Retinal dehydrogenase 1 (88-96)

Objectives: Aldehyde dehydrogenase 1 (ALDH1) is associated with tumorigenesis, and shown to identify cancer stem cells (CSC)-like cells. We aimed to investigate the significance of ALDH1 in oral squamous cell carcinoma (OSCC) and its correlation with DNMT3b and immune evasion in the present study. Methods: We retrospectively analyzed the clinical outcomes of OSCC patients and examined its correlation with the levels of ALDH1 in tumors and circulating myeloid-derived suppressor cells (MDSCs) in the peripheral blood. Furthermore, the relationships between the DNMT3b, ALDH1 expression, and immune response were examined via clinical specimens and cellular and animal experiments. We also investigated the therapeutic potential of DNA hypomethylating agents in OSCC. Results: Our data revealed that the levels of ALDH1 expression were linked to treatment resistance, CSC-like properties, higher circulating MDSC and poor prognosis for OSCC. The radiation resistance noted in ALDH1-positive tumors was associated with augmented radiation-induced increases in the expression of programmed death ligand (PD-L1) and the activation of MDSCs. Furthermore, there was a positive link between ALDH1 and DNMT3b expression shown by clinical specimens and cellular experiments. DNA hypomethylating agents attenuated the radioresistance of ALDH1-positive cancer cells associated with the decreased ALDH1 and the increased DNA damages. In addition, the activation of MDSCs and the expression of PD-L1 were significantly attenuated by epigenetic therapy. Conclusions: Our findings suggested that ALDH1 played an important role in treatment response and the tumor-promoting microenvironment in OSCC. Moreover, epigenetic therapy could be a promising strategy for the treatment of OSCC.

Few epitopes are available for vaccination therapy of patients with squamous cell carcinoma of the head and neck (SCCHN). Using a tumor-specific CTL, aldehyde dehydrogenase 1 family member A1 (ALDH1A1) was identified as a novel tumor antigen in SCCHN. Mass spectral analysis of peptides in tumor-derived lysates was used to determine that the CTL line recognized the HLA-A*0201 (HLA-A2) binding ALDH1A1(88-96) peptide. Expression of ALDH1A1 in established SCCHN cell lines, normal mucosa, and primary keratinocytes was studied by quantitative reverse transcription-PCR and immunostaining. Protein expression was further defined by immunoblot analysis, whereas ALDH1A1 activity was measured using ALDEFLUOR. ALDH1A1(88-96) peptide was identified as an HLA-A2-restricted, naturally presented, CD8(+) T-cell-defined tumor peptide. ALDH1A1(88-96) peptide-specific CD8(+) T cells recognized only HLA-A2(+) SCCHN cell lines, which overexpressed ALDH1A1, as well as targets transfected with ALDH1A1 cDNA. Target recognition was blocked by anti-HLA class I and anti-HLA-A2 antibodies. SCCHN cell lines overexpressing ALDH1 had high enzymatic activity. ALDH1A1 protein was expressed in 12 of 17 SCCHN, and 30 of 40 dysplastic mucosa samples, but not in normal mucosa. ALDH1A1 expression levels in target cells correlated with their recognition by ALDH1A1(88-96) peptide-specific CD8(+) T cells. Our findings identify ALDH1A1, a metabolic antigen, as a potential target for vaccination therapy in the cohort of SCCHN subjects with tumors overexpressing this protein. A smaller cohort of subjects with SCCHN, whose tumors express little to no ALDH1A1, and thus are deficient in conversion of retinal to retinoic acid, could benefit from chemoprevention therapy.