Biology subjects

Heer, C.

Publications and source records attributed to Heer, C..

3 recordsLinked to original sources

bioRxiv2026

Biomarker-Targeted O6-Guanine Alkylation Potentiates ATR Inhibitor Response in De Novo and Relapsed/Refractory AML

Acute myeloid leukemia (AML) remains limited by high relapse rates and a scarcity of biomarker-directed therapies, underscoring the need to identify actionable vulnerabilities and mechanisms of therapeutic resistance. O6-methylguanine-DNA methyltransferase (MGMT), a DNA repair enzyme that directly reverses mutagenic O6-alkylguanine lesions, is epigenetically silenced in multiple cancers. Although MGMT silencing is predictive of temozolomide (TMZ) response in glioblastoma with significant survival advantage, prior clinical trials of TMZ in AML have shown only modest responses. Therefore, the prevalence and therapeutic relevance of MGMT silencing, as well as genetic factors that modify its therapeutic response in AML, remain to be comprehensively investigated. Here, we first profiled MGMT status across a diverse cohort of 23 de novo and 16 relapsed/refractory (R/R) primary AMLs using an integrated analysis of MGMT mRNA expression, promoter methylation, and protein expression. We found that approximately 25-30% of AMLs harbor MGMT silencing, in contrast to consistent MGMT expression in healthy CD34+ hematopoietic stem and progenitor cells. We further identified frequent loss of mismatch repair (MMR) proteins in these AML cohorts, a known resistance mechanism against TMZ in glioblastoma. Using CRISPR knockout screening and genetically engineered AML models, we found that MMR loss also drives both upfront and acquired TMZ resistance in MGMT-silenced AML. These findings identify MMR deficiency as an important and previously underappreciated genetic contributor to the modest responses observed in prior trials of TMZ in AML. To therapeutically exploit MGMT silencing while bypassing genetic determinants of resistance, including MMR deficiency, we evaluated clinically and preclinically characterized MGMT-dependent DNA-alkylating agents and identified a fluoroethylating analog of TMZ, N3-(2-fluoroethyl) imidazotetrazine (KL50), with pronounced and selective activity in MGMT-silenced AML. KL50 retained antileukemic activity irrespective of MMR status, significantly prolonging survival in humanized MISTRG6 mice harboring primary AML patient-derived xenografts. Mechanistically, KL50 induced DNA damage through the time-dependent formation of interstrand DNA crosslinks, bypassing MMR dependence and triggering a replication stress response dominated by ATR signaling. Pharmacologic ATR inhibition synergized with KL50, producing marked antileukemic activity and significantly extending survival across AML models without compromising hematologic safety. Together, these findings establish MGMT silencing as a prevalent and therapeutically actionable biomarker in AML, define MMR status as a key determinant of TMZ response in AML but not KL50 sensitivity, and provide a translational rationale for combining low-dose O6-fluoroethylating imidazotetrazines with ATR inhibitors to target both de novo and R/R AML across diverse genetic backgrounds.

cancer biology↗

bioRxiv2020

Cocaine causes rapid remodeling of dopaminergic axons, synapses, and mitochondria

Dopaminergic (DA) neurons exert profound influences on behavior including addiction. However, how DA axons communicate with target neurons and how those communications change, for example, with drug exposure, remains poorly understood. We combine recent advances in cell type specific labeling for electron microscopy with large volume three-dimensional serial electron microscopy - connectomics- to detail DA connections in the Nucleus Accumbens (NAc) across multiple animals and after exposure to cocaine. We find that DA axonal varicosities are of four general types: 38% are empty, 25% contain few small ([~]50 nm diameter) vesicles, 19% contain few large ([~]133 nm diameter) vesicles, and 18% have mixed small and large vesicles, suggesting that DA axons may use multiple types of neurotransmitters. Individual DA axons were significantly more likely to contain multiple varicosities of the same type relative to chance, suggesting a new method of DA axon classification. Across all categories, we find only rare examples (<2%, 6/410) of varicosities making specific synapses with any neighboring neuron with the few examples being made exclusively on the shafts and soma of resident NAc neurons. Instead, we find much more frequently (15%) that DA varicosities form spinule-like structures: physical membrane interdigitations with nearby dendrites or excitatory and inhibitory axons. Days after a brief exposure to cocaine, DA axons were extensively branched relative to controls but with similar densities of varicosities and spinules. Additionally, cocaine exposure results in the formation of blind-ended "bulbs" in DA axons, filled with mitochondria, and reminiscent of axonal retraction in the developing and damaged brain. Every bulb was surrounded by elaborated glia further suggestive of active remodeling. Finally, mitochondrial lengths increased by [~]2.2 times relative to control throughout DA axons and NAc spiny dendrites after cocaine exposure but not in DA soma or DA dendrites. We conclude that DA axonal transmission is unlikely to be mediated via classical synapses in the NAc and that the major locus of anatomical plasticity of DA circuits after exposure to cocaine are large scale axonal rearrangements with correlated changes in mitochondria.

neuroscience↗

bioRxiv2020

The superoxide dismutase mimetic GC4419 enhances tumor killing when combined with stereotactic ablative radiation

The penta-aza macrocyclic manganese compound GC4419 is in phase 3 clinical trials as a modifier of mucositis in H&N cancer treated by radio-chemotherapy based upon its properties as a superoxide dismutase mimetic. In studies to address the potential for tumor radioprotection, a significant anti-tumor effect was identified in tumors generated from the non-small cell lung cancer (NSCLC) cell line H1299, when GC4419 was combined with radiation. This effect was directly related to the size of the radiation dose as demonstrated by greater efficacy in tumor growth delay when biologically equivalent irradiation regimens using a limited number of dose fractions was substantially more effective compared to regimens where the fraction number was higher and dose per fraction decreased. Furthermore, a TCD50 assay using H1299 tumors that tested the combination of GC4419 with radiation revealed a Dose Enhancement Factor of 1.67. Based upon these results the hypothesis that GC4419 was generating cytotoxic levels of hydrogen peroxide during the superoxide dismutation process. Peroxide flux did increase in cells exposed to GC4419 as did the expression of the oxidative stress markers 4-HNE and 3-NT. H1299 cells that overexpressed catalase were then challenged as tumors by the combination of radiation and GC4419 and the tumoricidal effect was nearly eliminated. The enhanced radiation response was not specific to NSCLC as similar findings were observed in human head and neck squamous cell carcinoma and pancreatic ductal adenocarcinoma xenografts. RNA sequencing analysis revealed that GC4419, in addition to generating high levels of hydrogen peroxide in irradiated cells, alters inflammatory and differentiation signaling in the tumor following irradiation. Together, these findings provide abundant evidence that the radioprotector GC4419 has dual functionality and will increase tumor response rates when combined with agents that generate high levels of superoxide like stereotactic ablative body radiotherapy (SAbR). Combining SAbR with GC4419 may be an effective strategy to enhance tumor response in general but may also allow for fully potent radiation doses to tumors that might not necessarily be able to tolerate such doses. The potential for protection of organs at risk may also be exploitable.

cancer biology↗