As the most common cause of acquired resistance to first-generation TKIs is a second EGFR mutation on codon 790, a third-generation EGFR TKI, osimertinib, has been developed to target this new mutation as well. MET amplification is another known mechanism of acquired resistance.ALK inhibitors such as crizotinib showed to be effective against tumors harboring ALK fusions. Most patients previously treated with crizotinib benefited from second-generation ALK inhibitors including ceritinib, alectinib and brigatinib. Resistance to ALK inhibitors can occur with novel acquired ALK mutations or amplifications.Also ROS1-positive tumors have shown high sensitivity to ALK inhibitors due to the high homology between the kinase domains of ROS1 and ALK. Immunotherapy
Immune response can be prevented via activation of immune checkpoints, which consist in the binding of a ligand protein (e.g. PD-L1) to a receptor (e.g. PD-1) on the immune cell surface. As a consequence, cancer cells expressing PD-L1 can inactivate T cells thus fostering tumor growth. Immune checkpoint inhibitors have been developed to restore T cell-mediated antitumor immunity by blocking either the ligand or the receptor.Immune checkpoint inhibitors have been approved for NSCLC, including anti-PD-1 nivolumab and pembrolizumab. Anti-PD-1 agents are used for patients with advanced NSCLC whose tumors progress after first-line cytotoxic chemotherapy. Pembrolizumab was established as a new standard of care for patients with advanced or metastatic NSCLC with high PD-L1 expression levels, and responses are even more pronounced for tumor with a high mutational burden (i.e.
To likely compensate for the cells energy demand, an upregulation of fatty acid β-oxidation and a decreased concentration of certain amino acids that feed anaplerotically into the citrate cycle, such as glutamine (via the fifth site of the citrate cycle), leucine, isoleucine, threonine (all via the sixth site of the citrate cycle) and aspartate (via the 10th site of the citrate cycle), could be detected. In summary, this reduced mitochondrial respiration and glycolytic flux results in impaired mitochondrial flexibility with a large dependence on fatty acid β-oxidation.However, neurons, with the exception of hypothalamic neurons, are not capable of satisfying their large energy demands by degrading fatty acids. It is speculated that an upregulation of β-oxidation also occurs in brain cells due to the hypofunctional mtFASII pathway. The consequence would be an increased risk for hypoxia and oxidative stress, which may contribute to neurological symptoms in the long term. Methylmalonic acid
Methylmalonic acid is formed from the essential amino acids valine, methionine, threonine and isoleucine, from odd-chained fatty acids, from propionate and from cholesterol side chain, on the degradation path into the citrate cycle. In this process, the last intermediate methylmalony-CoA can be converted to methymalonic acid by a deacylase before incorporation at the succinyl-CoA site of the citrate cycle. At this point, the acyl-CoA synthease encoded by ACSF3 could convert the methylmalonic acid back to methylmalonyl-CoA and then feed it to the citrate cycle with the help of the methylmalonyl-CoA mutase and its cofactor vitamin B12.