A cell stress signaling model of fetal hemoglobin induction: what doesn't kill red blood cells may make them stronger.

A major goal of hemoglobinopathy research is to develop treatments that correct the underlying molecular defects responsible for sickle cell disease and beta-thalassemia. One approach to achieving this goal is the pharmacologic induction of fetal hemoglobin (HbF). This strategy is capable of inhibiting the polymerization of sickle hemoglobin and correcting the globin chain imbalance of beta-thalassemia. Despite this promise, none of the currently available HbF-inducing agents exhibit the combination of efficacy, safety, and convenience of use that would make them applicable to most patients. The recent success of targeted drug therapies for malignant diseases suggests that this approach could be effective for developing optimal HbF-inducing agents. A first step in applying this approach is the identification of specific molecular targets. However, while >70 HbF-inducing agents have been described, neither molecular mechanisms nor target molecules have been definitively verified for any of these compounds. To help focus investigation in this area, we have reviewed known HbF-inducing agents and their proposed mechanisms of action. We find that in many cases, current models inadequately explain key experimental results. By integrating features of the erythropoietic stress model of HbF induction with data from recent intracellular signaling experiments, we have developed a new model that has the potential to explain several findings that are inconsistent with previous models and to unify most HbF-inducing agents under a common mechanism: cell stress signaling. If correct, this or related models could lead to new opportunities for development of targeted therapies for the beta-hemoglobinopathies.

Low molecular weight heparins as extended prophylaxis against recurrent thrombosis in cancer patients.

Cancer has been shown to be an independent risk factor for the development of venous thromboembolism (VTE; deep vein thrombosis and pulmonary embolism). Thromboprophylaxis reduces the incidence of VTE in patients with cancer; however, active cancer places patients at high risk for recurrent VTE, necessitating extended prophylactic regimens. Extended prophylaxis in patients with cancer can be problematic because of increased risk for bleeding. Oral anticoagulants, such as warfarin, have been the standard of care for extended prophylaxis, but maintaining a clinically effective level of anticoagulation can be difficult because of a wide range of drug interactions, a narrow therapeutic window, and an increased risk of bleeding complications, particularly in patients with cancer. Recent evidence indicates that long-term prophylaxis with low-molecular-weight heparins (LMWHs) is an effective and safe alternative to oral anticoagulation in patients with VTE and cancer, reducing the risk for recurrent VTE by up to 52%. LMWHs can also be seen as cost-effective for long-term prophylaxis, because higher drug acquisition costs are offset by the potential for reduced hospital stays, reduced need for coagulation monitoring, and fewer bleeding complications. Some studies suggest that LMWHs may also have direct antitumor effects and improve survival rates, most notably in patients with non-metastatic disease. Further clinical research is needed to evaluate the potential survival benefits of LMWH therapy in patients with cancer.

Venous thromboembolism prevention in cancer patients: the search for common antecedents.

Venous thromboembolism (VTE) is a well-recognized concomitant of cancer. Although treatment with warfarin is often difficult and tedious, the heparins, and particularly the low molecular weight heparins, have afforded improved care of the patient with cancer-associated VTE, but with increased cost and the need for self-injection. Development by the pharmaceutical industry of inhibitors of specific activated coagulation factors and P-selectin holds promise for improved control of thrombosis with reduced toxicity. Increasing understanding of the interplay between the coagulation mechanism and neoplasia has yielded clues to the upstream origins of both, which may lead to experimental intervention potentially capable of preventing both.