Provectus Biopharmaceuticals Announces Discovery of Unique PV-10-Induced STING Pathway Mechanism

Provectus recently announce that data from ongoing preclinical study of investigational autolytic cancer immunotherapy PV-10 (rose bengal disodium) was presented at the American Association for Cancer Research (AACR) 2020 Virtual Annual Meeting II, held online June 22-24, 2020. This PV-10 research has been led by Aru Narendran, MD, PhD, and his team of researchers at the University of Calgary in Alberta, Canada (UCalgary).

Dr. Narendran and his colleagues studied the effects of PV-10 treatment on primary cells and cell lines derived from pediatric leukemia patients. UCalgary showed that PV-10 treatment led to STING dimerization and the release of interferon gamma (IFNγ), indicating a potential immune activation mechanism of PV-10. UCalgary further showed that heat shock proteins (HSPs), which chaperone misfolded or abnormally folded proteins, associated with STING dimerization in PV-10-treated cells, indicating a mechanism that may lead to enhanced STING activation following PV-10 treatment.

A copy of the AACR poster presentation is available on Provectus’ website at

“The essence of cancer is the struggle for survival of these abnormal cells in the body. Over the course of their existence, cancer cells acquire multiple cellular pathways that become active or inactive in order for cancer to have a survival advantage against our immune system. This struggle changes the biology of cancer cells, which may have a direct impact on the activity of anticancer drugs within these cells,” Dr. Narendran said. “We observed these very dynamics from our research on PV-10 and pediatric leukemia cells. Classic STING activation does not occur through PV-10 treatment. Rather, STING forms a dimer complex following PV-10 treatment, which may potentially lead to effective immune activation and anticancer activity.”

Dr. Narendran added, “Our PV-10 research has enabled us to show, we believe for the first time, that heat shock proteins, which play important roles in the survival of cancer cells, are involved in STING activation. We also believe the involvement of heat shock proteins with STING is an important observation that requires further study.”

Dominic Rodrigues, Vice Chair of Provectus’ Board of Directors, said “We are grateful to Dr. Narendran, his team, and the University of Calgary for their consequential research on PV-10 to better understand the basic biology of cancer. This seminal discovery of PV-10-induced alterations of the STING pathway, which plays a pivotal role in innate immunity, contributes to an increasing body of knowledge about how and why PV-10 may function as an immunotherapy across a growing number of cancer types.”

By targeting tumor cell lysosomes, investigational new drug PV-10 treatment may yield immunogenic cell death in solid tumor cancers that results in tumor-specific reactivity in circulating T cells and a T cell mediated immune response against treatment refractory and immunologically cold tumors. Adaptive immunity can be enhanced by combining checkpoint blockade (CB) with PV-10.

PV-10 is undergoing clinical study for adult solid tumor cancers, such as relapsed and refractory cancers metastatic to the liver and metastatic melanoma. PV-10 is also undergoing preclinical study for relapsed and refractory pediatric solid tumor cancers (eg, neuroblastoma, Ewing sarcoma, rhabdomyosarcoma, and osteosarcoma) and relapsed and refractory pediatric blood cancers (such as acute lymphocytic leukemia and acute myelomonocytic leukemia).

Lysosomes are the central organelles for intracellular degradation of biological materials, and nearly all types of eukaryotic cells have them. Discovered by Christian de Duve, MD in 1955, lysosomes are linked to several biological processes, including cell death and immune response. In 1959, de Duve described them as “suicide bags” because their rupture causes cell death and tissue autolysis. He was awarded the Nobel Prize in 1974 for discovering and characterizing lysosomes, which are also linked to each of the three primary cell death pathways: apoptosis, autophagy, and necrosis.

Cancer cells, particularly advanced cancer cells, are very dependent on effective lysosomal functioning. Cancer progression and metastasis are associated with lysosomal compartment changes, which are closely correlated with (among other things) invasive growth, angiogenesis, and drug resistance.

