The speaker schedule for NOS is set up so that each session has something of a theme, and it was pretty easy to guess what Monday evening's theme was--organic chemistry as applied to nanomaterials. Instead of giving you a complete rundown of my day, I thought I'd focus on one element the two evening talks, given by Joseph DeSimone of UNC Chapel Hill and Chad Mirkin of Northwestern, had in common. Both labs are very interested in creating materials that will be used as drug or gene delivery agents. Most of the time, those drugs or genes need to get into the cell, which means that both groups needed to think about whether their materials get into cells, and how they do it.
DeSimone's team makes nanoparticles with custom sizes and shapes by borrowing stamp-and-mold type techniques from the semiconductor industry. His team was curious whether there was a specific particle size or shape that might be a better delivery agent, that might cross cell membranes more efficiently. The answer to that is a resounding yes- cells take up rod shaped particles far more quickly than other shapes. "They go into the cells like gangbusters," DeSimone said. If that shape doesn't ring a bell to you, it should- bacteria such as plague and salmonella are shaped like rods, and they can induce entry into cells, too.
The group also wanted to know how cells internalize the nanoparticles, but the answer isn't a straightforward one. Cells use a few different mechanisms for taking things in, and based on the tests they've conducted in cultured cells, these particles appear to be getting in through combinations of those methods.
If you'd like to learn more about this work, read PNAS2008, 105, 11613.
Meanwhile, Mirkin talked about his team's work with oligonucleotide-coated gold nanoparticles, which he's already used for many applications. In contrast to DeSimone's results, Mirkin's nanoparticles seem to get into cells in one way-endocytosis, he says. via endocytosis. But endocytosis is a class of processes, and Mirkin's group has yet to characterize the specific mode of endocytosis by which the particles get into cells, he says.
The talks were probably a bit of a departure from what most of the audience works on everyday, which was refreshing. But I was glad they discussed their work in this area. We still don't know very much about how things get into cells, whether they're small molecules or nanomaterials. Anybody making new nano-stuff should be doing these studies and more, because they give us clues about what happens to these particles in living things, the good effects and the bad. This is the kind of research that needs to be pursued (and publicized) with equal fervor to the discovery side.
UPDATED 6/10/09: clarifying specifics about endocytosis. Thanks to Joe DeSimone for pointing this out.