Atetrahydroisoquinoline (THIQ) core is able tomimic theAand B rings of 2-methoxyestradiol
(2ME2), an endogenous estrogen metabolite that demonstrates promising anticancer properties primarily
by disrupting microtubule dynamic instability parameters, but has very poor pharmaceutical
properties that can be improved by sulfamoylation. The non-steroidal THIQ-based microtubule disruptor
(STX3451), with enhanced pharmacokinetic and pharmacodynamic profiles, was explored for the
first time in radiation biology. We investigated whether 24 h pre-treatment with STX3451 could
pre-sensitize MCF-7 and MDA-MB-231 breast cancer cells to radiation. This regimen showed a
clear increase in cytotoxicity compared to the individual modalities, results that were contiguous
in spectrophotometric analysis, flow cytometric quantification of apoptosis induction, clonogenic
studies and microscopy techniques. Drug pre-treatment increased radiation-induced DNA damage,
with statistically more double-strand (ds) DNA breaks demonstrated. The latter could be due to
the induction of a radiation-sensitive metaphase block or the increased levels of reactive oxygen
species, both evident after compound exposure. STX3451 pre-exposure may also delay DNA repair
mechanisms, as the DNA damage response element ataxia telangiectasia mutated (ATM) was depressed.
These in vitro findings may translate into in vivo models, with the ultimate aim of reducing
both radiation and drug doses for maximal clinical effect with minimal adverse effects.
The compound STX3451 is not commercially available.
SUPPLEMENTARY MATERIAL : TABLE S1: Data analysis comparing flow cytometric quantification of individual cell cycle phases across 24-h and 48-h timelines. TABLE S2: Data analysis of flow cytometric quantification of the cell cycle distribution in MCF-7 cells exposed to STX3451 and radiation. TABLE S3: Statistical analysis of cell cycle distribution in MCF-7 cells exposed to STX3451 and radiation. TABLE S4: Data analysis comparing flow cytometric quantification of individual cell cycle phases across 24-h and 48-h timelines in MDA-MB-231 cells. TABLE S5: Statistical analysis of cell cycle progression in MDA-MB-231 cells exposed to STX3451 and radiation. TABLE S6: Statistical analysis of cell cycle distribution in MDA-MB-231 cells exposed to STX3451 and radiation. TABLE S7: Annexin-V analysis of MCF-7 cells 48-h. TABLE S8: Annexin-V statistical analysis of MDA-MB-231 48-h. TABLE S9: Colony formation in MCF-7 cells. TABLE S10: Colony formation in MDA-MB-231 cells. TABLE S11: The total number of Mn in MCF-7 cells that were terminated 2- and 24-h after radiation. TABLE S12: The total number of Mn in MDA-MB-231 cells terminated 2- and 24-h after radiation. TABLE S13: Number of Mn per cell in MCF-7 cells terminated 2-h after radiation. TABLE S14: Number of Mn per cell in MCF-7 cells terminated 24-h after radiation. TABLE S15: Number of Mn per cell in MDA-MB-231 cells terminated 2-h after radiation. TABLE S16: The number of Mn per cell in MDA-MB-231 cells that were terminated 24-h after radiation. TABLE S17: Superoxide detection in MCF-7 cells treated with the various modalities. TABLE S18: Superoxide detection in pre-sensitized MDA-MB-231 cells. TABLE S19: Statistical analysis of ATM expression in combination treated MCF-7 and MDA-MB-231 cells 2- and 24-h post-radiation. TABLE S20: Nontumored animal toxicity assay; VIDEO S1: not applicable.