APS8 Delays Tumor Growth in Mice by Inducing Apoptosis of Lung Adenocarcinoma Cells Expressing High Number of α7 Nicotinic Receptors

Abstract

The alkylpyridinium polymer APS8, a potent antagonist of α7 nicotinic acetylcholine receptors (nAChRs), selectively induces apoptosis in non-small cell lung cancer cells but not in normal lung fibroblasts. To explore the potential therapeutic value of APS8 for at least certain types of lung cancer, we determined its systemic and organ-specific toxicity in mice, evaluated its antitumor activity against adenocarcinoma xenograft models, and examined the in-vitro mechanisms of APS8 in terms of apoptosis, cytotoxicity, and viability. We also measured Ca2+ influx into cells, and evaluated the effects of APS8 on Ca2+ uptake while siRNA silencing of the gene for α7 nAChRs, CHRNA7. APS8 was not toxic to mice up to 5 mg/kg i.v., and no significant histological changes were observed in mice that survived APS8 treatment. Repetitive intratumoral injections of APS8 (4 mg/kg) significantly delayed growth of A549 cell tumors, and generally prevented regrowth of tumors, but were less effective in reducing growth of HT29 cell tumors. APS8 impaired the viability of A549 cells in a dose-dependent manner and induced apoptosis at micro molar concentrations. Nano molar APS8 caused minor cytotoxic effects, while cell lysis occurred at APS8 >3 µM. Furthermore, Ca2+ uptake was significantly reduced in APS8-treated A549 cells. Observed differences in response to APS8 can be attributed to the number of α7 nAChRs expressed in these cells, with those with more AChRs (i.e., A549 cells) being more sensitive to nAChR antagonists like APS8. We conclude that α7 nAChR antagonists like APS8 have potential to be used as therapeutics for tumors expressing large numbers of α7 nAChRs.

α-Conotoxins and α-Cobratoxin Promote, while Lipoxygenase and Cyclooxygenase Inhibitors Suppress the Proliferation of Glioma C6 Cells

“…Thus, epidemiological studies show that the agonists of these receptors, nicotine and its derivatives contained in tobacco smoke, contribute to the onset and development of tumors of the lung [ 1 ], breast [ 3 , 63 ], pancreas [ 64 , 65 ], head and neck [ 66 ], accelerating proliferation and suppressing apoptosis. On the contrary, blockade of nAChRs slows tumor growth in experimental models of lung [ 21 , 22 ] and breast [ 18 , 20 ] cancer. The effect of nicotine is realized with the participation of nAChRs containing α7 [ 1 , 67 ], α9 [ 1 , 15 , 68 ] and α5 [ 1 , 2 , 16 ] subunits.…”

“…The role of nAChRs in non-neuronal cells is a subject of extensive studies, but it is already clear that these receptors are involved in the regulation of proliferation and migration of cancer cells [ 13 , 14 ], promote tumor formation [ 15 ] and enhance the resistance of tumor cells to apoptosis [ 14 , 16 , 17 ]. In addition, a number of experimental studies have shown a slowdown in tumor growth in vivo under the action of nAChR blockers such as α-conotoxins [ 18 , 19 , 20 ], α-cobrotoxin [ 21 ] and alkylpyridinium polymer APS8 [ 22 ]. However, the cytotoxic properties of nicotine, agonist of the most of nAChRs, against both normal [ 23 , 24 , 25 , 26 ] and tumor [ 27 ] cells are known.…”

Cyclic Imine Pinnatoxin G is Cytotoxic to Cancer Cell Lines via Nicotinic Acetylcholine Receptor-Driven Classical Apoptosis

“…Ca 2+ channel blockers, such as amlodipine, induce G1 phase accumulation by alleviating Ca 2+ entry into A431 epidermoid cancer cells . Studies in lung and breast cancer cells, as well as chromaffin cells, have shown that activation of α7 subtype nAChRs results in an influx of Ca 2+ and activation of protein kinase C, followed by ERK and c-Myc, both increasing proliferation and inhibiting apoptosis and that antagonists can have the opposing effects. − A specific α7 nAChR inhibitor potently elicited cell death in lung cancer cells, and this was linked to upregulation of the caspases 3, 8, and 9 . There is also evidence that, in the brain, nAChRs are linked to neuroprotection, preventing cell death.…”

Targeting Alpha7 Nicotinic Acetylcholine Receptors in Lung Cancer: Insights, Challenges, and Therapeutic Strategies

“…APS8 can also block α4β2 nAChR, although its affinity for α7 nAChR is high. 69 Together with, MD-354 and compound 12, its N-methyl analogue containing a novel phenyl guanidine scaffold, were reported as noncompetitive α7 nAChR antagonists. 107,108 In the rat brain, compound 12 can compete [ 125 I]-bungarotoxin in the cerebral cortex, hippocampus, and hypothalamic mammillary nuclei, that express α7 nAChR.…”