Could A Neurotoxin Be The New Treatment for Bone Cancer Pain?

There are few diagnoses feared more than cancer. And, few conversations more difficult to discuss with clients than bone cancer. Clients walk in the clinic with what they believe is a simple limping dog and leave with a death sentence and a few months left to enjoy their pet.

By the time we diagnose these tumors they have usually spread. We may not see evidence of those satellite tumors in the chest, but odds are they are there, small, quiet, unorganized, lurking and waiting.

These cases require a patient, calm, repetitive approach. Clients need time to accept, understand, and process the diagnosis. They also need time to come to terms with the treatment options available to them.

I have written about osteosarcoma's and my personal opinions and belief that the one thing we must do for these patients is provide them with some way to manage their pain. Bone tumors are excruciatingly painful. So much so, that pets will refuse to move, eat, or interact on any level just to avoid moving because the pain is so intense. My advice, based on years of practicing and dozens of patients, has always been the same; Get rid of the pain by getting rid of the source. Amputate that useless limb that is killing your pet and killing their ability to live a pain free life for whatever amount of time they have left. They don't use that leg anyway, so get rid of it. I promise they won't miss it and they won't feel bad about looking "disfigured."

But, alas, I am not always able to convince my clients that this is the right decision. And at some point there are no opioids, steroids, NSAID's, or options left to manage their pain. These pets are put down because we cannot keep them comfortable.

It was with great delight and interest that I found the following article on a new treatment option for these patients.

Researchers at the University of Pennsylvania School of Veterinary Medicine injected a single dose of a SP-PAP, a neurotoxin, into the spinal cord, under general anesthesia, and found that the patients receiving the neurotoxin in the study were considerably less painful than those without it. The results were so promising that the drug and study is expected to be used for humans. 

Maybe someday very soon I can offer this instead of euthanasia as a way to keep my patients comfortable?

Please read more about bone tumors and treatment options at Heidi's Story.

Article abstract follows:

Intrathecal substance P-saporin in the dog: efficacy in bone cancer pain.

Anesthesiology. November 2013;119(5):1178-85.

Dorothy Cimino Brown¹; Kimberly Agnello

¹* Professor of Surgery, † Assistant Professor of Surgery, Department of Clinical Studies - Philadelphia, University of Pennsylvania, School of Veterinary Medicine, Philadelphia, Pennsylvania.

Article Abstract

BACKGROUND: Substance P-saporin (SP-SAP), a chemical conjugate of substance P and a recombinant version of the ribosome-inactivating protein, saporin, when administered intrathecally, acts as a targeted neurotoxin producing selective destruction of superficial neurokinin-1 receptor-bearing cells in the spinal dorsal horn. The goal of this study was to provide proof-of-concept data that a single intrathecal injection of SP-SAP could safely provide effective pain relief in spontaneous bone cancer pain in companion (pet) dogs. METHODS: In a single-blind, controlled study, 70 companion dogs with bone cancer pain were randomized to standard-of-care analgesic therapy alone (control, n=35) or intrathecal SP-SAP (20-60 µg) in addition to standard-of-care analgesic therapy (n=35). Activity, pain scores, and videography data were collected at baseline, 2 weeks postrandomization, and then monthly until death. RESULTS: Although the efficacy results at the 2-week postrandomization point were equivocal, the outcomes evaluated beyond 2 weeks revealed a positive effect of SP-SAP on chronic pain management. Significantly, more dogs in the control group (74%) required unblinding and adjustment in analgesic protocol or euthanasia within 6 weeks of randomization than dogs that were treated with SP-SAP (24%; P<0.001); and overall, dogs in the control group required unblinding significantly sooner than dogs that had been treated with SP-SAP (P<0.01). CONCLUSION: Intrathecal administration of SP-SAP in dogs with bone cancer produces a time-dependent antinociceptive effect with no evidence of development of deafferentation pain syndrome which can be seen with neurolytic therapies.

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