B cell receptor pathway in chronic lymphocytic leukemia: specific role of CC-292

Population Pharmacokinetics and Exposure Response Assessment of CC-292, a Potent BTK Inhibitor, in Patients With Chronic Lymphocytic Leukemia

CC‐292, a potent Bruton tyrosine kinase inhibitor, is under development for the treatment of B‐cell malignancies. An analysis was performed to develop a population pharmacokinetic model of CC‐292 and assess the influence of demographics and disease‐related covariates on CC‐292 exposure and to assess the exposure‐response (overall response rate) relationship in patients with chronic lymphocytic leukemia. Population pharmacokinetic analysis was based on a 2‐compartment base model conducted in NONMEM. Categorical exposure‐response analysis was performed using logistic regression in SAS. The population pharmacokinetic analysis results indicated that CC‐292 pharmacokinetic disposition is similar between healthy subjects and patients. CC‐292 showed a larger central compartment volume of distribution than the peripheral compartment volume of distribution (158 L and 72 L, respectively) and a faster clearance than intercompartmental clearance (134 L/h and 18.7 L/h, respectively), indicating that for CC‐292, clearance from blood occurs faster than distribution into deep tissues and organs. CC‐292 clearance is not affected by demographics or baseline clinical lab factors, except for sex. Although sex significantly reduced variation of apparent clearance, the sex effect on apparent clearance is unlikely to be clinically relevant. The exposure‐response analysis suggested that higher drug exposure is linearly correlated with higher overall response rate. A twice‐daily dose regimen showed higher overall response rate as compared to once‐daily dosing, consistent with a threshold concentration of approximately 300 ng/mL, above which the probability of overall response rate significantly increases.

PI3K signaling in cancer: beyond AKT

The phosphoinositide 3-kinase (PI3K) signaling pathway is one of the most frequently altered pathways in human cancer and has a critical role in driving tumor initiation and progression. Although PI3K and its lipid product phosphatidylinositol-3,4,5-trisphosphate (PIP₃) have been shown to activate multiple downstream signaling proteins, the vast majority of studies have focused on the protein kinase AKT as the dominant effector of PI3K signaling. However, recent studies have demonstrated many contexts under which other PIP₃-dependent signaling proteins critically contribute to cancer progression, illustrating the importance of understanding AKT-independent signaling downstream of PI3K. Here, we highlight three PI3K-dependent, but AKT-independent, signaling branches that have recently been shown to have important roles in promoting phenotypes associated with malignancy. First, the PDK1-mTORC2-SGK axis can substitute for AKT in survival, migration, and growth signaling and has emerged as a major mechanism of resistance to PI3K and AKT inhibitors. Second, Rac signaling mediates the reorganization of the actin cytoskeleton to regulate cancer cell migration, invasion, and metabolism. Finally, the TEC family kinase BTK has a critical role in B cell function and malignancy and represents a recent example of an effective therapeutic target in cancer. These mechanisms highlight how understanding PI3K-dependent, but AKT-independent, signaling mechanisms that drive cancer progression will be crucial for the development of novel and more effective approaches for targeting the PI3K pathway for therapeutic benefit in cancer.