Restoration of PTEN activity decreases metastases in an orthotopic model of colon cancer

Abstract

Background: Mutational loss of tumor suppressor phosphatase and tensin homologue deleted on chromosome ten (PTEN) is associated with malignant progression in many cancers, including colorectal cancer (CRC). PTEN is involved in negatively regulating the phosphatidylinositol 3-kinase/AKT oncogenic signaling pathway and has been implicated in the metastatic colonization process. Few in vivo models are available to study CRC metastasis. The purpose of this study was to determine the effect of restoring PTEN activity on metastases in an orthotopic murine model.

Methods: Green fluorescent protein labeled TENN, a highly metastatic human colon cancer cell line with mutational loss of PTEN gene and TENN clones (with restoration of PTEN gene) tumors were orthotopically implanted onto the colons of BALB/c nude mice and allowed to develop primary and metastatic tumors. Seven weeks post-implantation, mice were euthanized and organs extracted for examination.

Results: Both TENN and TENN clone cell lines demonstrated 100% primary invasion. However, compared with the parental TENN cells, which demonstrated 62% metastases to both lungs and liver, TENN clone cells showed an approximately 50% reduction in metastasis, with only 31.6% liver metastasis and no metastasis to the lungs (P = 0.02).

Conclusions: Our study shows that reactivation of PTEN tumor suppressor pathway leads to a 50% reduction in CRC metastasis without affecting primary tumor formation. Importantly, PTEN restoration also changed the organotropic homing from liver and lung metastasis to liver metastasis only. This in vivo study demonstrates that PTEN might act specifically as a metastasis suppressor and, thus, efforts to target the phosphatidylinositol 3-kinase/PTEN pathway are legitimate.

Keywords: Colorectal cancer; Metastases; PI3Kinase; PTEN.

Fig. 1. Identification of PTEN mutation in TENN colon cancer cells

(A, B) Sequencing analysis of 3 colon cancer cell lines (HCT116, DLD1 and TENN) showing mutation in PTEN gene of TENN cells. (C) Western blot analysis showing a loss of PTEN in TENN cells. Anti-β Actin used as a loading control.

Fig. 2. PTEN restoration leads to decreased metastatic colonization

Comparison of GFP images of primary tumors and liver/lung metastases in TENN and TENN clone mice.

Fig. 3

Histological comparison of primary tumors and liver/lung metastases by H&E staining in TENN and TENN clone in paraffin-embedded tissue sections.