Oncolytic virus and inhibitor for NEDD8-activating enzyme pevonedistat: Promising combination for cancer therapy?

One trendy strategy for oncolytic virus (OV)-mediated cancer immunotherapy is to explore rational combinations to achieve synergistic effects and maximize the therapeutic efficacy. In this issue of Molecular Therapy, Wong et al.¹ have explored a novel combination and demonstrated that pevonedistat, a first-in-class NEDD8-activating enzyme inhibitor, sensitizes cancer cells to increased infection of an oncolytic vesicular stomatitis virus (VSV), promotes tumor cell death, and improves therapeutic outcomes in oncolytic VSV-resistant murine cancer models.

OV-mediated cancer immunotherapy has shown great promise, as showcased by the approval of four different OVs for treating three types of cancer so far. Talimogene laherparepvec (T-VEC) was approved by the US Food and Drug Administration and the European Medicines Agency for treating advanced melanoma, and teserpaturev (G47Δ) was approved in Japan in 2021 for treating malignant glioblastoma. Yet, one of the most severe caveats is that OV-mediated monotherapy of cancer has often shown limited efficacy. Therefore, investigators have been developing various combination strategies to enhance its efficacy while maintaining high safety. The combination most intensively studied so far is the combined use of OV with immune checkpoint blockade. Even though this specific combination generated a lot of excitement initially, unfortunately, the first phase 3 trial of the combination, T-VEC with pembrolizumab, has resulted in disappointing clinical outcomes in patients with advanced melanoma.² This indicated that exploring other promising combinations is mandatory to make this novel class of anti-tumor agents realize their therapeutic potential. As OVs are multi-mechanistic living anti-cancer agents, working through oncolysis, anti-angiogenesis, and, most importantly, OV-elicited anti-tumor immunity, by reasoning, the other component(s) that could add functions complementary to the OV may work additively or synergistically to inhibit or eliminate the tumor, leading to enhanced efficacy of this therapeutic regimen.

Small-molecule modulators of signaling pathways have significantly impacted cancer-targeted therapy in the last two decades.³ Many small-molecule inhibitors have been developed targeting key molecules in relevant signaling pathways for cancer cells and/or immune cells. These include but are not limited to EGFR-KRAS, PI3K-AKT-mTOR, p53, and epigenetic or immune pathways. A variety of combinations with OVs for cancer immunotherapy have been studied and reviewed recently.⁴ However, inhibitors of the NEDD8-activating enzyme are relatively new, and no such combination had been studied before.

Pevonedistat (MLN4924) is a small molecular inhibitor of the NEDD8-activating enzyme and blocks cullin neddylation to inactivate cullin-RING ligase and lead to apoptotic cell death in cancer cells.⁵ This inhibitor is currently under clinical studies for multiple types of cancers. Pevonedistat possesses other functions beyond neddylation inhibition. It triggers EGFR dimerization and then activation of RAS/MAPK and PI3K/AKT1 signal pathways to stimulate tumor sphere formation and to inhibit ciliogenesis. It also triggers PKM2 tetramerization to promote glycolysis.⁶

In tumor, pevonedistat targets both cancer cells and immune cells. A mechanistic study identified p53 as an important mediator of the apoptotic response in cancer cells. Both extrinsic and intrinsic apoptotic pathways play roles in the process initiated by the compound in cancer cells. Depletion of the anti-apoptotic protein FLIP, a novel mediator of resistance to the inhibitor, enhanced apoptosis in a p53-, TRAIL-R2/DR5-, and caspase-8-dependent manner.⁷ Pevonedistat also sensitizes cancer cells to other therapeutic agents.⁸

