E1B19K--deleted oncolytic adenoviruses enhancee the cytotoxicity of DNA--damaging drugs in pancreatic cancer through deregulation of cell--cycle mechanisms

PhdPancreatic cancer is an aggressive disease with poor prognosis and a high fatality rate. Gemcitabine, the standard first-line chemotherapy for advanced disease, has negligible effects, necessitating the development of new therapies. We previously demonstrated that deletion of the anti-apoptotic gene E1B19K (AdΔ19K) in a replication-selective adenoviral mutant, caused synergistically-enhanced cell-killing when combined with low-dose DNA-damaging drugs in pancreatic cancer xenograft models. To delineate the cellular pathways targeted by the combination treatment we employed AdΔ19K and gemcitabine or irinotecan, with the goal of identifying cellular factors that are essential for the synergistic cell-killing. We hypothesised that AdΔ19K and DNA-damaging drugs act synergistically to deregulate cell-cycle mechanisms. Pancreatic cancer cell death induced by AdΔ19K and DNA-damaging drugs is apoptotic and time-dependent. AdΔ19K could not block DNA-damage responses (DDR) elicited by the drugs, despite virus-mediated degradation of the DDR factor Mre11. Mre11 siRNA-mediated knockdown augmented the synergistic cell death. Mitotic-index analysis in synchronised cells and immunofluorescence microscopy suggested that AdΔ19K promotes mitotic entry of gemcitabine-treated DNA-damaged cells. Moreover, AdΔ19K inhibited drug-induced accumulation of Claspin, a DDR protein whose degradation is required for checkpoint recovery. Treatment with AdΔ19K and gemcitabine accelerated Claspin degradation, and siRNA-mediated Claspin knockdown enhanced the synergistic cell death. Time-lapse microscopy in histoneH2B mCherry-expressing cells showed that AdΔ19K enhanced gemcitabine-induced mitotic catastrophe, characterised by prolonged mitosis, chromosome missegregation errors, cytokinesis failure and formation of multinucleated cells. Moreover, live-cell imaging revealed that the majority of cells treated with AdΔ19K and gemcitabine die before mitotic entry. 5 These findings suggest that E1B19K-deleted adenoviruses cannot prevent cell-cycle checkpoint responses elicited by DNA-damaging drugs, but enhance drug-induced cell death by downregulating DDR factors, such as Mre11 and Claspin. Additionally, the virus enhances mitotic catastrophe of DNA-damaged cells escaping cell-cycle checkpoints, eventually leading to increased apoptosis. Through these studies cellular pathways and factors involved in the synergistic cell killing were identified, that could be explored in the future to develop improved targeted therapies for pancreatic cancer.Pancreatic Cancer Research Fun

PARP inhibitor efficacy depends on CD8+ T cell recruitment via intratumoral STING pathway activation in BRCA-deficient models of triple-negative breast cancer.

Combinatorial clinical trials of PARP inhibitors with immunotherapies are ongoing, yet the immunomodulatory effects of PARP inhibition have been incompletely studied. Here, we sought to dissect the mechanisms underlying PARP inhibitor-induced changes in the tumor microenvironment of BRCA1-deficient triple-negative breast cancer (TNBC). We demonstrate that the PARP inhibitor olaparib induces CD8+ T cell infiltration and activation in vivo, and that CD8+ T cell depletion severely compromises anti-tumor efficacy. Olaparib-induced T cell recruitment is mediated through activation of the cGAS/STING pathway in tumor cells with paracrine activation of dendritic cells and is more pronounced in HR-deficient compared to HR-proficient TNBC cells and in vivo models. CRISPR-knockout of STING in cancer cells prevents proinflammatory signaling and is sufficient to abolish olaparib-induced T cell infiltration in vivo. These findings elucidate an additional mechanism of action of PARP inhibitors and provide rationale for combining PARP inhibition with immunotherapies for the treatment of TNBC

The Novel Oncolytic Adenoviral Mutant Ad5-3 Delta-A20T Retargeted to alpha v beta 6 Integrins Efficiently Eliminates Pancreatic Cancer Cells

