Dihydrofolate reductase inhibitors are an important class of drugs, as evidenced by their use as antibacterial, antimalarial, antifungal, and anticancer agents. Progress in understanding the biochemical basis of mechanisms responsible for enzyme selectivity and antiproliferative effects has renewed the interest in antifolates for cancer chemotherapy and prompted the medicinal chemistry community to develop novel and selective human DHFR inhibitors, thus leading to a new generation of DHFR inhibitors. This work summarizes the mechanism of action, chemical, and anticancer profile of the DHFR inhibitors discovered in the last six years. New strategies in DHFR drug discovery are also provided, in order to thoroughly delineate the current landscape for medicinal chemists interested in furthering this study in the anticancer field.

Pancreatic ductal adenocarcinoma (PDAC) is an extremely aggressive tumor characterized by early invasiveness, rapid progression and resistance to treatment. For more than twenty years, gemcitabine has been the main therapy for PDAC both in the palliative and adjuvant setting. After the introduction of FOLFIRINOX as an upfront treatment for metastatic disease, gemcitabine is still commonly used in combination with nab-paclitaxel as an alternative first-line regimen, as well as a monotherapy in elderly patients unfit for combination chemotherapy. As a hydrophilic nucleoside analogue, gemcitabine requires nucleoside transporters to permeate the plasma membrane, and a major role in the uptake of this drug is played by human equilibrative nucleoside transporter 1 (hENT-1). Several studies have proposed hENT-1 as a biomarker for gemcitabine efficacy in PDAC. A recent comprehensive multimodal analysis of hENT-1 status evaluated its predictive role by both immunohistochemistry (with five different antibodies), and quantitative-PCR, supporting the use of the 10D7G2 antibody. High hENT-1 levels observed with this antibody were associated with prolonged disease-free status and overall-survival in patients receiving gemcitabine adjuvant chemotherapy. This commentary aims to critically discuss this analysis and lists molecular factors influencing hENT-1 expression. Improved knowledge on these factors should help the identification of subgroups of patients who may benefit from specific therapies and overcome the limitations of traditional biomarker studies.

Background/Aim: The prolactin receptor (PRLR) is implicated in the tumorigenesis of breast and prostate cancers where it drives cell proliferation, survival, and migration. LFA102 is a humanized monoclonal antibody against PRLR with promising preclinical antitumor activity. To determine the maximum tolerated dose or a recommended dose, and to delineate the pharmacokinetic profile of LFA102 in Japanese patients, we conducted a phase I study. Patients and Methods: LFA102 was intravenously infused every 4 weeks to patients with advanced breast or castration-resistant prostate cancer, and the dose increased from 3 to 40 mg/kg. Results: Fourteen patients were treated, and toxicities were reported in 9 (64%) patients. They were all grade 1 or 2, and the most frequently observed toxicity was nausea (3 patients, 21%). No dose-limiting toxicities were observed. LFA102 did not show antitumor activity as a single agent. Conclusion: Treatment with LFA102 was well tolerated. Prolactin mediates its physiological effects through interactions with the prolactin receptor (PRLR). Following binding to PRLR, prolactin activates a wide array of downstream signals, including JAK2/STAT5, JAK1/STAT3, SRC, and FAK pathways leading to PI3K/AKT and RAF/MEK/ERK activation. These signaling cascades trigger cell proliferation, survival, migration, differentiation, and angiogenesis (1). Preclinical data show that mammary gland-or prostate-specific expression of prolactin in transgenic mice increases the incidence of breast and prostate tumors, respectively (2-4). In the clinic, PRLR overexpression is observed in many malignancies, including breast, prostate, ovarian, colorectal, and pancreatic cancers (5-8). Indeed, 95% of breast and prostate cancers are PRLR-positive (9, 10) and high levels of prolactin in the blood have been correlated with increased risk and poor prognosis in breast cancer (11-13). In prostate cancer, prolactin expression has been correlated with phosphorylation of Stat5 (a key mediator of prolactin signaling), high Gleason scores and unfavorable prognosis (14, 15). Prolactin protein is synthesized and secreted from the pituitary gland and from extrapituitary sites including breast and prostate tissues. The overexpression of PRLR in breast and prostate cancers stimulates their growth and contributes to their aggressiveness by autocrine and paracrine mechanisms (3, 16, 17). Furthermore, endogenous prolactin increased the constitutive tyrosine phosphorylation of HER2 in a breast cancer cell line, leading to enhanced growth through the RAS-MAPK pathway (18). Therefore, targeting the prolactin signaling pathway is an attractive endocrine therapeutic strategy. LFA102 is a humanized IgG1/ĸ monoclonal antibody (mAb) against PRLR. The antibody neutralizes all prolactin-induced intracellular signaling pathways examined in vitro, including those mediated through Stat5, Akt, and Erk1/2. Furthermore, LFA102 induces antibody-dependent cell-mediated cytotoxicity in vivo, and inhibits the growth of prolactin-dependent cell lines engineere...