Impact of High and Low Folate Diets on Tissue Folate Receptor Levels and Antitumor Responses Toward Folate-Drug Conjugates

Abstract

Herein, we present a detailed analysis on the effects of feeding laboratory mice both high and low folic acid (folate)-containing diets as related to associated changes in serum and red blood cell (RBC) folate levels, tissue-derived folate receptor levels, and the ability of folate-drug conjugates to bind and effectuate activity against folate receptor (FR)-positive tumor xenografts. Our data show that serum and RBC folate concentrations sharply drop immediately after mice are switched to low folate diets; however, both parameters reach steady-state, "humanlike" levels after 6 weeks. Interestingly, tissue-related folate binding capacities were also lowered during the dietary modulation period, whereas the net uptake of a radiolabeled folate conjugate was simultaneously increased 2.6-and 5-fold in FR-positive kidney and tumor tissue, respectively. Finally, the performances of several clinically and preclinically relevant folate-drug conjugates were evaluated against tumors in mice that were fed high or low folate diets. Except when administered at a dose level 6-fold less than that required to saturate endogenous FRs, no significant loss of antitumor activity was observed. From these findings, we conclude that lowering the dietary intake of folates in mice has little impact on the biological activity of repetitively dosed folate-targeted agents but that low folate diet regimens will reduce serum and RBC folate levels down to levels that more closely approximate the normal human ranges.

Pharmacokinetics, Biodistribution, and Toxicity of Folic Acid-Coated Antiretroviral Nanoformulations

“…BALB/c mice have serum folate concentrations of approximately 250 nM, compared to 25 nM in humans (23). Therefore, mice were kept on a folate-deficient diet for 2 weeks prior to any treatments to bring down their serum folate to concentrations comparable to those in humans.…”

“…It was reported previously that high serum folate concentra-tions, like those found in the serum of laboratory rodents, could potentially block the binding of FA-drug conjugates to the folate receptors in tissues (22). Because of that, a mouse model treated with a folate-deficient diet was developed for the purpose of lowering endogenous mouse serum folate concentrations toward the normal human range (23). Therefore, in this study mice on both a folate-deficient diet and a normal diet were used.…”

Maternal folate deficiency and metabolic dysfunction in offspring

“…There were two distinct phases in erythrocyte folate kinetics; an initial phase lasting approximately 2 weeks during which erythrocyte folate concentration remained largely unchanged followed by exponential 'decay' in erythrocyte folate concentration towards a new equilibrium after 4-5 weeks (25) . For comparison, Leamon et al reported that erythrocyte folate reached a new (lower) plateau in BALB/c mice approximately 6 week after transfer to a low folate diet (27) . Further studies showed that a milder nutritional insult (feeding 0·4 mg folic acid/kg diet) reduced maternal and offspring erythrocyte folate concentrations (measured at weaning) by about 50 % (25) .…”

Targeting Folate Receptors to Treat Invasive Urinary Bladder Cancer

“…2B; ref. 26). KB cell (American Type Culture Collection; ATCC) integrity was confirmed (Genetica DNA Labs, Cincinnati, Ohio) with cells being 100% identical to reference cells from the ATCC.…”

“…The in vivo activity and toxicity of EC0905 were determined in nu/nu mice (Balb/c-derived; Charles River, Wilmington, MA) fed a folate-free diet (Harlan diet #TD00434, Harlan Teklad, Madison, WI) to achieve serum folate concentrations similar to those in humans (26,27). EC0905 (2 mmol/kg) or vehicle control was administered intravenously 3 times per week for 2 weeks to mice with FR-positive KB xenografts, and tumor size and animal performance were monitored.…”