Correlation of in Situ Oxazolidine Formation with Highly Synergistic Cytotoxicity and DNA Cross-Linking in Cancer Cells from Combinations of Doxorubicin and Formaldehyde

Abstract

Anthracyclines are a class of antitumor compounds that are successful and widely used but suffer from cardiotoxicity and acquired tumor resistance. Formaldehyde interacts with anthracyclines to enhance antitumor efficacy, bypass resistance mechanisms, improve the therapeutic profile, and change the mechanism of action from a topoisomerase II poison to a DNA cross-linker. Contrary to current dogma, we show that both efficient DNA cross-linking and potent synergy in combination with formaldehyde correlate with the anthracycline's ability to form cyclic formaldehyde conjugates as oxazolidine moieties and that the cyclic conjugates are better cross-linking agents and cytotoxins than acyclic conjugates. We also provide evidence that suggests that the oxazolidine forms in situ, since cotreatment with doxorubicin and formaldehyde is highly cytotoxic to dox-resistant tumor cell lines, and that this benefit is absent in combinations of formaldehyde and epirubicin, which cannot form stable oxazolidines. These results have potential clinical implications in the active field of anthracycline prodrug design and development.

Synthesis of Acid-Labile Poly(Doxazolidine) as a Polyprodrug with an Ultra-High Drug Content for Self-Delivery of High-Performance Chemotherapeutics

“…Interestingly, an induction period of about 1 h could be seen in the drug release profile at pH 5.0. In such an acidic medium, both linkers between the Doxaz structural units, the hydrazone bond and the Mannich base, could be hydrolyzed, and therefore the main chains of the P­(Doxaz) polyprodrug were cleaved off into pieces. In the early stage (induction period), the P­(Doxaz) polyprodrug degraded into pieces, mainly the oligomers of Doxaz, which can hardly dissolve into water due to their polymerization degrees, along with a little small drug molecule (Doxaz).…”

Formaldehyde-Doxorubicin Dual Polymeric Drug Delivery System for Higher Efficacy and Limited Cardiotoxicity of Anthracyclines

“…[10] This finding and others has inspired the synthesis of doxorubicin-formaldehyde conjugates and several prodrugs such as Doxoform (DoxF), and Doxsaliform (DoxSF) have been produced and tested. [15][16][17][18] In addition to the aforementioned benefits of this drug combination, a higher uptake into multi-drug resistant MCF-7/Adr cells was also reported. [16] While these are promising results, the acyloxyalkyl ester prodrugs and Dox-formaldehyde prodrugs release formaldehyde by hydrolysis and metabolize very quickly with the stability and shelf-life of an aqueous therapeutic solution being limited to a few minutes.…”

The Mechanism of Dynamic Interaction between Doxorubicin and Calf Thymus DNA at the Single-Molecule Level Based on Confocal Raman Spectroscopy

“…One opinion is that the DOX generates semiquinone free radical through reduction reaction under the action of oxidoreductases, and then the reoxidation of semiquinone free radical initiates the generation of reactive oxygen species (ROS), which causes oxidative stress, DNA damage, peroxidation membrane damage, and ultimately results in the death of cancer cells [14,15]. Another opinion is that DOX directly intercalates into DNA molecules, thereby breaking the complex between DNA and Topo II enzyme, which prevents the reclosure of the DNA double helix structure of cancer cells, and eventually leads to the death of cancer cells [16][17][18]. However, the results of research on the insertion sites on DNA molecules are still inconsistent.…”