Preclinical discoveries at the Salk Institute for Biological Studies, a scientific research institute in La Jolla, California, have driven the translation of vitamin D receptor (VDR) biology into a first-in-human clinical trial targeting the dense, fibrotic microenvironment of pancreatic cancer.
A phase 1b study (NCT03520790) led by researchers at the Dana-Farber Cancer Institute demonstrates that paricalcitol (Zemplar®, AbbVie), a synthetic VDR agonist, can be safely combined with standard chemotherapy, remodels the tumor stroma, and may enhance patient outcomes. These findings validate foundational research and chart a path toward new combination strategies in a notoriously hard-to-treat malignancy.
Pancreatic ductal adenocarcinoma
Pancreatic ductal adenocarcinoma (PDAC) remains one of the most lethal malignancies, with dismal five-year survival rates and limited progress in therapeutic efficacy. [1] The tumor microenvironment—characterized by an extensive fibrotic (desmoplastic) stroma and immunosuppressive milieu—contributes substantially to therapeutic resistance.
Foundational work at the Salk Institute, led by Ronald Evans, PhD, uncovered the pivotal role of the nuclear hormone receptor superfamily, particularly the vitamin D receptor (VDR), in regulating fibroblast activity and tissue homeostasis. Preclinical models suggested that VDR activation could reprogram cancer-associated fibroblasts (CAFs) and sensitize tumors to chemotherapy. Here, we report the first clinical translation of these discoveries: a randomized trial evaluating the safety and biological effects of paricalcitol, an FDA-approved VDR agonist, in combination with standard chemotherapy in metastatic PDAC.[2]][3][4]
Reprogramming the Tumor Stroma
Evans and colleagues’ seminal studies demonstrated that VDR is highly expressed in tissue-resident fibroblasts, where it governs fibrotic and inflammatory responses. In murine models, synthetic vitamin D analogs such as paricalcitol reversed fibroblast activation, reduced hepatic fibrosis, and, crucially, in pancreatic cancer models, remodeled the tumor microenvironment to enhance chemotherapy responses.
These insights provided a compelling rationale for clinical translation—testing whether VDR agonists could break down the stromal barrier that shields pancreatic tumors from effective therapy.
Clinical Trial Design and Methods
A phase 1b, randomized, safety-focused clinical trial (NCT03520790) led by Dana-Farber Cancer Institute enrolled 36 patients with previously untreated metastatic PDAC. Participants received standard-of-care gemcitabine (Gemzar®; Eli Lilly & Co) in combination with nab-paclitaxel (Abraxane®; Bristol-Myers Squibb) alongside placebo, intravenous paricalcitol, or oral paricalcitol. The primary endpoint was safety; secondary endpoints included pharmacodynamic analysis of tumor biopsies. Paired biopsies—pre-treatment and after four to six weeks—underwent multiplex immunofluorescence and spatial transcriptomic profiling to assess stromal and immune changes.
Paricalcitol was safely administered with chemotherapy. Five of twelve patients receiving oral paricalcitol experienced grade 2–4 hypercalcemia that was manageable and required dose reduction. No unexpected toxicities emerged, confirming the feasibility of this combinatorial approach.
Molecular analyses revealed that paricalcitol reduced the activation of αSMA+ CAFs within tumors, without altering overall fibroblast numbers. Importantly, VDR agonism increased intratumoral CD8+ T cell infiltration and enhanced spatial proximity between T cells and tumor cells—changes associated with improved immune surveillance and response. These observations validate the preclinical hypothesis that VDR activation reprograms the stroma, rendering it less immunosuppressive and more permissive to therapy.
While not powered for efficacy, the study observed numerically higher partial response rates in the paricalcitol arms (42% vs 9% in placebo) and a greater proportion of patients progression-free at one year (21% vs 0%). Notably, VDR expression in tumor biopsies was heterogeneous across patients. Those with high VDR levels who received paricalcitol exhibited the most favorable responses and the longest survival, suggesting VDR expression as a potential predictive biomarker for response to stromal-targeted therapy.
