"Growth Hormone Supplementation in Dogs" TUMOR TIDBITS, A BIWEEKLY VETERINARY ONCOLOGY E-LETTER Number 64; August 9, 2002. Editor: Kevin A. Hahn, DVM, PhD, Dipl - ACVIM (Oncology) & Overall Nice Guy! ANNOUNCEMENTS *We are continuing to enroll dogs with lymphoma in our clinical trial evaluating an antiangiogenic (anti-blood vessel) agent. *We anticipate this fall enrolling dogs with hemangiosarcoma in an antiangiogenic clinical trial. *We are offering growth hormone (see today's Tidbit below) in dogs using a novel delivery method requiring one treatment with lasting positive effects. *Did you know that the most common and unrecognized syndrome in pets with cancer is wasting (cachexia)? Check our web site regularly for additional information and updates. Subscribe to our weekly email newsletter online! Call any of our 3 Oncologists (Hahn, King, Carreras), 2 Oncology Residents (Freeman, Turner) or our Oncology Nurses Monday-Friday or email Dr. Hahn for more information and patient consultations. ============================================ THIS WEEK'S TUMOR TIDBIT: GROWTH HORMONE SUPPLEMENTATION IN DOGS ============================================ WHAT IS CACHEXIA Cachexia is a classic clinical phenomenon, defined as accelerated loss of skeletal muscle can occur in the setting of cancer as well as in other chronic conditions. Weight loss, anorexia, muscle wasting, loss of adipose tissue and fatigue are characteristics of cachexia, and resulting in poor performance status. In addition to poor prognosis and impaired response to therapy, cachexia may be a direct cause of death. In this condition, patients have increased breakdown of proteins, decreased protein synthesis, negative nitrogen balance, increased basal energy expenditure- hypermetabolism, inadequate intake and reduced absorption add to these metabolic aberrations. Cytokines (TNF alpha, IL6, IL1beta) are the mediators of above metabolic state and are postulated to cause this syndrome. WHY GROWTH HORMONE Growth Hormone (GH) synthesis and secretion from the anterior pituitary is stimulated by growth hormone releasing hormone (GHRH), a hypothalamic hormone. GH secretion is effected at exceedingly low levels of GHRH (ca. 100 pg/ml) in the blood. Recombinant GH is also used as an anabolic agent in burn, sepsis, and AIDS patients, but resistance to GH action has been reported in malnutrition and infection. Exogenous GH administration has an anabolic effect on skeletal muscle in dogs. GH use has many clinical indications with beneficial effects, but therapy is associated with disadvantages: GH must be administered subcutaneous or intramuscularly once a day to three times a week for the entire length of the treatment; patients often present insulin resistance and impaired glucose tolerance. Alternative approaches for increasing GH action include the use of GHRH (to stimulate the synthesis and secretion of all GH isoforms; the molecular heterogeneity of such isoforms may have important implications in growth and homeostasis. Numerous studies have shown that continuous infusion with GHRH restores normal GH pulsatile pattern with no desensitization of GHRH receptors or depletion of GH supplies in humans, sheep or pigs. At the same time, this system is capable of maintaining an appropriate physiological feedback mechanism that is totally abolished in exogenous GH therapies. No side effects have been reported for GHRH therapies, while the beneficial effects of the therapy are proven. Chronic GHRH treatment in Beagle dogs results in a significant elevation in IGF-I that corresponds to an increased observation of GH related responses such as increased bone growth and mineral density. GHRH has a short half-life in plasma; therefore, intravenous or subcutaneous administration is necessary. As a chronic therapy, recombinant GHRH administration is not practical. A plasmid mediated therapy approach will overcome this primary limitation to recombinant GHRH use and may be preferable as data in animal models suggests that a single injection into the patients skeletal muscle would ensure physiologic GHRH expression for a long period of time. PRECLINICAL RESULTS To counteract catabolic state, anabolic agents have been studied. It has been shown in preclinical studies that, anabolic hormones like GH, IGF-I and IGF binding protein 3 (IGFBP-3) are effective in producing a benefit in cancer cachexia. GH is effective in increasing weight, lean body mass and work output in patients with cachexia due to acquired immune deficiency syndrome (AIDS). Our studies using GHRH are founded on several lines of supporting evidence, both direct and indirect: i) The GHRH-GH-IGF-I pathway has the ability to favor anabolic over catabolic processes even in critically ill patients. Stimulation of the GH-IGF-I axis reduces the number and dimension of metastasis in a cancer model or it has no effect on tumor growth. Old mice, treated with a growth hormone