In vivo CRISPR screens reveal the landscape of immune evasion pathways across cancer.

The immune system can eliminate tumors, but checkpoints enable immune escape. Here, we identify immune evasion mechanisms using genome-scale in vivo CRISPR screens across cancer models treated with immune checkpoint blockade (ICB). We identify immune evasion genes and important immune inhibitory checkpoints conserved across cancers, including the non-classical major histocompatibility complex class I (MHC class I) molecule Qa-1b/HLA-E. Surprisingly, loss of tumor interferon-γ (IFNγ) signaling sensitizes many models to immunity. The immune inhibitory effects of tumor IFN sensing are mediated through two mechanisms. First, tumor upregulation of classical MHC class I inhibits natural killer cells. Second, IFN-induced expression of Qa-1b inhibits CD8+ T cells via the NKG2A/CD94 receptor, which is induced by ICB. Finally, we show that strong IFN signatures are associated with poor response to ICB in individuals with renal cell carcinoma or melanoma. This study reveals that IFN-mediated upregulation of classical and non-classical MHC class I inhibitory checkpoints can facilitate immune escape.

Targeting mTORC1 Activity to Improve Efficacy of Radioligand Therapy in Cancer.

Radioligand therapy (RLT) represents an effective strategy to treat malignancy by cancer-selective delivery of radioactivity following systemic application. Despite recent therapeutic successes, cancer radioresistance and insufficient delivery of the radioactive ligands, as well as cytotoxicity to healthy organs, significantly impairs clinical efficacy. To improve disease management while minimizing toxicity, in recent years, the combination of RLT with molecular targeted therapies against cancer signaling networks showed encouraging outcomes. Characterization of the key deregulated oncogenic signaling pathways revealed their convergence to activate the mammalian target of rapamycin (mTOR), in which signaling plays an essential role in the regulation of cancer growth and survival. Therapeutic interference with hyperactivated mTOR pathways was extensively studied and led to the development of mTOR inhibitors for clinical applications. In this review, we outline the regulation and oncogenic role of mTOR signaling, as well as recapitulate and discuss mTOR complex 1 (mTORC1) inhibition to improve the efficacy of RLT in cancer.

SPECT Imaging of SST2-Expressing Tumors with 99mTc-Based Somatostatin Receptor Antagonists: The Role of Tetraamine, HYNIC, and Spacers.

[99mTc]Tc-HYNIC-TOC is the most widely used 99mTc-labeled somatostatin receptor (SST) agonist for the SPECT imaging of SST-expressing tumors, such as neuroendocrine tumors. Recently, radiolabeled SST antagonists have shown improved diagnostic efficacy over agonists. 99mTc-labeled SST antagonists are lacking in clinical practice. Surprisingly, when [99mTc]Tc-HYNIC was conjugated to the SST2 antagonist SS01, SST2 imaging was not feasible. This was not the case when [99mTc]Tc-N4 was conjugated to SS01. Here, we assessed the introduction of different spacers (X: ß-Ala, Ahx, Aun and PEG4) among HYNIC and SS01 with the aim of restoring the affinity of HYNIC conjugates. In addition, we used the alternative antagonist JR11 for determining the suitability of HYNIC with 99mTc-labeled SST2 antagonists. We performed a head-to-head comparison of the N4 conjugates of SS01 and JR11. [99mTc]Tc-HYNIC-TOC was used as a reference, and HEK-SST2 cells were used for in vitro and in vivo evaluation. EDDA was used as a co-ligand for all [99mTc]Tc-HYNIC conjugates. The introduction of Ahx restored, to a great extent, the SST2-mediated cellular uptake of the [99mTc]Tc-HYNIC-X conjugates (X: spacer), albeit lower than the corresponding [99mTc]Tc-N4-conjugates. SPECT/CT images showed that all 99mTc-labeled conjugates accumulated in the tumor and kidneys with [99mTc]Tc-HYNIC-PEG4-SS01, [99mTc]Tc-N4-SS01 and [99mTc]Tc-N4-JR11 having notably higher kidney uptake. Biodistribution studies showed similar or better tumor-to-non-tumor ratios for the [99mTc]Tc-HYNIC-Ahx conjugates, compared to the [99mTc]Tc-N4 counterparts. The [99mTc]Tc-HYNIC-Ahx conjugates of SS01 and JR11 were comparable to [99mTc]Tc-HYNIC-TOC as imaging agents. HYNIC is a suitable chelator for the development of 99mTc-labeled SST2 antagonists when a spacer of appropriate length, such as Ahx, is used.