One Two Punch: Combination Chemotherapy Knocks Out Pancreatic Cancer
Authors: Audrey Lumeau, Pierre Cordelier
Journal: Molecular Therapy (2020)

There is no cure for pancreatic cancer, which will soon become the second most common cause of cancer-related deaths worldwide.1Rahib L. Smith B.D. Aizenberg R. Rosenzweig A.B. Fleshman J.M. Matrisian L.M. Projecting cancer incidence and deaths to 2030: the unexpected burden of thyroid, liver, and pancreas cancers in the United States.Cancer Res. 2014; 74: 2913-2921Crossref PubMed Scopus (4212) Google Scholar Pancreatic cancer progresses silently for decades,2Yachida S. Jones S. Bozic I. Antal T. Leary R. Fu B. Kamiyama M. Hruban R.H. Eshleman J.R. Nowak M.A. et al.Distant metastasis occurs late during the genetic evolution of pancreatic cancer.Nature. 2010; 467: 1114-1117Crossref PubMed Scopus (1905) Google Scholar commonly resulting in late diagnoses, and limited therapeutic options exist for advanced tumors where surgery is no longer possible.3Neoptolemos J.P. Kleeff J. Michl P. Costello E. Greenhalf W. Palmer D.H. Therapeutic developments in pancreatic cancer: current and future perspectives.Nat. Rev. Gastroenterol. Hepatol. 2018; 15: 333-348Crossref PubMed Scopus (537) Google Scholar Therapies targeting the stroma as well as immunotherapies hold promise for the future,3Neoptolemos J.P. Kleeff J. Michl P. Costello E. Greenhalf W. Palmer D.H. Therapeutic developments in pancreatic cancer: current and future perspectives.Nat. Rev. Gastroenterol. Hepatol. 2018; 15: 333-348Crossref PubMed Scopus (537) Google Scholar and recent clinicals trials have revived our hopes for successful targeted therapies in highly selected patients.4Golan T. Hammel P. Reni M. Van Cutsem E. Macarulla T. Hall M.J. Park J.O. Hochhauser D. Arnold D. Oh D.Y. et al.Maintenance Olaparib for Germline BRCA-Mutated Metastatic Pancreatic Cancer.N. Engl. J. Med. 2019; 381: 317-327Crossref PubMed Scopus (1035) Google Scholar However, for most patients, chemotherapy-based regimens remain the safe bet.3Neoptolemos J.P. Kleeff J. Michl P. Costello E. Greenhalf W. Palmer D.H. Therapeutic developments in pancreatic cancer: current and future perspectives.Nat. Rev. Gastroenterol. Hepatol. 2018; 15: 333-348Crossref PubMed Scopus (537) Google Scholar To date, in the metastatic setting, FOLFIRINOX and gemcitabine ± nab-paclitaxel are standard treatment for patients with good performance status. Both combinations have shown a survival advantage over standard gemcitabine monotherapy alone.5Conroy T. Desseigne F. Ychou M. Bouché O. Guimbaud R. Bécouarn Y. Adenis A. Raoul J.L. Gourgou-Bourgade S. de la Fouchardière C. et al.Groupe Tumeurs Digestives of UnicancerPRODIGE IntergroupFOLFIRINOX versus gemcitabine for metastatic pancreatic cancer.N. Engl. J. Med. 2011; 364: 1817-1825Crossref PubMed Scopus (5127) Google Scholar,6Von Hoff D.D. Ramanathan R.K. Borad M.J. Laheru D.A. Smith L.S. Wood T.E. Korn R.L. Desai N. Trieu V. Iglesias J.L. et al.Gemcitabine plus nab-paclitaxel is an active regimen in patients with advanced pancreatic cancer: a phase I/II trial.J. Clin. Oncol. 2011; 29: 4548-4554Crossref PubMed Scopus (877) Google Scholar Unfortunately, molecular-based stratification of patients with advanced pancreatic cancer remains poorly developed. In this issue of Molecular Therapy, N’Guessan et al.7N’Guessan K.F. Davis H.W. Chu Z. Vallabhapurapu S.D. Lewis C.S. Franco R.S. Olowokure O. Ahmad S.A. Yeh J.J. Bogdanov V.Y. Qi X. Enhanced Efficacy of Combination of Gemcitabine and Phosphatidylserine-Targeted Nanovesicles against Pancreatic Cancer.Mol. Ther. 2020; 28 (this issue): 1876-1886Abstract Full Text Full Text PDF Scopus (9) Google Scholar describe a new combination strategy based on gemcitabine and lipophilic nanovesicles composed of dioleoylphosphatidylserine (DOPS) for delivery of saponin C (SapC-DOPS).7N’Guessan K.F. Davis H.W. Chu Z. Vallabhapurapu S.D. Lewis C.S. Franco R.S. Olowokure O. Ahmad S.A. Yeh J.J. Bogdanov V.Y. Qi X. Enhanced Efficacy of Combination of Gemcitabine and Phosphatidylserine-Targeted Nanovesicles against Pancreatic Cancer.Mol. Ther. 2020; 28 (this issue): 1876-1886Abstract Full Text Full Text PDF Scopus (9) Google Scholar SapC-DOPS targets extracellular phosphatidylserine (PS) and activates lysosomal enzymes, provoking apoptotic cell death via ceramide production. Gemcitabine is a nucleoside analog that interferes with DNA replication. The authors show that PS is regulated during the cell cycle and that combining gemcitabine and SapC-DOPS could eradicate pancreatic cancer cells during the G1 and G2/M phases, respectively. They further show that such a combination results in enhanced cancer cell cytotoxicity in relevant preclinical models. The authors elegantly showed that this therapeutic combination was effective regardless of the level of expression of PS on the surface of cancer cells: gemcitabine targets cells expressing low levels of PS, while SapC-DOPS targets cells with high levels of surface PS. However, the molecular mechanisms behind this distinct avidity and specificity remain unclear. One might speculate that cells exhibiting low levels of surface PS express a higher level of gemcitabine transporters, such as human equilibrative nucleoside transporter 1,8Maréchal R. Bachet J.