LP-118 is a novel B-cell lymphoma 2 / extra-large inhibitor that demonstrates efficacy in models of venetoclax-resistant chronic lymphocytic leukemia.

Patients with chronic lymphocytic leukemia (CLL) respond well to initial treatment with the Bcell lymphoma 2 (BCL2) inhibitor venetoclax. Upon relapse, they often retain sensitivity to BCL2 targeting, but durability of response remains a concern. We hypothesize that targeting both BCL2 and B-cell lymphoma-extra large (BCLXL) will be a successful strategy to treat CLL, including for patients who relapse on venetoclax. To test this hypothesis, we conducted a pre-clinical investigation of LP-118, a highly potent inhibitor of BCL2 with moderate BCLXL inhibition to minimize platelet toxicity. This study demonstrated that LP-118 induces efficient BAK activation, cytochrome C release, and apoptosis in both venetoclax naïve and resistant CLL cells. Significantly, LP-118 is effective in cell lines expressing the BCL2 G101V mutation and in cells expressing BCLXL but lacking BCL2 dependence. Using an immunocompetent mouse model, Eµ-TCL1, LP-118 demonstrates low platelet toxicity, which hampered earlier BCLXL inhibitors. Finally, LP-118 in the RS4;11 and OSU-CLL xenograft models results in decreases in tumor burden and survival advantage, respectively. These results provide a mechanistic rationale for the evaluation of LP-118 for the treatment of venetoclax responsive and relapsed CLL.

Targeting BTK through microRNA in chronic lymphocytic leukemia.

Bruton's tyrosine kinase (BTK) is a critical mediator of survival in B-cell neoplasms. Although BTK inhibitors have transformed therapy in chronic lymphocytic leukemia (CLL), patients with high-risk genetics are at risk for relapse and have a poor prognosis. Identification of novel therapeutic strategies for this group of patients is an urgent unmet clinical need, and therapies that target BTK via alternative mechanisms may fill this niche. Herein, we identify a set of microRNAs (miRs) that target BTK in primary CLL cells and show that the histone deacetylase (HDAC) repressor complex is recruited to these miR promoters to silence their expression. Targeting the HDACs by using either RNA interference against HDAC1 in CLL or a small molecule inhibitor (HDACi) in CLL and mantle cell lymphoma restored the expression of the BTK-targeting miRs with loss of BTK protein and downstream signaling and consequent cell death. We have also made the novel and clinically relevant discovery that inhibition of HDAC induces the BTK-targeting miRs in ibrutinib-sensitive and resistant CLL to effectively reduce both wild-type and C481S-mutant BTK. This finding identifies a novel strategy that may be promising as a therapeutic modality to eliminate the C481S-mutant BTK clone that drives resistance to ibrutinib and provides the rationale for a combination strategy that includes ibrutinib to dually target BTK to suppress its prosurvival signaling.

Synthesis and anticancer potential of novel xanthone derivatives with 3,6-substituted chains.

In an effort to develop new drug candidates with enhanced anticancer activity, our team synthesized and assessed the cytotoxicity of a series of novel xanthone derivatives with two longer 3,6-disubstituted amine carbonyl methoxy side chains on either benzene ring in selected human cancer cell lines. An MTT assay revealed that a set of compounds with lower IC50 values than the positive control, 5-FU, exhibited greater anticancer effects. The most potent derivative (XD8) exhibited anticancer activity in MDA-MB-231, PC-3, A549, AsPC-1, and HCT116 cells lines with IC50 values of 8.06, 6.18, 4.59, 4.76, and 6.09µM, respectively. Cell cycle analysis and apoptosis activation suggested that the mechanism of action of these derivatives includes cell cycle regulation and apoptosis induction.

Enhanced hydrogen desorption properties of LiAlH4 by doping lithium metatitanate.

