Background

Cutaneous T-cell lymphoma (CTCL) is a heterogeneous group of extranodal non-Hodgkin’s lymphoma. Mycosis fungoides (MF) is the most common types of CTCL and considered as a malignancy of skin-resident T cells. Chlormethine (CL), also known as mechlorethamine or nitrogen mustard, is a synthetic agent with well-known alkylating capacity. Its topical application has a long tradition in dermatology, as CL-containing products have been used for the treatment of MF since 1940. Recently, a novel CL gel formulation has been approved for the treatment of skin lesions in MF adult patients.

Objective

Here we aim to study the impact of CL on malignant skin T cells regarding their susceptibility to treatment, proliferation, DNA double strand breaks and the expression of alkylated-nucleotides-excision genes.

Methods

Tumour blood or skin T cells were isolated by magnetic-activated cell (MACS) sorting. Susceptibility to CL exposure was evaluated by MTT assay. Proliferation and DNA double strand breaks upon CL exposure were detected by BrdU proliferation assay and flowcytometry for γH2AX Ser139. Expression of alkylated-nucleotides-excision genes was measured by reverse transcription quantitative PCR (RT-qPCR).

Results

While CL exposure in vitro decreased time- and dose-dependently total blood T-cell viability, it did not statistically significantly influence neither blood nor skin T-cell proliferation. Of interest, when acting on skin T cells, CL induce DNA double stranded breaks predominately in the subpopulation of MF clonal malignant skin T cells but not the non-tumoral healthy T cells. Quantitative real-time PCR uncovered that several important genes involved in rescue of alkylated nucleotides were generally decreased in tumor T cells and CL exposure in vitro further significantly decreased the expression of FEN1 and BRCA2, two major alkylated-nucleotides-excision-repair genes.

Conclusion

This study sheds light on how CL affects malignant skin T cells from patients with MF and provides additional rationale for considering it as an early and valuable skin-directed treatment option for skin lymphoma.