ATP analog enhances the actions of a heat shock protein 90 inhibitor in multiple myeloma cells

Steroid sulfatase deficiency causes cellular senescence and abnormal differentiation by inducing Yippee-like 3 expression in human keratinocytes

Human steroid sulfatase (STS) is an enzyme that catalyzes the hydrolysis of dehydroepiandrosterone sulfate (DHEAS), estrone sulfate (E1S), and cholesterol sulfate. Abnormal expression of STS causes several diseases including colorectal, breast, and prostate cancer and refractory skin disease. In particular, accumulation of intracellular cholesterol sulfate by STS deficiency leads to a skin disorder with abnormal keratinization called X-linked ichthyosis (XLI). To determine the detailed mechanisms of XLI, we performed RNA sequencing (RNA-seq) analysis using human keratinocyte HaCaT cells treated with cholesterol and cholesterol sulfate. Of the genes with expression changes greater than 1.5-fold, Yippee-like 3 (YPEL3), a factor expected to affect cell differentiation, was found. Induction of YPEL3 causes permanent growth arrest, cellular senescence, and inhibition of metastasis in normal and tumor cells. In this study, we demonstrate that YPEL3 expression was induced by STS deficiency and, using the CRISPR/Cas9 system, a partial knock-out (STS^+/−) cell line was constructed to establish a disease model for XLI studies. Furthermore, we show that increased expression of YPEL3 in STS-deficient cell lines promoted cellular senescence and expression of keratinization-related proteins such as involucrin and loricrin. Our results suggest that upregulation of YPEL3 expression by STS deficiency may play a crucial role in inducing cellular senescence and abnormal differentiation in human keratinocytes.

Hsp90 inhibitor as a sensitizer of cancer cells to different therapies (review)

Hsp90 is a molecular chaperone that maintains the structural and functional integrity of various client proteins involved in signaling and many other functions of cancer cells. The natural inhibitors, ansamycins influence the Hsp90 chaperone function by preventing its binding to client proteins and resulting in their proteasomal degradation. N- and C-terminal inhibitors of Hsp90 and their analogues are widely tested as potential anticancer agents in vitro, in vivo as well as in clinical trials. It seems that Hsp90 competitive inhibitors target different tumor types at nanomolar concentrations and might have therapeutic benefit. On the contrary, some Hsp90 inhibitors increased toxicity and resistance of cancer cells induced by heat shock response, and through the interaction of survival signals, that occured as side effects of treatments, could be very effectively limited via combination of therapies. The aim of our review was to collect the data from experimental and clinical trials where Hsp90 inhibitor was combined with other therapies in order to prevent resistance as well as to potentiate the cytotoxic and/or antiproliferative effects.

Purinergic signalling and cancer

Receptors for extracellular nucleotides are widely expressed by mammalian cells. They mediate a large array of responses ranging from growth stimulation to apoptosis, from chemotaxis to cell differentiation and from nociception to cytokine release, as well as neurotransmission. Pharma industry is involved in the development and clinical testing of drugs selectively targeting the different P1 nucleoside and P2 nucleotide receptor subtypes. As described in detail in the present review, P2 receptors are expressed by all tumours, in some cases to a very high level. Activation or inhibition of selected P2 receptor subtypes brings about cancer cell death or growth inhibition. The field has been largely neglected by current research in oncology, yet the evidence presented in this review, most of which is based on in vitro studies, although with a limited amount from in vivo experiments and human studies, warrants further efforts to explore the therapeutic potential of purinoceptor targeting in cancer.

Human heat shock protein-specific cytotoxic T lymphocytes display potent antitumour immunity in multiple myeloma

Tumour cell-derived heat shock proteins (HSPs) are used as vaccines for immunotherapy of cancer patients. However, it is proposed that the peptide chaperoned on HSPs, not HSPs themselves, elicited a potent immune response. Given that HSPs are highly expressed by most myeloma cells and vital to myeloma cell survival, we reasoned that HSPs themselves might be an ideal myeloma antigen. In the present study, we explored the feasibility of targeting HSPs themselves for treating multiple myeloma. We identified and chose HLA-A*0201-binding peptides from human HSPB1 (HSP27) and HSP90AA1 (HSP90), and confirmed their immunogenicity in HLA-A*0201 transgenic mice. Dendritic cells pulsed with HSPB1 and HSP90AA1 peptides were used to stimulate peripheral blood mononuclear cells from healthy volunteers and myeloma patients to generate HSP peptide-specific cytotoxic T lymphocytes (CTLs). HSP peptide-specific CTLs efficiently lysed HLA-A*0201(+) myeloma cells (established cell lines and primary plasma cells) but not HLA-A*0201(-) myeloma cells in vitro, indicating that myeloma cells naturally express HSP peptides in the context of major histocompatibility complex class I molecules. More importantly, HSP peptide-specific CTLs effectively reduced tumour burden in the xenograft mouse model of myeloma. Our study clearly demonstrated that HSPs might be novel tumour antigens for immunotherapy of myeloma.

Integrative gene expression profiling reveals G6PD-mediated resistance to RNA-directed nucleoside analogues in B-cell neoplasms

The nucleoside analogues 8-amino-adenosine and 8-chloro-adenosine have been investigated in the context of B-lineage lymphoid malignancies by our laboratories due to the selective cytotoxicity they exhibit toward multiple myeloma (MM), chronic lymphocytic leukemia (CLL), and mantle cell lymphoma (MCL) cell lines and primary cells. Encouraging pharmacokinetic and pharmacodynamic properties of 8-chloro-adenosine being documented in an ongoing Phase I trial in CLL provide additional impetus for the study of these promising drugs. In order to foster a deeper understanding of the commonalities between their mechanisms of action and gain insight into specific patient cohorts positioned to achieve maximal benefit from treatment, we devised a novel two-tiered chemoinformatic screen to identify molecular determinants of responsiveness to these compounds. This screen entailed: 1) the elucidation of gene expression patterns highly associated with the anti-tumor activity of 8-chloro-adenosine in the NCI-60 cell line panel, 2) characterization of altered transcript abundances between paired MM and MCL cell lines exhibiting differential susceptibility to 8-amino-adenosine, and 3) integration of the resulting datasets. This approach generated a signature of seven unique genes including G6PD which encodes the rate-determining enzyme of the pentose phosphate pathway (PPP), glucose-6-phosphate dehydrogenase. Bioinformatic analysis of primary cell gene expression data demonstrated that G6PD is frequently overexpressed in MM and CLL, highlighting the potential clinical implications of this finding. Utilizing the paired sensitive and resistant MM and MCL cell lines as a model system, we go on to demonstrate through loss-of-function and gain-of-function studies that elevated G6PD expression is necessary to maintain resistance to 8-amino- and 8-chloro-adenosine but insufficient to induce de novo resistance in sensitive cells. Taken together, these results indicate that G6PD activity antagonizes the cytotoxicity of 8-substituted adenosine analogues and suggests that administration of these agents to patients with B-cell malignancies exhibiting normal levels of G6PD expression may be particularly efficacious.