[177Lu]Lu-DOTA-ZOL bone pain palliation in patients with skeletal metastases from various cancers: efficacy and safety results

Background [177Lu]Lu-DOTA-ZOL has shown promising results from the dosimetry and preclinical aspects, but data on its role in the clinical efficacy are limited. The objective of this study is to evaluate the efficacy and safety of [177Lu]Lu-DOTA-ZOL as a bone pain palliation agent in patients experiencing pain due to skeletal metastases from various cancers. Methods In total, 40 patients experiencing bone pain due to skeletal metastases were enrolled in this study. The patients were treated with a mean cumulative dose of 2.1 ± 0.6 GBq (1.3–2.7 GBq) [177Lu]Lu-DOTA-ZOL in a median follow-up duration of 10 months (IQR 8–14 months). The primary outcome endpoint was response assessment according to the visual analogue score (VAS). Secondary endpoints included analgesic score (AS), global pain assessment score, Eastern Cooperative Oncology Group Assessment performance status (ECOG), Karnofsky performance status, overall survival, and safety assessment by the National Cancer Institute’s Common Toxicity Criteria V5.0. Results In total, 40 patients (15 males and 25 females) with a mean age of 46.6 ± 15.08 years (range 24–78 years) were treated with either 1 (N = 15) or 2 (N = 25) cycles of [177Lu]Lu-DOTA-ZOL. According to the VAS response assessment criteria, complete, partial, and minimal responses were observed in 11 (27.5%), 20 (50%), and 5 patients (12.5%), respectively with an overall response rate of 90%. Global pain assessment criteria revealed complete, partial, minimal, and no response in 2 (5%), 25 (62.5%), 9 (22.5%), and 4 (10%) patients, respectively. Twenty-eight patients died and the estimated median overall survival was 13 months (95% CI 10–14 months). A significant improvement was observed in the VAS, AS, and ECOG status when compared to baseline. None of the patients experienced grade III/IV haematological, kidney, or hepatotoxicity due to [177Lu]Lu-DOTA-ZOL therapy. Conclusion [177Lu]Lu-DOTA-ZOL shows promising results and is an effective radiopharmaceutical in the treatment of bone pain due to skeletal metastases from various cancers.

immobility, or pathological fractures. At the same time, few patients are even asymptomatic, particularly in the early part of the disease with marrow metastases.
Several algorithms have been evolved over the last 3 decades for the management of metastatic bone pain and SREs [2] in which a range of systemic to locoregional therapies are advocated. The most common approaches in clinical practice are chemotherapy, hormonal therapy, bisphosphonates, monoclonal antibody, namely denosumab and analgesics like non-steroidal anti-inflammatory drugs and opioids, molecules signalling growth factors, antidepressants, and endothelin receptor antagonists. Locoregional therapies are offered only for patients with oligo-metastases, namely, external beam radiotherapy (EBRT). Even though the list seems vast, none of them are curative in practice, with a majority of patients limited to palliative care, and involve a multidisciplinary approach.
Palliative external beam radiotherapy is the most effective way of bone pain management. Studies have revealed that 80-90% of patients receiving EBRT have demonstrated complete or partial pain relief within 10-14 days from initiation of treatment. However, EBRT, as mentioned above, is only limited to the treatment of oligometastases or in a worst-case scenario to hemi-body irradiation [3].
Radionuclide therapy is a systemic form of internal radiotherapy which constitutes an essential option as a routine part of the multidisciplinary treatment approach for decades. Several beta-emitting radiometals have been exploited for this purpose that includes 89 Sr 186 Re, 188 Re, and 153 Sm. All of them have been incorporated into boneseeking phosphonates, except 89 Sr. The 89 Sr is a bivalent cation sharing properties similar to calcium. The same is true for 223 Ra, the most recent radionuclide which has been approved for pain palliation in prostate cancer without visceral metastasis [4], except that it is an alpha emitter. However, the availability and the cost of 223 Ra pose paramount restraints for most of the developing world. In this scenario, beta emitters are still affordable and an acceptable option. Owing to the suitable physical properties and decay characteristics of 177 Lu [t1/2 = 6.73 days Eβmax = 497 keV, Eγ) = 113 keV (6.4%), 208 keV (11%)], it is now widely used in clinical practice. It is either produced via the 176 Lu(n,γ) [5] or the 176 Yb(n,γ) pathway [6].

Materials and methods
The study was conducted at the Department of Nuclear Medicine, AIIMS, New Delhi, India. Skeletal metastases patients suffering from pain were referred from the Pain Clinic, Medical Oncology, and Radiation Oncology departments for [ 177 Lu]Lu-DOTA-ZOL pain palliation treatment. This cohort study involved patients who were treated with [ 177 Lu]Lu-DOTA-ZOL for pain palliation between January 2017 and February 2020.

Eligibility criteria
Eligibility criteria for the [ 177 Lu]Lu-DOTA-ZOL pain palliation treatment included: histologically confirmed breast, prostate, or lung cancers, progressive pain or pain requiring escalation of analgesics, patients with more than one site of pain corresponding to the avid uptake on [ 68 Ga]Ga-DOTA-ZOL PET/CT scan, patients with no prior history of radionuclide pain palliation therapy, Eastern Cooperative Oncology Group (ECOG) performance status ≤ 4, KPS ≥ 50, patient on or with history of prior bisphosphonates, patients with haematological, kidney, and liver function parameters within normal limits which included baseline haemoglobin of < 9 g/dL, platelet counts: < 75,000/μL, leukocyte counts: ≥ 4 × 10 9 /L, serum creatinine: > 1.4 mg/dL, serum bilirubin > 3 mg%, glomerular filtration rate (GFR): < 50 mL/ min per 1.73 m 2 body surface area (BSA). Patients with skeletal-related events involving pathological fractures and cord compression were not included.

