Neuroblastoma is a solid malignant tumor of the sympathetic nervous system, which accounts for 8–10% of childhood cancers. Considering the overall high risk and poor prognosis associated with neuroblastoma, effective therapeutics should be developed to improve patient survival and quality of life. A recent study showed that a proteasome inhibitor, carfilzomib (CFZ), reduced cell viability of SK-N-BE(2)-M17 neuroblastoma cells. Therefore, we investigated the molecular mechanisms by which CFZ lower the cell viability of neuroblastoma cells. CFZ reduced cell viability via cell cycle arrest at G2/M and apoptosis, which involved caspase activation (caspases-8, 9, 4, and 3), endoplasmic reticulum stress, reactive oxygen species production, mitochondrial membrane potential loss, and autophagy in a dose- and time-dependent manner. The effect of CFZ was additive to that of cisplatin (Cis), a well-known chemotherapeutic drug, in terms of cell viability reduction, cell cycle arrest, and apoptosis. Importantly, the additive effect of CFZ was maintained in Cis-resistant neuroblastoma cells. These results suggest that CFZ can be used in combination therapy for patients with neuroblastoma to overcome the resistance and adverse side effects of Cis.

Fluoxetine (FLX) is an antidepressant drug that belongs to the class of selective serotonin reuptake inhibitors. FLX is known to induce apoptosis in multiple types of cancer cells. In this study, the molecular mechanisms underlying the anti-cancer effects of FLX were investigated in SK-N-BE(2)-M17 human neuroblastoma cells. FLX induced apoptotic cell death, activation of caspase-4, -9, and -3, and expression of endoplasmic reticulum (ER) stress-associated proteins, including C/EBP homologous protein (CHOP). Inhibition of ER stress by treatment with the ER stress inhibitors, salubrinal and 4-phenylbutyric acid or CHOP siRNA transfection reduced FLX-induced cell death. FLX induced phosphorylation of mitogen-activated protein kinases (MAPKs) family, p38, JNK, and ERK, and an upstream kinase apoptosis signal kinase 1 (ASK1). Inhibition of MAPKs and ASK1 reduced FLX-induced cell death and CHOP expression. We then showed that FLX reduced mitochondrial membrane potential (MMP) and ER stress inhibitors as well as MAPK inhibitors ameliorated FLX-induced loss of MMP. Interestingly, FLX induced hyperacetylation of histone H3 and H4, upregulation of p300 histone acetyltransferase (HAT), and downregulation of histone deacetylases (HDACs). Treatment with a HAT inhibitor anacardic acid or p300 HAT siRNA transfection blocked FLX-induced apoptosis in SK-N-BE(2)-M17 cells. However, FLX did not induce histone acetylation and anacardic acid had no protective effect on FLX-induced cell death and CHOP expression in MYCN non-amplified SH-SY5Y human neuroblastoma and MYCN knockdowned SK-N-BE(2)-M17 cells. These findings suggest that FLX induces apoptosis in neuroblastoma through ER stress and mitochondrial dysfunction via the ASK1 and MAPK pathways and through histone hyperacetylation in a MYCN-dependent manner.

Proteasome inhibitors, such as bortezomib (BZ) and carfilzomib (CFZ), have been suggested as treatments for various cancers. To utilize BZ and/or CFZ as effective therapeutics for treating melanoma, we studied their molecular mechanisms using B16-F1 melanoma cells. Flow cytometry of Annexin V-fluorescein isothiocyanate-labeled cells indicated apoptosis induction by treatment with BZ and CFZ. Apoptosis was evidenced by the activation of various caspases, including caspase 3, 8, 9, and 12. Treatment with BZ and CFZ induced endoplasmic reticulum (ER) stress, as indicated by an increase in eIF2α phosphorylation and the expression of ER stress-associated proteins, including GRP78, ATF6α, ATF4, XBP1, and CCAAT/enhancer-binding protein homologous protein. The effects of CFZ on ER stress and apoptosis were lower than that of BZ. Nevertheless, CFZ and BZ synergistically induced ER stress and apoptosis in B16-F1 cells. Furthermore, the combinational pharmacological interactions of BZ and CFZ against the growth of B16-F1 melanoma cells were assessed by calculating the combination index and dose-reduction index with the CompuSyn software. We found that the combination of CFZ and BZ at submaximal concentrations could obtain dose reduction by exerting synergistic inhibitory effects on cell growth. Moreover, this drug combination reduced tumor growth in C57BL/6 syngeneic mice. Taken together, these results suggest that CFZ in combination with BZ may be a beneficial and potential strategy for melanoma treatment.

