Browsing by Author "Njoroge, Mathew"

Now showing 1 - 4 of 4
  • Thumbnail Image
    Item
    Open Access
    In vitro metabolism of tetrazole aminoquinolines and derivatives of metergoline and fusidic acid
    (2014) Njoroge, Mathew; Chibale, Kelly
    Drug metabolism is recognised as a key component of the drug discovery and development process. It exerts an influence on the action, duration of action and toxicity of a drug in vivo. The integration of drug metabolism studies is therefore crucial to compound progression through the various stages of the development process. This work details the in vitro metabolism work conducted during the early development of aminoquinoline tetrazoles, and derivatives of metergoline and fusidic acid as potential antiplasmodial and/or antimycobacterial agents.
  • No Thumbnail Available
    Item
    Open Access
    In vitro metabolism studies to inform physiologically-based pharmacokinetic modelling of mefloquine, ritonavir and proguanil
    (2024) Cloete, Cleavon K; Njoroge, Mathew; Chibale, Kelly
    Clinically observed variability in drug exposure has various negative implications, ranging from an increased possibility of adverse drug reactions to treatment failure. A key contributor to this variability is the contribution of drug metabolism, substantially mediated by the cytochrome P450 (CYP) enzyme superfamily. Thus, a valuable step in assessing the contribution of drug metabolism to variability in drug exposure is the measurement of the kinetics of CYP-mediated metabolism. However, this in vitro data needs to be translated to whole body in vivo clearance, which is also impacted by the physicochemical properties of a drug and how the drug interacts with physiological environments in the body. One method of doing so is through the use of physiologically based pharmacokinetic (PBPK) modelling. By combining in vitro data with available knowledge on the physicochemical properties of a drug PBPK modelling provides a mechanistic understanding of drug exposure. As such, the in vitro metabolic characteristics of 3 commonly used drugs, namely mefloquine, proguanil and ritonavir, were measured. This was done by measuring the microsomal metabolism of these drugs in human liver microsomes, then determining the fraction of the drug metabolized by CYP (fm,CYP) isoforms and confirming this metabolic pattern using recombinant CYP enzymes. In the case of mefloquine, it was found that the drug was metabolized mainly by CYP3A and CYP1A2. While mefloquine metabolism by CYP3A is widely reported, this is the first report of its metabolism by CYP1A2. Proguanil was found to be metabolized by a number of enzymes, namely CYP1A2, CYP2D6, CYP2C19 and CYP3A. This confirms reported data for CYP2C19 and CYP3A, and provides new data for CYP1A2 and CYP2D6. Lastly, ritonavir was found to be metabolized by CYP2D6 and CYP3A. These determined fm,CYPs were then used, along with available data from literature, to develop PBPK models for mefloquine, proguanil and cycloguanil as a metabolite of proguanil using a middle-out approach with the use of Simcyp modelling software. These models were verified by comparing the pharmacokinetic (PK) profiles they simulated to various PK profiles found in literature. The verified models were then applied to various scenarios of interest. In the case of mefloquine, these applications showed that in vitro data does not accurately scale to in vivo clearance which excludes the possibility of doing a bottom-up model for this compound. The verified PBPK model built using this data demonstrates the expected drug- drug interaction between mefloquine and a CYP1A2 inhibitor, fluvoxamine. The model also shows the limited effect of population differences on mefloquine PK, including the reported finding that polymorphisms of CYP3A5 do not affect mefloquine PK. Disease state may therefore have a bigger effect on the variability in mefloquine PK than variability in metabolism does. The model application for proguanil focussed on the potential effects of various CYP genotypes on proguanil metabolism given the number of polymorphic CYPs found to be involved in its metabolism. The effect of CYP2C19 polymorphisms on proguanil and cycloguanil exposure could be clearly demonstrated. Variability in metabolism by other CYPs does not have as big an impact on proguanil exposure, likely because of their lower contributions to the metabolism of the drug. Finally, a previously developed and verified ritonavir model was used, in conjunction with the mefloquine model developed and verified here, to explore the use of ritonavir as an inducer and inhibitor of CYP3A activity. This showed the limited ability of ritonavir to induce mefloquine metabolism, with it being a more capable inhibitor. The ability of ritonavir to induce CYP1A2 activity was also explored using the available model by optimizing its CYP1A2 induction capabilities through parameter optimization. This showed the importance of taking this induction into account when conducting DDI studies between ritonavir and substrates of CYP1A2. Overall, this work addresses gaps in the understanding of the in vitro metabolism of mefloquine, proguanil and ritonavir, and demonstrates how this data can be combined with PBPK modelling to understand and predict PK variability.
  • Thumbnail Image
    Item
    Open Access
    Synthesis and In Vitro Antiprotozoan Evaluation of 4-/8-Aminoquinoline-based Lactams and Tetrazoles
    (2020-12-15) Tukulula, Matshawandile; Louw, Stefan; Njoroge, Mathew; Chibale, Kelly
    A second generation of 4-aminoquinoline- and 8-aminoquinoline-based tetrazoles and lactams were synthesized via the Staudinger and Ugi multicomponent reactions. These compounds were subsequently evaluated in vitro for their potential antiplasmodium activity against a multidrug-resistant K1 strain and for their antitrypanosomal activity against a cultured T. b. rhodesiense STIB900 strain. Several of these compounds (4a–g) displayed good antiplasmodium activities (IC50 = 0.20–0.62 µM) that were comparable to the reference drugs, while their antitrypanosomal activity was moderate (200 µM) at pH 7.
  • Thumbnail Image
    Item
    Open Access
    Total Synthesis of the Antimycobacterial Natural Product Chlorflavonin and Analogs via a Late-Stage Ruthenium(II)-Catalyzed ortho-C(sp2)-H-Hydroxylation
    (2022-08-10) Berger, Alexander; Knak, Talea; Kiffe-Delf, Anna-Lene; Mudrovcic, Korana; Singh, Vinayak; Njoroge, Mathew; Burckhardt, Bjoern B.; Gopalswamy, Mohanraj; Lungerich, Beate; Ackermann, Lutz; Gohlke, Holger; Chibale, Kelly; Kalscheuer, Rainer; Kurz, Thomas
    The continuous, worldwide spread of multidrug-resistant (MDR) and extensively drug-resistant (XDR) tuberculosis (TB) endanger the World Health Organization’s (WHO) goal to end the global TB pandemic by the year 2035. During the past 50 years, very few new drugs have been approved by medical agencies to treat drug-resistant TB. Therefore, the development of novel antimycobacterial drug candidates to combat the threat of drug-resistant TB is urgent. In this work, we developed and optimized a total synthesis of the antimycobacterial natural flavonoid chlorflavonin by selective ruthenium(II)-catalyzed ortho-C(sp2)-H-hydroxylation of a substituted 3′-methoxyflavonoid skeleton. We extended our methodology to synthesize a small compound library of 14 structural analogs. The new analogs were tested for their antimycobacterial in vitro activity against Mycobacterium tuberculosis (Mtb) and their cytotoxicity against various human cell lines. The most promising new analog bromflavonin exhibited improved antimycobacterial in vitro activity against the virulent H37Rv strain of Mtb (Minimal Inhibitory Concentrations (MIC90) = 0.78 μm). In addition, we determined the chemical and metabolic stability as well as the pKa values of chlorflavonin and bromflavonin. Furthermore, we established a quantitative structure–activity relationship model using a thermodynamic integration approach. Our computations may be used for suggesting further structural changes to develop improved derivatives.