In previous studies, the research teams of Rice biochemist Natasha Kirienko and MD Anderson physician-scientist Marina Konopleva screened about 45,000 small-molecule compounds to find a few that targeted the liver. body.
In the new study, they selected eight of the most promising compounds, identified between five and 30 closely related analogs for each, and conducted tens of thousands of tests to reliably identify them. The system of toxicity of each analogously affects leukemia cells, both when used alone or in combination with existing chemotherapy drugs such as doxorubicin.
“One of the major challenges is to establish optimal conditions and dosages for testing on both cancer cells and healthy cells,” said study lead author Svetlana Panina, a researcher at the University Texas in Austin, who conducted the study during his postdoctoral research at Rice. .
“The results from our previously published cytotoxicity test are helpful, but very little is known about these small molecule compounds. None of them have been thoroughly characterized. in other studies and we basically had to start from scratch to determine the amounts to be used, what they do in the cells, everything. preliminary test.”
During previous work, Kirienko’s lab had shown eight compounds that target the energy-producing machinery inside cells called mitochondria. Tens to thousands of mitochondria are active every minute in every living cell, and like all machines, they wear out with use. Eight compounds produce mitophagy, which cells regularly use to disinfect and recycle mitochondria that have passed their infancy.
Leukemia treatment: New insights
During times of extreme stress, cells may temporarily bypass mitophagy for an emergency energy boost. Cancer is well known for hijacking these types of programs to promote pathological growth. For example, previous research has shown that leukemia cells have much more damaged mitochondria than healthy cells and are also more sensitive to mitochondrial damage than healthy cells. .
Kirienko and Konopleva reasoned that drugs that induce mitophagy can weaken leukemia cells and make them more susceptible to chemotherapy.
“We hypothesized that if they activate mitophagy, they might be particularly toxic to leukemia cells,” said Kirienko, corresponding author of the new study. “And indeed, we found that six out of eight small molecule compounds can be lethal to leukemia cells. Then we wanted to study them further. So we did. looked at closely related molecules and we looked at combinations.”
When two or more drugs are used in combination, researchers can also use them individually and compare the effectiveness of each regimen.
“There is a number called the synergy factor to quantify interactions between drugs,” says Kirienko. “If the coefficient is negative, the drugs antagonize and work against each other. A 0 means no effect and a positive number indicates a positive interaction. Anything over 10 is considered synergistic. ”
For example, a currently prescribed combination drug for leukemia — doxorubicin and cytarabine — has a composite factor of 13, Kirienko said. The team’s experiments showed that some mitophagy-inducing compounds were significantly more synergistic with doxorubicin. The most synergistic, a compound known as PS127B, has a factor of 29.
“The point of synergy is having a concentration, or dose, where a single drug isn’t lethal,” Kirienko said. “There is no death of healthy cells or cancer cells. But using the same concentration in combination can kill a significant amount of cancer cells and still have no effect on healthy cells.”
The team started by testing the toxicity of the compounds and combinations that induce mitophagy against cells with acute myeloid leukemia (AML), the most commonly diagnosed form of the disease. They then tested the six most effective AML-killing compounds against other forms of leukemia and found five were also effective at killing acute lymphoblastic leukemia cells ( ALL) and chronic myelogenous leukemia (CML). Controlled studies show that all mitophagy inducers are less harmful to healthy cells.
In their final experiments, the researchers tested one of the most effective mitochondrial-targeting compounds, PS127E, using an advanced technique known as xenograft modeling (PDX) derived from patient. In the PDX, also known as the “mice clinical trial,” mice were transplanted with cancer cells from a blood cancer patient. As the cells grew, the mice were exposed to a single drug or combination of drugs as a closer cell test of the treatment’s effectiveness. PDX tests on a compound, PS127E, showed it to be effective in killing AML cells in mice.
“While this is very promising, we are still a long way from having a new treatment that we can use in the clinic,” said Kirienko. “We still have a lot to explore. For example, we need to better understand how drugs work in cells. We need to fine-tune the dosage that we think is best and perhaps important. Most of all, we need to test more than one AML cancer drug.