329P - RANK/RANKL, ERBB-2: A putative dual targeting strategy in RANK+/Her2+ breast carcinomas patients

Background

Recent studies show that the RANK pathway is implicated in tumorigenesis and in Erb2-positive breast carcinomas. Overexpression is observed in about 20% of human breast cancers and is associated with poor prognosis. The activation of NF-kB-, the key mediator of RANKL signaling, partly explains the resistance of Erb2-positive patients to anti-Erb2 treatment. In this case, co-administration of anti-RANKL and anti-Erb2 treatment could be an interesting dual targeting strategy in RANK+/Her2+ patients.

Methods

Initially, human BC cell lines Her2+ (SKBR3, BT474) and Her2- (MCF7, MDA-MB-453) were used to test RANK/HER2 dimers (PLA method) in untreated and treated samples with denosumab. SCID mice were then used to study the effect of dual treatment (denosumab (D) plus trastuzumab (T)) in xenografts using BT474 cells. FFPE samples from 112 patients were used to measure the expression of RANK and RANKL by immunohistochemistry. Also, 12 fresh tissue samples were used to test genes through Real-time PCR.

Results

Denosumab led to RANK/ERBB2 heterodimers' decrease compared to the control cells in SKBR3 (1.2 vs. 5.4) and BT-474 (3.1 vs. 8.2), while no discernible difference was observed in MCF7 and MDA-MB-453 cells. In the In vivo experiments, a 23.8% additional volume reduction was observed in the double combination (T+D) compared to monotherapy with (T) and 48.2% in relation to the control group. In FFPE samples, there was a statistically significant difference in the expression of both RANK between Her2 groups (higher expression in Her2+ patients, P=0.04) and RANKL (higher expression in Her2- patients, P=0.032). The gene control showed that in Her2- tumors, there is a statistically significant increase in STAT3 (P=0.045), while there is a statistically significant decrease in Her2+ in the MTOR gene (P=0.013).

Conclusions

In conclusion, RANK dimerization with ERBB2 seems to play a fundamental role in the progress of ERBB2-positive breast carcinomas. The noticeable anti-tumor effect of denosumab, when combined with anti-ERBB2 agents in ERBB2-positive BC cells, raises the possibility for therapeutic strategies with existing drugs, at least in a specific BC subgroup of RANK-expressing ERBB2-positive patients.

Clinical trial identification

Editorial acknowledgement

Legal entity responsible for the study

The authors.

Funding

Has not received any funding.

Disclosure

All authors have declared no conflicts of interest.