Preclinical antitumor activity of the novel heat shock protein 90 inhibitor CH5164840 against human epidermal growth factor receptor 2 (HER2)-overexpressing cancers.

Heat shock protein 90 (Hsp90), a molecular chaperone that plays a significant role in the stability and maturation of client proteins, including oncogenic targets for cell transformation, proliferation, and survival, is an attractive target for cancer therapy. We identified the novel Hsp90 inhibitor, CH5164840, and investigated its induction of oncogenic client protein degradation, antiproliferative activity, and apoptosis against an NCI-N87 gastric cancer cell line and a BT-474 breast cancer cell line. Interestingly, CH5164840 demonstrated tumor selectivity both in vitro and in vivo, binding to tumor Hsp90 (which forms active multiple chaperone complexes) in vitro, and being distributed effectively to tumors in a mouse model, which, taken together, supports the decreased levels of phosphorylated Akt by CH5164840 that we observed in tumor tissues, but not in normal tissues. As well as being well tolerated, the oral administration of CH5164840 exhibited potent antitumor efficacy with regression in NCI-N87 and BT-474 tumor xenograft models. In addition, CH5164840 significantly enhanced antitumor efficacy against gastric and breast cancer models when combined with the human epidermal growth factor receptor 2 (HER2)-targeted agents, trastuzumab and lapatinib. These data demonstrate the potent antitumor efficacy of CH5164840 when administered alone, and its significant combination efficacy when combined with trastuzumab or lapatinib, supporting the clinical development of CH5164840 as an Hsp90 inhibitor for combination therapy with HER2-targeted agents against HER2-overexpressing tumors.

Bridging from preclinical to clinical studies for tyrosine kinase inhibitors based on pharmacokinetics/pharmacodynamics and toxicokinetics/toxicodynamics.

The purpose of this study was to provide a pharmacokinetics/pharmacodynamics and toxicokinetics/toxicodynamics bridging of kinase inhibitors by identifying the relationship between their clinical and preclinical (rat, dog, and monkey) data on exposure and efficacy/toxicity. For the eight kinase inhibitors approved in Japan (imatinib, gefitinib, erlotinib, sorafenib, sunitinib, nilotinib, dasatinib, and lapatinib), the human unbound area under the concentration-time curve at steady state (AUC(ss,u)) at the clinical dose correlated well with animal AUC(ss,u) at the no-observed-adverse-effect level (NOAEL) or maximum tolerated dose (MTD). The best correlation was observed for rat AUC(ss,u) at the MTD (p < 0.001). E(max) model analysis was performed using the efficacy of each drug in xenograft mice, and the efficacy at the human AUC of the clinical dose was evaluated. The predicted efficacy at the human AUC of the clinical dose varied from far below E(max) to around E(max) even in the tumor for which use of the drugs had been accepted. These results suggest that rat AUC(ss,u) at the MTD, but not the efficacy in xenograft mice, may be a useful parameter to estimate the human clinical dose of kinase inhibitors, which seems to be currently determined by toxicity rather than efficacy.

Comparison of in vitro metabolic conversion of capecitabine to 5-FU in rats, mice, monkeys and humans--toxicological implications.

Capecitabine is an oral anticancer prodrug which is converted to 5-fluorouracil (5-FU) via 3 enzymatic steps, these being 5'-deoxy-5-fluorocytidine (5'-DFCR), 5'-deoxy-5-fluorouridine (5'-DFUR), and finally 5-FU by carboxylesterase (CES), cytidine deaminase (CDA), and thymidine phosphorylase (TP), respectively. Because rats, mice and monkeys are used for preclinical safety studies, we investigated the in vitro conversion from capecitabine to 5-FU by hepatic and intestinal mucosal microsomes and cytosols, to compare their metabolic activity to that of humans. Capecitabine was hydrolyzed to 5'-DFCR in hepatic and intestinal mucosal microsomes in these animal species. In humans and monkeys, CL(int) (V(max)/K(m)) for the hydrolysis of capecitabine in intestine (expressed as µl/min/g tissue) was much lower than that in hepatic microsomes but, in rats and mice, CL(int) was higher in intestine than in liver. In humans and monkeys, similar K(m) values and inhibition patterns by tetrahydrouridine (THU) a CDA inhibitor, were observed in CDA activity of hepatic and intestinal cytosols. However, rats showed very low CDA activity and mice showed non-Michaelis-Menten kinetics and a different inhibition pattern by THU. K(m) values for TP activity were almost similar in rats, mice, monkeys and humans. In conclusion, it was confirmed that monkeys are a suitable animal model for the safety assessment of capecitabine in terms of metabolic enzymes and it was suggested that higher toxic incidences in mouse small intestine were related to high hydrolytic activity of capecitabine in the small intestine.

Bevacizumab improves the delivery and efficacy of paclitaxel.

It has been reported that bevacizumab in combination with paclitaxel significantly prolongs progression-free survival compared with paclitaxel alone in the initial treatment for metastatic breast cancer. To understand how bevacizumab enhances the efficacy of paclitaxel, we investigated the mechanism in a MX-1 human breast cancer xenograft model. The antitumor activity of bevacizumab at 5 mg/kg in combination with paclitaxel at 20 or 30 mg/kg was significantly higher than that of either agent alone. First, we measured the paclitaxel concentration in tumor to see whether bevacizumab enhances the activity by increasing the tumor concentration of paclitaxel. When given in combination with bevacizumab, the levels of paclitaxel in the tumor increased. Paclitaxel at 30 mg/kg with bevacizumab showed a similar tumor concentration as paclitaxel alone at either 60 or 100 mg/kg, with a similar degree of tumor growth inhibition. In contrast, no remarkable differences in paclitaxel concentration in the plasma or liver were observed between the paclitaxel monotherapy group and the paclitaxel plus bevacizumab group. An increase in paclitaxel concentration by bevacizumab was also found in another model, A549. In the same MX-1 model, vascular permeability in the tumor was significantly decreased by treatment with bevacizumab. There was no difference in microvessel density between the bevacizumab alone group and the combination group. Results suggest that the synergistic antitumor activity of paclitaxel and bevacizumab in combination may be a result of the increase in paclitaxel concentration in tumor resulting from the downregulation of vascular permeability when co-administered with bevacizumab.