Abstract 854: Inhibition of PRMT5 results in radiosensitization in lung cancer cell lines

Background: Protein arginine methylation is a post translational modification that influences signal transduction, mRNA splicing, gene transcription and DNA repair. Among the PRMT family members, PRMT5 is a type II enzyme that symmetrically methylates histone H4 at Arginine 3 and histone H3 at Arginine 8. Studies have recently linked this modification to carcinogenesis and metastasis. The function of PRMT5 in carcinogenesis is related to cell proliferation through modulation of E2F1, p53, EGFR, and CRAF. It is known to accelerate progression through the G1 phase of cell cycle by influencing proteins like CDK4 and CDK6. Previous work on human lung cancer specimens has demonstrated an overexpression of PRMT5 in cancerous tissue when compared to normal lung parenchyma. Suppression of PRMT5 significantly inhibits cell proliferation in lung cancer cell lines A549 and H1299. We hypothesized inhibition of PRMT5 can lead to increased radiosensitivity in lung cancer cells.

Method: Several lung cancer cell lines were used in the experiments, including A549, H1299 and H23. SiRNA (Dharmacon) and lentiviral shRNA (Sigma) were used to knock down (KD) PRMT5 levels transiently or stably in A549 cell line in which p53 is present in its wild type form. Forty eight hours after transient transfection, cells were plated for clonogenic survival assay and subsequently exposed to ionizing radiation at 0, 2, and 8 Gy. Cellular PRMT5 protein levels were estimated by western blotting analysis for PRMT5 KD and scramble control cell lines. The scramble control and siRNA knockdown cells were subjected to cell cycle analysis by flow cytometry. We also tested specific PRMT5 inhibitors with and without radiation therapy in the lung cancer cell lines to see if PRMT5 inhibitors could lead to increased radiosensitivity.

Results: We observed a >90% PRMT5 KD in transiently transfected cells at 48 h and 72 h post transfection as verified by western blot analysis. This transient KD lead to a small but significant decrease in colony survival after radiation. This radiosensitization was not observed in cells selected for stable KD of PRMT5 protein by lentiviral RNA transfection. There is an increase of cell population in G1 arrest in PRMT5 transient KD cells but not in stable KD cells. Additionally, cells treated with PRMT5 specific inhibitors (“cpd5” or “cpd65”) demonstrated increased radiosensitivity in A549 cells but not in H1299 suggesting that this effect may be p53-dependent.

Conclusion: PRMT5 inhibition by siRNA or its specific inhibitors lead to radiosensitivity in A549 lung cancer cell line. This effect may be partially dependent on p53-dependent cell cycle arrest. Further work to inhibit PRMT5 in other lung cancer cell lines with different p53 activities will be investigated.

Citation Format: Smitha Sharma, X Wu, P Smith, N Denko, C Li, H Lai, F Yan, K Shilo, A Chakravarti, S Sif, R Baiocchi, G Otterson, Meng Xu-Welliver. Inhibition of PRMT5 results in radiosensitization in lung cancer cell lines. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 854. doi:10.1158/1538-7445.AM2014-854

Phase I and pharmacokinetic study of mitomycin C and celecoxib as potential modulators of tumor resistance to irinotecan in patients with solid malignancies

PURPOSE

Based on the preclinical evidence of topoisomerase I (Topo-1) upregulation by mitomycin C(MMC) and decreased NF-kappaB activation by celecoxib, we evaluated combinations of irinotecan/MMC and irinotecan/MMC/celecoxib in patients with advanced solid malignancies.

PATIENTS-METHODS

Initially, patients received MMC on day 1 and irinotecan on days 2, 8, 15 and 22, every 6 weeks. MMC dose was fixed at 6 mg/m(2) and cumulative doses of >36 mg/m(2) were not permitted. Irinotecan was escalated in 25 mg/m(2) increments. Due to late-onset diarrhea, the schedule was subsequently shortened to 4 weeks, omitting irinotecan on days 15 and 22. In the second part of the study, celecoxib 400 mg orally twice daily was added to irinotecan/MMC regimen. Potential pharmacokinetic interactions and Topo-1 and DT-diaphorase (NQ01) gene expressions in peripheral-mononuclear cells were evaluated.

