A study at Colorado State University’s Animal Cancer Center is looking at a new way to treat cancer in animals and people. The study is investigating the impact of a drug on cells that suppress the immune system and allow cancer tumors to grow. Initial results in mice and dogs show that the drug can reverse suppression of the immune system and halt tumor growth in dogs and, in some cases, even shrink tumors.
Researchers are enrolling dogs who meet specific entry criteria into clinical studies designed to evaluate the safety and efficacy of a new drug delivery approach. The class of drugs being evaluated, called bisophosphonates, has been used for years to diminish bone pain in bone cancer patients. However, the studies at the Animal Cancer Center are looking at bisphosphonate drugs in combination with liposomes to target cells that suppress the immune system around specific types of tumors.
“To date, nearly a dozen dogs have been treated in the study. The tumor response rate — shrinkage of the tumor or suppression of growth — has been very encouraging,” said Dr. Steve Dow, a researcher and veterinarian in the Animal Cancer Center.
When the drugs are incorporated into liposomes, they target a population of white blood cells known as myeloid suppressor cells or MSC. When a person or animal develops cancer, the patient’s immune system may be suppressed by large numbers of MSC stimulated by the cancer. As tumors begin to grow, the number of MSC cells rises dramatically and the immune system becomes more suppressed. Liposome incorporated bisphosphonates, called liposomal bisphosphonates, target myeloid suppressor cells in tumors and the bloodstream and spleen, reversing their crippling effects on the immune system. This allows the body’s natural defenses against cancer cells to kick back into action. Initial research shows that the liposomal bisphosphonates may be effective against a number of different types of tumors.
“We believe the results will provide important insights into a new way of fighting many different kinds of tumors. If the results continue to be promising, they may help treat animals and humans with many different types of tumors,” Dow said.
MSCs also have a normal function in the body, responding to various infections by monitoring the immune system response. They keep the body’s natural immune response in check, preventing an exaggerated immune response that is harmful or fatal to the individual. In the case of cancer, MSC’s response to the cancer is normal, but unfortunately leads to the side effect of immune suppression, Dow said.
For the current clinical studies, Dow is working with Drs. Scott Hafeman, Amanda Guth and. Joe Sottnik in the Animal Cancer Center. The team is looking for dogs with soft tissue sarcomas and malignant histiocytosis, called MH, to enroll in the clinical trial.
Dogs with MH are often given a prognosis of only two to three months without treatment. These tumors are highly resistant to chemotherapy, and other options for treatment are limited. Dogs with soft tissue sarcomas, which are often located on limbs, have more options, such as surgery, amputation and radiation. They also are typically given a longer prognosis of six months to a few years. The use of MSC inhibitors such as biophosphates would not replace other treatment options, but would complement the existing opportunities to treat the disease.
Dogs that meet certain criteria can be enrolled in the studies. The soft tissue sarcoma study pays $500 toward the cost of treatment, such as surgery, at the end of the study. The study consists of six treatments over a time frame that ranges seven to 13 weeks, depending upon the treatment option that is selected. Dogs enrolled in the MH study are eligible to receive the drug at no cost, though all other charges are supported by the owners. To discuss opportunities to enroll in the study, contact the Animal Cancer Center at 970-221-4535 and talk to Dr. Scott Hafeman.
These studies are being supported by the Morris Animal Foundation, the Canine Health Foundation and the National Institutes of Health.