A mechanistic kinetic description of lactate dehydrogenase elucidating cancer diagnosis and inhibitor evaluation

Abstract

As a key enzyme for glycolysis, lactate dehydrogenase (LDH) remains as a topic of great interest in cancer study. Though a number of kinetic models have been applied to describe the dynamic behavior of LDH, few can reflect its actual mechanism, making it difficult to explain the observed substrate and competitor inhibitions at wide concentration ranges. A novel mechanistic kinetic model is developed based on the enzymatic processes and the interactive properties of LDH. Better kinetic simulation as well as new enzyme interactivity information and kinetic properties extracted from published articles via the novel model was presented. Case studies were presented to a comprehensive understanding of the effect of temperature, substrate, and inhibitor on LDH kinetic activities for promising application in cancer diagnosis, inhibitor evaluation, and adequate drug dosage prediction.

Keywords: Cancer diagnosis; inhibitor evaluation; kinetic model; lactate dehydrogenase; oligomeric enzyme.

Figure 1.

Scheme of mutual transformation of pyruvate and lactate catalyzed by lactate dehydrogenase.

Figure 2.

Structures of pyruvate and oxamate derived inhibitors.

Figure 3.

Sequential substrate binding and reaction processes on LDH at the coenzyme saturation condition.

Figure 4.

Typical substrate and inhibitor binding and reaction processes. (1 ≤ i, j, i + j ≤ 4). S, P, and I are the substrate, product, and competitive effector, respectively; α, β, and γ represent the kinetic constants change due to interactive effects.

Figure 5.

(A) Temperature effect on the activity of hLDH-1 with data taken from publications^,; (B) Van’t Hoff Equation simulation of hLDH-1 K values. hLDH-1 kinetic parameters at different reaction conditions are listed in the table. The dots denote the experimental data and the lines represent the simulation results.

Figure 6.

The initial rates of LDH from tumor human breast cells (T) and normal human breast cells (N) vary with substrate concentrations in conversion of pyruvate to lactate; The data were taken from the publication; Kinetic parameters of different LDH isoenzymes are listed in the table. The dots denote the experimental data and the lines represent the simulation results.

Figure 7.

(A) Inhibition of N-propyl oxamate on LDH for the conversion of pyruvate to lactate with experimental data taken from the publication. (B) Kinetic prediction of N-propyl oxamate required to inhibit LDH activity at 50 and 25% at 0.2 mM pyruvate concentration. The dots denote the experimental data and the lines represent the computing results.