May 15, 2015 (Vol. 35, No. 10)
Vicki Glaser Writer GEN
Gene Therapy Has Had Its Growing Pains, but It Is Now Coming Into Its Own
It seldom happens that a premature shoot of genius ever arrives at maturity. One such shoot, gene therapy, appears to be one of the exceptions. Gene therapy, which showed early promise as a means of replacing defective or missing genes, is branching out.
And it may yet produce abundant and diverse fruits. For example, gene therapy is being cultivated in cardiovascular applications, which are relevant to large, broad-based patient populations. Gene therapy approaches to cardiovascular and other diseases are being tended in billion-dollar collaborations, and they are being evaluated in late-stage clinical trials.
Current gene therapy products in development utilize a variety of viral vectors. Some of them integrate into the host cell genome to achieve long-term protein expression; others do not, aiming for only transient expression of a therapeutic product.
They vary in their disease targets, ranging from aggressive brain tumors, for which no curative treatments exist, to ocular diseases, which offer the advantage of accessibility and a contained treatment site. And while the term “gene therapy” may still connote delivery of a normal, replacement gene, at present it often refers to the targeted administration of an enzyme capable of converting a prodrug to an active compound at the site of a disease process, or of a gene product that can stimulate the immune system to recognize and kill tumor cells.
Recent evidence of the potential commercial value of gene therapy technology and products across a range of therapeutic areas includes the collaboration announced in April and valued at more than $1 billion that gives Bristol-Myers Squibb exclusive access to the gene therapy technology platform of uniQure for up to 10 disease targets, including the company’s lead gene therapy program for congestive heart failure.
At the Heart of the Matter
At a recent gene therapy event, the Phacilitate Cell & Gene Therapy Forum in Washington, DC, the organizer’s usual agenda —the exploration of commercialization and development models—was expanded to address manufacturing, product characterization, logistics, R&D, and regulatory challenges.
Gabor Rubanyi, M.D., Ph.D., CSO at Taxus Cardium Pharmaceuticals Group, presented interim data from the Phase III ASPIRE clinical trial to evaluate the company’s Generx® angiogenic gene therapy product candidate to treat patients with cardiac microvascular insufficiency and coronary artery disease (CAD).
It typically takes 20–25 years for a field to mature, and “we are there,” said Dr. Rubanyi. He reviewed the many obstacles the field of gene therapy has had to overcome, including identifying and optimizing safe and efficient viral vectors that have the correct properties for use in a particular disease target and patient population, designing and inserting the therapeutic genetic payloads, and determining the optimal means of delivering the gene therapy product.
“As with all new technology,” Dr. Rubanyi explained, “it was a reiterative process, progressing from the laboratory bench to bedside and back to the bench to overcome obstacles identified in early-stage clinical trials.”
Taxus Cardium has taken its angiogenic gene therapy product candidate into late-stage clinical trials, targeting cardiovascular disease, which affects large numbers of patients worldwide. According to Dr. Rubanyi, Generx is inexpensive to manufacture, and it could be a cost-effective CAD treatment, imposing just a fraction of the cost associated with alternative approaches such as coronary artery bypass graft (CABG) surgery, stents, or angioplasty.
The product consists of a nonreplicating adenovirus vector carrying the gene for fibroblast growth factor-4 (FGF-4). An interventional cardiologist administers the vector through a standard balloon catheter directly into the cardiac arteries, where it distributes throughout the microvasculature.
The company modified an earlier drug delivery protocol to enhance the permeability of the coronary arteries during the procedure, improving the ability of the vector to transfect heart cells. Short-term, transient expression of FGF-4 by the heart cells promotes the growth of new blood vessels, increasing blood flow to ischemic heart tissue after a myocardial infarction, for example.
In the Phase III trial, early results for the first 11 patients were “very impressive and encouraging,” in Dr. Rubanyi’s estimation: “Every patient treated had a significant improvement in blood flow to the previously ischemic areas, while the controls showed no improvement.”
Gene Delivery to the Eye
Oxford Biomedica is developing lentiviral-based gene therapy product candidates based on the company’s LentiVector® gene delivery system. The company’s product pipeline, disease targets, developmental strategy, and scale-up of production to prepare for clinical testing and commercialization were described in a presentation at the Phacilitate meeting entitled.
The presentation cited Oxford Biomedica’s substantial intellectual property portfolio, the company’s experience around lentiviral technology, and the high efficiency of delivery and stability of the company’s lentiviral vectors. Beyond these generalities, the presentation indicated that as a therapeutic gene delivery vehicle, lentivirus offers three particular advantages:
- Large-capacity payloads (7–8 kb compared to about 4 kb for adeno-associated virus).
- Integration into the host genome enabling long-term gene expression (>5 years in some studies to date) and a sustained therapeutic effect with a single dose.
- The ability to target and transfect dividing or nondividing cells.
