A novel indolocarbazole, ICP-1, abrogates DNA damage-induced cell cycle arrest and enhances cytotoxicity: similarities and differences to the cell cycle checkpoint abrogator UCN-01.
DNA damaging agents such as cisplatin arrest cell cycle progression at either G1, S, or G2 phase, although the G1 arrest is only seen in cells expressing the wild-type p53 tumor suppressor protein. We have reported that 7-hydroxystaurosporine (UCN-01) overcomes S and G2 phase arrest and enhances the cytotoxicity of cisplatin. Abrogation of arrest appears to be selective for cells defective in p53 and therefore provides a potential, tumor-targeted therapy. Unfortunately, UCN-01 binds avidly to human plasma proteins, limiting access to the tumor. A screen of related indolocarbazoles identified analogues with both beneficial and undesirable properties. This led to a synthetic program to develop a novel analogue rationally designed to overcome the obstacles observed with the other analogues. We report the synthesis and analysis of a novel analogue, ICP-1. This analogue abrogated S and G2 phase arrest and enhanced cytotoxicity induced by cisplatin only in p53 defective cells. ICP-1 also abrogated arrest and enhanced cell killing induced by the topoisomerase I inhibitor SN38. Analysis of proteins that regulate cell cycle arrest suggest both drugs inhibit checkpoint kinases Chk1 and/or Chk2. In contrast to UCN-01, checkpoint abrogation by ICP-1 was only slightly inhibited by human plasma. UCN-01 and ICP-1 differed significantly in other regards. UCN-01 potently enhanced the activity of 1-beta-D-arabinofuranosylcytosine in both p53 wild-type and mutant cells, whereas ICP-1 was inactive in this combination. This property of UCN-01 was independent of its ability to inhibit protein kinase C because more specific inhibitors of protein kinase C failed to enhance cell killing induced by 1-beta-D-arabinofuranosylcytosine. High concentrations of UCN-01 also inhibit C-TAK1 that results in S phase-arrested cells directly entering mitosis, but this property was not observed with ICP-1. Hence, ICP-1 appears to be a more selective inhibitor of the S and G2 cell cycle checkpoint than previously studied analogues and is worthy of study in preclinical tumor models.
Eastman
Alan
A
Department of Pharmacology, Dartmouth Medical School, Hanover, NH 03755, USA. alan.eastman@dartmouth.edu
Kohn
Ethan A
EA
Brown
Mary Kay
MK
Rathman
Joerg
J
Livingstone
Mark
M
Blank
David H
DH
Gribble
Gordon W
GW
D000470:Alkaloids / Q000494:pharmacology*; D000970:Antineoplastic Agents / Q000494:pharmacology*; D001943:Breast Neoplasms / Q000188:drug therapy; D002227:Carbazoles; D002453:Cell Cycle / Q000187:drug effects*; D002455:Cell Division / Q000187:drug effects; D002945:Cisplatin / Q000494:pharmacology*; D004247:DNA / Q000378:metabolism; D004249:DNA Damage / Q000187:drug effects*; D004305:Dose-Response Relationship, Drug; D005260:Female; D005434:Flow Cytometry; D016195:G2 Phase / Q000187:drug effects; D016158:Genes, p53; D006801:Humans; D015151:Immunoblotting; D007211:Indoles; D008956:Models, Chemical; D009154:Mutation; D011485:Protein Binding; D016196:S Phase / Q000187:drug effects; D019311:Staurosporine / Q000031:analogs & derivatives* / Q000737:chemistry / Q000494:pharmacology*; D013997:Time Factors; D014407:Tumor Cells, Cultured
D000470:Alkaloids; D000970:Antineoplastic Agents; D002227:Carbazoles; C473778:ICP-1 compound; D007211:Indoles; C054852:7-hydroxystaurosporine; D004247:DNA; D019311:Staurosporine; D002945:Cisplatin