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The Why: Targeting Angiogenesis in Various GI Malignancies

R. Danesi (Italy)

Romano Danesi talks about the morphology and mechanisms of angiogenesis and the drugs that target it. The presentation covers the role of VEGF – the most important mediator of angiogenesis.

Transcription

I will go through the basic concepts of angiogenesis in my presentation.

I had the chance to work with Dr Folkman many years ago when I started my anti-angiogenesis work at the NIH in Bethesda, Maryland.

Disclosures statement

These are my disclosures.

Full transcription

Full transcription

I will go through the basic concepts of angiogenesis in my presentation.

I had the chance to work with Dr Folkman many years ago when I started my anti-angiogenesis work at the NIH in Bethesda, Maryland.

Disclosures statement

These are my disclosures.

Growth factors and cells involved in angiogenesis development

Okay, so angiogenesis is a very complex process, much more complex than initially thought because as you can see in this slide, we have many factors involved in angiogenesis.

For sure, VEGF is the most important factor, the most powerful in terms of biological activity but also FGF, PDGF and other factors are involved in the process.

But also we have the cellular part of the process.  Endothelial cells are of course the most important cells involved in angiogenesis but also we know that bone marrow derived cells and also precursors are involved in the overall organisation of the angiogenesis process.

We know that angiogenesis is induced by hypoxia.  It is probably the most powerful inducer of angiogenesis and also angiogenesis induces inflammation inside the tumour and we will discuss more about the role of inflammation in the tumour.

Morphology of angiogenesis

            We consider angiogenesis inside the tumour as a chaotic process because as you can see in this slide, the organisation of the vascular pattern is abnormal, absolutely abnormal, very different from the normal pattern and this is important also for the delivery of drugs because we know that inside the tumour the delivery of drugs is reduced due to the chaotic organisation of angiogenesis, very different from normal angiogenesis.

Angiogenesis promotes cancer growth and metastasis

What we can do with angiogenesis is try to understand in which way a tumour, starting from the initial production of cells induces the angiogenetic switch to angiogenesis and tumour progression.

We know very well that VEGFR-1, VEGFR-2 and VEGFR-3 are the most important receptors involved in the process.  We don’t know exactly in which way there is a switch from a vascular tumour to a highly vascularised tumour, but we know that the actors of this process are VEGFA, VEGFB, VEGFC and other isoforms of VEGF and also placental growth factor.

Among the different receptors of VEGF, VEGFR-2 is the most important because it is involved in the induction of cell proliferation and migration.

VEGFR-3 is more involved in lymphangiogenesis and VEGFR-1 is more involved in the stabilisation of tumour vasculature.

VEGF is involved in angiogenesis, hypoxia and immunosuppressive mechanisms

Moving from this slide to this one, I would like to stress the concept that also angiogenesis is not only the production of new endothelial cells; it is also a complex process in which you have inflammation and also a tumour immunosuppression because the overproduction of VEGF induces a reduction of macrophages activity and the ?g… cells activity so the tumours in which you have an overproduction of VEGF, you also have immunosuppression.

This is a very interesting link between angiogenesis, immunosuppression and also this is the potential for new development in drug treatment.

Mechanism of action of anti-angiogenic drugs

If you look at the different drugs available for the inhibition of tumour angiogenesis, you have tyrosine kinase inhibitors like sorafenib and regorafenib.  They are multi-kinase inhibitors.  They target the tyrosine kinase activity of the different receptors, most importantly VEGFR-2 but not only VEGFR-2.

Also you have bevacizumab of course, the very strong inhibitor of VEGFA and also aflibercept and ramucirumab.

At variance with the other drugs like bevacizumab with ramucirumab you have direct inhibition of VEGFR-2.

It is very important to consider all together these drugs because you have a very important modulation of different biological passages in angiogenesis because you can reduce vascular cell proliferation, you can reduce lymphangiogenesis and you can modulate also the immunosuppression within the tumour.

VEGV is the most important mediator of angiogenesis

This slide shows you how important VEGF is in preclinical data because if you collect the data on gastrointestinal cell lines and you look at the numbers, just like numbers, you see that VEGF is highly overproduced by different cancer cell lines of gastrointestinal origin, much more than placental growth factor, IL-8 and bFGF.

Based on the preclinical data, in vitro data in particular you can see that VEGF is the most important cytokine produced by cancer cell lines in vitro.

Higher levels of VEGFR-2 in smaller tumours compared with large tumours

And also you have evidence in preclinical data again, but in vivo that for instance VEGFR-2 is associated with the early development of vasculature in cancer because as you can see here, small cancers growing inside nude mice have a very strong positivity for VEGFR-2.

If you look what happens in the large necrotic tumour, the expression of VEGFR-2 in the late phases of tumour development is reduced, so VEGFR-2 is important within the so-called angiogenic switch and this is also important to target pharmacologically.

Increased expression of HIF-1 in metastatic gastric cancer

If you also look at what happens in the gastric cancer which is the disease of main interest talking about VEGFR-2, and if you compare what happens in non-metastatic gastric cancer and also you compare what happens in metastatic cancer and you measure the amount of hypoxia inducible factor produced by cancer cells, you can see that the non-metastatic gastric cancer produces an amount of HIF significantly lower than metastatic gastric cancer.

Consider that HIF, hypoxia inducible factor is the most important factor to induce the production of VEGF inside the cells, so the over-expression of hypoxia inducible factor inside tumour cells is biologically relevant because it distinguishes between a non-metastatic and metastatic gastric cancer.

