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 Rose Bengal, a cheap industrial chemical that turns yarn and food
bright red, has been used as a diagnostic staining agent for some
time. Now, some scientists are looking at its potential to fight
various forms of cancer.
At the forefront is Provectus Biopharmaceuticals Inc, which is
testing a reformulated version of the industrial dye on melanoma,
the deadliest form of skin cancer. The Knoxville, Tennessee, company
reported promising results in a small melanoma study.
While some doctors are encouraged by the research, government
approval is years off and not guaranteed. The company must replicate
its early results on a bigger scale, and a U.S. Food and Drug
Administration decision is not expected before 2019.
Rose Bengal's potential against cancer was discovered by accident.
The salt was first patented in 1882 as a wool dye and has been used
for years as a diagnostic stain in tests for jaundice in newborns
and to detect eye damage.
In 1998, scientists who later founded Provectus were looking for a
safe photoreactive agent to use in an investigation of lasers
against cancer. Rose Bengal fit the bill.
As it turned out, the Rose Bengal solution appeared to work on its
own to dissolve tumors when directed injectly into them, recalled
Provectus Chief Technology Officer Eric Wachter, a former scientist
from Oak Ridge National Lab who co-founded the company. "It made the
lasers obsolete."
In a study of 80 people with advanced melanoma, half of the patients
who had all of their lesions injected appeared cancer free after an
average of two months. A year later, 11 percent continued to show no
signs of cancer, according to a report published the Annals of
Surgical Oncology.
The lesions were destroyed from the inside with no apparent harm to
healthy tissue, researchers said. Reported side effects included
injection site pain and blistering.
Final results from an ongoing 225-patient melanoma trial of the
experimental drug compared to chemotherapy are expected in early
2018. The hope is that the drug, known as PV-10, will prevent
melanoma from progressing beyond Stage III, in which the disease has
spread but not yet to other organs, and allow patients with more
advanced cancer to live longer.
"This is one of the really neat examples of what we call
repurposing, taking drugs that been around for years ... and
suddenly realizing that they may have an oncologic value," said Dr.
Vernon Sondak, head of cutaneous oncology at the Moffitt Cancer
Center in Tampa, Florida. Sondak has been running clinical trials
for Provectus.
IMMUNE SYSTEM RESPONSE
The company also has begun a melanoma trial of the drug with Merck's
Keytruda, a treatment that works by helping the immune system fight
cancer, to see if the combination has a more pronounced effect on
slowing disease than either alone.
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Doctors said they hoped PV-10 combinations would not create the
additional toxicity seen with some other combination therapies
because of its mild side effect profile.
In addition to PV-10 destroying injected skin lesions, researchers
noticed shrinkage in untreated lesions and tumors as far away as the
lungs, suggesting it may also provoke an immune system response.
"We've come to the conclusion that it is immune based," said Dr.
Sanjiv Agarwala, chief of medical oncology and hematology at St.
Luke's Cancer Center in Bethlehem, Pa. Agarwala, who has been
conducting PV-10 trials funded by Provectus, also has run several
cancer immunotherapy studies, including on Keytruda.
Dr. Patrick Hwu, an immunotherapy expert from MD Anderson Cancer
Center, said PV-10 is one of several interesting tumor ablation
techniques in the works.
"The biggest value will be if it can affect distant disease," said
Hwu, who is not involved in PV-10 testing.
Pfizer holds a co-patent on PV-10 for use in combination therapies,
and Boehringer Ingelheim has secured right of first refusal on use
of the drug against liver cancer in China, the companies told
Reuters.
Provectus estimates the cost of PV-10 from laboratory to approval
will be about $100 million, a fraction of the more than $1 billion
in research and development for a new drug that the industry often
cites to defend against criticism that medicine prices are too high.
Provectus executives say the small development tab - along with
relatively low manufacturing costs and easy handling requirements -
could make PV-10 a less expensive new treatment. But the final
decision on price is likely to be made by a bigger drugmaker, as
Provectus plans to put itself up for sale once its drug is approved.
The $95 million company trades at about 49 cents per share, off a
high of 98 cents last April, on very small volumes, possibly
reflecting investor uncertainty over the drug's prospects.
(Reporting by Bill Berkrot; Editing by Michele Gershberg and Lisa
Girion)
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