Dynamics of Age- versus Therapy-Related Clonal Hematopoiesis in Long-term Survivors of Pediatric Cancer.

We present the first comprehensive investigation of clonal hematopoiesis (CH) in 2,860 long-term survivors of pediatric cancer with a median follow-up time of 23.5 years. Deep sequencing over 39 CH-related genes reveals mutations in 15% of the survivors, significantly higher than the 8.5% in 324 community controls. CH in survivors is associated with exposures to alkylating agents, radiation, and bleomycin. Therapy-related CH shows significant enrichment in STAT3, characterized as a CH gene specific to survivors of Hodgkin lymphoma, and TP53. Single-cell profiling of peripheral blood samples revealed STAT3 mutations predominantly present in T cells and contributed by SBS25, a mutational signature associated with procarbazine exposure. Serial sample tracking reveals that larger clone size is a predictor for future expansion of age-related CH clones, whereas therapy-related CH remains stable decades after treatment. These data depict the distinct dynamics of these CH subtypes and support the need for longitudinal monitoring to determine the potential contribution to late effects. SIGNIFICANCE: This first comprehensive CH analysis in long-term survivors of pediatric cancer presents the elevated prevalence and therapy exposures/diagnostic spectrum associated with CH. Due to the contrasting dynamics of clonal expansion for age-related versus therapy-related CH, longitudinal monitoring is recommended to ascertain the long-term effects of therapy-induced CH in pediatric cancer survivors. See related commentary by Collord and Behjati, p. 811. This article is highlighted in the In This Issue feature, p. 799.

Preparation, Characterization and Dielectric Properties of Alginate-Based Composite Films Containing Lithium Silver Oxide Nanoparticles.

Polymer composites have found applications in diverse areas, ranging from the manufacturing of portable electronic devices to the fabrication of bioactive agent carriers. This article reports the preparation of composite films consisting of sodium alginate (SA) and lithium silver oxide (LAO) nanoparticles. The films are generated by solution casting; whereas the nanoparticles are fabricated by using the hydrothermal method. The effects of the nanoparticles on the morphological, thermal, and dielectric properties of the films are examined by using Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD) analysis, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM). Electrical measurements are also performed to determine the dielectric constant (ε'), dielectric loss (ε″), AC conductivity (σac), electrical moduli (M' and M″), and impedance (Z' and Z″). The composite films are shown to be crystalline in nature, with nanoparticles having a diameter of 30-45 nm effectively disseminated in the polymer matrix. They also display good dielectric properties. Our results suggest that the films warrant further exploration for possible use in microelectronic applications.

TOR signaling is a determinant of cell survival in response to DNA damage.

The conserved TOR (target of rapamycin) kinase is part of a TORC1 complex that regulates cellular responses to environmental stress, such as amino acid starvation and hypoxia. Dysregulation of Akt-TOR signaling has also been linked to the genesis of cancer, and thus, this pathway presents potential targets for cancer chemotherapeutics. Here we report that rapamycin-sensitive TORC1 signaling is required for the S-phase progression and viability of yeast cells in response to genotoxic stress. In the presence of the DNA-damaging agent methyl methanesulfonate (MMS), TOR-dependent cell survival required a functional S-phase checkpoint. Rapamycin inhibition of TORC1 signaling suppressed the Rad53 checkpoint-mediated induction of ribonucleotide reductase subunits Rnr1 and Rnr3, thereby abrogating MMS-induced mutagenesis and enhancing cell lethality. Moreover, cells deleted for RNR3 were hypersensitive to rapamycin plus MMS, providing the first demonstration that Rnr3 contributes to the survival of cells exposed to DNA damage. Our findings support a model whereby TORC1 acts as a survival pathway in response to genotoxic stress by maintaining the deoxynucleoside triphosphate pools necessary for error-prone translesion DNA polymerases. Thus, TOR-dependent cell survival in response to DNA-damaging agents coincides with increased mutation rates, which may contribute to the acquisition of chemotherapeutic drug resistance.

