Threshold levels of ABL tyrosine kinase inhibitors retained in chronic myeloid leukemia cells determine their commitment to apoptosis

The imatinib paradigm in chronic myelogenous leukemia (CML) established continuous BCR-ABL inhibition as a design principle for ABL tyrosine kinase inhibitors (TKI). However, clinical responses seen in patients treated with the ABL TKI dasatinib despite its much shorter plasma half-life and the apparent rapid restoration of BCR-ABL signaling activity following once-daily dosing suggested acute, potent inhibition of kinase activity may be sufficient to irrevocably commit CML cells to apoptosis. To determine the specific requirements for ABL TKI-induced CML cell death for a panel of clinically important ABL TKIs (imatinib, nilotinib, dasatinib, ponatinib, and DCC-2036), we interrogated response of CML cell lines and primary CML cells following acute drug exposure using intracellular fluorescence-activated cell sorting and immunoblot analyses of BCR-ABL signaling, apoptosis measurements, liquid chromatography/tandem mass spectrometry of intracellular drug levels, and biochemical TKI dissociation studies. Importantly, significant intracellular TKI stores were detected following drug washout, levels of which tracked with onset of apoptosis and incomplete return of BCR-ABL signaling, particularly pSTAT5, to baseline. Among TKIs tested, ponatinib showed the most robust capacity for apoptotic commitment showing sustained suppression of BCR-ABL signaling even at low intracellular levels following extensive washout, consistent with high-affinity binding and slow dissociation from ABL kinase. Together, our findings suggest commitment of CML cells to apoptosis requires protracted incomplete restoration of BCR-ABL signaling mediated by intracellular retention of TKIs above a quantifiable threshold. These studies refine our understanding of apoptotic commitment in CML cells and highlight parameters important to design of therapeutic kinase inhibitors for CML and other malignancies.

Choosing a concomitant chemotherapy and radiotherapy regimen for squamous cell head and neck cancer: A systematic review of the published literature with subgroup analysis

BACKGROUND

A systematic review was conducted to develop clinical recommendations for concomitant chemotherapy (CT) and radiotherapy (RT) in patients with locally advanced squamous cell head and neck cancer (SCHNC).

METHODS

Results of published randomized controlled trials (RCTs) were pooled using Meta-analyst(0.988) software.

RESULTS

A pooled analysis of 18 RCTs (20 comparisons) involving 3,192 patients detected a reduction in mortality for concomitant therapy compared with RT alone (odds ratio [OR], 0.62; 95% confidence interval [CI], 0.52-0.74; relative risk, 0.83; risk reduction, 11%; p < .00001). Platinum-based regimens involving 1,514 patients from nine trials (10 comparisons) were most effective (OR, 0.57; 95% CI, 0.46-0.71; p < .00001; risk reduction, 12%). Concomitant therapy produced more acute adverse effects than RT alone.

CONCLUSION

Platinum-based concomitant CT and RT is superior to conventional RT alone in improving survival in locally advanced SCHNC. Subgroup analyses can be used to help in choosing the most appropriate concomitant regimen.

The effects of prolonged hepatic ischaemia before 70 per cent partial hepatectomy in the dog

The effect of prolonged normothermic ischaemia before partial hepatectomy was assessed in 10 dogs. During the period of ischaemia, portal decompression was maintained. The survival rate for animals undergoing 75 minutes of total liver ischaemia was 60 per cent and 2 of the dogs died as a result of hypoglycaemia. High levels of alkaline phosphatase and transaminases in the survivors indicated a severe degree of hepatocyte damage. However, complete restoration of liver mass was noted 6 weeks after partial hepatectomy and was not impaired by the prolonged ischaemia. This study confirms the resistance of the dog liver to ischaemia before partial hepatectomy. The critical period beyond which ischaemia is followed by an increasing number of deaths and severe metabolic upset is in the region of 1 hours.

The mechanism of impaired coagulation after partial hepatectomy in the dog

Coagulation mechanisms were examined in the dog after a 70 per cent hepatectomy and the additional effect of varying periods of ischemia on the liver remnant. Dogs were submitted to a 70 per cent partial hepatectomy, and the liver remnant was rendered ischemic by occluding the vascular inflow. Portal decompression during ischemia was accomplished by allowing portal venous flow through the lobes subsequently resected. Dogs in the control group, those undergoing hepatectomy alone and those undergoing hepatectomy together with 60 minutes of ischemia time exhibited a fall in hemoglobin and hematocrit values, a transient leukocytosis, a small increase in kaolincephalin clotting time and a decline in platelet count but no significant thrombocytopenia. Prothrombin time was changed in dogs undergoing hepatectomy, but this was not affected by ischemia. The characteristic rise in plasma fibrinogen postoperatively was abolished, and fibrinogen levels were lower in dogs undergoing hepatectomy alone and fell significantly in dogs subjected to 30 to 60 minutes of ischemia of the liver remnant. Factors V and VII were decreased after hepatectomy, and Factor V was more severely reduced after 30 to 60 minutes of ischemia. There was no overt bleeding tendency. In ten dogs, the liver remnant was subjected to ischemia for 75 minutes. Four of these died within three days of operation, two with severe hypoglycemia and two with postoperative bleeding. All six surviving dogs exhibited gross coagulation defects. Prothrombin time rose, kaolin-cephalin clotting time increased and platelets fell to a greater degree than in any of the other dogs. Plasma fibrinogen level showed a profound fall, as did Factor V, the magnitude of these changes being greater than after a shorter period of ischemia. Factor VII was also decreased, but this did not appear to be related to the ischemic interval. In the clinical situation in which intrinsic coagulation mechanisms are shown to be impaired, treatment with Factor V and VII concentrates may be the best way of correcting the coagulation defect.