Cytotoxic

Cytotoxic describes a property of molecules, cells, or biological systems that are toxic to cells, causing cell damage or death. In biology, cytotoxicity refers to the ability of certain agents or cells to kill cells. The term is used in two main contexts: immunology, where immune cells kill infected or malignant cells, and pharmacology, where chemicals or drugs kill rapidly dividing cells.

Cytotoxic immune cells include cytotoxic T lymphocytes and natural killer cells. CTLs recognize infected or transformed cells via antigen presentation on MHC class I and induce apoptosis by releasing perforin and granzymes. NK cells detect stressed or abnormal cells by a balance of activating and inhibitory signals and can kill via similar pathways. Cytotoxicity can result in apoptosis, necrosis, or other forms of programmed cell death.

In cancer therapy, cytotoxic drugs are chemotherapeutic agents that kill rapidly dividing cells. Classes include alkylating agents, antimetabolites, DNA-damaging agents, and microtubule inhibitors. These drugs can be effective against tumors but also affect normal proliferating tissues, causing side effects such as myelosuppression, mucositis, and alopecia. Treatment regimens aim to maximize tumor kill while managing toxicity.

Cytotoxicity is routinely measured in research using assays that quantify cell death or membrane integrity, such as lactate dehydrogenase release, colorimetric MTT/MTS assays, or chromium-51 release assays. More modern methods use flow cytometry with viability dyes or caspase activation readouts. The term is also used to describe environmental toxins or pharmaceutical excipients that damage cells.