RESULTS

Forty-five patients were enrolled. Irinotecan 125 mg/m(2) on days 2 and 8 in combination with MMC 6 mg/m(2) on day 1 every 4 weeks is recommended for future studies; myelosuppression and diarrhea are dose-limiting. The addition of celecoxib resulted in unacceptable toxicities despite reductions on irinotecan's dose. No relevant pharmacokinetic interactions occurred between irinotecan and MMC, and mean increases in Topo-1, were observed. Sixteen of 36 patients evaluable for response-assessment had discernable anti-tumor activity, including 1 complete, 4 partial, 10 minor and 1 tumor marker response. Four patients had prolonged (>4 months) disease-stability (stable disease, not included in CR or PR). Patients experiencing complete and partial responses had higher increments in Topo-1 expression.

CONCLUSIONS

Modulation of irinotecan by MMC is feasible, devoid of pharmacological interactions and active in solid malignancies. The lack of improvement in therapeutic index does not support the addition of celecoxib.

A single center review of the experience with mitomycin C (MMC) and the risk of thrombotic thrombocytopenic purpura (TTP)/hemolytic uremic syndrome (HUS)

15167

Background: MMC related TTP/HUS has been reported between 4 and 15%, with a higher incidence in patients receiving cumulative doses of 60 mg or higher. It tends to occur within 4 months of drug administration independently of patients’ cancer status. The ability of MMC to upregulate enzymes relevant for new cytototoxic agents (topoisomerase I for CPT-11 and thymidine phosphorylase for capecitabine) make phamacobiologically based therapeutic combinations including MMC attractive. Methods: All patients (n=100) that participated in four institutional clinical studies from 2000 through 2004 were included. The studies were OSU 9947 (phase I trial of CPT-11 and MMC in solid tumors, n=31) OSU 0151 (phase II trial of CPT-11 and MMC in advanced esophageal and stomach cancer, n=41) OSU 0155 (phase II trial of CPT-11 and MMC in patients with refractory breast cancer, n=26) OSU 0330 (phase I study of capecitabine and MMC in patients with advanced GI tumors n=2). In each study, the maximum cumulative dose of MMC was 36 mg/m2. All patients were followed for clinical signs or symptoms of TTP/HUS including the presence of anemia, thrombocytopenia and renal insufficiency and had a thorough review of the peripheral smear. Results: The median cumulative dose was 12 mg/m2 (range 3–36 mg/m2). No patients met the clinical diagnosis of TTP/HUS except for one patient had anemia, thrombocytopenia and renal insufficiency but did not manifest any other findings consistent with TTP/HUS such as changes in mental status, azotemia or any other clinical symptom. The laboratory abnormalities resolved without intervention within seven days with subsequent continuation on the clinical trial. Conclusions: In this study we have demonstrated that by capping the cumulative dose of MMC to 36 mg/m2, the incidence of TTP/HUS is minimal. Furthermore, our preliminary analysis of an additional 100 patients treated with MMC at OSU shows no reported cases of TTP/HUS (additional data will be presented at the meeting). Since MMC is effective in a wide variety of solid tumors including breast, lung and GI malignancies and is inexpensive and easy to administer, further exploration of MMC in the treatment of solid malignancies is indicated including rational combination studies.

No significant financial relationships to disclose.

Safety and pharmacokinetics (PK) of AMG 706 in combination with panitumumab and gemcitabine-cisplatin in patients (pts) with advanced cancer

