Biweekly Raltitrexed in Combination with Irinotecan (RIR) as Second-Line Therapy for Patients with Metastatic Colorectal Cancer: A Non-Randomized, Open-Label Phase II Trial.


 Background Irinotecan-based doublet chemotherapy strategy was standard second-line backbone treatment for patients with oxaliplatin‑refractory metastatic colorectal cancer(mCRC). The aim of this study was to evaluate tolerability and efficacy of raltitrexed combined with irinotecan biweekly administered as the second-line therapy for mCRC patients.Methods The study was a single-center, non-randomized, open-label phase II trial. Patients with mCRC after failure with first-line treatment of oxaliplatin and fluoropyrimidine or its derivatives were enrolled. Irinotecan (180 mg/m2) and raltitrexed (2.5 mg/m2) were given intravenously on day 1. Cycles were repeated every 2 weeks. The primary endpoint was progression-free survival, and the secondary endpoints included overall response rate, disease control rate, overall survival and treatment related adverse events. Results Between December 2012 and October 2016, 35 patients were enrolled. 33 and 35 patients were assessed for response and safety, respectively. The overall response rate (ORR) was 8.6 %, and the disease control rate (DCR) was 71.4%. The median progression-free survival (PFS) was 4.5 months (95% CI 3.8–5.2). The median overall survival was 12.0 months (95% CI 8.5–15.5). Four patients received conversion therapy to no evidence of disease (NED), and 2 patients were still alive with beyond 24 months survival. The most common grade 3/4 hematological adverse events were leukopenia (8.6%), neutropenia (5.7%). The most common grade 3/4 nonhematological adverse events were anorexia (14.3%), vomiting (14.3%), nausea (11.4%) and fatigue (8.6%). Two patients discontinued the protocol treatment because of treatment-related gastrointestinal adverse events. No one died from treatment-related events. The incidence and severity of toxicity was irrelevant to UGT1A1 status.Conclusions The combination of irinotecan with raltitrexed is an active, convenient and acceptable toxic regimen for second-line treatment for mCRC patients, which needs further study as a chemotherapy backbone to be combined with targeted agents in mCRC.Trial registration No. ChiCTR-ONC-12002767. The study was registered with the Chinese Clinical Trial Registry at 29 Octorber 2012, http://www.chictr.org.cn/index.aspx.


Introduction
Colorectal cancer (CRC) is the third most common cancer worldwide, over 1 million new cases diagnosed each year and also ranks the third in terms of mortality in 2018 [1,2]. Only 4%-21% response rate (RR) is obtained in metastatic colorectal cancer (mCRC) patients who receive irinotecan-based second-line treatment [3,4]. Although targeted therapies, such as inhibitor of the epidermal growth factor (EGFR) or vascular endothelial growth factor (VEGF) are valuable additions to rst-or second-line options, chemotherapy remains the foundation of medical management of mCRC. Moreover, some of Chinese patients with mCRC could not be afford to targeted therapies due to their economic limitation. Therefore, irinotecan-based second-line chemotherapy also be reasonable option for mCRC patients. Practically, FOLFIRI (leucovorin and uorouracil plus irinotecan) is recommended as standard regimen in the secondline setting [3]. In addition, for Chinese mCRC patients, the second-line therapy of irinotecan-based chemotherapy, such as modi ed XELIRI (capecitabine plus irinotecan), is well tolerated and non-inferior to FOLFIRI with or without bevacizumab in terms of overall survival (OS) [5]. Irinotecan-based therapies were more effective than irinotecan alone [6] and modi ed doses of irinotecan combined other therapies also exhibited a more feasible tolerability and favorable e cacy [5,7,8], suggesting irinotecan-based chemotherapy strategy was standard second-line backbone treatment for mCRC.
Raltitrexed, a direct thymidylate synthase (TS) inhibitor presenting different anticancer mechanism from that of 5-uorouracil (5-FU), has been proved promising an e cacy, favorable toxicity pro le, and convenient administration schedule in patients with 5-FU-refractory [9,10]. What's more, administration of FOLFIRI requires a central venous catheter (CVC) and continuous infusion of 5-FU, which is inconvenient for patients and decreases their quality of life. Thus, regimen comprising raltitrexed via convenient and rapid venous injection was implemented to replace continuous infusion of 5-FU.
Therefore, a single center, non-randomized, phase II, trial was conducted to investigate the tolerability and e cacy of raltitrexed plus irinotecan (RIR) as a second-line therapy for mCRC patients.

