Efficacy and Safety of Ifosfamide and Mesna in Metastatic Castration-Resistant Prostate Cancer after Taxane-Based Chemotherapy and Novel Hormonal Therapy Failure

Abstract

Purpose

Limited treatment options exist for patients with metastatic castration-resistant prostate cancer (mCRPC) after the failure of taxane-based chemotherapy and novel hormonal therapy. Here, we report the safety and efficacy of ifosfamide and mesna in patients with mCRPC after the failure of taxane-based chemotherapy and novel hormonal therapy (NCT06236789).

Materials and Methods

Patients with histologically confirmed prostate cancer who had failed taxane-based chemotherapy and novel hormonal therapy received ifosfamide 2,500 mg/m² and mesna 1,500 mg/m² on days 1–3, repeated every 21 days. Safety, objective response rate, disease control rate, reduction in serum prostate-specific antigen (PSA) concentration by >50% (PSA₅₀) or >90% (PSA₉₀), radiographic progression-free survival (rPFS), and overall survival (OS) were analyzed.

Results

A total of 47 patients with mCRPC were included in the study. The median number of lines of treatment was 5 (range, 3 to 7). All patients were previously administered docetaxel and novel hormonal therapies including abiraterone (51.1%) and/or enzalutamide (61.7%). Thirty-eight patients (80.9%) were administered cabazitaxel. The objective response and disease control rates were 21.3% and 80.9%, respectively. PSA₅₀ and PSA₉₀ were achieved in 31.9% and 10.6%, respectively. During a median follow-up duration of 54.3 months, rPFS and OS were 5.0 and 9.0 months, respectively. All the patients experienced treatment-related adverse events of any grades; however, no new safety signs were detected. Genomic biomarker analysis revealed that alterations in the TP53 pathway were associated with inferior rPFS and OS.

Conclusion

Ifosfamide and mesna showed appreciable efficacy and manageable safety profiles in heavily treated patients with mCRPC.

Introduction

Prostate cancer is the most frequently diagnosed cancer in males in the United States and the fifth leading cause of cancer mortality in men worldwide [1,2]. Androgen deprivation therapy, with or without androgen receptor pathway inhibitors, improves survival and symptoms for patients with metastatic prostate cancer, however patients almost always develop a progressive form of the disease, namely metastatic castration-resistant prostate cancer (mCRPC) [3]. Despite advancements in therapeutics targeting prostate cancer biology, mCRPC continues to have a poor prognosis [4]. Taxane-based chemotherapy regimens, as well as several novel therapies, including novel hormonal agents such as abiraterone and enzalutamide, prostate-specific membrane antigen (PSMA) radioligand therapy, and poly(ADP-ribose) polymerase (PARP) inhibitors in subsets of patients with mCRPC are available [5]. However, the long-term prognosis for patients with mCRPC remains poor, and the majority of men with mCRPC eventually die from the disease, particularly those who failed to docetaxel and/or cabazitaxel [6]. For patients with mCRPC after failure with taxane-based chemotherapy, treatment options are limited. Although mitoxantrone is often administered due to its favorable effects on quality of life [7,8], few interventions have improved survival rates [9,10]. Recently, radioligand therapy including lutetium-177–PSMA-617 and radium-223, PARP inhibitors including olaparib, talazoparib, niraparib, and rucaparib have been approved by the U.S. Food and Drug Administration [11]. However, their accessibility remains limited due to regulatory approval, reimbursement challenges, and infrastructure in many regions.

Ifosfamide is an oxazaphosphorine agent. In a previous phase II trial, ifosfamide 1,500 mg/m² for 5 days every 21 days combined with mesna resulted in an objective response in 6.9% (2/29) of patients with mCRPC [12]. In another dose-finding study comparing continuous and fractionated ifosfamide infusion, a prostate-specific antigen (PSA) response was achieved in 31.0% (9/29) of patients with mCRPC [13]. However, the clinical implications of ifosfamide combined with mesna have not been investigated for contemporary heavily-treated mCRPC, prompting us to conduct a registration study in patients exposed to taxane-based chemotherapy and novel hormonal therapy to evaluate the safety and efficacy of ifosfamide combined with mesna (NCT06236789). Additionally, we used next-generation sequencing (NGS) to investigate the genomic landscape and predict the therapeutic benefits of ifosfamide combined with mesna in patients with mCRPC.

