Biology subjects

Carter, L. M.

Publications and source records attributed to Carter, L. M..

5 recordsLinked to original sources

bioRxiv2026

Heterochromatin protein 1α acts as an essential stabilizer of chromatin packing domains

Background: The spatial organization of the human genome emerges from an enzyme-guided self-assembly process in which chromatin has a bidirectional relationship with transcription. Central to this architecture are chromatin packing domains, 50-200 nm structures exhibiting mass-scaling behavior. Nascent domains arise through transcription and cohesin/CTCF-mediated loop extrusion, while their maturation depends on conditions that permit differential access of epigenetic enzymes to their dense cores and continuously lower density periphery, resulting in the accumulation of heterochromatic marks in domain cores and euchromatic marks outside of the domain cores. In turn, packing domains support transcription by creating an "ideal zone" peripherally to their cores due to a nonmonotonic dependence of transcription rate on local chromatin density. Results: We investigated the role of heterochromatin protein 1 alpha (HP1), a key chromatin crosslinking factor with affinity to H3K9me3 marks, in maintaining packing domain organization. Paradoxically, short-term HP1 degradation resulted in overall downregulation of genes, contrasting with the canonical view that repression of heterochromatin allows chromatin to become more accessible for transcription. While some packing domains persisted, heterochromatic cores of dense packing domains were disrupted. When exposed to hypoxia, HP1-depleted cells exhibited a dampened transcriptional response, showcasing that when domain maturation is disrupted, stress response pathways are not effectively activated. Conclusions: This work highlights HP1 crosslinking as an essential component of domain maturation, as HP1 loss disrupts domain geometry and inhibits efficient transcriptional reprogramming. Our findings suggest an intriguing perspective on the potential relationship between chromatin architecture and gene regulation that could inform chromatin engineering-based treatments.

genomics↗

bioRxiv2024

Targeted Alpha Therapy with Ac-Macropa-Isatuximab for CD38-positive Hematological Malignancies

BackgroundHematological malignancies include diverse cancers related to immune system cells and blood-forming tissue. Treatment resistance and relapse are common despite the introduction of novel therapeutics. Following the development of the PET probe [89Zr]Zr-DFO-isatuximab, targeting the overexpressed CD38 receptor, we developed [225Ac]Ac-Macropa-isatuximab for targeted alpha therapy in murine models of human multiple myeloma (MM) and lymphoma. MethodsIn vitro studies were performed using the CD38 expressing MM1.S (human MM) and Daudi (human lymphoma). Radiopharmaceutical therapy studies were performed in female NSG mice, and the disseminated disease models were established by intravenous injection of luciferase-transfected cells. Mice were randomized (n = 10 mice per cohort) and received a high activity (5.5 kBq) or low activity (2.7 kBq) of [225Ac]Ac-Macropa-Isatuximab in single or multiple cycles. Controls receiving untargeted [225Ac]Ac-Macropa-IgG or saline were included. Tumor burden was measured by bioluminescence imaging (BLI). Weight loss greater than 20% or leg paralysis were used as endpoints. Results[225Ac]Ac-Macropa-Isatuximab was obtained with high radiochemical yield and purity (>95%). It displayed high immunoreactivity and excellent stability in human serum over 10 days. The therapeutic effect of [225Ac]Ac-mcp-Isatuximab was significant for all the treatment cohorts compared to the saline control after administration of the first cycle. Low activities were better tolerated in general, resulting in extended median survivals. The most successful regimen in the MM model was the dual cycle of low activity, with a median survival of 60 days (P < 0.001). In the lymphoma model, the single high activity of 5.5 kBq and four low activity of 2.7 kBq resulted in similar median survivals of 143 days (P < 0.0001) and 147 days (P < 0.0001). These regimens resulted in complete responses with no detectable cancer cells in some cases. Remarkably, no significant kidney damage was observed in any of the models. Conclusion[225Ac]Ac-Macropa-Isatuximab selectively targets CD38, reducing tumor growth and, in some cases, tumor eradication, especially when applied in multiple cycles. Importantly, it has not been associated with significant toxicities at levels of administered activity required for therapeutic benefit, indicating its promise as a therapeutic option.

