BMS64 – Molecular and cellular toxicology
BMS64 – MOLECULAR AND
CELLULAR TOXICOLOGY
Opleiding: Master Biomedical Sciences
Onderwijsinstelling: Radboudumc
1
, BMS64 – Molecular and cellular toxicology
Content
Toxicans affecting receptors..............................................................................................................4
Types of drug/toxicant target...............................................................................................................................4
Drug-receptor interaction.....................................................................................................................................4
Concentration-effect relationship.........................................................................................................................5
Types of agonism/antagonism..............................................................................................................................5
Mitochondrial toxicity.......................................................................................................................6
Underestimation of mitochondrial toxicity...........................................................................................................6
Mitochondrial vulnerability and xenobiotic interference.....................................................................................6
Biotransformation.............................................................................................................................7
Phase I reactions....................................................................................................................................................7
Phase II reactions...................................................................................................................................................8
Biotransformation of acetaminophen (paracetamol)...........................................................................................8
Induction and suppression of biotransforming enzymes......................................................................................9
Transporters......................................................................................................................................9
ABC transporters...................................................................................................................................................9
ABCB..............................................................................................................................................................10
ABCC..............................................................................................................................................................10
ABCG..............................................................................................................................................................10
ABC structure................................................................................................................................................10
Measuring transport activity.........................................................................................................................10
SLC transporters..................................................................................................................................................11
Organic-anion transporting polypeptides – OATPs.......................................................................................11
Organic-anion transporter – OAT..................................................................................................................11
Organic-cation transporter – OCTs...............................................................................................................11
Organic-zwitterion/cation transporter - OCTNs............................................................................................11
Peptide transporters – PEPT.........................................................................................................................11
Multidrug and toxin extrusion reporters – MATEs.......................................................................................11
Signaling pathways and cellular disruption......................................................................................11
Cell regulation (signaling) – dysregulation of gene expression...........................................................................12
Cell regulation (signaling) – dysregulation of ongoing cell function...................................................................12
Cell maintenance – impaired internal maintenance...........................................................................................12
Autophagy.....................................................................................................................................................13
2
, BMS64 – Molecular and cellular toxicology
Necrosis.........................................................................................................................................................13
Apoptosis.......................................................................................................................................................14
What determines the form of cell death?....................................................................................................14
Neurotoxicology..............................................................................................................................15
Neurochemical transmission in the autonomic nervous system........................................................................15
Acetylcholine.................................................................................................................................................15
Norepinephrine.............................................................................................................................................15
Neurotoxicity’s....................................................................................................................................................16
n-Hexane.............................................................................................................................................................16
Spasmolytic drugs................................................................................................................................................16
Nerve agents.......................................................................................................................................................16
MPPP...................................................................................................................................................................17
Cocaine................................................................................................................................................................17
Benzodiazepine...................................................................................................................................................17
In silico methods.............................................................................................................................17
QSAR....................................................................................................................................................................17
Similarity searching.......................................................................................................................................17
Toxicophores.................................................................................................................................................18
Digitalis-like compounds.................................................................................................................18
Structure and mechanism of action of DLCs.......................................................................................................18
How to study DLCs...............................................................................................................................................18
Systems toxicology..........................................................................................................................19
Enabling technologies.........................................................................................................................................19
Biomarkers..........................................................................................................................................................19
3
, BMS64 – Molecular and cellular toxicology
Toxicans affecting receptors
Efficacy: refers to the maximum effect a drug can produce once it binds to its receptor, regardless of the dose.
Potency: refers to how much of a drug is needed to produce a given effect. Potency depends on both the
affinity of the drug for its receptor and its efficacy once bound.
↪ You can only compare potencies if the efficacy levels are similar
ED50: dose necessary to induce an effect at 50% of the maximal effect.
EC50: concentration of a drug that produces 50% of its maximum possible effect.
IC50: the concentration of an inhibitor that reduces a given response by 50%. It’s a standard measure of
antagonist potency.
