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- Hello, my name is Mark Mercola.
I'm a Professor of Cardiovascular Medicine
at Stanford University.
It's a pleasure to talk to you about
using induced pluripotent stem cells or iPSCs
for predicting and removing drug cardiotoxicity.
This work has been supported for many years by CIRM,
we're very grateful for that work
and establishing this platform in my laboratory.
So what is drug-induced cardiotoxicity?
This is the unintended adverse effect of medicines
on the electrical and/or the mechanical function
of the heart.
This can be a very major problem
for certain areas of medicine, such as oncology,
where as many as a third of the patients
who have been treated with oncology drugs
will develop some form of heart disease
as a consequence of their treatment.
It's also a major problem for pharmaceutical companies.
It's the major reason for drug attrition,
the drug failure during the development and in some cases,
even after market launch.
So we are using iPS cells to try to address this problem.
So what iPS cells are cells that we can derive
from your skin or your blood,
any other cell type in your body basically
by reprogramming them back to an embryological state.
This is was first done by Shinya Yamanaka
based on work done by John Gerden years before.
And the technology for this
won them the Nobel prize for medicine in 2012.
So once we have iPS cells,
which resemble cells of the early embryo,
we can direct their differentiation to different cell types
in the body, such as heart, muscle cells, brain cells,
kidney cells, intestinal cells, and so on.
And so you were able then to study disease
because of course the cells retain the genetics
of the original person.
So the person has a genetic disease.
You hope that some manifestation of that disease
will be reproduced in the laboratory.
And we can also study the effect of drugs on those cells.
So using this platform then,
the work that I'm gonna tell you about
creates muscle cell, heart muscle cells,
and you can see that in the video on the slide,
we treat those heart muscle cells with drugs
or drug candidates.
And in order to predict the adverse effects
that those molecules will have on the heart,
as well as to understand the influence of patient genetics
some people are much more susceptible than others,
to the adverse effect of drugs.
And we also would like to use this platform
to engineer safer drugs.
So my talk today will be divided into three parts.
I'll first talk about our recent work
to develop efficient means of producing
and increasing the fidelity
of disease modeling in iPS cells.
Secondly, I'll talk about using this platform
to optimize an existing drug
for a cardiac electrophysiologic disorder.
And thirdly, I'll talk about our work
to reengineer on oncology drug
to diminish its adverse effects.
I'll start with the first part.
Producing cardiomyocytes efficiently
and making better disease models.
So when we began this work with CIRM Funding back in 2008,
it was only possible to make small numbers
of cardiomyocytes,
certainly nothing that could be used
in high throughput drug screens.
So with grants, from CIRM to John Cashman,
medicinal chemist at the Human BioMolecular Institute,
and to me
and I was in those days
at the Sanford Burnham Prebys Institute
and at UCSD in San Diego,
we developed a screening platform
where we could look for compounds
that would drive stem cells,
in those days, embryonic stem cells
to form cardiac muscle cells.
And we hit upon a number of compounds that would do this.
One of them is shown here.
And these molecules are now the basis
of nearly all efficient protocols to produce cardiomyocytes.
More recently,
we've been using this platform to advance the maturity
of cardiomyocytes iPS cardiomyocytes.
These cells if we formed them by conventional means
are CIRMilar to cells,
of a very, very early embryo
for a few weeks, a month or so into gestation.
And that hampers disease modeling.
Which of course we're interested in the adult.
So we learned that if we switch the energy substrates
that the cells burn.
So rather than burning sugar,
we switched them to fat and other substrates.
Now we can drive the metabolic,
the structural and the electrophysiological aspects
of their maturation,
and that improves their ability to model diseases
as exemplified by dilated cardiomyopathy
or an electrophysiological disorder,
long-QT syndrome type 3.
So now the rest of the talk,
I'm gonna talk about our efforts to use this platform
for drug re-engineering.
And the idea here is to make a better version of a drug
that has some adverse effect on the heart of a patient
that limits the,
either the dosing or compromises the patient's health.
And so the idea is that we would create heart cells
from these people who have problems with some drug.
We would then in the dish visualize the effect of that drug
on the heart cells,
and then we would using high throughput screens
using robotic platforms,
such as what you're seeing in the video,
we would then develop better versions of those drugs,
understand what to tweak and the drug to make it safer
and yet retain its activity.
And that would then return that
the idea would be to return that drug
through a pharmaceutical development pipeline
back to the patient.
But the problem when we started this,
it was a rather audacious goal
because iPS cardiomyocytes
had never been used to drive a drug development campaign,
certainly not patient cells,
where we were looking at a patient phenotype.
So the question that we were all wondering
is will these assays in this platform
be statistically robust enough
to drive a medicinal chemistry exploration of a drug.
And so we needed a test case.
So with a CIRM Early Translation IV Grant
that was awarded to John Cashman and myself,
we set about to reengineer a drug that's used
for a cardiac electrophysiology disorder,
long-QT 3, and the drug was mexiletine.
We're grateful for the support of physiologists in New York
and in Chicago with their labs of Rocky Kass and Al George.
So what is long QT type 3?
It's a rare genetic disease
that causes ventricular tachycardia
and sudden cardiac death.
Most commonly in teenagers and young adults.
It's hallmark is that it has a prolongation
of the QT interval on the surface of electrocardiogram.
Now mexiletine will shorten that QT interval
and thereby reduce the risk
that the patient will develop a lethal arrhythmia.
But the problem is that mexiletine slightly higher doses
than what's achieved in patients,
can also induce electrical problems in heart muscle cells.
And although this isn't a huge problem clinically
because these patients are very well managed.
