Pancreatic cancer: current standards, working towards a new therapeutic approach

Abstract

Pancreatic cancer is the fourth leading cause of cancer deaths with a 5-year survival of 4–6%. Clinical challenges remain to be addressed, since few promising approaches to treat pancreatic cancer have been reported. Here we discuss the potential of a new biotherapeutic agent composed of a lysosomal protein (Saposin C, SapC) and an acidic phospholipid (dioleoylphosphatidylserine, DOPS) which can be assembled into stable nanovesicles (SapC-DOPS) for tackling pancreatic cancer. Phosphatidylserine (PS) is a lipid biomarker on membrane surface of pancreatic cancer cells and can be effectively targeted by SapC-DOPS nanovesicles for cancer-selective therapy. SapC-DOPS nanovesicles have shown excellent pre-clinical therapeutic and safety profiles. Safety profiles which suggests that this new approach is potentially a viable option for pancreatic cancer therapy that is worthy of further clinical development.

Keywords::

• chemotherapy
• combination treatment
• metastases
• monotherapy
• new approach
• pancreatic cancer therapy
• resistance
• SapC-DOPS nanovesicles
• toxicity

Pancreatic cancer remains the fourth most common cause of cancer-related death in men and women in the USA. In 2013, an estimated 45,220 people will be diagnosed with pancreatic cancer and 38,460 people will die of it [1]. The 5-year survival is 6%, and the majority of patients are diagnosed with metastatic disease. Median survival is 9 to 10 months for patients with locally advanced unresectable disease and about 4.5 months for those who present with metastases [2]. The incidence and mortality rates in pancreatic cancer are nearly identical, reflecting the inadequacy of current therapies. In order to look forward to new therapeutic approaches, it is important to understand the current acceptable standards of care based on landmark clinical trials in pancreatic cancer. Multiple potential therapeutic strategies exist, but this paper will focus on the current evidence-based category 1 National Comprehensive Cancer Network guidelines in metastatic disease as well as discuss saposin C-dioleoylphosphatidylserine (SapC-DOPS) nanovesicles as a potential new approach in the treatment of pancreatic cancer.

No chemotherapy agent with single-agent activity has been consistently associated with objective response rates above 10%, or median survival longer than 5–7 months. Gemcitabine is a National Comprehensive Cancer Network category 1 recommendation for patients with pancreatic cancer, particularly those with metastatic pancreatic cancer who do not wish to be treated with a very intensive chemotherapy regimen or those with an Eastern Cooperative Oncology Group performance status of two or greater who are not considered candidates for a more intensive first-line chemotherapy regimen. In a pivotal Phase II study of gemcitabine in patient with 5 fluorouracil (5-FU) – refractory pancreatic cancer, ‘clinical benefit’ was defined as an improvement in pain, performance status or weight without deterioration in any other factor [3], the objective response rate for patients with measurable disease was 11% with a clinical benefit in 27%. A subsequent trial was conducted that included 126 previously untreated patients with stage IV or locally advanced pancreatic cancer who were randomly assigned to 5-FU or gemcitabine [4]; gemcitabine was associated with significantly better clinical response (24 vs 5%), median overall survival (5.6 vs 4.4 months) and 1-year survival (18 vs 2%) compared to 5-FU. This led to the US FDA approval of gemcitabine for this disease in 1996.

Following gemcitabine approval, multiple Phase III clinical trials comparing gemcitabine to various chemotherapy doublets incorporating gemcitabine plus a study drug were embarked upon with no significant benefit observed until 2013. Since pancreatic cancers often express receptors for EGF [5], studies incorporating small-molecule tyrosine kinase inhibitors of the EGF receptor such as erlotinib, as well as monoclonal antibodies directed against this molecule, were conducted. A Phase III trial from the National Cancer Institute of Canada that directly compared gemcitabine with and without erlotinib in patients with metastatic or locally advanced pancreatic cancer demonstrated a statistically significant improvement in overall survival (6.2 vs 5.9 months) [6]. Following the results of this trial, the FDA approved erlotinib hydrochloride in combination with gemcitabine for the treatment of patients with locally advanced, unresectable or metastatic pancreatic carcinoma in 2005.

FOLFIRINOX, consisting of 5-FU, leucovorin, oxaliplatin and irinotecan, demonstrated superiority over gemcitabine in a randomized Phase II study. The study was expanded to a Phase III trial of 342 patients which showed a statistically significant improvement in overall survival (11.1 vs 6.8 months). Treatment-related toxicity was significantly worse with FOLFIRINOX and included grade 3 or 4 neutropenia (46 vs 21%), vomiting (15 vs 8%), diarrhea (13 vs 2%), thrombocytopenia (9.1 vs 3.6%), sensory neuropathy (9 vs 0%) and febrile neutropenia (5.4 vs 1.2%) [7]. Despite greater toxicity, FOLFIRINOX significantly improved global health status as compared to gemcitabine. Based on these results, FOLFIRINOX is now considered a category 1 recommendation for advanced pancreatic cancer.

