Inactivation of anthracyclines by serum heme proteins

Constraint-based modelling predicts metabolic signatures of low and high-grade serous ovarian cancer

Ovarian cancer is an aggressive, heterogeneous disease, burdened with late diagnosis and resistance to chemotherapy. Clinical features of ovarian cancer could be explained by investigating its metabolism, and how the regulation of specific pathways links to individual phenotypes. Ovarian cancer is of particular interest for metabolic research due to its heterogeneous nature, with five distinct subtypes having been identified, each of which may display a unique metabolic signature. To elucidate metabolic differences, constraint-based modelling (CBM) represents a powerful technology, inviting the integration of 'omics' data, such as transcriptomics. However, many CBM methods have not prioritised accurate growth rate predictions, and there are very few ovarian cancer genome-scale studies. Here, a novel method for CBM has been developed, employing the genome-scale model Human1 and flux balance analysis, enabling the integration of in vitro growth rates, transcriptomics data and media conditions to predict the metabolic behaviour of cells. Using low- and high-grade ovarian cancer, subtype-specific metabolic differences have been predicted, which have been supported by publicly available CRISPR-Cas9 data from the Cancer Cell Line Encyclopaedia and an extensive literature review. Metabolic drivers of aggressive, invasive phenotypes, as well as pathways responsible for increased chemoresistance in low-grade cell lines have been suggested. Experimental gene dependency data has been used to validate areas of the pentose phosphate pathway as essential for low-grade cellular growth, highlighting potential vulnerabilities for this ovarian cancer subtype.

Endothelial cells release soluble factors that support the long-term survival of filarial worms in vitro

The inability to maintain filarial nematodes in long-term in vitro culture greatly limits research into the basic biology of these parasites and hinders in vitro screening of novel anti-filarial agents. In this study, we sought to characterize nutrients that promote the long-term survival of filarial worms in vitro. Using microfilariae (MF) obtained from gerbils infected with Litomosoides sigmodontis, a filarial parasite of rodents, we found that Dulbecco's Modified Eagle Medium (DMEM) supplemented with 10% fetal bovine serum (FBS) resulted in MF survival of only 5 days. However, co-culturing MF with a mouse endothelial cell line (EOMA) enabled survival for 40 days. Culturing EOMA cells in transwell plates extended MF survival to the same degree as direct co-culture, suggesting that the factors microfilariae require are soluble in nature. Heat inactivation of EOMA conditioned media at 56 °C reduced MF survival by approximately 50%, and heat inactivation at 100 °C reduced survival to 3 days, demonstrating that both heat labile and heat stable factors are involved. EOMA cells require FBS to produce these factors, as conditioned media collected from EOMA cells grown in the absence of FBS failed to prolong survival. The removal of lipids also abrogated survival, indicating MF are likely utilizing lipid factors released by EOMA cells. Dialysis experiments demonstrate that at least some of the required factors are between 0.1 and 1 kDa in size. Importantly, L. sigmodontis adult worms also show significantly extended survival when cultured in EOMA conditioned media. Together, these results suggest that EOMA-produced factors include lipid-containing molecules, heat labile molecules (likely a protein), and micronutrients between 0.1 and 1 kDa in size. These studies have established a cell-free approach to maintaining MF and adult stage filarial worms in long-term in vitro culture and have taken important steps towards biochemically characterizing host-derived nutrients required for parasite survival.

Manganoporphyrins increase ascorbate-induced cytotoxicity by enhancing H2O2 generation

Renewed interest in using pharmacological ascorbate (AscH-) to treat cancer has prompted interest in leveraging its cytotoxic mechanism of action. A central feature of AscH- action in cancer cells is its ability to act as an electron donor to O2 for generating H2O2. We hypothesized that catalytic manganoporphyrins (MnP) would increase AscH- oxidation rates, thereby increasing H2O2 fluxes and cytotoxicity. Three different MnPs were tested (MnTBAP, MnT2EPyP, and MnT4MPyP), exhibiting a range of physicochemical and thermodynamic properties. Of the MnPs tested, MnT4MPyP exerted the greatest effect on increasing the rate of AscH- oxidation as determined by the concentration of ascorbate radical [Asc•-] and the rate of oxygen consumption. At concentrations that had minimal effects alone, combining MnPs and AscH- synergized to decrease clonogenic survival in human pancreatic cancer cells. This cytotoxic effect was reversed by catalase, but not superoxide dismutase, consistent with a mechanism mediated by H2O2. MnPs increased steady-state concentrations of Asc•- upon ex vivo addition to whole blood obtained either from mice infused with AscH- or patients treated with pharmacologic AscH-. Finally, tumor growth in vivo was inhibited more effectively by combining MnT4MPyP with AscH-. We concluded that MnPs increase the rate of oxidation of AscH- to leverage H2O2 flux and ascorbate-induced cytotoxicity.

