The Abscopal Effect and the Prospect of Using Cancer Against Itself
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By William Cavanagh,
Prostate Cancer Research Institute

Edited from PCRI Insights February, 2009 v 12.1

 

As discussed in the February 2008 issue of Insights, several clinical investigations are ongoing in the field of cancer (including prostate cancer) treatment. These investigations seek to mobilize the immune system and its highly specific destructive capability in order to impact cancer. In this article, I will highlight some further basic scientific findings that may subsequently provide evidence to use cancer as part of anti-cancer therapy. That is to say, someday we may “use cancer against itself”.

In order to try and make sense of this seeming conundrum, let’s consider a study1 published in 2004 by Dr. Sandra Demaria and others. Using four groups of experimental mice, they injected two tumors into each mouse, one injection on the left side and one on the right side. Under ordinary circumstances, both tumors will grow unabated on the mice, and ultimately will lead to the death of the animals.

As depicted in Figure 1, four different groups of mice were involved in the experiment. Group A. had no treatment Group B. received immune stimulation only; Group C. received radiation to the right-sided tumor only, and Group D. received both radiation to the right-sided tumor AND immune stimulation. (Immune stimulation in this study was achieved with Flt3 ligand, a growth factor that stimulates cells of the immune system).

Figure 1. Schematized illustration of the Demaria experiment described in the text. Arrow indicates significant slowing of the untreated tumor in Group D.

When the investigators irradiated the right-sided tumors in Groups C. and D, they were very careful to block the rest of the mouse with lead shielding so that the radiation only reached the single tumor. As noted above, Groups B. and D. received an immune system stimulant (Flt3 ligand) that is known to increase the number of immune cells, and specifically a type of immune cell called a dendritic cell.

In Group A., where no treatment was delivered, both tumors grew at a fast rate (see Figure 1). The tumors in the Group B mice – those that underwent immune stimulation only – grew at about the same rate.

In the mice that received radiation-only (Group C), the radiation was successful in impeding the growth of the right-sided tumor, which was the one that was radiated. The second tumor continued to grow as expected. But in the mice that received both radiation and the immune system stimulant (Group D), not only did the irradiated tumor slow its growth, but the growth rate of the second tumor slowed as well (arrow in Figure 1). Of the various groups of mice treated, only those that received radiation and immune stimulation showed this effect.

The Abscopal Effect

What Dr. Demaria and her colleagues demonstrated in this experiment is known as the “abscopal effect”, “ab-” being the Latin prefix for “away from”, and “scopus” being the Latin noun for “target”. In cancer treatment, an abscopal effect occurs when a particular treatment has an impact on a tumor that was not treated. The term is best known in radiation oncology2, wherein anecdotal observations have been collected for some years describing the regression of tumors in a patient who undergoes radiation treatments – but where the regressing tumors were not irradiated.

More importantly, Dr. Demaria’s group illustrated that this controversial effect is more than likely due to, or is mediated by, the immune system. The mice that underwent only irradiation of the first tumor had their second tumors grow as usual; the results were the same with the mice that underwent immune stimulation only. The mice that underwent both treatments exhibited this surprising impact on the untreated tumor.

How Does It Work?

Given these observations, it seems that both the radiation and the immune stimulation played a role in the abscopal effect seen in this experiment. Let’s examine the role each likely played, because it would be a tremendous advancement were we able to understand what was happening in these mice and to make it happen in cancer patients.

What appears to be occurring is that the radiation directed at the Group C. tumors caused cells from the tumor to die. When cells die (and I’m going to oversimplify for the sake of illustration), their contents scatter. The contents of cells are proteins, and as described in the earlier article on immunotherapy in the February 2008 issue of Insights, protein is what makes cells “do what they do”. It is very likely that cancer cells make certain proteins that allow them to grow without restraint, and to spread to different organs and grow there. The destructive nature of ionizing radiation can cause proteins to become separated from the cells that contain them, whereas a living cell holds on to its proteins pretty tightly.

Proteins are by and large the target of the immune system. Our immune systems keep us, for the most part, free from invaders (i.e. viruses, bacteria) because “their” protein differs from “our” protein. The immune system can detect this difference and can unleash an impressive display of force to eliminate the threat inside our bodies.

Because cancer in all likelihood also differs from our normal cells in terms of its protein, numerous groups of people around the world are trying to train the immune system to set upon cancer in the way it tears apart other undesirable organisms that attempt to cohabitate in the organs and tissues of humans. The difficulty has been, and continues to be, finding those proteins that differentiate cancer from our normal, well-behaved cells, with the idea that we can “train” an individual’s immune system to attack those proteins, and therefore the cancer.

