O6-alkylguanine-DNA alkyltransferase in cutaneous T-cell lymphoma: implications for treatment with alkylating agents.
Mycosis fungoides is a low-grade cutaneous T-cell lymphoma. Early treatment often involves the use of topical chemotherapy such as mechlorethamine or carmustine although single-agent oral chemotherapy with alkylators is common for advanced disease. Recently, in a Phase I study of the new alkylating agent temozolomide, two mycosis fungoides patients experienced a complete response. The mechanism of resistance to alkylating drugs such as temozolomide is thought to be due to the presence in tumor cells of the DNA repair protein, O6-alkylguanine-DNA alkyltransferase (AGT). The protein mediates a reaction with the O6-position of guanine in DNA, removing the lesion and leaving guanine intact. We, therefore, examined the levels of AGT in CD4+ T lymphocytes obtained by negative antibody selection from the blood of noncancerous individuals and mycosis fungoides patients, and in paraffin-embedded sections from mycosis fungoides patch, plaque, or tumor lesions and cells from involved lymph nodes. AGT protein levels were measured by quantitative immunofluorescence microscopy using a monoclonal antibody against human AGT. Using this approach, the mean level of our positive control (AGT-expressing cells) was 84,807 molecules/nucleus; values below 5,000 molecules/nucleus are considered very low. The mean AGT level in CD4+ T lymphocytes from noncancerous and cancerous individuals was 18,618 (n = 12) and 8,593 (n = 5), respectively. The mean fraction of outliers in circulating CD4+ T lymphocytes from mycosis fungoides patients was statistically significantly lower than T cells in lymph nodes. AGT molecules/nucleus from lymph node biopsies from 8 of 10 patients showed low (< 10,000 molecules/nucleus) or undetectable levels (n = 5) of AGT. The mean AGT level from samples of mycosis fungoides patch/plaque and tumor was also low at 221 (n = 4) and 2,363 (n = 6), respectively. Surprisingly, Hut78, a mycosis fungoides T-cell lymphoma cell line, was positive for AGT activity (median: 77,700 molecules/nucleus), and Hut102--another mycosis fungoides cell line--was low (median: 5,990 molecules/nucleus). Because AGT is a primary means of cell resistance to alkylating agents, the low level of AGT in neoplastic T lymphocytes from patients with mycosis fungoides suggests that treatment with alkylating agents producing O6-alkylguanine adducts, such as carmustine or temozolomide, may produce improved clinical outcomes.
Dolan
M E
ME
Department of Medicine, University of Chicago, Illinois 60637, USA. medolan@mcis.bsd.uchicago.edu
McRae
B L
BL
Ferries-Rowe
E
E
Belanich
M
M
van Seventer
G A
GA
Guitart
J
J
Pezen
D
D
Kuzel
T M
TM
Yarosh
D B
DB
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000477:Alkylating Agents / Q000627:therapeutic use*; D015496:CD4-Positive T-Lymphocytes / Q000201:enzymology; D002460:Cell Line; D002467:Cell Nucleus / Q000201:enzymology; D005260:Female; D005434:Flow Cytometry; D006801:Humans; D018189:Immunomagnetic Separation; D008198:Lymph Nodes / Q000201:enzymology; D008297:Male; D008856:Microscopy, Fluorescence; D008875:Middle Aged; D009182:Mycosis Fungoides / Q000188:drug therapy / Q000201:enzymology*; D019853:O(6)-Methylguanine-DNA Methyltransferase / Q000378:metabolism*; D012878:Skin Neoplasms / Q000188:drug therapy / Q000201:enzymology*
D000477:Alkylating Agents; D019853:O(6)-Methylguanine-DNA Methyltransferase