DR. SCHILDER: Our next speaker is Dr. Anil Sood from M.D. Anderson, who is going to take us through some issues on angiogenesis, and maybe some immune modulation as well.

TOP

Good morning, and thanks very much for giving me this opportunity to discuss antiangiogenic approaches.

My charge was to, today, really discuss in broad spectrum, really, the applications or potential relevance of antiangiogenic approaches.

So, I won't discuss as much of the direct preclinical data, but really discuss broad concepts related to tumor blood vessel development, and then followed by what are some of the rationales for antiangiogenic therapies, along with some of the emerging approaches that might be used.

Finally, I will discuss also some of the methods of assessment of responses in patients who get treated with these newer forms of therapies.

TOP

So, prior to, I think, initiating, or as we initiate, these kinds of studies, it is really important to also understand the mechanisms by which tumor blood vessels develop.

The traditional concept had been that tumors start as a vascular, small mass, and for it to go beyond one to two millimeters, that it would become hypoxic on its own, that really, the tumors would secrete pro-angiogenic factors. Those would then recruit blood vessels from the outside, and that would be the concept of angiogenesis.

Over the last few years, we have learned that, really, blood vessels and tumors are not that straightforward. It is not just that angiogenesis alone occurs.

There are other processes, such as vasculogenesis, whereby the precursor cells arrive and play a role in blood vessel development.

This concept of vessel co-option was introduced about five or six years ago, whereby initially the tumor mass, as shown here in blue, starts to attach to the existing blood vessels, and then the tumors produce factors, such as ANJ-2, that result, actually, in destabilization of the whole vasculature, and that the traditional angiogenesis really occurs more as a secondary event after central necrosis in a tumor occurs.

Blood vessels in tumors are even more complicated. So, beyond vessel co-option, other processes such as mosaic vessels have been described, whereby both endothelial cells and tumor cells line these blood vessels, along with a concept called vasculogenic mimicry, whereby tumor cells might play a role in actually directly developing a component of the vasculature in tumors.

TOP

The balance of factors that control blood vessel development in tumors has really shifted more toward the activators.

These are the kinds of molecules that might form the basis of newer therapies. These include some of the common ones that you have seen, such as VEGF, basis FGF, PDGF and so on, and some of the newer ones that will be emerging, such as the efrin zen-F receptors as well as integrins.

The inhibitors, for the most part, are downregulated in tumors, or the proportion of balance, again, has shifted more toward the pro-angiogenic side.

TOP

In addition, the blood vessels have at least two components. There are what are known as pericytes, which are mesenchymal in origin.

If you notice, the normal blood vessels on the left-hand side have -- the blue stain is the stain for pericytes, which are very, very tightly attached to the blood vessels.

If you notice a blood vessel in a tumor, the red shows CD31 for endothelial cells, the green shows pericytes. The pericytes are present, but they are abnormal, both in shape and in attachment, such that they also point toward the stroma.

However, we have learned that pericytes actually provide a survival advantage for blood vessels, such that as tumors develop, the blood vessels become more mature, and they become coated by pericytes, and opportunities to attack both of these pericytes and endothelial cells might provide even better antivascular approaches as we move forward.

TOP

Next, I will briefly discuss some of the antiangiogenesis approaches that might be relevant for ovarian cancer.

TOP

This was really one of the most exciting developments that, in 2004, bevacizumab was FDA approved. This was really the first antiangiogenic approach that came to fruition after close to three decades of work, and the pivotal trial, as most of you know, was performed in colorectal cancer. That was a positive study, in combination with chemotherapy.

TOP

VEGF is clearly a critical molecule for ovarian cancer and other cancer vasculature. Initially it was described as VPF by Hal Fvorak, and it is, indeed, a permeability factor. That is how it was initially described. It is a mitogen for endothelial cells.

I highlighted this, because this is really the basis for antiangiogenic or antivascular approaches, that it is a key survival factor for endothelial cells.