Materials and Methods

1. Study population

Eligible patients had histologically confirmed prostate cancer that had progressed following taxane-based chemotherapy. For patients who did not undergo bilateral orchiectomy, ongoing androgen deprivation with a luteinizing hormone–releasing hormone agonist was used. Pretreatment evaluation included a medical history, physical examination, complete blood count, chemistry profile, and serum PSA and alkaline phosphatase measurements. Computed tomography, magnetic resonance imaging, and bone scans were used for response evaluation. Other inclusion criteria included an Eastern Cooperative Oncology Group (ECOG) performance status (PS) score of 0-2, measurable lesions based on Response Evaluation Criteria in Solid Tumor (RECIST) ver. 1.1 criteria, and available serum PSA levels. Patients who had other primary cancers diagnosed within 3 years, history of organ transplantation, poor PS (ECOG PS ≥ 3), previous exposure to ifosfamide, did not have a baseline PSA level, or did not have a measurable lesion based on RECIST ver. 1.1 criteria were not enrolled. All patients were administered novel hormone therapy with either enzalutamide or abiraterone based on contemporary guidelines [14-16].

The study adhered to the principles of the Guidelines for Good Clinical Practice and the Declaration of Helsinki. The study protocol was reviewed and approved by the institutional review boards of the participating institutions. All the patients provided written informed consent for chemotherapy.

2. Endpoints

This study is retrospective cohort study. The primary endpoint of this study was objective response rate (ORR) as it provides a rapid and direct measure of antitumor activity that is less affected by post-treatment factors. Key secondary endpoints include safety, radiographic progression-free survival (rPFS), and overall survival (OS).

3. Hypothesis

In a randomized phase 3 trial comparing cabazitaxel and mitoxantrone for patients with mCRPC, the ORR of mitoxantrone was 4.4% [17]. Based on this result, the null hypothesis (ORR ≤ 5%) and alternative hypothesis (ORR ≥ 20%) were tested with 1-sided significance level of 5% and a power of 90%. This assumption required the target accrual of 39 patients. Considering a dropout rate of 10%, a minimum of 44 patients was required for efficacy analysis.

4. Treatment regimen

The patients received ifosfamide 2,500 mg/m² and mesna 1,500 mg/m² on days 1-3, repeated every 21 days. Doses were reduced or delayed in certain patients depending on the physician’s discretion or toxicity. Intrapatient dose escalation was not attempted. Treatment was continued until any of the following occurred: radiographic progression, an intercurrent illness that prevented additional treatment, unacceptable adverse event(s), general or specific changes in the patient’s condition that rendered additional treatment unacceptable (as judged by the investigator), or withdrawal of patient consent for treatment. Treatment beyond radiographic progression was not permitted. This regimen has not been covered by Korean national health insurance system.

5. Evaluation

Using RECIST ver. 1.1, the treatment response was categorized as complete response (CR), partial response (PR), stable disease (SD), or progressive disease. The ORR was defined as the summation of CR and PR. Disease control rate (DCR) was defined as the sum of CR, PR, and SD. PSA responses PSA₅₀ and PSA₉₀ were defined as a reduction in serum PSA concentration by > 50% and > 90%, respectively. rPFS was defined as the time between the start of treatment and the first date of progression or death.

Adverse events were evaluated and graded according to the Common Terminology Criteria for Adverse Events ver. 5.0. Laboratory assessments, including hematology and chemistry, and non-laboratory assessments, including physical examinations and review of system, were performed before starting chemotherapy, throughout the study, and at follow-up. Adverse events were monitored from the start of ifosfamide treatment to 28 days after discontinuation.

6. Next-generation sequencing

Tumor samples were collected before initiating ifosfamide and mesna treatment. If the tumor content of the sample was estimated to be ≥ 40% on pathological examination, targeted DNA and RNA sequencing were performed using TruSight Oncology 500 (Illumina). DNA and RNA (40 ng) were extracted from formalin-fixed, paraffin-embedded (FFPE) tissues using a Qiagen All Prep DNA/RNA FFPE kit (Qiagen), and libraries were prepared according to the manufacturer’s instructions. After hybridization capture-based target enrichment, pair-ended sequencing (2×101 bp) was performed using a NextSeq 550 Dx sequencer (Illumina) according to the manufacturer’s instructions. Genetic alterations were analyzed as described previously [18].