Types of drug/toxicant target
Acute toxicity of a chemical often starts with interaction with a biological target, but can also result from a
multitude of activated targets:
Receptors
Ligand-gated ion channel receptors: ligand binding opens the channel → ions flow immediately →
rapid cellular response (milliseconds).
G-protein coupled receptors (GPCRs): ligand binding activates G-proteins→ triggers second messengers
→ fast signaling (seconds).
Tyrosine kinase receptors: ligand binding → dimerization and autophosphorylation → kinase cascades
→ response in minutes.
Nuclear receptors: ligand diffuses into cell → binds intracellular receptor → complex binds DNA →
alters transcription → response in hours to days.
Ion channels
Voltage-gated Ca2+
channels
Na+, K+, Cl- channels
Enzymes
Oxidoreductases
Transferases
Hydrolases
Dehydrolases
Transporters
Neurotransmitter/Na+
symporters
Na+/K+ ATPase
Modern drug discovery relies on several “omics” technologies to identify and validate potential therapeutic
targets. Genomics identifies mutations, epigenetic, and post-transcriptional changes linked to disease.
Proteomics reveals protein expression and post-translational modifications, while metabolomics captures shifts
in cellular metabolites.
In the classic view of drug action, a drug acts on a single primary target to produce therapeutic effects, while
interactions with off-targets are responsible for side effects. The systems pharmacology perspective recognizes
that drugs often interact with multiple targets and influence complex cellular networks, leading to both
therapeutic outcomes and side effects.
Drug-receptor interaction
A comparison that describes the reversible interaction between a ligand (drug, toxin) and a receptor is
4
, BMS64 – Molecular and cellular toxicology
k1
→
[D] + [R] ← [DR] Kd = k2/k1
k2
[D] = drug concentration
[R] = free receptors
[DR] = bound receptors
k1 = association rate constant
k2 = dissociation rate constant
Kd = equilibrium dissociation constant (= concentration of ligand that results in 50% receptor occupancy)
Concentration-effect relationship
The concentration-effect relationship describes how the intensity or type of a biological response changes as
the concentration of a substance increases in an organism or a system. At very low concentrations, a chemical
may cause no observable effect because the amount of interaction with target molecules is too small. As
concentration rises, the likelihood that the substance will bind to receptors, enzymes, or other critical
biomolecules increases, and so does the magnitude of the effect. This relationship often follows a dose–
response curve, which is typically sigmoidal: initially flat at low concentrations, then showing a steep increase
in effect over a certain range and finally leveling off when maximum effect is reached because all available
targets are saturated. The Hill equation is a mathematical model used to describe how a biological response
depends on the concentration of a drug, toxin, or ligand that binds to a receptor or enzyme:
[ EA]
[ E¿¿ Amax ]=¿ ¿ ¿
[EA] = the observed effect at concentration [A] of the agonist
[EAmax] = the maximum effect that the system can produce with that agonist
[A] = the concentration of the agonist
[KA] = the equilibrium dissociation constant
n = the hill coefficient, describing the slope of the curve
Types of agonism/antagonism
Full agonist: a substance that binds to a receptor and produces the
maximum possible biological response for that receptor system.
Partial agonist: also binds to the receptor but produces only a
submaximal response, even if it occupies all available receptors.
↪ A partial agonist acts as an antagonist in the presence of a full
agonist (if they compete for the same receptor)
Inverse agonist: binds to the same receptor as an agonist but induces
the opposite effect.
Competitive antagonist: binds reversibly to the active site of the
receptor, blocking agonists from binding.
↪ Its effect can be overcome by increasing the concentration of the
agonist, which shifts the dose–response curve to the right without changing the maximum effect.
Non-competitive antagonist: binds either irreversibly to the active site or to another critical site such that
agonists cannot activate the receptor even if they bind.
↪ This reduces the maximum effect that can be achieved, and its effect cannot simply be overcome by adding
more agonist.
Allosteric antagonist: binds to a different (allosteric) site on the receptor rather than the main active site. By
doing so, it changes the receptor’s shape or function, reducing the ability of the agonist to bind or to activate
the receptor.
Functional antagonist: does not act directly on the same receptor but instead produces an effect that
physiologically opposes the action of an agonist.