Endothelial cells, in normal blood vessels, on average, divide once every three to five years, whereas, in tumor blood vessels, they divide more frequently.

Regardless, for a cell to survive for that length of time, there have to be factors that provide survival mechanisms. It has been clearly shown that VEGF plays a role in ovarian cancer growth, as well as endocytes production.

TOP

There have been many approaches that have been utilized for VEGF. The studies in ovarian cancer, specifically, to date, have focused on bevacizumab, which is a monoclonal antibody.

However, there are additional approaches, such as decoy receptors, the so-called VEGF trap, that might have even higher affinity, and might be an even more useful method for attacking VEGF. However, clinically, this is still in very, very early stages.

There are many other approaches, including small molecule tyrosine kinase inhibitors. PTK787 is primarily a VEGF receptor inhibitor. It also has some PDGFR activity.

Similarly, SU-11248,8778 is a dual EGFR and VEGFR inhibitor that is just completing phase I studies and, again, there are several other small molecule inhibitors that are being studied at present.

TOP

So, what is the rationale for combining angiogenesis inhibitors with chemotherapy? I think there are really multiple things that one has to consider, including that there are independent effects.

Given the key role that some of these factors play in survival of endothelial cells, if you knock out these factors, you can sensitize the endothelial cells to chemotherapy.

Other methods might include decreasing the interstitial pressure, and favoring diffusion of chemotherapy.

Tumors, by nature, are hypoxic in their environment and they have high interstitial pressure that might interfere with access to not just chemotherapy drugs, but even some of the other molecules, such as antibodies.

So, these approaches might actually reduce hypoxia and, furthermore, reduce production of endothelial growth factors, especially molecules that attack key conversing points such as SARC and, furthermore, reduce secretion of soluble tumor growth factors.

TOP

These therapies are not necessarily benign. Many of the angiogenic factors don't occur in isolation in tumors. They also play a critical role in normal physiological processes.

As a result, if you inhibit some of these molecules, you will see toxicity. So, hypertension has now been well described. It seems to occur anywhere form six percent up to 12 percent of patients. It can be controlled with antihypertensives.

Again, it makes sense, because the nitric oxide pathway through endothelial cells is modulated by anti-VEGF therapies.

You can have thrombosis and bleeding. Why? Because VEGF controls tissue factor, as well as it controls anti-fibrinolytic molecules, such that the relative changes in those molecules will determine whether thrombosis or bleeding will occur.

Proteinuria can occur, because mesangeal cells are affected by ant-VEGF therapy, and delayed wound healing and bowel perforation, although uncommon, are certainly very worrisome.

In the Herwitz phase III study, with colorectal cancer, six patients, or 1.5 percent of the patients, developed a bowel perforation. One died, five recovered, and three of those patients actually resumed therapy with no subsequent complications, the point being that certainly these kinds of complications one has to be mindful of, and think about strategically where is the best time, after surgery, that these kinds of therapy should be considered.

TOP

Now, briefly I just show you two slides on preclinical data, especially related to VEGF-trap, and paclitaxel chemotherapy.

This is a study whereby, in nude mice, in an orthotopic setting, the alpha-guard III cells were implanted. The four arms are control, VEGF-trap alone, paclitaxel, and then the combination.

You will notice that, in either agent alone, you see about a 50 percent inhibition of tumor growth, but look what happens. When you combine the two, you see a remarkable suppression of tumor growth. A site is essentially eliminated.

Again, this is at least an additive effective. I am cautious about calling something synergistic. However, this is at least an additive effect, primarily because you are sensitizing the endothelial cells by taking away its survival factor.

TOP

What is the evidence for the vasculature? These are lectin profusion studies that demonstrate a very tortuous and complicated blood vessel system in the control tumors.

By treating with VEGF trap alone, you can normalize the vasculature to a certain extent. The blood vessels become more straight, and they become less dilated as well.

Taxol alone has some effect, but combination has a remarkable effect in normalization and suppression of tumor vasculature.

TOP

I think we have to reconsider how do we give chemotherapy and what relevance does that have for novel therapeutic approaches.

