Identifying somatic mutations in PIK3CA-Related Overgrowth Spectrum – Implications for targeted therapeutic treatment

Dr Chung, Brian Hon Yin   (Principal Investigator (PI))

Professor Chan Godfrey Chi Fung   (Co-Investigator)

Dr. YEUNG Kit San   (Co-Investigator)

24

2016-05-01

2018-04-30

80470

Identifying somatic mutations in PIK3CA-Related Overgrowth Spectrum – Implications for targeted therapeutic treatment

mosaicism, PIK3CA, PIK3CA-Related Overgrowth Spectrum, somatic overgrowth

Paediatrics,Human Genetics/Clinical Genetics

201511159247

Seed Fund for PI Research – Basic Research

2015

Completed

Mutation in phosphatidylinositol-4, 5-bisphosphate 3-kinase (PIK3CA), one of the genes involved in the PI3K-AKT-mTOR signaling pathway, is associated with developmental mosaic disorders which are now collectively termed as ""PIK3CA-Related Overgrowth Spectrum (PROS)"" (Keppler-Noreuil et al., 2015). PROS can be further divided into two subgroups based on the affected systems, which are body asymmetrical overgrowth and central nervous system (CNS) overgrowth respectively. These diseases are collectively termed as PROS, because they are all caused by somatic mutations in PIK3CA. Studies showed that these somatic mutations activate the PI3K-AKT-mTOR pathway, resulting in abnormal overgrowth in PROS (Kurek et al., 2012; Osborn et al., 2015; Riviere et al., 2012). Body asymmetrical overgrowth includes many diseases such as CLOVES Syndrome (Kurek et al., 2012), Klippel-Trenaunay Syndrome (Luks et al., 2015), and Fibroadipose Hyperplasia (Lindhurst et al., 2012). These disease have totally different clinical presentations affecting different tissues and organs, yet common features are present, including congenital asymmetrical overgrowth of skeletal and/or fibroadipose tissues; vascular malformations and skin abnormalities. Depending on the organs with abnormal overgrowth, patients with body asymmetrical overgrowth could suffer from chronic pain, difficulties in movement, and even suffocation if the mass overgrowth is located on the neck region. Although having very different clinical presentations, they are now grouped together as PROS because they are caused by mutation in PIK3CA that can only be identified in affected overgrowth tissues. More than 80% of these patients have somatic mutations in one of the four mutation hotspots in PIK3CA (Luks et al., 2015). CNS overgrowth includes diseases such as Megalencephaly‐Polymicrogyria‐Polydactyly‐Hydrocephalus Syndrome (MPPH) and Megalencephaly‐Capillary Malformation Syndrome (MCAP) (Riviere et al., 2012). Individuals who have CNS overgrowth have megalencephaly and developmental delay. However unlike body asymmetrical overgrowth, CNS overgrowth does not have mutation hotspots, and somatic mutations can also be occurred in other genes in the PI3K-AKT-mTOR signaling pathway, including but not limited to PIK3R2, mTOR, AKT, CCND2 and PTEN (Baynam et al., 2015; Jansen et al., 2015; Lee et al., 2012; Mirzaa et al., 2014). Besides, these mutations can be identified in cells other than that of CNS, including blood and saliva. Identification of mutations in individuals with PROS is not easy, because the level of somatic mosaicism could as low as 1% only (Lindhurst et al., 2012; Luks et al., 2015; Riviere et al., 2012). Although the prevalence of each subtype of PROS is rare, the total number of patients having somatic mutation in PIK3CA leading to PROS is not that uncommon, as the genetics clinic at Queen Mary Hospital/The University of Hong Kong has received referral of more than 10 patients with suspected PROS in about two years’ time, and identified 12 retrospective patients that are suspected to be PROS. Therefore, genetic tests should be set up for these patients for identifying underlying genetic causes. Identification of the genetic causes in PROS patients is important because it has therapeutic implications. Surgical debulking and early intervention are now the only treatment available for PROS with body asymmetrical overgrowth and CNS overgrowth respectively. However, surgical debulking can only remove some of the overgrowth tissues, and recurrent growth of the affected tissues has been observed in patients, impairing the movement or even causing life-threating dangers. With the identification of somatic mutations in PIK3CA, there are drugs that potentially can be used for targeted treatment. It is shown that the PI3K-AKT-mTOR signaling pathway is activated in the overgrowth tissues of individuals with PROS, and many drugs that have been approved to be used in cancer therapy therefore could potentially be used in PROS as well. These FDA approved drugs include Sirolimus and Everolimus (mTOR inhibitor), Idelalisib (PI3K inhibitor) and Impavido (AKT inhibitor). However, more basic researches and clinical trials have to be conducted to study the effect of these approved drugs on PROS. In this study, we aim to develop assays and identify the potential FDA approved drugs that can be used for treatment in PROS. Specifically, we aim to: 1) develop digital PCR assays to identify the low level of somatic mutations in the mutation hotspots in patients with PROS of body overgrowth; 2) develop single-molecule molecular inversion probe (smMIP) assays to detect the low level of somatic mutations in patients with PROS of CNS overgrowth, and also in patients with RPOS of body overgrowth that do not have mutation in mutation hotspots; and 3) to establish cell lines and function assays to allow further study for drug screening. Specifically, immunoblotting assays and cell proliferation assays will be established.