Synthesis and bioevaluation of N-(arylalkyl)-homospermidine conjugates Songqiang Xie, a,b Pengfei Cheng, c Guangchao Liu, d Yuangfang Ma, d Jin Zhao, a Mounir Chehtane, e Annette R. Khaled, e Otto Phanstiel, IV f, * and Chaojie Wang a,c, * a Institute of Natural Products & Medicinal Chemistry, Henan University, Henan, Kaifeng 475001, China b College of Pharmacy, Henan University, Henan, Kaifeng 475001, China c Chemistry Department, Henan University, Henan, Kaifeng 475001, China d Medical College, Henan University, Henan, Kaifeng 475001, China e Biomolecular Science Center, University of Central Florida, Orlando, FL 32816, USA f Department of Chemistry, University of Central Florida, Orlando, FL 32816, USA Received 4 March 2007; revised 9 May 2007; accepted 2 June 2007 Available online 8 June 2007 Abstract—N 1 -(Arylalkyl)homospermidines (1c–1f) and terminally piperazine-substituted homospermidine conjugates (2a–2e) were synthesized and evaluated for cytotoxicity in mouse leukemia L1210, a-difluoromethylornithine (DFMO)-treated L1210, melanoma B16, spermidine (SPD)-treated B16, and HeLa cell lines. Results demonstrated that homospermidine was a more effective vector than piperazine-substituted homospermidine in ferrying diverse arenes into cells via the polyamine transporter. The leading com- pound, 9-anthracenemethyl-homospermidine (1a), was shown to induce apoptosis in B16 cells and IL-3 dependent FL5.12A pro- B cells. The novel conjugate 4-biphenylmethyl-homospermidine (1e) could also induce apoptosis. However, it exhibited different effect on the cell cycle of B16 cells compared to 1a. Ó 2007 Elsevier Ltd. All rights reserved. One of the main drawbacks of current cancer chemo- therapies is the non-selective delivery of anticancer drugs to both cancerous and normal tissues. The selec- tive delivery of antitumor drugs to targeted cells is a worthwhile endeavor. A success in this area would enhance drug potency and should reduce side effects attributed to non-specific delivery. This goal may be realized through conjugates between antitumor agents and smart vectors, which have elevated affinity for can- cer cells. 1 Polyamines are one such potential vector. In particular, polyamines are important growth factors essential for cell proliferation. Many tumor cell types be- come highly dependent on growth factor stimuli and can either biosynthesize these growth factors internally or import them from exogenous sources via the polyamine transporter (PAT). One hypothesis is that tumors are unable to biosynthesize enough polyamines to sustain their rapid growth rates and rely on the PAT to make up the difference. Structure–activity studies of PAT li- gands have demonstrated a wide structural tolerance of this transporter for non-native polyamine derivatives. 2,3 Indeed, some polyamine-drug conjugates have been reported, which follow this strategy. 4–6 Although the natural polyamines (putrescine, spermidine, and sperm- ine) have been used extensively as vectors, previous efforts revealed that the non-native triamine, homospe- rmidine, was better than its natural counterparts. 7,8 A series of N 1 -(arylalkyl)-homospermidine conjugates in which the N 1 -substituent was systematically altered from benzyl, naphthylmethyl, anthracenylmethyl to pyrenylmethyl were designed to evaluate the size limita- tions of the PAT. 9 These studies confirmed that the PAT could accommo- date even the relatively large pyrene group. However, N 1 -(anthracen-9-ylmethyl)-homospermidine (1a) and N 1 -(1-naphthyl-methyl)-homospermidine (1b) displayed the best PAT recognition and selectivity in a Chinese hamster ovary (CHO) screen involving CHO wt (PAT- active cells) versus the CHOMG (PAT inactive) mutant cells. 9 0960-894X/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.bmcl.2007.06.009 Keywords: Homospermidine; Polyamine conjugate; Synthesis; Apoptosis. * Corresponding authors. Tel.: +86 136 1981 0550 (C.W.); Tel.: +407 823 5410; fax: +407 823 2252 (O.P.); e-mail addresses: ophansti@mail.ucf.edu; wcjsxq@yahoo.com Bioorganic & Medicinal Chemistry Letters 17 (2007) 4471–4475