Prostate-specific membrane antigen (PSMA)-targeted radionuclide therapy (RNT) may increase tumor immunogenicity. We aimed at exploiting this effect by combining RNT with immunotherapy in a mouse model of prostate cancer (PC). Methods: C57BL/6-mice bearing syngeneic RM1-PGLS tumors were treated with 225 Ac-PSMA617, an anti-PD-1 antibody, or both. Therapeutic efficacy was assessed by tumor volume measurements (CT), time to progression (TTP), and survival. Results: PSMA RNT or anti-PD-1 alone tended to prolong TTP (isotype control, 25 d; anti-PD-1, 33.5 d [P 5 0.0153]; RNT, 30 d [P 5 0.1038]) and survival (control, 28 d; anti-PD-1, 37 d [P 5 0.0098]; RNT, 32 d [P 5 0.1018]). Combining PSMA RNT and anti-PD-1 significantly improved disease control compared with either monotherapy. TTP was extended to 47.5 d (P # 0.0199 vs. monotherapies), and survival to 51.5 d (P # 0.0251 vs. monotherapies). Conclusion: PSMA RNT and PD-1 blockade synergistically improve therapeutic outcomes in our PC model, supporting the evaluation of RNT and immunotherapy combinations for PC patients.

In sickle cell disease (SCD), very late antigen-4 (VLA-4 or integrin α4β1) mediates the adhesion of reticulocytes to inflamed, proinflammatory endothelium, a key process in promoting vaso-occlusive episodes (VOEs). We hypothesized that a radionuclide tracer targeting VLA-4 could be harnessed as a positron emission tomography (PET) imaging biomarker of VOEs. We tested the VLA-4 peptidomimetic PET tracer 64Cu-CB-TE1A1P-PEG4-LLP2A (64Cu-LLP2A) for imaging hyper-adhesion–associated VOEs in the SCD Townes mouse model. With lipopolysaccharide (LPS)-induced VOEs, 64Cu-LLP2A uptake was increased in the bone marrow of the humeri and femurs, common sites of VOEs in SCD mice compared with non-SCD mice. Treatment with a proven inhibitor of VOEs (the anti-mouse anti-P-selectin monoclonal antibody [mAb] RB40.34) during LPS stimulation led to a reduction in the uptake of 64Cu-LLP2A in the humeri and femurs to baseline levels, implying blockade of VOE hyper-adhesion. Flow cytometry with Cy3-LLP2A demonstrated an increased percentage of VLA-4–positive reticulocytes in SCD vs non-SCD mice in the bone and peripheral blood after treatment with LPS, which was abrogated by anti-P-selectin mAb treatment. These data, for the first time, show in vivo imaging of VLA-4–mediated hyper-adhesion, primarily of SCD reticulocytes, during VOEs. PET imaging with 64Cu-LLP2A may serve as a valuable, noninvasive method for identifying sites of vaso-occlusion and may provide an objective biomarker of disease severity and anti-P-selectin treatment efficacy in patients with SCD.

Bone is the most preferred site for colonization of metastatic breast cancer cells for each subtype of the disease. The standard of therapeutic care for breast cancer patients with bone metastasis includes bisphosphonates (e.g., zoledronic acid), which have poor oral bioavailability, and a humanized antibody (denosumab). However, these therapies are palliative, and a subset of patients still develop new bone lesions and/or experience serious adverse effects. Therefore, a safe and orally bioavailable intervention for therapy of osteolytic bone resorption is still a clinically unmet need. This study demonstrates suppression of breast cancer-induced bone resorption by a small molecule (sulforaphane, SFN) that is safe clinically and orally bioavailable. In vitro osteoclast differentiation was inhibited in a dosedependent manner upon addition of conditioned media from SFN-treated breast cancer cells representative of different sub-types. Targeted microarrays coupled with interrogation of The Cancer Genome Atlas data set revealed a novel SFN-regulated gene signature involving cross-regulation of runt-related transcription factor 2 (RUNX2) and nuclear factor-kB and their downstream effectors. Both RUNX2 and p65/p50 expression were higher in human breast cancer tissues compared with normal mammary tissues. RUNX2 was recruited at the promotor of NFKB1. Inhibition of osteoclast differentiation by SFN was augmented by doxycycline-inducible stable knockdown of RUNX2. Oral SFN administration significantly increased the percentage of bone volume/total volume of affected bones in the intracardiac MDA-MB-231-Luc model indicating in vivo suppression of osteolytic bone resorption by SFN. These results indicate that SFN is a novel inhibitor of breast cancer-induced osteolytic bone resorption in vitro and in vivo.

