Effects of ketamine, s-ketamine, and MK 801 on proliferation, apoptosis, and necrosis in pancreatic cancer cells


Three types of ionotropic glutamate receptors are known that are termed according
to their prototypic receptor-agonist N-methyl-D-aspartate (NMDA), 2-amino-3-(3-hydroxy-5-methyl-isoxazol-4-yl)
propanoic acid (AMPA), and kainate (KA) 19]. N-methyl-D-aspartate (NMDA), which belongs to the family of ionotropic glutamate
receptors, is vital for the transmission of stimulating signals between nerve cells
20]. Physiologically, NMDA plays a major role in processes of synaptic plasticity and
memory formation 21]. NMDA is also important during various-neurolopathological conditions, such as Alzheimer
disease, Parkinson disease, multiple sclerosis, epilepsy, or depression 22]. For many years, NMDA receptor expression was associated with the central nervous
system, but recent trials have shown that functional NMDA receptors may also be expressed
in tumors23]. The receptor type has already been successfully proven in various tumor cell lines,
for instance, in neuronal tumors (astrocytoma, glioma, and neuroblastoma), rhabdomyosarcoma,
medulloblastoma, thyroid carcinoma, lung carcinoma, colon carcinoma, and mamma carcinoma
as well as in T-cell chronic lymphocytic leukemia, multiple myeloma 23], and carcinoma of the larynx 25].

In the present study, NMDA receptor type R2a expression could be detected in the pancreatic
carcinoma cells PaTu8988t and Panc-1. However, the influence of the NMDA receptor
on the oncogenic behavior of cancer cells has not yet been sufficiently investigated.
Kalariti et al. assumed in 2005 that the NMDA receptor may be a critical factor in
tumor development, tumor growth, and the metastasis of tumor cells 26]. Furthermore, NMDA receptor expression in prostate carcinoma was increased in comparison
to healthy prostate tissue 27]. Watanabe et al. showed in 2008 that the NMDA receptor subunit R2a plays an important
role in regulating proliferation by accelerating the cell cycle in cell lines of gastric
cancer 28]. In other clinical studies, blocking of the NMDA receptor subunit R2a inhibited the
proliferation of cancer cells of lung carcinoma and esophagus carcinoma 29], 30].

The next step in our trial was therefore to investigate the impact of ketamine, s-ketamine,
and the noncompetitive NMDA receptor antagonist MK 801 on the proliferation, apoptosis,
and necrosis of pancreatic cancer cells.

In their study including 31 patients, Idyall et al. investigated the clinical effects
of intravenously injected ketamine and its pharmacokinetics. After the injection of
2 mg/kg of ketamine iv, plasma concentration was analyzed by means of gas–liquid chromatography.
The average maintenance dose was 41 ?g/kg/min, which corresponded to a plasma concentration
of 9.3 ?M 31].

As our aim was to investigate the direct effect of ketamine, s-ketamine and MK 801
on cancer cell lines, we used concentrations similar to clinically achievable plasma
concentrations (0,1 ?M – 1000 ?M).

We found that incubation with high-dose ketamine, s-ketamine, and MK 801 significantly
inhibited cell proliferation in all cell lines. Lee et al. described in 2009 that
administration of s-ketamine induced mitochondrial apoptosis in hepatocellular carcinoma
12]. In breast cancer cells, however, the anti-apoptotic protein BCL-2 was up-regulated,
and both cell invasion and the proliferation rate were increased 32]. In our study, all test substances also decreased the rate of apoptosis in pancreatic
cancer cells. The main effect of ketamine, s-ketamine, and MK 801 is based on the
noncompetitive blockade of the NMDA receptor complex. During this process, ketamine
binds to the phencyclidine (PCP) binding site inside the NMDA channel, inhibiting
the effectiveness of NMDA antagonists, such as glutamate, NMDA, or glycine 33].

Tumor progression including the proliferation and apoptosis of cells is regulated
by various signaling cascades. As a first messenger, calcium is of vital importance
in this respect 34]. NMDA receptor activation increases the intracellular calcium concentration and activates
Ca
2+
-dependent systolic guanylate cyclase 35]. Calcium influx into cell cytosol results in the calcium-dependent activation of
a secondary messenger, which may again activate proteins of various types???amongst
others transcription factors???that significantly influence the further behavior of
tumor cells 36].