Bioluminescence Imaging of Spontaneous Lymphomas and Contribution of Distinct NFκB Pathways.

The nuclear factor κB (NFκB) pathways have been implicated in tumorigenesis in several lymphoid malignancies, but the responsible mechanisms remain to be fully defined. EBV and HTLV-1 immortalized lymphoma cell lines with constitutively active NFκB were found to be resistant to inducers of the extrinsic and intrinsic apoptosis pathways. Several NFκB-target genes were over-expressed in these cell lines, including Bcl-xL, Fas-associated death domain-like IL-1β converting enzyme inhibitor protein (FLIP), and inhibitors of apoptosis (CIAP, XIAP, and survivin). Inhibition of the canonical or non-canonical NFκB pathways with small interfering RNAs (siRNA) or adenovirus expressing a stable form of inhibitor of NFκB (IκB) enhanced sensitivity to apoptosis inducers, and resulted in lower levels of expression these NFκB target genes. Repression of XIAP with siRNA was particularly potent in enhancing apoptosis sensitivity. These findings demonstrate an important role of both NFκB pathways in mediating resistance to apoptosis, and distinctive anti-apoptotic downstream target gene profiles responsible for this effect. In order to utilize HTLV-1 Tax activity as an in vivo biomarker for tumorigenesis, we generated transgenic mice with firefly luciferase driven by the HTLV-1 long terminal repeat (LTRLUC) and bred them with the GzBTax animals to produce double transgenic LTRLUC/GzBTax (LLT) mice which develop large granular lymphocytic leukemia, splenomegaly, localized bone destruction, and solid tumors of the ears, legs, nose, and tail. We found that the bioluminescence of the LLT mice

• serves as a reporter for spontaneous tumorigenesis in vivo,

• is transferable as a useful tumor marker in cell culture and allograft models derived from primary tumors,

• is inducible by immunomodulatory agents, and

• is a sensitive indicator for even the earliest events in tumor development.