Metformin is among the most widely prescribed drugs for the treatment of type 2 diabetes. Organic cation transporter 1 (OCT1) plays a role in the hepatic uptake of metformin, but its role in the therapeutic effects of the drug, which involve activation of AMP-activated protein kinase (AMPK), is unknown. Recent studies have shown that human OCT1 is highly polymorphic. We investigated whether OCT1 plays a role in the action of metformin and whether individuals with OCT1 polymorphisms have reduced response to the drug. In mouse hepatocytes, deletion of Oct1 resulted in a reduction in the effects of metformin on AMPK phosphorylation and gluconeogenesis. In Oct1-deficient mice the glucose-lowering effects of metformin were completely abolished. Seven nonsynonymous polymorphisms of OCT1 that exhibited reduced uptake of metformin were identified. Notably, OCT1-420del (allele frequency of about 20% in white Americans), previously shown to have normal activity for model substrates, had reduced activity for metformin. In clinical studies, the effects of metformin in glucose tolerance tests were significantly lower in individuals carrying reduced function polymorphisms of OCT1. Collectively, the data indicate that OCT1 is important for metformin therapeutic action and that genetic variation in OCT1 may contribute to variation in response to the drug.

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The SLC28 family consists of three subtypes of sodium-dependent, concentrative nucleoside transporters, CNT1, CNT2, and CNT3 (SLC28A1, SLC28A2, and SLC28A3, respectively), that transport both naturally occurring nucleosides and synthetic nucleoside analogs used in the treatment of various diseases. These subtypes differ in their substrate specificities: CNT1 is pyrimidine-nucleoside preferring, CNT2 is purine-nucleoside preferring, and CNT3 transports both pyrimidine and purine nucleosides. Recent studies have identified key amino acid residues that are determinants of pyrimidine and purine specificity of CNT1 and CNT2. The tissue distributions of the CNTs vary: CNT1 is localized primarily in epithelia, whereas CNT2 and CNT3 have more generalized distributions. Nucleoside transporters in the SLC28 and SLC29 families play critical roles in nucleoside salvage pathways where they mediate the first step of nucleotide biosynthesis. In addition, these transporters work in concert to terminate adenosine signaling. SLC28 family members are crucial determinants of response to a variety of anticancer and antiviral nucleoside analogs, as they modulate the entry of these analogs into target tissues. Further, this family is involved in the absorption and disposition of many nucleoside analogs. Several CNT single nucleoside polymorphisms (SNPs) have been identified, but have yet to be characterized.

When combined with TCS, lebrikizumab 125 mg taken every 4 weeks led to a significant improvement and was well tolerated in patients with moderate-to-severe AD.

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