Gene Therapy in the Treatment and Prevention of Erectile Dysfunction
Despite being the first-line treatment for erectile dysfunction today, PDE-5 inhibitors like Viagra, Levitra and Cialis are not right for everyone. Men with diabetes and post-prostatectomy patients do not respond well to these medications. Those suffering from heart conditions or taking nitrate medications are not recommended to take PDE-5 inhibitors too due to a risk of adverse reactions. As the demand for a reliable alternative treatment remains high in such patient groups, researchers like Jorgenson et al, Mansouri et al and more are turning their attention to gene therapy as a possible solution to the problem.
Global gene treatment market is expected to almost triple in volume within the next 5 years reaching $2.2Bn by 2024. Although it is mostly used to treat genetic disorders, cancer and cardiovascular disease at the moment, the spheres of its possible application continue expanding, with sexual and reproductive health conditions also covered. The main advantage of gene therapy as means of treating erectile dysfunction is that it addresses the cause of the condition and aims at curing it while most current treatments like PDE-5 inhibitors, alprostadil, etc. only provide temporary relief.
There are two important factors contributing to the safety and efficacy of gene therapy for erectile dysfunction. The first is the external location of the penis and the second is the low turnover rate of the smooth muscle cells lining the blood vessels inside the penile body. Due to these, generic material can be injected directly into the penis and remain there for long periods of time ensuring lasting treatment effect. Once injected, the genetic material stays close to the injection site and doesn’t enter the systemic circulation. Thus, the risk of it getting into any other organs or tissues and causing unwanted reactions is avoided.
Scientists have been researching the possibility of using gene therapy to treat ED since early 2000s. Most of the proposed treatments focused on the genes affecting smooth muscle relaxation and new blood vessel formation. One of these approaches includes intracavernous injections of hMaxi-K – a product using hSlo gene. hMaxi-K relaxes smooth muscles inside the penis facilitating an erection. Its safety and efficacy have been confirmed during Phase I and II clinical trials and it will proceed to Phase III trials in 2019. Although it is expected to be initially released as a medicine for patients with overactive bladder, the research of its anti-ED potential also continues.
Another approach developed by a group of scientists from Zurich uses a photosensitive gene construct that is injected into the patient’s penile tissue. When exposed to blue light, this gene construct makes the blood vessels inside the penis expand leading to an erection. The concept has been tested on male rats and produced great results.
What is more, gene therapy may be used not only to treat ED but also to prevent it as 30% of all cases of erectile dysfunction are suspected to be at least partially caused by genetics. A recent 2018 research shows there’s a relation between a genetic variation in the SIM1 locus – a specific part of the human genome – and impotence. The results of this study are highly reliable due to the amount of data collected in its course. It analyzes more than 36,000 male patients from the Kaiser Permanente Research Bank in the US and then verifies the findings in a cohort of 222,000 men from the UK Biobank. A further research by Bovijn et al using statistical data from the UK Biobank and the Estonian Genome Center also shows evidence that the genetic risk of type 2 diabetes is linked to erectile dysfunction. If the scientists find a way to fix the abovementioned genetic variation, many men will not develop the symptoms of erectile dysfunction at all or at least keep their sexual performance at an optimal level until a later stage of their lives.
Understanding the role of genes in male sexual function is the key to finding new ways to fight ED. This is especially important for those patients who can’t use PDE-5 inhibitors or other first- and second-line treatments because of nervous system disorders, diabetes or other conditions. Thanks to the recent findings, gene-based treatments are likely to go through clinical testing and enter the market in the next few years.
- E Jorgenson et al, Association between erectile dysfunction and a genetic variation in the SIM1 locus - https://www.pnas.org/content/115/43/11018
- M Mansouri et al, Application of light-controlled mammalian cells in synthetic biology - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6325585/
- Global gene therapy market volume prognosis, 2017-2024 - https://www.globenewswire.com/news-release/2019/01/18/1701759/0/en/Global-Gene-Therapy-Market-Will-Reach-USD-2-269-Million-By-2024-Zion-Market-Research.html
- S Melmed et al, Managing sexual dysfunction in men - https://books.google.com/books?id=iPIACwAAQBAJ&pg=PA815&lpg=PA815&dq=hmaxi-k+rat+study&source=bl&ots=UmGnxFNuGx&sig=ACfU3U0weEjZz1H1-g6BFVOG1gyOLWsIMQ&hl=ru&sa=X&redir_esc=y#v=onepage&q=hmaxi-k%20rat%20study&f=false
- hMaxi-K gene therapy for overactive bladder symptoms - https://european-biotechnology.com/up-to-date/latest-news/news/urovant-sciences-licenses-oab-gene-therapy.html
- N Arun et al, Safety and efficacy of hMaxi-K gene therapy in the treatment of erectile dysfunction - https://www.eusupplements.europeanurology.com/article/S1569-9056(18)32034-7/pdf
- T Kim et al, Erectile optogenetic stimulator - https://onlinelibrary.wiley.com/doi/abs/10.1002/anie.201412204
- Genetic causes of erectile dysfunction - https://www.sciencedaily.com/releases/2018/10/181008183357.htm
- J Bovijn et al, Genome risk locus for erectile dysfunction - https://www.cell.com/ajhg/fulltext/S0002-9297(18)30407-5#%20