Molecular self-assembly offers a ‘bottom-up’ route to fabrication with subnanometre precision of complex structures from simple components1. DNA has proven a versatile building block2–5 for programmable construction of such objects, including two-dimensional crystals6, nanotubes7–11, and three-dimensional wireframe nanopolyhedra12–17. Templated self-assembly of DNA18 into custom two-dimensional shapes on the megadalton scale has been demonstrated previously with a multiple-kilobase ‘scaffold strand’ that is folded into a flat array of antiparallel helices by interactions with hundreds of oligonucleotide ‘staple strands’19, 20. Here we extend this method to building custom three-dimensional shapes formed as pleated layers of helices constrained to a honeycomb lattice. We demonstrate the design and assembly of nanostructures approximating six shapes — monolith, square nut, railed bridge, genie bottle, stacked cross, slotted cross — with precisely controlled dimensions ranging from 10 to 100 nm. We also show hierarchical assembly of structures such as homomultimeric linear tracks and of heterotrimeric wireframe icosahedra. Proper assembly requires week-long folding times and calibrated monovalent and divalent cation concentrations. We anticipate that our strategy for self-assembling custom three-dimensional shapes will provide a general route to the manufacture of sophisticated devices bearing features on the nanometer scale.

Most previously reported methods for purifying DNA-origami nanostructures rely on agarose-gel electrophoresis (AGE) for separation. Although AGE is routinely used to yield 0.1–1 µg purified DNA nanostructures, obtaining >100 µg of purified DNA-origami structure through AGE is typically laborious because of the post-electrophoresis extraction, desalting and concentration steps. Here, we present a readily scalable purification approach utilizing rate-zonal centrifugation, which provides comparable separation resolution as AGE. The DNA nanostructures remain in aqueous solution throughout the purification process. Therefore, the desired products are easily recovered with consistently high yield (40–80%) and without contaminants such as residual agarose gel or DNA intercalating dyes. Seven distinct three-dimensional DNA-origami constructs were purified at the scale of 0.1–100 µg (final yield) per centrifuge tube, showing the versatility of this method. Given the commercially available equipment for gradient mixing and fraction collection, this method should be amenable to automation and further scale up for preparation of larger amounts (e.g. milligram quantities) of DNA nanostructures.

No abstract

No abstract

No abstract

Cyclin-dependent kinases 4 and 6 (Cdk4/6) are important components of cell cycle activation and control in early G(1) phase. Both enzymes and their regulators, e.g., cyclins, play critical roles in embryogenesis, homeostasis, and cancerogenesis. Cdk4/6 are attractive targets for cancer treatment. Recently, numerous selective small molecule inhibitors of Cdk4/6 have been developed. The potential of Cdk4/6 inhibitors, particularly, pyrido[2,3-d]pyrimidine derivatives, as both anti-cancer drugs and 124I- and 18F-radiolabeled tracers for cancer imaging using positron emission tomography is discussed.

The cyclin-dependent kinase (Cdk)-cyclin D/retinoblastoma (pRb)/E2F cascade, which controls the G1/S transition of cell cycle, has been found to be altered in many neoplasias. Inhibition of this pathway by using, for example, selective Cdk4 inhibitors has been suggested to be a promising approach for cancer therapy. We hypothesized that appropriately radiolabeled Cdk4 inhibitors are suitable probes for tumor imaging and may be helpful studying cell proliferation processes in vivo by positron emission tomography. Herein, we report the synthesis and biological, biochemical, and radiopharmacological characterizations of two 124I-labeled small molecule Cdk4 inhibitors (8-cyclopentyl-6-iodo-5-methyl-2-(4-piperazin-1-yl-phenylamino)-8H-pyrido[2,3-d]-pyrimidin-7-one (CKIA) and 8-cyclopentyl-6-iodo-5-methyl-2-(5-(piperazin-1-yl)-pyridin-2-yl-amino)-8H-pyrido[2,3-d]pyrimidin-7-one (CKIB)). Our data demonstrate a defined and specific inhibition of tumor cell proliferation through CKIA and CKIB by inhibition of the Cdk4/pRb/E2F pathway emphasizing potential therapeutic benefit of CKIA and CKIB. Furthermore, radiopharmacological properties of [124I]CKIA and [124I]CKIB observed in human tumor cells are promising prerequisites for in vivo biodistribution and imaging studies.

No abstract