Safety and efficacy of lobaplatin combined with 5-fluorouracil as first-line induction chemotherapy followed by lobaplatin-radiotherapy in locally advanced nasopharyngeal carcinoma: preliminary results of a prospective phase II trial

Background Due to improvements in imaging and radiological techniques as well as the use of chemotherapy, distant metastasis has become the predominant mode of treatment failure in patients with locally advanced nasopharyngeal carcinoma (LA-NPC). Platinum-based systemic chemotherapy has shown survival benefits and is now the standard strategy for systemic therapy in patients with LA-NPC. Notably, the third-generation platinum reagent lobaplatin has shown anti-tumor effects in several solid tumors with lower incidences of gastrointestinal, hepatic and renal toxicity relative to other platinum drugs. However, the safety and efficacy of lobaplatin as a first-line regimen in patients with LA-NPC are undetermined. Methods Patients with stage III–IVa-b NPC received lobaplatin at a dose of 30 mg/m2 on days 1 and 22 combined with a continuous 120-h intravenous injection of 5-fluorouracil at a dose of 4 g/m2 followed by lobaplatin at a dose of 50 mg/m2 on days 43 and 64 concomitant with intensity-modulated radiation therapy. Objective response rates and acute toxicity were assessed based on RECIST (1.1) and CTCAE v.3.0, respectively. Kaplan-Meier analysis was used to calculate survival rates. Results Fifty-nine patients were enrolled, and 44 patients (74.6%) received allocated cycles of chemotherapy. The objective response rates were 88.1% (95% confidence interval [CI], 0.77 to 0.95) and 100% after induction chemotherapy (ICT) and concurrent chemoradiotherapy (CRT), respectively. With a median follow-up period of 44 months, the 3-year estimated progression-free survival and overall survival were 86.4% (95% CI, 69.8 to 98.8) and 94.9% (95% CI, 89.5 to 100), respectively. The most common grade 3–4 toxicities were neutropenia (8.5%) and thrombocytopenia (40.7%) after ICT and CRT, respectively. Conclusion Lobaplatin combined with 5-fluorouracil followed by lobaplatin-RT treatment showed encouraging anti-tumor effects with tolerable toxicities in patients with LA-NPC. Randomized controlled trials of lobaplatin in patients with LA-NPC are warranted. Trial registration This trial was registered with the Chinese Clinical Trials Registry and approved on March 31st, 2012, number ChiCTR-ONC-12002060.


