Rationale

The DNA included in chromatin is identical in each cell of the body. The identity and function of a given cell which would otherwise be similar to all other cells, is provided by processes that permit the chromatin structure to open or close, so that the information contained within the DNA is made more or less accessible to transcription factors. Opening of the chromatin leads to RNA synthesis and eventually protein synthesis.

Epigenetics is defined as the mechanism that changes gene expression by ‘marking’ DNA or its associated proteins, without changing the DNA sequence itself. Modification of DNA-associated proteins, histones by, for example, the addition or removal of acetyl functional groups causes the chromatin structure to open or close. Hence, it is not surprising that deregulation of histone acetylation might lead to disease.

We have focused our research on enzymes that acetylate histones, histone acetyltransferase (HATs). Their activation leads to increased gene transcription and protein synthesis. Appia is testing the use of small molecules that enhance HAT activity in lymphoma as well as Alzheimer’s Disease and related dementia.

Mutations in HAT (histone acetyl transferases) enzyme genes, EP300 and CREBBP, are driving forces of lymphomas and when mutations are present, are linked to more aggressive behaving disease. HAT mutations have been identified in nearly 40% of diffuse large B-cell lymphoma and follicular lymphomas, the two most common types of lymphoma.

HATs add acetyl groups to histones. In so doing, they open-up chromatin to be more accessible to transcription factors, which leads to gene transcription, followed by synthesis of proteins including tumor suppressors.

HAT mutations may also contribute to decreased immune surveillance and immune evasion. With this knowledge in mind, activation of HAT enzymes could reverse these malignant characteristics and restore a normal healthy physiologic state.

Activating the body’s HAT enzymes increases histone acetylation. Appia has the license for the exclusive use of a library of compounds activating HATs including ~100 small molecules. For one of these compounds, YF2, Appia submitted an IND for Phase 1 to the FDA in the last quarter of 2021, which was approved in December 2021, with the goal of targeting these mutations in diffuse large B-cell lymphoma (DLCBL) and follicular lymphoma, the two most common lymphomas affecting 40,000 patients annually. Approximately 30% of patients with diffuse large B cell lymphoma die from their disease. There is a great need for new therapies which can change the natural history of this disease and increase the chance for a cure.

YF2 was chosen because it is the most selective of the analogues for cytotoxicity in cell lines harboring mutations in EP300, in contrast to others which lead to cytotoxicity irrespective of mutation status. YF2 led to a dose-dependent induction of CREBBP and p300 mediated acetylation of histone and tumor suppressor p53. In addition, it induces p300 mediated acetylation of oncogene BCL6. YF2 has enhanced solubility and membrane permeability. Additionally, YF2 demonstrated cytotoxic effects in a panel of primary patient lymphoma samples but was non-cytotoxic to blood cells from healthy donors.

YF2 has shown efficacy in three mouse models of DLCBL and is currently being investigated in a mouse model of T-cell Lymphoma. YF2 has passed full toxicological assessment in rats and dogs. Activation of HAT enzymes could represent a precision medicine treatment opportunity for lymphoma patients harboring HAT mutations. The ability to directly target this biology will limit off-target effects and likely reduce undesirable toxic side effects. There is substantial evidence to support YF2 as a first-in-class HAT activator drug.

Cancer is not the only pathology that can be targeted by HAT activators, for instance, histone acetylation has been involved in neurodegenerative processes. Memory is known to be modulated by epigenetics through regulation of gene expression. In the pipeline of drugs developed by Appia the HAT activator, RA013915, has shown efficacy in 4 different mouse models of Alzheimer’s disease. The compound stability combined with efficacy in Alzheimer’s disease models make it a good candidate for the therapy of Alzheimer’s disease and related dementias. RA013915 is in the process of being scaled-up for assessment of physical and chemical characteristics, as well as distribution, metabolic stability and fate followed by toxicology. The projected filing date for an IND with the FDA is Q1 2023.