Ascorbic acid: chemistry, biology and the treatment of cancer

Since the discovery of vitamin C, the number of its known biological functions is continually expanding. Both the names ascorbic acid and vitamin C reflect its antiscorbutic properties due to its role in the synthesis of collagen in connective tissues. Ascorbate acts as an electron-donor keeping iron in the ferrous state thereby maintaining the full activity of collagen hydroxylases; parallel reactions with a variety of dioxygenases affect the expression of a wide array of genes, for example via the HIF system, as well as via the epigenetic landscape of cells and tissues. In fact, all known physiological and biochemical functions of ascorbate are due to its action as an electron donor. The ability to donate one or two electrons makes AscH(-) an excellent reducing agent and antioxidant. Ascorbate readily undergoes pH-dependent autoxidation producing hydrogen peroxide (H(2)O(2)). In the presence of catalytic metals this oxidation is accelerated. In this review, we show that the chemical and biochemical nature of ascorbate contribute to its antioxidant as well as its prooxidant properties. Recent pharmacokinetic data indicate that intravenous (i.v.) administration of ascorbate bypasses the tight control of the gut producing highly elevated plasma levels; ascorbate at very high levels can act as prodrug to deliver a significant flux of H(2)O(2) to tumors. This new knowledge has rekindled interest and spurred new research into the clinical potential of pharmacological ascorbate. Knowledge and understanding of the mechanisms of action of pharmacological ascorbate bring a rationale to its use to treat disease especially the use of i.v. delivery of pharmacological ascorbate as an adjuvant in the treatment of cancer.

Heme as a source of iron to Leishmania infantum amastigotes

Amastigotes, the mammalian stage of Leishmania, must acquire iron from molecules accessing the macrophage parasitophorous vacuole (PV) where they inhabit. These molecules likely include non-heme and heme-bound forms of iron. Here we demonstrate that, in addition to the previously documented use of ferrous iron, Leishmania amastigotes are also capable of exploiting iron from hemin and hemoglobin for nutritional purposes. Moreover, evidence is presented that a ligand at the surface of amastigotes binds hemin with high-affinity (Kd=0.044nM). This ligand may function in intracellular transport of heme while hemoglobin internalization occurs through a different molecule. The co-existence in Leishmania amastigotes of different processes to acquire iron could constitute an infective strategy, ensuring parasites a substantial advantage in situations of iron limitation.

Doxorubicin inhibits oxidation of 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonate) (ABTS) by a lactoperoxidase/H(2)O(2) system by reacting with ABTS-derived radical

The effect of doxorubicin on oxidation of 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonate) (ABTS) by lactoperoxidase and hydrogen peroxide has been investigated. It was found that: (1) oxidation of ABTS to its radical cation (ABTS*(+)) is inhibited by doxorubicin as evidenced by its induction of a lag period, duration of which depends on doxorubicin concentration; (2) the inhibition is due to doxorubicin hydroquinone reducing the ABTS*(+) radical (stoichiometry 1: 1.8); (3) concomitant with the ABTS*(+) reduction is oxidation of doxorubicin; only when the doxorubicin concentration decreases to a near zero level, net oxidation of ABTS could be detected; (4) oxidation of doxorubicin leads to its degradation to 3-methoxysalicylic acid and 3-methoxyphthalic acid; (5) the efficacy of doxorubicin to quench ABTS*(+) is similar to the efficacy of p-hydroquinone, glutathione and Trolox C. These observations support the assertion that under certain conditions doxorubicin can function as an antioxidant. They also suggest that interaction of doxorubicin with oxidants may lead to its oxidative degradation.