7. Statistical analysis

Categorical and continuous variables were compared using Fisher’s exact test and the Wilcoxon rank-sum test, respectively. rPFS and OS were defined based on the time from the initiation of treatment until evidence of radiographic progression based on RECIST ver. 1.1 or death from any cause. Survival was plotted using Kaplan-Meier curves and compared using the log-rank test. The Cox proportional hazards model was used to assess the significant variables associated with rPFS and OS, including hazard ratios and 95% confidence intervals (CI). The censoring date was January 28, 2024. Statistical analyses were performed using SPSS ver. 26 (IBM Corp.) and GraphPad Prism ver. 6 (GraphPad Software).

Results

1. Patients and treatment characteristics

Between November 2016 and May 2023, 47 patients with mCRPC treated with ifosfamide and mesna after the failure of taxane-based chemotherapy and novel hormonal therapy were enrolled and analyzed. The baseline patient characteristics are shown in Table 1. The median number of lines of systemic treatment was 5 (range, 3 to 7). All patients were administered docetaxel, and 80.9% (38/47) were administered cabazitaxel. All patients received prior treatment with second-generation hormone therapies, including abiraterone (51.1%) or enzalutamide (61.7%). Thirty-six patients (76.6%) had visceral disease or measurable extrapelvic lymphadenopathy, including 28 (59.6%) with measurable visceral disease and 29 (61.7%) with measurable extrapelvic lymphadenopathy.

Table 1.

Baseline characteristics of patients

	No. (%) (n=47)
Age (yr), median (range)	69 (35-80)
ECOG PS
0	11 (23.4)
1	25 (53.2)
2	11 (23.4)
Metastatic sites
Bone	44 (93.6)
Lymph node	29 (61.7)
Lung	18 (38.3)
Liver	11 (23.4)
Brain	2 (4.3)
Peritoneum	1 (2.1)
Adrenal gland	1 (2.1)
Line of systemic treatment
3	1 (2.1)
4	7 (14.9)
5	32 (68.1)
6	5 (10.6)
7	2 (4.3)
Previous systemic treatment
Docetaxel	47 (100)
Cabazitaxel	38 (80.9)
Abiraterone	24 (51.1)
Enzalutamide	29 (61.7)
Mitoxantrone	6 (12.8)
Previous local treatment to prostate
Surgical resection	19 (40.4)
Radiotherapy	13 (27.7)

ECOG PS, Eastern Cooperative Oncology Group performance score.

At the time of data cutoff, one patient remained on the study treatment. In total, 46 patients (97.9%) discontinued the treatment. The primary reason for discontinuation was radiographic progression (80.4%), followed by patient refusal of further treatment due to adverse events (19.6%).

2. Efficacy and survival outcomes

At the data cutoff, 10 of the 47 patients with measurable disease achieved an investigator-assessed objective response based on RECIST ver. 1.1 (Fig. 1A), resulting in an ORR of 21.3% (95% CI, 9.1 to 33.4). DCR was 80.9% (95% CI, 69.2 to 92.5). PSA₅₀ and PSA₉₀ responses were achieved in 31.9% (95% CI, 18.1 to 45.7) and 10.6% (95% CI, 1.4 to 19.8) of the patients, respectively (Fig. 1B). Radiological and PSA responses showed a significant correlation (R=0.5847, p < 0.001).

Fig. 1.

Radiologic and prostate-specific antigen (PSA) responses. (A) Waterfall plot displaying the best percentage change from baseline in sum of target lesion diameters. (B) Waterfall plot displaying the best percentage change from baseline in prostate-specific antigen level. DCR, disease control rate; ORR, objective response rate

At the data cutoff point, the median follow-up duration was 54.3 months (95% CI, 24.2 to 84.5). Forty-six patients (97.9%) experienced radiographic progression upon treatment, and 40 patients (85.1%) died. The median rPFS for all treated patients was 5.0 months (95% CI, 2.8 to 7.3) (Fig. 2A). Median OS was 9.0 months (95% CI, 7.7 to 10.3), with 12-month OS rates of 31.3% (Fig. 2B).

