Use of biomarkers to improve immunosuppressive drug development and outcomes in renal organ transplantation: A meeting report

On September 27-28, 2018 the Food and Drug Administration (FDA) and the Critical Path Institute's Transplant Therapeutics Consortium convened a public workshop titled "Evidence-Based Treatment Decisions in Transplantation: The Right Dose & Regimen for the Right Patient/Individualized Treatment." The workshop facilitated cooperative engagement of transplant community stakeholders, including pharmaceutical industry, academic researchers, clinicians, patients, and regulators to discuss methods to advance the development of novel immunosuppressive drugs for use in solid organ transplantation. Day 1 focused on the utility of biomarkers in drug development_, with considerations for seeking regulatory endorsement for use in clinical trials. Biomarkers add value to drug development by improving patient selection criteria, safety monitoring, endpoint selection, and more. Regulatory endorsement through the FDA Biomarker Qualification Program encourages the use of biomarkers in drug development by instilling confidence and consistency in biomarker interpretation across trials. Public-private partnerships or consortia allow stakeholders to share expertise, resources, and data in pursuit of biomarker qualification. Biomarkers relevant to pretransplant risk assessment, early posttransplant care, and assessment of immune response, immunosuppressive drug efficacy, and graft function as discussed on day 1 of the workshop are described.

The importance of drug safety and tolerability in the development of new immunosuppressive therapy for transplant recipients: The Transplant Therapeutics Consortium's position statement

The Transplant Therapeutics Consortium (TTC) is a public-private partnership between the US Food and Drug Administration and the transplantation community including the transplantation societies and members of the biopharmaceutical industry. The TTC was formed to accelerate the process of developing new medical products for transplant patients. The initial goals of this collaboration are the following: (a) To define which aspects of the kidney transplant drug-development process have clear needs for improvement from an industry and regulatory perspective; (b) to define which of the unmet needs in the process could be positively impacted through the development of specific drug-development tools based on available data; and (c) to determine the most appropriate pathway to achieve regulatory acceptance of the proposed process-accelerating tools. The TTC has identified 2 major areas of emphasis: new biomarkers or endpoints for determining the efficacy of new therapies and new tools to assess the safety or tolerability of new therapies. This article presents the rationale and planned approach to develop new tools to assess safety and tolerability of therapies for transplant patients. We also discuss how similar efforts might support the continued development of patient-reported outcome measures in the future.

The effects of different buffers on the oxidation of DNA by thiols and ferric iron

Because buffers can act as metal ligands, they can effect several reactions necessary for DNA oxidation by ferric iron and thiols, such as iron reduction. Therefore, these reactions were studied in Hepes and phosphate buffers and unbuffered NaCl. Reduction of Fe3+ by dithiothreitol (DTT) and cysteine was observed in either Hepes or NaCl solutions, but not in phosphate buffer. Thiyl radicals were observed in Hepes, but there was much less thiyl radical production in the saline or phosphate solutions. Redox cycling between either DTT or cysteine and Fe3+ also resulted in dioxygen consumption in Hepes buffer. Reduction of Fe3+ and O2 resulted in the formation of an oxidant capable of producing 8-hydroxy-2'-deoxyguanosine (8-OHdG) in calf-thymus DNA. The highest levels of 8-OHdG were detected when DTT or cysteine and Fe3+ were incubated in Hepes, while much less DNA oxidation was detected when the experiment was done in a saline solution, and almost no DNA oxidation occurred in the phosphate buffer. These results demonstrate that the use of different buffers can greatly affect the ability of thiols to promote iron-dependent oxidations.

Liposome-delivered superoxide dismutase prevents nitric oxide-dependent motor neuron death induced by trophic factor withdrawal

Inhibition of nitric oxide synthesis prevents rat embryonic motor neurons from undergoing apoptosis when initially cultured without brain-derived neurotrophic factor. Using an improved cell culture medium, we found that the partial withdrawal of trophic support even weeks after motor neurons had differentiated into a mature phenotype still induced apoptosis through a process dependent upon nitric oxide. However, nitric oxide itself was not directly toxic to motor neurons. To investigate whether intracellular superoxide contributed to nitric oxide-dependent apoptosis, we developed a novel method using pH-sensitive liposomes to deliver Cu, Zn superoxide dismutase intracellularly into motor neurons. Intracellular superoxide dismutase prevented motor neuron apoptosis from trophic factor withdrawal, whereas empty liposomes, inactivated superoxide dismutase in liposomes or extracellular superoxide dismutase did not. Neither hydrogen peroxide nor nitrite added separately or in combination affected motor neuron survival. Our results suggest that a partial reduction in trophic support induced motor neuron apoptosis by a process requiring the endogenous production of both nitric oxide and superoxide, irrespective of the extent of motor neuron maturation in culture.

