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Gastric cancer (GC) is one of the most common malignancies worldwide. Patients with advanced GC need palliative care to ensure survival. This includes the use of chemotherapy agents, such as cisplatin, 5-fluorouracil, oxaliplatin, paclitaxel, and pemetrexed, as well as targeted agents. However, the emergence of drug resistance evidence in poor patient outcomes and poor prognosis is a motivation to determine the specific mechanism of drug resistance. Interestingly, circular RNAs (circRNAs) play an important part in the carcinogenesis and progression of GC and are involved in GC drug resistance. This review systematically summarizes the functions and mechanisms of circRNAs underlying GC drug resistance, especially chemoresistance. It also emphasizes that circRNAs can serve as promising targets for improving drug resistance and therapeutic efficacy.

The IL2 receptor (IL2R) is an attractive cancer immunotherapy target that controls immunosuppressive T regulatory cells (Treg) and antitumor T cells. Here we used IL2Rβ-selective IL2/anti-IL2 complexes (IL2c) to stimulate effector T cells preferentially in the orthotopic mouse ID8agg ovarian cancer model. Despite strong tumor rejection, IL2c unexpectedly lowered the tumor microenvironmental CD8+/Treg ratio. IL2c reduced tumor microenvironmental Treg suppression and induced a fragile Treg phenotype, helping explain improved efficacy despite numerically increased Tregs without affecting Treg in draining lymph nodes. IL2c also reduced Treg-mediated, high-affinity IL2R signaling needed for optimal Treg functions, a likely mechanism for reduced Treg suppression. Effector T-cell IL2R signaling was simultaneously improved, suggesting that IL2c inhibits Treg functions without hindering effector T cells, a limitation of most Treg depletion agents. Anti-PD-L1 antibody did not treat ID8agg, but adding IL2c generated complete tumor regressions and protective immune memory not achieved by either monotherapy. Similar anti-PD-L1 augmentation of IL2c and degradation of Treg functions were seen in subcutaneous B16 melanoma. Thus, IL2c is a multifunctional immunotherapy agent that stimulates immunity, reduces immunosuppression in a site-specific manner, and combines with other immunotherapies to treat distinct tumors in distinct anatomic compartments. Significance: These findings present CD122-targeted IL2 complexes as an advancement in cancer immunotherapy, as they reduce Treg immunosuppression, improve anticancer immunity, and boost PD-L1 immune checkpoint blockade efficacy in distinct tumors and anatomic locations.

The IL-2 receptor (IL-2R) is an attractive target for cancer immunotherapy as it controls both immune-suppressive regulatory T cells (Tregs) and anti-tumor T cells. We tested depleting Tregs as immunotherapy using anti-CD25 (high-affinity IL-2R subunit) antibodies (αCD25) in ID8agg mouse ovarian cancer (OC). αCD25 reduced ascites and Treg numbers but failed to reduce tumor burden, possibly because it depleted newly activated anti-tumor T cells in tumor-draining lymph nodes. Thus, αCD25 could be novel malignant ascites palliation, but has limited stand-alone efficacy. We then tested IL-2/anti-IL-2 complexes (IL-2c) that selectively stimulate medium-affinity (CD122/CD132) IL-2R thought to expand anti-tumor T cells preferentially, but with little Treg effects. In contrast to several single agents we tested that failed to treat ID8agg (e.g., αCD25, αPD-L1, IL-2 fusion toxin denileukin diftitox), IL-2c alone durably reduced ID8agg tumor burden despite lowering the tumor microenvironmental CD8+/Treg ratio. Thus, we hypothesized that IL-2c improved CD8+ function, reduced Treg function, or both. IL-2c increased polyfunctional IFN-γ+TNF-α+ anti-tumor T cells as expected, an effect that persists weeks after drug clearance. IL-2c also increased anti-tumor T cell CD25 expression that increased IL-2 sensitivity and STAT5 phosphorylation, a likely mechanism for increased polyfunctionality. Unexpectedly, IL-2c reduced the Treg functional mediators CD25, TIGIT and granzyme B, and reduced Treg suppressive function. Thus, favorable Treg modifications are a novel IL-2c mechanism of action. Adding αCD25 to IL-2c to deplete Tregs further unexpectedly worsened IL-2c efficacy in ID8agg and reduced effector memory T cells and polyfunctional T cells in the tumor microenvironment, suggesting a previously unappreciated role for CD25 in IL-2c therapy. Similar data were seen in B16 melanoma, suggesting αCD25 reduction of IL-2c efficacy is not tumor or compartment-specific (ID8agg is peritoneal and B16 is subcutaneous). αPD-L1, an ineffective monotherapy in ID8agg, combined with IL-2c to promote complete responses, suggesting potential for potent, novel combinatorial approaches. Our data suggest that antagonizing high affinity IL-2R (such as to deplete Tregs with αCD25) has limited cancer immunotherapy utility without more specific Treg targeting. In contrast, stimulating medium-affinity IL-2R with CD122-selective IL-2c has great translational promise by simultaneously improving beneficial anti-tumor T cells and reducing detrimental Treg function. Citation Format: Justin M. Drerup, Sri Lakshmi Pandeswara, Aijie Liu, Curtis A. Clark, Alvaro S. Padron, Wanjiao Chen, Vincent Hurez, Tyler J. Curiel. CD122-selective IL-2/anti-IL-2 complexes reduce regulatory T cell function and promote CD8+ T cell polyfunctionality for durable ovarian cancer immunotherapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1608. doi:10.1158/1538-7445.AM2017-1608