Assessment of a mouse xenograft model of primary colorectal cancer with special reference to perfluorooctane sulfonate

Abstract

Colorectal cancer ranks third among the most commonly diagnosed cancers in the United States. Current therapies have a range of side effects, and the development of a reliable animal model to speed the discovery of safe effective preventative therapies would be of great value. A cross-sectional study in a large Appalachian population recently showed an association between low circulating levels of perfluorooctane sulfonate (PFOS) and a reduced prevalence of colorectal cancer. A study using APC_min (C57BL/6J-Apc^Min/J) mice prone to familial adenomatous polyposis found PFOS was protective when exposure occurred during tumor development. To test the possible benefit of PFOS on spontaneous colorectal cancer, we developed a mouse model utilizing primary patient colorectal cancer implants into NSG (NOD.Cg-Prkdc^scidIl2rg^tm1Wjl /Sz) mice. Study goals included: (1) to assess potential factors supporting the successful use of colorectal cancer from heterogeneous tumors for PDX studies; and, (2) evaluate PFOS as a therapy in tumor matched pairs of mice randomized to receive PFOS or vehicle. The time in days for mice to grow primary tumors to 5 mm took almost 2 months (mean = 53.3, se = 5.7, range = 17-136). Age of mice at implantation, patient age, gender and race appeared to have no discernable effect on engraftment rates. Engraftment rates for low and high-grade patient tumors were similar. PFOS appeared to reduce tumor size dramatically in one group of tumors, those from the right ascending colon. That is, by 5 weeks of treatment in two mice, PFOS had eliminated their 52.4 mm³ and 124.6 mm³ masses completely, an effect that was sustained for 10 weeks of treatment; in contrast, their corresponding matched vehicle control mice had tumors that grew to 472.7 mm³ and 340.1 mm³ in size respectively during the same period. In a third xenograft mouse, the tumor growth was dramatically blunted although not eliminated, and compared favorably to their matched vehicle controls over the same period. These preliminary findings suggested that this mouse model may be advantageous for testing compounds of potential value in the treatment of colorectal cancer, and PFOS may have utility in selected cases.

Keywords: CRC; Model selection; NOD SCID Gamma mouse; NSG mouse; PDX; PFOS; Patient derived xenograft; Perfluorooctane sulfonate; Treatment.

Figure 1. Weight gain in NSG mice exposed to PFOS.

Weight gain (mean ± se) over 11 weeks in NSG mice (n = 5) receiving PFOS and every other week sulfa drug (6 weeks total) to show there was no significant toxicity. X, Treatment (weeks); Y, Mean weight gain from baseline (g). The abbreviation “se” stands for the standard error.

Figure 2. Comparison of PFOS water and vehicle water consumption.

Animal water consumption (mean ± se) in the PFOS and vehicle groups over the 10-week treatment period. The x-axis depicts treatment (in weeks), and the y-axis is the mean water consumption (g). Symbols: Trianges depict mice receiving PFOS treatment, and circular symbols depict mice receiving vehicle alone. The error bars represent standard errors (se).

Figure 3. PFOS and vehicle exposed NSG mice that responded.

Depicted are tumor volumes from baseline through the 10–week treatment period. Represented are three right ascending colon tumors from three different patients. Each frame consists of a matched pair of mice where PFOS (Trianges) had a beneficial effect on tumor growth when compared to mice receiving vehicle-only (circular symbols). The X-axis represents treatment (in weeks), and the Y-axis represents tumor growth difference (mm³) from baseline tumor growth. The length of time mice remained on study was determined using the tumor policy in Table 1.

Figure 4. PFOS and vehicle fed NSG mice showing tumor growth in the non-responder group.

Differences in calculated tumor volumes (mean ± se) from baseline in study animals over 5 weeks of treatment. All patient tumor implanted into NSG mice were from colon locations other than the ascending right colon (Sigmoid colon, n = 1; Cecum, n = 2). The X-axis represents treatment (in weeks), and the Y-axis depicts tumor growth in mm³ from baseline tumor growth. Symbols: Trianges represent animals receiving PFOS, and circular symbols represent mice that received vehicle alone. Animals were removed from study according to the criteria listed in Table 1.