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Abstract Precision medicine has drastically changed cancer treatment strategies including KRAS-mutant cancers which have been undruggable for decades. While intrinsic or acquired treatment resistance remains unresolved in many cases, epigenome-targeted therapy may be an option to overcome. We recently discovered the effectiveness of blocking small ubiquitin-like modifier (SUMO) signaling cascade (SUMOylation) in MYC-expressing KRAS-mutant cancer cells using a SUMO-activating enzyme E inhibitor TAK-981 that results in SUMOylation inhibition. Interestingly, TAK-981 promoted the degradation of MYC via the ubiquitin–proteasome system. Moreover, combination therapy with TAK-981 and MEK inhibitor trametinib remarkably regressed xenografted KRAS-mutant tumors by accumulating DNA damage and inducing apoptosis. Whereas our recent study revealed immune-independent antitumor efficacy, we evaluated the immune responses of cancer cells and immune cells in this study. We found that TAK-981-induced MYC downregulation promoted the activation of STING followed by Stat1 and MHC class I in KRAS-mutant cancer cells. Activation of dendritic cells or T cells treated with TAK-981 was also verified by upregulated activation markers in dendritic cells or skew-toward effector-like phenotypes in T cells. Furthermore, the enhanced immune-dependent antitumor efficacy of the combination therapy with TAK-981 and trametinib was confirmed by infiltration of immune cells into tumor tissues and immunodepleting-test using immunodepleting antibodies in syngeneic immunocompetent mouse models. Together with our recent study and here, the findings support that combination inhibition of SUMOylation and MEK comprehensively conquers MYC-expressing KRAS-mutant cancers by both immune-dependent and immune-independent antitumor responses.

Abstract Background KRAS mutations frequently occur in cancers, particularly pancreatic ductal adenocarcinoma, colorectal cancer, and non-small cell lung cancer. Although KRAS G12C inhibitors have recently been approved, effective precision therapies have not yet been established for all KRAS-mutant cancers. Many treatments for KRAS-mutant cancers, including epigenome-targeted drugs, are currently under investigation. Small ubiquitin-like modifier (SUMO) proteins are a family of small proteins covalently attached to and detached from other proteins in cells via the processes called SUMOylation and de-SUMOylation. We assessed whether SUMOylation inhibition was effective in KRAS-mutant cancer cells. Methods The efficacy of the first-in-class SUMO-activating enzyme E inhibitor TAK-981 (subasumstat) was assessed in multiple human and mouse KRAS-mutated cancer cell lines. A gene expression assay using a TaqMan array was used to identify biomarkers of TAK-981 efficacy. The biological roles of SUMOylation inhibition and subsequent regulatory mechanisms were investigated using immunoblot analysis, immunofluorescence assays, and mouse models. Results We discovered that TAK-981 downregulated the expression of the currently undruggable MYC and effectively suppressed the growth of MYC-expressing KRAS-mutant cancers across different tissue types. Moreover, TAK-981-resistant cells were sensitized to SUMOylation inhibition via MYC-overexpression. TAK-981 induced proteasomal degradation of MYC by altering the balance between SUMOylation and ubiquitination and promoting the binding of MYC and Fbxw7, a key factor in the ubiquitin–proteasome system. The efficacy of TAK-981 monotherapy in immunocompetent and immunodeficient mouse models using a mouse-derived CMT167 cell line was significant but modest. Since MAPK inhibition of the KRAS downstream pathway is crucial in KRAS-mutant cancer, we expected that co-inhibition of SUMOylation and MEK might be a good option. Surprisingly, combination treatment with TAK-981 and trametinib dramatically induced apoptosis in multiple cell lines and gene-engineered mouse-derived organoids. Moreover, combination therapy resulted in long-term tumor regression in mouse models using cell lines of different tissue types. Finally, we revealed that combination therapy complementally inhibited Rad51 and BRCA1 and accumulated DNA damage. Conclusions We found that MYC downregulation occurred via SUMOylation inhibition in KRAS-mutant cancer cells. Our findings indicate that dual inhibition of SUMOylation and MEK may be a promising treatment for MYC-expressing KRAS-mutant cancers by enhancing DNA damage accumulation.

Cancer cell clusters metastasize to distant organ by polyclonal manner. Here, the authors show that malignant subclone induces fibrotic niche generation in the liver by hepatic stellate cell activation, supporting survival and colonization of non-metastatic cells to develop polyclonal metastasis.

Both gain-of-function of mutant p53 (GOF) and loss of wild-type p53 (LOH) are independently associated with cancer. Here, the authors show that LOH promotes GOF tumourigenesis by increasing tumor-initiating ability and metastasis.

Humans walk, run, and change their speed in accordance with circumstances. These gaits are rhythmic motions generated by multi-articulated movements, which have specific spatiotemporal patterns. The kinematic characteristics depend on the gait and speed. In this study, we focused on the kinematic coordination of locomotor behavior to clarify the underlying mechanism for the effect of speed on the spatiotemporal kinematic patterns for each gait. In particular, we used seven elevation angles for the whole-body motion and separated the measured data into different phases depending on the foot-contact condition, that is, single-stance phase, double-stance phase, and flight phase, which have different physical constraints during locomotion. We extracted the spatiotemporal kinematic coordination patterns with singular value decomposition and investigated the effect of speed on the coordination patterns. Our results showed that most of the whole-body motion could be explained by only two sets of temporal and spatial coordination patterns in each phase. Furthermore, the temporal coordination patterns were invariant for different speeds, while the spatial coordination patterns varied. These findings will improve our understanding of human adaptation mechanisms to tune locomotor behavior for changing speed.

SLD5 forms a GINS complex with PSF1, PSF2 and PSF3, which is essential for the initiation of DNA replication in lower eukaryotes. Although these components are conserved in mammals, their biological function is unclear. We show here that targeted disruption of SLD5 in mice causes a defect in cell proliferation in the inner cell mass, resulting in embryonic lethality at the peri-implantation stage, indicating that SLD5 is essential for embryogenesis. Moreover, this phenotype of SLD5 mutant mice is quite similar compared with that of PSF1 mutant mice. We have previously reported that haploinsufficiency of PSF1 resulted in failure of acute proliferation of bone marrow hematopoietic stem cells (HSCs) during reconstitution of bone marrow ablated by 5-FU treatment. Since SLD5 was highly expressed in bone marrow, we investigated its involvement in bone marrow reconstitution after bone marrow ablation as observed in PSF1 heterozygous mutant mice. However, heterozygous deletion of the SLD5 gene was found not to significantly affect bone marrow reconstitution. On the other hand, abundant SLD5 expression was observed in human cancer cell lines and heterozygous deletion of the gene attenuated tumor progression in a murine model of spontaneous gastric cancer. These indicated that requirement and dependency of SLD5 for cell proliferation is different in different cell types.