Doxycycline

Although several new antibiotics have recently become available, in several clinical instances conventional antibiotics may be equally efficacious at a considerably lower cost. In today's era of cost containment, it is particularly relevant to revisit older, inexpensive antibiotics to reexplore their role in the face of the emergence of resistant microorganisms and competition from newer agents. Doxycycline is one such antibiotic. It is an inexpensive, broad-spectrum antimicrobial agent that remains the drug of first choice for several infections. In addition, it can be used for a variety of other indications. Adverse effects are infrequent and relatively minor. While interactions occur with several medications, none of these interactions has significant adverse consequences.

Chemotherapy is one of the standard methods for the treatment of malignant tumors. It aims to cause lethal damage to cellular structures, mainly DNA. Noteworthy, in recent years discoveries of novel anticancer agents from well-known antibiotics have opened up new treatment pathways for several cancer diseases. The aim of this review article is to describe new applications for the following antibiotics: doxycycline (DOX), salinomycin (SAL), monensin (MON) and ivermectin (IVR) as they are known to show anti-tumor activity, but have not yet been introduced into standard oncological therapy. To date, these agents have been used for the treatment of a broad-spectrum of bacterial and parasitic infectious diseases and are widely available, which is why they were selected. The data presented here clearly show that the antibiotics mentioned above should be recognised in the near future as novel agents able to eradicate cancer cells and cancer stem cells (CSCs) across several cancer types.

Cancer cells do create hostile microenvironment (deprivation of nutrients, accumulation of acidity, anoxic habitat). Those cells are not only adapted to this sanctuary environment, blunting of immunity but also, grow, migrate to the distal area (metastasis) and communicate with each other in a unique population structure and organization too (clonal expansion). The adaptation requirements push those types of adaptable cells (cancer cells) to be primitive cells. The prevailing pharmacological approach in treating cancer is developing a chemotherapeutic agent that acts on rapidly proliferating cells that are stuck with normally growing epithelium and bone marrow too. The latter approach has been drafted to work on cellular target under the term of "targeted therapy" believing that each target represents Achilles Heels of cancer. In this article, we try to introduce a new concept of cancer pharmacology, by offering new off-label use of Doxycycline, which is characterized by selective toxicity, as potential anticancer agents. This notion is relying on the absence of taxonomic barriers.