**Author details**

Sacrolysin, Melphalan, and Busulphan), have been recognized as a source of secondary cancers

Sometimes known carcinogens have became invaluable drugs widely applied in clinical oncology. The most impressive example is arsenic - a component of the well known Poison of Kings (As2O3). It was used in traditional Chinese medicine in the treatment of promyelocytic leukaemia and acute myelogenous leukaemia. Reaglar containing arsenic was used by Hipocrates as a component of antitumor liniment. Avicenna in the 11th c. recommended it for cancer, both internally and topically. In the 16th century Paracelsus used it as a drug but linked with a cancer disease. In 1786 Thomas Fowler discovered Fowler's Solution (a 1% aqueous solution of potassium arsenite, KAsO2),which was applied as first chemotherapeutic in chronic myeloid leukaemia treatment in 1865 by Lissauer and persisted till the introduction of the first modern cytotoxic drugs in the 1940s. In 1931, its use in chronic myeloid leukaemia was described. In the late 1960s in China, an arsenic containing liniment was rediscovered for use as an effective anticancer treatment in melanoma. First reports of the intravenous administra‐ tion of Fowler's Solution in acute promyelocytic leukaemia appeared in the 1990s, also in China. But in the 1990s IARC classified arsenic compounds as definite carcinogens. Despite this, in 2001 Fowler's Solution was accepted by FDA for the treatment of relapsed or refractory acute promyelocytic leukaemia in children. After being abandoned for decades, arsenic trioxide in the 21st c started to be prescribed as a drug for acute promyelocytic leukaemia, and still it is classified as definite anticancer. Recently some hope rises with realgar as well as new arsenic-based compounds (e.g. C-glycosides), which have been intensively studied. On the other hand, a very recent studies performed by Peter S. Nelson et al. indicated that chemo‐ therapy can damage healthy cells which secrete a protein WNT16B that sustains tumour growth and results in a resistance to further treatment [123]. This proves that chemotherapy itself can boost cancer growth. The paradox drug/carciogen concerns not only chemothera‐ peutics but also the methods, which revolutionized the treatment of cancer, being on the other hand carcinogenic, like X-Ray widely used in the diagnosis of cancer cells, cancer treatment and anticancer drug design, UV radiation being a basis of the photodynamic therapy. Para‐ celsus, father of toxicology already wrote "*All substances are poisons: there is none which is not a poison. The right dose differentiates a poison and a remedy.*" Paraphrasing him - the method and conditions of the use differentiates a carcinogen and anticancer drug. Thus the search for new drugs among carcinogens seems quite reasonable, while the protection against contact with

The recent advances in genomics and proteomics deliver a promise of understanding the true internal mechanisms of cancerogenesis - a basis for cancer diseases. They cover the knowledge of genes alteration caused by cancer, its influence on the proteins encoded by them, the interaction of these proteins with each other in living cells, the resulting changes in the specific tissues and finally the effect on the entire body. The achievements in this field delimit new fully rational directions in anticancer drug discovery and development of drugs addressing

and thus classified as definite carcinogens.

64 Drug Discovery

or exposure to a carcinogen is a necessity.

the specific needs (targeted drugs).

Jolanta Natalia Latosińska\* and Magdalena Latosińska

\*Address all correspondence to: jolanta.latosinska@amu.edu.pl

Faculty of Physics, Adam Mickiewicz University, Poznań, Poland