-B. Mackey J.R. Dalban C. Demetter P. Graham K. Couvelard A. Svrcek M. Bardier-Dupas A. Hammel P. et al.Levels of gemcitabine transport and metabolism proteins predict survival times of patients treated with gemcitabine for pancreatic adenocarcinoma.Gastroenterology. 2012; 143: 664-674.e6Abstract Full Text Full Text PDF PubMed Scopus (196) Google Scholar or enzymes such as deoxycytidine kinase, which is essential to gemcitabine phosphorylation and antitumoral activity, thereby sensitizing patients’ tumors to therapy.9Buscail L. Bournet B. Vernejoul F. Cambois G. Lulka H. Hanoun N. Dufresne M. Meulle A. Vignolle-Vidoni A. Ligat L. et al.First-in-man phase 1 clinical trial of gene therapy for advanced pancreatic cancer: safety, biodistribution, and preliminary clinical findings.Mol. Ther. 2015; 23: 779-789Abstract Full Text Full Text PDF PubMed Scopus (72) Google Scholar Alternatively, cells exhibiting low surface PS might also express low levels of enzymes that restrict gemcitabine efficacy, such as cytidine deaminase, which converts difluorodeoxycytidine (dFdC)-gemcitabine into an inactive difluorodeoxyuridine (dFdU)-gemcitabine metabolite that is rapidly excreted from the tumor cell.10Frances A. Cordelier P. The Emerging Role of Cytidine Deaminase in Human Diseases: A New Opportunity for Therapy?.Mol. Ther. 2020; 28: 357-366Abstract Full Text Full Text PDF PubMed Scopus (29) Google Scholar Differential analysis of gemcitabine metabolism in PS-high and -low cells should provide insight into this issue. The authors next found that PS expression is specifically regulated in pancreatic cancer cells during the cell cycle, with a maximum reached during S and G2/M phases. This increase might be at least in part due to a parallel increase in PS synthase 1 mRNA levels, whereas the expression of PS synthase 2 expression was unchanged. PS synthase 1 is thought to be regulated by N-Myc, Sp1, Sp3, and Sp4, but the regulation of its expression was not investigated in this study.11Tasseva G. Cole L. Vance J.E. N-Myc and SP regulate phosphatidylserine synthase-1 expression in brain and glial cells.J. Biol. Chem. 2011; 286: 1061-1073Abstract Full Text Full Text PDF PubMed Scopus (9) Google Scholar Interestingly, the authors observed that gemcitabine also increases surface PS expression, but the authors did not explore the effects of gemcitabine on the expression of PS synthase. It is more likely that this observed increase in expression reflects the elimination of PS-low expressing cells by this chemotherapeutic drug. Nevertheless, it would be interesting to address whether stratification of patients by PS expression might help select for better responders to this commonly prescribed therapy. Gemcitabine acts as an intercalating agent that targets replicating DNA during S phase. Following entry into the cell and subsequent phosphorylation, it masquerades as a deoxycytidine triphosphate that can be incorporated into DNA. An additional deoxynucleotide is subsequently added following the gemcitabine nucleotide at the end of the elongating DNA strand, which effectively prevents the DNA polymerase from proceeding. This locks the drug into the DNA as the proofreading enzymes are unable to remove gemcitabine from this position. In Figure 3B, N’Guessan et al.7N’Guessan K.F. Davis H.W. Chu Z. Vallabhapurapu S.D. Lewis C.S. Franco R.S. Olowokure O. Ahmad S.A. Yeh J.J. Bogdanov V.Y. Qi X. Enhanced Efficacy of Combination of Gemcitabine and Phosphatidylserine-Targeted Nanovesicles against Pancreatic Cancer.Mol. Ther. 2020; 28 (this issue): 1876-1886Abstract Full Text Full Text PDF Scopus (9) Google Scholar present, in our view, the most intriguing results of the manuscript. They made the assumption that gemcitabine treatment targets cells in G1 phase and increases the percentage of cells in G2/M-phase, and they cite Park et al.12Park S.H. Sung J.H. Kim E.J. Chung N. Berberine induces apoptosis via ROS generation in