Search

Heparan with a low affinity for antithrombin III has previously been demonstrated to inhibit thrombin generation in both normal plasma and plasma depleted of antithrombin III. In addition, standard heparin and heparin with a low affinity for antithrombin III have been demonstrated to have equivalent inhibitory actions on thrombin generation in plasma depleted of antithrombin III. These observations prompted the investigation of the effects of four normal vessel wall glycosaminoglycans (heparan sulfate, dermatan sulfate, chondroitin-4-sulfate, and chondroitin-6-sulfate) on the intrinsic pathway generation of thrombin and factor Xa and on the inactivation of thrombin and factor Xa in plasma. Heparan sulfate inhibited thrombin generation and accelerated the inactivation of added thrombin and factor Xa in normal plasma but not in antithrombin III-depleted plasma. In contrast, dermatan sulfate inhibited thrombin generation in both normal and antithrombin III-depleted plasma. In addition, heparan sulfate was an effective inhibitor of factor Xa generation, while dermatan sulfate was not. Neither chondroitin-4-sulfate nor chondroitin-6-sulfate inhibited the generation of thrombin or factor Xa nor did they accelerate the inactivation of factor Xa or thrombin by plasma. These results suggest that heparan sulfate acts primarily by potentiating antithrombin III, while dermatan sulfate acts by potentiating heparin cofactor II. The inhibition of thrombin generation by heparan sulfate and dermatan sulfate thus appears to occur by complementary pathways, both of which may contribute to the anticoagulation of blood in vivo.

Introduction:Chronic lymphocytic leukemia (CLL) is largely comprised of two major subsets, IGHV unmutated (U-CLL) and mutated (M-CLL) CLL, associated with progressive and indolent disease respectively. Approximately 15% patients harbour a 17p deletion and/or a TP53mutation which is largely associated with the worst clinical outcome. The development of BCR signalosome inhibitors such as ibrutinib and idelalisib have been instrumental in the treatment of CLL, however these drugs are not curative, only supress the disease and resistance is already developing particularly in patients with a complex karyotype associated with 17p del/ TP53mutation. Consequently continued development of novel therapies targeting pathways which enhance selective killing of tumor cells independently of p53 are urgently required. We previously demonstrated that 2-phenylacetylenesulfonamide (PAS), induced apoptosis of CLL cells in a p53-independent manner. PAS is suggested to inhibit heat shock protein (HSP) 70, a key protein involved in protein folding. Therefore in CLL cells, PAS would be predicted to cause cellular stress due to the accumulation of misfolded proteins resulting in the activation of the unfolded protein response (UPR). The UPR serves to protect cells from the consequences of protein misfolding and can function in part by activating pro-survival signaling, including the PI3K/AKT pathway. Under normal conditions the ER chaperone BiP inhibits activation of the UPR by binding the three ER transmembrane receptors; inositol-requiring enzyme 1 (IRE-1α), pancreatic ER kinase-like ER kinase (PERK) and activating transcription factor 6 (ATF6). Activation of the UPR leads to the upregulation of HSP family members including HSP70 in the cytosol and BiP/GRP78 in the endoplasmic reticulum (ER). These HSPs aid in refolding misfolded proteins or facilitate their degradation viathe proteasome. If the stress is resolved, the UPR signalling pathway is switched off; however, if stress persists the UPR remains active and switches from an anti-apoptotic to a pro-apoptotic signal via p38MAPK.