PD-1/PD-L1 Inhibitors + Co-therapies: The Future of NSCLC Therapy Lies in Smart Combinations

For a subset of patients battling non-small cell lung cancer (NSCLC), cancer immunotherapies, notably immune checkpoint inhibitors of programmed cell death protein 1 (PD-1) and programmed death-ligand 1 (PD-L1), have opened the door to a longer, fuller life. In patients with advanced NSCLC whose tumors show moderate to high expression of PD-L1 in at least 50% of tumor cells, treatment with PD-1 inhibitor, pembrolizumab (Keytruda®) alone has been shown to double average overall survival (OS) compared to chemotherapy, from 13.4 months to 26.3 months, and to significantly prolong progression-free survival (PFS) from 6 months to 10.3 months.^[1] For patients with advanced NSCLC whose tumors show expression of PD-L1 in less than 50% of tumor cells, triple combination regimens with PD-1 inhibitor, nivolumab (Opdivo®), CTLA-4 protein inhibitor, ipilimumab (Yervoy®), and platinum-doublet chemotherapy, average OS was prolonged by approximately 30% compared to chemotherapy alone (from 10.9 months to 15.6 months), with 63% of patients alive at 1 year compared to 47% with chemotherapy.[2]

For these patients, each added month can hold moments that matter profoundly, and with fewer setbacks from the disease, there’s more space to enjoy them — a meaningful, undeniable achievement. However, the numbers alone make it clear that too many people with NSCLC still gain too little from PD-1/PD-L1 inhibitors, for too short a time. In the KEYNOTE-024 and CheckMate 9LA studies referenced above, nearly 68% of the patients treated with pembrolizumab alone had passed away within five years, whereas 82% treated with the triple combination of nivolumab, ipilimumab and chemotherapy had passed away at five years.^[3] There is a broad consensus among oncologists and researchers that PD-1/PD-L1 inhibitors are only 20% effective in treating lung cancer, with those deriving the least benefit including patients with tumors with little to no immune cell infiltration (immunologically “cold” tumors), a high tumor burden or rapidly progressing disease, and those with underlying immunosuppression.[4]

The development of co-therapies to combine with PD-1/PD-L1 inhibitors has become essential to broadening the NSCLC population that may benefit from these therapies, priming lung tumors to become more responsive to immunotherapy, faster, and avoiding drug resistance.[5] Today, there are over 200 active and recruiting interventional combination studies in NSCLC involving pembrolizumab, reflecting a widespread recognition that available therapies, while transformative for some, are insufficient for most.[6] The volume of trials also reflects a forward-looking response to an evolving competitive and patent landscape, as Big Pharma companies seek to extend the clinical and commercial life of their cornerstone immunotherapies. Ultimately, what’s clear is this: combination strategies are shaping the future standard of care in NSCLC.

Within this landscape poised for novel combination regimens, L-DOS47 directly targets an entire class of immune escape that most other co-therapies for NSCLC leave untouched: the acidic tumor microenvironment (TME) and its impact on the tumor immune microenvironment (TIME), which is increasingly recognized as a decisive factor in the success or failure of cancer immunotherapies.[7]

Emerging Combination Strategies in NSCLC

Lung cancer remains the leading cause of cancer-related death worldwide, claiming more lives each year than colon, breast, and prostate cancers combined.[8] NSCLC accounts for approximately 85% of all lung cancer types, developing from the epithelial cells that line the surface of the airways and lungs, and comprised of a heterogenous group of tumors, primarily:[9]

Adenocarcinoma (ADC; arising from mucus-producing glandular epithelial cells and accounting for approximately 50% to 60% of NSCLCs);
Squamous cell carcinoma (SCC; originating from the squamous cells lining the respiratory tract and accounting for 30% to 35% of NSCLCs);[10]
Large-cell carcinoma of the lung (LCC; comprised of a group of large-cell lung cancers that progress more rapidly than other forms of NSCLC, accounting for 10% to 15% of NSCLC cases).[11]

Because early stages are often asymptomatic or symptoms are nonspecific, 40% of NSCLCs are diagnosed after they have metastasized to another part of the body, making NSCLC a cancer that is very difficult to treat.[12]

Since 2015, PD-1/PD-L1 inhibitors have emerged as the gold standard for first-line therapy in Stage III–IV NSCLC (alone, or in combination with chemotherapy).[13] PD-1 is a receptor and immune checkpoint protein found on the surface of immune cells, notably T cells, and PD-L1 is its ligand. In healthy tissue, PD-L1 binds to PD-1 to inhibit T cell activation when strength and duration of immune responses need to be regulated. However, PD-L1 is also expressed by certain tumor cells to silence T cell activation and suppress their ability to attack the tumor, effectively co-opting the immune system’s defense mechanisms against itself. In this context, PD-1/PD-L1 immune checkpoint blockade works to block the interaction between T cell PD-1 and tumor PD-L1, intercepting immune silencing by the tumor and taking the brakes off T cells to mount an anti-tumor immune response.

