Mouse eating

Photo by Steve Berger

Intermittent fasting inhibits the development and progression of acute lymphoblastic leukemia (ALL), according to preclinical research published in Nature Medicine.

Fasting had an inhibitory effect in mouse models of T-cell and B-cell ALL but not acute myeloid leukemia (AML).

“This study using mouse models indicates that the effects of fasting on blood cancers are type-dependent and provides a platform for identifying new targets for leukemia treatments,” said study author Chengcheng “Alec” Zhang, PhD, of UT Southwestern Medical Center in Dallas, Texas.

“We also identified a mechanism responsible for the differing response to the fasting treatment.”

For this study, Dr Zhang and his colleagues created mouse models of acute leukemia—N-Myc B-ALL, activated Notch1 T-ALL, MLL-AF9 AML, and AML driven by the AML1-Eto9a oncogene—and tested the effects of various dietary restriction plans.

The team used green or yellow florescent proteins to mark and trace the leukemia cells so they could determine if the cells’ levels rose or fell in response to the fasting treatment.

“Strikingly, we found that, in models of ALL, a regimen consisting of 6 cycles of 1 day of fasting followed by 1 day of feeding completely inhibited cancer development,” Dr Zhang said.

At the end of 7 weeks, fasted mice with B-ALL had virtually no detectible cancerous cells—an average of 0.48%—compared to an average of 67.68% of cells found to be cancerous in the test areas of the non-fasted B-ALL mice.

Dr Zhang noted that, compared to B-ALL mice that ate normally, the mice on alternate-day fasting had dramatic reductions in the percentage of ALL cells in the bone marrow and spleen, as well as reduced numbers of white blood cells.

In addition, the spleens and lymph nodes in the fasted mice with B-ALL were similar in size to those of normal mice.

“Although initially cancerous, the few fluorescent cells that remained in the fasted mice after 7 weeks appeared to behave like normal cells,” Dr Zhang said. “Mice in the [B-ALL] model group that ate normally died within 59 days, while 75% of the fasted mice survived more than 120 days without signs of leukemia.”

Dr Zhang and his colleagues said they observed similar results in the T-ALL model but not the AML models. There was no decrease in leukemia cells among fasted mice with AML. And fasting actually shortened survival time in these mice.

Identifying the mechanism

Fasting is known to reduce the level of leptin, a cell signaling molecule created by fat tissue. In addition, previous studies have shown weakened activity by leptin receptors in humans with ALL. For those reasons, the researchers studied both leptin levels and leptin receptors in the mouse models.

The team found that mice with ALL showed reduced leptin receptor activity that increased with intermittent fasting.

“We found that fasting decreased the levels of leptin circulating in the bloodstream as well as decreased the leptin levels in the bone marrow,” Dr Zhang said. “These effects became more pronounced with repeated cycles of fasting. After fasting, the rate at which the leptin levels recovered seemed to correspond to the rate at which the cancerous ALL cells were cleared from the blood.”

The researchers also found that AML was associated with higher levels of leptin receptors that were unaffected by fasting, which could help explain why the fasting treatment was ineffective against this type of leukemia.

It also suggests a mechanism—the leptin receptor pathway—by which fasting exerts its effects in ALL, Dr Zhang said.

“It will be important to determine whether ALL cells can become resistant to the effects of fasting,” he noted. “It also will be interesting to investigate whether we can find alternative ways that mimic fasting to block ALL development.”

Given that this study did not involve drug treatment, researchers are discussing with clinicians whether the tested regimen might be able to move forward quickly to clinical trials.

Intermittent fasting fights ALL, not AML, in mice