Urothelial tumors, accompanied by mutations of the tumor suppressor protein TP53 and dysregulation of mTOR signaling, are frequently associated with aggressive growth and invasiveness. We investigated whether targeting these two pathways would inhibit urothelial tumor growth and progression. Six-week-old transgenic UPII-SV40T male mice (n=15/group) were fed control diet (AIN-76A) or experimental diets containing mTOR inhibitor (rapamycin, 8 or 16 ppm), p53 stabilizing agent (CP31398 [CP], 150 ppm), or a combination. Mice were euthanized at 40 weeks of age. Urinary bladders were collected and evaluated to determine tumor weight and histopathology. Each agent alone, and in combination, significantly inhibited tumor growth. Treatment with rapamycin alone decreased tumor weight up to 67% (p<0.0001). Similarly, CP showed ~77% (p<0.0001) suppression of tumor weight. The combination of low-dose rapamycin and CP led to ~83% (p<0.0001) inhibition of tumor weight. There was no significant difference in tumor weights between rapamycin and CP treatments (p>0.05). However, there was a significant difference between 8 ppm rapamycin and the combination treatment. Tumor invasion was also significantly inhibited in 53% (p<0.005) and 66% (p<0.0005) mice after 8 ppm and 16 ppm rapamycin respectively. While tumor invasion was suppressed in 73% (p<0.0001) mice when CP was combined with 8 ppm rapamycin. These results suggest that targeting two or more pathways achieve better treatment efficacy than a single-agent high-dose strategy that could increase the risk of side effects. A combination of CP and rapamycin may be a promising method of inhibiting muscle-invasive urothelial TCC.
- Received May 14, 2015.
- Revision received September 17, 2015.
- Accepted October 12, 2015.
- Copyright © 2015, American Association for Cancer Research.