This task turns out to be tougher than it sounds (and it sounds pretty tough to begin with). Each cell among the trillions in our bodies is mind-bogglingly complex. The search continues for these “tumor-specific” proteins, and it will likely go on for some time.

But, as Dr. Demaria’s work shows, maybe we need look no further than the cancer that has already revealed itself – in this case the tumors that were implanted and were growing in the mice in the study. The radiation directed at the targeted tumor seems to have caused some of the tumor mass to die, causing the protein from this tumor to become separated from the cells that comprised the tumor.

But recall that the radiation by itself was insufficient to provoke an effect on the second tumor. However, where the immune system was stimulated at about the same time – voilà – the second tumor shows an abscopal effect. What is it that the immune stimulant was able to accomplish?

The Effects of the Immune Stimulation

The immune stimulation employed in this study is known to be very effective at causing a substantial increase in the number of circulating dendritic cells (DCs). DCs are truly impressive components of our immune systems (and those of mice too). DCs can be thought of as part of the intricate sensory apparatus of the immune system. Very simply stated, DCs can pick up protein, examine it, and cause other, more aggressive, components of the immune system to attack anything that has that particular protein attached to it.

So in boosting the number of DCs in some of the mice – while destroying part of the first tumor with radiation – the immune systems in those animals were able to activate against that particular tumor, and retard the growth of the second tumor. Hence the title of Dr. Demaria’s journal article that describes these results: “Ionizing Radiation Inhibition of Distant Untreated Tumors (Abscopal Effect) is Immune Mediated”. It all makes sense now, right?

Recent Studies

In the past few years, in fact, several other studies have appeared that continue to support the idea that treatments can be designed that involve the immune system in significantly impeding the progress of cancer outside of the directly treated area. These studies all use a methodology similar to that of Dr. Demaria’s group, that is, they implant two tumors, treat one of them, and observe the effect on a tumor implanted at some distance from the treated tumor.

But rather than use an immune stimulant that increases the number of DCs throughout the mouse’s body, recent studies report a methodology that goes straight to the source: they make DCs and flood the treated (first) tumor with them. I won’t go into how one “makes” DCs, but dramatic progress these past few decades has allowed immunologists to very reliably grow millions of DCs in the laboratory.

In order to observe the abscopal effect in experimental mice, we seem to need two things: (1) we need some sort of cancer-killing (tumoricidal) treatment, and (2) we need DCs that can process what’s left of the cancer cells after they have been (at least somewhat) destroyed. As I mentioned, DCs can be provided by the millions via modern technology. But how best to disrupt the “first” cancer in order to see the effect on the “second” cancer? According to published studies, the tumoricidal treatment to the first cancer in the mouse can be radiation therapy, chemotherapy3, or cryotherapy4.

Where DCs are injected into the treated cancer, all three have demonstrated results very similar to those of Dr. Demaria. That is, where the treatments – disruption and DC – are combined optimally, a clear and undeniable abscopal effect is observed. There are most certainly other factors that are involved in getting the immune system mobilized enough to inhibit the growth of cancer, but the disruption/DC combination seems to repeatedly result in an abscopal effect on cancer in the mouse.

This would appear to be a very interesting development. As we are all aware, cancer poses its most lethal threat when it spreads to sites that are difficult to reach with anti-cancer therapy. In the case of prostate cancer, its spread to the lymph nodes, bones, and other sites serves as a devastating blow to attempts to eradicate it through any means. If we were able to employ the immune system to provoke the kind of abscopal effect observed in the mice in the above-mentioned studies, we might be able to “reach” these disseminated, or metastatic, sites by focusing on some of the cancer that we can reach with tumoricidal or cancer-disruptive treatments.

Déjà Vu?

While this idea may sound novel and promising, a young immunologist explored this notion some 40 years ago. In the late 1960s, Dr. Richard Ablin, shown in Figure 2, was consulted by prostate cancer specialists in order to explore a set of truly unusual findings: it was found that some patients with metastatic prostate cancer experienced remarkable changes in the course of their disease following cryo treatment of their prostate cancers. As you might guess, only the prostate was treated in these patients. However, known lesions involving the lungs and skeleton were observed to regress or stop growing following the treatment of the prostate. (Abscopal effect, anyone?).

Figure 2: Dr. Richard Ablin

Dr. Ablin set about exploring the possible link between the freezing of a cancerous prostate and the sudden remission of metastatic cancers that were not treated. Believing the immune system to be the conduit between local (prostate) and distant (metastatic) treatment effects observed in these patients, Dr. Ablin initiated a series of experiments designed to detect the involvement of the immune system in scenarios involving the freezing of tissues.