High efficiency catalysts are needed to improve the kinetics of complex hydrides for practical applications. In this study, lithium metatitanate (Li2TiO3) is introduced in lithium alanate (LiAlH4), and the catalytic effect for notable complex/metal hydrides, such as LiAlH4, is investigated. Experiment results indicate that Li2TiO3 improves the kinetics of LiAlH4. In particular, Li2TiO3 dramatically improves the onset temperature of LiAlH4, which decreases to 75 °C and is within the temperature range for use in proton exchange membrane fuel cells. Transmission electron microscopy (TEM) observations help understand the catalytic effect of Li2TiO3 in the nanoscale. First principles calculations also show the improvement of H- and Li+ mobility by doping Li2TiO3, where calculations indicate that the physical origin of the catalytic effect is due to two factors: charge transfer and minor surface relaxation. Thus, experimental and theoretical evidence reveals the catalytic mechanism of Li2TiO3 in LiAlH4.

Histone deacetylases mediate the silencing of miR-15a, miR-16, and miR-29b in chronic lymphocytic leukemia.

Chronic lymphocytic leukemia (CLL) demonstrates a global down-regulation of miR-15a and miR-16 and a selective silencing of the related miR-29b in aggressive disease. Deletions in chromosome 13 [del(13q14)] partially account for the loss of expression of miR-15a and miR-16, but the mechanisms by which miR-29b becomes silenced is unknown. In the present study, we show that the histone deacetylases (HDACs) are overexpressed in CLL and mediate the epigenetic silencing of miR-15a, miR-16, and miR-29b. HDAC inhibition triggered the accumulation of the transcriptionally activating chromatin modification H3K4me2 and restored the expression of miR-15a, miR-16, and miR-29b in approximately 35% of samples. Ectopic expression of miR-15a and miR-16 and HDAC inhibition-induced expression of miR-15a, miR-16, or miR-29b in primary CLL cells was associated with declines in the levels of Mcl-1, but not Bcl-2, mitochondrial dysfunction, and induction of cell death. Therefore, our results show that HDACs aberrantly silence the expression of the critical tumor suppressors miR-15a, miR-16, and miR-29b in CLL. Deacetylase inhibition may be a therapeutic strategy that restores the expression of these miRs to antagonize Mcl-1, an important survival protein in these cells. Consequently, CLL patients who exhibit such epigenetic silencing may benefit from HDAC inhibitor-based therapy.

A new flavonoid regulates angiogenesis and reactive oxygen species production.

The tumor vascular system, which is critical to the survival and growth of solid tumors, has been an attractive target for anticancer research. Building on studies that show that some flavonoids have anticancer vascular effects, we developed and analyzed the flavonoid derivative R24 [3, 6-bis (2-oxiranylmethoxy)-9H-xanthen-9-one]. A CAM assay revealed that R24 disrupted neovascular formation; fewer dendrites were detected and overall dendritic length was shorter in the R24-treated chicken embryos. The antiproliferative effect of R24 was measured by MTT assay in A549 (lung cancer), AsPC-1 (pancreatic cancer), HCT-116 (colorectal cancer), and PC-3 (prostate cancer) cell lines. R24 reduced proliferation with an IC50 of 3.44, 3.59, 1.22, and 11.83 µM, respectively. Cell-cycle analysis and Annexin-V/propidium iodide staining showed that R24 induced apoptosis. In addition, R24 regulated intracellular ROS production in a dose-dependent manner. CM-H2DCFDA staining indicated that intracellular ROS production increased with the R24 dose. In summary, we found that R24 exhibits potent antiangiogenic and antiproliferative effects, induces apoptosis, and promotes ROS production.

Response patterns of cytokines/chemokines in two murine strains after irradiation.