Role of endogenous nitric oxide and peroxynitrite formation in the survival and death of motor neurons in culture

Motor neuron survival is highly dependent on trophic factor supply. Deprivation of trophic factors results in induction of neuronal NOS, which is also found in pathological conditions. Growing evidence suggests that motor neuron degeneration involves peroxynitrite formation. Trophic factors modulate peroxynitrite toxicity (Estévez et al., 1995; Shin et al., 1996; Spear et al., 1997). Whether a trophic factor prevents or potentiates peroxynitrite toxicity depends upon when the cells are exposed to the trophic factor (Table 1). These results strongly suggest that a trophic factor that can protect neurons under optimal conditions, but under stressful conditions can increase cell death. In this context, it is possible that trophic factors or cytokines produced as a response to damage may potentiate rather than prevent motor neuron death. A similar argument may apply to the therapeutic administration of trophic factors to treat neurodegenerative diseases. Similarly, the contrasting actions of NO on motor neurons may have important consequences for the potential use of nitric oxide synthase inhibitors in the treatment of ALS and other related neurodegenerative diseases.

Enhancement of peroxynitrite-induced apoptosis in PC12 cells by fibroblast growth factor-1 and nerve growth factor requires p21Ras activation and is suppressed by Bcl-2

Extracellular trophic factors can regulate whether cells subjected to oxidative stress will survive to proliferate or else undergo cell death. We have previously shown that about 35% of undifferentiated PC12 cells undergo apoptosis 18 h after exposure to peroxynitrite and that pretreatment with nerve growth factor (NGF) protects PC12 cells through activation of phosphatidylinositol (PI) 3-kinase. In contrast, pretreatment with acidic fibroblast growth factor (FGF-1) approximately doubled apoptosis. We report here that NGF added immediately after peroxynitrite treatment no longer protected against apoptosis, but instead enhanced apoptosis to the same extent as FGF. We further investigated which signaling pathways were involved in increasing the level of apoptosis. Overexpression of Bcl-2 blocked the increased apoptosis caused by NGF and FGF-1, but Bcl-2 did not prevent the induction of apoptosis by peroxynitrite alone. The increase in apoptosis caused by the trophic factors was also blocked by the expression of a dominant negative p21Ras mutant. Activation of PI 3-kinase by NGF pretreatment completely protected against both the enhanced apoptosis induced by FGF-1 pretreatment and NGF posttreatment and the apoptosis induced by peroxynitrite alone. Our results indicate that the enhancement of peroxynitrite-induced apoptosis caused by NGF and FGF-1 is dependent on the stimulation of a proapoptotic pathway involving p21Ras that can be suppressed by Bcl-2.

Nitric oxide-dependent production of cGMP supports the survival of rat embryonic motor neurons cultured with brain-derived neurotrophic factor

Trophic factor deprivation induces neuronal nitric oxide synthase (NOS) and apoptosis of rat embryonic motor neurons in culture. We report here that motor neurons constitutively express endothelial NOS that helps support the survival of motor neurons cultured with brain-derived neurotrophic factor (BDNF) by activating the nitric oxide-dependent soluble guanylate cyclase. Exposure of BDNF-treated motor neurons to nitro-L-arginine methyl ester (L-NAME) decreased cell survival 40-50% 24 hr after plating. Both low steady-state concentrations of exogenous nitric oxide (<0.1 microM) and cGMP analogs protected BDNF-treated motor neurons from death induced by L-NAME. Equivalent concentrations of cAMP analogs did not affect cell survival. Inhibition of nitric oxide-sensitive guanylate cyclase with 2 microM 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) reduced the survival of BDNF-treated motor neurons by 35%. cGMP analogs also protected from ODQ-induced motor neuron death, whereas exogenous nitric oxide did not. In all cases, cell death was prevented with caspase inhibitors. Our results suggest that nitric oxide-stimulated cGMP synthesis helps to prevent apoptosis in BDNF-treated motor neurons.

