FEniCS solver validation

Inês Sofia Vala

_{, Antonieta Ferreira}

_{, Isabel Monteiro Grillo}

_,

Susana Constantino Rosa Santos

1 _{Unidade de Biopatologia Vascular, Instituto de Medicina Molecular, Lisboa, Portugal.} 2 _{Faculdade de Medicina de Lisboa, Portugal.}

3 _{Serviço de Radioterapia do Hospital de Santa Maria, Lisboa, Portugal.}

* Corresponding author: Susana Constantino Rosa Santos Tel: 351 21 799 94 81; Fax: 351 21 799 94 77; E-Mail: [email protected]

ABSTRACT

Since tumor growth is angiogenesis-dependent, detailed molecular and cellular studies are thus needed to understand the parameters implicated in the interactions between the tumor and vasculature compartment with the objective of improving therapeutic strategies, not only for cancer treatment but also for preventing recurrence. In this context, the possible pro-angiogenic effects of radiotherapy on tumor vasculature, activating or promoting resistance on the endothelial cells (ECs), has been poorly characterized.

In the present study, while investigating the pro-angiogenic effects of low doses of irradiation in the vasculature, our results suggest that low doses of irradiation below 1.0 Gy are able to induce a pro-angiogenic response to wound healing without affecting cell survival or proliferation.

In order to confirm a differential response of ECs to low doses of radiation at molecular level, lung human microvascular ECs (HMVEC-L) were irradiated at 0.5 Gy and the level of tyrosine phospho- rylation was analysed. Our results show that low doses of ionizing radiation are responsible for an increase of the tyrosine phosphorylation level. In the future, we propose to identify the mechanisms whereby low doses of irradiation induce a pro-angiogenic response in the vasculature in order to know in which way this process may be involved in tumor re-growth.

INTRODUCTION

Angiogenesis is the development of new mi- crovessels from pre-existing vasculature and it is a requisite for many physiological and patho- logical processes such as wound healing and tu- mor growth. In 1971, Folkman proposed that tumor growth and metastasis are angiogenic de- pendent, and hence, blocking angiogenesis would be an effective strategy to arrest tumor growth and treat human cancer1_{. Several regulators of}

angiogenesis were identified and some of these represent therapeutic targets. One of the most important pro-angiogenic factors is the Vascular Endothelial Growth Factor (VEGF) that promotes endothelial cell proliferation,angiogenesis, and tumor growth, and maintains the elevated vascu- larpermeability of tumor vessels2_{. In addition,}

several studies demonstrate that VEGF may play a crucial role in tumor recurrence. It was sug- gested that VEGF release following surgical pro- cedures stimulates a local angiogenic response that might contribute towards the re-growth of the tumor3-6_{. On the other hand, irradiation was}

shown to lead to VEGF production by the tumor, which in turn may induce anti-apoptotic pathways and promote tumor re-growth7-14_{. Moreover, sev-}

eral studies demonstrated that anti-angiogenic approaches can enhance radiation-induced tumor growth inhibition by different mechanisms that include an increase in tumor oxygenation, a de- crease in vascular density and radiosensitization of endothelial cells (ECs)7-8_{. Interestingly, an-}

other study demonstrated that irradiation doses of 2 and 6 Gy induced EC migration and sprout- ing through up-regulation of the endothelial pro- angiogenic NO pathway15_{. This data is not con-}

tradictory with the concept that the cytotoxic effects of high doses of radiation on ECs contrib- ute to anti-tumoral treatment, as previously re- ported16_{, but suggest that a proportion of ECs did}

survive the radiation stress and this selected pop- ulation may undergo the angiogenic phenotypic shift.

The concept that irradiation itself may genera- te collateral effects conferring resistance to ECs brings the need to new approaches in order to avoid tumor re-growth after irradiation.

In the context of tumor cells per se it was described17 _{that radiation activates signalling path-}

ways which are involved in cell survival; inhibi- tion of these pathways decreases tumor growth and survival after irradiation. Indeed, in most of the studies, the final read-out of the co-therapy focused on the effects on tumor growth, but the impact of irradiation on the vasculature was not well addressed.

This issue becomes extremely important if we think about the radiotherapy procedure, since the total dose is fractionated in order to give time to normal cells (including endothelial cells) to recov- er. Typically the dose is given at 1.8-2.0 Gy per day for adults, or 1.5-1.7 Gy per day for children18_.

Moreover, in order to spare normal tissues, shaped radiation beams are aimed from several angles of exposure to intersect at the tumor, providing a much larger absorbed dose there than in the surrounding healthy tissues18_{. So, the amount of radiation re-}

ceived by tumor-surrounding vasculature is gener- ally much lower than the 1.8-2.0 Gy defined dose. This leads us to the following questions: what is the effect of those low doses of radiation below 2.0 Gy on the vascular cells? Are these low doses unable to trigger any vascular response or, on the contrary, they activate ECs promoting a pro-an- giogenic response?

If this is the case, how can this process be involved in tumor re-growth and how may these low doses of radiation be used as a therapy process in pathologies associated with deficient angiogenesis?

In this project, we’ve proposed to define a pro-angiogenic (activating) dose of ionizing ra- diation, and subsequently characterize ECs in response to this pro-angiogenic irradiation. The effects of irradiation are being studied on human lung microvasculature ECs (HMVEC-L) in order to identify the targets that could play a role in angiogenesis and tumor re-growth.

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