Curcumin and quercetin were evaluated in rats for their ability to modulate the carcinogenic activity of azoxymethane (AOM) in the colon and 7,12-dimethylbenz[a]anthracene (DMBA) in the mammary gland. In the AOM-induced colon cancer model, male Fischer 344 rats at 8 weeks of age started to receive either curcumin (8 and 16 g/kg) or quercetin (16.8 and 33.6 g/kg) in the diet and 1 week later, were administered AOM (30 mg/kg body wt.) by subcutaneous injection. The animals continued to receive the two agents in the diet until sacrificed 45 weeks later. Curcumin mediated a dose-dependent inhibition of the incidence and multiplicity of adenomas from 47% and 0.58 +/- 0.12 adenomas/rat in the AOM-treated control group to 19% and 0.22 +/- 0.08 and 0.06% and 0.08 +/- 0.06 adenomas/rat for the low and high dose groups, respectively. A low yield of adenocarcinomas (0.06 +/- 0.04 adenocarcinomas/rat) was induced by AOM which was not significantly altered by curcumin. Treatment with quercetin caused a dose-dependent increase in the yield of AOM-induced tumors in the colon from 0.06 +/- 0.04 adenocarcinoma/rat to 0.64 +/- 0.12 and 1.14 +/- 0.17 for the low and high dose groups, respectively. In the DMBA-induced mammary cancer model, curcumin or quercetin was administered at either 10 or 20 g/kg diet, beginning 7 days prior to DMBA and continually throughout the remainder of the experiment. Neither curcumin nor quercetin significantly altered the incidence of animals with tumors or the tumor multiplicity, while the high concentration of both agents significantly increased tumor latency. These results demonstrate different responses to these agents in the two models. While curcumin was highly effective as a chemopreventive agent in the colon model, it was only weakly effective in the mammary model. In contrast, quercetin which was also only weakly effective in the mammary model, caused a dose-dependent enhancement of tumors induced by AOM in the colon model.

Osteopontin is a secreted, adhesive glycoprotein, whose expression is markedly elevated in several types of cancer and premalignant lesions, implicating its association with carcinogenesis. To test the hypothesis that induced osteopontin is involved in tumor promotion in vivo, osteopontin-null and wild-type (WT) mice were subjected to a two-stage skin chemical carcinogenesis protocol. Mice were initiated with 7,12-dimethylbenz(a)anthracene (DMBA) applied on to the dorsal skin followed by twice weekly application of 12-Otetradecanoylphorbol-13-acetate (TPA) for 27 weeks. Osteopontin-null mice showed a marked decrease both in tumor/ papilloma incidence and multiplicity compared with WT mice. Osteopontin is minimally expressed in normal epidermis, but on treatment with TPA its expression is highly induced. To determine the possible mechanism(s) by which osteopontin regulates tumor development, we examined cell proliferation and cell survival. Epidermis from osteopontin-null and WT mice treated with TPA thrice or with DMBA followed by TPA for 11 weeks showed a similar increase in epidermal hyperplasia, suggesting that osteopontin does not mediate TPA-induced cell proliferation. Bromodeoxyuridine staining of papillomas and adjacent epidermis showed no difference in cell proliferation between groups. However, terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling analyses indicated a greater number of apoptotic cells in DMBA-treated skin and papillomas from osteopontinnull versus WT mice. These studies are the first to show that induction of the matricellular protein osteopontin facilitates DMBA/TPA-induced cutaneous carcinogenesis most likely through prevention of apoptosis.

In an initial study to determine if rosiglitazone had chemopreventive activity, Fischer-344 female rats were administered twice weekly doses of hydroxybutyl(butyl)nitrosamine (OH-BBN), a urinary bladder specific carcinogen, for 8 weeks. Two weeks following the last dose of OH-BBN, rats were administered rosiglitazone (50 mg/kg BW) daily by gavage for the remainder of the study (7 months). Only 57% of OH-BBN-treated animals developed palpable urinary bladder cancers during the course of the study, while all of the OH-BBN plus rosiglitazone treated rats developed large cancers (p < 0.01). Surprisingly, examination for PPAR gamma by immunohistochemistry in the urinary bladders of rats showed that while untreated bladder urothelium and preneoplastic lesions clearly expressed PPAR gamma, frank carcinomas exhibited significantly lower levels. This was confirmed by employing microarray studies of the same samples. In additional studies, lower doses of rosiglitazone (10, 2 and 0.4 mg/kg BW/day) were administered. The 10 mg/kg BW/day dose greatly enhanced bladder cancer incidence (p < 0.01). The dose of 2 mg/kg BW/day, which is roughly equivalent to a standard human dose, also significantly increased bladder cancer incidence (controls, 48%; rosiglitazone-treated, 84%). The lowest dose did not significantly increase tumor incidence (rosiglitazone at 0.4 mg/kg BW/day, 64%) or tumor weight in the rats, although there was a trend in that direction. Rosiglitazone alone (10 mg/kg BW/day) given in the absence of OH-BBN did not result in bladder cancer formation when given for 10 months. In summary, rosiglitazone over a wide dose range enhanced urinary bladder carcinogenesis in the OH-BBN model in rats.Published 2008 Wiley-Liss, Inc. This article is a US Government work, and, as such, is in the public domain in the United States of America.Key words: rosiglitazone; urinary bladder; cancer; PPAR gamma agonist The organ-specific carcinogen 4-hydroxybutyl(butyl)nitrosamine (OH-BBN) was observed over 30 years ago to induce urinary bladder cancers in rodents. 1 The tumors have a mixed histology with mostly transitional cell cancers and a smaller percent of squamous cell or mixed carcinomas. 2 Studies have shown that these tumors have a variety of gene expression changes routinely associated with bladder cancer in humans. These include increased levels of survivin and decreased levels of FHIT as determined by immunohistochemistry, 3,4 and various S100 proteins, cell cyclerelated genes and increased expression of genes associated with the EGFr and VEGF pathways as determined by gene microarrays. 5 The rodent cancer models have been used for several decades to evaluate potential chemopreventive agents against urinary bladder cancers. 1,2 The class of agents that has undergone the most complete examination are the COX inhibitors. 6-8 A wide variety of NSAIDS (piroxicam, indomethacin), as well as the selective COX-2 inhibitor celecoxib, have proven to be highly effective in inhibiting the formation of OH-BBN induced urinary bladder cancer...

Initiating treatment after OH-BBN or when bladder lesions already existed showed naproxen and Iressa to be effective in preventing formation of large cancers. Low dose aspirin and resveratrol were ineffective. In protocol 3, in which microscopic lesions were the end point, only Iressa was effective. Thus, an established cancer end point appears preferable. Naproxen, which has an excellent cardiovascular profile, or epidermal growth factor receptor inhibitors may be effective in an adjuvant setting.