It is important to note that the science of tumor immunology was in its earliest infancy at that time. It could be argued that it hadn’t even been born yet. The instruments and scientific capabilities that have made possible the contemporary understanding of the mammalian immune system had simply not yet been conceived.

Nonetheless, Dr. Ablin was able to generate and publish persuasive evidence from both human and animal studies that the immune system had responded to the freezing of the prostate. In experimental animals, he was able to show that auto-antibodies (immune protein) occurred in the serum of animals after freezing of the prostate and prostate-like glands. In other words, an immune response had occurred throughout the body following the freezing of a specific gland! Dr. Ablin termed this phenomenon the “cryo-immunologic response,” and coined the term and concept of cryoimmunotherapy5.

Unfortunately, the effect seen in humans was relatively rare and did not occur reliably following cryo treatment. At the time, Dr. Ablin postulated that the status of the immune system in a given patient – for instance a debilitated immune system in some cancer patients – could significantly influence the possibilities of seeing dramatic regressions based on the cryoimmunologic principle. He called this concept “immune-staging”, and we now know that he was probably right. But given the primitive understanding and lack of technology designed to manipulate the human immune system (the dendritic cell as we know it was not yet discovered), further investigation of the cryo-immunologic response was essentially abandoned.

Recent developments and the kinds of studies described above have precipitated a renewed interest in cryoimmunology and its possible application to human cancer treatment. It is important to appreciate that the highly controlled nature of animal experiments (such as the mouse experiments described above) often results in the observations being poorly, if at all, translatable to successful human treatment. However, given what appears to be a strong underlying set of observations across several different studies, human studies are likely to follow in the near future.

A Contemporary Approach in Human Subjects

Bostwick Laboratories has designed and initiated one such study, and is currently seeking patients to participate in it. To qualify for this study, patients must have cancer diagnosed in their prostate glands as well as at a limited number (three or fewer) of metastatic sites.

Having read to this point, by now you will have surmised that the cancer in the prostate will be frozen and thawed using state-of-the-art cryotherapy technology. Between 25 and 100 million DCs will be injected into the prostate once it has been cryosurgically destroyed and thawed back to body temperature. Based on the principles outlined above, the study will seek to evaluate the possibility of an abscopal effect occurring under these circumstances.

The study treatment will also involve patients undergoing a course of low dose cyclophosphamide for six months. I encourage anyone interested in this aspect of treatment to read Immunotherapy and Advanced Prostate Cancer in the February 2008 issue of Insights. Taken together, all aspects of the study treatment are designed to take advantage of what we now know about the functioning of the immune system, and to employ and motivate the immune system in these patients to replicate the results explored by Dr. Ablin decades ago.

It is important to understand that this trial is designed to examine the safety of the study treatment that is described below (the “Phase I” part), and also to begin to explore the potential for this treatment have an impact on the outcome of the disease that is treated (the “Phase IIa” part). An outline of the study treatment appears in Figure 3, in which each step in the process is enumerated as follows.

Figure 3: Clinical Flow Chart

The “CRITICAL” Study

Bostwick Laboratories – A Phase I/IIa Trial of Combined Cryotherapy and Intra-Tumoral Immunotherapy with Autologous Immature DCs (VDC2008) in Chemo-Naïve Men with Prostatic Adenocarcinoma and Limited Metastases to Lymph Nodes and/or Bone

1.) Screening and Enrollment
This important first step involves the establishment of “eligibility” for this study. Only patients who meet a rigorous set of “eligibility criteria” will be able to enter this trial and receive the study treatment. These criteria are fairly extensive, but, importantly, they require that cancer exist in both the prostate and at three or fewer sites outside the prostate and its local lymph nodes. The cancer must have become “androgen-independent” (a state also known as “hormone-refractory”), which means that the cancer has stopped being sensitive to hormonal therapy. Typically, such a state is determined when serum PSA measurements continue to climb even while combined hormonal blockade is being administered.

It will also be required that patients NOT have undergone chemotherapy in the past, and that several laboratory tests, including measurements of blood, liver, and kidney function, are all within normal range. These are just a few of the eligibility criteria to be used in determining study status.

It is highly recommended that anyone interested in determining his own status with regard to entry to this study contact one of the study investigators – Dr. Duke Bahn at the Prostate Institute of America (888.234.0004), or Dr. Mark Scholz at Prostate Oncology Specialists (310.827.7707). A complete list of study eligibility criteria is also located on the Internet at http://clinicaltrials.gov/ct2/show/NCT00753220.

2.) Dendritic Cell Manufacturing and Testing
For a patient who has “passed” all the study eligibility criteria – and who has read and signed the Informed Consent Form for this study – the next step is a trip to Seattle, where the next study steps will take place. In Seattle, a process known as “leukapheresis” [loo-kuh’-fer-ee-sis] will take place. Leukapheresis is a bit like having your blood drawn (everybody knows what that is like) – except this blood draw can take upwards of four hours.