Pevonedistat also modulates immune cells directly. The effects on natural killer (NK) cells are two dimensional. First, inhibition of neddylation by pevonedistat increases the expression of the NKG2D-activating receptor ligands MICA and MICB in multiple myeloma cells, making these cells more susceptible to NK cell degranulation and killing.⁹ Second, the inhibitor enhances NK cell-mediated degranulation and killing against cancer cells and improves therapeutic responses mediated by two approved drugs.¹⁰ Importantly, pevonedistat impacts adaptive anti-tumor immunity directly. The pharmacologic targeting reinvigorates T cell responses in lymphoid neoplasia, as pevonedistat-treated patient-derived CD8⁺ T cells showed upregulated tumor necrosis factor α (TNF-α) and interferon γ (IFNγ) and exhibited enhanced cytotoxicity.¹¹ Using human chronic lymphocytic leukemia-derived T cells, it was shown that pevonedistat treatment led to markedly differential expression of NF-κB-regulated genes and downregulation of IL-2 signaling during T cell activation, yet T cells evaded apoptosis. Meanwhile, it favorably modulated polarization of T cells with decreased regulatory T cell (Treg) differentiation and a shift toward Th1 phenotype, accompanied by increased IFNγ production. Experiments in vivo recapitulate these in vitro findings.¹² These studies convincingly demonstrate that pevonedistat positively regulates anti-tumor immunity and induces cancer cell death, and thus it may be used as an effective component for combinatorial therapeutic regimens.

In the study by Wong et al.,¹ the authors have made novel findings on the mechanisms and functions of pevonedistat. They showed that pevonedistat increases infectivity of the OV via blockade of type 1 IFN (IFNα and IFNβ) response through neddylation-dependent repression of ISGF3 and neddylation-independent inhibition of NF-κB nuclear translocation. This newly found property makes the inhibitor useful in enhancing the infectivity of an OV that naturally targets deficient innate immunity of cancer cells. The use of pevonedistat would expand the utility of this class of OVs to cancers that are not type 1 IFN (IFN-1)-signaling deficient per se.

One caveat of the study is that the enhanced therapeutic effect seems to be small, albeit statistically significant, especially when the effect was measured by extension of survival of the hosts. The reasons for the limited effect could be 2-fold. One is that the scheduling and dosing of pevonedistat with OV might have not been optimized in the study, and thus there is a great potential to achieve better effects after optimization. The other is that pevonedistat indeed plays an immunosuppressive role under the current dose of the drug and conditions used in the study. However, this action may be transient, as tumor-specific T cell activation appears to be unchanged. Further studies are necessary to get a definite answer.

Other important questions remain to be answered. First, the study has used only one OV, VSVΔ51; thus, we do not know if pevonedistat could improve the infectivity of other OVs that may or may not depend on deficient IFN pathways in cancer cells. Second, we still do not fully understand at the molecular level how this inhibitor modulates the functions of T cells and anti-tumor immunity in the tumor microenvironment (TME). Third, dimethyl fumarate and vanadium compounds have previously been identified by Dr. Diallo and collaborators to be sensitizers for VSV infection and potentiate oncolytic virotherapy.^13,14 In theory, compounds that inhibit IFN responses would overcome the partial resistance of human cancers to VSV-mediated therapy, exemplified in a study combining oncolytic VSV with JAK1/2-inhibitor ruxolitinib.¹⁵ Therefore, it is high time to make direct comparative analyses of these compounds in various tumor models, for their relative toxicity, efficacy, elicited anti-tumor immunity, and mechanisms of action, using not only VSV but also other OVs. These studies will be very informative to predict the real value of these compounds in OV-mediated cancer therapy in human patients. Finally, as heterogenicity is a hallmark of cancer, it is tempting to speculate that OV may work with two or more small-molecule modulators targeting different signaling pathways⁴ to act synergistically to enhance therapeutic efficacy.

In summary, Wong et al. showed that pevonedistat can overcome the resistance and enhance the infectivity of an oncolytic VSV for improved oncolytic virotherapy. Evidence from other studies is accumulating to show that pevonedistat alone can stimulate anti-tumor immunity. We believe that these two unique functions of pevonedistat make it an ideal component in combinational regimens with improved OV-mediated cancer immunotherapy.