Fig. 2.

Survival outcomes. (A) Kaplan-Meier plot of progression-free survival (PFS) of patients. (B) Kaplan-Meier plot of overall survival (OS) of patients. CI, confidence interval.

3. Safety

All patients experienced treatment-related adverse events of any grades (Table 2). The most commonly observed adverse events were anemia (n=47, 100.0%), lymphocyte count decreased (n=45, 95.7%), white blood cell count decreased (n=35, 74.5%), anorexia (n=32, 68.1%), and platelet count decreased (n=32, 68.1%). Thirty-five patients (74.5%) experienced at least one grade 3 or 4 toxicity event, including lymphocyte count decreased (n=29, 61.7%), anemia (n=23, 48.9%), and white blood cell count decreased (n=19, 40.4%). Grade 3 febrile neutropenia occurred in one patient (2.1%). There were no treatment-related deaths.

Table 2.

Summary of treatment-related adverse events

	Grade				Overall	Grade 3-4
	1	2	3	4
Hemoglobin decreased	14	10	23	0	47 (100)	23 (48.9)
Lymphocyte decreased	5	11	22	7	45 (95.7)	29 (61.7)
WBC decreased	5	11	14	5	35 (74.5)	19 (40.4)
Anorexia	6	26	0	0	32 (68.1)	0
PLT decreased	15	8	6	3	32 (68.1)	9 (19.1)
AST increased	22	4	5	0	31 (66.0)	5 (10.6)
Neutrophil decreased	3	11	8	7	29 (61.7)	15 (31.9)
Constipation	17	11	0	0	28 (59.6)	0
Nausea	10	14	0	0	24 (51.1)	0
Gastritis	10	5	0	0	15 (31.9)	0
Peripheral neuropathy	8	7	0	0	15 (31.9)	0
Dyspepsia	7	5	0	0	12 (25.5)	0
ALT increased	9	1	0	0	10 (21.3)	0
Diarrhea	5	2	0	0	7 (14.9)	0
Insomnia	5	2	0	0	7 (14.9)	0
Mucositis oral	5	0	0	0	5 (10.6)	0
Adrenal insufficiency	1	3	0	0	4 (8.5)	0
Hyperkalemia	2	0	0	0	2 (4.3)	0
Febrile neutropenia	0	0	1	0	1 (2.1)	1 (2.1)
Cough	1	0	0	0	1 (2.1)	0
Laryngeal hemorrhage	1	0	0	0	1 (2.1)	0
Pruritus	1	0	0	0	1 (2.1)	0

Values are presented as number (%). ALT, alanine transaminase; AST, aspartate transaminase; PLT, platelet; WBC, white blood cell.

4. NGS-based exploratory biomarker analysis

Seventeen patients (36.2%) underwent targeted DNA and RNA sequencing, and their baseline characteristics, except for age, did not significantly differ from those of patients who did not undergo NGS (S1 Table). Importantly, the survival outcomes were similar between patients with and without available NGS data (p=0.983 for rPFS and p=0.295 for OS, respectively). Samples for NGS testing were mainly obtained at the diagnosis of hormone-sensitive prostate cancer (14/17, 82.4%) and nearly half of them were obtained during surgical resection (8/17, 47.1%). Mutations in TP53 were the most frequently observed genetic alterations (7/17, 41.1%) (Fig. 3A). TMPRSS2::ERG fusion was observed in five patients (29.4%). Splicing variants in the androgen receptor co-occurred with amplification in three patients (17.6%). Among the 11 genes altered in more than three patients, no single genetic alteration was commonly associated with the rPFS and OS of the ifosfamide and mesna groups (Fig. 3B). In the analysis of oncogenic signaling pathways (Fig. 3C) [19], alterations in the TP53 pathway were significantly associated with worse rPFS and OS in patients treated with ifosfamide and mesna (Fig. 3D-F). However, alterations in the TP53 pathway (TP53, MDM2/4, and ATM) were not associated with OS in patients from The Cancer Genome Atlas cohort (S2 Fig.) [20].

