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Cancer affects all of us,

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especially the ones that come back[br]over and over again.

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The highly invasive [br]and drug-resistant ones,

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the ones that defy medical treatment,

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even when we throw our best drugs at them.

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Engineering at the molecular level,

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working at the smallest of scales,

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can provide exciting new ways

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to find the most aggressive[br]forms of cancer.

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Cancer is a very clever disease.

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There are some forms of cancer,

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which, fortunately, we've learned[br]how to address relatively well

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with known and established drugs[br]and surgery.

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But, there's some forms of cancer[br]that don't respond

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to these approaches

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and the tumor survives[br]or comes back,

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even after an onslaught of drugs.

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We can think of these[br]very aggresive forms of cancer

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as kind of super villains in a comic book.

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They're clever, they're adaptable,

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and they're very good at staying alive.

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And, like most super villains[br]these days,

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their super powers come from[br]a genetic mutation.

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The genes that are modified[br]inside these tumor cells

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can enable and encode for new[br]and unimagined modes of survival,

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allowing the cancer cell[br]to live through

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even our best chemotherapy treatments.

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One example is a trick [br]in which a gene allows

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a cell, even as the drug[br]approaches the cell,

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to push the drug out before the drug[br]can have any effect.

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Imagine the cell effectively[br]spits out the drug.

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This is just one example[br]of the many genetic tricks

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in the bad of our super villain, cancer.

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All due to mutant genes.

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So, we have a super villain[br]with incredible super powers

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and we need a new and [br]powerful mode of attack.

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Actually, we can turn off a gene,

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the key is a set of molecules[br]called siRNA.

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siRNA are short sequences[br]of genetic code

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that guide a cell to block[br]a certain gene.

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Each siRNA molecule[br]can turn off a specific gene

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inside the cell.

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For many years since its discovery,

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scientists have been very excited

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about how we can apply[br]these gene blockers in medicine.

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But, there is a problem.

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siRNA works well inside the cell.

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But if it gets exposed to the enzymes[br]that reside

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in our bloodstream and our tissues,

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it degrades within seconds.

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It has to be packaged, protected[br]through its journey through the body

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on its way to its final target[br]inside the cancer cell.

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So, here's our strategy:

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first, we'll dose the cancer cell[br]with siRNA, the gene blocker,

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and silence those viral genes,

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and they'll we'll whap (?) it[br]with a chemo drug.

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But how do we carry that out?

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Using molecular engineering,

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we can actually design [br]a super weapon

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that can travel through the blood stream.

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It has to be tiny enough[br]that it can get through the blood stream,

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it's got to be small enough[br]to penetrate the tumor tissue,

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and it's got to be tiny enough[br]to be taken up

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inside the cancer cell.

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To do this job well, it has to be[br]about one 100th the size

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of a human hair.

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Let's take a closer look[br]at how we can build this nanoparticle.

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First, let's start with [br]the nanoparticle core.

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It's a tiny capsule that contains[br]the chemotherapy drug.

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This is the poison that will[br]actually end the tumor cell's life.

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Around this core, we'll wrap[br]a very thin,

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nanometer-think blanket[br]of siRNA.

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This is our gene blocker.

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Because siRNA is strongly negatively charged,

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we can protect it with a nice[br]protect layer

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of postively charged polymer.

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The two oppositely charged molecules[br]stick together throough charge attracttion,

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and that provides us with a protective[br]layer