Future Directions
This trial represents a significant step in the clinical translation of stromal remodeling as a therapeutic strategy for pancreatic cancer. By targeting the tumor microenvironment with a VDR agonist, researchers demonstrated not only safety but also biological activity consistent with mechanistic preclinical data. The observed association between VDR expression and clinical benefit underscores the need for biomarker-driven patient selection in future studies.
Ongoing and future trials will need to evaluate the impact of VDR agonists on overall survival and establish optimal combination strategies, potentially incorporating immunotherapies. Additionally, prospective validation of VDR expression as a companion diagnostic is warranted.
The successful translation of Salk Institute’s basic research into a clinical trial exemplifies the power of targeting the tumor microenvironment in pancreatic cancer. Paricalcitol, a vitamin D analog, safely remodels the pancreatic tumor stroma, enhances immune infiltration, and shows early signs of improving chemotherapy response. These results pave the way for larger, biomarker-driven studies and offer hope for a new standard of care in PDAC.
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Clinical trials
Paricalcitol Plus Gemcitabine and Nab-paclitaxel in Metastatic Pancreatic Cancer – ClinicalTrials.gov ID NCT03520790
Highlights of Prescribing Information
Paricalcitol (Zemplar®, AbbVie)[Prescribing Information]
Gemcitabine (Gemzar®; Eli Lilly & Co)[Prescribing information]
Nab-paclitaxel (Abraxane®; Bristol-Myers Squibb)[Prescribing Information]
References
[1] Sarantis P, Koustas E, Papadimitropoulou A, Papavassiliou AG, Karamouzis MV. Pancreatic ductal adenocarcinoma: Treatment hurdles, tumor microenvironment and immunotherapy. World J Gastrointest Oncol. 2020 Feb 15;12(2):173-181. doi: 10.4251/wjgo.v12.i2.173. PMID: 32104548; PMCID: PMC7031151.
[2] Perez KJ, Dias Costa A, Jordan A, Karasic TB, Elganainy D, Kim S, Yuan C, Gui DY, Tan R, Hong SC, Wang X, Cristea S, Coleman E, Truitt M, Oh TG, Zheng H, Furniss CS, Brais L, Bird A, Remland J, Gocheva V, Thalappillil JS, Anderson M, Cleary JM, Enzinger A, Giannakis M, Ng K, Rubinson DA, Schlechter B, Surana R, Singh H, Abrams T, Teitelbaum U, Izgur N, Allen E, Winter PS, Raghavan S, Yeh JJ, Von Hoff D, Liddle C, Downes M, Evans RM, O’Dwyer P, Aguirre A, Nowak JA, Wolpin BM. Gemcitabine and nab-paclitaxel with or without the VDR agonist paricalcitol for metastatic pancreatic cancer: a randomized, multiarm, run-in phase trial. Nat Cancer. 2026 May 25. doi: 10.1038/s43018-026-01165-8. Epub ahead of print. PMID: 42185478.
[3] Evans RM, et al. Nuclear receptors and the control of metabolism. Nat Rev Mol Cell Biol.
[4] Sherman MH, Yu RT, Engle DD, Ding N, Atkins AR, Tiriac H, Collisson EA, Connor F, Van Dyke T, Kozlov S, Martin P, Tseng TW, Dawson DW, Donahue TR, Masamune A, Shimosegawa T, Apte MV, Wilson JS, Ng B, Lau SL, Gunton JE, Wahl GM, Hunter T, Drebin JA, O’Dwyer PJ, Liddle C, Tuveson DA, Downes M, Evans RM. Vitamin D receptor-mediated stromal reprogramming suppresses pancreatitis and enhances pancreatic cancer therapy. Cell. 2014 Sep 25;159(1):80-93. doi: 10.1016/j.cell.2014.08.007. PMID: 25259922; PMCID: PMC4177038.
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DOI
 Remodels Pancreatic Tumor Microenvironment in Early Clinical Trial){kind=link}