Osteosarcoma (OSA) is a highly aggressive and painful bone tumor that affects approximately 10,000 dogs per year in the USA and accounts for approximately 85% of all canine bone tumors. It most frequently affects the long bones of adult large and giant breed dogs including Irish Wolfhounds, Rottweilers, Labradors, Greyhounds, Newfoundlands and Great Danes. Although osteosarcoma initially appears as a local swelling oftentimes at the carpus (wrist), proximal humerus (shoulder) or distal femur/proximal tibia (knee), cancerous cells are thought to spread early in the course of disease from the primary bone tumor to the lungs and other bones. Indeed it is estimated that 90-95% of dogs have microscopic tumor spread (metastasis) at the time of diagnosis. The current standard of care treatment for OSA in dogs consists of limb amputation to remove the painful primary tumor, followed by systemic chemotherapy. Systemic chemotherapy is given after amputation to eliminate any cancer cells that have already spread away from the primary site. Although follow up chemotherapy significantly prolongs survival when compared to amputation alone, approximately 60% of patients still die within one year of diagnosis from tumor spread to the lungs and bone.
In order to improve the survival of dogs with osteosarcoma, we need to be more effective at targeting and killing the tumor cells that remain in the patient’s body after amputation and chemotherapy. If these cells can be effectively identified and destroyed then the chances of tumor recurrence and death due to osteosarcoma should be dramatically reduced.
“Cancer immunotherapy” describes the use of the patient’s own immune system to specifically target and kill tumor cells. Just as the immune system can specifically target and kill viruses or bacteria, it can also be activated to target and kill cancer cells. Therefore, if the immune system could be taught to recognize cancer cells (by vaccination) then it may be possible for it to destroy tumor cells that remain in the body after amputation and prevent tumor recurrence in dogs with osteosarcoma.
Over 100 years ago, an orthopedic surgeon at Memorial Sloane Kettering, names William Coley, injected a concoction of live bacteria into his human patients with osteosarcoma1. He documented some complete remissions in people that were known to have aggressive disease using this early form of “immune therapy.” More recently other investigators have used different strategies to activate the immune system in dogs with osteosarcoma to try to achieve the same effect2-4. Interestingly in these studies, the use of “immune therapy” prolonged overall survival in a number of dogs with osteosarcoma, after amputation. Finally, it is known that dogs that develop bacterial infections at the surgical site after amputation tend to have longer survival times than dogs that do not develop infections at the surgical site, again suggesting that activation of the immune system (in this case by the natural bacterial infection) may help in preventing the tumor from recurring5.
Taken together, these findings suggest that osteosarcoma might be a cancer that is amenable to immune therapy. To enhance the success of immune therapy and to reduce the chance of adverse side effects, it is necessary to identify a particular marker that is uniquely expressed by the cancer cells. The immune system can then be trained to recognize cells that express this marker and then kill them. Osteosarcoma cells express a marker known as Her2/neu (the same marker found in some women with breast cancer)6-9. Training the immune system to recognize and kill cells that express Her2/neu represents a promising strategy to treat osteosarcoma in dogs.
Ongoing phase I clinical trial in dogs with OSA
We are currently performing a phase I clinical trial to evaluate the safety and therapeutic effects of a genetically modified bacterial vaccine known as ADXS31-164 in dogs with naturally occurring OSA. The vaccine, which is supplied by Advaxis Inc. (North Brunswick, NJ) consists of a bacteria known as Listeria monocytogenes (L. monocytogenes) that has been modified to express Her2/neu. Her2/neu is a growth factor receptor that is expressed to different degrees on cancer cells including canine osteosarcoma cells. The Listeria bacteria induces a potent immune response and, as the bacteria also carries the Her2/neu protein, it will stimulate the patient’s immune system to recognize and kill target cells that express Her2/neu. Could this vaccine be used safely to stimulate the patient’s immune system against osteosarcoma cancer cells that express Her2/neu? Could this result in improved survival times for dogs with osteosarcoma?
Dogs that have been diagnosed with osteosarcoma and that have undergone the standard of care treatment that includes limb amputation and follow up chemotherapy with 4 doses of carboplatin are eligible for enrollment in this ongoing study. Prior to enrollment the dog’s bone tumor is evaluated in our laboratory to determine whether the tumor cells express the target protein (Her2/neu). Dogs with Her2/neu positive and Her2/neu negative tumors are both eligible for trial enrollment. Recent data suggests that the tumor cells that are responsible for forming metastatic disease (tumor initiating cells) express Her2/neu regardless of the Her2/neu status of the primary tumor8. Therefore dogs with Her2/neu negative primary tumors may also benefit from vaccination.