Given the length of the leukapheresis, you might guess that a whole lot of blood is drawn. In reality, blood is taken from the patient one “batch” at a time; the blood is processed in such a way that certain white blood cells are taken from each batch of blood, and the rest (the vast majority) of each batch goes right back into the circulation. When the process is finished, the processor has a very large number of white blood cells.

These white cells form the beginning point of the autologous (derived from self) dendritic cell product that will comprise the cells that will be injected into the prostate at the study treatment. The process of making the DCs, as well as the testing that is required to make they are ready to be injected, is complicated. But if all goes according to plan, the result of the quick trip to Seattle will result in a number of vials of the patient’s own DCs.

The reasons for the Seattle trip bear mentioning here. Basically, there are only a few places with laboratories where DCs can be manufactured. The sponsors of the study are evaluating facilities in Seattle to perform this manufacturing.

Also, recall that the leukapheresis procedure provides the beginning material for the dendritic cell manufacturing. Problem is, the cells in the leukapheresis “product” will start to die soon after they are drawn out the patient. By putting the leukapheresis process and the manufacturing process very close together, a high likelihood of generating a good dendritic cell product is ensured. the sponsors will of course pay for the trip to Seattle.

3.) Cyclophosphamide IV
This unwieldy looking word (Sigh-cloa-fos-fa’-mide) refers to a chemotherapy drug that has been used for many decades for many conditions. In this study, a very low dose of this drug will be administered into an arm vein three days before the “big” part of the treatment. The cyclophosphamide (let’s call it Cy) is intended to prepare the patient’s immune system for the treatment to follow, because Cy has been shown to reduce the numbers of an immune cell (the regulatory T cell or T-reg) that is thought to interfere with successful immunotherapy. In fact, several follow-up blood draws (the quick ones) will be performed in order to see how well this therapy is working in getting T-reg counts down.

This part of the treatment will be performed by Dr. Mark Scholz, at Prostate Oncology Specialists in Marina del Rey, California.

As you can see by skipping ahead to step 5, the Cy treatment will continue following the main study treatment, in the form of tablets that will be taken at home. The dose of Cy that is given, both before the study starts and in the tablet-based (p.o. = per orum = per mouth) therapy, is a dose that is not expected to result in the side effects that one usually thinks of when thinking about chemotherapy. However, one of the study objectives is an evaluation of how patients respond, side effect-wise, to this kind of treatment.

4.) Cryoablation and DC Injection
Now that all these preparations have been made, it is time to put the experimental treatment into action! Cryoablation of the prostate, performed by Dr. Duke Bahn, will be undertaken at Community Memorial Hospital in Ventura, California. The DCs will be shipped in their frozen state from Seattle right into the operating room, where they will be injected into a prostate cancer that has been frozen and thawed.

Drs. Bahn and Scholz will follow all study patients for approximately one year following the cryoablation/DC injection. There will be eight follow-up visits over that year, so it is important to understand the commitment made by the study patients.

If successful, the study will demonstrate that DCs made from an individual’s blood can be safely given back in tandem with a disruptive cryo treatment against a known cancer. An evaluation of whether or not such a strategy can be shown to result in an “abscopal” effect against other, metastatic, cancers will have to wait for the successful completion of this – and probably other – studies. But forward-thinking and properly planned and executed clinical trials must incorporate the latest understanding of cancer; otherwise, we will not be able to break through to the prostate

Editor’s note: see “Cancer Cryo-Immunotherapy“,
from Insights February 2006

References
1. Demaria S, Ng B, Devitt M, et al. Ionizing radiation inhibition of distant untreated tumors (abscopal effect) is immune mediated. International Journal of Radiation Oncology Biology Physics 58(3): 862-70, 2004.
2. Ohba K, Omagari K, Nakamura T, et al. Abscopal regression of hepatocellular carcinoma after radiotherapy for bone metastases. Gut 43(4): 575-7, 1998.
3. Song W and Levy R. Therapeutic vaccination against murine lymphoma by intratumoral injection of naïve DCs. Cancer Research 65(13):5958-64, 2005.
4. Machlenkin A, Goldberger O, Tirosh B, et al. Combined dendritic cell cryotherapy of tumor induces systemic antimetastatic immunity. Clinical Cancer Research 11: 4955- 61, 2005.
5. Ablin RJ, Gonder MJ, Soanes WA. Prospects for cryoimmunotherapy in cases of metastasizing carcinoma of the prostate. Cryobiology 8(3):271- 279, 1971.