Inhibition of integrin α₅β₁ function with a small peptide (ATN‐161) plus continuous 5‐FU infusion reduces colorectal liver metastases and improves survival in mice

Abstract

Integrin ␣ 5 ␤ 1 is expressed on activated endothelial cells and plays a critical role in tumor angiogenesis. We hypothesized that a novel integrin ␣ 5 ␤ 1 antagonist, ATN-161, would inhibit angiogenesis and growth of liver metastases in a murine model. We further hypothesized that combining ATN-161 with 5-fluorouracil (5-FU) chemotherapy would enhance the antineoplastic effect. Murine colon cancer cells (CT26) were injected into spleens of BALB/c mice to produce liver metastases. Four days thereafter, mice were given either ATN-161 (100 mg/kg, every 3rd day) or saline by intraperitoneal injection, with or without combination of continuousinfusion 5-FU (100 mg/kg/2 weeks), which was started on day 7. On day 20 after tumor cell inoculation, mice were killed and liver weights and number of liver metastases were determined. A follow-up study on survival was also conducted in which mice were randomized to receive ATN- Key words: angiogenesis; colon cancer; integrins; liver metastasesIntegrins are heterodimeric transmembrane glycoproteins that mediate their own function upon binding to components of the extracellular matrix such as fibronectin, vitronectin and collagen. Integrins are composed of various ␣-and ␤-subunits that form the receptor (reviewed in reference 1), and the unique dimer compositions determine the ability to bind to specific ligands.Integrins regulate cell adhesion and are expressed on the surface of many cell types, including tumor cells, ECs and numerous nonmalignant cell types. 2 In addition to their role in cell adhesion, integrins have been shown to affect intracellular signaling processes and thereby regulate cell survival and proliferation. 2-4 Recently, specific integrins have been identified as being crucial for mediating the angiogenic response of endothelial cells to angiogenic growth factors such as VEGF and bFGF. The integrins ␣ V ␤ 3 , ␣ V ␤ 5 and ␣ 5 ␤ 1 have been shown to play important roles in neoplastic and non-neoplastic angiogenesis by promoting EC migration, proliferation and survival. 5-8 Therefore, endothelial-specific integrins have become a promising target for anti-angiogenic approaches in antineoplastic regimens and in the treatment of nonmalignant angiogenic disorders. 9 -12 The integrin ␣ 5 ␤ 1 is of particular interest as a target since amounts of this integrin and its ligand fibronectin are significantly increased on tumor vessels of many solid malignancies. 13 In some types of cancer, integrin ␣ 5 ␤ 1 is also expressed on tumor cells and plays a direct role in tumor cell migration, invasion, and survival. 14,15 In colorectal cancers, ␣ 5 ␤ 1 overexpression has been associated with invasiveness and malignant progression. 14 However, only a few human colon cancer cell lines are known to express this integrin. 14,16,17 Recently, Livant et al. 15 demonstrated that a small peptide antagonist (amino-acid sequence PHSCN) to integrin ␣ 5 ␤ 1 significantly reduced neovascularization and formation of metastases in an animal model of prostate carcinoma that expresses integr...

Phase 1 trial of the antiangiogenic peptide ATN-161 (Ac-PHSCN-NH2), a beta integrin antagonist, in patients with solid tumours

“…Similar to the clinical development of other agents such as bevacizumab (Hurwitz et al, 2004;Wakelee and Schiller, 2005;Ahmed et al, 2004;Rini et al, 2005;Sledge, 2005), the best approach for phase 2 studies will be combinations of ATN-161 with chemotherapy rather than development as a single agent (Plunkett et al, , 2003Stoeltzing et al, 2003).…”

“…Attempts to show induction of apoptosis in MLL cells by ATN-161 were unsuccessful, suggesting that the inhibitory effects of ATN-161 on primary tumour growth and metastasis formation were the result of inhibition of new blood vessel growth rather than a direct effect on tumour cells. We have also generated preclinical data showing additive effects with diverse chemotherapy agents Plunkett et al, 2003;Stoeltzing et al, 2003). ATN-161 was not immunogenic in animal studies.…”

Integrins: roles in cancer development and as treatment targets

“…Once integrins a5b1 and avb3 are expressed, angiogenesis depends on each integrin as antagonists of each can block angiogenesis in vivo (Brooks et al, 1994a, b;Kim et al, 2000a). Antibody and peptide antagonists of integrins avb3 and a5b1 inhibit growth factor as well as tumour angiogenesis, tumour growth and tumour metastasis (Brooks et al, 1994a, b;Carron et al, 1998;Kim et al, 2000a;Stoeltzing et al, 2003). These studies indicate that these integrins function in part by promoting survival in proliferating endothelial cells in vivo (Brooks et al, 1994b;Kim et al, 2002).…”

“…A cyclic peptide inhibitor of integrin avb3/avb5, Cilengitide, is in Phase I/II trials for glioblastoma and other cancers (Burke et al, 2002;Eskens et al, 2003;Smith, 2003). Other promising integrin a5b1-and avb3-blocking peptides with antitumour angiogenesis and tumour metastasis activities are currently in preclinical development (Carron et al, 1998;Reinmuth et al, 2003;Stoeltzing et al, 2003). As Avastin, the antibody inhibitor of VEGF, has recently shown promise as a therapeutic for colon cancer in Phase III clinical trials (Fernando and Hurwitz, 2003), these integrin-based antiangiogenesis therapeutics hold great promise as powerful therapeutics for the treatment of cancer.…”

The Homeobox Transcription Factor Hox D3 Promotes Integrin α5β1 Expression and Function during Angiogenesis

“…Thus, Hox D3 may provide a switch to activate a program of angiogenesis that includes expression of both during ␣ v ␤ 3 and ␣ 5 ␤ 1 angiogenesis. Once integrins ␣ 5 ␤ 1 and ␣ v ␤ 3 are expressed, angiogenesis depends on each integrin as antagonists of each can block angiogenesis in vivo (10,(15)(16)(17)35).…”