15-Hydroxyprostaglandin dehydrogenase inactivation as a mechanism of resistance to celecoxib chemoprevention of colon tumors

Abstract

Pharmacologic inhibitors of the prostaglandin-synthesizing COX-2 oncogene prevent the development of premalignant human colon adenomas. However, resistance to treatment is common. In this study, we show that the adenoma prevention activity of the COX-2 inhibitor celecoxib requires the concomitant presence of the 15-hydroxyprostaglandin dehydrogenase (15-PGDH) tumor suppressor gene, and that loss of 15-PGDH expression imparts resistance to celecoxib's anti-tumor effects. We first demonstrate that the adenoma-preventive activity of celecoxib is abrogated in mice genetically lacking 15-PGDH. In FVB mice, celecoxib prevents 85% of azoxymethane-induced tumors >1 mm in size, but is essentially inactive in preventing tumor induction in 15-PGDH-null animals. Indeed, celecoxib treated 15-PGDH null animals develop more tumors than do celecoxib naive WT mice. In parallel with the loss of tumor prevention activity, celecoxib-mediated suppression of colonic PGE(2) levels is also markedly attenuated in 15-PGDH-null versus WT mice. Finally, as predicted by the murine models, humans with low colonic 15-PGDH levels also exhibit celecoxib resistance. Specifically, in a colon adenoma prevention trial, in all cases tested, individuals who developed new adenomas while receiving celecoxib treatment were also found as having low colonic 15-PGDH levels.

Fig. 1.

Celecoxib resistance in 15-PGDH knockout mice. (A) AOM induced colon tumor development in 15-PGDH+/+ FVB mice untreated (−) (n = 16) or treated (+) (n = 12) with celecoxib, versus FVB 15-PGDH−/− mice untreated (n = 13) or treated (n = 17) with celecoxib. P values represent comparisons of tumor numbers between groups, with asterisks indicating statistically significant values. Error bars designate SEM. (B) AOM induced development of large colon tumors (diameter >1 mm) in the same mice cohorts in A. (C) Gross morphology of representative colons from AOM-treated 15-PGDH+/+ and −/− mice administered celecoxib-containing (+) or celecoxib-free (−) diets. Arrows designate colon tumors. (D) Colonic mucosal PGE₂ levels (in ng/mg protein) in 15-PGDH+/+ FVB mice untreated (−) (n = 10) or treated (+) (n = 9) with celecoxib, versus FVB 15-PGDH−/− mice untreated (n = 12) or treated (n = 11) with celecoxib.

Fig. 2.

Celecoxib and 15-PGDH tissue levels in murine colonic mucosa. (A) Tissue levels of celecoxib were determined by MS in tissue homogenates of colonic mucosa obtained from 15-PGDH WT (+/+) (n = 20) or knockout (−/−) (n = 26) mice administered 2 weeks of a celecoxib-supplemented diet. Error bars designate SEM. Mice cohorts correspond to those of Fig. 1D. (B) Western analysis of 15-PGDH expression determined in colon mucosa from 3 sets of mice receiving 2 weeks of a control diet (−) or 2 weeks of a celecoxib-containing (+) diet. Actin protein levels serve as a loading control.

Fig. 3.

Celecoxib resistance in humans with low levels of 15-PGDH. Shown on the x axis are pretreatment 15-PGDH transcript levels measured by real-time PCR in RNA from rectal mucosal biopsies of 16 individuals enrolled in the APC trial (5). Bar heights on the y axis indicate number of recurrent adenomas detected in each individual at the completion of 36 months of celecoxib treatment, with blue bars denoting individuals with recurrent disease and minimal black bars indicating individuals with zero recurrences. The median level of 15-PGDH is denoted by the dashed red line, and the mean level is denoted by the dashed black line.