Phase I evaluation of an anti-breast carcinoma monoclonal antibody 260F9-recombinant ricin A chain immunoconjugate

Four women with metastatic breast cancer were treated with monoclonal antibody 260F9-recombinant ricin A chain, a ricin A chain immunoconjugate (IC) which targets a Mr 55,000 antigen expressed by human mammary carcinomas. Patients were treated by daily, 1-h i.v. injections for 6 to 8 consecutive days. Two patients were treated with 10 micrograms/kg daily and the two others were treated with 50 micrograms/kg daily. The trial was suspended after four patients had been treated because patients treated with a continuous infusion schedule with this IC had developed significant neurological toxicity at doses similar to those used in this study. The half-life of the IC showed a t 1/2 alpha of approximately 1.8 h, a t 1/2 beta of approximately 8.3 h, and a peak concentration of about 200 ng/ml, at the lower dose level, and showed a t 1/2 alpha of approximately 2.5 h, t 1/2 beta of about 10.4 h, and a peak concentration of 500 and 850 ng/ml for the two patients at the higher dose level. All four patients developed evidence of a human anticonjugate antibody response within 16 days of the onset of therapy. The treatment was associated with significant toxicity, manifested by a syndrome consisting of weight gain, edema, hypoalbuminemia, and dyspnea. Similar symptoms were observed in patients treated by continuous infusions of the IC. This clinical syndrome, seen at doses of IC which were insufficient to saturate antigen-expressing malignant tumor deposits in this trial, has been seen in other IC therapy trials and in clinical trials using the cytokine interleukin 2. To investigate a possible mechanism responsible for this toxicity, human monocytes were incubated with varying concentrations of IC. There was detectable binding of IC to human monocytes at IC concentrations which were achieved clinically in this trial. Furthermore, the binding appeared to be abrogated by preincubation of the monocytes with pooled human immunoglobulin, thus suggesting that binding occurs via Fc gamma receptor-mediated mechanisms. Binding was not affected if different linkers between recombinant ricin A chain and the antibody were used or if a different antibody moiety was used in the IC preparation. Chemically linked dimers of MOPC-21 bound to human monocytes at least as well as the ICs; this binding was not abrogated by preincubation with pooled human immunoglobulin. Since the IC preparations used in this clinical trial contained small percentages of dimers and/or multimers, the clinical toxicity syndromes which we observed may be related to this series of observations.(ABSTRACT TRUNCATED AT 400 WORDS)

Theory of the kinetic analysis of patch-clamp data

This paper describes a theory of the kinetic analysis of patch-clamp data. We assume that channel gating is a Markov process that can be described by a model consisting of n kinetic states and n(n - 1) rate constants at each voltage, and that patch-clamp data describe the occupancy of x different conductance levels over time. In general, all the kinetic information in a set of patch-clamp data is found in either two-dimensional dwell time histograms describing the frequency of observation of sequential dwell times of durations tau 1 and tau 2 (Fredkin, D. R., M. Montal, and J. A. Rice, 1985, Proceedings of the Berkeley Conference in Honor of Jerzy Neyman and Jack Kiefer, vol. 1, 269-289) or in three-point joint probability functions describing the probability that a channel is in a given conductance at time t, and at time t + tau 1, and at time t + tau 1 + tau 2. For the special case of channels with a single open state plus multiple closed states, one-dimensional analyses provide all of the kinetic information. Stationary patch-clamp data have information that can be used to determine H rate constants, where H = n(n - 1) - G and G is the number of intraconductance rate constants. Thus, to calculate H rate constants, G rate constants must be fixed. In general there are multiple sets of G rate constants that can be fixed to allow the calculation of H rate constants although not every set of G rate constants will work. Arbitrary assignment of the G intraconductance rate constants equal to zero always provides a solution and the calculation of H rate constants. Nonstationary patch-clamp data have information for the determination of H rate constants at a reference voltage plus n(n - 1) rate constants at all test voltages. Thus, nonstationary data have extra information about the voltage dependencies of rate constants that can be used to rule out kinetic models that cannot be disqualified on the basis of stationary data.

Adenosine aminohydrolase from Halobacterium cutirubrum

The extreme halophilic bacterium Halobacterium cutirubrum was examined for base, nucleoside, and nucleotide aminohydrolase activity on pyrimidine bases and their nucleosides and nucleotides. Only adenosine aminohydrolase activity was demonstrated. The enzyme was extracted from the cells and purified about 70-fold by liquid polymer two-phase fractionation, ammonium sulfate precipitation, and gel filtration. The enzyme has an apparent Km for adenosine of 4 × 10−5 M. The optimum pH is 7.5. The enzyme requires 4.0 M NaCl for maximal activity, but is irreversibly inactivated regardless of the concentration of NaCl when stored for extended periods of time.

Mechanism of action of 1- -D-ribofuranosyl-1,2,4-triazole-3-carboxamide (Virazole), a new broad-spectrum antiviral agent

The antiviral activity of the synthetic nucleoside, Virazole (1-beta-D-ribofuranosyl-1,2,4-triazole-3-carboxamide), against measles virus in Vero cell cultures was substantially reversed by xanthosine, guanosine, and to a slightly lesser extent by inosine. Virazole 5'-phosphate was subsequently found to be a potent competitive inhibitor of inosine 5'-phosphate dehydrogenase (IMP:NAD(+) oxidoreductase, EC 1.2.1.14) isolated from Escherichia coli (K(m) = 1.8 x 10(-5) M) with a K(i) of 2.7 x 10(-7) M. Guanosine 5'-phosphate (GMP) was a competitive inhibitor of this enzyme with a K(i) of 7.7 x 10(-5) M. Virazole 5'-phosphate was similarly active against IMP dehydrogenase isolated from Ehrlich ascites tumor cells, with a K(i) of 2.5 x 10(-7) M. The K(m) for this enzyme was 1.8 x 10(-5) M, and the K(i) for GMP was 2.2 x 10(-4) M. These results suggest that the antiviral activity of Virazole might be due to the inhibition of GMP biosynthesis in the infected cell at the step involving the conversion of IMP to xanthosine 5'-phosphate. This inhibition would consequently result in inhibition of the synthesis of vital viral nucleic acid.