Although well-differentiated thyroid carcinoma (WDTC) is characterized by a robust treatment response, aggressive subtypes, such as anaplastic thyroid carcinoma (ATC), remain highly lethal. To understand thyroid cancer evolution in both children and adults, we analyzed single-cell transcriptomes of 423,733 cells from 81 samples and spatially resolved key tumor and microenvironment populations across 28 tumors with spatial transcriptomics, including rare and unique composite WDTC/ATC tumors and pediatric diffuse sclerosing thyroid carcinomas. Additionally, we identified gene signatures of stromal cell populations in 5 large thyroid cancer bulk RNA-sequencing cohorts. Through this multi-institutional effort, we defined a population of POSTN ⁺ myofibroblast cancer-associated fibroblasts (myCAFs) that are intimately associated with invasive tumor cells and correlate with poor prognosis, lymph node metastasis, and disease progression in thyroid carcinoma. We also revealed a population of inflammatory CAFs that are distant to tumor cells and are found in the inflammatory stromal microenvironment of autoimmune thyroiditis. Together, our study provides spatial profiling of thyroid cancer evolution in samples with mixed WDTC/ATC histopathology and identifies a prognostic myCAF subtype with potential clinical utility in predicting aggressive disease in both children and adults.

Tenofovir disoproxil fumarate (TDF) and islatravir (ISL, 4′-ethynyl-2-fluoro-2′-deoxyadensine, or MK-8591) are highly potent nucleoside reverse transcriptase inhibitors. Resistance to TDF and ISL is conferred by K65R and M184V, respectively. Furthermore, K65R and M184V increase sensitivity to ISL and TDF, respectively. Therefore, these two nucleoside analogs have opposing resistance profiles and could present a high genetic barrier to resistance. To explore resistance to TDF and ISL in combination, we performed passaging experiments with HIV-1 WT, K65R, or M184V in the presence of ISL and TDF. We identified K65R, M184V, and S68G/N mutations. The mutant most resistant to ISL was S68N/M184V, yet it remained susceptible to TDF. To further confirm our cellular findings, we implemented an endogenous reverse transcriptase assay to verify in vitro potency. To better understand the impact of these resistance mutations in the context of global infection, we determined potency of ISL and TDF against HIV subtypes A, B, C, D, and circulating recombinant forms (CRF) 01_AE and 02_AG with and without resistance mutations. In all isolates studied, we found K65R imparted hypersensitivity to ISL whereas M184V conferred resistance. We demonstrated that the S68G polymorphism can enhance fitness of drug-resistant mutants in some genetic backgrounds. Collectively, the data suggest that the opposing resistance profiles of ISL and TDF suggest that a combination of the two drugs could be a promising drug regimen for the treatment of patients infected with any HIV-1 subtype, including those who have failed 3TC/FTC-based therapies.

Colorectal cancer (CRC) is one of the most diagnosed cancers and a leading contributor to cancer-related deaths in the United States. Clinically, standard treatment regimens include surgery, radiation, and chemotherapy; however, there has been increasing development and clinical use of targeted therapies for CRC. Unfortunately, many patients develop resistance to these treatments. Cetuximab, the first targeted therapy approved to treat advanced CRC, is a monoclonal antibody that targets the epidermal growth factor receptor and inhibits downstream pathway activation to restrict tumor cell growth and proliferation. CRC resistance to cetuximab has been well studied, and common resistance mechanisms include constitutive signal transduction through downstream protein mutations and promotion of the epithelial-to-mesenchymal transition. While the most common resistance mechanisms are known, a proportion of patients develop resistance through unknown mechanisms. One protein predicted to contribute to therapy resistance is RAC1, a small GTPase that is involved in cytoskeleton rearrangement, cell migration, motility, and proliferation. RAC1 has also been shown to be overexpressed in CRC. Despite evidence that RAC1 and its alternative splice isoform RAC1B play important roles in CRC and the pathways known to contribute to cetuximab resistance, there is a need to directly study the relationship between RAC1 and RAC1B and cetuximab resistance. This review highlights the recent studies investigating RAC1 and RAC1B in the context of CRC and suggests that these proteins could play a role in resistance to cetuximab.