Diphtheria toxin fused to granulocyte-macrophage colony-stimulating factor eliminates acute myeloid leukemia cells with the potential to initiate leukemia in immunodeficient mice, but spares normal hemopoietic stem cells

We studied the cell kill induced by granulocyte-macrophage colony-stimulating factor (GM-CSF ) fused to Diphtheria Toxin (DT-GM-CSF ) in acute myeloid leukemia (AML) samples and in populations of normal primitive hemopoietic progenitor cells. AML samples from three patients were incubated in vitro with 100 ng/mL DT-GM-CSF for 48 hours, and AML cell kill was determined in a proliferation assay, a clonogenic assay colony-forming unit-AML (CFU-AML) and a quantitative long-term bone marrow (BM) culture ie, the leukemic-cobblestone area forming cell assay (L-CAFC). To measure an effect on cells with in vivo leukemia initiating potential DT-GM-CSF exposed AML cells were transplanted into immunodeficient mice. In two out of three samples it was shown that all AML subsets, including those with long-term abilities in vivo (severe combined immunodeficient mice) and in vitro (L-CAFC assay) were reduced in number by DT-GM-CSF. Cell kill induced by DT-GM-CSF could be prevented by coincubation with an excess of GM-CSF, demonstrating that sensitivity to DT-GM-CSF is specifically mediated by the GM-CSF receptor. Therefore, binding and internalization of GM-CSF probably occur in immature AML precursors of these two cases of AML. The third AML sample was not responsive to either GM-CSF or DT-GM-CSF. The number of committed progenitors of normal bone marrow (burst-forming unit-erythroid, colony-forming unit granulocyte- macrophage, and cobble stone area forming cell [CAFC] week 2) and also the number of cells with long-term repopulating ability, assayed as week 6 CAFC, were unchanged after exposure to DT-GM-CSF (100 ng/mL, 48 hours). These studies show that DT-GM-CSF may be used to eliminate myeloid leukemic cells with long-term potential in vitro and in immunodeficient mice, whereas normal hemopoietic stem cells are spared.     

Management of traction wire fracture complicating mechanical basket lithotripsy

BACKGROUND AND STUDY AIMS: The application of basket catheters has become the main method of removing calculi from the biliary and pancreatic duct. However, larger or impacted stones have to be crushed and fragmented by mechanical lithotriptors before removal is possible. Sometimes, fracture of the traction wire occurs as a severe and fraught complication. We describe a precautionary measure which helps to manage this complication. PATIENTS AND METHODS: In a series of 569 consecutive patients suffering from bile or pancreatic duct stones we found 60 (10.5%) who required mechanical lithotripsy for oversized or impacted calculi. Mechanical lithotripsy was always performed initially with a long metal sheath (80 cm) in combination with a standard traction wire. If the traction wire fractured we replaced the long metal sheath stepwise by shorter ones (70cm, 60cm and 50 cm, respectively), allowing immediate continuation of the lithotriptic procedure using the same traction wire. RESULTS: During the lithotriptic procedure three of our patients (5%) were afflicted by traction wire fracture. Two patients could be relieved directly by changing the initial metal sheath to shorter ones. Because of the exceptional hardness of a pancreatic duct stone the third patient needed stone fragmentation by extracorporeal shock wave lithrotripsy (ESWL) before complete mechanical clearance of the duct could be accomplished. CONCLUSION: We advocate the initial use of a long metal sheath (80cm) to perform mechanical lithotripsy. In case of traction wire fracture the use of a shorter metal sheath allows immediate successful continuation of the procedure, thereby frequently avoiding procedures such as ESWL or surgery.     

Delay in resumption of the activity of tetracycline-regulatable promoter following removal of tetracycline analogues

The tetracycline-regulatable system (TRS) has become a widely adopted tool for modification of gene expression and analysis of gene function in mammalian cells, plants and transgenic animals. We have studied the potential application of the TRS in gene therapy, using a single vector containing both the tetracycline-controlled transactivator (tTA) and the tTA-responsive promoter (tRP) transcribing mouse GM-CSF. Stable 293 cells established using this vector were used to study the kinetics of the TRS in response to various tetracycline analogues. Dose-response studies show that doxycycline is the most potent-analogue in abolishing tTA activity. Kinetic studies indicate that, at 1,000 ng/ml, all the analogues have similar efficiencies in down-regulating the system in given time. In contrast, following the removal of the analogues, there is a temporal, dose-dependent delay in resumption of the tRP activity. The time taken for resumption of near-optimal tRP activity is approximately 48 h for tetracycline, 144 h for anhydrotetracycline, 192 h for minocycline and 216 h for doxycycline when cells were pretreated with 1000 ng/ml of these antibiotics. This property of the analogues can be employed in planning a desired course of transgene regulation.