5
BMS64 – MOLECULAR AND
CELLULAR TOXICOLOGY
Opleiding: Master Biomedical Sciences
Onderwijsinstelling: Radboudumc
1
, BMS64 – Molecular and cellular toxicology
Content
Toxicans affecting receptors..............................................................................................................4
Types of drug/toxicant target...............................................................................................................................4
Drug-receptor interaction.....................................................................................................................................4
Concentration-effect relationship.........................................................................................................................5
Types of agonism/antagonism..............................................................................................................................5
Mitochondrial toxicity.......................................................................................................................6
Underestimation of mitochondrial toxicity...........................................................................................................6
Mitochondrial vulnerability and xenobiotic interference.....................................................................................6
Biotransformation.............................................................................................................................7
Phase I reactions....................................................................................................................................................7
Phase II reactions...................................................................................................................................................8
Biotransformation of acetaminophen (paracetamol)...........................................................................................8
Induction and suppression of biotransforming enzymes......................................................................................9
Transporters......................................................................................................................................9
ABC transporters...................................................................................................................................................9
ABCB..............................................................................................................................................................10
ABCC..............................................................................................................................................................10
ABCG..............................................................................................................................................................10
ABC structure................................................................................................................................................10
Measuring transport activity.........................................................................................................................10
SLC transporters..................................................................................................................................................11
Organic-anion transporting polypeptides – OATPs.......................................................................................11
Organic-anion transporter – OAT..................................................................................................................11
Organic-cation transporter – OCTs...............................................................................................................11
Organic-zwitterion/cation transporter - OCTNs............................................................................................11
Peptide transporters – PEPT.........................................................................................................................11
Multidrug and toxin extrusion reporters – MATEs.......................................................................................11
Signaling pathways and cellular disruption......................................................................................11
Cell regulation (signaling) – dysregulation of gene expression...........................................................................12
Cell regulation (signaling) – dysregulation of ongoing cell function...................................................................12
Cell maintenance – impaired internal maintenance...........................................................................................12
Autophagy.....................................................................................................................................................13
2
, BMS64 – Molecular and cellular toxicology
Necrosis.........................................................................................................................................................13
Apoptosis.......................................................................................................................................................14
What determines the form of cell death?....................................................................................................14
Neurotoxicology..............................................................................................................................15
Neurochemical transmission in the autonomic nervous system........................................................................15
Acetylcholine.................................................................................................................................................15
Norepinephrine.............................................................................................................................................15
Neurotoxicity’s....................................................................................................................................................16
n-Hexane.............................................................................................................................................................16
Spasmolytic drugs................................................................................................................................................16
Nerve agents.......................................................................................................................................................16
MPPP...................................................................................................................................................................17
Cocaine................................................................................................................................................................17
Benzodiazepine...................................................................................................................................................17
In silico methods.............................................................................................................................17
QSAR....................................................................................................................................................................17
Similarity searching.......................................................................................................................................17
Toxicophores.................................................................................................................................................18
Digitalis-like compounds.................................................................................................................18
Structure and mechanism of action of DLCs.......................................................................................................18
How to study DLCs...............................................................................................................................................18
Systems toxicology..........................................................................................................................19
Enabling technologies.........................................................................................................................................19
Biomarkers..........................................................................................................................................................19
3
, BMS64 – Molecular and cellular toxicology
Toxicans affecting receptors
Efficacy: refers to the maximum effect a drug can produce once it binds to its receptor, regardless of the dose.
Potency: refers to how much of a drug is needed to produce a given effect. Potency depends on both the
affinity of the drug for its receptor and its efficacy once bound.
↪ You can only compare potencies if the efficacy levels are similar
ED50: dose necessary to induce an effect at 50% of the maximal effect.
EC50: concentration of a drug that produces 50% of its maximum possible effect.
IC50: the concentration of an inhibitor that reduces a given response by 50%. It’s a standard measure of
antagonist potency.
Types of drug/toxicant target
Acute toxicity of a chemical often starts with interaction with a biological target, but can also result from a
multitude of activated targets:
Receptors
Ligand-gated ion channel receptors: ligand binding opens the channel → ions flow immediately →
rapid cellular response (milliseconds).