14057

Background: AMG 706 is an oral, investigational multikinase (MKI) inhibitor with antiangiogenic and direct antitumor activity that selectively targets VEGF, PDGF and Kit receptors. Methods: This is an ongoing phase 1b, open-label, dose-finding study of AMG 706 plus panitumumab and gemcitabine-cisplatin. Objectives are to establish the maximum tolerated dose and to assess safety, objective response and PK of AMG 706 with this regimen. Pts =18 yrs with advanced cancer, ECOG 0–1, =1 prior chemotherapy for advanced disease and no prior oral VEGFr MKIs or anti EGFR therapy, received panitumumab (9mg/kg IV day 1 of each 3-wk cycle) plus gemcitabine (1250mg/m2 IV days 1 and 8) and cisplatin (75mg/m2 IV day 1), and escalating doses of AMG 706 given continuously from day 1 of cycle 1. Assessments included dose-limiting toxicities (DLT; cycle 1), PK and tumor response (every 6–9 wks from wk 6). Results: As of Nov 2006, 36 pts (NSCLC n=19; pancreatic cancer n=4; other n=10; unknown primary n=3) were enrolled; 42% had prior chemotherapy. There was 1 DLT: pulmonary embolism, grade 5 (50mg QD). Selected treatment-related adverse events in =10% of pts are shown in the table . 39% of pts receiving AMG 706 had thromboembolic events (TE); 25% receiving study therapy without AMG 706 had TEs. There was 1 case of cholecystitis (grade 1), 1 of gallbladder pain (grade 3). Preliminary data showed that AMG 706 PK at 125 mg QD was comparable to data from monotherapy studies at the same dose level. Based on 29 pts with available response data (too early to evaluate/data unavailable n=7), objective tumor responses per RECIST were: CR n=1, 3% (breast cancer); PR n=9, 31% (NSCLC n=6; pancreatic cancer n=2; unknown primary n=1); SD n=17, 59%; PD n=1, 3%. Conclusions: In this study of pts with advanced cancer, AMG 706 was tolerable when combined with panitumumab and gemcitabine-cisplatin, with little effect on AMG 706 PK. Further studies need to determine if the observed TE rate exceeds gemcitabine-cisplatin background rates.

[Table: see text]

No significant financial relationships to disclose.

The role of methylation leading to capecitabine resistant malignant mesothelioma

17105

Background: Malignant mesothelioma is a deadly malignancy whose global incidence continues to be on the rise. Established therapies have been less than optimal. The current therapeutic standard is intravenous pemetrexed, an antifolate medication. Yet, another folate antimetabolite, capecitabine, is significantly less effective than pemetrexed. The enzymes thymidylate synthase (TS), dihydropyrimidine dehydrogenase (DPD), and thymidylate phosphatase (TP) are critical to the efficacy of antifolates. Specifically, for capecitabine to be converted into a potent cytotoxic agent, the enzyme TP must be present and active. In one of four mesothelioma cell lines examined, the gene that encodes for TP, extracellular growth factor-1 (ECGF-1), is methylated. Methylation of this gene and the subsequent downregualtion of the TP enzyme confer a diminished cytotoxic effect by a capecitabine prodrug, dioxyfluridine (DFUR). Methods: Cells were cultured treated with and without 1uM decitabine (DAC) under identical conditions. DNA, RNA, and protein lysates were collected after 72 hours. Bisulfite-treated DNA was examined by MS-PCR for evidence of methylation of TS, DPD, and TP. RNA was collected and cDNA was synthesized. Real time PCR was utilized to detect the relative difference in RNA quantity. Western blots were done to evaluate the differences in protein expression between DAC treated and untreated cells. MTT assay was performed with DAC pretreated and untreated cell lines subsequently treated with DFUR and 5-fluorouracil. Results: One of the four mesothelioma cell lines showed consistent evidence of TP methylation by MS-PCR. The addition of 1uM DAC to the cell lines conferred a six-fold difference in expression of the methylated gene by both real time PCR as well as by Western blot. The prodrug DFUR subsequently shows increased cytotoxicity in the methylated cell line by MTT assay when pretreated with DAC compared when not exposed to the DAC. Conclusion: By demethylating the ECGF-1 gene with DAC, the now upregulated TP enzyme has an increased ability to convert DFUR to 5-FU; thus enhancing the cytotoxicity of a drug thought to be ineffective in malignant mesothelioma.

No significant financial relationships to disclose.

The effectiveness of darbepoetin alfa administered at 300 mcg every 3 weeks on clinical outcomes in elderly patients with chemotherapy-induced anemia

