Nanoparticle-based drug delivery in advanced pancreatic ductal adenocarcinoma: is it time to deliver yet?

Introduction

Pancreatic ductal adenocarcinoma (PDAC) has a dismal 5-year overall survival (OS) for all stages of disease which has only increased to 12% since 2012. This falls to 3% for patients presenting with metastatic PDAC (1). According to the Global Cancer Observatory (GLOBOCAN) data from 2020, PDAC accounted for over 466,003 deaths annually (2). Genomic research efforts have led to a deeper understanding of the mutational and structural landscape, dominated by oncogenic mutations, with Kirsten rat sarcoma viral oncogene (KRAS) mutations identified in 90% of patients. However, despite the recent advances to support KRAS inhibitors for PDAC, resistance may develop and chemotherapy will continue to contribute as the backbone in PDAC management. This underscores the urgent need to identify better treatment options and enhance drug delivery mechanisms. One of the first positive phase III trials with combination therapy in PDAC was Canadian Cancer Trials Group (CCTG) PA.3 combining the epidermal growth factor receptor (EGFR) inhibitor, erlotinib to gemcitabine (3). However, in the absence of a biomarker to enrich for response, the benefit was not felt clinically relevant. Since then, more combinations have moved into standard practice.

In the first-line metastatic setting, there are two available chemotherapy standard of care options, without evidence of biomarkers to guide the decision to choose one over the other. These options include: FOLFIRINOX often used in a modified version (mFOLFIRINOX) with reduced dose irinotecan and/or omission of bolus 5-fluorouracil or other variations) or gemcitabine combined with nano-particle albumin-bound paclitaxel (nab-paclitaxel) (4,5). The NAPOLI-3 trial has reported on the superiority of NALIRIFOX (liposomal irinotecan, oxaliplatin, leucovorin, and fluorouracil) over gemcitabine and nab-paclitaxel. This represents the first positive trial in PDAC in over a decade (6). Survival remains less than 1 year however, and many physicians will continue to use mFOLFIRINOX in the first-line setting given the substantial differences in cost and the similar survival. Furthermore, it has not been approved in several countries and physicians do not have access to it. Unfortunately, in PDAC biomarkers to direct therapies and to predict outcomes in the aforementioned regimens are lacking aside from germline or somatic alterations in BRCA1/2 (Breast Cancer Gene 1/2) or PALB2 (Partner and Localizer of BRCA2) (7). This is in stark contrast to lung cancer and breast cancer where the identification of biomarkers has totally altered the landscape to direct and tailor a more personalised approach translating into an outstanding survival benefit. In patients with PDAC on first-line therapy, resistance mechanisms emerge and become dominant, with almost 50% of patients unable to receive second line therapy. Chemotherapy combinations work through a number of different mechanisms, potentially resulting in significant associated toxicities. Therefore, developing drugs that more accurately target tumor cells, instead of normal cells and developing more specific drug delivery systems, has been the purpose of a large proportion of pan-cancer-related research.

Background and pre-clinical models

In recent years, there has been a growing focus on advancing nanotechnology to better target tumours in a more efficient and safer way (8). Nanoparticle (NP)-based drug delivery systems offer several benefits compared to conventional cytotoxic chemotherapy delivery methods. These advantages include improved pharmacokinetics, precise targeting of cancer cells, lower side effects and the ability to potentially overcome drug resistance mechanisms (9). NPs can carry various payloads, such as traditional chemotherapy drugs and nucleic acids (10). Their size and surface properties allow NPs to retain the therapeutic payload, minimizing exposure to healthy tissues and ideally preventing drug exposure to non-target areas (11). Certain types of NPs have also been demonstrated to help stabilise and increase the half-life of packaged drugs (11). NP deliver drugs to their desired destination in either a targeted or passive manner. They can be targeted by coupling a peptide or antibody to the surface of the NP, specific to a receptor on the target. In passive targeting, the NP is introduced to the circulatory system and passively directed to the target site based on properties such as shape, molecular site, temperature and pH (12). While the technology has been in development for over a decade, the implementation of this treatment delivery system to solid tumors has remained stagnant and it has not been introduced into standard of care practice, the reasoning for this is multifactorial, including manufacturing concerns, with some NP production methods not easily scalable for mass production. Limited clinical evidence, despite promising preclinical studies, clinical trials have not been carried out on a larger scale to establish safety and effectiveness. There have also been biocompatibility and toxicity concerns, particularly with “leaky” NPs containing highly toxic payloads (13,14). Anti-body drug conjugate delivery systems on the other hand are transforming the landscape of oncological treatment in several solid tumour sites, across all stages of disease (15).

