Development and Application of a Mechanistic Population Modeling Approach to Describe Abemaciclib Pharmacokinetics

Abemaciclib is an oral anticancer drug that inhibits cyclin dependent kinases 4 and 6 and is metabolized by cytochrome P450 3A in the intestines and liver to active metabolites. The objectives were (1) to develop a mechanistic model to characterize the pharmacokinetics (PK) of the active moieties and investigate the effect of patient factors and (2) apply the model to dat from two phase III breast cancer trials of abemaciclib in combination with endocrine therapy. To develop the model, data from seven phase I studies and two phase II studies including 421 patients with cancer and 65 healthy individuals were pooled for nonlinear mixed effects modeling. The PK was similar between patients and healthy subjects, and the effects of diarrhea, formulation, race, and patient covariates on exposure were negligible. Application of the model confirmed its predictive performance and that abemaciclib PK did not change when coadministered with endocrine therapy.

The role of the Golgi complex in the isolation and digestion of organelles

The origin of the membranes and lytic enzymes involved in autophagy has been studied in metamorphosing insect fat body. The Golgi complex has two functions in the organelle destruction which takes place when fat body cells change their activities. (1) It gives rise to envelopes which extermalize organelles scheduled for destruction. Microbodies, mitochodria and rough endoplasmic reticulum are sequentially removed from the cytoplasm by investment in isolation membranes. During the isolating phase, isolation membranes have the same osmiophilia as the outer saccular and microvesicular components of the Golgi complex, they do not contain lytic enzymes and they are specific in their adhesion to organelles scheduled for destruction. (2) The Golgi complex gives rist to lytic enzymes. Primary lysosomes which contain acid phosphatase fuse with the isolation bodies formed from invested organelles to become autophagic vacuoles. During this lytic phase, acid phosphatase is present in the inner saccules and microvesicular components of the Golgi complex, in the primary lysosomes seen fusing with isolation bodies and in autophagic vacuoles.