Background
Nasopharyngeal carcinoma (NPC), a malignancy derived from epithelial cells of the nasopharynx, is endemic in Southern China and Southeast Asia [1]. The development of high-resolution imaging and radiological techniques has increased the local control rate of NPC up to 95% [2], leaving distant metastasis as the major cause of treatment failure. To address this issue, a combined regimen of chemotherapy and radiotherapy has been recommended as the standard treatment strategy for locally advanced NPC (LA-NPC) [3]. However, the survival benefits of sequential chemotherapy for NPC patients are still controversial [4][5][6][7][8]. Induction chemotherapy (ICT) can improve both progression-free survival (PFS) and/or overall survival (OS) [8][9][10][11][12][13][14]. Ma J et al recently demonstrated that the introduction of cisplatin, fluorouracil, and docetaxel (TPF) induction chemotherapy to concurrent chemotherapy could significantly improve the PFS of patients with LA-NPC [15], while additional randomized controlled clinical trials to determine the role of systemic chemotherapy in NPC during the intensity modulation radiotherapy (IMRT) era are still underway.
A platinum-based regimen is recommended as the first-line chemotherapeutic strategy for NPC according to the NCCN guidelines. Cisplatin, the first anticancer reagent, has shown encouraging anti-tumor efficacy in NPC both alone and in combination with other treatments [3,5,16,17]. However, cisplatin can induce severe side effects, including dose-limiting nephrotoxicity, cumulative peripheral sensory neuropathy, ototoxicity and gastrointestinal reactions, such as nausea or vomiting, which can reduce patient compliance for chemotherapy administration or even cause treatment interruptions [18]. Moreover, the requirement of a massive fluid infusion of cisplatin to avoid renal toxicity extends the inpatient period and limits the application of this treatment in patients with heart and renal dysfunction. Lobaplatin, a thirdgeneration platinum reagent, forms DNA adducts and induces DNA damage, resulting in cell apoptosis, which is similar to the pharmacological mechanisms of other platinum reagents [19]. Lobaplatin has shown robust anti-tumor efficacy in multiple solid tumors, such as breast cancer, hepatocellular carcinoma, nonsmall cell lung cancer, transitional cell carcinoma, ovarian cancer and cervical squamous carcinoma [20][21][22][23], but without the above-listed toxicities. Moreover, lobaplatin has no multidrug resistance with other platinum drugs, such as cisplatin or carboplatinum [20]. Though lobaplatin costs approximately 16-fold more than cisplatin, there is no increased economic burden to patients due to the high insurance coverage of both reagents. Major characteristics of cisplatin and lobaplatin are compared in Table 1.
A combination of lobaplatin and docetaxel has exhibited particularly effective anti-tumor activity in recurrent and metastatic NPC [24]. Herein, to further determine the anti-tumor efficacy of lobaplatin in LA-NPC, we performed a phase II clinical trial to determine the safety and efficacy of lobaplatin combined with 5-fluorouracil (5-FU) as a first-line ICT strategy followed by lobaplatinradiotherapy (lobaplatin-RT) in LA-NPC.

Aim of study and end points
The main purpose of this trial was to test the feasibility and efficacy of delivering lobaplatin combined with 5-FU as a first-line ICT regimen followed by lobaplatin-RT in patients with LA-NPC. The primary end point was the objective response rate (ORR), and secondary end points included overall survival (OS), progression-free survival (PFS), distant metastasis-free survival (DMFS) and local recurrence-free survival (LRFS). Acute toxicities during ICT and lobaplatin-RT were also observed. The study was designed as a single arm, open-labeled phase II study.

Participant enrollment and characteristics
Regular evaluations were performed for all enrolled participants as previously described [2]. These included medical history, physical examination, pathology diagnosis, electrocardiogram, and laboratory testing, including but not limited to liver and kidney function and Epstein Barr virus (EBV) DNA copy number assessment. To ensure tumor margins were well-defined, magnetic resonance imaging (MRI) of the nasopharynx and neck were conducted in all patients, except those with contraindications (e.g., pacemaker or stent); for these cases, computed tomography (CT) was used. Regular work-ups including chest X-rays, abdominal sonography and bone scans, or positron emission tomography/computed tomography (PET/CT) as an optional substitution to evaluate distant metastases, were also performed based on patient preference and financial capacity. The patients were staged according to the American Joint Committee on Cancer (AJCC, 7 th edition) staging system based on the above imaging results.
The following inclusion criteria were applied for enrollment: untreated patients aged 18 to 60 years; stage III or IVa-b disease; histopathologically confirmed WHO type II or III NPC; leukocytes ≥ 4.0X10E9; neutrophils ≥ 1.5X10E9; platelets ≥ 100X10E9; hemoglobin ≥ 90 g/L; aminotransferase ≤ 2XUNL; serum creatinine ≤ 1.5XUNL; and no evidence of dysfunction in important organs (e.g., heart, lung, liver and kidney) or other malignancies. All participants provided informed consent. Patients who were known or suspected to be allergic to cisplatin, who had uncontrolled infection or a physical disease that could not tolerate chemotherapy/radiotherapy, or who could not coordinate contact for follow-up were excluded. Additionally, pregnant females or patients who underwent immune repressive treatment such as that following organ transplantation were also not admitted. Patients who could not tolerate the treatment toxicities or failed to receive planned treatment due to voluntary refusal or a physician's decision were withdrawn from the study.
From April 1, 2012 to Oct 31, 2012, 59 patients with confirmed undifferentiated nonkeratinizing NPC were enrolled in this study. Their demographic and clinical characteristics before treatment are listed in Table 2. The median age of the participants was 43 years. Fortythree (72.9%) males and 16 (27.1%) females were enrolled. Twenty-two participants (37.3%) had a high serum EBV DNA copy number (>4000 copies/ml) before treatment. Twenty-nine (49.2%) participants with stage III disease and 30 (50.8%) participants with stage IV a-b disease were enrolled.

