Selected ion flow tube-chemical ionization mass spectrometry was used to measure
formaldehyde levels in human
breast cancer cells in comparison with levels in cells treated with the
antitumor drugs doxorubicin (DOX) and
daunorubicin (DAU) and the
daunorubicin-
formaldehyde conjugate
Daunoform (DAUF). The measurement was performed on cell lysates and showed only background levels of
formaldehyde in untreated cells and
drug-treated resistant cells (MCF-7/Adr cells) but levels above background in DOX- and DAU-treated sensitive cells (MCF-7 cells). The level of
formaldehyde above background was a function of
drug concentration (0.5-50 microM), treatment time (3-24 h), cell density (0.3 x 10(6) to 7 x 10(6) cells/mL), and cell viability (0-100%). Higher levels of
formaldehyde were observed in lysates of MCF-7 cells treated at higher
drug levels, unless the treatment resulted in low cell viability. Elevated levels were directly related to cell density and were observed even with 0.5 microM
drug. A lower limit for excess
formaldehyde in MCF-7 cells treated with 0.5 microM 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 conjugate (DAUF) for 3 h showed only background levels of
formaldehyde. The results support a mechanism for
drug cytotoxicity which involves
drug induction of metabolic processes leading to
formaldehyde production followed by drug utilization of
formaldehyde to virtually cross-link
DNA.