Three weeks after receiving their last chemotherapy dose, potential trial candidates are evaluated at the University of Pennsylvania’s School of Veterinary Medicine. The initial screening of these patients includes full blood work, urine analysis, immune function analysis, chest radiographs and a full cardiac evaluation. Only dogs that are healthy with no other disease processes and no evidence of heart disease are eligible for the study.
All dogs receive the vaccine. There is no placebo control group. The dogs receive one vaccine every 3 weeks for a total of 3 vaccines. The vaccine is given intravenously and the dogs are hospitalized at the University of Pennsylvania’s Veterinary School for the day. Following completion of the vaccines, all the dogs are re-examined at UPenn every 2 months. During this time, they have chest radiographs taken, a cardiac evaluation performed and full blood work and urinalysis to make sure they remain systemically healthy.
Side effects of the vaccine
To date we have vaccinated a total of 12 dogs. Side effects of the vaccine have been minimal and include mild fever several hours after vaccine administration, which resolves spontaneously within a few hours.
Efficacy of the vaccine
While it is still too early in the course of the study to definitively say whether the vaccine is effective at increasing overall survival in dogs diagnosed with OSA, our preliminary results are very encouraging. Our first vaccinated dog, Sasha was diagnosed over 570 days ago and two more of our dogs vaccinated at the beginning of the study are alive and cancer free over 500 days post diagnosis. Other dogs that were vaccinated more recently are still doing well. We have now started to re-vaccinate long-term survivors on the study. The concept of re-vaccination is to boost the immune system so that it may continue to recognize and kill any cancer cells that may remain or arise again in the body. Given that the side effects of the vaccine are mild, the potential benefit of repeat vaccination outweighs the risks.
What is next for immune therapy of canine OSA?
Our initial phase I clinical trial aimed to evaluate the safety of the bone cancer vaccine ADXS31-164 and its ability to prolong overall survival in dogs that have undergone standard of care amputation and chemotherapy. However, some dogs are unable to tolerate limb amputation due to their large size or concurrent orthopedic or neurological problems. Treatment options for these dogs are limited and usually consist of palliative radiation and pain management using drugs such as tramadol and carprofen. Overall survival of dogs that undergo palliative radiation with pain medications is about 4 months. We are now interested in determining whether ADXS31-164 could be effective in dogs that have not undergone limb amputation but have instead received either palliative radiation or stereotactic radiation (CyberKnife). Although immune therapies generally function most effectively when there is a minimal amount of cancer in the body (i.e. after limb amputation when the large primary tumor has been removed), there are indications that radiation therapy and immune therapy function synergistically to increase an anti-tumor immune response. We believe that the effects of the radiation on the primary tumor will reduce the number of viable tumor cells (and reduce associated pain) and promote immune responses against tumor cells. We therefore are now initiating a clinical trial to determine whether palliative radiation followed by vaccination with ADXS31-164 can prolong overall survival in dogs that cannot undergo amputation. We hypothesize that combination radiation and immunotherapy may act together to kill the primary cancer cells and prevent tumor spread from the primary site. In this trial, all patients will receive palliative radiation (2 doses on 2 consecutive days) and then they will be randomized to receive either ADXS31-164 or a placebo. Dogs will receive either the ADXS31-164 vaccine or placebo every three weeks for a total of 8 times. Dogs will be evaluated every three weeks and assessed for lameness and pain, overall well-being and any evidence of tumor spread. This is a unique trial that combines two cancer treatment modalities (radiation and immune therapy) in an attempt to improve the outcome of large and giant breed dogs with osteosarcoma.
In summary, previous work has shown that osteosarcoma may be an “immune responsive” tumor and that the concept of preventing tumor spread using the immune system holds much promise. Furthermore, in light of our early trial results, the vaccine appears to be safe and vaccinated dogs are showing prolonged overall survival when compared to unvaccinated controls. There is still much work to do: Our studies will continue and as more patients are treated, survival trends will become apparent and statistically significance for outcome will be determined. We will also add an additional protocol to our studies to see if the same increases in overall survival would be obtained by vaccinating dogs that do not undergo amputation and receive only palliative radiation. One also wonders whether there would there ever be a scenario for prophylactic vaccination – to prevent osteosarcoma in dogs that may be predisposed to this disease. The future for this approach is exciting and it looks set to offer an additional potent weapon in our arsenal against osteosarcoma.
If you have a dog with osteosarcoma and are interested in participating in either of these trials please contact Dr. Nicola Mason at 215 898 3996 or by e-mail at firstname.lastname@example.org
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