Treatment
Allocated treatments including two cycles of ICT followed by two cycles of concomitant chemotherapy and radical intensity-modulated radiotherapy (IMRT) to the nasopharynx and neck were delivered to all patients. The ICT consisted of 30 mg/m 2 lobaplatin (intravenous infusion, day 1) and 4 g/m 2 5-fluorouracil (continuous 120-h intravenous injection) during each cycle. The concurrent chemotherapy consisted of 50 mg/m 2 lobaplatin (intravenous infusion, day 1) during each cycle. The interval of cycles was 3 weeks.
Radical IMRT was initiated on the same day as first concomitant chemotherapy. RT prescription doses of 68-70 Gy, 62-68 Gy and 54-60 Gy were delivered to the planning target volume (PTV) of the primary nasopharynx tumor, involved cervical lymph nodes and lymph node-negative areas, respectively. All patients received a regular fraction during RT, five fractions per week and 30-33 fractions in total.
National Cancer Institute (NCI) Common Toxicity Criteria (CTC) V.3.0 were used to determine acute adverse events. The prescription dose of chemotherapy was modified based on the toxicity induced by the previous chemotherapy cycle and was decreased to 75% of the allocated dose when a patient suffered from any of the following toxicities: granulocytopenia fever, platelet count ≤ 25,000/μL, or grade 3 nausea and/or vomiting. The prescription dose of chemotherapy was decreased to 50% of the planned dose when a patient developed any of the following toxicities: grade 4 or greater nausea and/or vomiting or creatinine clearance around 35-49 ml/min. Prophylactic administration of hematopoietic colonystimulating factor was performed on days 3-8 of the next chemotherapy cycle in the patients who developed grade 4 granulocytopenia. Chemotherapy was interrupted when patients developed grade 4 hematological, hepatic or kidney toxicity and was administered again if the toxicity decreased to grade 2 or less. Chemotherapy was no longer delivered to patients with a remitted time of over 2 weeks.

Assessment of efficacy and follow-up
Efficacy was assessed after two cycles of ICT, after concurrent chemoradiotherapy (CRT) and 3 months after CRT. Treatment response was evaluated based on Response Evaluation Criteria In Solid Tumors (RECIST 1.1). The follow-up frequency for the first 2 years and the 3 rd to 5 th years was 3 and 6 months, respectively. Regular examinations including physical examinations, indirect nasopharyngoscopy, fiber nasopharyngoscopy, and MRI of the nasopharynx and neck were used for efficacy evaluation and follow-up. Patients with confirmed local recurrence (LR) were diagnosed via MRI and biopsy. Diagnosis of distant metastasis (DM) was confirmed by a regular workup, including CT, MRI, bone scan or PET/CT, and needle biopsy when available. Salvage treatments including re-irradiation, surgery and/ or ablation to local lesion and/or systemic chemotherapy were performed in patients with LR or DM as long as they had the indications.
Statistical analysis SPSS 22.0 (SPSS, Chicago, IL) was used to perform all analyses in this study. A Simon Two-Stages Design was used to determine the sample size. We assumed the ORR to be 80%, and less than 60% was unacceptable. The estimated rate of loss to follow-up was 10%. We set the power to detect the effectiveness of the treatment strategy in our study as 0.9 with a two-sided significance of P = 0.05. Accordingly, a total of 59 evaluable patients were required. OS, PFS, LRFS and DMFS were calculated using Kaplan-Meier analysis. All time-to-event end  Fig. 1 Flowchart of the trial points were calculated from the first date of treatment to the date of treatment failure or the last day of follow-up. Patients who developed either DM or LR were followed up until death or until the last scheduled day of follow-up. All efficacy analyses were performed in the intention-to-treat population. All patients who received at least one cycle of chemotherapy were included in the toxicity analysis. This trial was registered with the Chinese Clinical Trials Registry, number ChiCTR-ONC-12002060.