Five of the company’s gene therapy product candidates target ocular diseases. Four of these were originally under option to Sanofi, which provided funding to get the products into the clinic. Sanofi has since taken development of two of the four products: StarGen™, to treat Stargardt disease; and UsherStat®, to treat Usher syndrome type 1B.
“We have treated more than 56 patients with lentivirus-based in vivo gene therapy and shown it to be quite safe, with no serious adverse events,” said Peter Nolan, chief business officer at Oxford Biomedica.
The company’s gene therapy product RetinoStat® is a lentiviral vector. It carries two antiangiogenic proteins, and it is administered subretinally to treat wet age-related macular degeneration (AMD). Phase I results are to be announced in May.
EncorStat®, which is in late preclinical development for the treatment of corneal graft rejection, contains the same two genes as RetinoStat. Glaucoma-GT, a collaborative development project with the Mayo Clinic to treat chronic glaucoma, is in preclinical studies. The product delivers two genes—COX-2 and a PGF-2a receptor gene—to reduce intraocular pressure.
The company is planning a Phase II trial with a new, more potent version of ProSavin®, a lentiviral gene therapy product to treat Parkinson’s disease that targets delivery of three genes to the striatum, in the subcortical region of the forebrain. These genes encode enzymes needed to produce dopamine, making it available at the site of dopaminergic neurons that control movement.
Aiming to increase the approximate 30% improvement seen in patients treated in a previous Phase I/II trial, the company has re-engineered the delivery vector so that 10–50 times more dopamine can be produced, offering the potential to administer lower doses and reduce the cost of treatment.
From a cost-of-goods and manufacturing perspective, Oxford Biomedica was “incentivized” to transition its production processes and to share the risks of doing so. Specifically, the company is transitioning away from using cell factories to produce its lentiviral vectors to using more robust, industrialized manufacturing processes. This change was inspired by the company’s development program with Novartis around the pharma giant’s CART-19 leukemia drug, explained Nolan, who added that Novartis’s desire “to compress the timeframe and get CART-19 onto the market as quickly as possible” has driven the accelerated scale-up of the technology and processes.
Avalanche Biotechnologies is developing gene therapy products to treat ocular disease, using single administration of an adeno-associated virus (AAV) vector directly to the eye to achieve sustained expression of a therapeutic protein. The company’s Ocular BioFactory™ technology platform is based on directed evolution involving the generation of diverse libraries of AAV variants and multiple rounds of screening and optimization to identify an optimal variant with novel properties for a specific disease.
AVA-101 to treat wet AMD is Avalanche Biotechnologies’ first product and is farthest along in its developmental pipeline. It predates the company’s Ocular BioFactory and is based on the naturally occurring AAV2 vector. AVA-101 is administered through a subretinal injection and transduces retinal cells, resulting in the production of sFLT-1, a naturally occurring anti-VEGF protein.
Avalanche used the Ocular BioFactory platform to develop AVA-201, a gene therapy candidate to treat patients with dry AMD who are at risk of converting to wet AMD. One goal of the directed evolution process was to identify a novel AAV vector that would be amenable to intravitreal injection.
“This patient population has excellent vision, and we’re hoping to maintain their vision with a one-time [less invasive] intravitreal injection,” said Roman Rubio, M.D., head of translational medicine at Avalanche.
The results of a Phase I trial of AVA-201 demonstrated a good safety profile and “encouraging biological activity in terms of the ability to maintain vision in patients with wet AMD and produce an anatomic effect, namely an improvement and/or maintenance in retinal thickness,” reported Dr. Rubio. Avalanche recently brought online a scalable baculovirus cell culture system and, going forward, will be producing its AAV vectors using this system to support their current and future pipeline.
Recently, Avalanche announced an exclusive license agreement with the University of Washington (Seattle) to develop gene therapy products using the Ocular BioFactory platform to treat color vision deficiency, commonly known as red-green color blindness. The aim of the collaboration is to produce an engineered AAV vector that, “with a single intravitreal injection can target the cone cells in the retina, restore the missing photopigment, and thereby restore the sensation of color these patients once lacked,” said Dr. Rubio.
Avalanche is currently developing a drug candidate for its AVA-311 program in collaboration with Regeneron Pharmaceuticals. The gene therapy targets juvenile X-linked retinoschisis, an orphan disease indication in which a lack of retinoschisin protein results in splitting of the retinal layers and associated vision loss.
The Promise of Immuno-Oncology
A long-perceived goal of next-generation anticancer therapeutics development, with the aim of delivering more targeted, more effective, and less toxic antitumor agents, is to activate a patient’s own immune system to be able to differentiate and destroy tumor cells—to seek out and eliminate errant cells, whether solid or liquid tumors or metastases. Strategies to achieve a safe, effective, and selective immuno-oncologic effect have proven challenging, but anticancer therapeutics based on this paradigm are moving through clinical testing. Some promising results suggest the potential to extend survival times, even in some of the most deadly forms of cancer such as brain tumors.
