²²⁵Ac-based radiopharmaceuticals for targeted alpha therapy (TAT) have shown positive outcomes in recent clinical trials and pre-clinical studies, and it has emerged as a promising solution for future cancer treatments. Small-animal in-vivo imaging is critical to better understand ²²⁵Ac radiopharmaceuticals biokinetics and to accelerate evaluation and discovery of new ²²⁵Ac radiopharmaceuticals. However, gamma-ray imaging of ²²⁵Ac and its daughters is challenging due to the extremely low injected activities, the low branching ratios of the emitted γ rays, and their broad range of energies. State-of-the-art scanners for single-photon emission computed tomography (SPECT) have sensitivity limitations when imaging such low activities, and imaging sessions of several hours are necessary, precluding in-vivo studies. We propose Compton imaging as an alternative to traditional SPECT imagers in order to enable a higher sensitivity and to decrease the minimum imageable activities of current systems. In this study, we explore a 3D-positioning cadmium zinc telluride (CZT) camera (M400, H3D) to achieve highly sensitive Compton imaging of ²²⁵Ac daughters at both high-energy (440 keV from ²¹³Bi) and low-energy gamma rays (²¹⁸ keV from ²²¹Fr). The Compton sensitivity of the imaging system with a source as close as possible from the detector (7 mm) were 1014(33) cps/MBq and 467(23) cps/MBq for ²¹³Bi and ²²¹Fr, respectively. We studied the response of the camera using ²²⁵Ac point sources, including the demonstration of simultaneous imaging of ²¹³Bi and ²²¹Fr from multiple ²²⁵Ac sources at sub-μCi activity levels, ranging from 7.4 kBq to 25.9 kBq, in a 18-minute imaging session. Furthermore, we performed a mouse phantom experiment to demonstrate that we could form high-sensitive Compton images of ²¹³Bi and ²²¹Fr, concluding that we can image a mouse phantom with an activity of ~ 0.55 MBq in just 9 and 36 seconds for ²¹³Bi and ²²¹Fr, respectively, with a single detector head and in a single bed position. This is equivalent to imaging an activity of 3.7 kBq, a typical tumor uptake in mouse experiments with ²²⁵Ac, in 23 minutes for ²¹³Bi and 90 minutes for ²²¹Fr with a small 5.7 cm × 5.7 cm area prototype. Increasing angular coverage would further increase sensitivity. Finally, we also compared Compton imaging with collimated imaging.

Unbiased shRNA library screens revealed that the estrogen receptor-1 (ESR-1) is a key factor regulating HIV-1 latency. In both Jurkat T cells and a Th17 primary cell model for HIV-1 latency, selective estrogen receptor modulators (SERMs, i.e., fulvestrant, raloxifene, and tamoxifen) are weak proviral activators and sensitize cells to latency-reversing agents (LRAs) including low doses of TNF-α (an NF-κB inducer), the histone deacetylase inhibitor vorinostat (soruberoylanilide hydroxamic acid, SAHA), and IL-15. To probe the physiologic relevance of these observations, leukapheresis samples from a cohort of 12 well-matched reproductive-age women and men on fully suppressive antiretroviral therapy were evaluated by an assay measuring the production of spliced envelope (env) mRNA (the EDITS assay) by next-generation sequencing. The cells were activated by T cell receptor (TCR) stimulation, IL-15, or SAHA in the presence of either β-estradiol or an SERM. β-Estradiol potently inhibited TCR activation of HIV-1 transcription, while SERMs enhanced the activity of most LRAs. Although both sexes responded to SERMs and β-estradiol, females showed much higher levels of inhibition in response to the hormone and higher reactivity in response to ESR-1 modulators than males. Importantly, the total inducible RNA reservoir, as measured by the EDITS assay, was significantly smaller in the women than in the men. We conclude that concurrent exposure to estrogen is likely to limit the efficacy of viral emergence from latency and that ESR-1 is a pharmacologically attractive target that can be exploited in the design of therapeutic strategies for latency reversal.