Apoptosis: Inducers and Inhibitors
Chemical modulators able to initiate or prevent programmed cell death are crucial tools to investigate the complex components of molecular pathways. As illustrated in the table below, apoptosis inducers include several examples of classic chemotherapeutic agents that interfere with DNA synthesis.
Common Inducers of Apoptosis
| Chemical | Mechanism of Action |
|---|---|
| Actinomycin D | Inhibits RNA polymerase; apoptosis inducer |
| AZD 5582 | Dimeric Smac mimetic; potent IAP inhibitor |
| AT 101 | Downregulates Bcl-2 and Mcl-1 |
| Camptothecin | Topoisomerase I inhibitor |
| Cisplatin | Platinum agent; induces DNA damage |
| Doxorubicin | Antitumor antibiotic agent; inhibits DNA topoisomerase II |
| Etoposide | Topoisomerase II inhibitor |
| Mitomycin C | DNA cross-linking antitumor agent |
| MSC 2032964A | Potent and selective ASK1 inhibitor; orally bioavailable |
| Nutlin 3 | MDM2 antagonist; inhibits MDM2-p53 interaction |
| Paclitaxel (Taxol) | Promotes assembly and inhibits disassembly of microtubules |
| PRIMA-1MET | Restores mutant p53 activity |
| Staurosporine | Broad spectrum protein kinase inhibitor |
| Vinblastine | Disrupts microtubules |
Caspase Inhibitors
Blocking the progression of apoptosis frequently involves either a cell-permeable, broad-spectrum caspase or caspase subtype-selective inhibitor. For instance, if measuring cytochrome c release from mitochondria, pan-caspase inhibitors will prevent the downstream activation of the caspase cascade. While caspase-mediated cell death is blocked, cell survival may not be long term. Similarly, cells treated with caspase inhibitors and death receptor ligands (e.g. TNF-α) are diverted to other cell death pathways (i.e. necroptosis). Learn more about Caspase Cleavage and Activation in apoptosis.
| Chemical | Mechanism of Action |
|---|---|
| Z-VAD-FMK | Irreversible pan-caspase inhibitor |
| Q-VD-OPH | Less toxic irreversible pan caspase inhibitor; used in in-vivo studies |
| Z-DEVD-FMK Caspase-3 Inhibitor | Cell-permeable, irreversible inhibitor of caspase 3 |
How to Determine an Effective Drug Concentration
The suitable drug concentration required to initiate or inhibit an apoptotic response in the majority of targeted cells can be determined by performing a dose titration experiment. For a good starting point, consult the literature to identify potential working concentrations. It is also important to understand the relationship between concentration and exposure times. If inducing apoptosis at a low dose, or with a mild stimulus, then a longer treatment time may be necessary.
Why are Experimental Controls Important?
All experiments measuring apoptosis should include both positive and negative controls. During data analysis, negative and positive controls are key to identify and separate healthy and apoptotic populations in experimental samples. Negative controls are also used to assess the health of vehicle-treated cells and serve as baseline measurements crucial for determining the magnitude of the apoptotic response. If cells lacking treatment with apoptosis inducers or treated with caspase inhibitors already show significant signs of cell death, then the activity and effect of the drug will be difficult to establish.