S. Carson Callahan Jr, MD, PhD

Radiation Oncology Resident

Department of Human Oncology


Intern, University of Wisconsin - Madison, Internal Medicine (2023)

MD, McGovern Medical School, (2022)

PhD, MD Anderson UTHealth - Houston, Cancer Biology (2022)

BA, Emory University, Chemistry (2013)

  • High enhancer activity is an epigenetic feature of HPV negative atypical head and neck squamous cell carcinoma Frontiers in cell and developmental biology
    Callahan SC, Kochat V, Liu Z, Raman AT, Divenko M, Schulz J, Terranova CJ, Ghosh AK, Tang M, Johnson FM, Wang J, Skinner HD, Pickering CR, Myers JN, Rai K
    2022 Jul 19;10:936168. doi: 10.3389/fcell.2022.936168. eCollection 2022.
    • More

      Head and neck squamous cell carcinoma (HNSCC) is a heterogeneous disease with significant mortality and frequent recurrence. Prior efforts to transcriptionally classify HNSCC into groups of varying prognoses have identified four accepted molecular subtypes of the disease: Atypical (AT), Basal (BA), Classical (CL), and Mesenchymal (MS). Here, we investigate the active enhancer landscapes of these subtypes using representative HNSCC cell lines and identify samples belonging to the AT subtype as having increased enhancer activity compared to the other 3 HNSCC subtypes. Cell lines belonging to the AT subtype are more resistant to enhancer-blocking bromodomain inhibitors (BETi). Examination of nascent transcripts reveals that both AT TCGA tumors and cell lines express higher levels of enhancer RNA (eRNA) transcripts for enhancers controlling BETi resistance pathways, such as lipid metabolism and MAPK signaling. Additionally, investigation of higher-order chromatin structure suggests more enhancer-promoter (E-P) contacts in the AT subtype, including on genes identified in the eRNA analysis. Consistently, known BETi resistance pathways are upregulated upon exposure to these inhibitors. Together, our results identify that the AT subtype of HNSCC is associated with higher enhancer activity, resistance to enhancer blockade, and increased signaling through pathways that could serve as future targets for sensitizing HNSCC to BET inhibition.

      PMID:35927986 | PMC:PMC9343809 | DOI:10.3389/fcell.2022.936168

      View details for PubMedID 35927986
  • Chromatin state dynamics confers specific therapeutic strategies in enhancer subtypes of colorectal cancer Gut
    Orouji E, Raman AT, Singh AK, Sorokin A, Arslan E, Ghosh AK, Schulz J, Terranova C, Jiang S, Tang M, Maitituoheti M, Callahan SC, Barrodia P, Tomczak K, Jiang Y, Jiang Z, Davis JS, Ghosh S, Lee HM, Reyes-Uribe L, Chang K, Liu Y, Chen H, Azhdarinia A, Morris J, Vilar E, Carmon KS, Kopetz SE, Rai K
    2022 May;71(5):938-949. doi: 10.1136/gutjnl-2020-322835. Epub 2021 May 31.
    • More

      OBJECTIVE: Enhancer aberrations are beginning to emerge as a key epigenetic feature of colorectal cancers (CRC), however, a comprehensive knowledge of chromatin state patterns in tumour progression, heterogeneity of these patterns and imparted therapeutic opportunities remain poorly described.

      DESIGN: We performed comprehensive epigenomic characterisation by mapping 222 chromatin profiles from 69 samples (33 colorectal adenocarcinomas, 4 adenomas, 21 matched normal tissues and 11 colon cancer cell lines) for six histone modification marks: H3K4me3 for Pol II-bound and CpG-rich promoters, H3K4me1 for poised enhancers, H3K27ac for enhancers and transcriptionally active promoters, H3K79me2 for transcribed regions, H3K27me3 for polycomb repressed regions and H3K9me3 for heterochromatin.

      RESULTS: We demonstrate that H3K27ac-marked active enhancer state could distinguish between different stages of CRC progression. By epigenomic editing, we present evidence that gains of tumour-specific enhancers for crucial oncogenes, such as ASCL2 and FZD10, was required for excessive proliferation. Consistently, combination of MEK plus bromodomain inhibition was found to have synergistic effects in CRC patient-derived xenograft models. Probing intertumour heterogeneity, we identified four distinct enhancer subtypes (EPIgenome-based Classification, EpiC), three of which correlate well with previously defined transcriptomic subtypes (consensus molecular subtypes, CMSs). Importantly, CMS2 can be divided into two EpiC subgroups with significant survival differences. Leveraging such correlation, we devised a combinatorial therapeutic strategy of enhancer-blocking bromodomain inhibitors with pathway-specific inhibitors (PARPi, EGFRi, TGFβi, mTORi and SRCi) for EpiC groups.

      CONCLUSION: Our data suggest that the dynamics of active enhancer underlies CRC progression and the patient-specific enhancer patterns can be leveraged for precision combination therapy.

      PMID:34059508 | PMC:PMC8745382 | DOI:10.1136/gutjnl-2020-322835

      View details for PubMedID 34059508

Contact Information