Homology Medicines Presents Data Showing Single Dose HMI-102 Resulted in Long-Term Correction of PKU, Including Reduction of Phe and Increased Brain Neurotransmitters in Murine Model

- Phase 1/2 pheNIX Study of Gene Therapy Candidate HMI-102 is Underway and Initial Clinical Data is Anticipated by Year End -

BEDFORD, Mass., June 17, 2019 (GLOBE NEWSWIRE) -- Homology Medicines, Inc. FIXX, a genetic medicines company, announced today the presentation of data highlighting the ability of a single administration of HMI-102, the Company's lead AAVHSC15 gene therapy candidate for the treatment of phenylketonuria (PKU) in adults, to achieve long-term correction of PKU in PAH^enu2 mice on a normal diet. These data, presented in an oral session at the European Society of Human Genetics Conference (ESHG), also demonstrated restoration of key neurotransmitters in the brain to normal levels. PKU is an inborn error of metabolism caused by a mutation in the PAH gene that results in a potentially toxic buildup of phenylalanine (Phe), an essential amino acid derived primarily from dietary protein. Homology recently announced the initiation of the pheNIX study, a Phase 1/2 gene therapy trial for adults with classic PKU, and expects to report initial clinical data from the study of HMI-102 by the end of 2019.

"These findings are part of a larger body of preclinical data demonstrating the therapeutic potential and efficacy of HMI-102, which provided a strong foundation for the recent initiation of our Phase 1/2 pheNIX study, the first gene therapy candidate for PKU to enter clinical trials," said Albert Seymour, Ph.D., Chief Scientific Officer of Homology Medicines. "With initial results from the pheNIX trial expected later this year, we believe that a one-time, potentially curative treatment that addresses the underlying cause of PKU may offer patients a sustained reduction of Phe and freedom from a life-long, protein-restricted diet."

Highlights of the oral presentation at ESHG in Gothenburg, Sweden, "HMI-102 Gene Therapy Sustainably Corrects PKU Phenotype in PAH^enu2 Mice on Normal Diet," include:

• Effective, sustained phenotype correction in PAH^enu2 murine model on a normal protein diet;
• Decreased serum Phe, as well as normalization of serum tyrosine levels and a change in coat color, both indicating a restoration of Phe metabolism; and
• Reduced brain Phe and the neurotransmitter metabolite, 5-HIAA to normal levels.

Homology has received Fast Track Designation for HMI-102 from the U.S. Food and Drug Administration (FDA), and the European Medicines Agency (EMA) granted orphan drug designation for HMI-102 in the United States and European Union, respectively.

About the pheNIX Phase 1/2 Clinical Study in PKU
The pheNIX study is designed to evaluate the safety and efficacy of HMI-102 gene therapy in a randomized, concurrently-controlled, dose-escalation study. The pheNIX study is expected to enroll up to 21 patients, ages 18-55 years old, who have been diagnosed with classic PKU and will receive a single dose of HMI-102, which uses Homology's AAVHSC15 vector. In addition to safety measures, the study will also evaluate reduction in serum Phe levels. The study design allows for expansion of the number of patients in any dose cohort as long as the dose selected has been deemed safe and effective by the Data Monitoring Committee and the Homology Review Team. A decision to expand a dose cohort would trigger the addition of a concurrent, randomized control arm consisting of classic PKU patients that will be monitored for Phe levels before they crossover into the treatment arm. Homology expects to report initial clinical data from the pheNIX study by the end of 2019. Additional information about the pheNIX study can be found at www.clinicaltrials.gov.

About Phenylketonuria (PKU)
PKU is a rare, inherited inborn error of metabolism caused by mutations in the PAH gene. The current standard of care is a highly restrictive diet, but it is not always effective, and there are currently no treatments available that address the genetic defect in PKU. If left untreated, PKU can result in progressive and severe neurological impairment. PKU affects approximately 16,500 people in the U.S., and an estimated 350 newborns are diagnosed each year.

About Homology Medicines, Inc.
Homology Medicines, Inc. is a genetic medicines company dedicated to transforming the lives of patients suffering from rare genetic diseases with significant unmet medical needs by curing the underlying cause of the disease. Homology's proprietary platform is designed to utilize its human hematopoietic stem cell-derived adeno-associated virus vectors (AAVHSCs) to precisely and efficiently deliver genetic medicines in vivo either through a gene therapy or nuclease-free gene editing modality across a broad range of genetic disorders. Homology has a management team with a successful track record of discovering, developing and commercializing therapeutics with a particular focus on rare diseases, and intellectual property covering its suite of 15 AAVHSCs. Homology believes that its compelling preclinical data, scientific expertise, product development strategy, manufacturing capabilities and intellectual property position it as a leader in the development of genetic medicines. For more information, please visit www.homologymedicines.com.

Forward-Looking Statements
This press release contains forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995. All statements contained in this press release that do not relate to matters of historical fact should be considered forward-looking statements, including statements regarding our expectations surrounding the design, initiation, enrollment and timing of the release of data for the pheNIX clinical trial in PKU; the potential, safety, efficacy, and regulatory and clinical progress of our product candidates; beliefs about preclinical data; and our position as a leader in the development of genetic medicines. These statements are neither promises nor guarantees, but involve known and unknown risks, uncertainties and other important factors that may cause our actual results, performance or achievements to be materially different from any future results, performance or achievements expressed or implied by the forward-looking statements, including, but not limited to, the following: we have and expect to continue to incur significant losses; our need for additional funding, which may not be available; failure to identify additional product candidates and develop or commercialize marketable products; the early stage of our development efforts; potential unforeseen events during clinical trials could cause delays or other adverse consequences; risks relating to the capabilities and potential expansion of our manufacturing facility; risks relating to the regulatory approval process; our product candidates may cause serious adverse side effects; inability to maintain our collaborations, or the failure of these collaborations; our reliance on third parties; effects of significant competition; failure to attract, retain and motivate qualified personnel; the possibility of system failures or security breaches; and risks relating to intellectual property. These and other important factors discussed under the caption "Risk Factors" in our Quarterly Report on Form 10-Q for the quarter ended March 31, 2019 and our other filings with the SEC could cause actual results to differ materially from those indicated by the forward-looking statements made in this press release. Any such forward-looking statements represent management's estimates as of the date of this press release. While we may elect to update such forward-looking statements at some point in the future, we disclaim any obligation to do so, even if subsequent events cause our views to change.