Outsiders to the pharmaceutical industry, three award-winning research scientists from the Department of Energy’s East Tennessee-based Oak Ridge National Laboratory embarked on a path of their own in the 1990s to develop a better way to fight cancer. Hailing from the nationally recognized federal government science and technology facility with a rich history of discovery and innovation, these three technology inventors had been searching for a drug candidate capable of killing cancer cells safely, specifically, completely and quickly. By the end of the decade Drs. Craig Dees, PhD, Timothy Scott, PhD and Eric Wachter, PhD had re-discovered what could turn out to be the ideal cancer killer: Rose Bengal, a molecule with a long and diverse medical history. Ironically the compound had lain around in plain sight of the global pharmaceutical industry for nearly 85 years before Dees et al. began their journey of demonstrating Rose Bengal’s cancer fighting potential.
Safely and effectively engaging the body’s immune system and its natural anti-cancer defenses, instead of destroying or misusing them, underscored the Tennessee trio’s approach to defeating the disease. They believed killing cancer tumors in the correct way held the key to successful medical treatment because a proper approach could enable the immune system to stimulate cancer-killing cells throughout the body. Dees, Scott and Wachter eventually founded Knoxville, Tennessee-based Provectus Biopharmaceuticals, Inc. (NYSE MKT: PVCT) in 2002 with the goal of developing Rose Bengal-based drugs to treat cancer. The founders’ vision was to have the company’s lead investigational oncology drug PV-10, an injectable 10% solution of Rose Bengal in saline, employed in the treatment of all solid tumor cancers before, during and after surgery, in combination with other therapeutic agents and therapies, and after all else fails.
Rose Bengal is the active pharmaceutical ingredient in PV-10. A water-soluble dye first created in 1882, it is a small molecule that has been used in the clinic for more than a century, as an additive to safranin victoria yellow for ocular pneumococcal infection, a stain for visualizing corneal ulcers, a marker for impaired liver function and now a cancer therapeutic. Prior to Provectus’ founding Rose Bengal already had an established FDA safety profile as an intravenous hepatic diagnostic called Robengatope®, and as a topical ophthalmic diagnostic under the trade names of Rosettes® and Minims®. Rose Bengal’s therapeutic benefits remained hidden until the 1980s when sufficient quantities were administered orally in preclinical studies carried out by Japanese researchers. Ironically, while investigating the tumorigenicity of red food dye No. 105 (also made from Rose Bengal) they observed dose-dependent survival increases in test mice.
In the view of Dees, Scott and Wachter properly destroying cancer tumors meant killing only tumors and doing so completely, quickly and, very importantly, safely (that is, leaving healthy tissue unharmed). They believed this approach was the only effective way of sustainably stimulating a person’s natural anti-cancer defenses. Instead of bathing the entire body or even parts of it with radiation, or filling the bloodstream with oral or intravenous chemotherapies or present-day immunotherapies, Dees et al. firmly held the position that stimulating the immune system was best achieved through treating tumor tissue by injecting into it a drug capable of destroying the entire tumor as quickly as possible without damaging surrounding healthy cells. Completely also meant everything from visible tumor tissue to occult or hidden cells in and immediately around the injection site. Quickly meant having the drug processed through and excreted from the body in short order. Antigens generated from the tumor destruction caused by drug injection then could be presented to the body’s cells responsible for selecting the best and most relevant antigens in order to encourage cancer-killing cells to replicate themselves throughout the body. Importantly, tumor antigens had to be viewed in context; physical tumor destruction techniques such as heating or freezing tissue destroyed fragile antigens and disrupted their relevant contextual structures. Disruption of cell membranes and removal of lipids, proteins, and complex carbohydrates destroyed the antigens’ context, which is to what immune system cells responded. Thermal destruction denatured potential antigens, changing their chemical structure so that they were no longer representative of the tumor cell. In order to work rapid destruction of tumors had to preserve both antigenic structure and biological context.
