Involvement of cyclooxygenase‐2 in the tumor site‐dependent production of parathyroid hormone‐related protein in colon 26 carcinoma

Abstract

It has been shown that in the mouse colon 26 tumor model, tumors grown in the subcutis (subcutis colon 26) caused early onset of cachectic syndromes, whereas those in the liver (liver colon 26) did not. Both interleukin (IL)-6 and parathyroid hormone-related protein (PTHrP) were involved in the development of cachectic syndromes in this tumor model. However, whether expression of PTHrP and IL-6 is differently regulated in the tumor microenvironment is unclear. In the present study, culturing the colon 26 cells under different conditions in vitro revealed that IL-6 production was increased by monolayer culture under a low-glucose condition but not by spheroid culture. In contrast, PTHrP production was increased by spheroid culture but not by monolayer culture, even under a low-glucose condition. Gene expression profiling revealed that the expression of cyclooxygenase (COX)-2 was up-regulated in both subcutis colon 26 and spheroid cultures, and that COX-2 inhibitor NS-398 suppressed PTHrP production in spheroid cultures. C ancer cachexia is a complex disease, and the development of cachectic syndromes does not correlate with tumor mass or metastases.(1) Several factors, such as tumor necrosis factor (TNF)-α, interleukin (IL)-1β, IL-6, leukemia inhibitory factor (LIF), interferon (IFN)-γ, and parathyroid hormone-related protein (PTHrP) are thought to cause cachectic symptoms in animal models.(2) Among these, PTHrP plays a key role in the development of cachexia. Nude rats and nude mice bearing the human lung cancer xenograft that expresses PTHrP and several inflammatory cytokines, including IL-6, develop cachectic syndromes such as body-weight loss, hypercalcemia, hypoglycemia, and hypolipidemia.(3) Administration of an anti-PTHrP antibody nearly completely cured cachectic symptoms as revealed by the restoration of body-weight gain and blood calcium, but neither affected the serum levels of IL-6 nor abolished acute-phase reactions.(3) Human cachectic cancer patients with elevated blood levels of PTHrP also showed increasing levels of multiple inflammatory cytokines, including IL-1β, IL-6, IL-8, IL-11, TNF-α, and IFN-γ.(4) Furthermore, gastroesophageal cancer patients with elevated blood PTHrP levels have been shown to have shorter survival than those with low blood PTHrP levels. (5) However, whether the expression of PTHrP and other inflammatory cytokines such as IL-6 is differently regulated in the microenvironments of tumors remains unexplored.It was demonstrated that mice with subcutaneously transplanted colon 26 (subcutis colon 26) developed cachectic symptoms, whereas those with intrahepatically transplanted colon 26 (liver colon 26) did not.(6) In addition, blood levels of PTHrP and IL-6 were elevated in mice with subcutis colon 26 (7) and both PTHrP and IL-6 have been shown to play important roles in the development of cachexia in the subcutis colon 26 model. (7,8) In the present study, the authors show that in mice bearing subcutis colon 26, PTHrP and IL-6 are differently expressed under different condition...

A Diet Rich in Fish Oil and Leucine Ameliorates Hypercalcemia in Tumour-Induced Cachectic Mice

“…DHA is known to reduce COX-2 activity [12], and PTHrP production is known to be stimulated upon stimulation of COX-2 [8]. Therefore, to further elucidate the possible mode of action of DHA, we determined whether COX-2 was involved in the PTHrP reducing effects of DHA in Experiment E. This was done by measuring PGE-2 production upon incubation of C26 cells with DHA.…”

“…Moreover, our results showed that the nutritional combination of fish oil and leucine reduced PTHrP levels in the tumour. Elevation of PTHrP in malignancy is thought to be mediated by an increase in COX-2 activity [8]. Therefore, the strong positive correlations of Ca 2+ levels with PGE-2, a major COX-2-mediated inflammatory mediator, might suggest that PTHrP is also involved in the induction of hypercalcemia.…”

“…One could also argue that it is unlikely that the proliferation of the cells changed, because XTT remained the same. PTHrP production in C26 cells has previously been related to COX-2 activity [8], and DHA is known to be able to inhibit COX-2 activity [12]. Therefore, our next step was to determine possible mediators of PTHrP by testing involvement of COX-2, as seen in Experiment E. To this end, we incubated a large number of cells with a specific COX-2 inhibitor CXB, and measured the effect of DHA on PGE-2 production and the effect of CXB on PTHrP and PGE-2 production.…”

“…Bone resorption can lead to TGFβ release, which in turn stimulates PTHrP secretion by tumour cells, thus initiating a vicious cycle [6,7]. The elevation of PTHrP in C26 adenocarcinoma cells has been reported to depend on an increase in cyclooxygenase 2 (COX-2) activity, which in parallel also results in an elevated PGE-2 production [8]. Apart from its effects on bone calcium turnover, PTHrP also directly stimulates muscle wasting and adipose tissue browning [9].…”

Molecular targeted therapies in adrenal, pituitary and parathyroid malignancies

“…Recently, it has been shown that truncated APC can target β-catenin for destruction, but only in the absence of COX enzyme activity, providing a possible molecular explanation for the promising results of COX-2 inhibition in colorectal cancer (Eisinger et al 2007). In vitro, the COX-2 inhibitor NS-398 suppressed parathyroid-related peptide (PTHrP) production in colorectal cancer (Saito et al 2007). Anti-PTH immunotherapy has been described in some case reports, demonstrating biochemical control and clinical improvement as well as reduction of the size of metastases (Betea et al 2004, Horie et al 2010.…”