Multiple myeloma cells' capacity to decompose H2O2 determines lenalidomide sensitivity.

Lenalidomide is an immunomodulatory drug (IMiDs) with clinical efficacy in multiple myeloma (MM) and other late B-cell neoplasms. Although cereblon (CRBN) is an essential requirement for IMiD action, the complete molecular and biochemical mechanisms responsible for lenalidomide-mediated sensitivity or resistance remain unknown. Here, we report that IMiDs work primarily via inhibition of peroxidase-mediated intracellular H2O2 decomposition in MM cells. MM cells with lower H2O2-decomposition capacity were more vulnerable to lenalidomide-induced H2O2 accumulation and associated cytotoxicity. CRBN-dependent degradation of IKZF1 and IKZF3 was a consequence of H2O2-mediated oxidative stress. Lenalidomide increased intracellular H2O2 levels by inhibiting thioredoxin reductase (TrxR) in cells expressing CRBN, causing accumulation of immunoglobulin light-chain dimers, significantly increasing endoplasmic reticulum stress and inducing cytotoxicity by activation of BH3-only protein Bim in MM. Other direct inhibitors of TrxR and thioredoxin (Trx) caused similar cytotoxicity, but in a CRBN-independent fashion. Our findings could help identify patients most likely to benefit from IMiDs and suggest direct TrxR or Trx inhibitors for MM therapy.

Different changes in protein and phosphoprotein levels result from serum starvation of high-grade glioma and adenocarcinoma cell lines.

Tumor cells undergoing serum starvation in vitro partially mimic metabolically stressed cells trying to adjust to a changed environment in vivo by inducing signal transduction and gene expression so that the tumor continues to grow. Our hypothesis is that the changes in protein and phosphoprotein levels after serum starvation may reflect the adapted phenotype of the tumor, which could be targeted for therapy. We used reverse-phase protein microarrays to interrogate five high-grade glioma cell lines and seven adenocarcinoma cell lines for differences in the level of 81 proteins and 25 phosphoproteins. All cell lines were studied in the well-fed condition of growth with 10% FBS and the starved condition of 0.5% FBS. Protein expression levels were normalized to beta-actin and trichotomized as increased (+1, upper 75th quartile), decreased (-1, lowest 25th quartile), or unchanged (0, others) to focus on the patterns of the biggest (and hopefully most robust) changes in protein and phosphoprotein levels. We examined these trichotomized values to better understand Starved-Fed differences among the cell lines and thereby gain better/clearer insight into the effects of serum starvation on potential cellular responses. In general, the expression of proteins and phosphoproteins 24 h after FBS starvation increased more often in glioma lines than in adenocarcinoma lines, which appeared to have fewer increased protein scores and more decreased scores. Many of the proteins increased in gliomas were downstream targets of the PTEN-PI-3 kinase-AKT, EGFR-MAPK-Stat, and transcription activator-polyamine signaling pathways. In adenocarcinomas, the expression of proteins and phosphoproteins generally increased in apoptosis pathways, while there were minor fluctuations in the other pathways above. Contrawise, gliomas become resistant to apoptosis after 24 h of serum starvation and upregulate transcription activators and polyamines more so than adenocarciomas.