Decitabine Sensitizes the Radioresistant Lung Adenocarcinoma to Pemetrexed Through Upregulation of Folate Receptor Alpha

Functional Characterization of Reduced Folate Carrier and Protein-Coupled Folate Transporter for Antifolates Accumulation in Non-Small Cell Lung Cancer Cells

Antifolates are important for chemotherapy in non-small cell lung cancer (NSCLC). They mainly rely on reduced folate carrier (RFC) and proton-coupled folate transporter (PCFT) to enter cells. PCFT is supposed to be the dominant transporter of the two in tumors, as it operates optimally at acidic pH and has limited transport activity at physiological pH, whereas RFC operates optimally at neutral pH. In this study, we found RFC showed a slightly pH-dependent uptake of antifolates, with similar affinity values at pH 7.4 and 6.5. PCFT showed a highly pH-dependent uptake of antifolates, with an optimum pH of 6.0 for pemetrexed and 5.5 for methotrexate. The Michaelis-Menten constant (Km ) value of PCFT for pemetrexed at pH 7.4 was more than 10 times higher than that at pH 6.5. Interestingly, we found that antifolate accumulations mediated by PCFT at acidic pH were significantly affected by the efflux transporter, breast cancer resistance protein (BCRP). The highest pemetrexed concentration was observed at pH 7.0-7.4 after a 60-minute accumulation in PCFT-expressing cells, which was further evidenced by the cytotoxicity of pemetrexed, with the IC50 value of pemetrexed at pH 7.4 being one-third of that at pH 6.5. In addition, the in vivo study indicated that increasing PCFT and RFC expression significantly enhanced the antitumor efficacy of pemetrexed despite the high expression of BCRP. These results suggest that both RFC and PCFT are important for antifolates accumulation in NSCLC, although there is an acidic microenvironment and high BCRP expression in tumors. SIGNIFICANCE STATEMENT: Evaluating the role of reduced folate carrier (RFC) and proton-coupled folate transporter (PCFT) on antifolates accumulation in non-small cell lung cancer (NSCLC) is necessary for new drug designs. By using cell models, we found both RFC and PCFT were important for antifolates accumulation in NSCLC. Breast cancer resistance protein (BCRP) significantly affected PCFT-mediated antifolates accumulation at acidic pH but not RFC-mediated pemetrexed accumulation at physiological pH. High expression of PCFT or RFC enhanced the cytotoxicity and antitumor effect of pemetrexed.

Composition of Conditioned Media from Radioresistant and Chemoresistant Cancer Cells Reveals miRNA and Other Secretory Factors Implicated in the Development of Resistance

Resistance to chemo- or radiotherapy is the main obstacle to consistent treatment outcomes in oncology patients. A deeper understanding of the mechanisms driving the development of resistance is required. This review focuses on secretory factors derived from chemo- and radioresistant cancer cells, cancer-associated fibroblasts (CAFs), mesenchymal stem cells (MSCs), and cancer stem cells (CSCs) that mediate the development of resistance in unexposed cells. The first line of evidence considers the experiments with conditioned media (CM) from chemo- and radioresistant cells, CAFs, MSCs, and CSCs that elevate resistance upon the ionizing radiation or anti-cancer drug exposure of previously untreated cells. The composition of CM revealed factors such as circular RNAs; interleukins; plasminogen activator inhibitor; and oncosome-shuttled lncRNAs, mRNAs, and miRNAs that aid in cellular communication and transmit signals inducing the chemo- and radioresistance of sensitive cancer cells. Data, demonstrating that radioresistant cancer cells become resistant to anti-neoplastic drug exposure and vice versa, are also discussed. The mechanisms driving the development of cross-resistance between chemotherapy and radiotherapy are highlighted. The secretion of resistance-mediating factors to intercellular fluid and blood brings attention to its diagnostic potential. Highly stable serum miRNA candidates were proposed by several studies as prognostic markers of radioresistance; however, clinical studies are needed to validate their utility. The ability to predict a treatment response with the help of the miRNA resistance status database will help with the selection of an effective therapeutic strategy. The possibility of miRNA-based therapy is currently being investigated with ongoing clinical studies, and such approaches can be used to alleviate resistance in oncology patients.

Association of Antifolate Response Signature Status and Clinical Activity of Pemetrexed-Platinum Chemotherapy in Non-Small Cell Lung Cancer: The Piedmont Study

PURPOSE

The Piedmont study is a prospectively designed retrospective evaluation of a new 48-gene antifolate response signature (AF-PRS) in patients with locally advanced/metastatic nonsquamous (NS) non-small cell lung cancer (NSCLC) treated with pemetrexed-containing platinum doublet chemotherapy (PMX-PDC). The study tested the hypothesis that AF-PRS identifies patients with NS-NSCLC who have a higher likelihood of responding positively to PMX-PDC. The goal was to gather clinical evidence supporting AF-PRS as a potential diagnostic test.

