physical Chemistry B 117(39):11584-95]. We then administered 200 μCi of the [64Cu]PNA wobble base agent, or the complementary G12D agent, or the wild type agent, by tail vein into 3-month-old G12D transgenic mice that developed spontaneous lung tumors. 4 hr and 24 hr later, mice were imaged in a Siemens Inveon microPET/CT scanner. The PET standard uptake value (SUV) with the G12D agent was 1.4, while SUV was 1.3 with the G12DVA wobble base agent, vs. 0.04 with the G12 wild type sequence. The wobble base approach enables detection of three different KRAS2 mutations, G12D, G12V, or G12A, with a single agent. mRNA PET imaging also enables external monitoring of therapeutic efficacy. Supported by NIH CA148565; IP owned by EW/MLT, licensed to MTTI. Citation Format: Eric Wickstrom, Chang-Po Chen, Matthew E. Wampole, Kaijun Zhang, Bishnuhari Paudyal, Antican Wang, Sushil Tripathi, Pardeep Kumar, Edith P. Mitchell, Bo Lu, Mathew L. Thakur, Brian D. Gray, Jeffrey A. Mattis. Hypoxanthine wobble base multimutant KRAS2 mRNA PET imaging agent in G12D mice. [abstract]. In: Proceedings of the AACR Special Conference on RAS Oncogenes: From Biology to Therapy; Feb 24-27, 2014; Lake Buena Vista, FL. Philadelphia (PA): AACR; Mol Cancer Res 2014;12(12 Suppl):Abstract nr B55. doi: 10.1158/1557-3125.RASONC14-B55