Despite their transformative potential, the efficacy of PD-1/PD-L1 inhibitors is largely dependent on how present and active the immune system is at the tumor site and how well it can mount a cell-mediated attack on cancer cells. This has driven a surge in the development of co-therapies for NSCLC designed to sensitize tumors to immunotherapy by addressing specific tumor mechanisms that enable cancer to thrive, reversing immune suppression, and delivering cytotoxic compounds directly to tumors to complement anti-cancer immunity:

KRAS Inhibitors — Mutations in the KRAS gene, specifically the G12C mutation, are present in approximately 13% of advanced, non-squamous NSCLCs.^[14] Whereas the KRAS protein produced by this gene acts as a signaling molecule for growth and division in healthy cells, diverse mutations can lead to uncontrolled cell growth and proliferation, and to the development of tumors and metastasis. KRAS inhibitors aim to bind selectively to mutated KRAS proteins, locking them into an inactive state and disrupting their signaling pathway that tells cancer cells to grow. An ongoing Phase II study in patients with advanced or metastatic KRAS G12C-positive NSCLC combining KRAS G12C inhibitor, adagrasib (Krazati®, approved for second-line therapy of KRAS G12C-positive metastatic NSCLC) with pembrolizumab has recently shown average OS of 18.3 months and PFS of 11 months, with the greatest benefit observed in patients whose tumors express PD-L1 at 50% or greater (PFS of 27.7 months).[15]

Dual Checkpoint Blockades — Combining agents to block more than one immune checkpoint, as in the CheckMate 9LA study referenced above pairing a PD-1 inhibitor with a CTLA-4 inhibitor, is being investigated to target complementary pathways of immune regulation. In this context, a promising approach is inhibition of lymphocyte-activation gene-3 (LAG-3), a protein expressed by diverse immune cells that serves as an immune regulator and is overexpressed in NSCLC.[16] Eftilagimod alpha (Efti) is an investigational soluble LAG-3 protein that binds to and activates immune antigen-presenting cells (APCs), enabling the (re)activation and proliferation of T cells, and potentially reversing resistance to PD-L1 inhibitors.[17] In a recent Phase II study as first-line therapy in patients with metastatic NSCLC unselected for PD-L1 (TACTI-002), the combination of Efti with pembrolizumab resulted in average OS of 20.2 months, with 44.7% of patients alive at 24 months, and anti-tumor activity seen across all PD-L1 levels.[18] Efti received Fast Track designation from the US FDA in 2022 as first-line treatment in combination with pembrolizumab for Stage IIIB/IV NSCLC with at least 1% PD-L1 expression.[19] A phase III clinical study is now underway to evaluate the combination of Efti, pembrolizumab and chemotherapy in patients with advanced and metastatic NSCLC (TACTI-004).[20]

Antibody‑Drug Conjugates (ADCs) — Combining the highly specific targeting capabilities of antibodies with potent anti-cancer medicines, ADCs are also emerging as promising partners for PD-1/PD-L1 inhibitors in NSCLC. A notable candidate is datopotamab deruxtecan (Dato-DXd), an ADC that targets trophoblast cell surface antigen 2 (Trop2), a cell-surface protein over-expressed in multiple tumors, including NSCLC, with an exactecan payload (an inhibitor of topoisomerase I).[21] Datopotamab deruxtecan is currently being evaluated in combination with pembrolizumab with/without platinum-based chemotherapy in patients with advanced/metastatic non-squamous NSCLC and less than 50% PD-L1 expression.[22]

Other co-therapy approaches with PD-L1/PD-1 inhibitors include new modalities of established oncology therapies, such as radiotherapy (stereotactic body radiation therapy, SBRT, and stereotactic ablative radiotherapy, SABR), or bispecific antibodies combining PD-L1/PD-1 blockade with a second tumor-targeting mechanism in a single compound.^[23] Notably, in a recent Phase III study in patients with PD-L1-positive advanced NSCLC, Ivonescimab, a bispecific antibody that targets both PD-1 and Vascular Endothelial Growth Factor (VEGF, a protein that plays a crucial role in tumor angiogenesis), has been reported to double average PFS compared to pembrolizumab (11.4 months compared to 5.82 months), representing a 49% reduction in risk of disease progression or death.[24] Overall survival results and confirmatory studies with ivonescimab in broader patient populations will be critical in determining whether these early gains in progression-free survival translate into a sustained, generalizable benefit.

