Illuminating cancer systems with genetically engineered mouse models and coupled luciferase reporters in vivo

Abstract

Bioluminescent imaging (BLI) is a powerful noninvasive tool that has dramatically accelerated the in vivo interrogation of cancer systems and longitudinal analysis of mouse models of cancer over the past decade. Various luciferase enzymes have been genetically engineered into mouse models (GEMM) of cancer, which permit investigation of cellular and molecular events associated with oncogenic transcription, posttranslational processing, protein-protein interactions, transformation, and oncogene addiction in live cells and animals. Luciferase-coupled GEMMs ultimately serve as a noninvasive, repetitive, longitudinal, and physiologic means by which cancer systems and therapeutic responses can be investigated accurately within the autochthonous context of a living animal.

Figure 1. Whole animal imaging of p21 promoter activity

(A) Schematic representation of p21^FLuc reporter mice with luciferase knocked into the endogenous p21 locus. (B) Non-invasive, whole animal imaging of p53-dependent p21 promoter activity in response to radiation in p21^+/FLucTrp53^+/+ and p21^+/FLucTrp53^fl/fl mice. (C) Low-light, bioluminescence microscopy of p21 promoter activity in various p21^+/FLuc live tissues, including the villi from the small intestine, throughout the liver, in the epithelial cell layer below the keratinized penile spines, as well as the epithelial cell layer of the vagina. Bars, 200 μm; 50 μm for the penis. Images from Tinkum, et al, (37) were modified and reprinted with permission from Molecular and Cellular Biology.

Figure 2. Imaging inflammation and tumor-associated lymphangiogenesis

(A) Schematic representation of the Vegfr3^EGFPluc reporter knocked in downstream of the endogenous Vegfr3 locus, which utilizes an internal ribosome entry site (IRES) for monitoring Vegfr3 expression. (B) DMBA/TPA-induced skin papillomas in Vegfr3^EGFPluc/+ reporter mice displayed localized lymphangiogenesis as indicated by the black arrows. (C) Whole body imaging of tumor-activated lymphangiogenesis over time in a B16-V5 melanoma xenograft model at distant lymph nodes (red arrows) prior to metastasis of the primary tumor xenograft in female Vegfr3^EGFPluc/+ reporter mice. Images from Martinez-Corral, et al, (51) modified and reprinted with permission from Proceedings of the National Academy of Sciences.

Figure 3. Imaging whole animal Notch1 loss-of-heterozygosity (LOH) and surveying subsequent tumor development

(A) Schematic representation of Notch1-Cre;Notch^fl; Rosa->CBR cells prior to Notch1 ligand activation. (B) Upon activation, cleavage of NOTCH1 (between S2 and S3) permits translocation of the Notch-intracellular-domain (NCID)-Cre fusion into the nucleus where it excises both the remaining wildtype Notch1^fl allele, and the floxed stop cassette preceding CBR. Through these series of Cre-mediated excisions, lineage tracking of Notch1 LOH can be longitudinally imaged via the genetically-coupled floxed Rosa->CBR reporter. (C) Whole animal imaging of the development and progression of Notch1 LOH-induced angiosarcomas of the liver as imaged in Notch1⁺or Notch1^fl mice crossed to Notch1-Cre;Rosa->CBR reporter mice. Images from Liu, et al, (72) modified and reprinted with permission from Journal of Clinical Investigation.