Acridones circumvent P-glycoprotein-associated multidrug resistance (MDR) in cancer cells.

Multidrug resistance (MDR) mediated by overexpression of MDR1 P-glycoprotein (P-gp) is one of the best characterized transporter-mediated barriers to successful chemotherapy in cancer patients. Chemosensitizers are the agents that increase the sensitivity of multidrug-resistant cells to the toxic influence of previously less effective drugs. In an attempt to find such vital chemosensitizers, a series of N(10)-substituted-2-chloroacridone analogous (1-17) have been synthesized. Compound 1 was prepared by the Ullmann condensation of o-chlorobenzoic acid and p-chloroaniline followed by cyclization. The N-(omega-chloroalkyl) analogues were found to undergo iodide catalyzed nucleophilic substitution reaction with secondary amines and the resultant products were characterized by spectral methods. The lipophilicity expressed in log(10)P and pK(a) of compounds has been determined. All compounds were examined for their ability to increase the uptake of vinblastine (VLB) in MDR KBCh(R)-8-5 cells and the results showed that the compounds 6, 8, 11-14, 16, and 17 at their respective IC(50) concentrations caused a 1.0- to 1.7-fold greater accumulation of VLB than did a similar concentration of the standard modulator, verapamil (VRP). Results of the efflux experiment showed that VRP and each of the modulators significantly inhibited the efflux of VLB, suggesting that they may be competitors for P-gp. All modulators effectively competing with [(3)H]azidopine for binding to P-gp pointed out this transport membrane protein as their likely site of action. Compounds at IC(10) were evaluated for their efficacy to modulate the cytotoxicity of VLB and the results showed that modulators 11, 13, 14, 16, and 17 were able to completely reverse the 25-fold resistance of KBCh(R)-8-5 cells to VLB. Examination of the relationship between lipophilicity and antagonism of MDR showed a reasonable correlation suggesting that hydrophobicity is one of the determinants of potency for anti-MDR activity of 2-chloroacridones. The results allowed us to draw preliminary conclusions about structural features of 2-chloroacridones important for MDR modulation.

Anti-calmodulin acridone derivatives modulate vinblastine resistance in multidrug resistant (MDR) cancer cells.

Multidrug resistance (MDR) is one of the main obstacles limiting the efficacy of chemotherapy treatment of tumors. Parent acridones 1A and 1B were prepared by the Ullmann reaction followed by cyclization and N-alkylation. N-(omega-Chloroalkyl) analogues were subjected to iodide catalyzed nucleophilic substitution reaction with secondary amines to get the compounds 3A-13A and 3B-13B, which enhanced the uptake of vinblastine in KBChR-8-5 cells to a greater extent (2.6-13.1-fold relative to control) than verapamil. The study on the structure-activity relationship revealed that substitution of -H at position C-4 in acridone nucleus by -OCH3 increased the cytotoxic and anti-MDR activities. The ability of acridones to inhibit calmodulin dependent cyclic AMP phosphodiesterase has been determined and the results have shown a strong positive correlation between anti-calmodulin activity and cytotoxicity in KBChR-8-5 cells or anti-MDR activity.

Synthesis and chemical characterization of 2-methoxy-N(10)-substituted acridones needed to reverse vinblastine resistance in multidrug resistant (MDR) cancer cells.

