Rhodacyanine derivative selectively targets cancer cells and overcomes tamoxifen resistance

MKT-077, a rhodacyanine dye, was shown to produce cancer specific cell death. However, complications prevented the use of this compound beyond clinical trials. Here we describe YM-1, a derivative of MKT-077. We found that YM-1 was more cytotoxic and localized differently than MKT-077. YM-1 demonstrated this cytotoxicity across multiple cancer cell lines. This toxicity was limited to cancer cell lines; immortalized cell models were unaffected. Brief applications of YM-1 were found to be non-toxic. Brief treatment with YM-1 restored tamoxifen sensitivity to a refractory tamoxifen-resistant MCF7 cell model. This effect is potentially due to altered estrogen receptor alpha phosphorylation, an outcome precipitated by selective reductions in Akt levels (Akt/PKB). Thus, modifications to the rhodocyanine scaffold could potentially be made to improve efficacy and pharmacokinetic properties. Moreover, the impact on tamoxifen sensitivity could be a new utility for this compound family.

Bending tau into shape: the emerging role of peptidyl-prolyl isomerases in tauopathies

The Hsp90-associated cis-trans peptidyl-prolyl isomerase--FK506 binding protein 51 (FKBP51)--was recently found to co-localize with the microtubule (MT)-associated protein tau in neurons and physically interact with tau in brain tissues from humans who died from Alzheimer's disease (AD). Tau pathologically aggregates in neurons, a process that is closely linked with cognitive deficits in AD. Tau typically functions to stabilize and bundle MTs. Cellular events like calcium influx destabilize MTs, disengaging tau. This excess tau should be degraded, but sometimes it is stabilized and forms higher-order aggregates, a pathogenic hallmark of tauopathies. FKBP51 was also found to increase in forebrain neurons with age, further supporting a novel role for FKBP51 in tau processing. This, combined with compelling evidence that the prolyl isomerase Pin1 regulates tau stability and phosphorylation dynamics, suggests an emerging role for isomerization in tau pathogenesis.

Abstract 2094: Hsp70 inhibitors overcome tamoxifen resistance, in cell culture model

A prevalent problem in the use of chemotherapies for the treatment of human cancers is the potential for the development of resistance. While the exact nature of the mechanisms involved in resistance development vary based on cancer type as well as the nature of the therapeutics; some oncogenic factors have been established to have roles in the desensitization to common treatments. Previous data from our lab demonstrated Hsp70 inhibitors can reduce Akt levels. a major proliferation and survival factor also linked to estrogen receptor therapeutic based resistance. We have, Uusing these Hsp70 ATPase-inhibiting compounds and ain a cell culture model of tamoxifen resistant breast cancer, we have identified compounds which can re-sensitize resistant cells. These compounds inhibit cytosolic and mitochondrial members of the 70-kDA heat-shock protein family. These compounds also reduce Akt levels, a major proliferation and survival factor also linked to estrogen receptor therapeutic based resistance, as well as Thus, in addition to reducing Akt levels and possibly other oncogenic chaperone clients, these drugs may also interrupt mitochondrial function leading to reduced viability in the presence of tamoxifen. With these mechanisms in mind, we now have data that Ttamoxifen resistant MCF7 cells regained sensitivity to tamoxifen after brief treatments with Hsp70-family inhibitors. The resistant cells were grown in media containing tamoxifen. This media was replaced with media containing an Hsp70 inhibitor compound for four hours. After the four hours, the Hsp70 inhibitor media was removed and tamoxifen-containing media was reapplied to the cells. Multiple viability and cytotoxicity assays confirm the drop in viability and increased cytotoxicity following these treatments. These studies demonstrate that Hsp70 family members are potentially valuable targets for new cancer therapeutics.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2094. doi:10.1158/1538-7445.AM2011-2094