Mistiming Death: Modeling the Time-Domain Variability of Tumor Apoptosis and Implications for Molecular Imaging of Cell Death

Advancing the understanding of the role of apoptosis in lung cancer immunotherapy: Global research trends, key themes, and emerging frontiers

Apoptosis is vital for improving the efficacy of lung cancer (LC) immunotherapy by targeting cancer cell elimination. Despite its importance, there is a lack of comprehensive bibliometric studies analyzing global research on apoptosis in LC immunotherapy. This analysis aims to address this gap by highlighting key trends, contributors, and future directions. A total of 969 publications from 1996 to 2024 were extracted from the Web of Science Core Collection. Analysis was conducted using VOSviewer, CiteSpace, and the R package 'bibliometrix.' The study included contributions from 6,894 researchers across 1,469 institutions in 61 countries, with research published in 356 journals. The volume of publications has steadily increased, led by China and the United States, with Sichuan University as the top contributor. The journal Cancers published the most articles, while Cancer Research had the highest co-citations. Yu-Quan Wei was the leading author, and Jemal, A. was the most frequently co-cited. Key research themes include "cell death mechanisms," "immune regulation," "combination therapies," "gene and nanomedicine applications," and "traditional Chinese medicine (TCM)." Future research is likely to focus on "coordinated regulation of multiple cell death pathways," "modulation of the tumor immune microenvironment," "optimization of combination therapies," "novel strategies in gene regulation," and the "integration of TCM" for personalized treatment. This is the first bibliometric analysis on the role of apoptosis in LC immunotherapy, providing an landscape of global research patterns and emerging therapeutic strategies. The findings offer insights to guide future research and optimize treatment approaches.

Can the Discovery of High-Impact Diagnostics Be Improved by Matching the Sampling Rate of Clinical Diagnostics to the Frequency Domain of Diagnostic Information?

Over the past 30 years, academic and industrial research investigators have developed molecular reporters to visualize cell death in complex biological systems. In parallel, clinical researchers, chemists, biochemists, and molecular biologists have endeavored to translate these molecular tools into clinical imaging agents. Despite these efforts, there are no clinically approved imaging methodologies with which to image cell death consistently and quantitatively. One reason may reside in the intrinsic mismatch between the sampling frequency of translational molecular imaging and the biochemical kinetics that define cell death. Beyond cell death imaging, many active research programs are now attempting to create translational diagnostic pharmaceuticals to image immunological, fibrotic, amyloidotic, and metabolic pathways. Each of these pathways is defined by a unique set of biochemical rate constants, some of which are associated with key predictive pathways. Exhaustively sampling all permutations of pathways and kinetic constants would seem to be an intractable strategy for target identification and validation. Sampling theory, if applied to these pathways, could accelerate the translation of high-impact diagnostics through prioritization of pathways for either AI enhanced diagnostic imaging or AI-enhanced wearable devices. In this perspective, we identify the Nyquist sampling rate as a key criterion for evaluating the optimal application for novel diagnostics. Sampling theory states that to fully characterize a band-limited, stationary, temporal data set, the signal must be sampled at more than twice the rate of the fastest frequency in the signal or, for diagnostics, the discriminatory signal. Through the study of the medical imaging process chain, Nyquist sampling rates of 0.25 day-1 and, more likely, slower than 0.02 day-1 were determined to provide high quality information. By prioritizing low-frequency predictive processes, or "state changes,", imaging researchers may improve the "hit rate" of research programs by appropriately matching the rate of change in diagnostic and predictive information with the limiting sampling rate of medical imaging. Critically, however, high-frequency diagnostic information (and therefore high-frequency biological processes) need not be ignored; these processes are simply better interrogated through continuous monitoring, e.g., by wearable devices combined with machine learning or artificial intelligence.

Is System xc- a Suitable Target for Tumour Detection and Response Assessment with Imaging?

System xc- is upregulated in cancer cells and can be imaged using novel radiotracers, most commonly with (4S)-4-(3-[18F]fluoropropyl)-L-glutamic acid (18F-FSPG). The aim of this review was to summarise the use of 18F-FSPG in humans, explore the benefits and limitations of 18F-FSPG, and assess the potential for further use of 18F-FSPG in cancer patients. To date, ten papers have described the use of 18F-FSPG in human cancers. These studies involved small numbers of patients (range 1-26) and assessed the use of 18F-FSPG as a general oncological diagnostic agent across different cancer types. These clinical trials were contrasting in their findings, limiting the scope of 18F-FSPG PET/CT as a purely diagnostic agent, primarily due to heterogeneity of 18F-FSPG retention both between cancer types and patients. Despite these limitations, a potential further application for 18F-FSPG is in the assessment of early treatment response and prediction of treatment resistance. Animal models of cancer have shown that changes in 18F-FSPG retention following effective therapy precede glycolytic changes, as indicated by 18F-FDG, and changes in tumour volume, as measured by CT. If these results could be replicated in human clinical trials, imaging with 18F-FSPG PET/CT would offer an exciting route towards addressing the currently unmet clinical needs of treatment resistance prediction and early imaging assessment of therapy response.