Assessment of treatment efficacy
Fifty-two (88.1%) participants experienced an objective response (OR) after two cycles of ICT, with eight (13.6%) and 44 (74.6%) participants experiencing a complete response (CR) and a partial response (PR), respectively. After a complete course of treatment, all (100%) patients experienced an OR, with 47 (79.7%) and 12 (20.3%) participants experiencing a CR and PR, respectively. Of these 12 participants, seven and four individuals experienced residual disease in the cervical lymph nodes or nasopharynx. One patient had persistent disease in both sites after CRT. Three months after CRT, 51 (86.4%) and two (3.4%) patients experienced CR and PR, respectively, with six patients being lost to follow-up at this time (Table 3). Of the two patients who experienced PR 3 months after CRT, one had residual disease in the nasopharynx and experienced CR 6 months after CRT and the other had persistent and stable disease in the cervical lymph nodes during the close follow-up.

Failure patterns
Over a median follow-up time of 44 months (range from 1 to 47 months), eight (13.6%) patients experienced disease progression, with a range of progression time of 11 to 31 months. Of these patients, two (3.4%) developed local relapse, one in the nasopharynx and the other in the cervical lymph nodes. Moreover, six (10.2%) patients developed DM. The sites of DM were the liver (n = 1), the lung (n = 3) and multiple organs (n = 2). Three (5.1%) patients with DM died of cancer progression, and the OS time ranged from 1 to 15 months. The 3-year estimated survival rates and the 95% confidence intervals (CIs) for all time-to-event end points are listed in Table 4. Kaplan-Meier survival curves for OS or PFS and DMFS or LRFS are shown in Figs. 2 and 3. The median of all time-to-event end points had not been reached until after the paper was published.