EXPERIMENTAL DESIGN

Residual pretreatment FFPE tumor samples and clinical data were analyzed from 105 patients treated with first-line (1L) PMX-PDC. Ninety-five patients had sufficient RNA sequencing (RNA-seq) data quality and clinical annotation for inclusion in the analysis. Associations between AF-PRS status and associate genes and outcome measures including progression-free survival (PFS) and clinical response were evaluated.

RESULTS

Overall, 53% of patients were AF-PRS(+), which was associated with extended PFS, but not overall survival, versus AF-PRS(-) (16.6 months vs. 6.6 months; P = 0.025). In patients who were stage I to III patients at the time of treatment, PFS was further extended in AF-PRS(+) versus AF-PRS(-) (36.2 months vs. 9.3 months; P = 0.03). Complete response (CR) to therapy was noted in 14 of 95 patients. AF-PRS(+) preferentially selected a majority (79%) of CRs, which were evenly split between patients stage I to III (six of seven) and stage IV (five of seven) at the time of treatment.

CONCLUSIONS

AF-PRS identified a significant population of patients with extended PFS and/or clinical response following PMX-PDC treatment. AF-PRS may be a useful diagnostic test for patients indicated for systemic chemotherapy, especially when determining the optimal PDC regimen for locally advanced disease.

Ubenimex Combined with Pemetrexed Upregulates SOCS1 to Inhibit Lung Adenocarcinoma Progression via the JAK2-STAT3 Signaling Pathway

To study the effects of ubenimex (UBE) combined with pemetrexed (PEM) on lung adenocarcinoma cell behavior and its molecular mechanism, the tissue samples from lung adenocarcinoma patients who received PEM chemotherapy, those with PEM combined with UBE chemotherapy, and healthy volunteers were retrieved and analyzed. The expression levels of the suppressor of cytokine signaling 1 (SOCS1) in the human lung adenocarcinoma cancer cell lines A549 and PC-9 and tissues were detected by qRT-PCR. MTT assay was performed for cell proliferation. Cell apoptosis was detected by flow cytometry. Cell invasion ability was assessed using the Transwell assay. The expression levels of the JAK2/STAT3 signaling pathway proteins and apoptosis-related proteins were detected by Western blot. The antitumor effect of PEM combined with UBE was tested in nude mice using the tumor formation assay. Our results showed that UBE treatment, alone or combined with PEM, inhibited lung adenocarcinoma cell migration, invasion, and proliferation; promoted apoptosis; significantly increased the G0/G1-phase cell ratio; reduced the S-phase cell ratio; and inhibited the in vivo growth of tumor cells. UBE alone or in combination with PEM also inhibited the JAK2/STAT3 signaling pathway in lung adenocarcinoma cells. In addition, UBE combined with PEM therapy was associated with increased SOCS1 expression in patients' serum and knocking down SOCS1 reversed the antitumor effects of UBE and PEM. Overall, combination therapy with UBE and PEM could inhibit the JAK2-STAT3 signaling pathway by upregulating SOCS1 expression to hinder the progression of lung adenocarcinoma cells.

miR‑148a promotes cell sensitivity through downregulating SOS2 in radiation‑resistant non‑small cell lung cancer cells

Non-small cell lung carcinoma (NSCLC) is the most common type of lung cancer; however, radioresistance is a significant barrier in NSCLC radiotherapy. MicroRNA (miR)-148a has been reported to be a tumor suppressor in various types of cancer, including NSCLC. In the present study, the potential role of miR-148a in regulating radiosensitivity of NSCLC cells was investigated. Serum miR-148a expression was evaluated by reverse transcription-quantitative PCR in patients with NSCLC and healthy controls. The effects of miR-148a on cell viability, migration and invasion were assessed by Cell Counting Kit-8 and Transwell assays in radiation-resistant NSCLC cells. Serum miR-148a was downregulated in patients with NSCLC compared with healthy controls and its expression was significantly increased after radiotherapy. By contrast, miR-148a expression was decreased in the radioresistant patients compared with the radiosensitivity patients. Additionally, miR-148a overexpression inhibited the cell proliferation, migration and invasion of radiation-resistant NSCLC cells. In addition, miR-148a had putative binding site with Son of Sevenless 2 (SOS2) and negatively regulated SOS2 expression. Silencing SOS2 expression significantly suppressed miR-148a inhibitor-induced increase in radiosensitivity in NSCLC. In conclusion, the results of the present study suggested that miR-148a could enhance the radiosensitivity of NSCLC cells through targeting SOS2, thus providing potential therapeutic targets to improve radiotherapy in NSCLC.