1. ¹Division of Pharmacology and Chemotherapy, Department of Internal Medicine, University of Pisa, Pisa, Italy
2. ²Division of Medical Oncology, General Hospital of Livorno, Department of Oncology, University of Pisa, Pisa, Italy
3. ³Division of Surgical, Molecular and Ultrastructural Pathology, Department of Oncology, University of Pisa, Pisa, Italy
4. ⁴Molecular and Cellular Biology Research, Sunnybrook Health Sciences Centre, Toronto, Ontario, Canada
5. ⁵Department of Medical Biophysics, University of Toronto, Toronto, Ontario, Canada

Correspondence: Dr G Bocci, Division of Pharmacology and Chemotherapy, Department of Internal Medicine, University of Pisa, Via Roma, 55, Pisa I-56126, Italy. E-mail: g.bocci@med.unipi.it

Received 21 November 2007; Revised 10 March 2008; Accepted 26 March 2008; Published online 29 April 2008.

Abstract

Metronomic chemotherapy refers to the administration of chemotherapy at low, nontoxic doses on a frequent schedule with no prolonged breaks. The aim of the study is to rationally develop a CPT-11 metronomic regimen in preclinical settings of colon cancer. In vitro cell proliferation, apoptosis and thrombospondin-1/vascular endothelial growth factor (TSP-1/VEGF) expression analyses were performed on endothelial (HUVEC, HMVEC-d) and colorectal cancer (HT-29, SW620) cells exposed for 144 h to metronomic concentrations of SN-38, the active metabolite of CPT-11. HT-29 human colorectal cancer xenograft model was used, and tumour growth, microvessel density and VEGF/TSP-1 quantification was performed in tumours. In vitro and in vivo combination studies with the tyrosine inhibitor semaxinib were also performed. SN-38 preferentially inhibited endothelial cell proliferation alone and interacted synergistically with semaxinib; it induced apoptosis and increased the expression and secretion of TSP-1. Metronomic CPT-11 alone and combined with semaxinib significantly inhibits tumour growth in the absence of toxicity, which was accompanied by decreases in microvessel density and increases in TSP-1 gene expression in tumour tissues. In vitro results show the antiangiogenic properties of low-concentration SN-38, suggesting a key role of TSP-1 in this effect. In vivo, the CPT-11 metronomic schedule is effective against tumour and microvessel growth without toxic effect on mice.