A role for RANKL signaling in testicular germ cell tumors

The bone factor RANKL is expressed in testicular germ cell tumors and RANKL inhibition affects tumor growth and proliferation.

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One of the most frequent solid tumors that affect young men are testicular germ cell tumors (TGCTs) (1). TGCTs originate from a common precursor called GCNIS (germ cell neoplasia in situ), which is a transformed fetal gonocyte present at the wrong time. Hormonal changes and reorganization of the testis during puberty may trigger proliferation of GCNIS cells and facilitate the malignant transformation into an invasive tumor (2). Patients with TGCTs have a high cure rate due to the efficacy of surgery, radiation, and most importantly the responsiveness of TGCTs towards cisplatin-based chemotherapy (3). However, several long-term adverse effects like metabolic and cardiovascular complications are common in these young patients which highlights a need for alternative or chemotherapy sparing treatments. Our lab has for several years worked with the interaction between the skeleton and the gonads and we recently found the bone factor RANKL to have a role in the testis as a regulator of male fertility (4). RANKL signals through its receptor RANK and the interaction can be blocked endogenously by the soluble decoy receptor OPG or pharmacologically by the antibody Denosumab which is used to treat osteoporosis (5). In our current study, (https://www.nature.com/articles/s41416-022-01810-w) the expression of RANKL signaling pathway in TGCTs and the effects of blocking this pathway were investigated. 

We found that RANKL, RANK, and OPG were expressed in several subtypes of TGCTs and the precursor stage GCNIS and that the expression pattern changes thoroughly from the pattern observed in normal testis tissue. When RANKL signaling was inhibited in vitro in a TGCT cell line or in vivo in a xenograft model, proliferation and tumor growth were reduced. Concomitantly, proliferation of human testis tissue containing GCNIS was decreased. This led us to investigate the potential of RANKL inhibition as a strategy for chemotherapy sparing or for chemotherapy resistant tumors. Unfortunately, the combination of RANKL inhibition and cisplatin treatment had no effects on cisplatin sensitivity or resistance when TGCT cell lines was co-treated. However, using RNA sequencing we found that changes in gene expression in the cell lines were induced upon RANKL inhibition. Soluble RANKL was also measurable in the serum from TGCT patients, but we found no prognostic value of this.

To conclude, our study shows a novel role of RANKL signaling in TGCTs and most importantly points towards future studies of how RANKL might be important for the malignant transformation of GCNIS and maybe even development of invasive potential.

 

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Christine Hjorth Andreassen

PhD-student, Rigshospitalet