Ovarian function suppression with a GnRH analogue: D-ser(But[t])[6]-Arzgly[10]-LHRH (Goserelin) in hormone dependent canine mammary cancer

Canine Mammary Tumors: Classification, Biomarkers, Traditional and Personalized Therapies

In recent years, many studies have focused their attention on the dog as a proper animal model for human cancer. In dogs, mammary tumors develop spontaneously, involving a complex interplay between tumor cells and the immune system and revealing several molecular and clinical similarities to human breast cancer. In this review, we summarized the major features of canine mammary tumor, risk factors, and the most important biomarkers used for diagnosis and treatment. Traditional therapy of mammary tumors in dogs includes surgery, which is the first choice, followed by chemotherapy, radiotherapy, or hormonal therapy. However, these therapeutic strategies may not always be sufficient on their own; advancements in understanding cancer mechanisms and the development of innovative treatments offer hope for improved outcomes for oncologic patients. There is still a growing interest in the use of personalized medicine, which should play an irreplaceable role in the research not only in human cancer therapy, but also in veterinary oncology. Moreover, immunotherapy may represent a novel and promising therapeutic option in canine mammary cancers. The study of novel therapeutic approaches is essential for future research in both human and veterinary oncology.

Reversible Control of Reproduction In Queens: Mastering the use of reproductive drugs to manipulate cyclicity

BACKGROUND

The literature is full of papers reporting side effects of progestogens in cats; however, they are, in fact, safe drugs, as discussed in this article. Gonadotropin-releasing hormone (GnRH) agonists and melatonin are additionally a practical solution for controlling cyclicity in queens, but they also have some contraindications and need to be used carefully.

CLINICAL RELEVANCE

Mastering the use of reproductive drugs allows feline practitioners to handle many more clinical situations than can be solved using surgery. It is not necessary to be a specialist in reproduction to be able to halt cyclicity in a valuable breeding queen using hormones.

EQUIPMENT AND TECHNICAL SKILLS

A sound knowledge of appropriate dosages and criteria for patient selection for all reproductive drugs currently used in feline reproduction is the best guarantee of owner satisfaction and of ensuring the queen's health. Availability of a serum progesterone assay, either in-house or via an external laboratory, is also important, in order to confirm a queen is at an appropriate stage of the reproductive cycle for treatment.

AUDIENCE

This article is aimed principally (but not exclusively) at veterinarians working with cat breeders and whose clientele is increasingly interested in alternative methods of controlling reproduction in pet queens. Surgery is no longer the only choice, and practitioners who manage to keep abreast of new developments will be able to address clients' needs in a modern, professional way.

EVIDENCE BASE

This review draws on a vast body of scientific evidence-based literature. Previously, personal (and sometimes misinformed) opinions, such as the proposed dangerous side effects of progestogens, have been perpetuated in the scientific literature. The papers cited in this review have therefore been carefully scrutinised to distinguish reliable information based on controlled studies from non-evidence-based information.

Ultrasonic attenuation of canine mammary tumours

BACKGROUND

Canine mammary tumours (CMTs) are the most common neoplasm appearing in female dogs and are considered the equivalent animal model of human breast cancer. However, in the literature, there is a gap for ultrasonic characterisation of these tumours. In this study, experimental measurements for acoustic attenuation and propagation speed of three surgically excised malignant CMTs were implemented.

METHODS

The three tumours were fixed in formaldehyde for up to 72 h and a total of five sample pieces were sectioned from the three tumours to account for the varied morphology observed along the tumours. The through-transmission and pulse-echo techniques were employed for experimental measurements of the acoustic attenuation and propagation speed.

RESULTS

Acoustic propagation speed of the five samples as measured at 2.7 MHz was in the range of 1568-1636 m/s. Correspondingly, acoustic attenuation was in the range of 1.95-3.45 dB/cm.MHz. Variations in both speed and attenuation were observed between samples acquired from the same tumour.

CONCLUSIONS

Present findings suggest that both acoustic attenuation and propagation speed of CMTs are higher than normal canine tissues due to increased heterogeneity and varied morphology visually observed between the tumour specimens and evidenced by histological examination. Nevertheless, experimental results could aid in enhancing the use of ultrasound in the diagnosis and treatment of CMTs as well as provide essential data for comparative oncology.

