B. L. Rademacher1, T. Steeno1, K. A. Matkowskyj2, A. Auyeung1, E. H. Carchman1 1University Of Wisconsin,Surgery,Madison, WI, USA 2University Of Wisconsin,Pathology And Laboratory Medicine,Madison, WI, USA
Introduction: Autophagy is thought to have a dual role in cancer; protective against carcinogenesis, while an important pro-survival mechanism for tumor cells, especially in the setting of treatment (chemotherapy or radiation). We have previously been shown, both pharmacologically and genetically, that autophagy is important in preventing anal carcinogenesis. However, the role of autophagy in already established cancer, in terms of tumor growth and “patient” survival, has yet to be examined. We hypothesized that autophagy is a protective mechanism used by tumor cells to address their increased metabolic needs and that by knocking out autophagy we would decrease tumor growth rates and improve survival.
Methods: We generated a conditional, genetic knockout mouse model for the essential autophagic protein Atg7. The generated mice carry Atg7f/f gene globally. They also carry an inducible CreER transgene is expressed from an epithelial-specific K14 transcriptional promotor, and its activity is induced by topical exposure to 4-OH tamoxifen (4-OH TAM), resulting in the knockout of the essential autophagic protein Atg7. For this study, the anuses of the mice were treated with the carcinogen, 7,12 dimethylbenz[a]anthracene (DMBA), until anal cancer developed (2-5 mm in diameter upon entry into the study). Fourteen of the mice were then treated with 4-OH TAM to knockout autophagy locally while twelve were not. Tumor sizes were then measured weekly until euthanasia requirements were met or the mouse died. Tumor volumes were then calculated and normalized to day 0 (date of treatment with 4-OH TAM or not). These tumor volumes were then log transformed, then regressed linearly against time in days, resulting in a slope that equates to the tumor growth rate. Differences in tumor growth rates and mouse survival between the two treatment groups were then examined via independent samples t-test and Kaplan-Meier statistics with Log-Rank comparison, respectively.
Results: Mice treated with 4-OH TAM had a statistically significant longer mean survival compared to control mice not treated with tamoxifen (98 days vs 49 days, p-value 0.018). In terms of tumor growth rates, there was a trend to decreased mean tumor growth rates in the 4-OH Tam treated group compared to the control group (0.00167 mm/day +/- 0.003 vs 0.00129 mm/day+/-, p-value 0.725).
Conclusion: The localized knockout of autophagy in anal tumors resulted in a trend in decreased growth rates with a significant increase in mouse survival. Increased sample sizes are needed to reduce the variance in tumor growth rates to further elucidate the role of autophagy in tumor growth.