The “Carolyn Trial” reviewed here is a phase I/IIa trial in advanced PDAC treated with cytotoxic drug-packaged, EGFR-targeted nanocells and glycolipid-packaged nanocells, in patient who had exhausted all other treatment options (16).

Pre-clinical studies are frequently overlooked in the presence of clinical trial results. They play the foundational role in our understanding of the genetic and molecular mechanisms of disease as well as the pharmacodynamics and pharmacokinetics of the trial drugs being developed to treat the disease. Robust design and execution of these studies help improve the predictive value of preclinical studies translating into successful clinical trials.

The generally accepted definition of a NP is an engineered particle with one or more dimensions measuring between 1 and 100 nm. The particle described in the Carolyn study is somewhat larger, measuring 400 nm in diameter. It has been referred to as a minicell in their referenced preclinical studies (17-19) and is designated as EnGeneIC Dream Vector (EDV) in the study.

Previous studies by the group discuss the generation of the bacterially derived minicells or EDV, these essentially are a 400 nm lipopolysaccharide (LPS) coat with an empty core. The study team discuss their packaging with cytotoxic agents, their robustness, and in particular their ability to retain the incorporated drug without undesired efflux, which has been a limitation of other nano-particle/polymer technologies (18). This is a significant concern when administering a super-toxic chemotherapeutic, and the desire to limit off-target effects (18,20). Preclinical studies have been carried out in various murine models as well as small studies in larger mammals with dogs and pigs. Although no safety signals were generated from these studies, they were carried out in a small number of animals, two dogs and three pigs, with only five intravenous doses of minicells being delivered (17-19). Due to the limited nature of these studies, such as small sample size and limited dosing schedule, toxicity data from repeated and extended administration of the minicells cannot be extrapolated.

In the phase I/IIa Carolyn trial, they package the EDV/minicells with either PNU-159682 or α-galactosyl ceramide (αGC). PNU-159682 is a secondary metabolite of nemorubicin which itself is a derivative of doxorubicin. PNU-159682 is more potent than either nemorubicin (800–2,400-fold) and Doxorubicin (2,100–6,400-fold). αGC is a glycolipid which stimulates invariant natural killer T-cells (iNKT cells). The EDV/minicells packaged with PNU-159682 are targeted to tumor cells by attaching an EGFR antibody to the polysaccharide component of the LPS coat and designated E-EDV-D682 by the study team. They have suggested in their preclinical studies this to be effective against multidrug resistant PDACs. The αGC packaged EDV/minicell does not have an antibody on its LPS coat and reaches its target in a passive manner, designated EDV-αGC by the study team.

The Carolyn study team have referenced previous studies that described how αGC is displayed by major histocompatibility complex (MHC) class 1 like molecule CD1d (cluster of differentiation 1d) and recognized by the iNKT cell surface receptor stimulating an immune response (17-19). This is built upon through the use of the mouse allograph, where they demonstrate that iNKT cells extracted from spleens of mice treated with mEGFR-EDV-D682 plus EDV-αGC are more effective at killing KPC-1242 mouse pancreatic cancer cells compared to iNKT cells extracted from mice treated with just the vector or vector plus drug without αGC, suggesting a synergistic role of αGC when paired with drug. The murine studies were carried out solely in female mice. This can be considered a relative limitation of the preclinical studies. Over the past decade best practice has been to carry out animal studies in both sexes. In 2014 the National Institute of Health published a policy that sex in cell line and animal studies should be balanced unless studying a sex-specific disease such as ovarian or testicular cancer (21). Many global research funding bodies have made similar recommendations over the last 10 years for numerous justifiable reasons (22). For example, and relevant to this study, there are clear sex differences in immune response (23), which cannot be evaluated from studies on single-sex animals. We therefore must question the preclinical results and the basis upon which this phase I/IIa study rationale was based. Furthermore, their cited preclinical models date back more than a decade, which should be acknowledged in their publication of results.

