Immune checkpoint inhibitors (ICIs) blocking the cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) and programmed cell death protein/ligand 1 (PD-1/PD-L1) improve the survival and treatment response rates in both melanoma and non-small cell lung cancer (NSCLC) in the setting of metastatic disease.1–8 However, despite the remarkable response of ICIs in a subset of patients, approximately 50%–80% of patients in these trials do not respond or develop adaptive resistance to therapy.1–8

Cyclo-oxygenase-2 (COX2) gene is frequently overexpressed in melanoma, NSCLC and other cancers, and the consequential production of prostaglandin E2 (PGE₂) associates with poor prognoses.9 10 The pro-tumoral effect of the COX2-PGE₂ axis links to tumor cell proliferation and differentiation, chronic inflammation, angiogenesis, and tumor immunosuppression.9 Also, the inhibition of COX2 activity using aspirin reduces the incidence, mortality, and risk of metastasis in colorectal cancer.11–15

Preclinical studies demonstrate that the COX2 pathway contributes to tumor immune evasion in melanoma models. COX2 expression allows tumor cells to evade type I interferon-mediated immunity, and the combination of COX and PD-1 inhibition results in remarkable therapeutic synergy in murine melanoma models.16 A follow-up study from the same group reveals that tumor-derived PGE₂ impairs the ability of natural killer cells to recruit dendritic cells intratumorally, posing another mechanism of immune checkpoint exploited by tumor cells.17 Analysis of The Cancer Genome Atlas database positively correlates a COX-deficient immune molecular signature with improved survival outcomes across several tumor types, including melanoma and NSCLC, underscoring the translational value of this mechanistic discovery.17

Based on these data, we hypothesize that the use of COX inhibitors (COXi) could improve the efficacy of ICI as measured by time-to-progression (TTP), objective response rate (ORR) and overall survival (OS) after initiating ICI therapy in a cohort of patients with metastatic melanoma and NSCLC that were treated only with ICI.

Our study demonstrated that, among patients with metastatic melanoma and NSCLC, COXi use during the first courses of ICI (ICI+COXi) was associated with longer TTP. ORR at 6 months were significantly higher in patients who received ICI+COXi compared with those who received ICI alone in both melanoma and NSCLC cohorts. While COXi use had no effect on OS in the melanoma cohort, it associated with improved OS in patients with metastatic NSCLC. Furthermore, we detected a significant interaction between COXi use and pretreatment NLR on TTP in the melanoma cohort, with ICI+COXi seeming to negate the negative predictive value of high pretreatment NLR. Subset analysis by the type of ICI received revealed a significant benefit of COXi in prolonging TTP in patients with melanoma treated with CTLA-4 inhibitor. Finally, we validated our results using a modified melanoma cohort after RECIST assessment and showed similar outcomes.

COX2-mediated PGE₂ synthesis suppresses antitumor immunity through diverse mechanisms, including inhibition of myeloid cell activation, decreased natural killer and dendritic cell recruitment, regulatory T-cell induction, and decreased proliferation and effector function of CD4/8 T-cells, and COX inhibition has been shown to overcome tumor immune evasion and synergize with checkpoint blockade in animal models.16 17 However, there is a paucity of clinical evidence to date that demonstrates the potential therapeutic benefit of concurrent COXi use with ICIs. Our results demonstrate the potential benefit of COXi use in prolonging TTP with ICI, which support our hypothesis that concomitant COXi use may potentiate the efficacy of ICIs through inhibiting COX2-mediated immunosuppression. Although not available in this study, serum PGE2 or other related immune biomarkers for assessing COX2 activity may serve as important biological correlatives for future prospective studies.

Clinical evidence also indirectly supports the potential synergy between COXi and ICIs. A secondary analysis of two prospective cohort studies correlated improved colorectal cancer survival from aspirin use with low tumorous CD274 (PD-L1) expression.13 Differential effect of CD274 status on the antitumor efficacy of aspirin underscores the potential multiplicity of immunosuppressive mechanisms deployed by tumors. Furthermore, greater cancer survival with aspirin use in CD274-low tumors suggests that blockade of the PD-1/PD-L1 axis in CD274-high tumors may synergize with the immunomodulatory effects of COX inhibition. On the other hand, Botti et al revealed that COX2 expression positively correlated with PD-L1 expression in melanoma tumor samples, implying that the synergy from concomitant COX inhibition may potentially be more pronounced in patients with higher predicted response to PD-1/PD-L1 checkpoint blockade.18 The elucidated mechanism of action suggests that COX inhibition leads to antitumor dendritic cell activation, which occurs upstream of checkpoint blockade.16 17 As such, design of future prospective trials investigating the synergy between COXi and ICI would likely gain from testing concomitant COXi use with ICI, which is reflected in our study methodology of analyzing patients who have at least received COXi during their first two cycles of ICI.

