(TIME.com) -- It's called ibrutinib, and it's a potential breakthrough in tr
eating chronic lymphocytic leukemia (CLL) that could leave patients with few
er side effects than chemotherapy.
In research published in the New England Journal of Medicine (NEJM), scienti
sts report that the experimental drug, which differs from broadly acting che
motherapy agents by specifically targeting certain cancer-causing processes,
significantly prolongs the life of patients.
Ibrutinib is currently being tested on tumors that target the body's immune
system, such as CLL and mantle cell lymphoma (MCL).
CLL is the second most common form of leukemia among adults in the U.S., and
about 15,000 Americans, most of whom are elderly, are diagnosed with the bl
ood and bone marrow cancer every year.
The drug is the first to bind to and block the activity of a protein known a
s Bruton's tyrosine kinase (BTK), which plays an important role in helping i
mmune cell tumors, which develop from abnormally growing blood stem cells, t
o grow.
Once ibrutinib binds to the immune system's B-cells, it prevents tumors grow
ing in these cells from signaling for the nutrients they need to grow and di
vide. According to the study, the drug doesn't seem to affect the body's T-c
ells, as chemotherapy agents do, so patients experience fewer side effects.
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Early work on animals showed that the experimental drug effectively shut dow
n tumor cell division, so the researchers tested the compound on 85 CLL pati
ents who had all tried and failed to respond to at least two other anti-canc
er treatments. Some even harbored genetic mutations associated with particul
arly aggressive forms of CLL that typically lead to death within two years o
f diagnosis.
The patients were randomized to take one of two different doses of an ibruti
nib pill a day. After nearly two years of treatment, 71% of this hard-to-tre
at group had responded with slower tumor growth, and at 26 months, 75% showe
d no additional progression of their cancer. At the end of the study period,
83% of the participants were still alive, and most of the patients only com
plained of diarrhea and fatigue.
"This is truly a breakthrough drug for CLL. I have been a CLL specialist sin
ce 1997, and we have not had a drug like this come into the field yet," says
study author Dr. John C. Byrd, the director of the division of hematology a
t The Ohio State University Comprehensive Cancer Center.
"The most common thing I have heard patients say is that it brings their dis
ease under control and makes them feel how they did before their cancer. I'v
e heard that at least a dozen times."
The scientists and patients were most encouraged by the fact that the the dr
ug helped them to enjoy a longer period of time, on average, in which their
tumors remained stable and didn't progress, than they they had while using c
hemotherapy agents.
The MCL patients showed similarly positive results. MCL is an aggressive for
m of non-Hodgkin lymphoma that generally doesn't respond to existing chemoth
erpay, immune-based treatment or stem cell transplants.
But in a separate study also appearing in NEJM involving 111 advanced MCL pa
tients, about 68% of the participants responded to ibrutinib and 58% were al
ive after 18 months on the therapy. The response rate was encouraging since
the last agent to treat MCL was approved by the Food and Drug Administration
(FDA) with a 30% response rate.
That efficacy data, combined with the experimental drug's favorable side eff
ect profile, has some doctors hoping that ibrutinib might one day replace th
e harsher chemotherapy agents that are currently the standard of care for th
ese cancers.
"With chemotherapy, you get it for a specific period of time because patient
s cannot tolerate the side effects long term. This is an oral medicine that
targets something the leukemia cells are dependent on but the rest of the bo
dy isn't," says Byrd.
"People can take a pill once a day and generally they tolerate it well. The
side effects are much less than the chemo or other therapies that would be u
sed in this setting."
Ibutrinib is the first agent to specifically target the BTK pathway, but it'
s part of a wave of new anti-cancer agents that have been developed to act a
s more precise, smart bomb medications that destroy just cancer cells while
leaving healthy cells intact. That allows them to minimize the often intoler
able side effects of harsher drugs like chemotherapy agents, which tend to w
ipe out both healthy and cancerous cells at once.
"In some situations there have been some medications we have tested where pa
tients have said they would rather not be treated and pass (away) from their
leukemia than go through the side effects of their medicine that is not goi
ng to cure them," says Byrd.
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Both of the clinical trials, which were sponsored by ibrutinib's developer,
Pharmacyclics, involved older adults, who are most often affected by these c
ancers, so the researchers believe the results should be applicable to most
patients diagnosed with these diseases.
The studies also suggest that patients may benefit from longer progression-f
ree survival if they start therapy earlier in the course of their disease.
"Right now, after this drug gets approved, it will likely be used in the set
ting of relapse initially, but there are ongoing studies that are looking at
it for initial therapy. It is something that is especially (beneficial) for
elderly patients who do not tolerate chemotherapy well. This will likely re
place chemotherapy," says Bryd.
The fact that even patients with the most aggressive types of CLL, which are
driven by genetic mutations, responded to ibrutinib also hints that the exp
erimental drug may become an important part of treating these cancers in com
ing years.
The FDA designated it as breakthrough therapy, and Pharmacyclics and Janssen
, who are jointly developing the drug, plan to file a New Drug Application (
NDA) with the FDA for the use of ibrutinib to treat B-cell malignancies by 2
014.
