Chronic stress enhances progression of acute lymphoblastic leukemia via ß-adrenergic signaling.

Clinical studies suggest that stress-related biobehavioral factors can accelerate the progression of hematopoietic cancers such as acute lymphoblastic leukemia (ALL), but it is unclear whether such effects are causal or what biological pathways mediate such effects. Given the network of sympathetic nervous system (SNS) fibers that innervates the bone marrow to regulate normal (non-leukemic) hematopoietic progenitor cells, we tested the possibility that stress-induced SNS signaling might also affect ALL progression. In an orthotopic mouse model, Nalm-6 human pre-B ALL cells were transduced with the luciferase gene for longitudinal bioluminescent imaging and injected i.v. into male SCID mice for bone marrow engraftment. Two weeks of daily restraint stress significantly enhanced ALL tumor burden and dissemination in comparison to controls, and this effect was blocked by the ß-adrenergic antagonist, propranolol. Although Nalm-6 ALL cells expressed mRNA for ß1- and ß3-adrenergic receptors, they showed no evidence of cAMP signaling in response to norepinephrine, and norepinephrine failed to enhance Nalm-6 proliferation in vitro. These results show that chronic stress can accelerate the progression of human pre-B ALL tumor load via a ß-adrenergic signaling pathway that likely involves indirect regulation of ALL biology via alterations in the function of other host cell types such as immune cells or the bone marrow microenvironment.

Determination of a humane endpoint in the L1210 model of murine leukemia.

The purpose of our study was to derive an alternate end-point to death or moribund appearance for the frequently used L1210 model of murine leukemia. In reviewing the published literature, we were unable to identify a suitable intermediate marker of substantive disease that predicted outcome in the BDF1 recipient of the L1210 leukemia. In an attempt to refine the use of animals in our laboratory, we developed a scoring sheet for behavioral and physical changes that followed intravenous injection of L1210 lymphocytic leukemia cells into BDF1 recipients. At 12-h intervals for the first 2 days after tumor-cell injection and at 6-h intervals thereafter, animals were observed and scored for each parameter. When death was imminent, animals were euthanized by inhalation of methoxyflurane followed by decapitation. Changes in physical and behavioral characteristics then were correlated with the end-point of death. Changes occurred in the mice approximately 7 days after tumor cell inoculation and 24 h before death. The earliest of these signs was hunched posture, followed by one or more other characteristics including decreased activity, increased facial swelling, ears in backward position, abdominal swelling, squinting eyes, and labored breathing. From these data, we were able to develop criteria for early euthanasia. Use of these intermediate end-points likely will substantially reduce the stress on the animals without compromising scientific outcomes in experiments using this or related preclinical models of cancer.