|Systematic (IUPAC) name|
|Pregnancy cat.||D (AU) D (US)|
|Legal status||℞ Prescription only|
|Mol. mass||261.086 g/mol|
|Melt. point||2 °C (36 °F)|
|(what is this?)|
An alkylating agent adds an alkyl group (CnH2n+1) to DNA. It attaches the alkyl group to the guanine base of DNA, at the number 7 nitrogen atom of the imidazole ring. This interferes with DNA replication by forming intrastrand and interstrand DNA crosslinks.
Cyclophosphamide has severe and life-threatening adverse effects, including acute myeloid leukemia, bladder cancer, hemorrhagic cystitis, and permanent infertility, especially at higher doses. For autoimmune diseases, doctors often substitute less-toxic methotrexate or azathioprine after an acute crisis.
Cyclophosphamide is used to treat cancer and immune diseases.
The main use of cyclophosphamide is with other chemotherapy agents in the treatment of lymphomas, some forms of brain cancer, leukemia and some solid tumors. It is a chemotherapy drug that works by inducing the death of certain T cells.
A 2004 study showed the biological actions of cyclophosphamide are dose-dependent. At higher doses, it is associated with increased cytotoxicity and immunosuppression, while at low, continuous doses, it shows immunostimulatory and antiangiogenic properties. A 2009 study of 17 patients with docetaxel-resistant metastatic hormone refractory prostate cancer showed a prostate-specific antigen (PSA) decrease in 9 of the 17 patients. Median survival was 24 months for the entire group, and 60 months for those with a PSA response. The study concluded low-dose cyclophosphamide "might be a viable alternative" treatment for docetaxel-resistant MHRPC and "is an interesting candidate for combination therapies, e.g., immunotherapy, tyrosine kinase inhibitors, and antiangiogenisis."
Cyclophosphamide also decreases the immune system's response to various diseases and conditions. Therefore, it has been used in autoimmune diseases where disease-modifying antirheumatic drugs (DMARDs) have been ineffective. For example, systemic lupus erythematosus with severe lupus nephritis may respond to pulsed cyclophosphamide. Cyclophosphamide is also used to treat minimal change disease, severe rheumatoid arthritis, Wegener's granulomatosis (with trade name Cytoxan), and multiple sclerosis (with trade name Revimmune).
Cyclophosphamide is converted by mixed-function oxidase enzymes (cytochrome P450 system) in the liver to active metabolites. The main active metabolite is 4-hydroxycyclophosphamide, which exists in equilibrium with its tautomer, aldophosphamide. Most of the aldophosphamide is oxidised by the enzyme aldehyde dehydrogenase (ALDH) to make carboxyphosphamide. A small proportion of aldophosphamide freely diffuses into cells, it is decomposed into two compounds, phosphoramide mustard and acrolein. Acrolein is toxic to the bladder epithelium and can lead to hemorrhagic cystitis. This can be prevented through the use of aggressive hydration and/or mesna.
- Elimination of T regulatory cells (CD4+CD25+ T cells) in naive and tumor-bearing hosts
- Induction of T cell growth factors, such as type I IFNs, and/or
- Enhanced grafting of adoptively transferred, tumor-reactive effector T cells by the creation of an immunologic space niche.
Thus, cyclophosphamide preconditioning of recipient hosts (for donor T cells) has been used to enhance immunity in naïve hosts, and to enhance adoptive T cell immunotherapy regimens, as well as active vaccination strategies, inducing objective antitumor immunity.
Mechanism of action
The main effect of cyclophosphamide is due to its metabolite phosphoramide mustard. This metabolite is only formed in cells that have low levels of ALDH.
Phosphoramide mustard forms DNA crosslinks both between and within DNA strands at guanine N-7 positions (known as interstrand and intrastrand crosslinkages, respectively). This is irreversible and leads to cell apoptosis.
Cyclophosphamide has relatively little typical chemotherapy toxicity as ALDHs are present in relatively large concentrations in bone marrow stem cells, liver and intestinal epithelium. ALDHs protect these actively proliferating tissues against toxic effects of phosphoramide mustard and acrolein by converting aldophosphamide to carboxyphosphamide that does not give rise to the toxic metabolites phosphoramide mustard and acrolein.
Adverse drug reactions include chemotherapy-induced nausea and vomiting, bone marrow suppression, stomach ache, hemorrhagic cystitis, diarrhea, darkening of the skin/nails, alopecia (hair loss) or thinning of hair, changes in color and texture of the hair, and lethargy. Hemorrhagic cystitis is a frequent complication, but this is prevented by adequate fluid intake and mesna (sodium 2-mercaptoethane sulfonate), a sulfhydryl donor which binds acrolein.
Cyclophosphamide is itself carcinogenic, potentially causing transitional cell carcinoma of the bladder as a long-term complication. It can lower the body's ability to fight an infection. It can cause temporary or (rarely) permanent sterility. A serious potential side effect is acute myeloid leukemia, referred to as secondary AML (therapy-related AML, or "t-AML"), thought to occur either by cyclophosphamide inducing mutations or selecting for a high-risk myeloid clone. The risk may be dependent on dose and a number of other factors, including the condition being treated, other agents or treatment modalities used (including radiotherapy), treatment intensity and length of treatment. For some regimens, it is a very rare occurrence. For instance, CMF-therapy for breast cancer (where the cumulative dose is typically less than 20 grams of cyclophosphamide) seems to carry an AML risk of less than 1/2000th, with some studies even finding no increased risk compared to the background population. Other treatment regimens involving higher doses may carry risks of 1-2% or higher, depending on regimen. Cyclophosphamide-induced AML, when it happens, typically presents some years after treatment, with incidence peaking around 3–9 years. After nine years, the risk has fallen to the level of the regular population. When AML occurs, it is often preceded by a myelodysplastic syndrome phase, before developing into overt acute leukemia. Cyclophosphamide-induced leukemia will often involve complex cytogenetics, which carries a worse prognosis than de novo AML.
Other side effects include:
- easy bruising/bleeding
- gross and microscopic hematuria
- joint pain
- mouth sores
- slow-healing existing wounds
- syndrome of inappropriate antidiuretic hormone (SIADH)
- unusual decrease in the amount of urine
- unusual tiredness or weakness
As reported by O.M. Colvin in his study of the development of cyclophosphomide and its clinical applications,
Phosphoramide mustard, one of the principle toxic metabolites of cyclophosphamide, was synthesized and reported by Friedman and Seligman in 1954 ...It was postulated that the presence of the phosphate bond to the nitrogen atom could inactivate the nitrogen mustard moiety, but the phosphate bond would be cleaved in gastric cancers and other tumors which had a high phosphamidase content. However, in studies carried out after the clinical efficacy of cyclophosphamide was demonstrated, phosphoramide mustard proved to be cytotoxic in vitro (footnote omitted), but to have a low therapeutic index in vivo.
Cyclophosphamide and the related nitrogen mustard-derived alkylating agent ifosfamide were developed by Norbert Brock and ASTA (now Baxter Oncology). Brock and his team synthesised and screened more than 1,000 candidate oxazaphosphorine compounds. They converted the base nitrogen mustard into a nontoxic "transport form". This transport form was a prodrug, subsequently actively transported into the cancer cells. Once in the cells, the prodrug was enzymatically converted into the active, toxic form. The first clinical trials were published at the end of the 1950s. In 1959 it became the eighth cytotoxic anticancer agent to be approved by the FDA.
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