pharmacology and toxicology↗

bioRxiv2024

mRNA expression is co-regulated by non-nucleolar RNA polymerase I

The relationship between gene transcription and chromatin organization is an area of active study. Due to its role in mRNA synthesis, many studies have focused on the regulaton of RNA polymerase II (Pol-II) function by supranucleosomal structure and vice-versa. In contrast, there is little work on the function of RNA polymerase I (Pol-I) in non-nucleolar chromatin. Prior work has shown that Pol-I engages with components of Pol-II on rDNA, but its role in global transcription and chromatin structure beyond the nucleolus has largely been ignored. By pairing auxin-inducible degron technology with nanoscopic imaging, RNA-Seq, and Hi-C, we found that Pol-I and Pol-II co-regulate conformationally defined chromatin domains and mRNA synthesis. Mechanistically, Pol-I maintains the positioning of intronic and intergenic chromatin within domains for the proper expression of exon elements. Consequently, Pol-I loss disrupts genome connectivity, in situ chromatin domains, and the expression of mRNA, genome-wide.

genomics↗

bioRxiv2024

Chromatin packing domains persist after RAD21 depletion in 3D.

Understanding chromatin organization requires integrating measurements of genome connectivity and physical structure. Prior work demonstrates that RAD21 depletion results in the complete loss of topologically associated and loop domains on Hi-C, but the corresponding change in physical structure has not been studied using electron microscopy. Pairing chromatin scanning transmission electron tomography with Hi-C, we study the role of cohesin in regulating the spatially resolved, conformationally defined chromatin packing domains. We find that only 20% of packing domains are lost on electron microscopy upon RAD21 depletion with the effect primarily on small, poorly packed (nascent) domains. Overall, this contrasts with the prevailing understanding of genome regulation, indicating that while cohesin influences domain formation, non-cohesin mediated mechanisms predominantly regulate the 3D genomic physical structure.

genomics↗

bioRxiv2019

Targeted brain tumor radiotherapy using an Auger emitter

Glioblastoma multiforme is a highly aggressive form of brain cancer whose location, tendency to infiltrate healthy surrounding tissue, and heterogeneity significantly limit survival, with scant progress having been made in recent decades. 123I-MAPi (Iodine-123 Meitner-Auger PARP1 inhibitor) is a precise therapeutic tool composed of a PARP1 inhibitor radiolabeled with an Auger- and gamma-emitting iodine isotope. Here, the PARP inhibitor, which binds to the DNA repair enzyme PARP1, specifically targets cancer cells, sparing healthy tissue, and carries a radioactive payload within reach of the cancer cells DNA. The high relative biological efficacy of Auger electrons within their short range of action is leveraged to inflict DNA damage and cell death with high precision. The gamma ray emission of 123I-MAPi allows for the imaging of tumor progression and therapy response, and for patient dosimetry calculation. Here we demonstrated the efficacy and specificity of this small molecule radiotheranostic in a complex preclinical model. In vitro and in vivo studies demonstrate high tumor uptake and a prolonged survival in mice treated with 123I-MAPi when compared to vehicle controls. Different methods of drug delivery were investigated to develop this technology for clinical applications, including convection enhanced delivery (CED) and intrathecal injection. Taken together, these results represent the first full characterization of an Auger-emitting PARP inhibitor, demonstrate a survival benefit in mouse models of GBM, and confirm the high potential of 123I-MAPi for clinical translation.\n\nOne Sentence SummaryA novel PARP1-targeted Auger radiotherapeutic shows translational potential as a theranostic tool for imaging and killing cancer cells, resulting in tumor delineation and prolonged survival in a glioblastoma model.

cancer biology↗