The role of tumor vasculature in optimizing tumor response to Photo-dynamic Therapy

Dorsthorst, M. te (Manon) (2014) The role of tumor vasculature in optimizing tumor response to Photo-dynamic Therapy. thesis, Medicine.

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Abstract

Introduction: Photodynamic therapy (PDT) involves the administration of a photosensitizer (PS) followed by local illumination with visible light of an appropriate wavelength to activate the drug, for anti-tumor effect. However, pathologic tumor vessels may impact both the delivery of the photosensitizer, and the presence of oxygen, which can negatively affect PDT efficacy. Improving the understanding of the effect of tumor vasculature on PDT, and possible means to modify this effect, may ultimately contribute to optimize PDT efficacy. Therefore, the specific aim of this project is to study the impact of two factors to normalize pathologic tumor vasculature: collagen and anti-vascular endothelial growth factor (VEGF) antibody, in a xenograft mouse model, on PDT outcome. Materials and methods: Xenograft mouse model: inbred female C3H/Km mice were xenografted with the RIF-1 mouse radiation-induced sarcoma cell line. PDT treatment: 7 to 10 days post-inoculation (at tumor size 6-8.5 mm diameter), animals received Photofrin by tail vein injection. PDT was performed by administration of light by means of the Ceralas diode laser (Biolitec AG) to a total of 135 J/cm² to each tumor. During PDT, the mice were anesthetized by inhalation of isoflurane in medical air. Tumors were collected 1 hour after PDT after mice were sacrificed. Sections of 14μm were cut on a cryostat from the frozen tumors. Interventions: the effect of adding collagen 0.02mg into tumor cell suspension was assessed in 4 groups of mice: plus collagen, plus or minus PDT; control groups minus collagen, plus or minus PDT. In the mouse anti-VEGF intervention groups, injections of 10 μg/mouse given on day -2 and day-1 before the delivery of PDT. The effect was assessed in 4 groups of mice: plus mouse anti-VEGF, plus or minus PDT; isotype control groups, plus or minus PDT. To assess long term effect of adding collagen on PDT outcome, tumor regrowth was measured 75 days after PDT in 2 groups of mice: plus or minus collagen. Tumor assessments: vessel morphology was assessed on tumor slides by immunohistochemical staining for collagen type IV antibody, and anti-CD31 antibody rat-anti-mouse. Indirect hypoxia measurement was performed by endogenous Hoechst (EH) staining. PS uptake was measured by fluorescence spectrophotometry. Tumor response was assessed by measuring tumor volume. Tumor volume was measured in 2 orthogonal directions. (Volume = diameter x width² x 3.14/6) Absence of tumor after 75 days was defined as a cure. When the tumor volume exceeded 400 mm³ mice were euthanized and noted as recurrence tumor growth. Statistics: significant differences for all measurements were established using t-test assuming unequal variance. Results: In the mice treated with PDT, no difference with regard to tumor vasculature was found between groups plus or minus collagen; or plus or minus anti-VEGF treatment. Lower PS uptake and spread were found in RIF 3.35 ng/mg (drug concentration – height) in comparing to RIF + collagen 2.ng/mg/, p-value 0.047. However, a ~55% cure rate was observed in mice with collagen supplemented tumors after PDT, compared to a ~15% cure rate without collagen. Conclusion: addition of collagen to a RIF-1 tumor xenograft, positively affects cure rate after PDT, despite the fact that in the present study no effect of interventions with collagen or anti-VGF treatment could be demonstrated on tumor vasculature, or PS delivery. Therefore, PDT optimization can be potentially obtained by means of collagen, but, contrasting to previous thoughts, this appears to be independent of its effect on tumor vasculature.

Item Type:	Thesis (Thesis)
Supervisor name:	Schroder, Dr. C.P. and Department of Oncology and University Medical Center Groningen
Supervisor name:	Busch, Theresa M. and Department of Radiation Oncology and Smilow Center for Translational Research and Philadelphia USA
Faculty:	Medical Sciences
Date Deposited:	25 Jun 2020 11:04
Last Modified:	25 Jun 2020 11:04
URI:	https://umcg.studenttheses.ub.rug.nl/id/eprint/2381

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