Spotlight pubs.acs.org/crt
■
COMMENSAL BIF IDOBACTERIUM ENHANCES ANTITUMOR IMMUNITY IN VIVO Cancer immmunotherapies exploit the host immune system to specifically target tumor cells without damaging normal tissue. However, favorable clinical outcomes to these treatments are more frequent in patients who demonstrate T cell infiltration of tumors before treatment. It is unclear why this endogenous immune response varies between individuals. As intestinal microbiota can shape systemic immune responses, Thomas F. Gajewski and his team investigated whether commensal bacteria in the gut influence spontaneous antitumor immune responses ((2015) Science, 350, 1084−1089). The authors compared melanoma growth in genetically similar mice which came from two different mouse facilities, JAX and TAC, and harbored different commensal microbiota. They found that tumors grew more aggressively in TAC mice, while tumorspecific T cell responses were significantly higher in JAX mice. These differences in tumor growth and antitumor immunity were eliminated when the murine populations were housed together prior to tumor implantation, after which all animals presented with the JAX bacterial phenotype. Similarly, prophylactic transfer of JAX fecal suspensions into TAC mice resulted in increased CD8+ T cell tumor infiltration and delayed tumor growth, demonstrating that intestinal microbial composition can influence antitumor immunity. As the endogenous antitumoral immune response can affect immunotherapeutic activity, the researchers treated TAC mice with established tumors with JAX fecal material alone or in conjunction with therapeutic antibodies that block immune inhibitory pathways. They found that the combination indeed improved antitumor T cell responses. Further research identified Bifidobacterium as the microbe associated with improved antitumor effects. The scientists found that the bacteria signal immune pathways which regulate host dendritic cell activation and cytokine production, leading to enhanced tumor-specific CD8+ T cells. As gut microbe composition alters innate immune function, it may be beneficial to consider commensal microbial manipulation in combination with anticancer immunotherapy. Abigail Druck Shudofsky
■
TARGETING CASEIN KINASE 1δ IN BREAST CANCER INHIBITS β-CATENIN ACTIVITY AND TUMOR GROWTH
overexpressing it counteracts the inhibitory anticancer effects of SR-3029. The researchers identified hundreds of genes whose expression significantly correlates with CK1δ expression. These overlapped with genes of the canonical Wnt/β-catenin pathway, suggesting that CK1δ activates this carcinogenic signaling cascade. Treating CK1δ-overexpressing breast cancer cells with SR-3029 reduced the active pool of β-catenin, repressing the expression of downstream target genes associated with breast cancer tumorigenesis. Accordingly, CK1δ knockdown blocked Wnt/β-catenin signaling in human breast cancer cells and caused apoptosis, while constitutively activated β-catenin negated the effects of CK1δ silencing. The scientists demonstrated a direct connection between CK1δ activation, β-catenin expression, and SR-3029 sensitivity. Their research shows that CK1δ is required for the growth and survival of certain breast cancer cells but can be effectively targeted to treat breast cancers with abnormal Wnt/β-catenin signaling. Abigail Druck Shudofskyh
Figure courtesy of Dr. Derek Duckett.
■
Targeted breast cancer treatment has improved overall disease survival rates, yet some highly aggressive breast cancers lack such treatment options. Casein kinase 1δ (CK1δ) is a serine/ threonine kinase which regulates various cellular processes and has been implicated in cancers. Derek R. Duckett and his collaborators investigated the role of CK1δ in breast cancer and whether it could be targeted for cancer treatment ((2015) Sci. Transl. Med., 7, 318ra202). The authors compared CK1δ expression in human breast tumors and normal mammary tissue and determined that it was highly elevated in invasive carcinomas across four major breast cancer subtypes. They found that CK1δ-overexpressing cell types were particularly sensitive to the small-molecule inhibitor SR-3029 which triggered rapid apoptosis. In multiple preclinical models, SR-3029 potently impaired breast cancer tumor growth and caused breast tumor regression with no toxicity. Further experiments showed that the drug selectively targets CK1δ; silencing the kinase causes breast cancer cell apoptosis, and © 2016 American Chemical Society
CHRONIC EXOGENOUS HSP70 ADMINISTRATION HAS COGNITIVE, BEHAVIORAL, AND MOLECULAR NEUROPROTECTIVE EFFECTS ON AGING MICE Heat Shock Protein 70 (Hsp70) is a molecular chaperone that plays a protective role in various neurodegenerative disorders associated with aging, but its synthesis, induction, and activity in neuronal tissues decrease with age. As intranasally injected Hsp70 can enter murine neurons, Evgeny Nudler and his team explored the effect of exogenous Hsp70 on longevity ((2015) PNAS, 112, 16006−16011). The authors chronically administered recombinant exogenous human Hsp70 (eHsp70) to middle-aged (12 mo) and old (17 mo) mice, and assessed them after 5 and 9 mo of intranasal treatment. They found that eHsp70 prolonged lifespans Published: April 18, 2016 617
DOI: 10.1021/acs.chemrestox.6b00093 Chem. Res. Toxicol. 2016, 29, 617−618
