gms | German Medical Science

Objective: Vascular targeting strategies have become a promising approach for tumor diagnostics and therapy. The alternatively spliced extra domain A (ED-A) of fibronectin represents a promising neoangiogenic marker in this concept. The aim of our study was to characterize biodistribution characteristics of an ED-A small immunoprotein (F8-SIP) during anti-angiogenesis and to analyze the microcirculatory effects of F8-SIP mediated photodynamic therapy (PDT).

Methods: SF126 glioma cells were implanted into dorsal skinfold chambers (DSC) of nude mice (n=5 per group). Microvascular and interstitial accumulation of F8-SIP, microvascular blood flow rate and preferential binding sites were analyzed after intravenous application of ALEXA555-F8-SIP using intravital microscopy. Treatment with Sunitinib (i.p., 40 mg/kg/day) was initiated on day 6 after tumor cell implantation and was applied daily for 6 days. Intravital microscopic analyses were performed on day 8 (acute phase [AP]) and on day 12 (end phase [EP]) after tumor cell implantation and compared to tumors without therapy (basic group [BG]). In PDT experiments red light irradiation (150j/cm²) was applied on tumors after i.v. administration of photosensitizer-coupled F8-SIP and microcirculatory alterations as well as tumor size were analyzed daily for 4 days.

Results: Antiangiogenic treatment increased microvascular binding (EP, t24: 102±4,9 vs. BG, t24: 85,5±6,8; p<0,05). Extravasation of F8-SIP into tumor interstitium was significantly increased in both therapy groups (AP, t24: 76,2±4,9 and EP, t24: 77,5±9,9 vs. BG, t24: 61,4±6,3; p<0,05, respectively). PDT resulted in short initial hyperperfusion followed by significantly reduced functional vessel density (Pre-PDT: 200±122 cm/cm²; Post-PDT:80±74cm/cm²), microvascular blood flow rate (Pre-PDT:42±29nl/s; Post-PDT:18±10nl/s) and perfusion index (Pre-PDT: 0,65±0,14; Post-PDT:0,38±0,32). Microcirculatory failure recovered to normal values 24-48h after single PDT. Single PDT led to short-term reduction of tumor growth 48h after treatment (PDT: 115±31mm³; Control: 205±91mm³) followed by recovery of growth rate. Only repetitive PDT induced long-term reduction of tumor growth (PDT: 139±44mm³; Control: 322±112mm³)

Conclusions: F8-SIP represents a useful tool to specifically target tumor microvessels. Our results provide insights into microvascular consequences of F8 vascular targeting strategies useful for future diagnostic and therapeutic interventions.