At the Phacilitate conference, Douglas Jolly, Ph.D., executive vice president of research and pharmaceutical development at Tocagen, discussed interim results from the company’s Phase I/II trials of Toca 511 and Toca FC in patients with recurrent high-grade glioma (HGG). More than 93 patients have so far been treated with the company’s two-part gene therapy regimen, which delivers the gene for an enzyme capable of converting a prodrug to an anticancer therapeutic at the site of the tumor.
The therapy combines initial administration of Toca 511, a retroviral replicating vector (RRV) that preferentially infects tumor (replicating) cells and has been genetically engineered to carry the gene for cytosine deaminase (CD), an enzyme that catalyzes conversion of the antifungal drug flucytosine (5-FC) to the anticancer agent 5-fluorouracil (5-FU) inside cancer cells. After allowing time for the virus to spread through the tumor and surrounding cells, patients receive cycles of Toca FC, an oral, extended-release formulation of flucytosine.
Preclinical model data show that this treatment both kills cells directly and then elicits an antitumor immune response that prevents tumor recurrence.
In 25 HGG patients with first or second recurrence that received injections of Toca 511 directly into the tumor bed following surgical resection, median survival (based on interim data) was about 14 months, compared to a typical 7–8 month survival time for these patients. Data from the trial provide evidence of the engineered retrovirus including the CD gene in glioma cells, indicating that the vector is delivering the 5-FC converting enzyme to the tumor, reported Dr. Jolly.
Tocagen is planning a Phase II/III registration trial using the above protocol, anticipated to begin later this year. The company has also initiated a clinical study in which administration of Toca 511 is via intravenous injection.
“Preclinical studies have shown that Toca 511 and Toca FC are active across all cancer types we have tested,” asserted Harry Gruber, M.D., CEO of Tocagen. The company’s preclinical work in solid tumors has so far focused mainly on colorectal and breast cancer. Additional application areas being explored include RRVs to deliver RNA interference genes targeted against immune checkpoints such as programmed death-ligand 1 (PD-L1).
Margarita Gutova, M.D., associate research professor, department of neurosciences, Beckman Research Institute of the City of Hope National Medical Center, described a novel Terumo-based production scale-up method to generate large numbers of stem cells for clinical trials.
Dr. Gutova works in the translational research laboratory of Karen Aboody, M.D., who has pioneered the field of neural stem cell (NSC) cancer therapy, harnessing the natural ability of these cells to home directly to invasive brain tumor sites. The NSCs can cross the blood-brain barrier, migrate through normal brain tissue, and selectively target tumor cells to deliver an anticancer gene therapy.
Dr. Gutova is leading an effort to treat the most common malignant pediatric brain tumor, medulloblastoma. Her goal is to localize tumor-killing drug concentrations while minimizing exposure to normal cells to decrease toxic side-effects.
The engineered NSCs deliver a modified carboxylesterase, which converts irinotecan to the 1,000 times more potent topoisomerase-1 inhibitor SN-38. Following delivery of NSCs, irinotecan is administered, and the CE produced by the stem cells activates the drug selectively at the tumor sites.
Dr. Gutova and colleagues are also conducting preclinical studies on intranasal delivery of NSCs to target brain tumor sites. Results to date indicate that the NSCs delivered intranasally in mice cross the blood-brain barrier, migrate to tumor sites in the brain, and do not distribute to normal, noncancerous areas of the brain or to other peripheral tissues.
At Phacilitate, she described her team’s collaborative work with Terumo to scale up production of NSCs to generate large cell banks efficiently and cost effectively. Using the closed, automated Quantum Cell Expansion System, they have achieved reproducible expansion of NSCs that showed characteristics comparable to those expanded using a conventional cell culture method.
Assessing Gene Therapy’s Future
Although scientists first began seriously discussing gene therapy over 40 years ago and the FDA approved the first gene therapy experiment in 1990, the field has not taken off to the degree many had hoped. Why not?
“Gene therapy could be further along if the investment community had come along earlier,” says Terry R. Flotte, M.D., executive deputy chancellor, provost, and dean of the school of medicine at the University of Massachusetts. “It has been hurt by the decrease in NIH funding and the irrational fear of gene therapy that occurred after the Gelsinger [death].”
Jesse Gelsinger was an 18-year-old who died in 1999 during a gene therapy clinical trial.
Dr. Flotte, an associate editor of Human Gene Therapy, published by Mary Ann Liebert, is optimistic about gene therapy’s future.
“Recent successes began in 2008 with the publication of three separate papers on three parallel trials showing real, tangible improvement in vision in patients with a rare genetic disease affecting the retina (Leber congenital amaurosis), which was followed by other clinical successes in hemophilia and with CAR-T cells for lymphoma,” noted Dr. Flotte, who will take over as editor-in-chief of the publication in July.
“Another success has been an increase in venture funding coincident with Nasdaq’s rise.” He believes that five years from now “we should have five to ten licensed gene therapy products in the U.S. In ten years, it will be finding a clinical niche.