Treatment with Imatinib in NSCLC is associated with decrease of phosphorylated PDGFR-β and VEGF expression, decrease in interstitial fluid pressure and improvement of oxygenation

Abstract

Elevated intratumoral interstitial fluid pressure (IFP) and tumour hypoxia are independent predictive factors for poor survival and poor treatment response in cancer patients. However, the relationship between IFP and tumour hypoxia has not yet been clearly established. Preclinical studies have shown that lowering IFP improves treatment response to cytotoxic therapy. Interstitial fluid pressure can be reduced by inhibition of phosphorylated platelet-derived growth factor receptor-b (p-PDGFR-b), a tyrosine kinase receptor frequently overexpressed in cancer stroma, and/or by inhibition of VEGF, a growth factor commonly overexpressed in tumours overexpressing p-PDGFR-b. We hypothesised that Imatinib, a specific PDGFR-b inhibitor will, in addition to p-PDGFR-b inhibition, downregulate VEGF, decrease IFP and improve tumour oxygenation. A549 human lung adenocarcinoma xenografts overexpressing PDGFR-b were grown in nude mice. Tumour-bearing animals were randomised to control and treatment groups (Imatinib 50 mg kg À1 via gavage for 4 days). Interstitial fluid pressure was measured in both groups before and after treatment. EF5, a hypoxia marker, was administered 3 h before being killed. Tumours were sectioned and stained for p-PDGFR-b, VEGF and EF5 binding. Stained sections were viewed with a fluorescence microscope and image analysis was performed. Imatinib treatment resulted in significant reduction of p-PDGFR-b, VEGF and IFP. Tumour oxygenation was also significantly improved. This study shows that p-PDGFR-b-overexpressing tumours can be effectively treated with Imatinib to decrease tumour IFP. Importantly, this is the first study demonstrating that Imatinib treatment improves tumour oxygenation and downregulates tumour VEGF expression.

Treatment with imatinib improves drug delivery and efficacy in NSCLC xenografts

“…Indeed, in preclinical studies, imatinib therapy has normalised the tumour microenvironment by decreasing IFP, increasing transcapillary transport of oxygen and 51 Cr-EDTA, and lowering VEGF and microvessel density (Pietras et al, 2001;Vlahovic et al, 2006). The current study further demonstrates a significant decrease in density of immature endothelial cells (CD105 þ ), with a trend towards higher endothelial cell maturity (lower CD105 -CD31 ratio, Figure 2B).…”

“…We first used histology to test the vascular effects of imatinib, specifically assessing microvessel density (CD31 positivity), pericyte coverage (a-SMA positivity), and endothelial cell immaturity (CD105 positivity). Then, we followed up on recently published data that demonstrate that pretreatment with imatinib increases delivery of small molecules to tumours (Pietras et al, 2001;Vlahovic et al, 2006). We evaluated the antitumour efficacy of imatinib plus docetaxel (a small molecule chemotherapeutic commonly used for NSCLC treatment) in comparison with either agent alone.…”

“…Non-small cell lung carcinoma exhibits high IFP, upregulated PDGF, and a poor clinical prognosis, making this a particularly valuable model for impaired drug delivery (Kawai et al, 1997;Vlahovic et al, 2006). Interstitial hypertension particularly affects macromolecular therapies such as liposomes, antibodies, and proteins, as they require convective transport to cross the capillary wall (Jain and Baxter, 1988;Yuan, 1998;Netti et al, 1999).…”

“…Blocking VEGF prunes immature vessels, increases fraction of pericyte-covered vessels, and decreases vessel permeability, dilation and tortuosity Willett et al, 2004;Jain, 2005). Inhibition of PDGF or PDGFRb also prunes immature vessels, and additionally decreases contraction of the interstitial space and proliferation of stroma (Heuchel et al, 1999;Pietras et al, 2001;George, 2003;Matei et al, 2004;Vlahovic et al, 2006). Imatinib (Gleevec, Novartis Pharmaceuticals Corp., East Hanover, NJ, USA) is a synthetic small molecule that inhibits phosphorylation of a number of tyrosine kinase receptors including PDGFR, c-kit, and bcr-abl (Buchdunger et al, 1995;George, 2003;Matei et al, 2004).…”

“…In colonic xenografts, Pietras et al (2001) demonstrated that imatinib decreases IFP and thereby increases transcapillary transport of small molecules. We have recently reported the effects of imatinib on NSCLC xenografts, showing that 4 days of therapy (50 mg kg À1 gavage) significantly decreases IFP and microvascular density, lowers VEGF levels, and improves tumour oxygen delivery (Vlahovic et al, 2006). In the current study, we have continued this work by investigating whether pretreatment with imatinib can be used to affect tumour vasculature and consequently improve the efficacy of traditional chemotherapeutics in NSCLC xenografts.…”