Mass spectrometric measurement of formaldehyde generated in breast cancer cells upon treatment with anthracycline antitumor drugs

Selected ion flow tube-chemical ionization mass spectrometry was used to me asure formaldehyde levels in human breast cancer cells in comparison with l evels in cells treated with the antitumor drugs doxorubicin (DOX) and dauno rubicin (DAU) and the daunorubicin-formaldehyde conjugate Daunoform (DAUF). The measurement was performed on cell lysates and showed only background l evels of formaldehyde in untreated cells and drug-treated resistant cells ( MCF-7/Adr cells) but levels above background in DOX- and DAU-treated sensit ive cells (MCF-7 cells), The level of formaldehyde above background was a f unction of drug concentration (0.5-50 mu M), treatment time (3-24 h), cell density (0.3 x 10(6) to 7 x 10(6) cells/mL), and cell viability (0-100%). H igher levels of formaldehyde were observed in lysates of MCF-7 cells treate d at higher drug levels, unless the treatment resulted in low cell viabilit y. Elevated levels were directly related to cell density and were observed even with 0.5 mu M drug. A lower limit for excess formaldehyde in MCF-7 cel ls treated with 0.5 mu M DAU for 24 h is 0.3 mM. Control experiments showed that formaldehyde was not produced after cell lysis. Lysates of sensitive and resistant cells treated with 0.5 micromolar equiv of the formaldehyde c onjugate (DAUF) for 3 h showed only background levels of formaldehyde. The results support a mechanism for drug cytotoxicity which involves drug induc tion of metabolic processes leading to formaldehyde production followed by drug utilization of formaldehyde to virtually crosslink DNA.