Following encouraging results of a Phase I/II study of nanoparticle albumin-bound (nab)-paclitaxel in combination with gemcitabine in patients with previously untreated metastatic pancreatic cancer [8], a Phase III study was initiated. There was a statistically significant median overall survival benefit of 8.5 versus 6.7 months in the nab-paclitaxel–gemcitabine group compared to the gemcitabine arm. The most common adverse events of grade 3 or higher were neutropenia (38% in the nab-paclitaxel–gemcitabine group versus 27% in the gemcitabine group), fatigue (17 vs 7%), neuropathy (17 vs 1%) and febrile neutropenia (3 vs 1%) [9]. Following the results of this trial, the FDA approved nab-paclitaxel in combination with gemcitabine for the first-line treatment of patients with metastatic adenocarcinoma of the pancreas in 2013.

Therapeutic strategies targeting angiogenesis were evaluated in a Phase III study but were unsuccessful [10], and strategies for molecular targeting of RAS mutations are currently under study [11] as well as multiple vaccine trials. Although obvious progress has been made in chemotherapy for pancreatic cancer over recent years, significant challenges persist, including chemotherapy toxicities, resistance to chemotherapy, genetic and epigenetic complexity and heterogeneity and redundancies or multiple ‘cross-talks’ in molecular signaling pathways. Below, we present a novel approach using protein-lipid (SapC-DOPS) nanovesicles that have shown robust preclinical therapeutic potential for pancreatic cancer by selectively targeting surface acidic phospholipids of cancer cells [12].

Saposin C (SapC) is a stable 80-amino acid protein that distributes in lysosomes of all cell types. SapC, a membrane-associated molecule, induces fusion of acidic phospholipid-rich membranes in acidic pH environments, as are often found around tumor cells [13–16]. PS is an abundant acidic phospholipid that naturally occurs in biologic membranes. A unique lyophilized formulation of SapC and an acidic phospholipid DOPS can be used to obtain stable nanovesicles with an average diameter of approximately 200 nm using a co-solvent water system [12,17–19]. Administration of SapC-DOPS nanovesicles has been shown to have potent cancer-selective targeting and anti-tumor efficacy in xenografted preclinical pancreatic cancer models [12].

Increased surface PS exposure has been identified on human pancreatic cancer cells [12]. Surface PS level of pancreatic cancer cells appear to be higher compared to other tumor types. Fusiogenicity of SapC leads to the selective targeting function of SapC-DOPS nanovesicles to pancreatic cancer cells through surface-exposed PS. This targeting effect can be effectively blocked by specific PS-binding proteins in cancer cells, such as lactadherin or β2-glycoprotein [12,19]. Clearly, tumor cell-death induction activity by SapC-DOPS correlates with surface PS levels on human pancreatic cancer cells. SapC-DOPS anti-pancreatic cancer efficacy is independent of genetic alterations of single or multiple genes/proteins. There is no significant correlation between genetic profile and PS exposure in tested human pancreatic cancer cells.

In fact, SapC-DOPS has shown strong inhibitory impact on pancreatic cancer cells regardless of their genetic modifications. In untransformed cells, asymmetric membrane acidic phospholipid distribution leads to a low PS exposure on the outer membrane surface. Therefore, SapC-DOPS shows weak binding to these cells and has a strong safety profile. No gross toxicities were observed in a preclinical safety investigation [18]. Interestingly, combination treatment of gemcitabine with SapC-DOPS shows synergic efficacy that is likely due to PS exposure enhancement by gemcitabine [Qi et al., Unpublished Data]. Such a combination approach can be adopted with other agents or therapeutics that can increase surface PS on pancreatic cancer cells.

A mechanism of action study demonstrated that SapC-DOPS nanovesicles induce apoptotic cell death of human pancreatic cancer cells in part via a ceramide- and caspase-mediated signaling pathway [12,18]. SapC enhances the biological activity of lysosomal acid sphingomyelinase (ASMase). In cancer cells, ASMase leaks out from lysosomes and moves to plasma membranes. SapC can stimulate the activity of ASMase when SapC-DOPS nanovesicles fuse with surface PS of cancer cell membranes. This activation elevates the levels of ceramide, a secondary messenger, followed by activation of caspases that induce apoptotic cell death [12,18].

In addition to its therapeutic application, SapC-DOPS nanovesicles can also incorporate hydrophobic or hydrophilic probes and agents for pancreatic cancer imaging and detection. It has been demonstrated that fluorescently labeled SapC-DOPS nanovesicles allow selective visualization of primary and metastatic pancreatic tumors in vivo [12,20]. The nanovesicles can also carry contrast agents (iron or gadolinium) for MRI of cancer [21]. Preclinical studies of SapC-DOPS as a novel anticancer agent demonstrate a toxicology and pharmacology profile that favors advancement to early-phase clinical trials. We propose testing this in pancreatic cancer and considering this in other tumors with high surface PS expression.

Financial & competing interests disclosure

X Qi is listed as an inventor on the patent for SapC-DOPS technology that is the subject of this research. Consistent with current Cincinnati Children’s Hospital Medical Center policies, the development and commercialization of this technology has been licensed to Bexion Pharmaceuticals, LLC, in which X Qi, holds a minor (<5%) equity interest. O Olowokure has no relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. Writing assistance was provided by J Racadio, and was funded by the Division of Hematology-Oncology, University of Cincinnati College of Medicine. This work was supported in part by Start Up Fund from University of Cincinnati (to X Qi), 1R01CA158372 (to X Qi), and New Drug State Key Project grant number 009ZX09102-205 (to X Qi).

The authors have no other relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript apart from those disclosed.