PV-10 selectively accumulates in the lysosomes of cancer cells upon contact, disrupting the lysosomes and causing the cells to die. Provectus, external collaborators, and other researchers have independently shown that PV-10 (RB) triggers each of the three primary cell death pathways: apoptosis, autophagy, and necrosis.

Cancer Cell Autolytic Death via PV-10: PV-10 induced autolytic cell death, or death by self-digestion, in Hepa1-6 murine hepatocellular carcinoma (HCC) cells can be viewed in this Provectus video of the event (ethidium homodimer 1 [ED-1] stains DNA, but is excluded from intact nuclei; lysosensor green [LSG] stains intact lysosomes; the video is provided in 30-second frames; the event has a duration of approximately one hour). Exposure to PV-10 triggers the disruption of lysosomes, followed by nucleus failure and autolytic cell death. Identical responses have been shown by the Company in HTB-133 human breast carcinoma (which can be viewed in this Provectus video; this event has a duration of approximately two hours) and H69Ar human multidrug-resistant small cell lung carcinoma. Cancer cell autolytic cell death was reproduced by research collaborators in neuroblastoma cells to show that lysosomes are disrupted upon exposure to PV-10.5

PV-10 causes acute autolytic destruction of injected tumors (ie, cell death), mediating the release of danger-associated molecular pattern molecules (DAMPs) and tumor antigens that may initiate an immunologic cascade where local response by the innate immune system may facilitate systemic anti-tumor immunity by the adaptive immune system. The DAMP release-mediated adaptive immune response activates lymphocytes, including CD8+ T cells, CD4+ T cells, and NKT cells, based on clinical and preclinical experience in multiple tumor types. Mediated immune signaling pathways may include an effect on STING, which plays an important role in innate immunity.

ODD status has been granted to PV-10 by the US FDA for the treatments of metastatic melanoma in 2006, hepatocellular carcinoma in 2011, neuroblastoma in 2018, and ocular melanoma (including uveal melanoma) in 2019.

Rose bengal disodium (RB) (4,5,6,7-tetrachloro-2’,4’,5’,7’-tetraiodofluorescein disodium salt) is a small molecule halogenated xanthene and PV-10’s active pharmaceutical ingredient. The company manufactures RB using a patented process designed to meet stringent modern global quality requirements for pharmaceuticals and pharmaceutical ingredients (Good Manufacturing Practice, or GMP). PV-10 drug product is an injectable formulation of 10% w/v GMP RB in 0.9% saline, supplied in single-use glass vials containing 5 mL (to deliver) of solution, and administered without dilution to solid tumors via intratumoral injection.

Provectus’ IP includes a family of US and international (a number of countries in Asia, Europe, and North America) patents that protect the process by which GMP RB and related halogenated xanthenes are produced, avoiding the formation of previously unknown impurities that exist in commercial grade RB in uncontrolled amounts. The requirement to control these impurities is in accordance with International Council on Harmonisation (ICH) guidelines for the manufacturing of an injectable pharmaceutical. US patent numbers are 8,530,675, 9,273,022, and 9,422,260, with expirations ranging from 2030 to 2031.

The Company’s IP also includes a family of US and international (a number of countries in Asia, Europe, and North America) patents that protect the combination of PV-10 and systemic immunomodulatory therapy (e.g., anti-CTLA-4, anti-PD-1, and anti-PD-L1 agents) for the treatment of a range of solid tumor cancers. US patent numbers are 9,107,887, 9,808,524, 9,839,688, and 10,471,144, with expirations ranging from 2032 to 2035; US patent application numbers include 20200138942.

Provectus Biopharmaceuticals, Inc. is a clinical-stage biotechnology company developing a new class of drugs based on an entirely and wholly owned family of chemical small molecules called halogenated xanthenes. Information about the company’s clinical trials can be found at the NIH registry, For more information, visit