Geldanamycin and its derivatives as Hsp90 inhibitors

The Hsp90 molecule, one of the most abundant heat shock proteins in mammalian cells, maintains homeostasis and prevents stress-induced cellular damage. Hsp90 is expressed under normal conditions at a level of about 1-2 Percent of total proteins, while its expression increases 2-10 fold in cancer cells. The two main constitutively expressed isoforms of Hsp90 are known as Hsp90-alpha and Hsp90-beta, and their upregulation is associated with tumor progression, invasion and formation of metastases, as well as development of drug resistance. The Hsp90 is a key target for many newly established, potent anticancer agents containing Hsp90 N-terminal ATP binding inhibitors, such as geldanamycin, and its analogues 17AAG and 17DMAG. The therapeutic usage of geldanamycin has been limited due to its poor water solubility and severe hepatotoxicity. Therefore, its analogues, including 17AAG, 17DMAG, Tanespimycin and Retaspimycin hydrochloride, with improved pharmacokinetic profiles, have been developed.

Diallyl trisulfide-induced prostate cancer cell death is associated with Akt/PKB dephosphorylation mediated by P-p66shc

Purpose

P66Shc, an isoform of adaptor proteins, is known to mediate various signals including those leading to apoptosis or cell proliferation. Previously, we have shown that diallyl trisulfide (DATS)-induced prostate cancer cell death was mediated by increased ROS formation. In this study, we investigated the role of p66Shc protein and its serine 36 phosphorylation in DATS induced decrease in prostate cancer cell viability (PC-3).

Methods

PC-3 prostate cancer cells were used in this study. Stable cell lines expressing p66ShcS36A or an empty vector have been obtained. Cell viability, concentration of ROS, changes in P-p66Shc and P-Akt and DNA damage were determined.

Results

We observed that DATS treatment increased p66Shc phosphorylation at serine 36. Importantly, the phosphorylation was abolished by JNK inhibitor SP600125. Cells expressing plasmid-encoded variant of p66ShcS36A showed much higher resistance to DATS-induced cells death. In addition to that, we observed that DATS-induced ROS formation was completely abolished in cells expressing the p66ShcS36A variant. Interestingly, SP600125 proved to prevent DATS-induced Akt inactivation. In order to confirm that the observed effect is related to phosphorylation of p66Shc, we performed experiments on a stable cell line expressing p66ShcS36A. In such cells, DATS-induced Akt dephosphorylation was significantly reduced. On the other hand, hydrogen peroxide induced Akt activation in PC-3 cells, which was abrogated in cells expressing p66ShcS36A.

Conclusions

Our results uncover a novel signaling pathway with p66Shc being indispensable for DATS-induced inactivation of Akt due to hypophosphorylation.

P66Shc mediated ferritin degradation--a novel mechanism of ROS formation

Diallyl trisulfide (DATS) has been shown to induce the formation of reactive oxygen species (ROS) in prostate cancer cells, which was accompanied by a decrease in the ferritin protein level and an increase in the labile iron pool (LIP). However, the mechanism of the ferritin degradation has not been fully elucidated. In this paper we demonstrate that DATS-induced ROS formation depends on p66Shc. In cells stably expressing a dominant negative mutant of p66Shc (p66ShcS36A), DATS did not induce ROS formation. In addition, in cells expressing p66ShcS36A neither an increase in ferritin H degradation nor an increase in LIP were observed. Cells stably expressing p66ShcS36A also possess higher levels of ferritin H compared to PC-3 cells transfected with an empty vector. Moreover, DATS-induced G2/M arrest is completely abrogated in cells expressing p66ShcS36A. Mouse embryonic fibroblasts (MEFs) derived from wild-type (WT) or p66Shc knockout mouse have been used to evaluate if p66Shc involvement in DATS-induced signaling is cell specific. DATS induced G2/M arrest in WT MEFs but had no effect in the p66Shc(-/-) cell line. Moreover, increases in LIP and ROS formation were significantly attenuated in p66Shc(-/-) MEFs treated with DATS.

Up-regulation of ferritin ubiquitination in skeletal muscle of transgenic rats bearing the G93A hmSOD1 gene mutation

In the present study we measured the levels of protein carbolnyls and the H and L subunits of ferritin in three hind limb muscles, [Extensor digitorum longus, Tibialis anterior and Soleus] of transgenic rats bearing the G93A hmSOD1 gene and of their non-transgenic littermates. All of the muscles from the transgenic animals showed significantly higher protein carbonyl levels, compared to the respective muscles from control non-transgenic animals. In two muscles (Tibialis anterior and Soleus) from transgenic rats, both L and H subunits of ferritin were upregulated. Moreover, we observed that the electrophoretic mobility of both ferritin subunits was retarded which indicates their post-translational modification. Ferritin immunoprecipitation experiments show an increased ubiquitination of both H and L ferritin in all muscles from the transgenic animals. Our data show for the first time that ferritin ubiquitination could be responsible for oxidative stress in muscles of rats bearing the G93A hmSOD1, consequently ferritin is not able to control the labile iron pool.