and Cellular and Molecular Pharmacology at UCSF.

And I'm going to tell you today about the process of drug discovery and development

in two parts: part one it will be screening of compounds and in that regard I'll be joined by my colleague

Michelle Arkin.

Hi, I'm going to talk after Jim gives an early history of drug discovery

and talks a little bit about target identification, then I'll talk about the process of screening

and hit identification.

Great, see you in a bit.

This slide shows some of the products of modern drug discoveries,

such as Lipitor, which is used for cholesterol lowering,

or a more recent drug, Gleevec, which an anti-cancer drug.

These compounds were discovered through a very rational, systematic

process, involves a lot of exciting scientific discoveries

as well as a lot of serendipity, luck and hard work.

To understand how we found these compounds, it's useful for us to review

how drug discovery came to be,

what's the sort of brief history of drug discovery, as I'll show you on the following slide.

To understand the modern drug discovery development process today

it's useful to review the history, briefly,

of drug discovery. Prior to 1900, most drugs, in fact only a few really,

were identified through human screening.

Natural products, for instance, aspirin, was discovered from tree bark.

Quinine was discovered. And even illicit drugs like cocaine were discovered.

Long about the turn of the century, 1906,

the Food and Drug Administration was established

because a number of these kinds of potions or elixirs were found to neither be safe nor efficacious

and it was necessary to regulate these in a systematic way.

And this led to the development of animal based screening, for example, to discover anesthetics,

bacterial screening to identify antibiotics, and the like,

tissue screening to identify compounds that could react with neurological receptors,

like GPCRs, HTS, high throughput screening,

now very common discovery technology, as you'll hear a lot more about in this talk,

for discovering target-based compounds.

And then, lastly, mechanism-based discovery, which was used for HIV drugs and the like

as well as molecular and cellular based screening for kinase inhibitors.

And finally, genomics, to actually profile patients to determine who will be affected and who won't be affected.

So, in fact, this process, the history of drug discovery,

had gone from the human to the molecular target

and this now in reverse reflects what we actually do today.

Shown on this slide is what, in sort of general terms,

the modern drug discovery process.

And this process starts off with a disease,

and from that disease one tries to, through a lot of biochemical

cell-based, genetic and other means identify

what is the target or the molecular species in a cell, in an organism,

that's causing that disease.

One then develops a drug to that target, as you can see here,

and then, having identified that target, one then needs to identify

a compound that will interact with that target in a phase called lead discovery.

This is a chemical process where we identify the first compounds

that are actually important in modifying a disease

and then once compounds are identified, typically in cells and then in animals,

they're prepared for clinical trials in this process called drug development,

which is, this phase is really about interfacing the compounds that we discovered here

to the human biology that we wish to effect here.

And if successful, we'll come out of this process with a drug.

Now, this process is a long winded process. It typically takes about now about 10-15 years

to discover a drug and it's expensive too.

It's about half a billion to a billion dollars to develop a drug.

So, when you're thinking about the pills that you take in a bottle,

think about a shopping mall, because that's easily the cost that it takes to get to the drugs that we end up using.

Ok, I wanted to just review quickly what kind of classes, what kind of molecules constitute drugs.

There's actually three basic classes and they include

the small molecule, organic compounds,

typically, these are compounds whose molecular weight is less than five hundred

and they're taken, generally, orally,

although they can also be taken as an injectable.

And they represent the kind of classic drug that you think of when you go to a pharmacy,

that you would buy over the counter, for example.

There's another class of very important drugs known as the protein therapeutic drugs.

These are typically injectable drugs, molecular weights of over ten thousand,

often up to a hundred thousand, or even higher.

And they are the important class of biotherapeutics

and they represent about thirty percent of drug sales today.

The other class of drugs, actually one of the very first to be developed

are the vaccines. And these are

basically viruses, pieces of viruses, that are used to elicit an immune response to a disease.

So these are the basic categories and today I'm going to focus on small molecule drug discovery,

leaving these other two categories alone for another talk.

So, the process of small molecule discovery is a long and winding road.

And it starts off with identifying what is the most critical target that's involved

in mediating the disease. So, identifying the disease target.

Having identified that target, generally a protein target,

one then goes through a process known as hit identification, shown here,

and the role of hit identification is to get the first compounds that actually engage the target.

Which compounds actually bind to the protein of interest

and can begin our drug discovery process.

From there, taking that isolated protein in a test tube, we need to show that that compound

actually works in a cell.

And so, this begins this process called hit to lead

which is to generate a compound which has cellular potency.

The next stage, sort of drawing from there, to a larger scale,

is the lead optimization stage.

This is a critical stage in which one actually shows that these compounds

that have been generated have animal efficacy and actually work in a pharmacological model

for the disease. The next stage after that is the IND enabling stage,

this is the stage that is preparing compounds for clinical trials.

Primarily, it involves animal tox experiments, in addition, chemical synthesis, scale,

and formulations experiments, and at the end of this process, one would hope to have a package

that you could convince the food and drug administration that you have a compound

that is going to be both safe and efficacious when administered to humans.

