J . Med. Chem. 1994,37, 3812-3818
3812
Peptide-Linked 1,3-Dialkyl-3-acyltriazenes:Gastrin Receptor Directed Antineoplastic Alkylating Agents Brigitte F. Schmidt, Lidia Hernandez, Carol Rouzer, Grzegorz Czenvinski, Gwendolyn Chmurny,? and Christopher J. Michejda* Molecular Aspects of Drug Design Section, MSL, ABL-Basic Research Program, NCI-Frederick Cancer Research and Development Center, Frederick, Maryland 21 702 Received August 23, 1993@
The gastrin receptor is expressed in various human cancers, such as the adenocarcinoma of the colon. The peptide hormone gastrin and the C-terminal peptides derived from it act as growth factors for these cancers. The hypothesis for the present work was to use the gastrin receptor as a target for appropriately constructed cytotoxic agents. We developed methods to link tetragastrin and pentagastrin by their N-termini to cytotoxic l-(2-chloroethyl)-3-benzyl3-succinoyltriazene. These compounds, CBS-4 and CBS-5, respectively, whose complete structures were determined by multinuclear NMR and mass spectrometry, competed effectively with gastrin in an assay using either guinea pig stomach fundus or the rat acinar tumor cell line AR42J as the source of the receptor. CBS-5 was cytotoxic to AR42J cells but was not toxic to A549 human lung cancer cells, which do not express the receptor.
Introduction skin peptide, caerulein, are members of a family of gastrointestinal peptides, which share a common carColon cancer has one of the highest incidence rates boxyl terminal pentapeptide amide and exert their for all cancers in Western countries, especially in the effects on a particular target tissue by interacting with U.S.l It has been a very difficult cancer to treat by the same class of receptors.'" Structure-activity studchemotherapeutic methods, and no clearly effective ies with varying peptide sequences have been perdrugs for adenocarcinoma of the colon are available. formed.lla-d The results indicate that the smallest Several reports have been published discussing the role peptides which exhibit GR binding affinity are the of gastrointestinal hormones in the etiology and progtetragastrin and pentagastrin amide. Thus, the GRnosis of gastrointestinal carcinomas.2a-d It was shown binding ability of these small peptides could be used, that normal human gastric and colonic mucosa and in principle, t o target cytotoxic agents attached t o the adenocarcinomas of the human stomach and colon N-terminus of the peptide. contain specific gastrin-binding r e ~ e p t o r s . ~In~a' ~cliniWe focused our attention on 1,3-dialkyltriazenes as cal study: 38 of 67 patients suffering from primary the cytotoxic moiety. Triazenes in general show mutacolon cancers exhibited significant levels of the gastrin geniciza,b and c a r c i n ~ g e n i c properties. l~~~~ Antitumor binding receptor. Gastrin has been reported to promote activity of various triazenes has also been demthe growth of colonic tumors in vivo5 and in some colon o n ~ t r a t e d .1,3-Dialkyl~ ~ ~ ~ ~ and 1,3,3-trialkyltriazenes tumor cell lines.6a-c Further evidence for its function are very sensitive to proteolytic decomposition and as a growth factor is the in vitro antiproliferative effect hydrolyze under physiological conditions with half-lives of gastrin antagonists, such as proglumide and benzomeasured in ~ e c 0 n d s . l However, ~~ their stability in tript, on colon carcinoma cells.7arb buffer was dramatically improved by substituting 1,3Other tumors arising from hormone-responsive tisdialkyltriazenes with acyl groups;15half-life times in the sues, notably breast cancer, have been treated successrange of 2-1000 min were observed, depending on the fully by endocrine-related procedures,8a,b when the acyl group. Some of these acyl triazenes have been tumor had been shown to have specific receptors for the found to possess significant chemotherapeutic prophormone(s) that stimulate growth of the tissue. e r t i e ~ . lFor ~ ~the design of a carrier-linked 1,3-dialkylOne of the major problems with chemotherapeutic triazene conjugate it was therefore appropriate to use drugs in general are their severe side effects due to an acyl-functionalized linker between the peptide and unspecific interactions with naturally highly proliferathe triazene, which would yield a drug with a reasonable tive tissue. Some attempts have been made t o enhance stability under physiological conditions. This paper the specificity of drugs by using hormones or antihordiscusses our attempts to prepare peptide-linked acylmones as carriers of cytotoxic agents to target specific which would exhibit strong binding to GR. receptors which may be present in tumor t i s ~ u e . ~ ~ -triazenes ~ These studies were largely focused on steroid receptors, Results and Discussion such as estrogen or progesterone receptor. We chose to examine the potential of the gastrin receptor (GR) We chose tetragastrin (Trp-Met-Asp-Phe-NHz)and as a target for chemotherapeutic drugs in the treatment P-alanine-modified pentagastrin (P-Ala-Trp-Met-Aspof gastrointestinal tumors. Phe-NHz) for our initial studies in targeting the triGastrin, cholecystokinin (CCK), and the amphibian azene. Since the crucial part for the recognition of gastrointestinal peptides by the receptor is the carboxyl + Current address: Chemical Synthesis and Analysis Laboratory, terminal sequence Trp-Met-Asp-Phe-amide,there is a Program Resources, Inc./DYN Corp., NCI-Frederick Cancer Research logical requirement to attach these peptides to the and Development Center, Frederick, MD 21702. Abstract published in Advance ACS Abstracts, September 1,1994. cytotoxic moiety by their N-terminal amino function. We @
This article not subject to US.Copyright. Published 1994 by the American Chemical Society
Journal of Medicinal Chemistry, 1994, Vol. 37, No. 22 3813
Peptide-Linked 1,3-Dialkyl-3-acyltriazenes
Scheme 1
Scheme 2 1
0
I
R
I1 O
L
"I
O
J
2
1
Trp-Met-Asp-PhcNH,
II
CI -N=N-N:~
