The role of APOBEC3B in lung tumor evolution and targeted cancer therapy resistance

In this study, the impact of the apolipoprotein B mRNA-editing catalytic subunit-like (APOBEC) enzyme APOBEC3B (A3B) on epidermal growth factor receptor (EGFR)-driven lung cancer was assessed. A3B expression in EGFR mutant (EGFRmut) non-small-cell lung cancer (NSCLC) mouse models constrained tumorigenesis, while A3B expression in tumors treated with EGFR-targeted cancer therapy was associated with treatment resistance. Analyses of human NSCLC models treated with EGFR-targeted therapy showed upregulation of A3B and revealed therapy-induced activation of nuclear factor kappa B (NF-κB) as an inducer of A3B expression. Significantly reduced viability was observed with A3B deficiency, and A3B was required for the enrichment of APOBEC mutation signatures, in targeted therapy-treated human NSCLC preclinical models. Upregulation of A3B was confirmed in patients with NSCLC treated with EGFR-targeted therapy. This study uncovers the multifaceted roles of A3B in NSCLC and identifies A3B as a potential target for more durable responses to targeted cancer therapy.</p

Oral Verruciform Xanthoma within Lichen Planus: A Case Report and Literature Review

Background. Verruciform xanthoma is an uncommon benign tumor, which exhibits a wide range of clinical patterns. The occurrence of the lesion in patients with immune-mediated mucocutaneous diseases may suggest a role of localized epithelial cell damage and chronic inflammation in its pathogenesis. Case Report. A case of verruciform xanthoma on the tongue of a 56-year-old female with oral lichen planus is reported. An asymptomatic pink-white lesion with a granular surface was observed in the left lateral lingual border, which was closely associated with a white plaque and striae. An incisional biopsy was performed, and histologically, epithelial projections in a verrucous pattern were observed. In the subepithelial connective tissue, aggregates of foamy cells that exhibited immunoreactivity for CD68 were noted. The final diagnosis was verruciform xanthoma. The mucosa adjacent to the lesion demonstrated histopathological features consistent with lichen planus. Conclusions. A total of twelve cases of oral verruciform xanthomas in patients with oral lichen planus including the present case have been reported in the literature. The clinician should be aware that verruciform xanthoma may mimic malignancy, and therefore, biopsy is required for definitive diagnosis to be established, especially when this tumor develops within conditions that show potential for malignant transformation

Mutational impact of APOBEC3A and APOBEC3B in a human cell line and comparisons to breast cancer.

A prominent source of mutation in cancer is single-stranded DNA cytosine deamination by cellular APOBEC3 enzymes, which results in signature C-to-T and C-to-G mutations in TCA and TCT motifs. Although multiple enzymes have been implicated, reports conflict and it is unclear which protein(s) are responsible. Here we report the development of a selectable system to quantify genome mutation and demonstrate its utility by comparing the mutagenic activities of three leading candidates-APOBEC3A, APOBEC3B, and APOBEC3H. The human cell line, HAP1, is engineered to express the thymidine kinase (TK) gene of HSV-1, which confers sensitivity to ganciclovir. Expression of APOBEC3A and APOBEC3B, but not catalytic mutant controls or APOBEC3H, triggers increased frequencies of TK mutation and similar TC-biased cytosine mutation profiles in the selectable TK reporter gene. Whole genome sequences from independent clones enabled an analysis of thousands of single base substitution mutations and extraction of local sequence preferences with APOBEC3A preferring YTCW motifs 70% of the time and APOBEC3B 50% of the time (Y = C/T; W = A/T). Signature comparisons with breast tumor whole genome sequences indicate that most malignancies manifest intermediate percentages of APOBEC3 signature mutations in YTCW motifs, mostly between 50 and 70%, suggesting that both enzymes contribute in a combinatorial manner to the overall mutation landscape. Although the vast majority of APOBEC3A- and APOBEC3B-induced single base substitution mutations occur outside of predicted chromosomal DNA hairpin structures, whole genome sequence analyses and supporting biochemical studies also indicate that both enzymes are capable of deaminating the single-stranded loop regions of DNA hairpins at elevated rates. These studies combine to help resolve a long-standing etiologic debate on the source of APOBEC3 signature mutations in cancer and indicate that future diagnostic and therapeutic efforts should focus on both APOBEC3A and APOBEC3B

A Rabbit Monoclonal Antibody against the Antiviral and Cancer Genomic DNA Mutating Enzyme APOBEC3B

The DNA cytosine deaminase APOBEC3B (A3B) is normally an antiviral factor in the innate immune response. However, A3B has been implicated in cancer mutagenesis, particularly in solid tumors of the bladder, breast, cervix, head/neck, and lung. Here, we report data on the generation and characterization of a rabbit monoclonal antibody (mAb) for human A3B. One mAb, 5210-87-13, demonstrates utility in multiple applications, including ELISA, immunoblot, immunofluorescence microscopy, and immunohistochemistry. In head-to-head tests with commercial reagents, 5210-87-13 was the only rabbit monoclonal suitable for detecting native A3B and for immunohistochemical quantification of A3B in tumor tissues. This novel mAb has the potential to enable a wide range of fundamental and clinical studies on A3B in human biology and disease

An immunogenic model of KRAS-mutant lung cancer enables evaluation of targeted therapy and immunotherapy combinations

Mutations in oncogenes such as KRAS and EGFR cause a high proportion of lung cancers. Drugs targeting these proteins cause tumor regression but ultimately fail to elicit cures. As a result, there is an intense interest in how to best combine targeted therapies with other treatments, such as immunotherapies. However, preclinical systems for studying the interaction of lung tumors with the host immune system are inadequate, in part due to the low tumor mutational burden in genetically engineered mouse models. Here we set out to develop mouse models of mutant KRAS-driven lung cancer with an elevated tumor mutational burden by expressing the human DNA cytosine deaminase, APOBEC3B, to mimic the mutational signature seen in human lung cancer. This failed to substantially increase clonal tumor mutational burden and autochthonous tumors remained refractory to immunotherapy. However, establishing clonal cell lines from these tumors enabled the generation of an immunogenic syngeneic transplantation model of KRAS-mutant lung adenocarcinoma that was sensitive to immunotherapy. Unexpectedly, anti-tumor immune responses were not directed against neoantigens but instead targeted derepressed endogenous retroviral antigens. The ability of KRASG12C inhibitors to cause regression of KRASG12C-expressing tumors was markedly potentiated by the adaptive immune system, highlighting the importance of using immunocompetent models for evaluating targeted therapies. Overall, this model provides a unique opportunity for the study of combinations of targeted and immunotherapies in immune-hot lung cancer