The closer we look at combination co-therapy strategies, the clearer it becomes that the landscape is necessarily fragmented, with the emergence of increasingly personalized and precision approaches to NSCLC. However, most remain focused on a limited set of immune escape pathways. The next leap forward will require co-therapies that address additional, decisive barriers to immune activity in NSCLC, broadening and sustaining the benefit of PD-1/PD-L1 inhibitors across diverse tumor profiles.

L-DOS47 as a Co-Therapy for PD-1/PD-L1 Inhibitors in NSCLC

Helix BioPharma’s lead candidate, Tumor Defense Breaker™ L-DOS47, is an antibody-enzyme conjugate that complements immune reactivation triggered by PD-1/PD-L1 checkpoint inhibitors, by targeting another, critical immune escape mechanism in solid tumors: the acidic, immune-suppressive TME.[25]

The TME acts as a master regulator of immune suppression in solid tumors, creating the dynamic conditions that allow cancer to adapt, grow, multiply and evade immune detection, while systematically sabotaging anti-cancer immune access and function.[26] Importantly, tumor metabolism and the accumulation of lactate metabolites renders the extracellular pH (pHe) of the TME acidic in solid tumors, with a pHe range of 6.4 to 7.1 (whereas the pHe of healthy tissue is approximately 7.4).[27] This acidic milieu has been shown to increase PD-L1 expression by human lung cancer cells, strengthening PD-1/PD-L1 inhibitory signaling, and impairs the effector functions of various immune cells, including T cells, natural killer cells, dendritic cells and macrophages.[28] TME acidity further alters drug structure and charge, reducing the uptake of anti-cancer therapies into the tumor and affecting the delivery and potency of anti-cancer drugs, including chemotherapy and radiation.[29]

L-DOS47 consists of a urease enzyme conjugated to approximately 10 single-domain antibodies (nanobodies) with a high binding specificity for carcinoembryonic antigen-related cell adhesion molecule 6 (CEACAM6), a cell-surface protein lowly expressed in healthy epithelial tissue and highly expressed in difficult-to-treat solid tumors, including NSCLC (particularly lung adenocarcinoma).[30] The nanobodies recognize CEACAM6 where it is abnormally abundant on tumor cells, sparing healthy tissue, and delivering the enzymatic payload of L-DOS47 directly to the tumor surface.[31]

In tumor cells, overexpression and misregulation of CEACAM6 activates cancer signaling pathways that promote tumor cell survival and growth, and helps detaching cancer cells avoid programmed cell death (anoikis), promoting cancer progression and metastasis.[32] Although the intended effect of the nanobodies in L-DOS47 is to deliver the urease payload directly to the tumor cells, recent studies suggest that CEACAM6 blockade inhibiting the interaction of CEACAM6 with CEACAM1 (also a cell-surface protein expressed on the cell surface of immune cells) reactivates the anti-tumor response of T cells.[33] This checkpoint-like mechanism mirrors, in principle, the PD-1/PD-L1 axis, where disrupting ligand–receptor interactions can reinvigorate suppressed T cell activity against tumors. Taken together, these findings suggest that targeting CEACAM6 may offer dual benefits, by both weakening tumor cell survival and restoring immune activity — though this activity has not been confirmed with the L-DOS47 nanobodies.

