Buserelin

Buserelin is a synthetic GnRH agonist peptide widely approved in Europe, Canada, and other regions under brand names including Suprefact and Suprecur for prostate cancer, endometriosis, and female infertility. It is not approved in the United States but is a first-line hormonal therapy in many countries. Available as subcutaneous injection, nasal spray, or implant, it achieves sex steroid suppression equivalent to surgical castration through pituitary GnRH receptor desensitization.

Buserelin is a GnRH superagonist with approximately 20–170 times the potency of endogenous GnRH for stimulating LH and FSH secretion. Structural modifications — D-serine(tBu) at position 6 and ethylamide at the C-terminus — confer enzymatic stability and high receptor binding affinity. Initial administration triggers an LH/FSH flare response. With continuous exposure (unlike pulsatile endogenous GnRH), buserelin maintains constant GnRH receptor occupancy, inducing receptor downregulation and uncoupling. Within 2–4 weeks, pituitary gonadotrophs become desensitized, LH and FSH secretion collapses, and gonadal testosterone or estradiol falls to castrate levels. In prostate cancer, androgen withdrawal inhibits androgen receptor signaling that drives tumor proliferation.

European clinical trials established buserelin as effective ADT for advanced prostate cancer, achieving castrate testosterone in >95% of patients within 4 weeks. Long-term (3-year) data demonstrate disease stabilization comparable to orchiectomy. For endometriosis, 6-month nasal spray or implant treatment reduces lesion extent and pain scores significantly. In IVF protocols, buserelin down-regulation is used in the long protocol to synchronize follicular development, though GnRH antagonists are increasingly preferred due to shorter treatment duration. Buserelin's clinical profile is similar to leuprolide and other GnRH agonists in its class.

Peptides commonly paired with Buserelin for synergistic effects.