Targeted gene silencing to induce permanent sterility

Comprehensive Evaluation and Future Perspectives of Non-Surgical Contraceptive Methods in Female Cats and Dogs

The issue of stray cats and dogs is a global concern with considerable implications for animal welfare and public health. This review aims to provide an updated and comprehensive analysis of non-surgical contraceptive methods tested in studies controlled in vivo in feline and canine females. Immunocontraception via vaccination against gonadotropin-releasing hormone (GnRH), the luteinizing hormone receptor, zona pellucida proteins, and sperm, or use of viral-vectored delivery, is yet developing. Hormonal treatment (progestins, androgens, or GnRH) analogs act directly to block the reproductive axis. However, it produced essential side effects. Analogs of kisspeptin, non-steroid anti-inflammatory drugs such as firocoxib, and delivery of cytotoxins to the pituitary have shown non-conclusive results. Additional methods have also been tested, such as intraovarian injection of necrosing compounds or intravaginal and intrauterine devices. At present, neither of these methods offers permanent sterility that can replace surgical sterilization techniques. To our knowledge, none are currently authorized by the Food and Drug Administration (FDA) or the European Medicines Agency (EMA) for contraceptive methods or sterilization of cats or dogs. Therefore, it is necessary to continue the development of a compound that warrants the sterility of cats and dogs.

Epigenetic repression of gonadotropin gene expression via a GnRH-mediated DNA delivery system

The reproductive axis is activated by gonadotropin-releasing hormone (GnRH), which stimulates the pituitary gonadotropes to secrete hormones that drive gonadal function and steroidogenesis. Thus repression of this axis, which is conserved across mammals and sexes, can reduce steroid levels and/or prevent reproduction. Steroid-dependent pathologies, including various cancers, are commonly treated with GnRH super-analogs which have long-term side-effects, while humane solutions for controlling reproduction in domestic and wild animal populations are lacking. GnRH-conjugated toxins are undergoing clinical trials for GnRHR-expressing cancer cells, and have been examined for gonadotrope ablation in animals, but showed low and/or transient effects and administration of toxins has many potential complications. Here we exploit GnRH targeting to gonadotropes to deliver DNA encoding an effector that induces gonadotropin gene repressive epigenetic modifications which are perpetuated over time. Several layers of specificity are endowed through targeting to GnRHR-expressing cells and due to local cleavage of the peptide packaging the DNA; the DNA-encoded effector is expressed and directed to the target genes by the DNA binding domain of a highly specific transcription factor. This design has multiple advantages over existing methods of shutting down the reproductive axis, and its modular design should allow adaptation for broad applications.

Engineering a gene silencing viral construct that targets the cat hypothalamus to induce permanent sterility: An update

The intent of this contribution is to provide an update of the progress we have made towards developing a method/treatment to permanently sterilize cats. Our approach employs two complementary methodologies: RNA interference (RNAi) to silence genes involved in the central control of reproduction and a virus-based gene therapy system intended to deliver RNAi selectively to the hypothalamus (where these genes are expressed) via the systemic administration of modified viruses. We selected the hypothalamus because it contains neurons expressing Kiss1 and Tac3, two genes essential for reproduction and fertility. We chose the non-pathogenic adeno-associated virus (AAV) as a vector whose tropism could be modified to target the hypothalamus. The issues that must be overcome to utilize this vector as a delivery vehicle to induce sterility include modification of the wild-type AAV to target the hypothalamic region of the brain with a simultaneous reduction in targeting of peripheral tissues and non-hypothalamic brain regions, identification of RNAi targets that will effectively reduce the expression of Kiss1 and Tac3 without off-target effects, and determination if neutralizing antibodies to the AAV serotype of choice are present in cats. Successful resolution of these issues will pave the way for the development of a powerful tool to induce the permanent sterility in cats.

No surgery required: the future of feline sterilization: An overview of the Michelson Prize & Grants in Reproductive Biology

OVERVIEW

For many years, researchers have been studying reproduction of cats and dogs, including approaches to non-surgical sterilization, but scant funding has been available for this work. Recognizing the need to fund research and to attract researchers from the biomedical community to apply their expertise to this area, the Michelson Prize & Grants (MPG) in Reproductive Biology program was founded. Since 2009, it has funded 34 research projects in seven countries toward discovery of a safe single-administration lifetime non-surgical sterilant in male and female cats and dogs.

GOAL

The goal of the MPG program is the reduction or elimination of the approximately 2.7 million deaths of healthy shelter cats and dogs in the US every year. The successful product is expected to be a single-dose injectable product approved by the US Food and Drug Administration as a veterinary prescription item. The most optimistic prediction is that such a product will reach the hands of practicing veterinarians within the next decade.

AREAS OF RESEARCH

Active research is in progress using approaches such as immunocontraception with a single-administration vaccine against gonadotropin releasing hormone (GnRH). Long-term therapy with GnRH agonists such as deslorelin administered in controlled-release devices is also being studied. Other scientists are targeting cells in the brain or gonads with cytotoxins, such as are used in cancer chemotherapy. Gene therapy expressing proteins that suppress reproduction and gene silencing of peptides essential to reproduction are further avenues of research. Findings are available at www.michelsonprizeandgrants.org/michelson-grants/research-findings.