Abstract 5297: Role of p38 MAPK signaling pathway in the inhibition of breast tumor progression induced by Glypican-3 (GPC3)

Proceedings: AACR Annual Meeting 2014; April 5-9, 2014; San Diego, CA Glypican-3 (GPC3) is expressed in normal mammary tissues, but it disappears in tumors. We have transfected the GPC3 gene into murine mammary adenocarcinoma LM3 cells, demonstrating that this proteoglycan acts as a metastasis suppressor. GPC3 reexpressing clones are less metastatic in vivo, showing reduced migration and increased susceptibility to apoptosis in vitro. In relation to GPC3 signaling pathway, we have reported that LM3-GPC3 cells exhibit an inhibition of Akt and canonical Wnt pathways, while they show an activation of non-canonical Wnt and p38 signaling. The aim of this work was to study if the effects of GPC3 on breast tumor progression could be due to p38 activation. LM3-GPC3 or LM3-vector cells were inoculated s.c. into female BALB/c mice. One day later, the p38 inhibitor SB203580 or the vehicle DMSO, were injected i.p. into LM3-GPC3 cells-bearing mice, every 24 h for 10 days. Daily, we recorded the largest and smallest diameter of tumors. Thirty days post-inoculation, mice were killed. We evaluated primary tumor invasiveness behavior by macroscopic examination and histopathological study. We also analyze the spontaneous lungs metastasis, through the counting of macroscopic nodules. LM3-GPC3 and LM3-vector clones generated s.c. tumors showing similar latency and tumorigenic capacity, irrespective of SB203580 treatment (Latency in days, Md [Rg]: 8 [8-10]. Tumorigenicity: 100%). LM3-GPC3 tumors presented a growth rate higher than LM3-vector, while tumors treated with SB203580 grew faster (mm3/day: 17.6±1.9 -GPC3; 15.8±0.9 -vector, 28.2±1.6 -GPC3+SB203580; p<0.05). On the other hand, while only about 30% of LM3-GPC3 tumors showed macroscopic invasion with ulceration compared to 100% of LM3-vector ones, the SB203580 treatment induced an increase in LM3-GPC3 tumors ulceration (reaching 100% affected tumors). This was confirmed through hematoxylin-eosin staining and microscopic examination. We observed only 40% of LM3-GPC3 tumors with occasional invasion of the muscle and dermis, in contrast to 100% of LM3-vector tumors with muscle, dermis and epidermis invasion. The SB203580 treatment was able to revert the GPC3 inhibitory effect on local invasion, inducing invasion of the muscle, dermis and epidermis in all cases. We observed that all tumors generated only lung spontaneous metastasis. While about 90% of LM3-vector tumors-bearing mice developed metastasis, there were no LM3-GPC3 tumors-bearing mice that did it. However, the treatment with p38 inhibitor induced a partial reversion of the GPC3 effect, showing metastasis in 60% of the animals. In sum, we have confirmed that GPC3 acts as metastasis suppressor in the present breast cancer model. Also, we demonstrated that GPC3 would be able to inhibit invasiveness and metastatic capacities trough p38 activation. We trust that our results could be the bases to explore new molecular targets against metastatic disease. Citation Format: Rocio S. Tascon, Lilian F. Castillo, Fernanda Roca, Elisa Bal de Kier Joffe, Maria G. Peters. Role of p38 MAPK signaling pathway in the inhibition of breast tumor progression induced by Glypican-3 (GPC3). [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 5297. doi:10.1158/1538-7445.AM2014-5297