Reduction of metastasis using a non-volatile buffer

Abstract

The tumor microenvironment is acidic as a consequence of upregulated glycolysis and poor perfusion and this acidity, in turn, promotes invasion and metastasis. We have recently demonstrated that chronic consumption of sodium bicarbonate increased tumor pH and reduced spontaneous and experimental metastases. This occurred without affecting systemic pH, which was compensated. Additionally, these prior data did not rule out the possibility that bicarbonate was working though effects on carbonic anhydrase, and not as a buffer per se. Here, we present evidence that chronic ingestion of a non-volatile buffer, 2-imidazole-1-yl-3-ethoxycarbonylpropionic acid (IEPA) with a pKa of 6.9 also reduced metastasis in an experimental PC3M prostate cancer mouse model. Animals (n = 30) were injected with luciferase expressing PC3M prostate cancer cells either subcutaneously (s.c., n = 10) or intravenously (i.v., n = 20). Four days prior to inoculations, half of the animals for each experiment were provided drinking water containing 200 mM IEPA buffer. Animals were imaged weekly to follow metastasis, and these data showed that animals treated with IEPA had significantly fewer experimental lung metastasis compared to control groups (P < 0.04). Consistent with prior work, the pH of treated tumors was elevated compared to controls. IEPA is observable by in vivo magnetic resonance spectroscopy and this was used to measure the presence of IEPA in the bladder, confirming that it was orally available. The results of this study indicate that metastasis can be reduced by non-volatile buffers as well as bicarbonate and thus the effect appears to be due to pH buffering per se.

Hypoxia-induced carbonic anhydrase IX as a target for cancer therapy: From biology to clinical use

“…In particular, reduction of extracellular acidosis can increase the uptake and cytotoxic effects of weakly basic drugs, including doxorubicin. Interestingly, chronic ingestion of sodium bicarbonate solution was shown to enhance the capacity of doxorubicin to decrease the tumor size [166]. Specific inhibition of CA IX activity by indanesulfonamide enhanced the effect of tumor irradiation [79].…”

Molecular Connections between Cancer Cell Metabolism and the Tumor Microenvironment

“…These new developments may also be advantageous for imaging purposes and may be applicable to solid tumors, ischemia, stroke, and infection [220,221,222]. Furthermore, to reduce the effects of acidosis on drug activity under acidic conditions, systemic buffer therapy has been proven to be effective in alkalizing the tumor microenvironment [223,224,225]. In several reports oral administration of buffers such as lysine, sodium bicarbonate, or 2-imidazole-1-yl-3-ethoxycarbonylpropionic acid (IEPA) was used to systemically buffer mice in order to reduce tumor growth and metastasis [223,224,225].…”

“…Furthermore, to reduce the effects of acidosis on drug activity under acidic conditions, systemic buffer therapy has been proven to be effective in alkalizing the tumor microenvironment [223,224,225]. In several reports oral administration of buffers such as lysine, sodium bicarbonate, or 2-imidazole-1-yl-3-ethoxycarbonylpropionic acid (IEPA) was used to systemically buffer mice in order to reduce tumor growth and metastasis [223,224,225]. Using systemic buffers may increase the activity of certain drugs that are normally inactive in such acidic environments [216,219].…”

Buffer Therapy for Cancer

“…Previously we have shown that an amino acid, lysine, reduces metastasis in a prostate cancer model, which we hypothesized occurs through buffering of peri-tumoral pH [32]. Lysine has three pKas and can be protonated at the side chain amino group, backbone amino group and carboxyl group.…”

“…PC-3M cells were cultured as detailed previously [32]. In preparation for injection, PC-3M cells were trypsinized and washed once with sterile 1X PBS before being suspended at a concentration of 2.4 × 10 6 cells in 200 μL PBS.…”