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Despite the promise of new medications that promote the death of cancer cells in people with acute myeloid leukemia, leukemic cells often adopt features that let them evade the drugs’ effects within a year.

Now, new research using human samples and mouse models has found that resistance of leukemia cells to a widely prescribed drug called venetoclax occurs because of a rapid increase in the breakdown and turnover of mitochondria, structures inside the cell that help power its functions. In addition to their role in producing energy, mitochondria also tell cells to die under certain adverse conditions.

This process of programmed cell death often goes wrong in cancer. Damaged mitochondria can also undergo mitophagy—a form of “self-eating” that prevents them from sending death signals to their cells.

Led by scientists at ��ɫtv Langone Health and its Laura and Isaac Perlmutter Cancer Center, the study showed that mitophagy helps leukemia cells evade the killing effects of venetoclax, a drug in a class of medications known as BH3 mimetics.

, researchers found that the levels of several genes associated with mitophagy were increased in 20 leukemia patient samples, compared with normal controls. The level of these genes was even higher in samples from patients with leukemia with drug resistance than in those patients with leukemia who were not. Particularly notable was the increased expression of the gene for mitofusin-2 (MFN2), which codes for a key protein in the outer mitochondrial membrane.

Further experiments using mice into which bone marrow from patients with acute myeloid leukemia was transplanted showed that the drug chloroquine, a known mitophagy inhibitor, restored the ability of venetoclax to kill the cancer cells.

“Overcoming resistance to BH3 mimetic drugs like venetoclax is of unique clinical significance because these medications are often used for treating people with acute myeloid leukemia,” said study co-lead investigator Christina Glytsou, PhD, a former postdoctoral researcher at ��ɫtv Grossman School of Medicine and now an assistant professor at Rutgers University.

“Acute myeloid leukemia is notoriously difficult to treat, with fewer than a third of those affected living longer than five years after their diagnosis, so it is important to maximize the impact of existing therapies,” said study co-lead investigator , an instructor in the .

“Our preclinical findings suggest that combining BH3 mimetics like venetoclax with either MFN2 or general mitophagy inhibitors could possibly serve as a future therapy for acute myeloid leukemia, as current drug treatments are stalled due to drug resistance,” said study senior investigator .

Dr. Aifantis, the Hermann M. Biggs Professor of Pathology and chair of the Department of Pathology at ��ɫtv Grossman School of Medicine and a member of Perlmutter Cancer Center, says the research team plans to design a clinical trial to test whether chloroquine prevents drug resistance in people with acute myeloid leukemia when it is used in combination with venetoclax.

Speaking about other study results, the researchers say they found not only that MFN2 was overly active in people with drug-resistant disease but also that cancer cells exposed to similar cell-death-inducing compounds demonstrated a doubling in mitophagy rates.

Additional testing in cancer cells engineered to lack MFN2 showed increased sensitivity to drugs similar to venetoclax compared with cells that had functional MFN2. The new study and previous research by the team showing misshapen mitochondria in drug-resistant leukemic cells confirmed that increased mitophagy was the source of the problem.

Acute myeloid leukemia, the most common form of adult leukemia, originates in the bone marrow cells and involves the rapid buildup of abnormal blood cells. The blood cancer results in the deaths of more than 11,500 Americans annually. Current treatments include chemotherapy and a limited number of targeted drug therapies. Bone marrow transplantation has also been used when other options fail.

Funding support for the study was provided by National Institutes of Health grants P30CA016087, P30CA013330, R01CA178394, R01CA173636, R01CA228135, R01CA229086, R01CA242020, and K99CA252602. Additional funding support was provided by the Leukemia & Lymphoma Society and by AstraZeneca, which provided several of the BH3 mimetic drugs used in these experiments.

Dr. Aifantis has received additional research funding from AstraZeneca. This arrangement is being managed in accordance with the policies and practices of ��ɫtv Langone Health.

Besides Dr. Chen and Dr. Aifantis, other ��ɫtv Langone study investigators are Wafa Al-Santli, Hua Zhou, , Soobeom Lee, Audrey Lasry, Zhengxi Sun, Dimitrios Papaioannou, Michael Cammer, Kun Wang, and . Other study co-investigators are Emmanouil Zacharioudakis and Evripidis Gavathiotis, at Albert Einstein College of Medicine in New York, who have filed a patent on mitofusin inhibition based on this research; Tomasz Zal, Malgorzata Anna Zal, Bing Carter, Jo Ishizawa, and Michael Andreeff, at the University of Texas MD Anderson Cancer Center in Houston; and Raoul Tibes, at AstraZeneca in Cambridge, United Kingdom.

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