Phase II Study of Ramucirumab Plus Irinotecan Combination Therapy as Second-Line Treatment in Patients with Advanced Gastric Cancer: HGCSG1603.

BACKGROUND: Ramucirumab is a human IgG1 monoclonal vascular endothelial growth factor receptor-2 antibody that inhibits tumor cell growth and affects the tumor cell microenvironment. We assessed the efficacy and safety of ramucirumab plus irinotecan combination therapy as second-line treatment in patients with previously treated advanced gastric cancer. MATERIALS AND METHODS: Patients with advanced gastric cancer refractory or intolerant to primary chemotherapy were included. Ramucirumab 8 mg/kg plus irinotecan 150 mg/m2 combination therapy was administered every 2 weeks. The primary endpoint was progression-free survival rate at 6 months and secondary endpoints were overall survival, progression-free survival, response rate, safety, and dose intensity for each drug. RESULTS: Thirty-five patients were enrolled between January 2018 and September 2019. The progression-free survival rate at 6 months was 26.5% [95%CI, 13.2%-41.8%, P = .1353)]. Median progression-free and overall survivals were 4.2 months (95%CI, 2.5-5.4 months) and 9.6 months (95%CI, 6.4-16.6 months), respectively. The overall response rate was 25.9% (95%CI, 11.1-36.3%) and disease control rate was 85.2% (95%CI, 66.3-95.8%). Grade ≥3 adverse events that occurred in >10% of patients included neutropenia, leucopenia, anemia, anorexia, and febrile neutropenia. No death or new safety signals with a causal relation to the study treatment were observed. CONCLUSION: Although the primary endpoint was not achieved statistically, combination therapy of ramucirumab plus irinotecan showed anticancer activity and a manageable safety profile for second-line treatment of patients with advanced gastric cancer.

Identification of amphiphysin 1 as an endogenous substrate for CDKL5, a protein kinase associated with X-linked neurodevelopmental disorder.

Cyclin-dependent kinase-like 5 (CDKL5) is a Ser/Thr protein kinase predominantly expressed in brain and mutations of its gene are known to be associated with neurodevelopmental disorders such as X-linked West syndrome and Rett syndrome. However, the physiological substrates of CDKL5 that are directly linked to these neurodevelopmental disorders are currently unknown. In this study, we explored endogenous substrates for CDKL5 in mouse brain extracts fractionated by a liquid-phase isoelectric focusing. In conjunction with CDKL5 phosphorylation assay, this approach detected a protein band with an apparent molecular mass of 120kDa that is remarkably phosphorylated by CDKL5. This 120-kDa protein was identified as amphiphysin 1 (Amph1) by LC-MS/MS analysis, and the site of phosphorylation by CDKL5 was determined to be Ser-293. The phosphorylation mimic mutants, Amph1(S293E) and Amph1(S293D), showed significantly reduced affinity for endophilin, a protein involved in synaptic vesicle endocytosis. Introduction of point mutations in the catalytic domain of CDKL5, which are disease-causing missense mutations found in Rett patients, resulted in the impairment of kinase activity toward Amph1. These results suggest that Amph1 is the cytoplasmic substrate for CDKL5 and that its phosphorylation may play crucial roles in the neuronal development.

Detection of protein kinase substrates in tissue extracts after separation by isoelectric focusing.

Here we report a simple and useful method to detect endogenous substrates of protein kinases. When crude tissue extracts were resolved by liquid-phase isoelectric focusing (MicroRotofor) and the separated protein fractions were phosphorylated by protein kinases such as Ca(2+)/calmodulin-dependent protein kinase I or cAMP-dependent protein kinase, various proteins in the different fractions were efficiently phosphorylated. Since a higher number of substrates could significantly be detected using the resolved fractions by MicroRotofor as compared to direct analysis of the original tissue extracts, our present method will be applicable to the screening of endogenous substrates for various protein kinases.

Cyclin-dependent kinase-like 5 binds and phosphorylates DNA methyltransferase 1.

DNA methyltransferase 1 (Dnmt1) is an enzyme that recognizes and methylates hemimethylated CpG after DNA replication to maintain methylation patterns. Although the N-terminal region of Dnmt1 is known to interact with various proteins, such as methyl-CpG-binding protein 2 (MeCP2), the associations of protein kinases with this region have not been reported. In the present study, we found that a 110-kDa protein kinase in mouse brain could bind to the N-terminal domain of Dnmt1. This 110-kDa kinase was identified as cyclin-dependent kinase-like 5 (CDKL5) by LC-MS/MS analysis. CDKL5 and Dnmt1 were found to colocalize in nuclei and appeared to interact with each other. Catalytically active CDKL5, CDKL5(1-352), phosphorylated the N-terminal region of Dnmt1 in the presence of DNA. Considering that defects in the MeCP2 or CDKL5 genes cause Rett syndrome, we propose that the interaction between Dnmt1 and CDKL5 may contribute to the pathogenic processes of Rett syndrome.