Chemical Research in Toxicology
Spotlight
discovered and determined to be biologically relevant for protein function regulation. The scientists looked at the conservation of these site residues, hypothesizing that there would be high sequence conservation among orthologous proteins if they shared similar regulatory mechanisms. This was indeed the case in the majority of secondary binding sites examined, suggesting a conserved biological function. Further analysis determined that physiochemical properties such as surface polarity and residue mobility were analogous between secondary and primary sites. These comparable features indicate that secondary sites may serve as drug targets, providing an alternative mechanism for regulating protein function without directly inhibiting primary sites. Abigail Druck Shudofsky
in both age groups and improved learning and spatial memory of old animals. Additionally, older mice who began treatment at 22 months displayed less anxiety and more exploratory behaviors than control animals. The researchers hypothesized that eHsp70 protects neuronal function in aging cells and investigated this on a molecular level. While neuron density and levels of the glycoprotein synaptophysin, which reflects synapse health, typically decrease with age, the scientists found that old mice treated with eHsp70 displayed higher neuronal density and synaptophysin levels in multiple regions of the brain compared to those in untreated animals. Conversely, levels of lipofuscin, a substance that increases with age, were significantly lowered in brains of treated mice. Additionally, while proteasomal activity in the brain generally decreases with age, it was significantly increased in the cortex of eHsp70-treated animals. This enhanced activity, which correlates with an increase in longevity, is due to an increased amount of proteasomes containing an immune subunit expressed in response to stress. This research indicates that long-term intranasal Hsp70 administration has therapeutic potential to protect against age-related neurological deficits. Abigail Druck Shudofsky
■
■
NAPHTHALIMIDE COMPOUND ACTIVATES P53 AND INDUCES APOPTOSIS IN NONSMALL-CELL LUNG CANCER CELLS
FRAGMENT-BASED SCREENING USING X-RAY CRYSTALLOGRAPHY IDENTIFIES FUNCTIONAL SECONDARY BINDING SITES ON PROTEINS
Figure courtesy of Dr. Zhen-Feng Chen.
The tumor suppressor p53 is constitutively inactivated in nonsmall-cell lung cancer (NSCLC). As such, Yan Peng, ZhenFeng Chen, and their team synthesized and analyzed a naphthalimide derivative, NA-17, which restores p53 function and has anti-NSCLC activity ((2016) J. Biol. Chem., 291, 4211− 4225). The authors found that the compound directly interacts with p53 and activates it by inducing phosphorylation of serine-392. NA-17 suppressed the proliferation of various NSCLC carcinoma cell lines in a manner which correlated with phosphorylation and activation of endogenous p53 levels, indicating that the anticancer activity was a result of the drugdependent p53-restoration. The dose-dependent inhibitory activity of NA-17 was also seen in a wide range of cancer cell lines with inactivated p53. Similarly, in vivo drug treatment of tumor-bearing mice showed significant tumor growth inhibition with little signs of toxicity. The researchers found that NA-17 affects antiproliferation in two ways: by inducing G1 phase cell cycle arrest and by triggering apoptosis. The drug-activated phospho-p53 accumulates in the nucleus where it binds target DNA and stimulates the transcription of p21, an inhibitor of cyclins and cyclindependent kinases which are needed for cellular progression from G1 to S phase. Additionally, NA-17 treatment causes phospho-p53 to accumulate in the mitochondria, where it binds and sequesters the antiapoptotic protein Bcl-xl, activating the pro-apoptotic protein Bak and inducing apoptosis. Together, these mechanisms cause the anticancer effect of NA-17. Abigail Druck Shudofsky
Reprinted with permission from Ludlow et al. (2015) Detection of Secondary Binding Sites in Proteins Using Fragment Screening PNAS, 112 (52), 15910−15915.
Ligand binding to “secondary” sites on proteins, which are separate from their “primary” active sites, can modulate protein function. As such, targeting these secondary sites provides an orthogonal mechanism for regulating the biological activity of a protein. However, it is difficult to identify these sites as they may have no known function or binding partner. X-ray crystallography screening of diverse fragment libraries can determine direct binding to different areas of a target protein surface. A team led by Harren Jhoti analyzed fragment binding data from previous such screens which they had done to determine if secondary binding sites are a general feature of proteins ((2015) PNAS, 112, 15910−15910). The authors evaluated 5,590 holo X-ray crystal structures comprising 4,950 distinct compounds and 24 protein targets with broad functions that likely need extensive regulation. (See above for a representative target protein, HSPA2, bound to fragments.) After labeling primary sites, the researchers established that secondary binding sites were present in the majority of analyzed proteins. Some of these sites were newly 618
DOI: 10.1021/acs.chemrestox.6b00093 Chem. Res. Toxicol. 2016, 29, 617−618
