Anthracyclines are a class of drugs used in cancer chemotherapy extracted from Streptomyces bacterium such as Streptomyces peucetius var. caesius.
These compounds are used to treat many cancers, including leukemias, lymphomas, breast, stomach, uterine, ovarian, bladder cancer, and lung cancers.
The anthracyclines are among the most effective anticancer treatments ever developed and are effective against more types of cancer than any other class of chemotherapeutic agents. Their main adverse effect is cardiotoxicity, which considerably limits their usefulness. Use of anthracyclines has also been shown to be significantly associated with cycle 1 severe or febrile neutropenia. Other adverse effects include vomiting.
The first anthracycline discovered was daunorubicin (trade name Daunomycin), which is produced naturally by Streptomyces peucetius, a species of actinobacteria. Doxorubicin (trade name Adriamycin) was developed shortly after, and many other related compounds have followed, although few are in clinical use.
Anthracyclines are used to treat various cancers and as of 2012 were among the most commonly used chemotherapeutic agents. Doxorubicin and its derivative, epirubicin, are used in breast cancer, childhood solid tumors, soft tissue sarcomas, and aggressive lymphomas. Daunorubicin is used to treat acute lymphoblastic or myeloblastic leukemias, and its derivative, idarubicin is used in multiple myeloma, non-Hodgkin’s lymphomas, and breast cancer. Other anthracycline derivates include nemorubicin, used for treatment of hepatocellular carcinoma, pixantrone, used as a second-line treatment of non-Hodgkin’s lymphomas, sabarubicin, used for non-small cell lung cancer, hormone refractory metastatic prostate cancer, and platinum- or taxane-resistant ovarian cancer, and valrubicin, which is used for the topical treatment of bladder cancer.
Mechanism of Action
Anthracyclines have four mechanisms of action:
Inhibition of DNA and RNA synthesis by intercalating between base pairs of the DNA/RNA strand, thus preventing the replication of rapidly growing cancer cells.
Inhibition of topoisomerase II enzyme, preventing the relaxing of supercoiled DNA and thus blocking DNA transcription and replication. Some sources say that topoisomerase II inhibitors prevent topoisomerase II turning over which is needed for dissociation of topoisomerase II from its nucleic acid substrate. In other words, topoisomerase II inhibitors stabilise the topoisomerase II complex after it has broken the DNA chain. This leads to topoisomerase II mediated DNA-cleavage, producing DNA breaks.
Iron-mediated generation of free oxygen radicals that damage the DNA, proteins and cell membranes.
Induction of histone eviction from chromatin that deregulates DNA damage response, epigenome and transcriptome.
Anthracyclines can cause cardiotoxicity. This cardiotoxicity may be caused by many factors, which may include inhibition and/or poisoning of topoisomerase-IIB in cardiomyocytes, interference with the ryanodine receptors of the sarcoplasmic reticulum, free radical formation in the heart, or from buildup of metabolic products of the anthracycline in the heart. The cardiotoxicity often presents as ECG changes (especially change in the frequency of QRS complex) and arrhythmias, or as a cardiomyopathy leading to heart failure (sometimes presenting many years after treatment). This cardiotoxicity is related to a patient’s cumulative lifetime dose. A patient’s lifetime dose is calculated during treatment, and anthracycline treatment is usually stopped (or at least re-evaluated by the oncologist) upon reaching the maximum cumulative dose of the particular anthracycline.
There exists evidence that the effect of cardiotoxicity increases in long-term survivors, from 2% after 2 years to 5% after 15 years.
In addition to staying below the cumulative doses, various prevention measures may be employed by the oncologist in order to reduce the risk of cardiotoxicity. Cardiac monitoring are recommended at 3, 6, and 9 months. Other measures include the use of Dexrazoxane, the use of liposomal preparations of doxorubicin when appropriate, as well as the administration of doxorubicin over longer infusion rates:
Dexrazoxane is a cardioprotective drug that is sometimes used to reduce the risk of cardiotoxicity. It has been found to reduce the risk of anthracycline cardiotoxicity by about one-third, without affecting response to chemotherapy or overall survival. The potential adverse effects of dexrazoxane are not known.
The liposomal formulations of daunorubicin and doxorubicin are less toxic to cardiac tissue than the non-liposomal form because a lower proportion of drug administered in the liposome form is delivered to the heart.
Longer infusion rates will result in a reduced plasma level and a much lower left ventricular peak concentration.
At least one study which found lower verbal memory performance on tests of immediate and delayed recall suggests that anthracycline may increase the risk for developing “chemobrain”.
Daunorubicin was first isolated from streptomyces early in the 1960s by groups in Italy (at Farmitalia) and France (at Rhone-Poulenc), each of which published in 1963. Doxorubicin was discovered after a strain of Streptomyces was mutated to produce different compounds.
Effort soon began to develop derivatives with better activity and less cardiotoxicity. Most of these derivatives were made by tweaking compounds produced by bacteria, or by modifying the bacteria themselves. Amrubicin was the first derivative created by de novo synthesis and was first published in 1989 by scientists from Sumitomo.