G-protein coupled receptors (GPCRs): ligand binding activates G-proteins→ triggers second messengers
→ fast signaling (seconds).
Tyrosine kinase receptors: ligand binding → dimerization and autophosphorylation → kinase cascades
→ response in minutes.
Nuclear receptors: ligand diffuses into cell → binds intracellular receptor → complex binds DNA →
alters transcription → response in hours to days.
Ion channels
Voltage-gated Ca2+
channels
Na+, K+, Cl- channels
Enzymes
Oxidoreductases
Transferases
Hydrolases
Dehydrolases
Transporters
Neurotransmitter/Na+
symporters
Na+/K+ ATPase
Modern drug discovery relies on several “omics” technologies to identify and validate potential therapeutic
targets. Genomics identifies mutations, epigenetic, and post-transcriptional changes linked to disease.
Proteomics reveals protein expression and post-translational modifications, while metabolomics captures shifts
in cellular metabolites.
In the classic view of drug action, a drug acts on a single primary target to produce therapeutic effects, while
interactions with off-targets are responsible for side effects. The systems pharmacology perspective recognizes
that drugs often interact with multiple targets and influence complex cellular networks, leading to both
therapeutic outcomes and side effects.
Drug-receptor interaction
A comparison that describes the reversible interaction between a ligand (drug, toxin) and a receptor is
4
, BMS64 – Molecular and cellular toxicology
k1
→
[D] + [R] ← [DR] Kd = k2/k1
k2
[D] = drug concentration
[R] = free receptors
[DR] = bound receptors
k1 = association rate constant
k2 = dissociation rate constant
Kd = equilibrium dissociation constant (= concentration of ligand that results in 50% receptor occupancy)
Concentration-effect relationship
The concentration-effect relationship describes how the intensity or type of a biological response changes as
the concentration of a substance increases in an organism or a system. At very low concentrations, a chemical
may cause no observable effect because the amount of interaction with target molecules is too small. As
concentration rises, the likelihood that the substance will bind to receptors, enzymes, or other critical
biomolecules increases, and so does the magnitude of the effect. This relationship often follows a dose–
response curve, which is typically sigmoidal: initially flat at low concentrations, then showing a steep increase
in effect over a certain range and finally leveling off when maximum effect is reached because all available
targets are saturated. The Hill equation is a mathematical model used to describe how a biological response
depends on the concentration of a drug, toxin, or ligand that binds to a receptor or enzyme:
[ EA]
[ E¿¿ Amax ]=¿ ¿ ¿
[EA] = the observed effect at concentration [A] of the agonist
[EAmax] = the maximum effect that the system can produce with that agonist
[A] = the concentration of the agonist
[KA] = the equilibrium dissociation constant
n = the hill coefficient, describing the slope of the curve
Types of agonism/antagonism
Full agonist: a substance that binds to a receptor and produces the
maximum possible biological response for that receptor system.
Partial agonist: also binds to the receptor but produces only a
submaximal response, even if it occupies all available receptors.
↪ A partial agonist acts as an antagonist in the presence of a full
agonist (if they compete for the same receptor)
Inverse agonist: binds to the same receptor as an agonist but induces
the opposite effect.
Competitive antagonist: binds reversibly to the active site of the
receptor, blocking agonists from binding.
↪ Its effect can be overcome by increasing the concentration of the
agonist, which shifts the dose–response curve to the right without changing the maximum effect.
Non-competitive antagonist: binds either irreversibly to the active site or to another critical site such that
agonists cannot activate the receptor even if they bind.
↪ This reduces the maximum effect that can be achieved, and its effect cannot simply be overcome by adding
more agonist.
Allosteric antagonist: binds to a different (allosteric) site on the receptor rather than the main active site. By
doing so, it changes the receptor’s shape or function, reducing the ability of the agonist to bind or to activate
the receptor.
Functional antagonist: does not act directly on the same receptor but instead produces an effect that
physiologically opposes the action of an agonist.
5