Study design and eligibility
This study was a single-center, non-randomized, open-label phase II trial registered in November 2012 (registration No. ChiCTR-ONC-12002767). The primary endpoint was progression free survival (PFS). The secondary endpoints were overall response rate (ORR), disease control rate (DCR), overall survival (OS) and toxicity. Inclusion criteria were as follows: (a) histopathologically proven colorectal adenocarcinoma; (b) non-resectable metastases; (c) aged 18 years or older; (d) life expectancy of ≥ 3 months at the time of enrolment; (e) ECOG performance status of 0 or 1; (f) no second-line treatment, and failure after prior uorouracil or its derivatives-based ( uoropyrimidine or Capecitabine or S-1, plus oxaliplatin) chemotherapy as rst-line therapy for metastatic disease or in the adjuvant setting (relapse within 6 months of adjuvant therapy); (g) at least 2 weeks since prior chemotherapy and 4 weeks since prior radiotherapy, prior radiotherapy to non-target lesions allowed and no prior radiotherapy to target lesions unless disease progression is documented within the radiation port;(h) at least one measurable lesion based on the Response Evaluation Criteria in Solid Tumors (RECIST) criteria (version 1.0); (i) adequate hematologic, hepatic and renal function (j) signed written informed consent. Exclusion criteria were as follows: (a) patients with diagnosed angina or myocardial infarction < 3 months prior to enrollment; (b) other prior malignancy; (c) with untreated or symptomatic central nervous system metastases; (d) severe and/or uncontrolled medical conditions or active infections; (e) active in ammatory bowel disease or other bowel disease causing long-term chronic diarrhea, or total or obvious bowel obstruction.

Treatment schedule
All patients had previously failed oxaliplatin-based regimens in combination with uoropyrimidines or its derivatives (FOLFOX/CapeOX). The patients had received intravenous infusion of irinotecan (180 mg/m 2 ) over 90 min, in combination with raltitrexed 2.5 mg/m 2 (max 6 mg) intravenous on day 1 every 2 weeks. Without a minimum or maximum number of treatment cycles, treatment would be discontinued in the event of progressive disease (PD), conversion surgery, unacceptable adverse events, patient's refusal to the treatment, withdrawal of consent, or by physician's decision. Patients were not forced to test for homozygosity or double heterozygosity for UDP-glucuronosyltransferase 1A1 (UGT1A1) polymorphisms (UGT1A1*6 and UGT1A1*28) at baseline or during the treatment.

E cacy and Toxicity
Patients who received at least one treatment course were included in e cacy and toxicity analyses. Laboratory tests and safety evaluation were performed prior to treatment and biweekly thereafter.
Response evaluation was based on RECIST (version 1.0) criteria every 3-4 cycles of chemotherapy or every 2 months if treatment was delayed. PFS was de ned as the time from registration until objective tumor progression or death. Conversion surgery was permitted after chemotherapy judged by MDT or surgeon, if the patient underwent conversion surgery, PFS was de ned as the time from registration to the date of progression or death after surgery. OS was de ned as the time from registration until death from any cause. Toxicity was assessed according to the Common Terminology Criteria for Adverse Events (CTCAE) (version 3.0). Toxicities could be managed by dose reduction or discontinuation of chemotherapeutic drugs. The doses of irinotecan and raltitrexed were reduced by 25% in case of grade 4 hematotoxicity and/or if any other grade 3/4 severe organ toxicity was observed in the previous cycle. Treatment would be delayed for up to 4 weeks until adverse effects resolved or at least recovered to grade 2 or judged by the investigator. Any patient who required more than 4 weeks for recovery of adverse events was taken off the study.