About six years ago, a concept called metronomic schedule of chemotherapy was introduced. . The concept of metronomic therapy is based on using one tenth to one twentieth of chemotherapy dose, of what an MTD dose would be. However, there are no prolonged breaks in the schedule.

Weekly chemotherapy is only semi-metronomic. It is not a true metronomic schedule of chemotherapy. A true metronomic schedule is, essentially, a daily administration of chemotherapy.

However, the primary target is the endothelial cell, or the host in this setting, not the tumor cell. This schedule may have enhanced antiangiogenic and pro-apoptotic activities.

It seems to have fewer systemic side effects because of the lower doses of chemotherapy, and certainly early studies demonstrate potential feasibility for long-term treatment.

TOP

Dr. Burger has already mentioned some of these studies, and the 170D study with VEGF antibody or bevacizumab, where even alone there were responses seen, around 18 percent in this particular study.

Then the second study is with metronomic cytoxan, given orally continuously, in combination with bevacizumab, where even a higher response rate was seen in a recurrent setting.

TOP

Again, the side effects from these therapies are not unexpected, and have been seen similarly in other tumor types. GI hypertension, and some proteinuria have been seen.

TOP

So, some of the planned clinical trials, again, I will go through this fairly rapidly, because most of you will know these already.

TOP

GOG-218 is going to have Taxol carboplatin with a placebo versus bevacizumab, and then there is a consolidation arm to ongoing treatment with bevacizumab.

TOP

GOG-213, as many of you know, has gone through multiple permutations. However, this is the final schema that has been settled on. Again, because of time, I won't go through all the details, but it takes advantage of combining chemotherapy with bevacizumab, plus also in colon cancer, there is data to show that this particular combination is even more appealing, and there have been higher response rates demonstrated.

TOP

This is a SPORE trial that will be initiated at M.D. Anderson briefly. It is a combination of VEGF trap, with a lead-in phase, where VEGF trap alone is given, and then docetaxel will be added, starting with the second cycle.

In order to understand the mechanisms by which these therapies might work, we are going to asses multiple surrogate markers, including tissue imaging, as well as circulating endothelial cells, as well as circulating precursor cells, to assess the efficacy of this approach.

TOP

So, now, again, some broad concepts. As we enter this era of antiangiogenesis approaches, how should we assess patients?

There are, to date, no validated tests that are present. However, there are many that I think hold potential for answering these questions.

So, with regard to imaging, one could use dynamic MRI to look at changes in both blood vessel permeability as well as perfusion, pep-4 metabolism, and then tissues for surrogates, such as a hair follicle assay for EGFR phosphorylation, circulating markers such as cytokines, circulating endothelial cells, and even circulating nucleic acids which, in early preclinical studies, seem to demonstrate potential for monitoring.

TOP

In the last couple of slides, I really want to discuss a couple of other points, which are related to the traditional ways of developing any therapy have been based on maximal tolerated dose, or MTD.

I think some of these concepts are perhaps not realistic for biological therapies. With some of the antiangiogenic approaches, MTDs are not reached.

Really, the concepts perhaps should go more toward optimal biological dose, or another word being biologically effective dose. How does one assess that? I think that has to be answered, perhaps using surrogate markers.

Scheduling certainly is a key issue, whether some of these therapies should be given simultaneously, in certain other sequences…

Surrogate biomarker assays have already been mentioned, optimal clinical settings, such that toxicity, at least, has to be considered, whether or not some of these therapies are given right after surgery or not.

Then, novel combinations and delivery methods will certainly come about, and then vascular targeting agents are newer therapies that actually seem to collapse the core circulation of tumors.

TOP

In conclusion, ovarian cancer is really an excellent model for antiangiogenic therapies, and preclinical data suggests at least additive effects of antiangiogenic therapy with chemotherapy.

TOP

With that, I would like to acknowledge several members of the lab as well as collaborators, and support from the NCI for our work. Thank you.

TOP