Therapeutic value of prenatal rapamycin treatment in a mouse brain model of tuberous sclerosis complex

Abstract

Epileptic seizures, particularly infantile spasms, are often seen in infants with tuberous sclerosis complex (TSC) soon after birth. It is feared that there are long-term developmental and cognitive consequences from ongoing, frequent epilepsy. In addition, the hallmark brain pathology of TSC, cortical tubers and giant cells are fully developed at late gestational ages. These observations have led us to examine the benefit of prenatal rapamycin in a new fetal brain model of TSC. In this Tsc1(cc) Nes-cre(+) mouse model, recombination and loss of Tsc1 in neural progenitor cells leads to brain enlargement, hyperactivation of mTOR, and neonatal death on P0 due to reduced pup-maternal interaction. A single dose of prenatal rapamycin given to pregnant dams (1 mg/kg, subcutaneous) rescued the lethality of mutant mice. This one dose of prenatal rapamycin treatment reduced hyperactivation of the mTOR pathway in the mutant brain without causing apparent pregnancy loss. Continued postnatal rapamycin beginning at day 8 extended the survival of these mice to a median of 12 days with complete suppression of hyperactive mTOR. However, the rapamycin-treated mutants developed enlarged brains with an increased number of brain cells, displaying marked runting and developmental delay. These observations demonstrate the therapeutic benefit and limitations of prenatal rapamycin in a prenatal-onset brain model of TSC. Our data also suggest the possibility and limitations of this approach for TSC infants and mothers.

mTOR Signaling in Epilepsy: Insights from Malformations of Cortical Development

“…Subsequent studies confirmed seizure relief in several mouse TSC models (for review, see Feliciano et al 2013). Three recent preclinical studies have also shown that in utero prenatal treatment with rapamycin can prevent or significantly diminish the morphological consequences of Tsc1 or Tsc2 loss in the mouse (Anderl et al 2011;Tsai et al 2012b;Way et al 2012). These findings suggest that in utero rapamycin could be used in the setting of a prenatal TSC diagnosis; however, rapamycin alone may have deleterious effects of fetal brain development that may warrant further consideration (Tsai et al 2013).…”

Possible Prevention of Tuberous Sclerosis Complex Lesions

“…Early treatment with rapamycin prevented the development of epilepsy and underlying brain abnormalities associated with epileptogenesis as well as premature death in mouse models of TSC. 10,11 Despite these promising findings that support a preventative approach, it is important to note that the rapamycintreated mutants developed enlarged brains with more brain cells, displaying marked runting and developmental delay. 10,12 In our patient, everolimus treatment was well tolerated overall.…”

“…10,11 Despite these promising findings that support a preventative approach, it is important to note that the rapamycintreated mutants developed enlarged brains with more brain cells, displaying marked runting and developmental delay. 10,12 In our patient, everolimus treatment was well tolerated overall. The only treatment-related toxicity was grade 3 stomatitis and, possibly, decrease in plasma fibrinogen, which normalized after dose reduction.…”

Survival benefit and phenotypic improvement by hamartin gene therapy in a tuberous sclerosis mouse brain model

“…Models include the Eker rat with a germ line mutation in Tsc2 (Yeung, 2004), conditional floxed Tsc1 and Tsc2 mouse alleles which can be crossed with transgenic mice bearing (non-inducible or inducible) Cre recombinase under different cell-specific promoters, which are active, for example, in astrocytes (Uhlmann et al, 2002), neural progenitor cells (Carson et al, 2012; Anderl et al, 2011), and early neurons (Meikle et al, 2007). Other stochastic models have been achieved by electroporation of a Cre expression cassette into floxed neonatal mouse brains (Feliciano et al, 2013) or intracerebral ventricular (ICV) injection of an adeno-associated virus (AAV) vector encoding Cre into newborn floxed mice (Prabhakar et al, 2013).…”

“…Most of these TSC mouse brain models have reduced body weight, tremor, hunched posture, seizures and motor abnormalities, with median survival varying from 0 to 180 days. Continuous treatment with rapamycin and analogues that block mTOR activity have been shown to lead to dramatic survival benefit in several models, with a decrease in neural cell size, increased myelination, decreased seizures and improved behavior (Anderl et al, 2011; Meikle et al, 2008; Carson et al, 2012; Zeng et al, 2008). This drug benefit persists for a short while after treatment is ended, but then severe symptoms reappear followed by death.…”