In an attempt to find clinically useful modulators of multidrug resistance (MDR), a series of 19 N(10)-substituted-2-methoxyacridone analogues has been synthesized. 2-Methoxyacridone and its derivatives (1-19) were synthesized. Compound 1 was prepared by the Ullmann condensation of o-chlorobenzoic acid and p-anisidine followed by cyclization using polyphosphoric acid. This compound undergoes N-alkylation in the presence of phase transfer catalyst (PTC). Stirring of 2-methoxy acridone with 1-bromo-3-chloropropane or 1-bromo-4-chlorobutane in a two-phase system consisting of organic phase (tetrahydrofuran) and 6N potassium hydroxide in the presence of tetrabutylammonium bromide leads to the formation of compounds 2 and 11 in good yield. N-(omega-Chloroalkyl) analogues were found to undergo iodide catalyzed nucleophilic substitution reaction with various secondary amines. Products were characterized by UV, IR, 1H and 13C NMR, mass-spectral data and elemental analysis. The lipophilicity expressed in log(10) P and pK(a) of compounds have been determined. All compounds were examined for their ability to increase the uptake of vinblastine (VLB) in MDR KBCh(R)-8-5 cells and the results showed that the compounds 7, 10, 12, and 15-19 at 100 microM caused a 1.05- to 1.7-fold greater accumulation of vinblastine than did a similar concentration of the standard modulator, verapamil (VRP). However, the effects on VLB uptake were specific because these derivatives had little effect in the parental drug sensitive line KB-3-1. Steady state accumulation of VLB, a substrate for P-glycoprotein (P-gp) mediated efflux, was studied in the MDR cell line KBCh(R)-8-5 in the presence and absence of novel MDR modulators. Results of the efflux experiment showed that VRP and each of the modulators (1-19) significantly inhibited the efflux of VLB, suggesting that they may be competitors for P-gp. From among the compounds examined, 14 except 1, 2, 4, 8, and 11, exhibited greater efflux inhibiting activity than VRP. All the 19 compounds effectively compete with [(3)H] azidopine for binding to P-gp, pointed out this transport membrane protein as their likely site of action. Cytotoxicity has been determined and the IC(50) values lie in the range 8.00-18.50 microM for propyl and 4-15 microM for butyl derivatives against KBCh(R)-8-5 cells suggesting that the antiproliferative activity increases as chain length increases from 3 to 4 carbons at N(10)-position. Compounds at IC(10) were evaluated for their efficacy to modulate the cytotoxicity of VLB in KBCh(R)-8-5 cells and found that the modulators enhanced the cytotoxicity of VLB by 5- to 35-fold. Modulators 12, 14-16, and 19 like VRP, were able to completely reverse the 24-fold resistance of KBCh(R)-8-5 cells to VLB. Examination of the relationship between lipophilicity and antagonism of MDR showed a reasonable correlation suggesting that hydrophobicity is one of the determinants of potency for anti-MDR activity of 2-methoxyacridones.

The deubiquitinating enzyme Doa4p protects cells from DNA topoisomerase I poisons.

DNA topoisomerase I (Top1p) catalyzes changes in DNA topology via the formation of an enzyme-DNA covalent complex that is reversibly stabilized by the antitumor drug, camptothecin (CPT). During S-phase, collisions with replication forks convert these complexes into cytotoxic DNA lesions that trigger cell cycle arrest and cell death. To investigate cellular responses to CPT-induced DNA damage, a yeast genetic screen identified conditional tah mutants with enhanced sensitivity to self-poisoning DNA topoisomerase I mutant (Top1T722Ap), which mimics the action of CPT. Mutant alleles of three genes, DOA4, SLA1 and SLA2, were recovered. A nonsense mutation in DOA4 eliminated the catalytic residues of the Doa4p deubiquitinating enzyme, yet retained the rhodanase domain. At 36 degrees C, this doa4-10 mutant exhibited increased sensitivity to CPT, osmotic stress, and hydroxyurea, and a reversible petite phenotype. However, the accumulation of pre-vacuolar class E vesicles that was observed in doa4Delta cells was not detected in the doa4-10 mutant. Mutations in SLA1 or SLA2, which alter actin cytoskeleton architecture, induced a conditional synthetic lethal phenotype in combination with doa4-10 in the absence of DNA damage. Here actin cytoskeleton defects coincided with the enhanced fragility of large-budded cells. In contrast, the enhanced sensitivity of doa4-10 mutant cells to Top1T722Ap was unrelated to alterations in endocytosis and was selectively suppressed by increased dosage of the ribonucleotide reductase inhibitor Sml1p. Additional studies suggest a role for Doa4p in the Rad9p checkpoint response to Top1p poisons. These findings indicate a functional link between ubiquitin-mediated proteolysis and cellular resistance to CPT-induced DNA damage.