PURPOSE: To determine the plasma concentrations of acute responding cytokines/chemokines following 9-Gy ionizing radiation in C57BL/6 (radiation tolerant) and C3H/HeN (radiation sensitive) murine strains. METHODS AND MATERIALS: Mice (5/group) received 9-Gy total body irradiation (TBI), and the plasma from each mouse was collected at 6h or 1, 2, 4, or 10 days after TBI. A multiplex bead array was used to assess the levels of 32 cytokines/chemokines in plasma to determine their common and strain-specific temporal responses. RESULTS: The plasma levels of five cytokines/chemokines (Axl, FasL, ICAM-1, TARC, and TSLP) were beyond the detectable level. Five (VEGF, IL-2, IL-5, IL-17, and CD30) were unaffected by irradiation in either strain. Temporal patterns were similar in both murine strains for 10 of the cytokines tested, including G-CSF, IL-6, TCA-3, MCP-1, MIP-1γ, KC, CXCL 13, CXCL 16, MDC, and TIMP-1; the other 12 molecules (GM-CSF, IL-3, SCF, IL-1ß, IL-4, IL-10, IL-12p70, MIP-1α, Eotaxin, TNF-α, sTNF-R1, and CD40) showed strain-specific response patterns. While a number of cytokines had temporal response patterns following TBI, the strains exhibited quantitatively different results. CONCLUSIONS: The levels of 27 of the 32 plasma cytokines measured indicate the following: (1) different cytokine concentrations and temporal patterns in the two strains may partly explain different radiation sensitivities and sequelae following irradiation; (2) many of the cytokines/chemokines exhibit similar temporal responses in the two strains. These responses suggest the potential value of using a panel of cytokine/chemokine temporal patterns for radiation dosimetry. Although radiation doses will be difficult to quantitate due to the large variation in levels and temporal responses exhibited in the two murine strains, serial measurements of cytokines might help identify subjects exposed to radiation.

Specific activation of microRNA106b enables the p73 apoptotic response in chronic lymphocytic leukemia by targeting the ubiquitin ligase Itch for degradation.

Chronic lymphocytic leukemia (CLL) is characterized by cells that exhibit dysfunctional apoptosis. Here, we show that deacetylase inhibition led to the E2F1- and myc-mediated transcriptional activation of the microRNA miR106b in primary CLL cells. Induction of miR106b was associated with a down-regulation in the levels of the E3-ubiquitin ligase Itch. Decreases in Itch protein levels were associated with a reciprocal accumulation of its proapoptotic substrate, TAp73 (p73), and induction of p53 up-regulated modulator of apoptosis (PUMA) mRNA and protein. This event was accompanied by mitochondrial dysfunction, processing of caspase-9, and apoptosis of CLL cells. Ectopic expression of miR106b in CLL cells demonstrated that Itch was a direct target of miR106b such that miR106b-induced decreases in Itch resulted in an accumulation of p73. Thus, our results identify a novel regulatory mechanism wherein microRNA regulate cell survival by mediating the posttranscriptional down-regulation of an ubiquitin ligase, leading to the induction of a proapoptotic regulator in malignant cells. Silencing of miRNA expression in CLL may selectively suppress proapoptotic pathways, providing such tumors with a survival advantage. Consequently, chemotherapeutic drugs that activate miR106b could initiate a p53-independent mechanism that targets CLL cells.

Antioxidant properties of select radiation mitigators based on semicarbazone and pyrazole derivatives of curcumin.

Fifty-eight semicarbazone and pyrazole derivatives of curcumin have been developed as potential mitigation agents to treat acute radiation syndrome (ARS). Pyridyl (D12, D13), furyl (D56), and phenyl (D68) derivatives of curcumin semi-carbazones were found to provide the highest dose modifying factors (DMF) with respect to survival in sub-TBI (bone marrow sparing) exposures in mouse models. To investigate the basis for the mitigating effects of these agents on ARS, we examined their oxidation potentials and radical scavenging properties in comparison to other semicarbazone and pyrazole curcumin derivatives with less effective DMFs. Comparisons between D12, D13, D56, and D68 and other semicarbazone and pyrazole derivatives of curcumin did not show a sufficient difference in reducing properties and hydrogen atom donating properties for these properties to be the basis of the dose modifying activities of these compounds. Therefore, their DMFs likely reflect structure-activity relationship(s),wherein interaction with key receptors or alteration of enzyme expression result in modifications of cellular or tissue responses to radiation, rather than on the derivatives' ability to modify radiation-induced flux of free radicals through direct interaction with these radicals.

