Abstract 565: Anti-CD44 antibody treatment inhibits pancreatic cancer metastasis and post-radiotherapy recurrence

Abstract

Abstract Adhesion molecule CD44 is a cell surface glycoprotein, involved in adhesion of extracellular matrix, angiogenesis, cell proliferation, differentiation and migration. Elevated CD44 expression was correlated with poor prognosis in many malignancies, including pancreatic cancer. Recent studies suggest that CD44 is a marker for cancer initiating cells or cancer stem cells. The effects of anti-CD44 monoclonal antibody (MAb) on pancreatic cancer, especially combination therapy with radiation remain largely unknown. In the current study, we evaluated the efficacy of anti-CD44s MAb treatment for human pancreatic cancer both in vitro and in vivo in xenograft models. The anti-CD44s MAb, H4C4, was Protein-A/G affinity purified from ascites and its specific reactivity with cell surface CD44 was confirmed using cellular ELISA. Two human pancreatic cancer cell lines were tested, including MiaPaCa-2 and Panc-1. Anti-CD44s MAb H4C4 significantly inhibited cell growth in MiaPaCa-2 and Panc-1 cells in vitro as compared with control normal mouse IgG (NIgG). Since as a cell adhesion molecule, CD44 plays an important role in anchorage-independent cell growth, we carried out tumorsphere culture assay by culturing cancer cells on ultra-low attachment plates in serum-free condition with either H4C4 or NIgG. The results show that H4C4 dramatically decreased the tumorsphere formation and sphere size in the CD44+ cells. In tumor formation assays, 1 hr pre-incubation of MiaPaCa-2 cells with H4C4 totally blocked tumorigenesis after s.q. implantation in nude mice, but not with NIgG. To evaluate the efficacy of anti-CD44s MAb treatment in vivo, we employed the pancreatic cancer MiaPaCa-2 and Panc-1 orthotopic models in nude mice. The mice received H4C4 or NIgG 4 mg/kg, i.v., three times per week for 5 weeks. H4C4 treatment significantly inhibited tumor growth and metastasis (p<0.01 vs. NIgG, n=5). We also employed a post-radiotherapy tumor recurrence model to evaluate the activity of H4C4 on tumor recurrence. All mice with MIAPaCa-2 xenograft tumors were treated by radiation of 2 Gy, every other day for 24 days (total dose 24 Gy). When all the tumors regressed, the mice were randomized and then treated by i.v. injection of H4C4 or NIgG, 4 mg/kg, three times per week for 8 weeks. H4C4 treatment significantly reduced the post-radiotherapy tumor recurrence, the recurrence rate was 4/20 in H4C4 group and 17/20 NIgG group on Day 100 (p<0.01, n=20). Taken together, our data demonstrate that anti-CD44s MAb strongly inhibits the CD44+ tumor growth, metastasis and recurrence in pancreatic cancer models. Mechanism studies indicate that H4C4 blocked CD44-STAT3 signaling pathway, accompanied by reduction of pancreatic cancer stem cells. Our data demonstrate that CD44 may be a promising molecular target for inhibiting metastasis and post-radiotherapy recurrence of human pancreatic cancer. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 565. doi:10.1158/1538-7445.AM2011-565