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Background Recently, there are growing needs of immune modulators that can convert cold tumors into hot tumors, which can be utilized for combination treatment with existing immune related therapies. An orally available small molecule that is capable of activating innate immune response can be an ideal candidate to meet those needs. Upon binding to 2’3’-cGAMP, STING activates TBK1-IRF3 signaling cascade in cancer cells as well as host cells and promotes innate immune responses against cancer cells, leading to T cell mediated anti-tumor immunity by facilitating T cell priming and infiltration. Ectonucleotide pyrophosphatase/phosphodiesterase 1 (ENPP1), a transmembrane protein highly expressed in subset of cancer cells, has been known to hydrolyze 2’3’-cGAMP and negatively regulates the STING activation. Inhibition of ENPP1 can prevent 2’3’-cGAMP degradation in tumor microenvironment (TME) and restore STING activation, leading to innate immune responses. It has been shown that ENPP1 inhibitor can enhance anti-tumor immunity by restoring 2’3’-cGAMP level in TME and can prevent tumor growth when co-treated with immune checkpoint blockade (ICB) as well as with radiation therapy. Methods The activity of ENPP1 inhibitors were measured in enzymatic assay using 2’3’-cGAMP as substrate and in cellular STING activation assay using IRF3-responsive reporter. Also, the effects on innate immune response were estimated in LIN (Lymphocyte INfiltration) assay measuring lymphocyte infiltration and TMED (TME in Dish) assay measuring tumor spheroid growth and immune cell activation. In vivo efficacy of TXN10128 (PO dosing) was evaluated in MC38 syngeneic model in combination with and anti-PD-L1 (IV dosing). Tumor growth was monitored and immune cells in tumor were analyzed. Results TXN10128 inhibited ENPP1 activity with single digit nanomolar potency in enzyme assay and further induced STING activation in cellular assay. In 3D spheroid co-culture condition, TXN10128 enhances lymphocyte infiltration and inhibits the spheroid growth. TXN10128 has a drug-like properties desirable for oral administration in terms of physicochemical properties and pharmacokinetics parameters. Systemic exposure of TXN10128 by PO dosing resulted in synergistic tumor growth inhibition with anti-PD-L1 antibody and improved tumor-infiltrating lymphocytes (TIL) profile as expected in MC38 syngeneic model. Additional in vivo studies are on-going to expand applicable cancer types to TXN10128 treatment. Conclusions TXN10128 is a potent and selective ENPP1 inhibitor that can exert immune response in 3D co-culture condition, which is consistent with tumor growth inhibition and favorable TIL profile in animal model. Together with promising drug-likeness, these studies demonstrate that TXN10128 is a suitable candidate for clinical investigation as a combination partner with existing immunotherapies. Citation Format: Sungjoon Kim, Imran Ali, Ahran Yu, Sun woo Lee, Sung young Park, Jung hwan Choi, Yong-yea Park, Chan sun Park. Orally available ENPP1 inhibitor, TXN10128, restores STING activation in tumor microenvironment and confers anti-tumor responses in combination with immune checkpoint blockade [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2021 Oct 7-10. Philadelphia (PA): AACR; Mol Cancer Ther 2021;20(12 Suppl):Abstract nr LBA009.