Understanding the benefits and challenges of first-line cyclin-dependent kinases 4 and 6 inhibitors in advanced breast cancer among postmenopausal women

Nuclear Mechanisms Involved in Endocrine Resistance

Endocrine therapy is a standard treatment offered to patients with ERα (estrogen receptor α)-positive breast cancer. In endocrine therapy, ERα is either directly targeted by anti-estrogens or indirectly by aromatase inhibitors which cause estrogen deficiency. Resistance to these drugs (endocrine resistance) compromises the efficiency of this treatment and requires additional measures. Endocrine resistance is often caused by deregulation of the PI3K/AKT/mTOR pathway and/or cyclin-dependent kinase 4 and 6 activities allowing inhibitors of these factors to be used clinically to counteract endocrine resistance. The nuclear mechanisms involved in endocrine resistance are beginning to emerge. Exploring these mechanisms may reveal additional druggable targets, which could help to further improve patients' outcome in an endocrine resistance setting. This review intends to summarize our current knowledge on the nuclear mechanisms linked to endocrine resistance.

Inhibiting CDK4/6 in Breast Cancer with Palbociclib, Ribociclib, and Abemaciclib: Similarities and Differences

The cyclin-dependent kinase (CDK) 4/6 inhibitors belong to a new class of drugs that interrupt proliferation of malignant cells by inhibiting progression through the cell cycle. Three such inhibitors, palbociclib, ribociclib, and abemaciclib were recently approved for breast cancer treatment in various settings and combination regimens. On the basis of their impressive efficacy, all three CDK4/6 inhibitors now play an important role in the treatment of patients with HR+, HER2- breast cancer; however, their optimal use still needs to be established. The three drugs have many similarities in both pharmacokinetics and pharmacodynamics. However, there are some differences on the basis of which the choice for a particular CDK4/6 inhibitor for an individual patient can be important. In this article, the clinical pharmacokinetic and pharmacodynamic profiles of the three CDK4/6 inhibitors are reviewed and important future directions of the clinical applicability of CDK4/6 inhibitors will be discussed.

Charge and Size Dual Switchable Nanocage for Novel Triple-Interlocked Combination Therapy Pattern

Combination therapy is a current hot topic in cancer treatment. Multiple synergistic effects elicited by combined drugs are essential in improving antitumor activity. Herein, a pH-triggered charge and size dual switchable nanocage co-loaded with abemaciclib and IMD-0354 (PA/PI-ND) is reported, exhibiting a novel triple-interlocked combination of chemotherapy, immunotherapy, and chemoimmunotherapy. The charge reversal polymer NGR-poly(ethylene glycol)-poly(l-lysine)-dimethylmaleic anhydride (NGR-PEG-PLL-DMA, ND) in PA/PI-ND promotes the pH-triggered charge reversal from negative to positive and size reduction from about 180 to 10 nm in an acidic tumor microenvironment, which greatly enhances cellular uptake and tumor tissue deep penetration. With the PA/PI-ND triple-interlocked combination therapy, the chemotherapeutic effect is enhanced by the action of abemaciclib to induce cell cycle arrest in the G1 phase, together with the reduction in cyclin D levels caused by IMD-0354. The dual anti-tumor promoting immunotherapy is achieved by abemaciclib selectively inhibiting the proliferation of regulatory T cells (Tregs) and by IMD-0354 promoting tumor-associated macrophage (TAM) repolarization from an M2 to M1 phenotype. Furthermore, PA/PI-ND has improved anti-tumor efficiency resulting from the third synergistic effect provided by chemoimmunotherapy. Taken together, PA/PI-ND is a promising strategy to guide the design of future drug delivery carriers and cancer combination therapy.