Evan R. Abt

Small cell carcinoma is a highly lethal cancer variant often found with neuroendocrine (NE) features, as exemplified by small cell lung cancer and small cell NE prostate cancer (SCPC). A genome-wide CRISPR dependency screen using SCPC models generated through human prostate cell transformation identifies a requirement for the transcription factor E2F3. E2F3 dependency is linked to RB inactivation, a near universal occurrence across small cell cancers. The requirement for E2F3 is shared by RB-deficient cells originating from the prostate, lung, and adnexa. In RB-deficient cancer cells, E2F3 inhibition restrains cell cycle progression, proliferation, and tumor growth in vivo. Inhibition of de novo pyrimidine synthesis limits E2F3 expression and suppresses small cell carcinoma proliferation in culture. Directly or indirectly targeting E2F3 to leverage a pan-cancer synthetic lethality resulting from RB inactivation represents a potential treatment strategy.

Supplementary Fig. 1 STING agonist diABZI synergizes with MAPK inhibition in PDAC by enhancing apoptosis.

Supplementary Fig. 4 Immunoblot analysis demonstrating the effect of ± 100 U/ml exogenous IFN on CFPAC-1 and SUIT2 parental cells compared to their respective IFNAR-deficient isogenic cell lines. (B) Immunoblot analysis of CFPAC-1 parental and IFNAR1-KO cells exposed to ± 1 µM diABZI ± 100 nM trametinib for 24 h (C)Immunoblot analysis of the effects of ± 100 U/ml exogenous IFN ± 1 µM diABZI for 24 h.

Supplementary Fig. 2 Tumor growth is inhibited by STING agonism and MEK inhibition in vivo.

Supplementary Fig. 3 MEK inhibition amplifies STING-induced transcription of IFNB1, IL-6, and TNFA in multiple PDAC cell lines.

Supplementary Fig. 5 IL6 is not responsible for the synergistic effects of STING agonism and MEK inhibition.

Supplementary Resources and Table

Nucleoside metabolism regulates immune cell development and function, but the therapeutic implications of this link have yet to be fully realized. Evidence for the importance of nucleoside metabolism in immune system control was provided by observations of immunodeficiency and autoimmunity across patients with genetic errors that alter nucleoside synthesis or breakdown. Research over the past several decades has uncovered a multifaceted role for nucleosides in mediating immune responses that involves their function as metabolic precursors and as ligands for immune receptors. These findings prompted the development of treatments that block the production of the immunosuppressive nucleoside adenosine for cancer immunotherapy. Guanosine and pyrimidine nucleosides also mediate immune outcomes, and the key regulators of their metabolism are promising new targets to unleash anti-cancer immune responses or dampen autoimmune reactions. This review provides an overview of (i) recent research concerning the mechanisms underlying nucleoside-mediated immune regulation, (ii) the current landscape of therapeutic targets for immune modulation within nucleoside metabolism, and (iii) opportunities for developing improved preclinical models that recapitulate human nucleoside metabolism, which are needed to advance new metabolism-targeting therapies toward the clinic.

Combining a T cell-targeting mRNA vaccine encoding the conserved SARS-CoV-2 RNA-dependent RNA polymerase, RdRp, with a Spike-encoding mRNA vaccine may offer an additional pathway toward COVID-19 protection. Here, we show that a nucleoside-modified RdRp mRNA vaccine raises robust and durable CD8+ T cell responses in mice. Immunization drives a CD8+ T cell response enriched toward a specific RdRp epitope. Unexpectedly, coadministration of mRNA vaccines encoding RdRp or the Spike Receptor Binding Domain (RBD) dampens RBD-specific immune responses. Contralateral administration reduces the suppression of RBD-specific T cell responses while type I interferon signaling blockade restores RBD-specific antibodies. A staggered immunization strategy maintains both RBD vaccine-mediated antibody and T cell responses as well as protection against lethal SARS-CoV-2 challenge in human ACE2 transgenic mice. In HLA-A2.1 transgenic mice, the RdRp vaccine elicits CD8+ T cell responses against HLA-A*02:01-restricted epitopes recognized by human donor T cells. These results highlight RdRp as a candidate antigen for COVID-19 vaccines. The findings also offer insights into crafting effective multivalent mRNA vaccines to broaden CD8+ T cell responses against SARS-CoV-2 and potentially other viruses with pandemic potential.

Adenocarcinomas from multiple tissues can converge to treatment-resistant small cell neuroendocrine (SCN) cancers composed of ASCL1, POU2F3, NEUROD1, and YAP1 subtypes. We investigated how mitochondrial metabolism influences SCN cancer (SCNC) progression. Extensive bioinformatics analyses encompassing thousands of patient tumors and human cancer cell lines uncovered enhanced expression of proliferator-activatedreceptor gamma coactivator 1-alpha (PGC-1α), a potent regulator of mitochondrial oxidative phosphorylation (OXPHOS), across several SCNCs. PGC-1α correlated tightly with increased expression of the lineage marker Achaete-scute homolog 1, (ASCL1) through a positive feedback mechanism. Analyses using a human prostate tissue-based SCN transformation system showed that the ASCL1 subtype has heightened PGC-1α expression and OXPHOS activity. PGC-1α inhibition diminished OXPHOS, reduced SCNC cell proliferation, and blocked SCN prostate tumor formation. Conversely, PGC-1α overexpression enhanced OXPHOS, validated by small-animal Positron Emission Tomography mitochondrial imaging, tripled the SCN prostate tumor formation rate, and promoted commitment to the ASCL1 lineage. These results establish PGC-1α as a driver of SCNC progression and subtype determination, highlighting metabolic vulnerabilities in SCNCs across different tissues.