Discussion
Presently, concurrent chemotherapy with or without ICT is the standard treatment strategy for patients with LA-NPC [25]. Although the survival benefits of ICT have been inconsistent across prior studies, ICT can theoretically shrink local regional tumors and eradicate micrometastases, resulting in reduced RT volume, decreased RT dose needed for organs at risk and a slower rate of DM. Moreover, a prior study showed that changing from adjuvant cisplatin and 5fluorouracil to induction cisplatin and capecitabine caused a favorable trend of increasing efficacy with  less toxicity in LA-NPC [8]. Similarly, several phase II/III studies have shown encouraging outcomes following ICT in patients with LA-NPC [5,8,14,15,26,27]. Platinum drugs are the most widely used agent for both ICT and CRT in patients with NPC.
Lobaplatin is a third-generation platinum agent that shows less gastrointestinal, auricular, liver and renal toxicity than cisplatin or carboplatin [18]. Lobaplatin combined with or without other reagents has shown encouraging or equivalent anti-tumor efficacy but with less toxicity in squamous cell carcinoma than cisplatin [23,28,29]. Notably, lobaplatin combined with docetaxel also showed anti-tumor effects in recurrent or metastatic NPC [24,30]. However, as the anti-tumor efficacy of lobaplatin as a first-line strategy in LA-NPC was not determined, we conducted the current prospective phase II clinical trial.
In previous studies, ORRs following the addition of different ICT regimens with and without CRT in LA-NPC were 79.4-90.0% and 85.3-100%, respectively, after ICT and a full course of treatment [5,8,17,26]. In the present study, the ORR was encouraging after two cycles of ICT and CRT compared with a previous study in which patients with LA-NPC received cisplatin-5-fluorouracil ICT followed by cisplatin-radiotherapy (88.1% vs. 79.4%, 100% vs. 85.3%, respectively) [31]. Moreover, the 3-year OS and PFS rates of our study are also comparable with previous studies (94.9% vs. 80.0-95.0% and 86.4% vs. 54.0-89.9%) [5,8,17,26,31]. Although there is a bias in comparing our study with previous reports, we were able to estimate lobaplatin's activity as a first-line reagent in LA-NPC. However, randomized controlled studies are needed to compare the efficacy of lobaplatin and other reagents as a first-line systemic treatment for LA-NPC.
In this study, 74.6% of the patients received allocated cycles of chemotherapy, and the remaining participants received two or three cycles of chemotherapy mainly as a result of grade 3-4 thrombocytopenia, which has been reported as the major dose-limiting toxicity of lobaplatin [20]. Similarly, thrombocytopenia was also the most frequent grade 3-4 toxicity in our study. However, both thrombocytopenia and other hematological toxicities could be cured using hematopoietic colonystimulating factor, which was acceptable. No grade 3 or 4 nausea or vomiting was observed in our study, and the rate of this complication appeared to be much lower than that following cisplatin-5fluorouracil ICT treatment (0% vs. 23.5%) [31]. As lobaplatin has no or limited renal toxicity, a highvolume fluid infusion is not required during chemotherapy, which could shorten the inpatient period and improve patient compliance. Moreover, the lack of requirement for fluid infusion would allow patients with renal or cardiac dysfunction to receive this treatment, thus expanding the potential population with LA-NPC who could benefit from systemic chemotherapy.
A main limitation of this study is that it was not blinded. Neither the investigators nor the patients were blinded, which might have introduced observation bias from the investigators and psychological bias from the patients. Moreover, it was a single-arm trial from a single institution; therefore, the superiority of lobaplatin over other platinum reagents for treatment of LA-NPC could not be defined, and the efficacy of lobaplatin in other non-endemic areas is also needed. Additionally, six patients were lost to follow-up by 3 months after treatment, leaving the lost-to-follow-up rate (about 10%) higher than in similar studies [7,32], which might have resulted in bias when forming conclusions. Additionally, longterm follow-up is required to document the longterm efficacy and late toxicities of lobaplatin in patients with LA-NPC.
Altogether, lobaplatin showed promising anti-tumor activity with tolerable toxicity when used as a firstline treatment strategy in patients with LA-NPC; however, it might not be the best choice for patients with a low reserve of bone marrow, such as patients over 60 years old. Moreover, lobaplatin has no crossover drug resistance with other platinum reagents [18] and therefore can be used as a substitute in patients resistant to other platinum-based agents. However, further randomized controlled trials are needed to determine the anti-tumor efficacy of lobaplatin compared with other chemotherapeutic reagents in patients with LA-NPC and to help define the best subpopulation that will achieve maximum survival benefits with this drug.

Conclusions
We reported the short-term results produced by administering lobaplatin-5-fluorouracil ICT followed by lobaplatin-RT in patients with LA-NPC. A multi-center phase III randomized controlled trial is currently being undertaken by our group and collaborators to determine the efficacy of lobaplatin-5-fluorouracil followed by lobaplatin-RT vs. cisplatin-5-fluorouracil followed by cisplatin-RT in patients with LA-NPC. At the time of this writing, the patients in this trial were still undergoing follow-up.   ]. The first five funders supported the design of the study and data collection. The latter two funders supported data analysis and manuscript writing.

Availability of data and materials
The datasets collected and analyzed during the current study are available from the corresponding authors on reasonable request, but no information infringing on the privacy of the participants will be given.