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Inactivation of Ret/Ptc1 oncoprotein and inhibition of papillary thyroid carcinoma cell proliferation by indolinone
C Lanzi1, G Cassinelli, G Cuccuru
1Preclinical Chemotherapy and Pharmacology Unit, Department of Experimental Oncology, Istituto Nazionale Tumori, via G. Venezian 1, 20133 Milan, Italy. cinzia.lanzi@istitutotumori.mi.it
Abstract:
Genetic alterations causing oncogenic activation of the RET gene are recognized as pathogenic events in papillary and medullary thyroid carcinomas. Inhibition of Ret oncoprotein functions could thereby represent a specific therapeutic approach. We previously described the inhibitory activity of the 2-indolinone derivative RPI-1 (formerly Cpdl) on the tyrosine kinase activity and transforming ability of the products of the RET/PTC1 oncogene exogenously expressed in murine cells. In the present study, we investigated the effects of RPI-1 in the human papillary thyroid carcinoma cell line TPC-1 spontaneously harboring the RET/PTC1 rearrangement. Treatment with RPI-1 inhibited cell proliferation and induced accumulation of cells at the G2 cell cycle phase. In treated cells, Ret/Ptc1 tyrosine phosphorylation was abolished along with its binding to Shc and phospholipase C(gamma), thereby indicating abrogation of constitutive signaling mediated by the oncoprotein. Activation of JNK2 and AKT was abolished, thus supporting the drug inhibitory efficacy on downstream pathways. In addition, cell growth inhibition was associated with a reduction in telomerase activity by nearly 85%. These findings in a cellular context relevant to the pathological function of RET oncogenes support the role of Ret oncoproteins as useful targets for therapeutic intervention, and suggest RPI-1 as a promising candidate for preclinical development in the treatment of thyroid tumors expressing RET oncogenes.
Insights
The 2-indolinone derivative RPI-1 effectively inhibits RET oncoprotein activity in thyroid cancer cells. This targeted approach halts cancer cell proliferation and reduces telomerase activity, showing promise for treating RET-driven thyroid tumors.
Area of Science:
- Oncology
- Molecular Biology
- Pharmacology
Background:
- RET gene alterations drive thyroid cancer development.
- Targeting RET oncoprotein offers a specific therapeutic strategy.
- RPI-1 previously showed inhibitory effects on RET/PTC1 in murine cells.
Purpose of the Study:
- To evaluate the effects of RPI-1 on the human papillary thyroid carcinoma cell line TPC-1.
- To investigate RPI-1's impact on RET/PTC1 signaling pathways and cell proliferation.
- To assess RPI-1's potential as a therapeutic agent for RET-driven thyroid cancers.
Main Methods:
- Treatment of TPC-1 cells with RPI-1.
- Analysis of cell proliferation and cell cycle progression (G2 phase accumulation).
- Assessment of Ret/Ptc1 tyrosine phosphorylation, Shc and phospholipase C(gamma) binding, JNK2 and AKT activation, and telomerase activity.
Main Results:
- RPI-1 inhibited TPC-1 cell proliferation and induced G2 cell cycle arrest.
- RPI-1 abolished Ret/Ptc1 tyrosine phosphorylation and downstream signaling (Shc, phospholipase C(gamma), JNK2, AKT).
- RPI-1 reduced telomerase activity by approximately 85%.
Conclusions:
- RPI-1 effectively inhibits RET oncoprotein signaling and proliferation in a relevant thyroid cancer model.
- These findings support RET oncoproteins as therapeutic targets.
- RPI-1 demonstrates potential for preclinical development in treating RET-expressing thyroid tumors.