Mechanism and management of AKT inhibitor-induced hyperglycemia.

PURPOSE: Insulin-like growth factor-I receptor and phosphoinositide 3-kinase/AKT/mammalian target of rapamycin pathways are among the most active areas of drug discovery in cancer research. However, due to their integral roles in insulin signaling, inhibitors targeting these pathways often lead to hyperglycemia and hyperinsulinemia. We investigated the mechanism of hyperglycemia induced by GSK690693, a pan-AKT kinase inhibitor in clinical development, as well as methods to ameliorate these side effects. EXPERIMENTAL DESIGN: The effect of GSK690693 on blood glucose, insulin, and glucagon levels was characterized in mice. We then evaluated the effects of commonly prescribed antidiabetic agents on GSK690693-induced hyperglycemia. The mechanism of blood glucose increase was evaluated using fasting and tracer uptake studies and by measuring liver glycogen levels. Finally, approaches to manage AKT inhibitor-induced hyperglycemia were designed using fasting and low carbohydrate diet. RESULTS: We report that treatment with antidiabetic agents does not significantly affect GSK690693-induced hyperglycemia in rodents. However, administration of GSK690693 in mice significantly reduces liver glycogen (approximately 90%), suggesting that GSK690693 may inhibit glycogen synthesis and/or activate glycogenolysis. Consistent with this observation, fasting before drug administration reduces baseline liver glycogen levels and attenuates hyperglycemia. Further, GSK690693 also inhibits peripheral glucose uptake and introduction of a low-carbohydrate (7%) or 0% carbohydrate diet after GSK690693 administration effectively reduces diet-induced hyperglycemia in mice. CONCLUSIONS: The mechanism of GSK690693-induced hyperglycemia is related to peripheral insulin resistance, increased gluconeogenesis, and/or hepatic glycogenolysis. A combination of fasting and low carbohydrate diet can reduce the magnitude of hyperglycemia induced by an AKT inhibitor.

Effect of casopitant, a novel NK-1 receptor antagonist, on the pharmacokinetics and pharmacodynamics of steady-state warfarin.

Casopitant, a novel NK-1 receptor antagonist under investigation for the prevention of postoperative and chemotherapy-induced nausea and vomiting, is a weak to moderate inhibitor of CYP3A and a moderate inducer of CYP2C9 in vitro. Furthermore, both CYP enzymes are involved in the metabolism of R- and S-warfarin, respectively. This clinical study was conducted to explore the potential drug-drug interaction between casopitant and warfarin. In total, 97 healthy participants were enrolled and 54 completed the study. Participants received individualized daily dosing of warfarin to an international normalized ratio (INR) of 1.3 to 2.3 over a 14-day period (period 1). Immediately following period 1, participants entered period 2 and were randomized to receive either regimen A (oral casopitant [150 mg day 1, 50 mg days 2 and 3] and warfarin [days 1-10]) or regimen B (oral casopitant 60 mg and warfarin [days 1-14]). INR assessments were performed daily. The steady-state C(max) and AUC of R- and S-warfarin were not altered by regimen A, but R-warfarin AUC was increased 1.31-fold (90% confidence interval [CI]: 1.22, 1.41), and S-warfarin AUC was increased 1.27-fold (90% CI: 1.18, 1.38) on day 14 in regimen B. Steady-state INR values were not affected by either casopitant regimen.

Characterization of an Akt kinase inhibitor with potent pharmacodynamic and antitumor activity.

Akt kinases 1, 2, and 3 are important regulators of cell survival and have been shown to be constitutively active in a variety of human tumors. GSK690693 is a novel ATP-competitive, low-nanomolar pan-Akt kinase inhibitor. It is selective for the Akt isoforms versus the majority of kinases in other families; however, it does inhibit additional members of the AGC kinase family. It causes dose-dependent reductions in the phosphorylation state of multiple proteins downstream of Akt, including GSK3 beta, PRAS40, and Forkhead. GSK690693 inhibited proliferation and induced apoptosis in a subset of tumor cells with potency consistent with intracellular inhibition of Akt kinase activity. In immune-compromised mice implanted with human BT474 breast carcinoma xenografts, a single i.p. administration of GSK690693 inhibited GSK3 beta phosphorylation in a dose- and time-dependent manner. After a single dose of GSK690693, >3 micromol/L drug concentration in BT474 tumor xenografts correlated with a sustained decrease in GSK3 beta phosphorylation. Consistent with the role of Akt in insulin signaling, treatment with GSK690693 resulted in acute and transient increases in blood glucose level. Daily administration of GSK690693 produced significant antitumor activity in mice bearing established human SKOV-3 ovarian, LNCaP prostate, and BT474 and HCC-1954 breast carcinoma xenografts. Immunohistochemical analysis of tumor xenografts after repeat dosing with GSK690693 showed reductions in phosphorylated Akt substrates in vivo. These results support further evaluation of GSK690693 as an anticancer agent.

Adenocarcinoma cells exposed in vitro to Navelbine or Taxol increase Ep-CAM expression through a novel mechanism.

Ep-CAM antigen expression was shown to vary by phase across the cell cycle. Following pretreatment of various adenocarcinoma cells in culture with clinically relevant concentrations of vinorelbine tartrate (Navelbine) or paclitaxel (Taxol), cell surface expression of Ep-CAM antigen increased by two- to ten-fold compared to that of untreated control cells and was associated with arrest of cell cycle progression and accumulation of cells in the S and G2/M phases. We demonstrated that increases in cell surface antigen expression resulted in improved biological effectiveness of the targeting antibody as measured in vitro by antibody-dependent cellular cytotoxicity and in vivo by enhanced antibody targeting to Ep-CAM-expressing xenografts in mice pretreated with Navelbine. No effect on cell cycle progression or Ep-CAM antigen expression was seen with human interferon-alpha and interferon-gamma, agents that increase gene expression of various tumor and normal antigens and may upregulate some antigens. Thus, the upregulation of cell surface Ep-CAM expression following pretreatment with G2/M blockers is through a novel mechanism involving residence time of the antigen on the cell surface. This significant increase in Ep-CAM expression appears to be tumor-specific since we saw no increase in antigen expression on normal epithelial cells. Studies to reveal relative internalization rates suggest that the increase in cell surface expression of Ep-CAM following pretreatment with G2/M blockers is a consequence of an inhibition of normal cycles of antigen endocytosis and expression on the cell surface. The present work provides a mechanism for the improved clinical efficacy of therapeutic antibodies used in combination with traditional cell cycle-specific chemotherapeutic drugs.