Patients with high VEGF serum levels have worse OS than those with low VEGF levels

This is also important under a clinical point of view because if you stratify the patients for instance for VEGF production, and this is a paper published in patients with gastric cancer, if you stratify patients on the basis of VEGF production and you put a cut off around the 761 pg/ml you can distinguish two populations of patients.

The first one in which the production of VEGF is lower than the cut off, the survival is longer compared to patients with overproduction of VEGF in which the aggressiveness of the tumour is much higher and the survival is much lower.

So there is an interesting link between VEGF production and tumour aggressiveness and this is reflected by this evidence in patients.  We have additional publications concerning the same issue.

From anti-angiogenic response to acquired resistance

So it is important to target VEGF – this is the proof and talking about the evolution of anti-cancer drugs and anti-cancer angiogenesis manipulation, you can see here that at the initial stage tumour growth is promoted by angiogenesis.

If you treat tumour cells with anti-angiogenesis drugs you can induce hypoxia is also associated with tumour inhibition but also the potential to elicit resistance mechanisms like overproduction of PDGF, FGF and other factors and also FGF.

So the management of tumours resistant to anti-angiogenesis agents is critical and we need to combine drugs together in a rational way.  For instance combining together anti-angiogenesis drugs, chemotherapeutic drugs is a reasonable approach.

Conclusions

And so we can conclude that VEGF has a very pleiotropic role because it plays a role in angiogenesis, in inflammation and immunity.  This is very different again compared to what we initially knew about angiogenesis because at the beginning we thought that angiogenesis was just a simple production on new blood vessels.

So angiogenesis and VEGF play a critical role in tumour biology.  There is a correlation which is very important to validate the target between VEGF production and tumour aggressive behaviour and also we know that the clinical data confirm this, that anti-angiogenic agents and cytotoxic drugs can be potentially combined.

Mechanism of action of anti-angiogenic drugs

I will leave you with this slide just to give an introduction to the following talks and again, I would like to collect questions.  If you have them, it would be a pleasure to answer your questions and this is the scenario we have today concerning the drugs we have to manipulate angiogenesis.

Thank you so much for your attention.  [Applause]

Lordick:  Thank you very much.  Just stay there because we have some minutes for discussion and this was a very, very nice overview and I think also very understandable for all of us.

Maybe my first question to you will be what was the right and the correct answer to the introductory question that we had?  We had some heterogeneity in the answers, so some percent for bevacizumab, some for ramucirumab, some for three drugs.

Danesi:  What we missed today is the biomarker of course with angiogenesis.  That would be very useful for the definition of the best treatment, but again the difference between the behaviour of patients in terms of overall survival, comparing patients with high production versus low production of VEGF tells you that VEGF, VEGF receptors and particularly VEGFR-2 are the important targets for gastrointestinal cancer management.

Lordick:  Are there any questions from you, from the audience?  You can write me an email and you can also go to the microphones and ask questions.

I also want to make you aware that there were some of you who took photographs.  It’s always good when you are taking photographs, we realise that you are really interested in what is shown, but just remember that all the slides will be available on the GI cancer resource website which I showed to you at the beginning.  All the talks will be available there and you can copy it and look at the pictures there.

There was one question that came to my mind when you showed the I would say nice prognostic discrimination, high VEGF levels, low VEGF levels.  It seems to be relatively easy to define prognostic factors in this cascade, but why according to your opinion and expertise have you not been successful yet to identify strong predictive factors?  Why is this so difficult?  Is it a systemimmanent problem or did we not do the right research yet?

Danesi:  Perhaps the right answer is that we have many actors in angiogenesis, so it depends on the stage of angiogenesis; early versus intermediate versus late.  It depends on the drugs used to manage angiogenesis, so it is difficult to say this is the right biomarker because the process is very complex, there are many cells involved, there are many factors involved.  There is a pressure of anti-angiogenesis treatment, so it is a dynamic process and it is very difficult to understand in which way a biomarker could help you, but we will see probably in the future.

Lordick:  This brings me to one of the questions that was asked via email and it is; is there any benefit of combining anti-angiogenic compounds or is there any sequence which might be useful if it’s such a responsive network?

Danesi:  It’s interesting to think about the development of resistance.  For instance, a tumour starts with VEGF as a main actor and then perhaps under the selective pressure of combined anti-angiogenesis and chemotherapeutic agents might over-express additional factors like placental growth factor.

We know that if you treat cells with a cytotoxic agent you increase, for instance, the expression of VEGF in placental growth factor so the combination or the sequence of anti-angiogenetic agents is an important issue.

Lordick:  But it’s not yet proven which sequence is the best?

Danesi:  That’s right, yes.

Lordick:  So a lot of space for clinical studies.  There is another interesting question for you as a clinical pharmacologist; is there any cytotoxic agent which is the ideal backbone or combination partner for anti-antiogenic drugs?

Danesi:  Taxanes are perhaps the first cytotoxic agents demonstrated to have also anti-angiogenic activity, so it makes sense to combine like taxane, like paclitaxel with anti-angiogenic agents.

Also we have preclinical evidence of the inhibitory activity of irinotecan on hypoxia inducible factor and again it makes a potential reason to combine these agents.

Lordick:  Maybe one last question probably according to the schedule; when we look at this graph here there is also one question targeting angiogenesis via the ligand VEGF inhibition.  Is it different from targeting another receptor, VEGFR-2 or other targets?

Danesi:  Targeting for instance VEGFR-2 is important because as you can see in this slide, there are different isoforms of VEGF to bind VEGFR-2.  So under a pharmacological point of view, if you block the VEGFR-2 you reduce the ability of all the ligands to bind the receptor.

So it’s a different way.  Perhaps it’s more effective in terms of number of ligands that you can block.

Lordick:  Thank you very much.