Short communication Discovery of a marine-derived bis-indole alkaloid fascaplysin, as a new class of potent P-glycoprotein inducer and establishment of its structureeactivity relationship Sudhakar Manda a, b , Sadhana Sharma c , Abubakar Wani c , Prashant Joshi a, b , Vikas Kumar b, d , Santosh K. Guru c , Sonali S. Bharate d , Shashi Bhushan b, c , Ram A. Vishwakarma a, b , Ajay Kumar c, ** , Sandip B. Bharate a, b, * a Medicinal Chemistry Division, CSIR-Indian Institute of Integrative Medicine, Canal Road, Jammu 180001, India b Academy of Scientific & Innovative Research (AcSIR), CSIR-Indian Institute of Integrative Medicine, Canal Road, Jammu 180001, India c Cancer Pharmacology Division, CSIR-Indian Institute of Integrative Medicine, Canal Road, Jammu 180001, India d Preformulation Laboratory, PKPD Division, CSIR-Indian Institute of Integrative Medicine, Canal Road, Jammu 180001, India article info Article history: Received 14 August 2015 Received in revised form 10 October 2015 Accepted 28 October 2015 Available online 31 October 2015 Keywords: Fascaplysin b-carboline P-glycoprotein induction Acetylcholinesterase Quaternary analogs Alzheimer's disease abstract The screening of IIIM natural products repository for P-gp modulatory activity in P-gp over-expressing human adenocarcinoma LS-180 cells led to the identification of 7 natural products viz. withaferin, podophyllotoxin, 3-demethylcolchicine, agnuside, reserpine, seseberecine and fascaplysin as P-gp in- ducers. Fascaplysin (6a), a marine-derived bis-indole alkaloid, was the most potent among all of them, showing induction of P-gp with EC 50 value of 25 nM. P-gp induction is one of the recently targeted strategy to increase amyloid-b clearance from Alzheimer brains. Thus, we pursued a medicinal chemistry of fascaplysin to establish its structureeactivity relationship for P-gp induction activity. Four series of analogs viz. substituted quaternary fascaplysin analogs, D-ring opened quaternary analogs, D-ring opened non-quaternary analogs, and b-carbolinium analogs were synthesized and screened for P-gp induction activity. Among the total of 48 analogs screened, only quaternary nitrogen containing analogs 6aeg and 10a, 10hel displayed promising P-gp induction activity; whereas non-planar non-quaternary analogs 9aem, 13aen, 15aeh were devoid of this activity. The P-gp induction activity of best compounds was then confirmed by western-blot analysis, which indicated that fascaplysin (6a) along with 4,5- difluoro analog of fascaplysin 6f and D-ring opened analog 10j displayed 4e8 fold increase in P-gp expression in LS-180 cells at 1 mM. Additionally, compounds 6a and 6f also showed inhibition of ace- tylcholinestease (AChE), an enzyme responsible for neuronal loss in Alzheimer's disease. Thus, fasca- plysin and its analogs showing promising P-gp induction along with AChE inhibition at 1 mM, with good safety window (LS-180: IC 50 > 10 mM, hGF: 4 mM), clearly indicates their promise for development as an anti-Alzheimer agent. © 2015 Elsevier Masson SAS. All rights reserved. 1. Introduction Alzheimer's disease (AD) is the most common form of senile dementia and the fourth highest cause of disability and death in the elderly. It is characterized by the presence of three main brain hallmarks viz. diffuse neuronal loss with a particular involvement of the cholinergic system, extracellular protein deposits (amyloid-b plaques) and intracellular protein deposits (neurofibrillary tangles, NFTs) [1e3]. All current therapies are based on the cholinergic hypothesis and demonstrate only symptomatic treatment. P- glycoprotein (P-gp) is highly expressed on the luminal surface of brain capillary endothelial cells and contributes to the BBB. The recent two independent clinical studies [4,5] observed that AD patients have decreased clearance of CNS amyloid-b compared to healthy volunteers. The rate of Ab production is same as that in healthy volunteers; whereas rate of clearance is impaired by 25e30%. High levels of Ab then initiates cascade of events * Corresponding author. Medicinal Chemistry Division, CSIR-Indian Institute of Integrative Medicine, Canal Road, Jammu 180001, India. ** Corresponding author. E-mail addresses: ajaykmahajan@hotmail.com (A. Kumar), sbharate@iiim.ac.in (S.B. Bharate). Contents lists available at ScienceDirect European Journal of Medicinal Chemistry journal homepage: http://www.elsevier.com/locate/ejmech http://dx.doi.org/10.1016/j.ejmech.2015.10.049 0223-5234/© 2015 Elsevier Masson SAS. All rights reserved. European Journal of Medicinal Chemistry 107 (2016) 1e11