Novel insights in folate receptors and transporters: implications for disease and treatment of immune diseases and cancer

Targeted cancer treatment using folate-conjugated sponge-like ZIF-8 nanoparticles: a review

ZIF-8 (zeolitic imidazolate framework-8) is a potential drug delivery system because of its unique properties, which include a large surface area, a large pore capacity, a large loading capacity, and outstanding stability under physiological conditions. ZIF-8 nanoparticles may be readily functionalized with targeting ligands for the identification and absorption of particular cancer cells, enhancing the efficacy of chemotherapeutic medicines and reducing adverse effects. ZIF-8 is also pH-responsive, allowing medication release in the acidic milieu of cancer cells. Because of its tunable structure, it can be easily functionalized to design cancer-specific targeted medicines. The delivery of ZIF-8 to cancer cells can be facilitated by folic acid-conjugation. Hence, it can bind to overexpressed folate receptors on the surface of cancer cells, which holds the promise of reducing unwanted deliveries. As a result of its importance in cancer treatment, the folate-conjugated ZIF-8 was the major focus of this review.

Folate in maternal rheumatoid arthritis-filial autism spectrum disorder continuum

Rheumatoid Arthritis (RA) is an inflammatory autoimmune disease that affects women three times more than men. Epidemiological studies found that the incidence of Autism Spectrum Disorder (ASD), a neurological and developmental disorder, in children born to mothers suffering from RA is higher compared with the control population. Considering that the pathogenesis of ASD could be traced back to pregnancy and in uterine conditions, and the evidence of reduced folate levels in the brain of ASD-affected children, we aimed to study the role of folate, as an important nutritional factor during pregnancy, in associating maternal RA to ASD development in the offspring. Folate balance during RA could be influenced twice, initially during the immune activation associated with disease onset, and later during the treatment with anti-folate drugs, with a potential consequence of folate deficiency. Maternal folate deficiency during pregnancy could increase homocysteine levels, oxidative stress, and global DNA hypomethylation, all known risk factors in ASD pathogenesis. These effects could be intensified by genetic polymorphisms in the folate system, which were also found as genetic risk factors for both RA and ASD. The available evidence suggests that folate level as an important factor during RA, pregnancy and ASD could have pathological and therapeutical significance and should be carefully monitored and investigated in the RA-pregnancy-ASD axis.

Glycosylphosphatidylinositol biosynthesis and remodeling are required for neural tube closure, heart development, and cranial neural crest cell survival

Glycosylphosphatidylinositol (GPI) anchors attach nearly 150 proteins to the cell membrane. Patients with pathogenic variants in GPI biosynthesis genes develop diverse phenotypes including seizures, dysmorphic facial features and cleft palate through an unknown mechanism. We identified a novel mouse mutant (cleft lip/palate, edema and exencephaly; Clpex) with a hypo-morphic mutation in Post-Glycophosphatidylinositol Attachment to Proteins-2 (Pgap2), a component of the GPI biosynthesis pathway. The Clpex mutation decreases surface GPI expression. Surprisingly, Pgap2 showed tissue-specific expression with enrichment in the brain and face. We found the Clpex phenotype is due to apoptosis of neural crest cells (NCCs) and the cranial neuroepithelium. We showed folinic acid supplementation in utero can partially rescue the cleft lip phenotype. Finally, we generated a novel mouse model of NCC-specific total GPI deficiency. These mutants developed median cleft lip and palate demonstrating a previously undocumented cell autonomous role for GPI biosynthesis in NCC development.

The folate receptor β as a macrophage-mediated imaging and therapeutic target in rheumatoid arthritis

Macrophages play a key role in the pathophysiology of rheumatoid arthritis (RA). Notably, positive correlations have been reported between synovial macrophage infiltration and disease activity as well as therapy outcome in RA patients. Hence, macrophages can serve as an important target for both imaging disease activity and drug delivery in RA. Folate receptor β (FRβ) is a glycosylphosphatidyl (GPI)-anchored plasma membrane protein being expressed on myeloid cells and activated macrophages. FRβ harbors a nanomolar binding affinity for folic acid allowing this receptor to be exploited for RA disease imaging (e.g., folate-conjugated PET tracers) and therapeutic targeting (e.g., folate antagonists and folate-conjugated drugs). This review provides an overview of these emerging applications in RA by summarizing and discussing properties of FRβ, expression of FRβ in relation to macrophage polarization, FRβ-targeted in vivo imaging modalities, and FRβ-directed drug targeting.

Randomized phase 2 study of gemcitabine and cisplatin with or without vitamin supplementation in patients with advanced esophagogastric cancer

Purpose

Preclinical research and prior clinical observations demonstrated reduced toxicity and suggested enhanced efficacy of cisplatin due to folic acid and vitamin B12 suppletion. In this randomized phase 2 trial, we evaluated the addition of folic acid and vitamin B12 to first-line palliative cisplatin and gemcitabine in patients with advanced esophagogastric cancer (AEGC).

Methods

Patients with AEGC were randomized to gemcitabine 1250 mg/m² (i.v. days 1, 8) and cisplatin 80 mg/m² (i.v. day 1) q 3 weeks with or without folic acid (450 µg/day p.o.) and vitamin B12 (1000 µg i.m. q 9 weeks). The primary endpoint was response rate (RR). Secondary endpoints included overall survival (OS), time to progression (TTP), toxicity, and exploratory biomarker analyses. Cisplatin sensitivity and intracellular platinum levels were determined in adenocarcinoma cell lines cultured under high and low folate conditions in vitro.