Statistical analysis
On the basis of the data from the previous study based on 6-month PFS rate and ORR, the Simon (1989) two-stage optimal design was used to determine the number of patients in this phase II study. With a 5% alpha risk and a 15% beta risk, we determined a rst-stage 6-month PFS probability of 10% (which if true, implied discontinuing the trial) and a minimal rate of 6-month PFS of 30% (which if true, implied moving on to the second stage of the trial). The number of patients to be included was calculated to be 12

Treatment exposure
The median number of treatment cycles was 4 (from 1 to 9 cycles). Treatment delay and dose reduction caused by treatment related adverse events (TAEs) occurred in 15(42.8%) and 4(11.4%) patients respectively. Treatment was discontinued because of PD in 17 patients (48.6%), conversion to surgery/radiotherapy to no evidence of disease (NED) in 4 (3 in surgery and 1 in radiotherapy, 11.4%), TAEs in 2 (5.7%), non-TAEs (ileus) in 1 (2.9%), patient refusal to continue or other reasons in 10 patients (28.6%), and 1 patient (2.9%) discontinued due to sudden death after 1 cycle chemotherapy (regard associated with disease). Adverse events (AEs) leading to withdrawal in 2 patients were mainly associated with gastrointestinal toxicity (Anorexia/Nausea/ Vomiting).

E cacy
The percentages of the relative dose intensities (RDI) of the planned dose were 100% (median) and 97.9% (mean) for raltitrexed and irinotecan. Tumor responses are listed in Table 2. RR and the disease control rate (DCR) were 8.6% and 71.4%, respectively. The median PFS was 4.5 months (95% CI 3.8-5.2) (Fig. 1) ,ranged from 0.5 to 18 months, and 1 patient was progressive after conversion surgery receiving resurgery presenting 18 months in PFS. The median OS was 12.0 months (95% CI 8.5-15.5), ranged from 0.5 month to not reached (Fig. 2). The median follow-up period was 12 months (ranged 0.5-52). 2 patients were still alive with beyond 24 months survival up date to the last following-up in June-2020.