18511

Background: Chemotherapy-induced anemia (CIA) is common in patients (pts) receiving chemotherapy, and reduces health-related quality of life. The primary objective of this exploratory analysis was to describe the effectiveness of darbepoetin alfa administered at 300 mcg every 3 weeks (Q3W) in elderly (≥ 65 years old) and younger pts (< 65 years old) with CIA. Methods: We analyzed data on 1493 pts, enrolled in a multicenter, open-label, 16-week study and who received ≥ 1 dose of darbepoetin alfa. Eligible pts were ≥ 18 years old, had a non-myeloid malignancy, and were anemic (hemoglobin [Hb] < 11 g/dL). Pts were analyzed stratified by age (≥ 65 and < 65 years old) and baseline (BL) Hb (< 10 or ≥ 10 g/dL). Hb-based endpoints were analyzed using 2 approaches: the last value carried forward (LVCF) method, where missing Hb values or values within 28 days of a red blood cell (RBC) transfusion were imputed, or an available data approach, where missing Hb values were not imputed. Pt-reported outcomes were assessed using the Functional Assessment of Cancer Therapy-Fatigue (FACT-F) scale. Results: Pt demographics and disease characteristics varied between the age strata: in the ≥ 65-stratum (mean age = 73.7, n = 724), 52% of pts were women and the most common cancer was gastrointestinal (27%); in the < 65-stratum (mean age = 52.1, n = 769), 69% of pts were women and the most common cancer was breast (41%). Mean (SD) BL FACT-F scores for pts ≥ 65 and < 65 were 27.5 (12.8) vs 27.2 (12.1) for the < 10-g/dL strata and 29.0 (12.5) vs 27.5 (12.0) for the ≥ 10-g/dL strata. Study endpoints are shown in the table. The safety profile was as expected for each age group. Conclusions: Darbepoetin alfa 300 mcg Q3W appears to be as effective in achieving and maintaining Hb between 11 to 13 g/dL in elderly pts as in younger pts with CIA. Since chemotherapy is often administered Q3W, synchronizing darbepoetin alfa treatment with pts’ chemotherapy schedules may simplify the treatment of CIA in this pt population.

[Table: see text]

[Table: see text]

Cell cycle regulation of the G0/G1 transition in 5-fluorouracil-sensitive and -resistant human colon cancer cell lines

PURPOSE

Resistance to 5-fluorouracil (5-FU) has been associated with thymidylate synthase (TS) gene amplification and increased TS protein levels. Increased TS protein expression has also been found to be a significant independent prognostic factor for disease-free survival and overall survival in patients treated with adjuvant 5-FU-based chemotherapy. In these studies and in our prior preclinical studies, TS has been considered a marker of proliferative capacity. The purpose of the current study was to further evaluate the association between TS levels and cell cycle regulation, by investigating cell cycle kinetics in a 5-FU-resistant cell line with constitutive overexpression of TS. The influence of increased TS levels on cell cycle progression may provide insight into methods to overcome 5-FU resistance.

MATERIALS

5-FU-sensitive NCI H630(WT) and 5-FU-resistant NCI H630(R1) (with 15- to 20-fold higher TS protein levels) were utilized in this investigation to determine the influence of constitutive overexpression of TS on cell cycle kinetics.

RESULTS

There was no apparent influence of increased TS levels on cell cycle distribution during asynchronous growth, and both cell lines reach plateau growth phase in 120 hours, arresting in G0/G1 as determined by flow cytometry. In the H630(WT) cells, this G0/ G1 arrest was associated with a 14- to 17-fold reduction in TS activity and protein levels (using the TS-106 monoclonal antibody), whereas in the H630(R1) cells, only a two- to fivefold reduction was noted. Flow cytometry analysis utilizing Ki-67 indicated that there was no evidence of a G0 population in the confluent H630(R1), whereas 26% +/- 7% of confluent H630(WT) cells were Ki-67 negative (G0) and the remainder had low Ki-67 signal intensity. Analysis of pRb phosphorylation and p16 and p21 expression suggested that the arrest point for both cell lines was before the point at which Rb phosphorylation takes place, yet the confluent H630(R1) cells had threefold higher p21 than confluent H630(WT) cells.

DISCUSSION

These data suggest that the 5-FU-resistant H630(R1) cell lines arrest at a later point in G0/G1 and have a potentially greater capacity for proliferation.

Genetic etiology of lung cancer

Although the clinical management of lung cancer has not changed substantially over the past decade, this same time period has witnessed exciting new developments concerning the origins of this disease. These findings support the hypothesis that lung cancer, as well as other common adult tumors, arise as a result of somatic mutations to a specific group of cellular genes referred to as oncogenes and tumor suppressor genes. New strategies for the prevention and treatment of lung cancer will emerge as we identify the mechanisms that control mutation rates for these target genes and gain a better understanding of the role these genes play in coordinating normal cell growth and differentiation.