Canine mammary tumours, an overview

Canine mammary tumours (CMTs) are the most common neoplasms in intact female dogs. Although the prevalence of these tumours decreases in regions where preventive ovari(ohyster)ectomy is performed, it remains an important disease entity in veterinary medicine. Moreover, treatment options are limited in comparison with human breast cancer. Nevertheless, recent human treatment protocols might have potential in bitches suffering from CMTs.

Spaying-induced coat changes: the role of gonadotropins, GnRH and GnRH treatment on the hair cycle of female dogs

Although spaying can result in qualitative hair coat changes in dogs, the influence of spaying on the hair growth cycle has never been described. The study aims were to examine the effect of spaying and gonadotropin-releasing hormone (GnRH) treatment on canine hair coat, cycle stages of hair follicles, plasma gonadotropin concentrations and mRNA transcription of luteinizing hormone (LH) and GnRH receptors in hair follicles. Fifteen female dogs were examined before and 1 year after spaying and 24 spayed dogs before and after GnRH treatment. Spaying resulted in increased plasma gonadotropin concentrations and increased anagen : telogen ratio of hair follicles, but only 20% of the dogs developed coat changes. No differences were found in mRNA transcription of LH and GnRH receptors. GnRH treatment resulted in reduced plasma gonadotropin concentrations and improvement of coat changes in 79% of patients. This was associated with an increase in catagen hair follicles without changes in the anagen : telogen ratio. The present study demonstrated that spaying had an effect on the anagen : telogen ratio of hair follicles. Spaying-induced coat changes did not correlate with the anagen : telogen ratio. GnRH treatment reduced gonadotropin concentrations and reversed coat changes in some dogs, but had no effect on the hair growth cycle other than increasing the number of catagen hair follicles. A weak positive correlation between the plasma LH concentration and the anagen : telogen ratio was noted; however, our data did not suggest a direct receptor-mediated hormonal effect on the hair follicle. The present study did not identify the pathomechanism of spaying-induced coat changes.

New GnRH analogs in canine reproduction

Gonadotropin-releasing hormone (GnRH) analogs, which include agonists and antagonists, have been produced by amino acid substitutions of the native GnRH molecule to create greater potency and longer duration of effectiveness. The aim of this article was to review the pharmacological effects and the existing clinical literature of new GnRH analogs, namely agonists released from long-term formulations and third generation antagonists, in domestic dogs. Long-term administration of agonists functions through desensitization and down-regulation of GnRH pituitary receptors inhibiting gonadotropin production and release after an initial stimulation. Conversely, GnRH antagonists bind to gonadotrope GnRH receptors and compete successfully with endogenous GnRH for occupancy, thereby inhibiting the pituitary-gonadal axis immediately. There is a promising place for both agonists and antagonists in future canine reproduction. They can be used in the control of estrous cycle, hormone-dependent diseases as well as in contraception. Some information on the effectiveness and safety of these new analogs in canine reproduction is already available, yet further work is needed before they could be widely recommended. The increase in gonadotropins and gonadal steroids following administration of agonists might have adverse effects when used on hormone-dependent diseases. This initial "flare" should also be carefully managed in anestrous and prepubertal bitches. At present, the main application of antagonists seems limited to situations where an acute endocrine, inhibitory effect is required, e.g. proestrus or pregnancy termination. Future commercial availability of long-acting, single-dose antagonists could go far towards controlling pet population.

Dopamine agonists, anti-progestins, anti-androgens, long-term-release GnRH agonists and anti-estrogens in canine reproduction: a review