Discussion
In the present study, our results indicated that the combination of irinotecan and raltitrexed might be an e cient and tolerable second-line regimen for patients with oxaliplatin-refractory mCRC, achieving a median PFS with 4.5 months, a median OS with 12.0 months and ORR with 8.6%, respectively. RIR as an active regimen in gastrointestinal malignancies has been demonstrated in a phase I clinical and pharmacogenetic trial [11]. Other published single-arm studies also considered RIR as a suboptimal e cient schedule at the expense of moderate toxicity for patients with metastatic CRC in rst-or secondline treatment [12][13][14]. Moreover, a randomized phase II study compared RIR with raltitrexed alone as second-line treatment in patients with gemcitabine-pretreated advanced pancreatic adenocarcinoma and also indicated that the combination therapy with superior survival [15]. To our knowledge, there are no available randomized data evaluating the effects of RIR versus FOLFIRI in the second-line setting in patients with oxaliplatin-refractory mCRC. The median PFS and ORR in this study (4.5 months and 8.6%) was comparable or relatively better in comparison to those observed in the randomized GERCOR study (second-line FOLFIRI achieved 4% for ORR and 2.5 months for median PFS) [3] Four patients (11.4%) experienced tumor shrinkage during their protocol treatment and could undergo conversion treatment to NED, which enable them to achieve a better survival. Notably, most patients enrolled in the study with heavy metastatic tumor burden: only 7(20%) patients presented single metastatic site, while 12(34.3%) patients presented multiple metastatic sites(≥ 3). Considering the numbers of metastatic sites and lesions burden, the prognosis of the enrolled patients in our study might be worse than the similar studies of irinotecan-based regimen as second-line therapy, indicating that the e cacy on PFS and ORR in this study were warranted.
Previously, major concerns regarding the safety of irinotecan plus raltitrexed were observed in several phase II studies, although there were no treatment-related deaths, high incidence of grade 3/4 diarrhea and/or neutropenia even regarded this combination as a suboptimal regimen for mCRC [12,14,16] Accordingly, there were scarcely reports to investigate RIR in the subsequent long-term period. To avoid the onset of TAEs caused by RIR, dose-reduced combination administrated biweekly was adopted in our study. The incidence of nausea (80.0%) and fatigue (71.4%), alopecia (65.7%) were shown, the grade 3 treatment-related hematological and nonhematological AEs were under 15%, with 28.6% diarrhea and no grade 3/4 diarrhea.10 patients refused further treatment without PD or unaccepted AEs. However, the gastrointestinal toxicities seemed to be manageable and no grade 4 TAEs was observed. Likewise, in BICC-C trial [17] and EORTC 40015 study [18], grade 3-4 AEs, consisting mainly of gastrointestinal toxicities even treatment-related deaths, occurred more frequently in patients treated with XELIRI than in those treated with FOLFIRI. Therefore, XELIRI regimen has not yet been accepted as a standard therapy in authoritative guidelines [19,20]. Whereas, modi ed XELIRI (relatively dose-reduction) as a well-tolerated and effective treatment for mCRC has been proved in several studies [5,7,21]. The lower dose intensity of irinotecan plus raltitrexed in patients with gemcitabine-pretreated advanced pancreatic adenocarcinoma also exhibited a better tolerability and ease of administration [15]. Thus, further consideration is also needed to determine the optimal dose for this regimen, especially in combined with targeted therapies such as cetuximab or bevacizumab.
In accord with previous reports [22], the high frequent occurrence of expected hepatic toxicity mainly included the reversible, clinically insigni cant increases in transaminases, although severe events (grade 3 or 4) were infrequent. As a result, it was reasonable to give a special attention to the hepatic function of patient before each cycle to prevent the severe hepatic toxicity from happening, especially for patients with heavy metastatic burden in liver. Moreover, in view of uoropyrimidines induced cardiotoxicity [23,24] and hand-foot syndrome (HFS) [25,26], the cardiotoxic safety pro le of raltitrexed in patients with CRC was fully con rmed in a series of studies [27][28][29], since neither cardiotoxic AEs nor HFS was observed in our study, suggesting raltitrexed seemed to have a better toxicity pro le compared to capecitabine or 5-FU, especially because of a lower incidence of HFS and cardiotoxicity. RIR might be an alternative to FOLFIRI and XELIRI for patients with mCRC who were not candidates for uoropyrimidine-based combination therapy. Notably, to extend the duration of RIR chemotherapy as long as possible, it is necessary for clinicians to be alert the incidence of severe adverse effects and maintain the patient's quality of life. The replacement of continuous intravenous 5-FU with raltitrexed could be more convenient, which is a promising method for reducing side effects and supposed to be a feasible schedule administration on an out-patient basis.
However, chemotherapy alone remains major mainstream treatment, especially for patients in developing countries, where targeted agents are not covered by health insurance. RIR was seldom reported in previous studies, thus, the main purpose of this study was to evaluate e cacy and safety of the chemotherapeutic combination and to assess if RIR could be regarded as one of the reference doublet cytotoxic chemotherapy in the second-line setting. It is meaningful to accept RIR as a new treatment for mCRC patients before the combination bevacizumab or cetuximab with RIR in current study. Meanwhile, ulterior exploring the e cacy and toxicity of RIR plus targeted agents is necessary in further investigations.

Study Limitations
This study was the di culty in comparing e cacy and toxicities with the standard second-line regimen such as FOLFIRI, because the present study was a prospective single-arm non-randomized controlled phase II study, moreover, we could not recognize the e cacy and tolerance when without addition standard targeted agents to this combination.

Conclusion
Our study suggests that the combination of irinotecan with raltitrexed is an active and acceptable toxic regimen for second-line treatment of the mCRC. Accordingly, we reckon that it represents an attractive and convenient alternative for the treatment of these patients. A large randomized trial is needed to compare the e cacy and toxicity of this regimen with the standard FOLFIRI with or without targeted agents in patients with mCRC in the future.