First-Line Dual Checkpoint Blockade for NSCLC?

Adding a second checkpoint inhibitor to chemotherapy improves outcomes among patients with non–small cell lung cancer (NSCLC) who have STK11 and/or KEAP1 mutations, according to the authors of a new paper.

These findings, drawn from a post hoc analysis of phase 3 data, are backed up by cell line and mouse data revealing clear mechanisms of efficacy, making the collective evidence compelling enough to reshape clinical practice, reported lead author Ferdinandos Skoulidis, MD, PhD, of The University of Texas MD Anderson Cancer Center, Houston.

“Although STK11 and KEAP1 mutations are associated with limited benefit from PD-1 or PD-L1 [PD-(L)1] inhibition, the association between these mutations and benefit from combinations of PD-(L)1 inhibitors with chemotherapy is not yet as well established,” the investigators wrote in Nature.

Skoulidis and colleagues conducted the subgroup analysis of POSEIDON trial data and characterized underlying biologic mechanisms using mouse models to address this knowledge gap.

What Were the Original Findings of POSEIDON?

The POSEIDON trial involved 1013 patients with metastatic NSCLC. Treatment arms included standard chemotherapy alone, chemotherapy plus programmed death ligand 1 (PD-L1) inhibitor durvalumab, and chemotherapy plus durvalumab and cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) inhibitor tremelimumab.

Adding durvalumab to chemotherapy significantly improved median progression-free survival (PFS) but not median overall survival (OS), while dual checkpoint blockade boosted both PFS and OS.

These findings provided support for the dual approach in the first-line setting, but not preferentially so. Experts called for more long-term data, questioned the survival benefit in terms of the increased toxicity, and noted the lack of biomarkers for patient selection.

What Did Post Hoc Analysis Highlight About POSEIDON?

The present analysis aimed to validate two actionable biomarkers.

“We and others have previously observed that alterations in STK11 and KEAP1 can promote an immunosuppressive tumor microenvironment and together might be responsible for half or more of the primary resistance to PD-(L)1 inhibition among patients with nsNSCLC when given as monotherapy,” Skoulidis and colleagues wrote.

From the original 1013 patients, 612 had non-squamous NSCLC and were evaluable for mutations. Among them, 87 had STK11 mutations and 37 had KEAP1 mutations.

As anticipated, patients in the STK11/KEAP1 subgroup saw little to no benefit from adding durvalumab to chemotherapy, but adding tremelimumab on top yielded notable improvement.

This was first observed in the objective response rate, which was 42.9% with dual checkpoint blockade plus chemotherapy vs 30.2% with single checkpoint blockade plus chemotherapy and 28% for chemotherapy alone. Durations of response improved in kind.

Survival outcomes also trended toward improvement in the dual checkpoint arm, which had a median OS of 15.8 months vs 7.3 months for durvalumab plus chemotherapy (hazard ratio [HR], 0.64; 95% CI, 0.40-1.04) and 10.5 months for chemotherapy alone (HR, 0.50; 95% CI, 0.29-0.87). PFS showed similar trends.

How Do Findings Relate to Previous NSCLC Subgroup Research?

Skoulidis and colleagues noted that their findings align with those of the CheckMate 9LA trial, which showed that patients with STK11 and/or KEAP1 mutations had better outcomes with dual checkpoint blockade plus chemotherapy than with chemotherapy alone.

“These data support the hypothesis that CTLA-4 inhibition can mitigate the resistance to chemotherapy plus PD-(L)1 inhibition observed in patients who have STK11 and/or KEAP1 mutations and suggest that this group of patients derives greater benefit from CTLA-4 inhibition than do patients who lack either alteration,” Skoulidis and colleagues wrote.

Grace Dy, MD, professor of oncology in the Department of Medicine at Roswell Park Comprehensive Cancer Center, Buffalo, New York, noted that in the present analysis, PD-L1 expression status did not predict outcomes; however, patients with STK11 and/or KEAP1 mutations typically have low or negative PD-L1 expression, which has been linked with better responses to CTLA-4 inhibition in multiple trials.

“In the CheckMate 227 and CheckMate 9LA studies, we have seen that patients with PD-L1–negative tumors appear to derive greater and more durable long-term overall survival benefit from dual immune checkpoint blockade compared to patients receiving anti-PD1-based therapy alone,” Dy said in a written comment. “While we take the necessary caveats on cross-trial comparisons, the same survival trend favoring CTLA-4-based immune checkpoint blockade is seen compared to the tail of the survival curves observed in PD-L1–negative patients enrolled in the KEYNOTE studies (KEYNOTE-189, KEYNOTE-407).”

Detecting improvements in survival within PD-L1 patients “may not be readily apparent until later when looking at the tail of the survival curves,” she added.

