The Role of Speedy/RINGO Protein in Breast Cancer as a Future Biomarker.

Background/aim: Cyclin-dependent kinases (CDKs) are proteins that require the binding of regulatory subunits called cyclins and play a key role in cell cycle progression and activation. CDKs play a key role in carcinogenesis of many solid malignancies, and inhibition of these proteins has produced anti-cancer effects demonstrated in preclinical studies. This narrative review was conducted to develop a hypothetical approach to determine whether Speedy/RINGO, a protein associated with CDK2, could be a possible predictive factor in breast cancer patients treated with a CDK4/6 inhibitor.

Materials and methods: A literature search was conducted in PubMed, Web of Science, Medline, and Google Scholars search engines to match the following words: "Speedy/RINGO" or "Spy1" and "CDKs" or "Cyclin-dependent kinases (CDKs)" and "CDK4/6 inhibitors" and "Regulation" and "Molecular" and "Breast cancer" and "Carcinogenesis". Only articles investigating the relationship between the Speedy/RINGO protein and CDKs at the molecular level were included. Literature information was compiled by trying to establish a relationship with our hypothesis question.

Results: Speedy/RINGO is a tightly regulated proto-oncogenic mammalian protein playing important roles in the somatic cell cycle. Studies have emphasized that although it does not have amino acid sequence homology with cyclins, it can activate CDK2. In addition, results showing molecular compensation of CDK4/6 inhibition through CDK2 activation, also showed that CDK2 can predict drug resistance. Another important finding was that overexpressed Speedy/RINGO, during CDK4/6 inhibitor treatment, could strongly activate CDK2, resulting in a negative response to treatment.

Conclusion: Although many predictive factors have been investigated to indicate response to CDK4/6 inhibitors or determine drug resistance, a consensus biomarker has yet to be established. In light of the information obtained from our review, it can be concluded that the Speedy/RINGO protein may have an important role as a predictive biomarker in terms of response to treatment, continuity of treatment and drug resistance in patients treated with CDK4/6 inhibitors.