Translational mixed-effects PKPD modelling of recombinant human growth hormone - from hypophysectomized rat to patients

BACKGROUND AND PURPOSE: We aimed to develop a mechanistic mixed‐effects pharmacokinetic (PK)–pharmacodynamic (PD) (PKPD) model for recombinant human growth hormone (rhGH) in hypophysectomized rats and to predict the human PKPD relationship. EXPERIMENTAL APPROACH: A non‐linear mixed‐effects model was developed from experimental PKPD studies of rhGH and effects of long‐term treatment as measured by insulin‐like growth factor 1 (IGF‐1) and bodyweight gain in rats. Modelled parameter values were scaled to human values using the allometric approach with fixed exponents for PKs and unscaled for PDs and validated through simulations relative to patient data. KEY RESULTS: The final model described rhGH PK as a two compartmental model with parallel linear and non‐linear elimination terms, parallel first‐order absorption with a total s.c. bioavailability of 87% in rats. Induction of IGF‐1 was described by an indirect response model with stimulation of k(in) and related to rhGH exposure through an E(max) relationship. Increase in bodyweight was directly linked to individual concentrations of IGF‐1 by a linear relation. The scaled model provided robust predictions of human systemic PK of rhGH, but exposure following s.c. administration was over predicted. After correction of the human s.c. absorption model, the induction model for IGF‐1 well described the human PKPD data. CONCLUSIONS: A translational mechanistic PKPD model for rhGH was successfully developed from experimental rat data. The model links a clinically relevant biomarker, IGF‐1, to a primary clinical end‐point, growth/bodyweight gain. Scaling of the model parameters provided robust predictions of the human PKPD in growth hormone‐deficient patients including variability

Rolling-circle plasmids from Bacillus subtilis: complete nucleotide sequences and analyses of genes of pTA1015, pTA1040, pTA1050 and pTA1060, and comparisons with related plasmids from Gram-positive bacteria

Most small plasmids of Gram-positive bacteria use the rolling-circle mechanism of replication and several of these have been studied in considerable detail at the DNA level and for the function of their genes. Although most of the common laboratory Bacillus subtilis 168 strains do not contain plasmids, several industrial strains and natural soil isolates do contain rolling-circle replicating (RCR) plasmids. So far, knowledge about these plasmids was mainly limited to: (i) a classification into seven groups, based on size and restriction patterns; and (ii) DNA sequences of the replication region of a limited number of them. To increase the knowledge, also with respect to other functions specified by these plasmids, we have determined the complete DNA sequence of four plasmids, representing different groups, and performed computer-assisted and experimental analyses on the possible function of their genes. The plasmids analyzed are pTA1015 (5.8 kbp), pTA1040 (7.8 kbp), pTA1050 (8.4 kbp), and pTA1060 (8.7 kbp). These plasmids have a structural organization similar to most other known RCR plasmids. They contain highly related replication functions, both for leading and lagging strand synthesis. pTA1015 and pTA1060 contain a mobilization gene enabling their conjugative transfer. Strikingly, in addition to the conserved replication modules, these plasmids contain unique module(s) with genes which are not present on known RCR plasmids of other Gram-positive bacteria. Examples are genes encoding a type I signal peptidase and genes encoding proteins belonging to the family of response regulator aspartate phosphatases. The latter are likely to be involved in the regulation of post-exponential phase processes. The presence of these modules on plasmids may reflect an adaptation to the special conditions to which the host cells were exposed. (C) 1998 Federation of European Microbiological Societies. Published by Elsevier Science B.V

Global transcriptional regulator KorC coordinates expression of three backbone modules of the broad-host-range RA3 plasmid from IncU incompatibility group.

The broad-host-range conjugative RA3 plasmid from IncU incompatibility group has been isolated from the fish pathogen Aeromonas hydrophila. DNA sequencing has revealed a mosaic modular structure of RA3 with the stabilization module showing some similarity to IncP-1 genes and the conjugative transfer module highly similar to that from PromA plasmids. The integrity of the mosaic plasmid genome seems to be specified by its regulatory network. In this paper the transcriptional regulator KorC was analyzed. KorCRA3 (98 amino acids) is encoded in the stabilization region and represses four strong promoters by binding to a conserved palindrome sequence, designated OC on the basis of homology to the KorC operator sequences in IncP-1 plasmids. Two of the KorCRA3-regulated promoters precede the first two cistrons in the stabilization module, one fires towards replication module, remaining one controls a tricistronic operon, whose products are involved in the conjugative transfer process. Despite the similarity between the binding sites in IncU and IncP-1 plasmids, no cross-reactivity between their KorC proteins has been detected. KorC emerges as a global regulator of RA3, coordinating all its backbone functions: replication, stable maintenance and conjugative transfer