1939P - BrafV600E-induced cancer inflammation in a mouse model of thyroid tumorigenesis

Background

Cancer-associated inflammation is an established cofactor of tumor development and progression. In thyroid carcinoma (TC) immunotherapy is gaining ground, with tumors displaying a diverse inflammatory cell infiltrate and expression of cytokines. Although an association between inflammation and TC is recognized, a cause-effect relationship at the molecular level is not understood. In mice, inducible targeting of BRAFV600E to thyroid follicular cells by Cre recombinase linked to thyroglobulin promotor (TgCreER ^T2 ) give rise to papillary TC. However, synchronous expression of Braf in most thyroid cells causes grave reduction in tumor surrounding tissue, obstructing microenvironment studies and obscures early changes. Omitting induction in TgCreER ^T2 ;Braf ^CA/+ mice, utilizing “Cre leakiness”, TC is developed spontaneously in a preserved microenvironment. Here, we explored inflammatory contribution to carcinogenesis in TgCreER ^T2 ;Braf ^CA/+ mice by characterizing major pro-inflammatory cytokines encompassing early and later tumor stages and the effect of Braf kinase inhibition.

Methods

Thyroids of TgCreER ^T2 ;Braf ^CA/+ mice were analyzed by qPCR and western blot protein expression profiling of cytokines Tnf-a, IL1b and IL6 at 1, 3, 6 and 12 months of age. To investigate reversibility of the inflammatory response to Braf^CA/+ activation, mutant mice aged 6 months were fed with Braf kinase inhibitor Vemurafenib (PLX4720) or control dietary pellets for 4 weeks.

Results

All cytokines showed a gradual increase of gene expression between age 1 to 6 months in non-induced mutant mice, and a subsequent decrease at 12 months. Western blot confirmed upregulation of protein expression at age 1 to 6 months, and a further increase at 12 months. Interindividual variation of expression was high at all ages. The PLX4720-treated cohort had significant reduction of cytokine and protein expression compared to the untreated.

Conclusions

Inflammatory response due to Braf activation is an early event in thyroid carcinoma development, with a time-course dependent expression pattern. Targeted Braf inhibition significantly down-regulates cytokine expression.

Clinical trial identification

Editorial acknowledgement

Legal entity responsible for the study

Mikael Nilsson Sahlgrenska Centre for Cancer Research, Institute of Biomedicine, Gothenburg university Gothenburg, Sweden.

Funding

Cancerfonden (Swedish Cancer Society).

Disclosure

All authors have declared no conflicts of interest.