Then begins the all-important human clinical trials

if the FDA agrees with you.

In the first trail, is for human safety. This is typically done in a dose escalation,

kind of trial, with healthy volunteers, although in certain disease settings, like cancer,

you can use people with cancer.

And the goal of this is really to find out

what is the circulatory lifetime of the drug in humans

and how safe is the drug if its dose is increased.

The next phase, phase two, is involved in determining the efficacy of the drug

in a disease setting. So, this would be taking patients with the disease,

treating them with your drug at a level that's below any toxicity that was observed in phase one

and in ranging doses to find out what is the efficacy of the drug as a function of its dose

and what's the best dose to best effect the disease.

So, from these small trials, then, one then moves into a much larger, what's called registration trial,

phase three, in which one then fixes the dose, fixes the disease,

fixes the formulation, and then treats a large number of cohorts, both with and without the drug

to determine how effective the drug is. And at the end of this time, if your drug is safe and efficacious, you'll submit

what's known as a new drug application, an NDA,

to the FDA. They will either, they will review it and agree with you or not,

that you have a drug that's ready to go into humans

and at the end of that process, you have this pill down here,

which will then be launched with great fanfare, because this process is, as you'll see, a very long and arduous one.

Ok so I'm going to start at the beginning here with target ID.

What's causing the disease? How is it, what is the actual molecular target that we want to go after?

This link to the disease of interest.

And this is actually a very, very, can be a very long process

to find out what causing the disease.

Many diseases we don't have a clue as to what their cause is.

And in fact, ironically, even with all the tests that we might do to validate a target,

the final validation of a target is not known until you get down here with the pill itself,

to see if that is actually effective in a human.

Ok, so just briefly, what are the general causes of disease, what are the things that we think about.

First thing is, I like to think is it a bug or is it in the body?

Is it an infectious agent

or is it a host imbalance? So, for instance, if it's an infectious agent,

that's causing the disease, generally these days, we have sequences of the pathogenic bacteria.

We'll find a target that's not in humans

and then we'll take that protein target and go after that

in the drug discovery process.

If however, it's a disease like host imbalance, maybe it's a metabolic disease or cardiovascular disease or cancer

you first have to decide is it due, is the disease caused by an underactive protein,

for instance, people with diabetes,

they're not as responsive to insulin and so by giving them back insulin

you can hope to modify and ameliorate that condition.

Other diseases, for instance, here, many cancers are caused by overactive proteins

such as kinases, and so there's a lot of interest in discovering drugs

that would inhibit specific kinases for cancer.

Ok, that is just sort of a very skimmed view of this process, but just to give you a sense.

Once you have identified the target, this target process actually can be very complex.

So, the human genome is vast, there's some twenty thousand genes

that code for proteins. And finding exactly which one is causing the disease

can be challenging. So, one you've come up with the protein,

and the gene that encodes it for that particular disease,

you're ready to go on to another very important consideration.

Which is that not only do you need to go after the biology of the target,

the target itself, which is causing the disease, but that target is

itself has to be amenable to small molecule discovery.

And by that I mean it has to be something that we think could bind a small molecule.

because that in the end is ultimately what we want to do.

What I show here is a recent drug target

known as the BCR-Abl protein, shown in this space filling view here,

and in it is the small molecule known as Gleevec,

which was found to bind to it.

And you can see that these are, it was thought that this would be a good drug target because it was known

that kinases such as this bind ATP, and ATP targets have pockets in them for which we can find small molecule surrogates.

And indeed, they did find them for Gleevec.

Another property to look at is does the site have a cavity or a hot-spot,

an energetic region in the molecule that can bind a small molecule

So these kinds of considerations sort of define the druggability of the target.

So, first you have to determine the biology of it,

and its link to a disease, and next the druggability of the target.

based on whether or not we think we can find compounds that will engage the target.

Ok, now certain targets really like to bind small molecules.

And in fact, one of the favored disease targets are GPCRs,

G-coupled protein receptors. They naturally bind small molecules

and they've been traditionally great targets for going after for small molecules.

and in fact about forty five percent of the approved drugs are GPCRs.

Other targets which are of great interest in terms of the biology are kinases, that I had mentioned

proteases and protein-protein targets.

These targets can bind small molecules, but in general, they bind them weaker

than GPCRs and that probably accounts for why we see so much activity in finding GPCR inhibitors than others.

We then want to talk about what is it that we're looking for at the end?

What is it we hope this drug will be?

Well, first of all, most oral drugs, we'd love them to be just a single, daily dose.

That you only have to take it once

and typically, that would mean something less than a hundred milligrams of the drug that you would take.

Just for example, here's a pill bottle of Ibuprofen,

in here are tablets which are about in total two hundred milligrams or so, less than half of that is the drug itself

because the rest is the formulation

for the drug.

Now, in order for that to be the case, in order for us to be

at a drug dose of a hundred milligrams per day,

there's certain molecular properties that a compound's going to have to show.

And one of them is it's going to have to bind to the target with a high affinity