It nonetheless has induced concerns
that it might induce or aggravate an arrhythmia.
So even though it's not such a huge clinical problem,
it's a wonderful test case for this platform
because we can see the electrophysiological
problems of cardiomyocytes quite clearly
in these iPS cardiomyocytes assays.
So we needed a patient.
So Rocky Kass in New York and his clinical collaborators
had identified a boy
born with a particularly serious form of long QT 3.
He was actually diagnosed in utero
and implanted with a dual chamber ICD
that you can see here to control his arrhythmia.
You can see the prolongation of the QT interval
on the electrocardiogram,
and he was treated with mexiletine and responded quite well.
So we then made iPS cardiomyocytes from this boy,
and we wanted to record their electrical activity,
it's much like what is doing in clinic
with an electrocardiogram,
but we do it optically
and you can see the beating of the cardiomyocytes,
and here you can see a normal electrical activity
of cardiomyocytes.
And here you can see a rhythmic activity.
We've got a prolongation of the action,
but so-called action potential.
And you get these extra spikes
known as early after depolarizations.
So using this platform
and using iPS cardiomyocytes made from the boy,
we were able to run through and libraries
of structural analogs of mexiletine
and identify what would be the good and the bad
determinants in those structures.
So we were looking for molecules that will shorten
the action potential,
but mexiletine on its own,
when you give it into too high doses
will cause prolongation and these after depolarizations
and that's bad.
What we were able to do eventually,
was fine for molecules that would only shorten,
but even at high concentrations would not prolong.
So we produced a safer version of the drug.
And this molecule has worked in studies
to block the arrhythmia caused by long QT 3.
Now emboldened by that we now set out to do,
which is really what I've always wanted to do,
which is to reengineer on oncology drugs.
These are as I said,
a serious problem about a third of cancer survivors
will suffer cardiac problems
as a consequence of their treatment.
It's not just old cancer drugs,
but even the new molecularly targeted therapeutics
that have this problem.
We assembled a large team co-directed by a medicinal chemist
Sanjay Malhotra at Stanford
and Ioannis Karakikes a stem cell biologist at Stanford.
And these are the postdoctoral fellows,
the trainees who worked on this project.
So the drug we focused on was ponatinib.
It's used to treat Chronic Myelogenous Leukemia
because it inhibits the oncogene known as BCR-ABL.
Now BCR-ABL in its normal form
is inhibited by a relative of ponatinib
known as a imatinib.
That is a safe molecule,
but unfortunately in large number of patients
have a mutation that arises
in the BCR-ABL gene
and that mutation renders the protein in sensitive
to imatinib in all other first line defense drugs for CML.
Ponatinib is the only effective drug
against this mutation that's been approved.
So, whereas imatinib is safe as I told you,
ponatinib is cardiotoxic
eight percent of people who have taken it
have developed heart failure,
many more have developed heart disease.
But since imatinib is safe,
we thought the problem with ponatinib
is an off target effect.
So we wanted to remove it.
And the iPS platform is ideal for this
because we don't need to know the actual reason
why the drug is bad.
We just need to know that it has bad effects
that we can see in the dish.
It's difficult to know the exact reason
because these molecules target many, many proteins
in the cell,
at least 50 structurally related molecules
to the BCR-ABL gene and as many as three or four times
as many non kinase targets.
So what we did was we took the structure of ponatinib,
we started tweaking parts of the compound
in order to map the parts of the molecule
that are important for its antitumor effects
and important for the cardiotoxic effect so the drug.
And we were guided by the structures
of the relatively safe compound imatinib.
So we synthesized many analogs in an iterative process
and tested them in parallel in iPS cardiomyocytes,
in vascular cells, which form tubes
and in the tumor cells, both normal,
BCR-ABL, and mutated BCR-ABL.
And the idea was to define the structural determinants
for the good and the bad aspects of ponatinib.
And to cut to the chase,
I'm gonna show you two examples of improved molecules.
And in this heat map representation here,
red is bad and white is safe.
And these are different indices of cardiotoxicity
in the dish.
Imatinib is white, so safe.
Ponatinib is red, so bad.
And to these two analogs here you can see are mostly white.
And when we can see that on the
endothelial tumors vascular genesis asset,
you can see that they do not disrupt the vasculature,
whereas ponatinib does even at high doses,
and yet they continue to block
the growth of the tumor cells the smaller number
indicates better inhibition of the tumor.
And so our new drugs like ponatinib will inhibit,
and even the mutant tumors with a mutant kinase,
they will also inhibit.
So, and this works not only in vitro
those prior data where in vitro,
but it also works in vivo
if we have tumors human tumors in mice.
And by treating with ponatinib or with our new drugs,
we can reduce the tumor burden substantially.
So what I've told you then is that in parallel
using cardiomyocytes vascular assays and tumor assays,
we could engineer a safer version of the CML drug ponatinib.
We learned that there are different determinants
for the good and bad aspects of the molecule
and that the new molecules that we've produced
retain the anticancer effect,
but have decreased cardiotoxic effects in vitro.
And they have acceptable properties to go into animals
and they show antitumor activity
against in xenograft models,
comparable to ponatinib, but without the cardiotoxicity.
This work as I said,
has been supported by CIRM Funding
specifically for these projects
throughout the 10 year history,
as well as it's been aided by CIRM Training Grants
to the Sanford Burnham, The Scripps Institute,
The Salk Institute
and the university of California at San Diego.
I directed the training grant at the Sanford Burnham.
It's also been aided by CIRM Infrastructure Grants
to the three institutes,
those three institutions in San Diego.
Thank you very much.
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