A recent exploratory analysis of the REMAGUS02 trial reported survival detriment with COX2-inhibitor celecoxib use in PTGS2 (COX2)-low breast cancer patients, but not in PTGS2-high patients, who received neoadjuvant docetaxel chemotherapy.19 There was significant interaction between celecoxib use and PTGS2 expression, suggesting that both the deleterious effect of celecoxib use with chemotherapy and the therapeutic benefit of COX inhibition in PTGS2-high patients are at play. Several other prospective trials also reported a lack of benefit or association with poorer outcomes with COX2-inhibitor use in patients receiving chemotherapy.20 21 This is in contrast with our results, but given the immunosuppressive function of PTGS2 overexpression, one would expect greater therapeutic synergy of COXi with ICIs, compared with with chemotherapy. In addition, most patients in our cohort used aspirin and NSAIDs, rather than selective COX2-inhibitors.

Our analysis demonstrated that low pretreatment NLR associated with response to ICI in the melanoma cohort, with high NLR (>5) correlating to decreased TTP and OS. Remarkably, our results also showed that the detrimental effect of high pretreatment NLR on TTP was reversed or negated in patients with melanoma who received concurrent COXi with ICIs; the associated benefit from concomitant COXi use was greater in patients with high NLR than in those with low NLR. Emerging evidence indicates that pretreatment NLR is a prognostic marker for a wide range of malignancies, with NLR values of >4 or>5 being associated with worsening OS and/or disease-free survival.22–24 Results from retrospective analyses of patients with melanoma and NSCLC were also suggestive of NLR having potential predictive value in the response to immunotherapy.25 26 To date, the underlying biological mechanism of NLR as a novel biomarker is unclear and efforts are underway to elucidate this. Likely an oversimplification, NLR represents the balance between the immunosuppressive protumor neutrophil population and the adaptive antitumor immunity conferred by lymphocytes.23 27 This implies that COX inhibition may potentially mitigate systemic immune tolerance characterized by high NLR. Although there was no association between NLR and TTP in the NSCLC cohort, the association between NLR and OS was significant. Future prospective studies are warranted to validate the effect of COXi on the predictive value of NLR in patients receiving ICIs.

Stratification of patients with melanoma by the ICI types used revealed a significant increase in TTP associated with COXi use in patients who received anti-CTLA-4 (ipilimumab) monotherapy. While COXi use was not significantly associated with an increase in TTP in the subgroups of patients who received PD-1/PD-L1 blockade or CTLA-4/PD-1 combination, there were trends that skewed largely toward favorable outcomes with COXi use. The lack of statistical significance is likely due to small sample sizes in subgroup analysis. However, our results indicate that the benefit of COX inhibition may be more pronounced when combined with anti-CTLA-4 blockade. It is possible that greater synergy exists between CTLA-4 blockade and COXi, given that both agents target the initial cascades of T cell priming by dendritic cells.16 17 28

Although data for concurrent COXi use with ICIs must be obtained from real-world studies such as this one, given the lack of prospective evidence, there are several limitations to consider. Outcomes of this study were assessed retrospectively, and therefore, are subject to potential bias and confounding from unmeasured variables. However, we were able to validate our results through objective response assessment by radiologists per the RECIST criteria. The sample size of this study is relatively small, given that this is a single institution study with multiple exclusion criteria in patient selection aimed to minimize confounding bias. As such, we were unable to demonstrate statistical significance in all the endpoints of our subgroup analysis, although many of our reported 95% CIs are suggestive of favorable trends. Another limitation of this work is that PD-L1 status was not available in most of our melanoma and NSCLC patients, and therefore, was not included in our model. While PD-L1 expression in the tumor is predictive of response to PD-1 blockade therapy in several cancers, PD-L1 is not routinely tested in melanoma or used to select patients for treatment, as even PD-L1-negative patients may respond.3 29 Alternatively, we collected tumor mutation burden data that were available for a subset of patients that underwent genomic testing (Foundation Medicine), but the limited available data were insufficient for inclusion in multivariate analysis. Currently, it remains unclear how tumor mutation burden impacts melanoma in regards to predicting response to ICI therapies.30

In conclusion, our study showed that concomitant COXi use during ICI therapy for patients with metastatic melanoma and NSCLC is associated with dramatic improvements in outcomes. This analysis is, to our knowledge, the first report of the beneficial effect of COXi use in patients receiving ICIs. We also found an intriguing interaction between NLR and COXi use on TTP in patients with melanoma, suggesting the potential role of COXi to reverse immune tolerance in cancer patients. Our findings provide clinical evidence to support the underlying mechanism of synergy between ICI and COXi through reversing the immunosuppressive state of tumor microenvironment. These findings merit prospective study to evaluate this low-cost and easily implementable strategy that has potential to significantly improve the outcomes of patients receiving ICI.