At the tumor site, the urease enzyme component of L-DOS47 interacts with tumor-local urea, converting it into ammonia and bicarbonate, which increases the extracellular pH (pHe) of the TME. Ammonia has cytotoxic properties, which recently have been discovered to depend strongly on extracellular pH — with higher pH increasing the proportion of membrane-permeable ammonia and thereby enhancing its ability to disrupt intracellular organelle function and impair tumor cell growth.[34] In parallel, elevating alkaline bicarbonate extracellularly at the tumor site has been shown to neutralize the pHe of the TME, increase tumor chemosensitivity (enabling ionizable, weak-base chemotherapeutics, such as doxorubicin, to penetrate tumor cell membranes), and increase the immune cell population within tumors (including T cells, B cells and macrophages).[35] Enriching the tumor immune microenvironment (TIME) with immune cells contributes to turning immunologically “cold” tumors “hot”, while neutralizing the acidic pHe of the TME has been found to decrease tumor PD-L1 levels back toward baseline in animal models, relieving checkpoint-mediated suppression of T cells and enabling them to express immune-activating cytokines.[36]

This multiplicity of immune- and therapy-enhancing effects is supported by the state of the evidence with L-DOS47. The specificity and cytotoxicity (via ammonia elevation) of L-DOS47 have been confirmed previously in different CEACAM6-expressing cancer cell lines (BxPC-3 pancreatic, A549 lung, MCF7 breast, and CEACAM6-transfected H23 lung), in which response to L-DOS47 was positively correlated with the levels of CEACAM6 expression.[37] In an unpublished in vitro study, a 0.4 unit increase in pH with L-DOS47 has been shown to significantly enhance secretion of the cytokine, Interleukin-2 (IL-2) by activated CD8+ T cells — a potent signaling molecule that stimulates growth and activity of T cells and B cells, approved for the treatment of metastatic cancers.[38]

Subsequently, L-DOS47 has been assessed as a monotherapy and as a combination therapy with chemotherapeutics, pemetrexed and carboplatin, in a Phase IB study in patients with Stage IV recurrent or metastatic non-squamous NSCLC. The latter study showed encouraging progression-free survival and clinical benefit signals with chemotherapy, with a 41.7% objective response rate (ORR) and 75% clinical benefit.[39] For reference, earlier studies with pemetrexed and carboplatin have reported ORRs ranging from 24% to 31% in the general NSCLC population.[40] More recently, coupling anti-PD1 pembrolizumab with L-DOS47 has been shown to synergistically limit tumor growth in a mouse model of pancreatic adenocarcinoma (PDAC, which also highly expresses CEACAM6), shrinking tumor volume by 70% and tumor weight by 50% more that pembrolizumab alone within 28 days.[41]

Unlocking the Next Frontier in NSCLC Combination Therapy

The next wave of progress in NSCLC will come from combinations that dismantle multiple, converging tumor defense mechanisms. Most co-therapies in development continue to focus on a narrow set of immune escape pathways, leaving the acidic, immune-suppressive tumor microenvironment largely unaddressed.

L-DOS47 directly targets this decisive barrier, selectively binding to CEACAM6 on tumor cells and enzymatically neutralizing tumor acidity to restore immune infiltration and activity, help turn immunologically “cold” tumors “hot”, and enhance the therapeutic reach of PD-1/PD-L1 inhibitors. As we prepare to advance L-DOS47 into clinical trials to measure its efficacy and safety in combination with a PD-1 inhibitor, pembrolizumab, in NSCLC, L-DOS47 positions pHe modulation as a novel therapeutic approach to complement checkpoint blockade — with the potential to extend the reach of immunotherapy and make hard-to-treat cancers vincible.

References

[1] https://ascopubs.org/doi/10.1200/JCO.21.00174

[2] https://www.thelancet.com/journals/lanonc/article/PIIS1470-2045(20)30641-0/abstract

[3] https://ascopubs.org/doi/10.1200/JCO.21.00174; https://www.ejcancer.com/article/S0959-8049(24)00952-3/fulltext

[4] https://pmc.ncbi.nlm.nih.gov/articles/PMC7242804/

[5] https://pmc.ncbi.nlm.nih.gov/articles/PMC7242804/

[6]https://clinicaltrials.gov/search?cond=NSCLC&intr=pembrolizumab&aggFilters=ages:adult,status:act%20rec,studyType:int&term=combination

[7] https://www.nature.com/articles/s41392-020-00449-4

[8] https://www.who.int/news-room/fact-sheets/detail/lung-cancer

[9] https://pmc.ncbi.nlm.nih.gov/articles/PMC10047909/; https://pmc.ncbi.nlm.nih.gov/articles/PMC7017323/

[10] https://www.mdanderson.org/cancerwise/5-things-to-know-about-squamous-cell-carcinoma-of-the-lungs.h00-159618645.html

[11] https://www.moffitt.org/cancers/lung-cancer/diagnosis/types/large-cell-carcinoma/