Antioxidant properties of quercetin.

UNLABELLED: Quercetin, a plant-derived aglycone form of flavonoid glycosides, has been used as a nutritional supplement and may be beneficial against a variety of diseases, including cancer. We examined the antioxidant properties of quercetin. The reduction potential of quercetin was measured at various pH values using voltammetric methods, and its total antioxidant capacity (TAC) was measured using the phosphomolybdenum method. The effect of quercetin on production of reactive oxygen species (ROS) and nitric oxide (NO) in LPS-stimulated human THP-1 acute monocytic leukemia cells was determined by flow cytometry using CM-H2DCFDA dye. The results were compared with curcumin, a natural product exhibiting a similar range of reported health benefits. RESULTS: 1) Quercetin has a higher reduction potential compared with curcumin at three different pH settings and is comparable to Trolox at pH 7-9.5; 2) its TAC is 3.5 fold higher than curcumin; 3) it reduced LPS-induced ROS to near normal levels; 4) it reduced LPS-induced NO production. These data provide a physico-chemical basis for comparing antioxidants, with potential benefits individually or in combination.

The multi-kinase inhibitor TG02 induces apoptosis and blocks B-cell receptor signaling in chronic lymphocytic leukemia through dual mechanisms of action.

The constitutive activation of B-cell receptor (BCR) signaling, together with the overexpression of the Bcl-2 family anti-apoptotic proteins, represents two hallmarks of chronic lymphocytic leukemia (CLL) that drive leukemia cell proliferation and sustain their survival. TG02 is a small molecule multi-kinase inhibitor that simultaneously targets both of these facets of CLL pathogenesis. First, its inhibition of cyclin-dependent kinase 9 blocked the activation of RNA polymerase II and transcription. This led to the depletion of Mcl-1 and rapid induction of apoptosis in the primary CLL cells. This mechanism of apoptosis was independent of CLL prognostic factors or prior treatment history, but dependent on the expression of BAX and BAK. Second, TG02, which inhibits the members of the BCR signaling pathway such as Lck and Fyn, blocked BCR-crosslinking-induced activation of NF-κB and Akt, indicating abrogation of BCR signaling. Finally, the combination of TG02 and ibrutinib demonstrated moderate synergy, suggesting a future combination of TG02 with ibrutinib, or use in patients that are refractory to the BCR antagonists. Thus, the dual inhibitory activity on both the CLL survival pathway and BCR signaling identifies TG02 as a unique compound for clinical development in CLL and possibly other B cell malignancies.

Eye formation in the absence of retina.

Eye development is a complex process that involves the formation of the retina and the lens, collectively called the eyeball, as well as the formation of auxiliary eye structures such as the eyelid, lacrimal gland, cornea and conjunctiva. The developmental requirements for the formation of each individual structure are only partially understood. We have shown previously that the homeobox-containing gene Rx is a key component in eye formation, as retinal structures do not develop and retina-specific gene expression is not observed in Rx-deficient mice. In addition, Rx-/- embryos do not develop any lens structure, despite the fact that Rx is not expressed in the lens. This demonstrates that during normal mammalian development, retina-specific gene expression is necessary for lens formation. In this paper we show that lens formation can be restored in Rx-deficient embryos experimentally, by the elimination of beta-catenin expression in the head surface ectoderm. This suggests that beta-catenin is involved in lens specification either through Wnt signaling or through its function in cell adhesion. In contrast to lens formation, we demonstrate that the development of auxiliary eye structures does not depend on retina-specific gene expression or retinal morphogenesis. These results point to the existence of two separate developmental processes involved in the formation of the eye and its associated structures. One involved in the formation of the eyeball and the second involved in the formation of the auxiliary eye structures.

Replication of murine mitochondrial DNA following irradiation.