Nitric oxide and superoxide contribute to motor neuron apoptosis induced by trophic factor deprivation

Primary cultures of rat embryonic motor neurons deprived of brain-derived neurotrophic factor (BDNF) induce neuronal nitric oxide synthase (NOS) within 18 hr. Subsequently, >60% of the neurons undergo apoptosis between 18 and 24 hr after plating. Nitro-L-arginine and nitro-L-arginine methyl ester (L-NAME) prevented motor neuron death induced by trophic factor deprivation. Exogenous generation of nitric oxide at concentrations lower than 100 nM overcame the protection by L-NAME. Manganese tetrakis (4-benzoyl acid) porphyrin, a cell-permeant superoxide scavenger, also prevented nitric oxide-dependent motor neuron death. Motor neurons cultured without trophic support rapidly became immunoreactive for nitrotyrosine when compared with motor neurons incubated with BDNF, L-NAME, or manganese TBAP. Our results suggest that peroxynitrite, a strong oxidant formed by the reaction of NO and superoxide, plays an important role in the induction of apoptosis in motor neurons deprived of trophic factors and that BDNF supports motor neuron survival in part by preventing neuronal NOS expression.

Nerve growth factor protects PC12 cells against peroxynitrite-induced apoptosis via a mechanism dependent on phosphatidylinositol 3-kinase

Nerve growth factor (NGF) prevents apoptosis induced by the oxidant peroxynitrite in undifferentiated PC12 rat pheochromocytoma cells. Previous studies have shown that activation of phosphatidylinositol 3-kinase (PI 3-kinase) by NGF via the TrkA receptor tyrosine kinase protects PC12 cells from serum deprivation-induced apoptosis. We found that two PI 3-kinase inhibitors, wortmannin and LY294002, eliminated the protection NGF provided against peroxynitrite-induced apoptosis at concentrations consistent with their effectiveness as PI 3-kinase inhibitors. When the activity of PI 3-kinase was assayed in phosphotyrosine immunoprecipitates after treatment of PC12 cells with peroxynitrite, PI 3-kinase activity was reduced by 50% of that detected in control cells, whereas PI 3-kinase activity in NGF-treated cells was unaffected by peroxynitrite. If an antibody against PI 3-kinase was used to immunoprecipitate the enzyme, treatment with peroxynitrite had no effect on activity. Therefore, peroxynitrite appeared to disrupt interactions between PI 3-kinase and phosphotyrosine proteins, rather than directly inhibiting the enzyme. NGF also activates p21Ras-dependent pathways, but this did not appear to be required for NGF to exert its protective effect against peroxynitrite. PC12 cells expressing a dominant inhibitory mutant of p21Ras were equally susceptible to peroxynitrite-induced apoptosis, which was prevented by NGF. Wortmannin was also able to block the protective effect of NGF in the p21Ras mutant cell line. Although many signaling pathways are activated by NGF, these results suggest that a PI 3-kinase-dependent pathway is important for inhibiting peroxynitrite-induced apoptosis.

Prenatal and postnatal ethanol exposure influences preweanling rats' behavioral and autonomic responding to ethanol odor

The specific question was how prenatal and/or postnatal experience with ethanol influences cardiac and behavioral responses to the odor of ethanol on postnatal day (PD) 16. In each of two experiments, pregnant rats were given ethanol or water on gestational days 17-20. Offspring were exposed on PD12 to one of three conditions: intragastric administration of 6% ethanol, indirect exposure to ethanol from littermates, or no treatment. Results of Experiment 1 indicated that, regardless of prenatal ethanol exposure, 16-day-olds exposed on PD12 either directly or indirectly to ethanol expressed a greater increase in HR in response to ethanol odor than pups not postnatally exposed to ethanol. In Experiment 2, in which a lower ethanol dose was used postnatally, an interaction between pre- and postnatal ethanol exposure was observed; that is, pups exposed pre- and postnatally to ethanol showed the greatest increases in HR and the smallest increases in motor activity in response to ethanol odor. In both experiments motor activity was dissociated from increases in HR. The results are discussed in terms of what is learned, prenatally and postnatally, in association with the chemosensory properties of ethanol.

