PI3K/mTOR inhibition potentiates and extends palbociclib activity in anaplastic thyroid cancer

Area of Science:

• Oncology
• Molecular Biology
• Cancer Therapeutics

Background:

• Anaplastic thyroid carcinoma (ATC) is a highly aggressive thyroid cancer subtype with poor prognosis.
• Therapeutic resistance limits treatment efficacy in ATC, necessitating novel therapeutic targets.
• RB1 tumor suppressor loss is rare in ATC, suggesting targeting cell cycle regulators like cyclin D/CDK4 may be effective.

Purpose of the Study:

• To investigate the efficacy of CDK4/6 inhibition in RB1 wild-type ATC.
• To explore therapeutic strategies to overcome resistance to CDK4/6 inhibitors in ATC.
• To evaluate the synergistic potential of combining CDK4/6 and PI3K/mTOR inhibitors for ATC treatment.

Main Methods:

• In vitro proliferation assays using ATC cell lines treated with palbociclib (CDK4/6 inhibitor).
• In vivo efficacy studies using a xenograft mouse model of ATC.
• Combination therapy assessment using palbociclib and omipalisib (PI3K/mTOR inhibitor).

Main Results:

• Palbociclib inhibited proliferation in RB1 wild-type ATC cell lines and demonstrated in vivo efficacy.
• ATC cells rapidly developed resistance to palbociclib, associated with increased cyclin D1 and D3 levels.
• Combined palbociclib and omipalisib treatment synergistically reduced proliferation and tumor growth, even in cell lines without PI3K mutations.

Conclusions:

• CDK4/6 inhibition is a potential therapeutic avenue for RB1 wild-type ATC.
• Combined inhibition of PI3K/mTOR and CDK4/6 overcomes resistance mechanisms and demonstrates significant anti-tumor activity.
• This combination therapy represents a promising novel approach for treating aggressive, therapy-resistant anaplastic thyroid cancer.