Establishment and characterization of two breast cancer xenografts in immunodeficient mice for studies on hormone-dependent and hormone-independent tumor growth, progression and invasion

Background

Breast cancer studies in cell culture and in animals have been performed using a limited number of well-characterized, but old, cell lines and xenograft lines. With the aim of developing new breast cancer model systems, particularly for in vivo biology studies related to hormone-dependent and hormone-independent tumor growth, progression and invasion, and for use in experimental therapy studies, we have collected and implanted biopsy tissues from patients operated for mammary carcinomas in immunodeficient animals.

Methods

Primary tumor tissue from 30 patients with breast cancer (staged as T2 tumors) was harvested and implanted in SCID mice, in a subcutaneous pocket containing Matrigel. All mice were implanted with continuous-release estrogen pellets. The tumors were transferred when reaching a size of approximately 15 mm, to new animals using the same technique. Tumor tissue was harvested for further morphological and molecular characterization from passage six.

Results

Of 32 tumors implanted into mice, two gave rise to viable tumors beyond passage four. One of these proved to be estrogen receptor alpha (ERα)-positive and the other ERα-negative. Both showed characteristic epithelial cell morphology. Separate experiments showed that even the ERα-negative tumor was growth accelerated in the estrogen-supplemented animal. RNA expression analysis confirmed the ERα status in the tumors. Furthermore, the expression of the estrogen-regulated genes TFF1 and CCND1 were high in the ERα-positive tumor but absent in the ERα-negative tumor. Although described as being ERα regulated, the VEGF transcript was expressed in the ERα-negative tumor, but not in the ERα-positive tumor. A difference between the tumors was also seen in the expression of other genes relevant to the tumor growth, progression and invasion, as CDKN1A, COM1, TIMP-1 and MMP-14 demonstrated a high expression in the ERα-negative tumor and a low or missing expression in the ERα-positive tumor. The expression of CDK4, TIMP-2 and MMP-2 was similar in the two different tumors.

Conclusion

As in other studies, the establishment of breast cancer xeonografts is difficult, with a success rate below 10%. However, the two established breast cancer xenograft lines have different characteristics and show marked differences in gene expression patterns that can be related to their ERα status. Further studies and characterization have been initiated using RNA expression microarray analysis.