The effect of radiation on the mitochondrial genome in vivo is largely unknown. Though mitochondrial DNA (mtDNA) is vital for cellular survival and proliferation, it has little DNA repair machinery compared with nuclear DNA (nDNA). A better understanding of how radiation affects mtDNA should lead to new approaches for radiation protection. We have developed a new system using real-time PCR that sensitively detects the change in copy number of mtDNA compared with nDNA. In each sample, the DNA sequence coding 18S rRNA served as the nDNA reference in a run simultaneously with a mtDNA sequence. Small bowel collected 24 hours after 2 Gy or 4 Gy total body irradiation (TBI) exhibited increased levels of mtDNA compared with control mice. A 4 Gy dose produced a greater effect than 2 Gy. Similarly, in bone marrow collected 24 hours after 4 Gy or 7 Gy TBI, 7 Gy produced a greater response than 4 Gy. As a function of time, a greater effect was seen at 48 hours compared with 24 hours. In conclusion, we found that radiation increased the ratio of mtDNA:nDNA and that this effect seems to be tissue independent and seems to increase with radiation dose and duration following radiation exposure.

CNDAC-Induced DNA Double-Strand Breaks Cause Aberrant Mitosis Prior to Cell Death.

Incorporation of the clinically active deoxycytidine analogue 2'-C-cyano-2'-deoxy-1-ß-D-arabino-pentofuranosyl-cytosine (CNDAC) into DNA generates single-strand breaks that are subsequently converted to double-strand breaks (DSB). Here, we investigated the cellular manifestations of these breaks that link these mechanisms to cell death, and we further tested the relevance of DNA repair pathways in protection of cells against CNDAC damage. The present investigations demonstrate that following exposure to CNDAC and a wash into drug-free medium, chromosomal aberrations, DNA strand breaks, and multinucleate cells arose. These portended loss of viability and were dependent upon exposure time, CNDAC concentration, and passage through mitosis. Following a pulse incubation with CNDAC, live cell imaging using GFP-tagged histone H2B as a marker demonstrated a normal rate of progression to mitosis, but a concentration-dependent delay in passage to a second mitosis. Progression through mitosis was also delayed and accompanied by formation of multinucleate cells. CNDAC-treated cells lacking XPF-ERCC1 nuclease function showed a 16-fold increase in chromosome aberrations. Chromosomal damage in Rad51D-mutant cells (homologous recombination repair deficient) were even more severely affected with extensive aberrations. Rodent or human Polq (POLQ) mutant cells, defective in Pol θ-mediated alternative end joining, did not show enhanced cellular sensitivity to CNDAC. These findings are consistent with formation of DSBs in the second S-phase following exposure, resulting in chromosome aberrations, aberrant mitoses, and subsequent apoptosis.

Anti-cancer effect of resveratrol is associated with induction of apoptosis via a mitochondrial pathway alignment.

Resveratrol, a phytoalexin found in the skin of grapes, is believed to have multiple bioactivities including anti-cancer, anti-carcinogenesis and antiinflammatory. The mechanisms by which resveratrol might produce these effects are not well understood. In this study, malignant human pancreatic cancer cells were treated without or with resveratrol in combination with ionizing radiation (IR), and then the mitochondrial function of treated cells was evaluated using several standardized assays. They include the Calcein AM method for mitochondria transition pore; the JC-1 staining method for mitochondria membrane potential; the CM-H2DCFDA method for reactive oxygen species; and the Annexin V/propidium iodide (PI) method for apoptosis/cell death. Our results indicated that (1) pore function was partially intact after resveratrol, but resveratrol probably interfered with the accumulation of intracellular Calcein AM; (2) depolarization of the mitochondria membrane was increased in the resveratrol treated cells, consistent with mitochondrial dysfunction; (3) ROS was slightly increased with resveratrol, a phenomenon that was greatly increased when this agent was combined with IR; and (4) in parallel with the above changes in mitochondrial and drug transport, cells treated with resveratrol showed increased apoptosis as measured by Annexin V/PI staining. In summary, the anti-cancer effect of resveratrol is associated with the damage of mitochondrial function that leads to increased ROS, apoptosis, and possibly intracellular drug accumulation via inhibition of proteins involved in multi-drug resistance (MDR).

