During World War I, one of the
horrors of trench warfare was a poisonous yellow cloud
called mustard gas. For those unlucky enough to be exposed, it made the air impossible to breathe,
burned their eyes, and caused huge blisters on exposed skin. Scientists tried desperately to develop an
antidote to this vicious weapon of war. In the process they discovered the gas
was irrevocably damaging the bone marrow of affected soldiers— halting its
ability to make blood cells. Despite these awful effects,
it gave scientists an idea. Cancer cells share a characteristic with
bone marrow: both replicate rapidly. So could one of the atrocities of war become a champion in the
fight against cancer? Researchers in the 1930s
investigated this idea by injecting compounds derived
from mustard gas into the veins of cancer patients. It took time and trial and error to find
treatments that did more good than harm, but by the end of World War II, they discovered what became known
as the first chemotherapy drugs. Today, there are more than 100. Chemotherapy drugs are delivered
through pills and injections and use "cytotoxic agents," which means
compounds that are toxic to living cells. Essentially, these medicines cause some
level of harm to all cells in the body— even healthy ones. But they reserve their most powerful
effects for rapidly-dividing cells, which is precisely the hallmark of cancer. Take, for example, those first
chemotherapy drugs, which are still used today and
are called alkylating agents. They’re injected into the bloodstream, which delivers them to
cells all over the body. Once inside, when the cell exposes
its DNA in order to copy it, they damage the building blocks of
DNA’s double helix structure, which can lead to cell death unless
the damage is repaired. Because cancer cells multiply rapidly, they take in a high concentration
of alkylating agents, and their DNA is frequently exposed
and rarely repaired. So they die off more often
than most other cells, which have time to fix damaged DNA and don’t accumulate the same
concentrations of alkylating agents. Another form of chemotherapy involves
compounds called microtubule stabilizers. Cells have small tubes that assemble
to help with cell division and DNA replication, then break back down. When microtubule stabilizers
get inside a cell, they keep those tiny tubes
from disassembling. That prevents the cell from completing
its replication, leading to its death. These are just two examples of the six
classes of chemotherapy drugs we use to treat cancer today. But despite its huge benefits,
chemotherapy has one big disadvantage: it affects other healthy cells in the body
that naturally have to renew rapidly. Hair follicles, the cells of the mouth,
the gastrointestinal lining, the reproductive system, and bone marrow
are hit nearly as hard as cancer. Similar to cancer cells, the rapid
production of these normal cells means that they’re reaching for
resources more frequently— and are therefore more exposed to
the effects of chemo drugs. That leads to several common side
effects of chemotherapy, including hair loss, fatigue, infertility,
nausea, and vomiting. Doctors commonly prescribe options
to help manage these side-effects, such as strong anti-nausea medications. For hair loss, devices called cold caps
can help lower the temperature around the head and
constrict blood vessels, limiting the amount of chemotherapy
drugs that reach hair follicles. And once a course of chemo
treatment is over, the healthy tissues that’ve been badly
affected by the drug will recover and begin to renew as usual. In 2018 alone, over 17 million people
world-wide received a cancer diagnosis. But chemotherapy and other treatments
have changed the outlook for so many. Just take the fact that up to 95% of
individuals with testicular cancer survive it, thanks to advances
in treatment. Even in people with acute myeloid
leukemia— an aggressive blood cancer— chemotherapy puts an estimated
60% of patients under 60 into remission following their
first phase of treatment. Researchers are still developing
more precise interventions that only target the intended
cancer cells. That’ll help improve survival rates
while leaving healthy tissues with reduced harm, making one of the best tools we have
in the fight against cancer even better.
