CDK4/6 Inhibitor Resistance in Hormone Receptor-Positive Metastatic Breast Cancer: Translational Research, Clinical Trials, and Future Directions

PI3K/AKT/mTOR inhibitors for hormone receptor-positive advanced breast cancer

Dysregulation of the phosphatidylinositol 3-kinase/protein kinase B/mammalian target of rapamycin (PI3K/AKT/mTOR) pathway plays a pivotal role in the development and progression of various cancers. In hormone receptor-positive (HR+)/human epidermal growth factor receptor 2-negative (HER2-) advanced breast cancer, aberrations in this pathway are increasingly recognized as key drivers of resistance to endocrine therapy and cyclin-dependent kinase 4/6 (CDK4/6) inhibitors, the first-line treatments for this disease subtype. Recognizing the urgent need for alternative therapeutic strategies, significant advancements have been made in developing PI3K/AKT/mTOR inhibitors for HR+ advanced/metastatic breast cancer. Among these inhibitors, capivasertib and alpelisib have received approval as targeted therapies for this indication. This review provides a comprehensive summary of the latest developments in PI3K/AKT/mTOR inhibitors for HR+ breast cancer. It also delves into different aspects, including sampling, testing method and timing, of PI3K/AKT/mTOR diagnostic testing. Additionally, the review discusses key considerations for integrating these inhibitors into clinical practice, such as timing and choice of PI3K/AKT/mTOR inhibitors, and management of treatment toxicities. By examining these different aspects, this review aims to provide valuable insights into optimizing the clinical utility of PI3K/AKT/mTOR inhibitors in HR+ advanced breast cancer.

CDK4/6 inhibitors in HR-positive breast cancer immunotherapy

Breast cancer is the most prevalent malignant tumour among women. Approximately 70 % of patients are hormone receptor (HR)-positive and undergo endocrine therapy as the main form of treatment; however, the efficacy of this type of therapy is limited by some factors, such as drug resistance and complex tumour microenvironments. Using network pharmacology and molecular docking, this study examined how CDK4/6 inhibitors enhance the effects of immunotherapy for HR-positive breast cancer, focusing on their effects on the tumour microenvironment (TME) and immune cell activity. CDK4/6 inhibitor influence crucial signalling pathways, including TP53 and EGFR, underscoring their importance in modulating immune responses and combating drug resistance. Our analysis revealed that the combination of CDK4/6 inhibitors with other immunotherapies, such as immune checkpoint inhibitors, might play an important role in improving the effectiveness of treatment in patients with cancer. This study provides new perspectives on treatment options for HR-positive breast cancers, promoting ongoing research and improvements in therapeutic approaches.

Advancements in breast cancer management: a comprehensive review of ribociclib combined with endocrine therapy

Background

In this review, the complicated landscape of breast cancer management is explored with a focus on the promising synergies between ribociclib and endocrine therapy. Ribociclib mainly acts as a cyclin-dependent kinase 4/6 (CDK4/6) inhibitor, which disrupts cell cycle progression necessary for tumor growth. This, in combination with endocrine therapy, aims to produce hormone receptor-positive breast cancers, which is a very relevant subtype with challenging therapeutics.

Methods

A comprehensive review was conducted using multiple databases, PubMed, Embase, Scopus, Cochrane Library, and Web of Science, covering the period from January 1990 to May 2024.

Results

Pharmacokinetic studies underscore the efficacy and tolerability of ribociclib, thus providing vital information for dose adjustments, particularly among patients with renal and hepatic impairments. Ribociclib's value in extending progression-free survival and improving overall survival has been shown by clinical trials such as the MONALEESA series. Quality of life considerations and patient-reported outcomes from these trials indicate that ribociclib has a broader effect on the well-being of the patients. However, despite the success experienced by this drug in clinical practice, it still has some side effects, including hematologic toxicity, hepatotoxicity, and thromboembolism associated with it. Ribociclib resistance mechanisms are multifaceted mixtures comprising genetic variations or mutations, compensatory signaling pathways, and epigenomic changes. While overcoming resistance remains challenging, ongoing research seeks to reconcile.

