A Bayesian Approach to Dose–Response Assessment and Synergy and Its Application to In Vitro Dose–Response Studies

Summary In this article, we propose a Bayesian approach to dose–response assessment and the assessment of synergy between two combined agents. We consider the case of an in vitro ovarian cancer research study aimed at investigating the antiproliferative activities of four agents, alone and paired, in two human ovarian cancer cell lines. In this article, independent dose–response experiments were repeated three times. Each experiment included replicates at investigated dose levels including control (no drug). We have developed a Bayesian hierarchical nonlinear regression model that accounts for variability between experiments, variability within experiments (i.e., replicates), and variability in the observed responses of the controls. We use Markov chain Monte Carlo to fit the model to the data and carry out posterior inference on quantities of interest (e.g., median inhibitory concentration IC ₅₀ ). In addition, we have developed a method, based on Loewe additivity, that allows one to assess the presence of synergy with honest accounting of uncertainty. Extensive simulation studies show that our proposed approach is more reliable in declaring synergy compared to current standard analyses such as the median‐effect principle/combination index method ( Chou and Talalay, 1984 , Advances in Enzyme Regulation 22, 27–55), which ignore important sources of variability and uncertainty.     

Serotherapy of ovarian cancer

The development of monoclonal antibodies has permitted the identification of several ovarian-tumor-associated antigens which might serve as targets for serotherapy in vivo. With the exception of antibodies directed against growth factor receptors, unmodified monoclonal reagents must activate complement (C') components or bind effector cells to destroy tumor targets. Antibody-dependent cell-mediated cytotoxicity (ADCC) may be particularly important for eliminating tumor cells in vivo. A shortage of functionally active effector cells can limit the efficacy of serotherapy with heteroantisera or monoclonal reagents. The use of immunostimulants such as Corynebacterium parvum has increased the number and activity of effector cells for ADCC within the peritoneal compartment of mice and of patients with ovarian cancer. Intraperitoneal serotherapy can achieve direct contact between antibody and microscopic deposits of ovarian tumor cells which persist following cytoreductive operations and cytotoxic chemotherapy. Conjugation of monoclonal antibodies with radionuclides, drugs or toxins might increase the potency of serotherapy and circumvent the effector shortage. Clinical studies to date have evaluated radionuclide conjugates for imaging and for therapy. Patients with a small volume of disease have responded to treatment. Preclinical models suggest that drug and toxin conjugates might also prove active. Recent studies have demonstrated a synergistic interaction between different immunotoxins. Ovarian carcinoma is likely to be a valuable clinical model for evaluating immunoconjugates which react with epithelial tumor cells.     

Experimental conditions influence [3H]-dihydroalprenolol binding characteristics to living HeLa cells due to morphological changes: a warning

Harvesting of plated growing HeLa cells, followed by incubation of these cells without any addition at 37 degrees C was found to cause changes in the cell shape. This phenomenon is accompanied by a diminished binding of the beta-adrenergic antagonist [3H]-dihydroalprenolol and the alpha-adrenergic antagonist phentolamine to a binding compartment not representing beta-adrenergic receptors. These binding sites have a high affinity for hydrophobic agents and most probably represent lipophilic structures in the cellular membrane. Changes in the cell shape obviously cause alterations in the physical properties of the plasma membrane. This might lead to misinterpretations of the results from experiments in which the redistribution of beta-adrenergic receptors is followed during incubation with agonists, as receptor occupation with subsequent receptor redistribution is possibly accompanied by effects on the membrane microviscosity. It is concluded that investigations performed in order to follow physiological events like receptor redistribution and desensitization processes, may be obfuscated by changes in the normal physical state of the living cells.     

Effect of gold therapy in rheumatoid arthritis on leukopoiesis and granulocyte phagocytosis]

In 12 patients with rheumatoid arthritis the investigations of leukopoiesis and granulocytic phagocytosis were carried out before and after a gold therapy. A marked reduction of granulocytic phagocytosis could be observed here which decreased after the gold therapy, yet remained below the values of a normal collective. Partly contrary informations are discussed. The disturbance of the phagocytosis capacity of granulocytes may possibly be due to a rheumatic factor.     

Monitoring of oxidative free radical damage in vivo: analytical aspects.

Free radical damage is an important factor in many pathological and toxicological processes. During the last decade a wide range of methods has been developed to determine free radical damage in various biological fluids and at various stages of development. This review offers an overview of the state of the art of monitoring free radical damage in vivo, with special emphasis on the analytical aspects of non-invasive methods.     

Anthracycline-Induced Oxygen Consumption and Oxidative Damage in Rat Liver Microsomes are not Necessarily Coupled: A study with 8 structurally related anthracyclines

The stimulative effect of 8 anthracyclines (the parent compounds daunorubicin and doxorubicin and 6 structurally closely related anthracyclines) on the production of thiobarbituric acid (TBA)-reactive material was investigated in liver microsomes. Except for daunorubicinone and doxorubicinone, all derivatives stimulated NADPH-dependent production of TBA-reactive material. Doxorubicinone had no effect, daunorubicinone inhibited TBA-reactivity at concentrations up to 50 μM. However, the latter two compounds stimulated oxygen consumption in the presence of EDTA to a degree comparable to that induced by the parent compounds. Since the oxygen uptake under these circumstances represents redox cycling of the drugs, apparently redox cycling and production of TBA-reactive material were not coupled for these compounds.

Spectral measurements showed no decisive role for interaction with free iron (Fe³⁺) ions in the non-coupling of redox cycling and production of TBA reactive material. Evidence for a role of bound iron ions was not obtained.

It is discussed that for the aglycones oxygen consumption and production of TBA reactive material might be non-coupled through their different interaction with microsomal RNA.     

DNA barcoding of a new record of epi-endophytic green algae Ulvella leptochaete (Ulvellaceae,Chlorophyta) in India

Epi-endophytic green algae comprise one of the most diverse and phylogenetically primitive groups of green algae and are considered to be ubiquitous in the world’s oceans; however, no reports of these algae exist from India. Here we report the serendipitous discovery of Ulvella growing on intertidal green algae Cladophora glomerata and benthic red algae Laurencia obtusa collected from India. DNA barcodes at nuclear ribosomal DNA Internal Transcriber Spacer (nrDNA ITS) 1 and 2 regions for Indian isolates from the west and east coasts have been generated for the first time. Based on morphology and DNA barcoding, isolates were identified as Ulvella leptochaete. Phylogenetic reconstruction of concatenated dataset using Maximum Likelihood method differentiated Indian isolates from other accessions of this alga available in Genbank, albeit with low bootstrap support. Monophyly of Ulvella leptochaete was obvious in both of our phylogenetic analyses. With this first report of epi-endophytic algae from Indian territorial waters, the dire need to catalogue its cryptic diversity is highlighted and avenues of future research are discussed.