Provectus’ lead investigational oncology drug PV-10 has a two-prong approach to fighting cancer. First, the “local effect” of tumor ablation (destruction) sees a patient’s tumor burden rapidly reduced after injection of PV-10 into his or her accessible cancerous lesions. Selective targeting by Rose Bengal minimizes side effects. Unlike many other cancer drugs, PV-10 does not rely on a single pathway to work and also has no known resistance. Second, the “systemic effect” of a tumor-specific immune response causes regression of untreated tumors, potentially prolonging progression-free survival and possibly enabling PV-10’s combination with immunomodulatory drugs and other systemic therapies for use in lesions that are inaccessible to a direct injection.
PV-10’s potential clinical value proposition to patients and their physicians is multi-faceted: It is simple to store, handle, and use and reuse. The drug thus far has shown modest local and transient toxicity that is predominantly confined to the injection site and minimal-to-no systemic toxicity. In regards to local efficacy PV-10 injection may lead to rapid, durable, complete tumor destruction, and induction of antigen release in injected lesions. It may promptly heal injected lesion sites completely after tumor destruction. In regards to systemic efficacy the drug may reliably, reproducibly induce regional and systemic immune effects potentially capable of destroying occult tumor cells, “bystander” lesions and distant metastatic lesions regardless of prior treatments. PV-10 may have multi-indication viability. Clinical trials to date and an ongoing expanded access program have treated more than 240 cancer patients (recurrent breast cancer, hepatocellular carcinoma and metastatic liver cancer, melanoma). It may be orthogonal, potentially having a low risk of clinically relevant drug-drug interactions. The drug may be agnostic, possibly compatible with all disease presentations. PV-10’s pharmacokinetics may be comparable and consistent.
Researchers at Moffitt Cancer Center in Tampa, Florida and the University of Illinois in Chicago have reproduced Dees et al.’s original preclinical work that first demonstrated PV-10’s two-prong approach and ability to fight cancer in multiple indications: e.g., the tumor ablation (the local effect) through the destruction of injected tumors, a tumor-specific immune response through the destruction of non-injected tumors and tumor-specific IFN-γ production in melanoma, breast cancer and colorectal cancer.
Provectus’ clinical development program is spearheaded by a pivotal trial currently being conducted in melanoma, and an early stage trial hepatocellular cancer (“HCC”) and metastatic liver cancer. In a Phase 2 trial that formed the basis for the current pivotal Phase 3 trial (registration study), 80 patients with stage IIIB-IV melanoma refractory to a median of six prior interventions received injections into their melanoma lesions up to four times over a 16-week period and were followed for 52 weeks. The overall response rate for the 28 patients who had all their existing melanoma lesions injected with PV-10, was 71% with 50% achieving a complete response. This subgroup of 28 patients who had all their lesions injected achieved a progression free survival of 9.8 months, which according to the Phase 3 trial’s principal investigator Dr. Sanjiv Agarwala, M.D at St. Luke’s Hospital and Health Network of Bethlehem, Pennsylvania compares favorably with historical progression free survivals of less than 2.5 months for systemic chemotherapy dacarbazine and temozolomide.
The company’s current early-stage study of 6 patients with non-resectable HCC (primary liver cancer) and 7 patients with other forms of cancer metastatic to the liver (secondary liver cancer) saw then undergo a single percutaneous injection of PV-10 guided by CT to one target lesion in the liver. At up to 54 months follow-up 10 out of these 13 initial patients were alive, with one death due to cardiac comorbidity, one to serious adverse events and one to HCC progression. Adverse events were generally limited to injection site reactions and photosensitivity and resolved without sequelae, with elevated liver enzymes observed during the first week after treatment. As with melanoma, PV-10 is believed to have a local chemoablative effect in HCC and metastatic liver disease where the agent enters lysosomes causing tumor necrosis that can stimulate immunological effects. Studies in melanoma patients injected with PV-10 have shown increased T cells in peripheral blood following injection including CD8+, CD4+, CD3+ and NKT.
Provectus recently announced the signing of a letter of intent with Boehringer Ingelheim China to collaborate in bringing PV-10 to market in mainland China.
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