Role of RecA and the SOS Response in Thymineless Death in Escherichia coli

Thymineless death (TLD) is a classic and enigmatic phenomenon, documented in bacterial, yeast, and human cells, whereby cells lose viability rapidly when deprived of thymine. Despite its being the essential mode of action of important chemotherapeutic agents, and despite having been studied extensively for decades, the basic mechanisms of TLD have remained elusive. In Escherichia coli, several proteins involved in homologous recombination (HR) are required for TLD, however, surprisingly, RecA, the central HR protein and activator of the SOS DNA–damage response was reported not to be. We demonstrate that RecA and the SOS response are required for a substantial fraction of TLD. We show that some of the Rec proteins implicated previously promote TLD via facilitating activation of the SOS response and that, of the roughly 40 proteins upregulated by SOS, SulA, an SOS–inducible inhibitor of cell division, accounts for most or all of how SOS causes TLD. The data imply that much of TLD results from an irreversible cell-cycle checkpoint due to blocked cell division. FISH analyses of the DNA in cells undergoing TLD reveal blocked replication and apparent DNA loss with the region near the replication origin underrepresented initially and the region near the terminus lost later. Models implicating formation of single-strand DNA at blocked replication forks, a SulA-blocked cell cycle, and RecQ/RecJ-catalyzed DNA degradation and HR are discussed. The data predict the importance of DNA damage-response and HR networks to TLD and chemotherapy resistance in humans

Safety biomarkers and the clinical development of oncology therapeutics: Considerations for cardiovascular safety and risk management

During the clinical development of oncology therapeutics, new safety biomarkers are being employed with broad applications and implications for risk management and regulatory approval. Clinical laboratory results, used as safety biomarkers, can influence decision making at many levels during the clinical development and regulatory review of investigational cancer therapies, including (1) initial eligibility for protocol therapy; (2) analyses used to estimate and characterize the safety profile; and (3) treatment delivery, based on specific rules to modify or discontinue protocol treatment. With the increasing applications of safety biomarkers in clinical studies, consideration must be given to possible unintended consequences, including (1) restricted access to promising treatments; (2) delays in study completion; and (3) limitations to dose delivery, escalation, and determination of the maximal tolerated dose, the recommended phase 2 dose, and the optimal biologic dose selected for registration studies. This review will compare and contrast 2 biomarkers for cardiac safety that are employed in an increasing number of clinical programs designed for investigational oncology therapeutics: (1) assessment of left ventricular ejection fraction by either echocardiography or multigated acquisition scan; and (2) electrophysiological measurement of QT/QTc duration, assessed by electrocardiogram, for predicting risk of a potentially fatal arrhythmia called torsades de pointes. While these and other new safety biomarkers have major value in the development of oncology therapeutics, their applications require careful consideration to avoid unintended consequences that could negatively affect (1) the care of patients with advanced malignancy and (2) the advancement of promising new agents

Pre-Treatment Ferritin Level and Alveolar-Arterial Oxygen Gradient Can Predict Mortality Rate Due to Acute/Subacute Interstitial Pneumonia in Dermatomyositis Treated by Cyclosporine A/Glucocorticosteroid Combination Therapy: A Case Control Study

BACKGROUND: Acute/subacute interstitial pneumonia in dermatomyositis (DM-A/SIP) is a disease associated with a poor prognosis that resists treatment with glucocorticosteroids (GC) and progresses rapidly in a period of weeks to months to death. We retrospectively studied outcomes, prognostic factors, and their relations with survival rate in patients with DM-A/SIP treated with early cyclosporine A (CSA)/GC combination therapy and 2-hour postdose blood concentration monitoring. METHODS: This study comprised 32 DM-A/SIP patients who were simultaneously treated with CSA and prednisolone. Clinical and laboratory findings were compared between those who died due to DM-A/SIP and those surviving 24 weeks after beginning of therapy. Prognostic factors were extracted, and their relations with the survival rate were evaluated. RESULTS: Of the 32 DM-A/SIP patients, 25 survived, 5 died of DM-A/SIP, and 2 died of infections. In those who died due to DM-A/SIP, ferritin level and the alveolar-arterial oxygen gradient were significantly increased compared with the survivors (P<0.001 and P = 0.002, respectively). Multivariate analyses showed that ferritin and alveolar-arterial oxygen gradient were independent prognostic factors of poor outcome. The survival rate 24 weeks after beginning of treatment was significantly lower in those with a ferritin level of ≥600 ng/ml and alveolar-arterial oxygen gradient of ≥45 Torr (P<0.001 and P<0.001, respectively). All patients with both prognostic factors died, and the outcome was significantly poorer in these patients than in those with one or neither of the prognostic factors (P<0.001). CONCLUSIONS: We identified pre-treatment high serum ferritin level and high alveolar-arterial oxygen gradient as poor prognostic factors in DM-A/SIP patients undergoing early CSA/GC combination therapy and showed that the outcomes were poor in patients with both factors