Novel microtubule-targeting agents, pyrrolo-1,5-benzoxazepines, induce apoptosis in multi-drug-resistant cancer cells.
OBJECTIVE
The development of multi-drug resistance (MDR) due to the expression of members of the ATP binding cassette (ABC) transporter family is a major obstacle in cancer treatment. The broad range of substrate specificities associated with these transporters leads to the efflux of many anti-cancer drugs from tumour cells. Therefore, the development of new chemotherapeutic agents that are not substrates of these transporters is important. We have recently demonstrated that some members of a novel series of pyrrolo-1,5-benzoxazepine (PBOX) compounds are microtubule-depolymerising agents that potently induce apoptosis in several cancer cell lines and impair growth of mouse breast tumours. The aim of this current study was to establish whether PBOXs were capable of inducing apoptosis in cancer cells expressing either P-glycoprotein or breast cancer resistance protein (BCRP), two of the main ABC transporters associated with MDR.


METHODS
We performed in vitro studies to assess the effects of PBOXs on cell proliferation, cell cycle and apoptosis in human cancer cell lines and their drug-resistant substrains expressing either P-glycoprotein or BCRP. In addition, we performed a preliminary molecular docking study to examine interactions between PBOXs and P-glycoprotein.


RESULTS
We established that three representative PBOXs, PBOX-6, -15 and -16 were capable of inducing apoptosis in drug-resistant HL60-MDR1 cells (expressing P-glycoprotein) and HL60-ABCG2 cells (expressing BCRP) with similar potencies as in parental human promyelocytic leukaemia HL60 cells. Likewise, resistance to PBOX-6 and -16 was not evident in P-glycoprotein-expressing A2780-ADR cells in comparison with parent human ovarian carcinoma A2780 cells. Finally, we deduced by molecular docking that PBOX-6 is not likely to form favourable interactions with the substrate binding site of P-glycoprotein.


CONCLUSIONS
Our results suggest that pro-apoptotic PBOX compounds may be potential candidates for the treatment of P-glycoprotein- or BCRP-associated MDR cancers.
Nathwani
Seema-Maria
SM
School of Biochemistry and Immunology, Trinity College, Dublin 2, Ireland. nathwans@tcd.ie
Butler
Stephen
S
Fayne
Darren
D
McGovern
Naomi N
NN
Sarkadi
Balazs
B
Meegan
Mary J
MJ
Lloyd
David G
DG
Campiani
Giuseppe
G
Lawler
Mark
M
Williams
D Clive
DC
Zisterer
Daniela M
DM
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000378:metabolism; D000070997:ATP Binding Cassette Transporter, Subfamily G, Member 2; D018528:ATP-Binding Cassette Transporters / Q000378:metabolism; D000970:Antineoplastic Agents / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects*; D001552:Benzazepines / Q000494:pharmacology; D002219:Carbamates / Q000494:pharmacology; D002453:Cell Cycle / Q000187:drug effects; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D018432:Drug Resistance, Multiple; D019008:Drug Resistance, Neoplasm; D018922:HL-60 Cells; D006801:Humans; D008870:Microtubules / Q000187:drug effects / Q000378:metabolism; D009363:Neoplasm Proteins / Q000378:metabolism; D009369:Neoplasms / Q000188:drug therapy / Q000473:pathology; D010077:Oxazepines / Q000494:pharmacology*; D011758:Pyrroles / Q000494:pharmacology*; D050257:Tubulin Modulators / Q000494:pharmacology*
C550734:4-((N,N-dimethylcarbamoyl)oxy)-5-(naphth-1-yl)naphtho(2,3-b)pyrrolo(1,2-d)(1,4)oxazepine; C514160:4-acetoxy-5-(1-(naphthyl))naphtho(2,3-b)pyrrolo(2,1-d)(1,4)oxazepine; C116614:ABCG2 protein, human; D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000070997:ATP Binding Cassette Transporter, Subfamily G, Member 2; D018528:ATP-Binding Cassette Transporters; D000970:Antineoplastic Agents; D001552:Benzazepines; D002219:Carbamates; D009363:Neoplasm Proteins; D010077:Oxazepines; D011758:Pyrroles; D050257:Tubulin Modulators; C418868:PBOX-6