Serum thymidine kinase activity in patients with HR-positive/HER2-negative advanced breast cancer treated with ribociclib plus letrozole: Results from the prospective BioItaLEE trial.

BACKGROUND: Thymidine kinase 1 (TK1) is an enzyme downstream of the CDK4/6 pathway, with a critical role in DNA synthesis; serum TK1 activity (sTKa) is a novel liquid biopsy biomarker of tumour cell proliferation. METHODS: The phase IIIb, BioItaLEE trial (NCT03439046) collected sera from postmenopausal patients with hormone receptor-positive (HR+), HER2-negative (HER2-) advanced breast cancer (ABC) treated with first-line ribociclib plus letrozole at baseline, day 15 of cycle 1 (C1D15), day 1 of cycle 2 (C2D1), and at first imaging. Associations between sTKa assessed at different time points or sTKa dynamic patterns, and progression-free survival (PFS) were evaluated using multivariate Cox models. RESULTS: Overall, 287 patients were enroled. Median follow-up was 26.9 months. High sTKa (>median) at baseline was associated with higher risk of progression (hazard ratio [HR], 2.21; 95% confidence interval [95% CI], 1.45, 3.37; P = 0.0002); similar results were observed for patients with high sTKa levels at C1D15 and C2D1. Early sTKa dynamic patterns were strongly predictive of PFS. The pattern with high sTKa levels at C2D1 following initial decrease at C1D15 was associated with higher risk of progression versus the pattern with low sTKa levels at both time points (HR, 2.89; 95% CI, 1.57, 5.31; P = 0.0006), while the pattern with high sTKa levels at C1D15 was associated with the shortest PFS (HR, 5.65; CI: 2.84, 11.2; P < 0.0001). Baseline and dynamic sTKa changes provided independent information. CONCLUSIONS: sTKa appears to be a new promising prognostic and pharmacodynamic biomarker in patients with HR+/HER2- ABC treated with ribociclib plus letrozole as first-line therapy.

The endocytic adaptor Eps15 controls marginal zone B cell numbers.

Eps15 is an endocytic adaptor protein involved in clathrin and non-clathrin mediated endocytosis. In Caenorhabditis elegans and Drosophila melanogaster lack of Eps15 leads to defects in synaptic vesicle recycling and synapse formation. We generated Eps15-KO mice to investigate its function in mammals. Eps15-KO mice are born at the expected Mendelian ratio and are fertile. Using a large-scale phenotype screen covering more than 300 parameters correlated to human disease, we found that Eps15-KO mice did not show any sign of disease or neural deficits. Instead, altered blood parameters pointed to an immunological defect. By competitive bone marrow transplantation we demonstrated that Eps15-KO hematopoietic precursor cells were more efficient than the WT counterparts in repopulating B220⁺ bone marrow cells, CD19⁻ thymocytes and splenic marginal zone (MZ) B cells. Eps15-KO mice showed a 2-fold increase in MZ B cell numbers when compared with controls. Using reverse bone marrow transplantation, we found that Eps15 regulates MZ B cell numbers in a cell autonomous manner. FACS analysis showed that although MZ B cells were increased in Eps15-KO mice, transitional and pre-MZ B cell numbers were unaffected. The increase in MZ B cell numbers in Eps15 KO mice was not dependent on altered BCR signaling or Notch activity. In conclusion, in mammals, the endocytic adaptor protein Eps15 is a regulator of B-cell lymphopoiesis.

Increased ethanol resistance and consumption in Eps8 knockout mice correlates with altered actin dynamics.

Dynamic modulation of the actin cytoskeleton is critical for synaptic plasticity, abnormalities of which are thought to contribute to mental illness and addiction. Here we report that mice lacking Eps8, a regulator of actin dynamics, are resistant to some acute intoxicating effects of ethanol and show increased ethanol consumption. In the brain, the N-methyl-D-aspartate (NMDA) receptor is a major target of ethanol. We show that Eps8 is localized to postsynaptic structures and is part of the NMDA receptor complex. Moreover, in Eps8 null mice, NMDA receptor currents and their sensitivity to inhibition by ethanol are abnormal. In addition, Eps8 null neurons are resistant to the actin-remodeling activities of NMDA and ethanol. We propose that proper regulation of the actin cytoskeleton is a key determinant of cellular and behavioral responses to ethanol.