Over the last 10 years, new drugs have been applied to canine reproduction, widening the spectrum of therapeutic possibilities for diseases that were previously surgically treated, and facilitating better control of the estrous cycle and fertility. Some are not approved for use in dogs; their use is experimental and further clinical trials are necessary. Dopamine agonists such as cabergoline, bromocriptine or metergoline are ergoderivative alkaloids that exert an anti-prolactinergic effect via stimulation of D2 pituitary receptors or inhibition of central serotoninergic ones. Their main indication is suppression of lactation. Anti-prolactinergic compounds have also been successfully used for pregnancy termination and shortening of interestrous intervals. Anti-progestins, (e.g. mifepristone and aglepristone) are synthetic steroids that bind with high affinity to progesterone (P4) receptors, preventing P4 from exerting its biological effects. Anti-progestins have been indicated in P4-dependent conditions, such as pregnancy termination, induction of parturition and the medical treatment of pyometra. Several groups of drugs have been described to have anti-androgenic properties through different mechanisms of action: progestins, receptor binding anti-androgens (e.g. flutamide), competitive enzyme inhibitors (e.g. finasteride), aromatase inhibitors, and GnRH agonists. Their main application is medical treatment of benign prostatic hyperplasia. Long-term release formulations of GnRH agonists (e.g. leuprolide or deslorelin acetate) postponed puberty and reversibly suppressed reproductive function in male and female dogs for periods exceeding 1 year. Anti-estrogens (e.g. clomiphene and tamoxifen citrate) are synthetic non-steroidal type I anti-estrogenic compounds that competitively block estrogen receptors with a combined antagonist-agonistic effect. In dogs, their action is more agonistic than antagonistic.

Spontaneous and genetically engineered animal models; use in preclinical cancer drug development

The preclinical development of anticancer drugs has been based primarily on the transplantation of murine or human cancers into mice. Alternatives to these transplantation models are animals that naturally develop cancers with features relevant to the human disease. The first group of these models arises in mice that are genetically engineered to develop cancer. The second group includes pet dogs and cats that naturally develop cancer. This review will discuss the use and integration of these spontaneous cancer models into a comprehensive and comparative approach to preclinical drug development. Examples of their successful use and an outline of their relative strengths and weaknesses will be provided.

Direct effect of a gonadotropin-releasing hormone agonist on the growth of canine mammary tumour cells

Gonadotropin-releasing hormone (GnRH) agonist exert "in vivo" an inhibitory action on the growth of hormone-dependent canine mammary tumours (Lombardi et al. [1999] J. Vet. Pharmacol Ther. 22(1):56-61). The present experiments have been performed "in vitro" in order to investigate the mechanisms involved in this direct antiproliferative action of GnRH agonists. In particular, the aim was to study whether these compounds might exert their antiproliferative effect by interfering with the stimulatory action of epidermal growth factor (EGF). To this purpose, the effects of GnRH agonist, Goserelin (GnRH-A), on the mitogenic action of EGF, on EGF-activated intracellular signaling mechanisms (intracellular calcium and nitric oxide production) as well as on ATP induced cell proliferation and signalling, and on the binding of EGF receptors have been evaluated in primary culture of canine mammary tumour cells. The results of these "in vitro" studies show that GnRH-A counteracts the mitogenic action of EGF and ATP, decreases the EGF/ATP-induced calcium signalling and reduces EGF binding, probably by means of NO-induced [Ca2+]i downregulation. These data suggest that GnRH agonists may inhibit the proliferation of the tumour cells by interfering with the stimulatory action of EGF.

Modulation of anthracycline activity in canine mammary tumour cells in vitro by medroxyprogesterone acetate

Failure of chemotherapy with anthracyclines as a result of drug resistance and toxicity is a major problem in the clinical management of neoplasia. The aim of the present study was to evaluate the activity of medroxyprogesterone acetate (MPA) as a chemosensitiser on anthracycline cytotoxicity. The study investigated whether such an effect could be related to an increase in lipid peroxidation, nitric oxide production, membrane fluidity and intracellular anthracycline concentration. The results showed that anthracyclines decreased nitric oxide production but increased membrane viscosity (polarisation constant) and lipid hydroperoxide formation in canine mammary tumour cells. Moreover, it was found that both drug-induced cytotoxicity and membrane viscosity increased in the presence of MPA. Conversely, lipid hydroperoxides decreased in MPA-supplemented cells. Medroxyprogesterone acetate did not show any effect on nitric oxide production. The two anthracyclines used (doxorubicin and idarubicin) showed differential intranuclear accumulation in canine mammary tumour cells, and MPA significantly modified intracellular concentration of anthracyclines.