78 Science & technology The Economist February 13th 2021
given them more than 2,000 new samples,
from which they have been able to create
more than 400 extra cell lines. Encourag-
ingly, 30% of these represent cancers that
are either rare or occur mostly in chil-
dren—both groups that researchers need
more examples of.
Once the cancerous cells have been per-
suaded to start growing in DepMap's Petri
dishes, the next step is to examine them for
weaknesses. So far, the teams have tested
around 6,000 drugs—about half the num-
ber ever licensed for any disease—against
more than 500 cancers. They have already
turned up some promising candidates. Te-
poxalin, an arthritis medicine for pets, ap-
pears to kill cancers in which a gene called
ABCB1is overactive. Disulfiram, used to
treat alcoholism, seems toxic to certain tu-
mours that lack genes involved with the
processing of heavy metals.
New technology means it is not only
drugs which can be analysed systematical-
ly. Matthew Garnett, of the Sanger Insti-
tute, discussed using crispr-cas9 to do
the same for genes. crispr-cas9 is a set of
chemical scissors employed by bacteria to
chop up and deactivate dnaintroduced by
viruses that prey on them. Repurposed as
an all-purpose dna-cutting device, it has
become one of biology's most useful tools.Cut to the chase
Dr Garnett described how researchers at
the Sanger had used crispr-cas9 to dis-
able, one by one, nearly every gene in hun-
dreds of cancer-cell lines. This permitted
them to discover which genes are essential
for a tumour's survival and might therefore
make promising targets for new drugs. He
gave the example of wrn, a gene involved
in fixing damaged dna. Cancer cells are of-
ten already deficient in dna-repair mecha-
nisms, and some seem reliant on wrnfor
survival. Based on those results, Dr Garnett
said, drug companies are already develop-
ing drugs designed to suppress either wrn
itself, or the protein it produces.
Deconstructing cancer cells’ genomes
has yielded other insights, too. Dr Boehm
noted that examining the rate at which
genes are expressed—that is, used to make
proteins—is often more useful for predict-
ing vulnerabilities than looking for muta-
tions in the genetic code. This, he said, is
especially true of some childhood cancers,
which often exhibit few mutations.
An encouraging start, then. But there is
a long way to go. Dr Boehm estimated that,
despite having analysed all the genes and
thousands of drugs for around 1,000 differ-
ent sorts of cancer, the project remains
about 90% unfinished. This may be an un-
derestimate. As Fiona Behan, another of
the Sanger’s DepMap researchers, pointed
out, besides examining individual genes
in isolation, disabling several at once may
also yield useful insights. In that case,though, the number of possible combina-
tions would be astronomical.
Moreover, not all results in Petri dishes
bear fruit in human beings. Andrea Califa-
no of Columbia University observed that
cancer cells which have adapted to grow in
laboratories often have different patterns
of gene expression from those that grow in
bodies. Nevertheless, as Dr Garnett told the
meeting, the success rate for developing
new cancer drugs is, at the moment, de-
pressingly low. If DepMap can uncover
plausible targets for developers to aim at,
that may start to change. Sustainable constructionUrban growth
M
ore than half the world’s population
dwell in cities, and by 2050 the unex-
pects that proportion to reach 68%. This
means more homes, roads and other in-
frastructure. In India alone, the equivalent
of a city the size of Chicago will have to be
developed every year to meet demand for
housing. Such a construction boom does,
though, bode ill for tackling climate
change, because making steel and con-
crete, two of the most common building
materials, generates around 8% of the
world’s anthropogenic carbon-dioxide
emissions. If cities are to expand and be-
come greener at the same time, they will
have to be made from something else.As it happens, Chicago might become
part of the answer. In recent years, as archi-
tects have become increasingly interested
in modern timber-construction methods,
wooden buildings have been getting stead-
ily taller. The current record is held by the
85-metre-tall Mjostarnet building in Nor-
way (see picture), completed in 2019. But
this would be dwarfed by the River Beech
Tower, a 228-metre edifice proposed for a
site beside the Chicago river.
As the aaasmeeting heard this week,
wood is one of the most promising sus-
tainable alternatives to steel and concrete.
It is not, however, everyday lumber, chip-
board or plywood that is attracting the in-
terest of architects. Rather, it is a material
called engineered timber. This is a com-
posite of different layers, each designed to
meet the requirements of specific compo-
nents such as floors, panels, cross-braces
and beams. Besides engineering the shape
of a component, designers can align the
grains in the layers to provide levels of
strength that rival steel, in a product that is
up to 80% lighter. Engineered timber is,
moreover, usually prefabricated into large
sections of a building in a factory. That cuts
down on the number of deliveries that
have to be made to a construction site.
All this makes a big difference to car-
bon-dioxide emissions. Michael Ramage
of the University of Cambridge told the
meeting of a 300-square-metre four-storey
wooden building constructed in that city.
Erecting this generated 126 tonnes of CO 2.
Had it been made with concrete the tally
would have risen to 310 tonnes. If steel had
been used, emissions would have topped
498 tonnes. Indeed, from one point of
view, this building might actually be
viewed as “carbon negative”. When trees
grow they lock carbon up in their wood—in
this case the equivalent of 540 tonnes of
CO 2. Preserved in Cambridge rather than
recycled by beetles, fungi and bacteria,
that carbon represents a long-term sub-
traction of CO 2 from the atmosphere.
If building with wood takes off, it does
raise concern about there being enough
trees to go round. But with sustainably
managed forests that should not be a prob-
lem, says Dr Ramage. A family-sized apart-
ment requires about 30 cubic metres of
timber, and he estimates Europe’s sustain-
able forests alone grow that amount every
seven seconds. Nor is fire a risk, for engi-
neered timber does not burn easily. Ac-
cording to a report by the Potsdam Insti-
tute for Climate Impact Research, in Ger-
many, large structural timbers are fire re-
sistant because their inner cores are
protected by a charring layer if burnt. It is
therefore hard for a fire to destroy them.
And, for extra incombustibility, fireproof-
ing layers can be added to the timber. All in
all, then, it looks as if wood as a building
material may get a new lease of life. Theaaashears about cities made of
wooden buildingsA block of wood