Metabolic activation, DNA adducts, and H-ras mutations in human neoplastic and non-neoplastic laryngeal tissue

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Abstract
Metabolic activation, DNA adducts, and H‐ras mutations were examined in human laryngeal tissue (n = 16) from both smoker and non/ex‐smoker patients with laryngeal cancer. DNA adducts detected by 32P‐postlabelling were evident only in smokers (n = 13); in fact, smoking cessation for as little as 10 months resulted in no DNA adducts detected (n = 3). Total DNA adduct levels in these samples were significantly correlated with levels of cytochromes P‐4502C and 1A1 in laryngeal microsomes. Moreover, the P‐4501A1 levels represent the highest yet found in human tissues. In contrast, laryngeal microsomes did not have detectable P‐4501A2 activity, while laryngeal cytosols showed appreciable N‐acetyltransferase activity for p‐aminobenzoic acid (NAT1) but not sulfamethazine (NAT2). DNA was extracted from laryngeal specimens and amplified by PCR. Nylon filter dot or slot blots were hybridized with 32P‐labelled probes for codons 12, 13, and 61 of the H‐ras gene. Sixty percent of specimens demonstrated mutations in either codon 12, 13, or 61; a single common and specific mutation was a Gln → Glu transversion in codon 61. This mutation appeared in 5 laryngeal specimens, all from smokers. These results implicate cigarette smoke components, bioactivated by CYP1A1 and/or CYP2C, in DNA adduct formation. These results also demonstrate a probable smoking‐related H‐ras Gln → Glu transversion in codon 61.

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