Effects of glutathione on Fenton reagent-dependent radical production and DNA oxidation

The effects of glutathione (GSH) on the generation of radicals and the oxidation of DNA by Fenton reagent were studied. Hydroxyl radicals and thiyl radicals were detected by electron spin resonance spin trapping when GSH-Fe(II) reacted with H2O2; however, the mixture was ineffective at promoting the hydroxylation of 2'-deoxyguanosine in calf thymus DNA. When the concentrations of ferrous iron and hydrogen peroxide were both 100 microM, the concentration of GSH required to inhibit 8-hydroxy-2'-deoxyguanosine (8-OHdG) production by 92% was 1 mM. Other thiol compounds were also effective at inhibiting 8-OHdG formation; however, mannitol and benzoate were ineffective at inhibiting 8-OHdG formation when present at the same concentration. Single strand breaks were detected in phi X174 plasmid DNA treated with 2 microM Fe(II) and 2 microM H2O2; furthermore, the addition of 50 microM GSH to this system inhibited single strand break formation by 95%. In conclusion, GSH protected DNA from oxidation by Fe(II) and H2O2 even though it did not completely inhibit the production of radicals by the Fenton reaction.

Hydroxylation of deoxyguanosine in DNA by copper and thiols

DNA was incubated with glutathione (GSH) and copper and then assayed for 8-hydroxydeoxyguanosine (8-OHdG) in order to better understand the antioxidant and prooxidant characteristics of GSH in copper-dependent DNA damage. Ratios of GSH to Cu(II) less than 3 resulted in 8-OHdG production; however, higher ratios did not generate 8-OHdG. A combination of GSH and Cu(I) (10:1) was used to determine if DNA oxidation occurred upon the addition of H2O2. No increase in 8-OHdG was noted until the concentration of H2O2 was almost half that of GSH, and then a substantial increase of 8-OHdG was detected. The stoichiometry of thiol oxidation by H2O2 was 2 mol GSH oxidized per 1 mol H2O2. Oxidation of Cu(I) was not detected until most of the thiol had been oxidized. When cysteine and Cu(I) was used instead of GSH and Cu(I), there was considerable hydroxylation of deoxyguanosine. The glycyl carboxyl, the gamma-glutamate carboxyl, and the amine of GSH were altered to determine their role in the peptide's ability to inhibit Cu-dependent damage. In the presence of Cu(I), H2O2, and DNA, these GSH analogs behaved similarly to GSH. However, when S-methylglutathione was used in this system, it was very effective at promoting oxidative damage to DNA. This indicated that the thiol ligand of GSH was essential for inhibition of Cu-dependent damage, while the carboxyl groups and the amine were not essential ligands. In conclusion, GSH can catalyze the in vitro hydroxylation of deoxyguanosine when the ratio of GSH to Cu is low, however, when the ratio is high GSH is an effective antioxidant.

Thiol-mediated NTA-Fe(III) reduction and lipid peroxidation

The nephrotoxicity of nitrilotriacetate chelated Fe(III) (NTA-Fe(III)) has been linked to the metabolism of glutathione (GSH) by gamma-glutamyl transpeptidase and a dipeptidase. The products of these enzymes are cysteinyl-glycine (cys-gly) and cysteine (cys), which are proposed to be the reductants of NTA-Fe(III) to cause oxidative damage to various biomolecules. The ability of cys-gly and cys to cause in vitro NTA-Fe(III)-dependent lipid peroxidation correlated directly with their ability to reduce NTA-Fe(III). GSH reduced iron at a much slower rate and did not stimulate lipid peroxidation. It has been proposed that GSH, cys-gly and cys reduce iron at different rates because their thiols have different pKas. However, increasing the amount of GS-, by raising the pH, did not cause a corresponding increase in the rate of iron reduction. The monomethyl ester of GSH reduced NTA-Fe(III) at the same rate as GSH, but the dimethyl ester of GSH reduced NTA-Fe(III) approximately 30 times faster. From this we conclude that GSH does not reduce NTA-Fe(III) at the same rate as cys-gly and cys because of the liganding between GSH and the iron.