A first-in-human study of [68Ga]Ga-CDI: a positron emitting radiopharmaceutical for imaging tumour cell death

PURPOSE

This study assesses human biodistribution, radiation dosimetry, safety and tumour uptake of cell death indicator labelled with ⁶⁸Ga ([⁶⁸Ga]Ga-CDI), a novel radiopharmaceutical that can image multiple forms of cell death.

METHODS

Five participants with at least one extracranial site of solid malignancy > 2 cm and no active cancer treatment in the 8 weeks prior to the study were enrolled. Participants were administered 205 ± 4.1 MBq (range, 200-211 MBq) of [⁶⁸Ga]Ga-CDI and 8 serial PET scans acquired: the first commencing immediately and the last 3 h later. Participants were monitored for clinical, laboratory and electrocardiographic side effects and adverse events. Urine and blood radioactivity was measured. Spherical volumes of interest were drawn over tumour, blood pool and organs to determine biodistribution and calculate dosimetry. In one participant, tumour specimens were analysed for cell death using terminal deoxynucleotidyl transferase dUTP nick end labelling (TUNEL) staining.

RESULTS

[⁶⁸Ga]Ga-CDI is safe and well-tolerated with no side effects or adverse events. [⁶⁸Ga]Ga-CDI is renally excreted, demonstrates low levels of physiologic uptake in the other organs and has excellent imaging characteristics. The mean effective dose was 2.17E - 02 ± 4.61E - 03 mSv/MBq. It images constitutive tumour cell death and correlates with tumour cell death on histology.

CONCLUSION

[⁶⁸Ga]Ga-CDI is a novel cell death imaging radiopharmaceutical that is safe, has low radiation dosimetry and excellent biodistribution and imaging characteristics. It has potential advantages over previously investigated radiopharmaceuticals for imaging of cell death and has progressed to a proof-of-concept trial.

TRIAL REGISTRATION

ACTRN12621000641897 (28/5/2021, retrospectively registered).

Latest Advances in Imaging Oxidative Stress in Cancer

Oxidative stress is the imbalance of harmful reactive oxygen species (ROS) and the action of neutralizing antioxidant mechanisms. If left unchecked, the deleterious effects of oxidative stress result in damage to DNA, proteins, and membranes, ultimately leading to cell death. Tumors are highly proliferative and consequently generate high levels of mitochondrial ROS. To compensate for this and maintain redox homeostasis, cancer cells upregulate protective antioxidant pathways, which are further amplified in drug-resistant tumors. This review provides an overview of the latest molecular imaging techniques designed to image oxidative stress in cancer. New probes can now assess heterogeneous ROS and antioxidant production within tumors and across lesions. Together, the noninvasive imaging of these dynamic processes holds great promise for monitoring response to treatment and predicting drug resistance and may provide insight into the metastatic potential of tumors.

Molecular Imaging of Apoptosis: The Case of Caspase-3 Radiotracers

The molecular imaging of apoptosis remains an important method for the diagnosis and monitoring of the progression of certain diseases and the evaluation of the efficacy of anticancer apoptosis-inducing therapies. Among the multiple biomarkers involved in apoptosis, activated caspase-3 is an attractive target, as it is the most abundant of the executioner caspases. Nuclear imaging is a good candidate, as it combines a high depth of tissue penetration and high sensitivity, features necessary to detect small changes in levels of apoptosis. However, designing a caspase-3 radiotracer comes with challenges, such as selectivity, cell permeability and transient caspase-3 activation. In this review, we discuss the different caspase-3 radiotracers for the imaging of apoptosis together with the challenges of the translation of various apoptosis-imaging strategies in clinical trials.

Development of [18F]ICMT-11 for Imaging Caspase-3/7 Activity during Therapy-Induced Apoptosis

Insufficient apoptosis is a recognised hallmark of cancer. A strategy to quantitatively measure apoptosis in vivo would be of immense value in both drug discovery and routine patient management. The first irreversible step in the apoptosis cascade is activation of the "executioner" caspase-3 enzyme to commence cleavage of key structural proteins. One strategy to measure caspase-3 activity is Positron Emission Tomography using isatin-5-sulfonamide radiotracers. One such radiotracer is [18F]ICMT-11, which has progressed to clinical application. This review summarises the design and development process for [18F]ICMT-11, suggesting potential avenues for further innovation.