Antioxidants reduce consequences of radiation exposure.

Antioxidants have been studied for their capacity to reduce the cytotoxic effects of radiation in normal tissues for at least 50 years. Early research identified sulfur-containing antioxidants as those with the most beneficial therapeutic ratio, even though these compounds have substantial toxicity when given in-vivo. Other antioxidant molecules (small molecules and enzymatic) have been studied for their capacity to prevent radiation toxicity both with regard to reduction of radiation-related cytotoxicity and for reduction of indirect radiation effects including long-term oxidative damage. Finally, categories of radiation protectors that are not primarily antioxidants, including those that act through acceleration of cell proliferation (e.g. growth factors), prevention of apoptosis, other cellular signaling effects (e.g. cytokine signal modifiers), or augmentation of DNA repair, all have direct or indirect effects on cellular redox state and levels of endogenous antioxidants. In this review we discuss what is known about the radioprotective properties of antioxidants, and what those properties tell us about the DNA and other cellular targets of radiation.

Synthesis and evaluation of novel 1-(1H-1,2,4-triazol-1-yl)-2-(2,4-difluorophenyl)-3-[(4-substitutedphenyl)-piperazin-1-yl]-propan-2-ols as antifungal agents.

A series of 1-(1H-1,2,4-triazol-1-yl)-2-(2,4-difluorophenyl)-3-[(4-substitutedphenyl)-piperazin-1-yl]-propan-2-ols have been designed and synthesized on the basis of the structure-activity relationships and antimycotic mechanism of azole antifungal agents. Their structures were confirmed by elemental analysis, IR, MS, (1)H NMR and (13)C NMR. Results of preliminary antifungal tests against six human pathogenic fungi (Candida albicans, Candida parapsilosis, Cryptococcus neoformans, Candida tropicalis, inherently fluconazole-resistant Candida krusei, Candida glabrata) in vitro showed that all title compounds exhibited activity against fungi tested to some extent except against C. tropicalis. Compound 5b showed higher activity against C. albicans, C. parapsilosis and C. krusei than fluconazole, and its MIC values were determined to be 0.5microg/mL, 1microg/mL and 4microg/mL, respectively. Compound 5k showed higher activities against Torulopsis glabrata than fluconazole (with the MIC value of 2microg/mL). Compounds 5a, 5c, 5f, 5g, 5i exhibited higher activities against C. parapsilosis than fluconazole (with the MIC values of 2microg/mL, 2microg/mL, 2microg/mL, 1microg/mL and 2microg/mL, respectively).

The long noncoding RNA, treRNA, decreases DNA damage and is associated with poor response to chemotherapy in chronic lymphocytic leukemia.

The study of long noncoding RNAs (lncRNAs) is an emerging area of cancer research, in part due to their ability to serve as disease biomarkers. However, few studies have investigated lncRNAs in chronic lymphocytic leukemia (CLL). We have identified one particular lncRNA, treRNA, which is overexpressed in CLL B-cells. We measured transcript expression in 144 CLL patient samples and separated samples into high or low expression of treRNA relative to the overall median. We found that high expression of treRNA is significantly associated with shorter time to treatment. High treRNA also correlates with poor prognostic indicators such as unmutated IGHV and high ZAP70 protein expression. We validated these initial findings in samples collected in a clinical trial comparing the nucleoside analog fludarabine alone or in combination with the alkylating agent cyclophosphamide in untreated CLL samples collected prior to starting therapy (E2997). High expression of treRNA was independently prognostic for shorter progression free survival in patients receiving fludarabine plus cyclophosphamide. Given these results, in order to study the role of treRNA in DNA damage response we generated a model cell line system where treRNA was over-expressed in the human B-CLL cell line OSU-CLL. Relative to the vector control line, there was less cell death in OSU-CLL over-expressing treRNA after exposure to fludarabine and mafosfamide, due in part to a reduction in DNA damage. Therefore, we suggest that treRNA is a novel biomarker in CLL associated with aggressive disease and poor response to chemotherapy through enhanced protection against cytotoxic mediated DNA damage.