Conclusion

Ribociclib combined with endocrine therapy represents a significant advancement in breast cancer treatment, albeit with challenges that necessitate ongoing research and holistic patient care approaches.

Synthesis and Preclinical Evaluation of Novel 68Ga-DOTA-RBB as Potential PET Radiotracer for Imaging CDK4/6 in Tumors

Many malignant tumors, including breast cancer, exhibit amplification and overexpression of cyclin-dependent kinase 4 and 6 (CDK4/6). Ribociclib, approved and used in clinical treatment, acts as a highly selective CDK4/6 inhibitor for ER+/HER2- breast cancer. By modifying ribociclib with the chelator DOTA, we designed and synthesized a novel CDK4/6-positive PET imaging agent, which was radiolabeled by 68Ga for radioactive tagging. The radiotracer demonstrates high radiochemical purity, excellent stability in vitro and in vivo, and favorable pharmacokinetic characteristics. Cell uptake experiments using MCF-7 cells indicate that an excess of ribociclib (RBB) can inhibit cellular uptake of 68Ga-DOTA-RBB. Imaging and biodistribution experiments in MCF-7 tumor-bearing nude mice show significant radioactive accumulation in the tumor. However, preadministration of excess ribociclib results in a substantial reduction in radioactive accumulation within the tumor. On the basis of our explorations, 68Ga-DOTA-RBB, as a targeted imaging agent for CDK4/6-positive tumors, holds significant potential application values.

Cyclin-Dependent Kinase 4/6 Inhibitors as Neoadjuvant Therapy of Hormone Receptor-Positive/HER2-Negative Early Breast Cancer: What do we Know so Far?

The introduction of cyclin-dependent kinase 4/6 (CDK4/6) inhibitors to the treatment of hormone receptor-positive and human epidermal growth factor receptor 2-negative (HR+/HER2-) metastatic breast cancer is regarded as one of the greatest achievements of the last decades in breast oncology. To date, palbociclib, abemaciclib and ribociclib are the 3 approved CDK4/6 inhibitors that combined with endocrine therapy are now considered as the standard first-line treatment of metastatic HR+/HER2- breast cancer. The great success of these drugs in the setting of metastatic disease and the need to combat the high risk of recurrence have paved the way for a number of clinical trials to explore the use of CDK4/6 inhibitors in the neoadjuvant treatment of early breast cancer. In this review, we summarize the main findings of clinical trials that examined the use of CDK4/6 inhibitors in combination with hormone therapy or chemotherapy as neoadjuvant treatment of hormone receptor-positive and HER2-negative breast cancer. Active clinical trials that investigate different treatment schemes are also briefly presented and current limitations and future goals are discussed.

Distinct Mechanisms of Resistance to CDK4/6 Inhibitors Require Specific Subsequent Treatment Strategies: One Size Does Not Fit All

Cyclin-dependent kinase (CDK) 4/6 inhibitors have transformed the treatment landscape of patients with hormone receptor-positive breast cancers. However, despite improvements in clinical outcomes, the approximately 70% of patients with tumors that are not intrinsically resistant to a CDK4/6 inhibitor still ultimately acquire resistance, which leads to a dilemma for clinicians when deciding which treatment to offer patients when they demonstrate disease progression on a CDK4/6 inhibitor. As such, many groups have sought to understand the mechanisms of resistance to CDK4/6 inhibitors, mostly focusing on genetic alterations associated with resistance. Though several recurrent mutations have been described, they are not consistent enough to guide clinical practice or generate novel rational treatment options. Two recent publications have used transcriptomic analysis to unravel distinct mechanisms driving resistance to individual CDK4/6 inhibitors and in doing so have identified biomarkers that could potentially help identify the next course of treatment for patients following disease progression.