Chinese Chemical Letters
Original article
Novel NO-releasing derivatives of betulinic acid with antitumor
activity
a
a,
Jin-Hong Liu a,1, Zi-Fei Zhu a,1, Jia Tang a, Ai-Qin Jiang b, , Liu-Fang Hu , Li Chen
*
*
a Department of Natural Medicinal Chemistry, China Pharmaceutical University, Nanjing 210009, China
b Medical School of Nanjing University, Nanjing 210093, China
A R T I C L E I N F O
A B S T R A C T
Article history:
Thirteen novel NO-releasing derivatives of betulinic acid (BA) bearing two types of NO-donors (nitrates
and furoxans) were synthesized and evaluated for their antitumor activity. The results showed that
furoxan-based derivatives exhibited higher antitumor activity than nitrate-based derivatives, with
compounds 11a and 11b displaying promising potency against B16 cell lines and HepG2 cell lines
Received 20 November 2014
Received in revised form 11 February 2015
Accepted 17 March 2015
Available online 13 April 2015
(IC50 < 1
mmol/L). We supposed that NO-releasing amount of these derivatives which can be detected by
Griess method may contribute more to their antitumor activity. As a result, furoxan-based derivatives
released larger amount of NO than that of nitrate-based derivatives, which partially explained the higher
anti-tumor activity of the former.
Keywords:
Betulinic acid (BA)
Derivatives
ß 2015 Chinese Chemical Society and Institute of Materia Medica, Chinese Academy of Medical Sciences.
Published by Elsevier B.V. All rights reserved.
NO-releasing
Anti-tumor
NO donors
1. Introduction
NO donors to tissue targeting compounds could achieve organ-
delivery effect. In practical application for anticancer research, it is
Nitric oxide (NO) is a multifunctional molecular involved in a
variety of physiological and pathological processes. Generated by
nitric oxide synthase (NOS) from oxidation of L-arginine, NO binds
more feasible to generate novel NO-drug hybrids by linking various
NO donors to a parent compound (with anti-tumor activity) to
display the synergistic anti-tumor activity.
to its primary receptor, the soluble guanylylcyclase, leading to the
synthesis of the signal transducer cGMP [1,2]. Also, NO could be
produced from nitrogen oxides such as nitrite and nitrate, which
can serve as storage pools for NO when enzymatic activity of NOS is
suppressed [3]. Besides the wide implications of NO derivatives in
the treatment of vascular disorders [4], NO level or NOS activity
was observed to be correlated with clinical tumorigenesis [5–8].
Particularly, cell survival signaling is significantly affected by the
level of NO. Generally, NO is considered to promote tumor
angiogenesis at low concentration, however, it contributes to
apoptosis in tumor cells at high concentration [9–11].
Given the fact of the high-active property of NO, NO donors,
including organic nitrates, furoxans, metal-NO complexes, S-
nitrosothiols, sydnonimines, diazeniumdiolates (NONOates), and
NO-drug hybrids, with the controllable NO-releasing property are
attractive substitutes for NO [12]. More specifically, conjugation of
Betulinic acid (BA) is a natural pentacyclic triterpene with anti-
tumor [13] and anti-HIV activities [14,15], and so on. It was
reported that BA exhibited selective toxicity to varieties of tumor
cells but not normal tissues, which can be an ideal lead compound
for anticancer treatment [16]. In the present study, based on the
principle of pro-drug, we designed a series of novel NO-BA hybrids
which 3-hydroxyl group and 28-carboxyl group of BA were chosen
to be coupled with NO donors, nitrate and furoxan, respectively.
Considering that increasing the electron density in A-ring of BA can
improve its anti-tumor activity, therefore, we selected an oxime
group in C-3 position of BA to be a parent compound, along with 3-
O-derivatives. In addition to investigating the effect of different
length and structure of the linker which attaches BA and NO donor,
we also considered the fact that tumor cells display the character of
‘‘addicted nitrogen’’ and increase the transfer rate of amino acids,
as a result, we supposed that introducing amino acids into the
target compounds may enhance their selectivity to tumor cells.
Consequently, we introduce amino acids into the linker of BA and
furoxans.
*
Corresponding authors.
Totally, 13 NO-BA hybrids were successfully synthesized, with
their structures characterized by IR, 1H NMR and MS. The in vitro
anti-tumor activities were determined in mouse melanoma B16
(L. Chen).
1
These authors contributed equally to this work.
1001-8417/ß 2015 Chinese Chemical Society and Institute of Materia Medica, Chinese Academy of Medical Sciences. Published by Elsevier B.V. All rights reserved.