HDAC Inhibition Induces MicroRNA-182, which Targets RAD51 and Impairs HR Repair to Sensitize Cells to Sapacitabine in Acute Myelogenous Leukemia.

PURPOSE: The double-strand breaks elicited by sapacitabine, a clinically active nucleoside analogue prodrug, are repaired by RAD51 and the homologous recombination repair (HR) pathway, which could potentially limit its toxicity. We investigated the mechanism by which histone deacetylase (HDAC) inhibitors targeted RAD51 and HR to sensitize acute myelogenous leukemia (AML) cells to sapacitabine. EXPERIMENTAL DESIGN: Chromatin immunoprecipitation identified the role of HDACs in silencing miR-182 in AML. Immunoblotting, gene expression, overexpression, or inhibition of miR-182 and luciferase assays established that miR-182 directly targeted RAD51. HR reporter assays, apoptotic assays, and colony-forming assays established that the miR-182, as well as the HDAC inhibition-mediated decreases in RAD51 inhibited HR repair and sensitized cells to sapacitabine. RESULTS: The gene repressors, HDAC1 and HDAC2, became recruited to the promoter of miR-182 to silence its expression in AML. HDAC inhibition induced miR-182 in AML cell lines and primary AML blasts. miR-182 targeted RAD51 protein both in luciferase assays and in AML cells. Overexpression of miR-182, as well as HDAC inhibition-mediated induction of miR-182 were linked to time- and dose-dependent decreases in the levels of RAD51, an inhibition of HR, increased levels of residual damage, and decreased survival after exposure to double-strand damage-inducing agents. CONCLUSIONS: Our findings define the mechanism by which HDAC inhibition induces miR-182 to target RAD51 and highlights a novel pharmacologic strategy that compromises the ability of AML cells to conduct HR, thereby sensitizing AML cells to DNA-damaging agents that activate HR as a repair and potential resistance mechanism. Clin Cancer Res; 22(14); 3537-49. ©2016 AACR.

PicoGreen assay of circular DNA for radiation biodosimetry.

We developed a simple, rapid and quantitative assay using the fluorescent probe PicoGreen to measure the concentration of ionizing radiation-induced double-stranded DNA (dsDNA) in mouse plasma, and we correlated this concentration with the radiation dose. With 70 µl of blood obtained by fingerstick, this 30 min assay reduces protein interference without extending sample processing time. Plasma from nonirradiated mice (BALB/c and NIH Swiss) was pooled, diluted and spiked with dsDNA to establish sensitivity and reproducibility of the assay to quantify plasma dsDNA. The assay was then used to directly quantify dsDNA in plasma at 0-48 h after mice received 0-10 Gy total-body irradiation (TBI). There are three optimal conditions for this assay: 1:10 dilution of plasma in water; 1:200 dilution of PicoGreen reagent in water; and calibration of radiation-induced dsDNA concentration through a standard addition method using serial spiking of samples with genomic dsDNA. Using the internal standard calibration curve of the spiked samples method, the signal developed within 5 min, exhibiting a linear signal (r(2) = 0.997). The radiation-induced elevation of plasma DNA in mice started at 1-3 h, peaked at 9 h and gradually returned to baseline at 24 h after TBI (6 Gy). DNA levels in plasma collected from mice 9 h after 0-10 Gy TBI correlated strongly with dose (r(2) = 0.991 and 0.947 for BALB/c and NIH Swiss, respectively). Using the PicoGreen assay, we observed a radiation dose-dependent response in extracellular plasma DNA 9 h after irradiation with an assay time ≤ 30 min.