Results

Adenocarcinoma cells cultured in medium with high folate levels were more sensitive to cisplatin and this was associated with increased intracellular platinum levels. In the randomized phase 2 clinical trial, which ran from October 2004 to September 2013, treatment was initiated in 78 of 82 randomized pts, 39 in each study arm. The RR was similar; 42.1% for supplemented patients vs. 32.4% for unsupplemented patients; p = 0.4. Median OS and TTP were 10.0 and 5.9 months for supplemented vs. 7.7 and 5.4 months for unsupplemented patients (OS, p = 0.9; TTP, p = 0.9). Plasma homocysteine was lower in the supplemented group [n = 20, 6.9 ± 1.6 (mean ± standard error of mean, SEM) µM; vs. 12.5 ± 4.0 µM; p < 0.001]. There was no significant difference in the C_max of gemcitabine and cisplatin in the two treatment groups.

Conclusion

Folic acid and vitamin B12 supplementation do not improve the RR, PFS, or OS of cisplatin and gemcitabine in patients with AEGC.

In-vivo monitoring of anti-folate therapy in arthritic rats using [18F]fluoro-PEG-folate and positron emission tomography

Background

Folate receptor β (FRβ) is involved in facilitating cellular uptake of folates and anti-folates (such as methotrexate (MTX)). In rheumatoid arthritis, FRβ is expressed on synovial macrophages and recently has been explored as a biomarker for imaging in arthritic rats using the folate-based positron emission tomography (PET) tracer [¹⁸F]fluoro-PEG-folate. The purpose of this study was to examine whether this folate tracer can also be used to monitor therapeutic efficacy of MTX in arthritic rats.

Methods

Arthritic rats received either no treatment or MTX therapy (1 mg/kg, either 2× or 4×). Healthy rats did not receive any arthritic induction or therapy. [¹⁸F]fluoro-PEG-folate PET-CT scans (60 min) were performed before and after MTX therapy. Following PET, the ex-vivo tissue distribution of radioactivity was determined in excised knees and multiple tissues. Synovial macrophage infiltration in knee sections was quantified by immunohistochemistry using ED1 and ED2 antibodies.

Results

PET scans clearly visualized increased uptake of [¹⁸F]fluoro-PEG-folate in arthritic knees compared with contralateral knees. Significantly lower standard uptake values (1.5-fold, p < 0.01) were observed in arthritic knees of both MTX-treated groups after therapy, approximating the levels seen in healthy rats. Consistently, ex-vivo tissue distribution demonstrated a 2–4-fold lower tracer uptake in the arthritic knee of 2× and 4× MTX-treated rats, respectively, compared with control rats. These results were corroborated with significantly reduced (2–4-fold, p < 0.01) ED1-positive and ED2-positive synovial macrophages in arthritic knees of the MTX-treated rats compared with those of the control rats.

Conclusion

This study in arthritic rats underscores the potential and usefulness of [¹⁸F]fluoro-PEG-folate PET as a therapeutic monitoring tool of MTX therapy and potentially other anti-folate treatment of arthritis.

Mirvetuximab Soravtansine (IMGN853), a Folate Receptor Alpha-Targeting Antibody-Drug Conjugate, Potentiates the Activity of Standard of Care Therapeutics in Ovarian Cancer Models

Elevated folate receptor alpha (FRα) expression is characteristic of epithelial ovarian cancer (EOC), thus establishing this receptor as a candidate target for the development of novel therapeutics to treat this disease. Mirvetuximab soravtansine (IMGN853) is an antibody-drug conjugate (ADC) that targets FRα for tumor-directed delivery of the maytansinoid DM4, a potent agent that induces mitotic arrest by suppressing microtubule dynamics. Here, combinations of IMGN853 with approved therapeutics were evaluated in preclinical models of EOC. Combinations of IMGN853 with carboplatin or doxorubicin resulted in synergistic antiproliferative effects in the IGROV-1 ovarian cancer cell line in vitro. IMGN853 potentiated the cytotoxic activity of carboplatin via growth arrest and augmented DNA damage; cell cycle perturbations were also observed in cells treated with the IMGN853/doxorubicin combination. These benefits translated into improved antitumor activity in patient-derived xenograft models in vivo in both the platinum-sensitive (IMGN853/carboplatin) and platinum-resistant (IMGN853/pegylated liposomal doxorubicin) settings. IMGN853 co-treatment also improved the in vivo efficacy of bevacizumab in platinum-resistant EOC models, with combination regimens causing significant regressions and complete responses in the majority of tumor-bearing mice. Histological analysis of OV-90 ovarian xenograft tumors revealed that concurrent administration of IMGN853 and bevacizumab caused rapid disruption of tumor microvasculature and extensive necrosis, underscoring the superior bioactivity profile of the combination regimen. Overall, these demonstrations of combinatorial benefit conferred by the addition of the first FRα-targeting ADC to established therapies provide a compelling framework for the potential application of IMGN853 in the treatment of patients with advanced ovarian cancer.