One potential benefit of the large size of the EDV/minicells is that it stays within the vasculature, instead of leaking into healthy tissue, allowing it to specifically reach the tumor environment by exploiting the leaky vasculature that is a hallmark of tumors, minimizing toxicity and delivering more potent doses locally to tumor cells. This mechanism of action is discussed in their preclinical studies noted that there is debate surrounding how EDV/minicells are distributed in the tumor microenvironment; however, it is not tested, and this mechanism remains purely speculative (17,18). EDV are also phagocytosed by macrophages and dendritic cells triggering both innate and adaptive immune responses specific to the tumor, increasing antitumor activity. Based on the pre-clinical models, they attempt to demonstrate that EDV-αGC added to E-EDV-D682 could potentially augment antitumor activity and improve responses.

The Carolyn phase I/IIa

This clinical trial explored different dosing regimens across two Australian cancer centres. As expected, primary endpoints included safety, tumour response, and OS, while secondary endpoints included progression-free survival (PFS) and cytokine response. Eligible patients had advanced PDAC and EGFR expression on tissue assessment by immunohistochemistry, on historical tissue samples. The complicated study design explored five dosing regimens to determine safety: regimen 1 and regimen 2 both followed an 8-week schedule with different dosing patterns; initially they included a bi-weekly dosing schedule for the first 2 weeks of the cycle. Regimen 3, 4 and 5 followed a 5-week schedule with variations in timing and delivery methods, including bolus administration instead of infusion, while maintaining the same dosing schedule. The trial followed a classic dose escalation protocol. The full dosing schedule is outlined in Table 1. Between 2019 and 2022, a total of 25 patients were enrolled in the study. Of these, 18 patients received at least one cycle of treatment, one patient withdrew consent, and seven patients (28%) were withdrawn before completing the first cycle due to rapidly progressive disease and associated co-morbidities. Tumor response assessment for OS and PFS involved two groups: patients who received at least one dose of treatment and those who completed at least one cycle of treatment. Given the aggressive nature of advanced pancreatic cancer, rapid loss of patients from the study is not unusual.

The therapy appears to be well tolerated. Safety results showed that 76% of the 25 patients experienced at least one treatment-related adverse event (AE), all of which were mild to moderate (grade 1 or grade 2). Common treatment-related AEs included infusion-related reactions, headache, lethargy, and back pain. Notably, no patients experienced grade 3, 4, or 5 treatment-related AEs. Although the two longest times to development of progressive disease were 10.3 and 12 months, the median PFS (mPFS) was 1.8 months. There is limited data from both the preclinical animal models and the clinical trial to establish if there is a cumulative toxicity of either the drug and delivery mechanism over a longer treatment period. There is also limited information on how PNU-159682 is metabolized or excreted. It is important to note that although the number of EDV delivered to the patient is relatively well controlled, review of the supplementary data demonstrates a large variation in the concentration of both αGC and PNU-159682 being packaged into the EDV, with an approximate 30% variability in dose of PNU-159682 and αGC between tested batches of EDV. This should raise concerns over the accuracy and consistency of the dose of PNU-159682 and αGC being delivered to patients.

In the small evaluable subset, which includes patients who completed at least one cycle of EDV treatment, 17 patients, 47.1% (overall 28.6%) exhibited stable disease (SD) at the end of cycle 1. Notably, the most promising response occurred in regimen 2, where one patient showed SD at cycle 1 and partial response from cycle 2 to cycle 6 before withdrawing after cycle 6. By the end of cycle 1, 9 patients (53%) showed unconfirmed progressive disease on radiological examination. Response was evaluated by Response Evaluation Criteria in Solid Tumors (RECIST) 1.1.