secretagogue for 3 weeks exhibited a statistically significant increase in thymic cellularity and differentiation. When inoculated with a transplantable lymphoma cell line, EL4, the treated old mice showed statistically significant reduction in tumor size and metastases. Patients with AIDS cachexia, in whom the causal mechanisms likely overlap with cancer cachexia, have benefited from stimulation of the GH/IGF-I axis. WHAT IS ELECTROPORATION Direct intramuscular plasmid DNA injection followed by electroporation is a method for the local and controlled delivery of plasmid DNA into skeletal muscle. It has the advantage that it uses very low plasmid quantities per kilogram of body weight, rather than the high quantities typically used with passive delivery modalities. Electroporation has been used to transfect tumor cells after injection of plasmid DNA, or to deliver the antitumoral drug bleomycin to tumors in humans. Electroporation also has been used in rodents and other small animals, and in our previous experiments the technique was successfully used to enhance plasmid DNA uptake and expression to pigs. WHY USE IT IN CANCER PATIENTS In combination, these characteristics make it possible to treat cachectic cancer patients with plasmid derived GHRH. In this study we show that plasmid GHRH therapy stimulates GH and IGF-I release. This directly improves the patients immune function and the anabolic state of the patient observed as increases in hemoglobin, hematocrit, red blood cell counts, and total serum protein values. TNF-alpha, a major indicator of cachexia, is decreased. Clinically, enhanced immune function, reversal of treatment- associated anemia and cancer-associated wasting with a return to normal body composition is observed. The technique described in this report warrants further investigation as a measure to improve the cancer patient's quality of life and potentially their survival. OUR METHODS A myogenic plasmid vector expressing GHRH was delivered intramuscularly into 15 dogs with advanced stage of spontaneous cancer and incorporated into the myocyte by electroporation. Red blood cell count, hematocrit, hemoglobin, level of circulating lymphocytes, serum total protein, TNF-alpha, and growth hormone were measured. The condition of inclusion was a survival of at least 14 days post-injection (in order to allow for plasmid activation and expression of GHRH from the skeletal muscle). Eleven dogs were under treatment using chemotherapy, radiotherapy, or combination therapy. Nineteen non-injected dogs with spontaneous malignancies, in treatment in the clinic in the same time window, were used as contemporary case matched controls. Blood samples were collected before plasmid injection, 9-27 and 28- 56 days post-injection. OUR RESULTS There was a significant increase in hematocrit, red blood cell count, hemoglobin, level of circulating lymphocytes, and serum protein in injected dogs versus control dogs. TNF-alpha values were significantly decreased. Biochemistry profiles were normal. Clinicians or owners noted no adverse effects. Eleven injected dogs survived for at least 56 days after the injection. Complete data was collected in all cases. Injected animals showed signs of improved protein metabolism, with total proteins slightly increased by 4.4% and bone remodeling, with Ca/PO4 ratio increased by 13.8%. Both of these changes are classically associated with GH increase. Glucose levels were normal at all time points tested. All other metabolic constants were unmodified and within the normal range. Hemoglobin, hematocrit and red blood cell values significantly decreased in non-injected dogs compared to injected dogs. OUR CONCLUSIONS This technique normalized GH levels in injected dogs versus case matched control dogs and therefore has implications in the management of dogs with cancer to abrogate treatment-associated and cancer-associated wasting and anemia. WHAT DO WE DO FOR OUR PATIENTS AT GULF COAST? We recommend a thorough clinical evaluation with complete laboratory and imaging evaluation and if wasting is a concern or will be a concern during cancer treatment, supplementation with growth hormone using the electroporation method is safe and is beneficial to the pet's quality of life. It would also be indicated in the pet with other chronic disorders such as heart, kidney or liver dysfunction. SUGGESTED READING * Veterinary Oncology, From "The Practical Veterinarian Series". By Hahn KA. Butterworth-Heinemann Press, 2002. ============================================ I hope this info helps and don't hesitate to call or email us at Gulf Coast Veterinary Oncology! Kevin Kevin A. Hahn, DVM, PhD Diplomate American College of Veterinary Internal Medicine (Oncology) & Overall Nice Guy Gulf Coast Veterinary Diagnostic Imaging & Oncology 1111 West Loop South, Suite 150, Houston, TX 77027 P: 713.693.1166 F: 713.693.1167 W: www.gcvs.com Email: drhahn@gcvs.com