Metastatic pancreatic ductal adenocarcinomas (PDAC) are incurable due to the rapid development of resistance to all current therapeutics. Oncolytic adenoviral mutants have emerged as a promising new strategy that negates such resistance. In contrast to normal tissue, the majority of PDACs express the αvβ6 integrin receptor. To exploit this feature, we modified our previously reported oncolytic adenovirus, AdΔΔ, to selectively target αvβ6 integrins to facilitate systemic delivery. Structural modifications to AdΔΔ include the expression of the small but potent αvβ6-binding peptide, A20FMDV2, and ablation of binding to the native coxsackie and adenovirus receptor (CAR) within the fiber knob region. The resultant mutant, Ad5-3Δ-A20T, infected and killed αvβ6 integrin–expressing cells more effectively than the parental wild-type (Ad5wt) virus and AdΔΔ. Viral uptake through αvβ6 integrins rather than native viral receptors (CAR, αvβ3 and αvβ5 integrins) promoted viral propagation and spread. Superior efficacy of Ad5-3Δ-A20T compared with Ad5wt was demonstrated in 3D organotypic cocultures, and similar potency between the two viruses was observed in Suit-2 in vivo models. Importantly, Ad5-3Δ-A20T infected pancreatic stellate cells at low levels, which may further facilitate viral spread and cancer cell elimination either as a single agent or in combination with the chemotherapy drug, gemcitabine. We demonstrate that Ad5-3Δ-A20T is highly selective for αvβ6 integrin–expressing pancreatic cancer cells, and with further development, this new and exciting strategy can potentially be extended to improve the systemic delivery of adenoviruses to pancreatic cancer patients

"Elia in Wartime"

As I detailed in the last number of the Bulletin the Society recently acquired a cache of papers belonging to Herbert Grant Smith (1883-1974) stalwart member of the Charles Lamb Society and editor of the Charles Lamb Society Bulletin 1948-72. We were very pleased to be able to purchase this material, and, while currently housed in a banana box in the University of Leicester, it will find a home in the main CLS collection, now housed in the Guildhall Library in the City of London

A first-in-class Polymerase Theta Inhibitor selectively targets Homologous-Recombination-Deficient Tumors.

DNA polymerase theta (POLθ) is synthetic lethal with Homologous Recombination (HR) deficiency and thus a candidate target for HR-deficient cancers. Through high-throughput small molecule screens we identified the antibiotic Novobiocin (NVB) as a specific POLθ inhibitor that selectively kills HR-deficient tumor cells in vitro and in vivo. NVB directly binds to the POLθ ATPase domain, inhibits its ATPase activity, and phenocopies POLθ depletion. NVB kills HR-deficient breast and ovarian tumors in GEMM, xenograft and PDX models. Increased POLθ levels predict NVB sensitivity, and BRCA-deficient tumor cells with acquired resistance to PARP inhibitors (PARPi) are sensitive to NVB in vitro and in vivo. Mechanistically, NVB-mediated cell death in PARPi-resistant cells arises from increased double-strand break end resection, leading to accumulation of single-strand DNA intermediates and non-functional RAD51 foci. Our results demonstrate that NVB may be useful alone or in combination with PARPi in treating HR-deficient tumors, including those with acquired PARPi resistance. (151/150)

Discovery and characterization of orally bioavailable 4-chloro-6-fluoroisophthalamides as covalent PPARG inverse-agonists

PPAR gamma (PPARG) is a ligand activated transcription factor that regulates genes involved in inflammation, bone biology, lipid homeostasis, as well as a master regulator of adipogenesis and a potential lineage driver of luminal bladder cancer. While PPARG agonists lead to transcriptional activation of canonical target genes, inverse agonists have the opposite effect through inducing a transcriptionally repressive complex leading to repression of canonical target gene expression. While many agonists have been described and tested clinically, inverse agonists offer an underexplored avenue to modulate PPARG biology in vivo. Current inverse agonists lack favorable in vivo properties; herein we describe the discovery and characterization of a series of orally bioavailable 4-chloro-6-fluoroisophthalamides as covalent PPARG inverse-agonists, BAY-5516, BAY-5094, and BAY-9683. Structural studies of this series revealed distinct pre- and post-covalent binding positions, which led to the hypothesis that interactions in the pre-covalent conformation are primarily responsible for driving affinity, while interactions in the post-covalent conformation are more responsible for cellular functional effects by enhancing PPARG interactions with its corepressors. The need to simultaneously optimize for two distinct states may partially explain the steep SAR observed. Exquisite selectivity was achieved over related nuclear receptors in the subfamily due in part to a covalent warhead with low reactivity through an SNAr mechanism in addition to the specificity gained through covalent binding to a reactive cysteine uniquely positioned within the PPARG LBD. BAY-5516, BAY-5094, and BAY-9683 lead to pharmacodynamic regulation of PPARG target gene expression in vivo comparable to known inverse agonist SR10221 and represent new tools for future in vivo studies to explore their potential utility for treatment of disorders of hyperactivated PPARG including luminal bladder cancer and other disorders