Abstract 954: COX-2 inhibition reduces bone tumor growth in animal models:A role for celecoxib treatment in cAMP/protein kinase A-induced tumors

Abstract

Abstract Background: Carney Complex (CNC) is a multiple neoplasia syndrome characterized by skin lesions, endocrine and other tumors, including osteochondromyxomas. It is caused by inactivating mutations in the PRKAR1A gene encoding the regulatory type 1A subunit of cAMP-dependent protein kinase A (PKA). This subunit is the main suppressor of activity of catalytic subunit (PRCKACA) of PKA which regulates cell proliferation and differentiation. Loss of PRKAR1A increases PKA activity and causes tumors in CNC-affected tissues. Mice with deletion of one prkar1a allele (prkar1a+/−) develop various CNC-like tumors and multiple tail osteotic lesions. Further deletion of a prkaca allele on the prkar1a+/− background unexpectedly increases the number and severity of bone lesions and reduces their age of onset. Recent data indicate that increased PKA activity stimulates the inflammasome without inflammation in mouse and human cells. The released prostaglandin E2 (PGE2) further increases cAMP, which in turn activates PKA and Wnt signaling and promotes the growth of these bony tumors. These data led us to investigate celecoxib, which is a selective inhibitor of cyclooxygenase-2 (COX-2) and therefore of PGE2's release, in prkar1α+/−/prkacα+/− mice. Methods: Eleven out of twenty-two mice 6-12 months old were exposed to celecoxib-containing diet (1,500 mg/kg of NIH-31 diet). The remaining mice were fed the standard NIH-31 diet. After a six-week treatment, we looked at the number, the PKA and phosphodiesterase (PDE) activities, c AMP levels and histology of bony lesions. Sixteen and seven days before sacrifice, mice were injected with calcein which labels bone forming surfaces. From calcein fluorescence observed under microscope, the rate of apposition of cortical bone at periosteal side was measured. This rate reflects tumor growth rate because growing tumors remain encapsulated by cortical bone forming at periosteal side and resorbing at endosteal side. Results: Celecoxib reduced the rate of tumor growth by two-fold as measured by calcein labeling (p=0.016). Histological examination revealed decreased cellularity in the lesions of treated animals due to treatment effect on the tumor cells. Treatment reduced PKA enzymatic activity in the tail tumors as measured by high-performance liquid chromatography (4.0 vs 3.0 CMP/ug protein, p=0.07) whereas cAMP levels and total PDE activity did not change. The expression of all inflammasome-related genes (ets-1, caspase-1, il1b and cox2) was down-regulated by at least 70% in the bone tumors from treated animals compared to controls. Conclusion: COX-2 inhibition reduces PKA activity and bone tumor growth in prkar1α+/−/prkacα+/− mice. Since local tumor control is clinically meaningful for patients with cAMP-induced tumors, celecoxib may merit consideration as the first molecular targeted therapy in this setting. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 954. doi:1538-7445.AM2012-954