Inhibition of tyrosine kinases PDGFR and C‐Kit by imatinib mesylate interferes with postnatal testicular development in the rat

Abstract

The tyrosine kinase receptor c-kit and its interaction with the ligand, stem cell factor (SCF), play an essential role in the developing testis. C-kit is important for the development of the Leydig cells and for the migration, proliferation and survival of spermatogonia. Platelet-derived growth factor (PDGF) and its tyrosine kinase receptor (PDGFR) are important for the development of Leydig cells and myoid cells. The chemotherapeutic agent, imatinib mesylate (STI571, Glivec; Novartis) inhibits both of these tyrosine kinase receptors. Three-day treatment of immature male rats (SD) with imatinib (150 mg/kg) on postnatal days 5-7 delayed the formation of germ-line stem cell pool, reduced proliferation of type A spermatogonia and induced germ cell apoptosis. PDGFR-mediated proliferation of mesenchymal myoid precursors was also decreased and the length of the seminiferous cord was reduced. However, at the age of 11 weeks the exposed animals had normal epididymal sperm counts, whereas plasma levels of luteinizing hormone and follicle stimulating hormone were significantly increased. Imatinib serves as a good tool to study postnatal formation of the male germ-line stem cell pool and factors determining the final testicular size. As development of the human testis is controlled by the same mechanisms, further studies with primate and human models are needed to explore whether imatinib affects the testis in children as well.

Platelet-Derived Growth Factor Receptor β-Subtype Regulates Proliferation and Migration of Gonocytes

“…This time interval was selected to cover exactly the period of neonatal gonocyte proliferation and migration and to avoid the confounding effect on c-kit inhibition that may take place at later times. Indeed, Nurmio et al (40) reported that imatinib administration in P5-P7 rat blocked or delayed migration of gonocytes from the center of the seminiferous tubules to the basement membrane, delayed the formation of the germline stem cell pool, reduced proliferation of type A spermatogonia normally observed at P8, and induced germ cell apoptosis. They attributed all these events to the inhibition of c-kit.…”

“…The pattern of successive expression, disappearance, and reexpression of c-kit indicates that the timing of administration of a compound with multiple targets, such as imatinib, is critical to establish the identity of the affected molecule. The time interval selected by Nurmio et al (40) spans not only the period of the initial expression of c-kit by spermatogonia but also the period of expression of PDGFR-␤ by gonocytes. Thus, we strongly suspect that although the reduced proliferation of spermatogonia after imatinib administration from P5-P7 may be due to c-kit inhibition, the effect of imatinib on gonocytes should be assigned to the PDGFR-␤ blockage probably occurring during the first day of treatment.…”

Morphologic manifestations of testicular and epididymal toxicity

“…Chemotherapeutic agents, compounds altering the balance of endogenous apoptotic and anti-apoptotic proteins (e.g. p53, Fas, and Bcl systems), [7][8][9] and compounds interfering with growth factors supporting spermatogonia (e.g., stem cell factor or its receptor c-kit) 10 can all cause spermatogonial death and loss across multiple species. [11][12][13] (also see Murphy and Richburg, this issue)…”

A detailed protocol for a rapid analysis of testicular cell populations using flow cytometry

“…Flow cytometry has been used as a more data‐intensive method to study the behavior of the different testicular cell populations. A golden standard for flow cytometry analysis of testicular cells has been the use of stoichiometric DNA stains to study the different germ cell populations based on their DNA content (Toppari et al ., 1985, 1986, 1988; Nurmio et al ., 2007; Michaelis et al ., 2013). …”