title: The anti-tumour effect of low-dose continuous chemotherapy may partly be mediated by thrombospondin.
abstract: BACKGROUND
  Tumour growth is dependent on angiogenesis. Antiangiogenic chemotherapy, i.e. continuous or metronomic low-dose chemotherapy, is a method for administrating cytostatics at a low and well-tolerated concentration without prolonged breaks. The target is the genetically stable endothelial cells playing a pivotal role in angiogenesis within the tumour. Different mediators could mediate the antiangiogenic effect of metronomic chemotherapy. One of these mediators could be thrombospondin (TSP). TSP is a potent inhibitor of angiogenesis and might therefore be important in controlling tumour growth. This study was designed to evaluate the effects of low-dose continuous or moderate-dose bolus chemotherapy on tumour growth and on tumour expression of TSP.
  
  
  METHODS
  Rats bearing a malignant prostate tumour (Dunning AT-1) not expressing TSP were treated systemically with cyclophosphamide, doxorubicin or paclitaxel and the combination of cyclophosphamide and doxorubicin. Tumour growth and body weight were measured during the treatment. CD36, one of TSP's main receptors, was also analysed. The expression pattern of TSP-1, TSP-2 and CD36 was investigated using immunohistochemistry and Western blot analyses. Q-PCR was used to analyse TSP-1 mRNA expression.
  
  
  RESULTS
  Low-dose cyclophosphamide and paclitaxel re-induced the expression of TSP in the tumours. However, following a bolus dose of doxorubicin, tumours showed no expression of TSP. Both cyclophosphamide and doxorubicin treatments decreased the tumour weight by more than 60% compared with vehicle controls. When cyclophosphamide and doxorubicin were combined the tumour weight was reduced by 47%, while paclitaxel reduced the tumour weight by 18% compared to the vehicle controls.
  
  
  CONCLUSIONS
  Systemic low-dose continuous treatment of a rat prostate cancer model with cyclophosphamide and paclitaxel induced the expression of TSP in tumour tissue and inhibited tumour growth. These findings support the hypothesis that the anti-tumour effect of low-dose metronomic chemotherapy, at least with certain chemotherapeutics, is partly mediated by induction of endogenous antiangiogenic factors.
authors.affiliation: Department of Urology, Institute of Surgical Sciences, Sahlgrenska Academy, Göteborg University, Sahlgrenska University Hospital, Sweden. jan-erik.damber@urology.gu.se
authors.forename: Jan-Erik
authors.initials: JE
authors.lastname: Damber
authors.forename: Christina
authors.initials: C
authors.lastname: Vallbo
authors.forename: Per
authors.initials: P
authors.lastname: Albertsson
authors.forename: Bo
authors.initials: B
authors.lastname: Lennernäs
authors.forename: Klas
authors.initials: K
authors.lastname: Norrby
mesh_terms: D000818:Animals; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000008:administration & dosage / Q000494:pharmacology / Q000627:therapeutic use; D004305:Dose-Response Relationship, Drug; D004334:Drug Administration Schedule; D008297:Male; D009368:Neoplasm Transplantation; D009389:Neovascularization, Pathologic / Q000188:drug therapy / Q000378:metabolism; D011471:Prostatic Neoplasms / Q000098:blood supply / Q000188:drug therapy / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D019699:Thrombospondins / Q000037:antagonists & inhibitors* / Q000096:biosynthesis; D016896:Treatment Outcome
chemical_list: D019699:Thrombospondins