PANC-1 and MIA-PaCa2 pancreatic cell lines.Braz. J. Med. Biol. Res. 2015; 48: 111-119Crossref PubMed Google Scholar to support this contention. However, in the referenced paper, gemcitabine is shown to halt cell proliferation by S phase blockade. Hence, in the review cited by N’Guessan et al.7N’Guessan K.F. Davis H.W. Chu Z. Vallabhapurapu S.D. Lewis C.S. Franco R.S. Olowokure O. Ahmad S.A. Yeh J.J. Bogdanov V.Y. Qi X. Enhanced Efficacy of Combination of Gemcitabine and Phosphatidylserine-Targeted Nanovesicles against Pancreatic Cancer.Mol. Ther. 2020; 28 (this issue): 1876-1886Abstract Full Text Full Text PDF Scopus (9) Google Scholar to support this role for gemcitabine in G1 phase, Mills et al.13Mills C.C. Kolb E.A. Sampson V.B. Development of Chemotherapy with Cell-Cycle Inhibitors for Adult and Pediatric Cancer Therapy.Cancer Res. 2018; 78: 320-325Crossref PubMed Scopus (83) Google Scholar describe the chemotherapy as selectively cytotoxic to cells in S phase. To support their working model, N’Guessan et al.7N’Guessan K.F. Davis H.W. Chu Z. Vallabhapurapu S.D. Lewis C.S. Franco R.S. Olowokure O. Ahmad S.A. Yeh J.J. Bogdanov V.Y. Qi X. Enhanced Efficacy of Combination of Gemcitabine and Phosphatidylserine-Targeted Nanovesicles against Pancreatic Cancer.Mol. Ther. 2020; 28 (this issue): 1876-1886Abstract Full Text Full Text PDF Scopus (9) Google Scholar synchronized cells in G1 phase using hydroxyurea. Hydroxyurea inhibits ribonucleotide reductase, the enzyme that catalyzes the formation of deoxyribonucleotides from ribonucleotides for DNA synthesis. However, high concentrations or prolonged treatment with low doses of hydroxyurea can result in cell death due to irreversible DNA damage. N’Guessan et al.7N’Guessan K.F. Davis H.W. Chu Z. Vallabhapurapu S.D. Lewis C.S. Franco R.S. Olowokure O. Ahmad S.A. Yeh J.J. Bogdanov V.Y. Qi X. Enhanced Efficacy of Combination of Gemcitabine and Phosphatidylserine-Targeted Nanovesicles against Pancreatic Cancer.Mol. Ther. 2020; 28 (this issue): 1876-1886Abstract Full Text Full Text PDF Scopus (9) Google Scholar used both high dose (4 mM) and prolonged treatment (24 h). It will be necessary to test other drugs targeting G1- or S phases using the same approach to tweeze out the cell-cycle specificity of action of gemcitabine. In vivo, the therapeutic efficacy of the new combination therapy in relevant experimental models of pancreatic cancer was convincing. Repeated administrations of SapC-DOPS and gemcitabine significantly decreased subcutaneous tumor size and mass in immunocompromised animals and significantly prolonged survival of immunocompetent mice with orthotopic, highly aggressive pancreatic tumors. If we take a bit of a step back, the working model is that gemcitabine is targeting cells in G1 phase, a hypothesis that will need to be explored in more detail, while cells in G2/M phase fall prey to SapC-DOPS. Surprisingly, the authors have not explored the potential of sequential treatments, which may increase the therapeutic index of this approach, both in vitro and in vivo. While the authors clearly show that SapC-DOPS can definitely hit the tumor target, it is quite possible that delivery might be an issue in patients due to the dense, impenetrable stroma of pancreatic tumors.14von Ahrens D. Bhagat T.D. Nagrath D. Maitra A. Verma A. The role of stromal cancer-associated fibroblasts in pancreatic cancer.J. Hematol. Oncol. 2017; 10: 76Crossref PubMed Scopus (231) Google Scholar New combinations that incorporate targeting of the tumor stroma may lie ahead,15Provenzano P.P. Cuevas C. Chang A.E. Goel V.K. Von Hoff D.D. Hingorani S.R. Enzymatic targeting of the stroma ablates physical barriers to treatment of pancreatic ductal adenocarcinoma.Cancer Cell. 2012; 21: 418-429Abstract Full Text Full Text PDF PubMed Scopus (1405) Google Scholar and it could be interesting in future studies to address the level of expression of PS on the surface of cancer-activated fibroblasts. In loving memory of my grandma who recently passed away at the age of 106. Enhanced Efficacy of Combination of Gemcitabine and Phosphatidylserine-Targeted Nanovesicles against Pancreatic CancerN’Guessan et al.Molecular TherapyJune 8, 2020In BriefSapC-DOPS nanovesicles, combined with standard care, gemcitabine/Abraxane, significantly inhibits pancreatic tumor growth and increases the survival of pancreatic tumor-bearing mice compared with either drug alone. Results of the study suggest that a phosphatidylserine and a cell-cycle-targeted mechanism regulate the enhanced therapeutic efficacy of the combination treatment. Full-Text PDF Open Archive