Molecular insight into the T798M gatekeeper mutation-caused acquired resistance to tyrosine kinase inhibitors in ErbB2-positive breast cancer

Catalytic activity in vitro of the human protein kinase ASK1 mutants: Experimental and molecular simulation study

Kinases have become an important class of targets for drug discovery since the milestone approval of imatinib in 2001. Although a great success has been achieved for targeting kinases with over 70 inhibitors approved by the FDA, it is inevitable that drug resistance would emerge during treatment. Thus, assessment of the kinase mutations is an essential issue for the development of the next generation inhibitors. Apoptosis signal-regulating kinase 1 (ASK1) is a crucial regulator of classical mitogen-activated protein kinase cascade that is being explored under several clinical trials as a promising target. Herein, we investigate the catalytic activity in vitro of ASK1 by constructing two mutants: M754T and H729L, from gatekeeper and αC-helix, respectively. Compared to wild type, the mutation of M754T and H729L results in a roughly 3-fold and 2-fold decrease in binding affinity experimentally. In addition, their binding modes with substrate are theoretically predicted and compared by molecular dynamics. Trajectory analyses of simulations indicate that the decrease of binding affinity should be attributed to the loss of H-bond interaction with gatekeeper methionine. Unexpectedly, the conformation of αC-helix in H729L mutant did not alter significantly during the simulations, although the putatively important H-bond with H729 is lost. These simulations showed the regulatory role of H729 in αC-helix is maintained by leucine residue through the interaction with non-polar residues around H729 site.

Effect of TTLL6 expression on CDDP sensitivity of EC109/CDDP cells in hypoxia/acidosis microenvironment

Multidrug resistance is a major obstacle to the effective treatment of esophageal carcinoma. It occurs more readily in hypoxia and acidosis microenvironment. TTLL6 is one of Tubulin tyrosine ligase-like family members. In this study, the effect of TTLL6 on the regulation of cisplatin (CDDP) sensitivity was evaluated in CDDP-resistant esophageal carcinoma (EC) cells both in vitro and in vivo. In hypoxia/acidosis condition, overexpression of TTLL6 in EC109/CDDP cells significantly lowered the IC₅₀ of CDDP and increased the CDDP-induced apoptosis; while knockdown of TTLL6 expression in EC109/CDDP cells exhibited the opposite effects. Further study showed that, mechanistically, TTLL6 was inversely correlated with ERBB2 and TOPOIIA, and positively correlated with apoptosis-associated factor Caspase 9. Furthermore, animal model confirmed that TTLL6 negatively regulated the growth of xenograft tumor after chemotherapy. Alternated expression of TTLL6 also regulated the expression of ERBB2, TOPOIIA and Caspase 9 in EC109/CDDP cells in vivo. In conclusion, our results suggest that TTLL6 could reverse the drug resistant of EC109/CDDP cells, it might provide a potential treatment strategy for the clinical reversing the chemotherapy resistance.

An insertion mutation of ERBB2 enhances breast cancer cell growth and confers resistance to lapatinib through AKT signaling pathway

In clinical practice, some breast cancer (BC) patients carry a rare ERBB2 in-frame insertion (p. Pro780_Tyr781insGlySerPro) and are resistant to anti-ERBB2 therapy. To explore the potential procarcinogenic role of this ERBB2 mutation, we conducted the present study using BC cells overexpressing wild-type (WT) ERBB2 or P780-Y781 ERBB2 [mutated (MT)]. MDA-MB-231 and MCF-7 cells were transfected with the following plasmids using a lentivirus system: negative control (ERBB2-NC), WT ERBB2 overexpression (ERBB2-WT), and P780-Y781 ERBB2 overexpression (ERBB2-MT). P780-Y781 ERBB2 conferred significant resistance to lapatinib, as assessed by cell viability and colony counts. Analysis of the cell cycle showed that the P780-Y781 ERBB2 group showed an elevated proportion of cells in S, G2, and M phases compared with WT ERBB2 when exposed to lapatinib. Following lapatinib treatment, phosphorylated AKT (p-AKT) was strongly upregulated in the P780-Y781 ERBB2 group. Among ERBB2+ patients, the P780-Y781 ERBB2 group showed increased levels of p-AKT. Furthermore, the AKT inhibitor perifosine effectively suppressed lapatinib resistance, as indicated by the lapatinib inhibition curve and results of the colony formation assay, and decreased AKT phosphorylation. Altogether, we discovered a procarcinogenic mutation of ERBB2 that enhances BC cell growth through AKT signaling and causes resistance to lapatinib. Patients with this in-frame insertion mutation of ERBB2 should be recommended other therapeutic strategies apart from ERBB2 tyrosine kinase inhibitors, in particular lapatinib.