Neutrophilic inflammation correlates with severe tuberculosis (TB), a disease caused by Mycobacterium tuberculosis (Mtb). Granulomas are lesions that form in TB, and a PET probe for following neutrophil recruitment to granulomas could predict disease progression. We tested the formyl peptide receptor 1 (FPR1)-targeting peptide FLFLF in Mtb-infected macaques. Preliminary studies in mice demonstrated specificity for neutrophils. In macaques, 64Cu-FLFLF was retained in lung granulomas and analysis of lung granulomas identified positive correlations between 64Cu-FLFLF and neutrophil and macrophage numbers (R2 = 0.8681 and 0.7643, respectively), and weaker correlations for T cells and B cells (R2 = 0.5744 and 0.5908, respectively), suggesting that multiple cell types drive 64Cu-FLFLF avidity. By PET/CT imaging, we found that granulomas retained 64Cu-FLFLF but with less avidity than the glucose analog 18F-FDG. These studies suggest that neutrophil-specific probes have potential PET/CT applications in TB, but important issues need to be addressed before they can be used in nonhuman primates and humans.

Background PSMA-TO-1 (“Tumor-Optimized-1”) is a novel PSMA ligand with longer circulation time than PSMA-617. We compared the biodistribution in subcutaneous tumor-bearing mice of PSMA-TO-1, PSMA-617 and PSMA-11 when labeled with 68Ga and 177Lu, and the survival after treatment with 225Ac-PSMA-TO-1/-617 in a murine model of disseminated prostate cancer. We also report dosimetry data of 177Lu-PSMA-TO1/-617 in prostate cancer patients. Methods First, PET images of 68Ga-PSMA-TO-1/-617/-11 were acquired on consecutive days in three mice bearing subcutaneous C4-2 xenografts. Second, 50 subcutaneous tumor-bearing mice received either 30 MBq of 177Lu-PSMA-617 or 177Lu-PSMA-TO-1 and were sacrificed at 1, 4, 24, 48 and 168 h for ex vivo gamma counting and biodistribution. Third, mice bearing disseminated lesions via intracardiac inoculation were treated with either 40 kBq of 225Ac-PSMA-617, 225Ac-PSMA-TO-1, or remained untreated and followed for survival. Additionally, 3 metastatic castration-resistant prostate cancer patients received 500 MBq of 177Lu-PSMA-TO-1 under compassionate use for dosimetry purposes. Planar images with an additional SPECT/CT acquisition were acquired for dosimetry calculations. Results Tumor uptake measured by PET imaging of 68Ga-labeled agents in mice was highest using PSMA-617, followed by PSMA-TO-1 and PSMA-11. 177Lu-PSMA tumor uptake measured by ex vivo gamma counting at subsequent time points tended to be greater for PSMA-TO-1 up to 1 week following treatment (p > 0.13 at all time points). This was, however, accompanied by increased kidney uptake and a 26-fold higher kidney dose of PSMA-TO-1 compared with PSMA-617 in mice. Mice treated with a single-cycle 225Ac-PSMA-TO-1 survived longer than those treated with 225Ac-PSMA-617 and untreated mice, respectively (17.8, 14.5 and 7.7 weeks, respectively; p < 0.0001). Kidney, salivary gland, bone marrow and mean ± SD tumor dose coefficients (Gy/GBq) for 177Lu-PSMA-TO-1 in patients #01/#02/#03 were 2.5/2.4/3.0, 1.0/2.5/2.3, 0.14/0.11/0.10 and 0.42 ± 0.03/4.45 ± 0.07/1.8 ± 0.57, respectively. Conclusions PSMA-TO-1 tumor uptake tended to be greater than that of PSMA-617 in both preclinical and clinical settings. Mice treated with 225Ac-PSMA-TO-1 conferred a significant survival benefit compared to 225Ac-PSMA-617 despite the accompanying increased kidney uptake. In humans, PSMA-TO-1 dosimetry estimates suggest increased tumor absorbed doses; however, the kidneys, salivary glands and bone marrow are also exposed to higher radiation doses. Thus, additional preclinical studies are needed before further clinical use.