Fig. 3.

Correlation of genetic alteration with outcomes to treatment. (A) Oncoplot showing the pathogenic alterations encompassing mutation, copy number alteration, fusion, and splicing variants. (B) The corresponding statistics for survival among patients treated with ifosfamide and mesna combination therapy with alterations in a single gene. (C) Curated pathways for genetic alterations. (D) The corresponding statistics for survival among patients treated with ifosfamide and mesna combination therapy with alterations in oncogenic signaling pathways. (E) Kaplan-Meier plot of the progression-free survival (PFS) of patients according to the presence of alterations in TP53 pathway. (F) Kaplan-Meier plot of overall survival (OS) of patients according to the presence of alterations in the TP53 pathway. CI, confidence interval; HR, hazard ratio.

Discussion

In this registration study, ifosfamide combined with mesna demonstrated clinical activity and an acceptable safety profile in patients with mCRPC who progressed to taxane-based chemotherapy and novel hormonal therapy. The ORR, DCR, PSA₅₀ and PSA₉₀ responses, median rPFS, and median OS were 21.3%, 80.9%, 31.9%, 10.6%, 5.0 months, and 9.0 months, respectively. The outcomes reported here are encouraging, considering that the study population in this registration study encompassed heavily treated patients who failed taxane and novel hormonal therapies.

Currently, several agents, including cabazitaxel, radioligand therapy, and mitoxantrone, can be administered to patients with mCRPC who progress to docetaxel and novel hormonal therapy [17,21,22]. In particular, there are few treatment options for patients with mCRPC who progress to cabazitaxel. All patients enrolled in this study experienced failure of previous docetaxel treatment, and 80.9% experienced failure of previous cabazitaxel treatment. The safety profile of ifosfamide and mesna in this study was as expected, with no newly emerging treatment-related adverse events, and the rate of discontinuation due to treatment-related adverse events was less than 20%, consistent with other malignancies [23,24]. Moreover, no treatment-related deaths were documented in this study. A recent phase 3 study of cabozantinib plus atezolizumab compared to novel hormonal therapy in patients with mCRPC (CONTACT-2; NCT04446117) demonstrated an rPFS of 6.3 months for patients enrolled in the experimental arm, comparable to the rPFS in this study [25], although target population was different between two studies.

Hence, ifosfamide and mesna can be suggested as salvage treatment options for patients with heavily treated mCRPC, warranting further randomized investigation.

In this study, we performed a correlative biomarker study using NGS in 17 patients. Although a single genetic alteration is not sufficient to predict treatment outcomes, oncogenic signaling pathway analysis can predict the therapeutic benefits of ifosfamide and mesna. Among the 10 relevant pathways, alterations in the TP53 pathway were observed in nine patients (52.9%), including seven patients with TP53 mutations, two patients with ATM mutations, two patients with MDM2 amplification, and one patient with MDM4 amplification. Additionally, alterations in the TP53 pathway were significantly associated with rPFS (median rPFS, 9.7 vs. 1.8 months in patients without and with TP53 pathway alterations) and OS (median OS, 21.2 vs. 5.0 months in patients without and with TP53 pathway alterations). Previous studies have suggested that TP53-based molecular mechanisms can induce resistance to chemotherapy [26,27]. Consistently, our study revealed that alterations in the TP53 pathway were associated with worse outcomes in patients treated with ifosfamide and mesna. Collectively, exploratory biomarker analysis using NGS revealed a genetically defined subgroup of patients who derived more benefits from ifosfamide combined with mesna, suggesting future strategies to enrich patients with favorable treatment outcomes.

In conclusion, ifosfamide plus mesna showed antitumor activity and tolerability in patients with mCRPC who progressed to previous taxane-based chemotherapy and novel hormonal therapy. These data support the rationale for further evaluation of this combination therapy in patients with refractory mCRPC. Future large-scale studies would provide data regarding the safety and efficacy of this regimen in, as the current study is limited by small sample size and exploratory biomarker. Further evaluation of optimal combination partners also has potential to provide relevant data for the development of effective strategies for the treatment of patients with heavily treated mCRPC.

Electronic Supplementary Material

Supplementary materials are available at Cancer Research and Treatment website (https://www.e-crt.org).