What Mechanisms of Action Explain Relative Benefits of Dual Checkpoint Blockade?

To elucidate underlying mechanisms of action, Skoulidis and colleagues conducted a series of experiments involving cell lines and mouse models of Stk11- and Keap1-deficient NSCLC.

“For us, it was critical to provide mechanistic support for the observed clinical benefit in POSEIDON, especially since this is based on a retrospective subgroup analysis,” Skoulidis said in an interview.

Their efforts revealed a strong link between the mutations and resistance to PD-(L)1 inhibition.

Inactivation of Stk11 and Keap1 promoted an immunosuppressive tumor microenvironment, marked by increased infiltration of suppressive myeloid cells and a reduction in CD8+ effector T cells. This immune imbalance contributed to evasion of immune destruction and limited the efficacy of programmed cell death protein 1 (PD-1) blockade.

Dual checkpoint blockade reprogrammed the immune microenvironment, leading to increased activation of CD4+ T helper (Th) cells, specifically the Th1 subtype, while inducing tumoricidal changes in myeloid cells. Consequently, antitumor responses improved, resulting in tumor regression and prolonged survival, compared with PD-1 monotherapy.

“Addition of CTLA-4 [inhibition] turns the two cardinal components of the suppressive microenvironment of these tumors on its head, and that’s why we believe we are observing this clinical benefit,” Skoulidis said. “This is not a mere association…but also based on very solid mechanistic data across a multitude of different models.”

Are Data Sufficient to Shift to First-Line Dual Checkpoint Blockade?

“Our work strengthens the available evidence that this regimen — and chemoimmunotherapy more broadly, with dual immune checkpoint blockade — constitutes a preferred approach for these patients,” Skoulidis said. “I personally, and I think physicians within MD Anderson, as well as a lot of physicians that I talk to, are already using — based on these data — the POSEIDON regimen, as well as, more broadly, chemoimmunotherapy with dual immune checkpoint for patients with these alterations.”

This view, however, remains contested by some oncologists.

Lei Deng, MD, assistant professor in the Division of Hematology and Oncology at the University of Washington, Fred Hutchinson Cancer Center, Seattle, called the new data “intriguing” and “hypothesis-generating,” but stopped short of supporting preferential first-line use.

“This study is a post hoc analysis, so you don’t have a lot of patients,” Deng said. “It is still not strong enough or definitive enough to make it standard of care to use dual checkpoint blockade for [patients with STK11 and/or KEAP1 mutations].”

The cell line and mouse data help explain biologic mechanisms of efficacy, he said, but these findings do not obviate toxicity concerns.

“You are adding one more agent, and this agent is more toxic than single checkpoint blockade,” Deng said. “So, if you weigh the risk, it is known, [but] the benefit is suggestive. I am not sure if the risk-benefit ratio would argue for routine implementation of this regimen yet.”

On the other hand, he noted, the combination is the US Food and Drug Administration–approved in this setting, so “it is not wrong to use it.”

Jyoti Malhotra, MD, director of thoracic medical oncology at City of Hope Orange County in Irvine, California, had a similar take.

“The clinical data presented so far is exploratory and limited by the small sample size,” Malhotra said in a written comment. “Data from an ongoing phase 3 trial (TRITON) is awaited before dual checkpoint blockade becomes the standard of care in this setting.”

Hossein Borghaei, DO, chief of the Division of Thoracic Medical Oncology at Fox Chase Cancer Center, Philadelphia, was also unequivocal when asked if dual checkpoint blockade with chemotherapy should be considered the preferred first-line treatment option in patients with STK11 and/or KEAP1 mutations.

“No,” he said in a written comment. “The data and the hypothesis are very strong, but it is all based on retrospective clinical data, cell line data, and mouse models. We need a randomized study to test the hypothesis.”

Incidentally, Borghaei is on the steering committee for the TRITON trial. He shared this potential conflict of interest before praising Skoulidis and colleagues for their efforts, noting that the present findings underscore the broader importance of widespread tumor profiling and access to resultant data.

“This is a beautiful story that has developed over the last few years based on the research by the group from MD Anderson who has reported the current Nature article,” he said. “This highlights the possible utility of collecting sequencing data on [all] patients’ tumors. These sorts of understandings and new ideas could arise only if there is access to this information.”

The study was supported by AstraZeneca, the National Cancer Institute, the Gunnigar Fund, and others. The investigators disclosed additional relationships with Novartis, Merck, Amgen, and others. Deng disclosed relationships with Merck, BridgeBio, MJH Life Sciences, and others. Dy disclosed relationships with Eli Lilly and Company, Janssen Pharmaceuticals, Meru, and others. Malhotra has previously served as a consultant for AstraZeneca. Borghaei has served as a consultant for AstraZeneca and is on the steering committee for the TRITON trial.