OS analysis revealed that the median OS for subset 1, comprising patients who received at least one dose of treatment which we believe relates to one intravenous EDV delivered therapy but not having to complete a full cycle, was 4.4 months. Among the 17 patients who completed at least one cycle of treatment, the median OS was 6.9 months. For the seven patients withdrawn before completing one cycle, the median OS was 1.8 months. Within the subset of patients who completed one cycle, one patient had not received any prior treatment, while six had received only one line of prior chemotherapy (subgroup 1), and 10 had received more than one line of prior treatment (subgroup 2). The median OS for subgroup 1 was 6.9 months and for subgroup 2 was 7 months. However, the comparison between these groups did not yield statistical significance (P=0.51).

PFS analysis was based on 22 progressions recorded, with three patients censored. The median PFS was 1.8 months. Among the subset that completed one cycle of treatment, the median PFS was 2.2 months. Notably, two patients experienced the longest development of progressive disease at 12 and 10.3 months, respectively, and these patients were in treatment regimens 2 and 4 (Table 1).

Regarding body weight stabilization, weight loss is a significant marker in PDAC, making this observation noteworthy. The authors noted that only 3 out of 17 patients experienced weight loss of at least 5% of their pre-treatment weight. Interestingly, six patients showed weight gain during the treatment period. Finally, the authors measured inflammatory cytokines (IL-6, IL-8, TNF-alpha, IFN-gamma), but did not observe any major significant changes in these markers.

Conclusions and future directions

The Carolyn trial/ENG 9 is the first study where PNU-159682 was administered intravenously in patients. Nine to 76 repeat doses of EGFR-EDV-D682/GC were delivered in the 17 patients with advanced PDAC, and the results showed minimal to no toxicity. Targeting is accomplished by attaching antibodies to the EDVs, which specifically recognize EGFR, an overexpressed protein on the surface of these patients PDAC tumor cells. This overexpression has been previously identified in the patients’ historical tumor samples as part of inclusion criteria. The safety findings here are a truly remarkable observation given the significant toxicity that these patients experience when receiving standard of care therapy. There are some signals emerging from their results that this method of drug delivery may play a role to overcome multidrug resistance in tumor cells found in patients with late-stage PDAC who are heavily pre-treated. The questions that remain include, are we targeting the cells with the correct chemotherapy agents, and, despite the efficacy demonstrated in vivo and in vitro studies in animal models, more research is needed to understand the long-term side effects of NP use, particularly in terms of systemic toxicity and clinical translation. Given the small numbers, it is difficult to conclude that any one of the treatment regimens utilized here is superior to the other. Furthermore, is EGFR the most appropriate target in PDAC, with the modern genomic data and in the era of KRAS inhibition? A KRAS-based new technology delivery system may be of more meaningful clinical benefit to patients.

PDAC is one of the oncological pathologies with the highest associated mortality rate. The treatment of PDAC is still a continuous challenge with regards to the emergence of early chemoresistance. Thus, all technologies should be considered as potential strategies to deliver drugs that would allow tumor-directed administration of cytotoxic drugs. To put this current study and results into context, while there are several promising observations plus good toxicity and safety signals, more work with trial technology is needed and perhaps incorporated into the current treatment paradigm in this disease. Locally advanced PDAC populations may be an ideal population to study as they are often left out of novel systemic trials. Further NP delivery-based studies are ultimately needed in larger clinical trials to confirm the longer-term benefits for patients with advanced PDAC who desperately need such developments.

Acknowledgments

Funding: None.

Footnote

Provenance and Peer Review: This article was commissioned by the editorial office, AME Clinical Trials Review. The article has undergone external peer review.

Peer Review File: Available at https://actr.amegroups.com/article/view/10.21037/actr-24-35/prf

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://actr.amegroups.com/article/view/10.21037/actr-24-35/coif). The authors have no conflicts of interest to declare.

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