[ 177 Lu]Lu-DOTA-ZOL synthesis
The stock solution consisted of 1 mg DOTA-ZOL dissolved in 1 mL ultrapure water to give a concentration of 60 µg/60 µL. The 60 µL of DOTA-ZOL was radiolabelled with [ 177 Lu]LuCl 3 which was obtained from BRIT, India, in sodium ascorbate buffer, pH 4, in 0.01 M supra pure HCl with a specific activity ranging between 370 and 740 GBq/mg. The radiolabelled solution was heated at 95 °C for 30 min. Radiochemical quality control was carried out using the instant thin-layer chromatography method with sodium citrate buffer as the solvent.

Treatment protocol and follow-up [ 177 Lu]Lu-DOTA-ZOL infusion
The patients who fulfilled the eligibility criteria were administered with a fixed dose of 1295 MBq ( [8]. The infusion involved a dilution of [ 177 Lu]Lu-DOTA-ZOL in 10 mL normal saline (0.9%), which was administered intravenously over 5 min, with subsequent flushing of 20 mL normal saline. The entire process was performed on an in-patient basis, and patients were discharged in a few hours of observation if they do not show any adverse reaction to [ 177 Lu]Lu-DOTA-ZOL. Figure 1 shows biodistribution and uptake of [ 177 Lu]Lu-DOTA-ZOL therapy in a patient with skeletal metastases from prostate cancer, while Fig. 2 gives similar data of [ 177 Lu]Lu-DOTA-ZOL therapy in a patient with skeletal metastases from breast cancer.

Follow-up
The treatment was repeated if necessary at 3-monthly intervals. Post-[ 177 Lu]Lu-DOTA-ZOL administration, patients were assessed at 2, 4, 8, and 12 weeks. Patients were assessed for laboratory parameters, and the adverse events were recorded according to the National Cancer Institute for Common Toxicity Criteria version (CTC) 5.0 [28]. The visual analogue score (VAS) [29], global pain assessment score, analgesic score (AS), Karnofsky performance status (KPS) [30,31], and assessment of pain relief were recorded in the patient case files on each visit. Patients were instructed to maintain a diary and document the pain relief parameters such as initiation of pain relief, duration of pain relief, time of increase and/or

Treatment response assessment Primary outcome endpoint
The primary outcome endpoint was response assessment by VAS. According to this criteria, the complete response (CR), partial response (PR), minimal response(MR), and no response (NR) were categorised as > 70% reduction, 40-70% reduction, 20-40% reduction, and < 20% decrease in VAS or increase in pain, respectively [29].

Secondary outcome endpoints
Other clinical response assessment parameters involved analgesic score (AS), Karnofsky performance status (KPS), Eastern Cooperative Oncology Group (ECOG) performance status, global pain assessment, adverse event profile, and overall survival. Analgesic scoring was conducted as per the Urological Group of the European Organization of Research and Treatment of Cancer (EORTC, Protocol 30921). As per EORTC protocol, the analgesic score is the product of two five-point scales (the type of analgesic and the frequency of its administration). A decline in the analgesic score was documented as a response to treatment.
Additionally, global pain response assessment was analysed according to the criteria adopted by Thapa et al. [32] that considered changes in both VAS and analgesic scores (rather than a single parameter). According to the criteria, the present study design considered post-therapy changes in both VAS and analgesic scores on a sliding scale. The global pain assessment criteria are accordingly complete (75% decrease in analgesic score with change in pain score), partial (50-75% decrease in analgesic score with a change in pain score), minimal (25-50% decrease in analgesic score with a change in pain score), or none (no change in pain score or, 25% decrease in the analgesic score). The KPS was scaled from 100 to 0. The ECOG status ranged from 0 to 5. All adverse events were assessed as per the National Cancer Institute's Common Toxicity Criteria (NCI-CTC) version 5.0. The overall survival (OS) was defined as the time from the initiation of [ 177 Lu]Lu-DOTA-ZOL treatment to the time of death. The death could be attributed to any cause or the last telephonic contact.

Statistical analysis
The normality of the data was examined by the D' Agostino-Pearson test. The data were presented as mean standard deviation (SD), median, and/or interquartile range (IQR). Unpaired samples t test (parametric test) or Mann-Whitney U test (nonparametric test) was performed for two independent patient groups. The paired t test (parametric test) or Wilcoxon signed-rank test (nonparametric test) was executed to compare parameters at pre-and post-treatment time points. Kaplan-Meier curves analysis was conducted to calculate the overall survival. MedCalc software was used for statistical analyses. P values ≤ 0.05 were considered significant.

Patients
Forty documented skeletal metastases patients including 15 males and 25 females with a mean age of 46.6 ± 15.08 years (range 24-78 years) were enrolled and treated with [ 177 Lu]Lu-DOTA-ZOL for bone pain palliation therapy. The patients were treated between January 2017 and February 2020 with the median follow-up duration of 10 (IQR 8-14) months.
The baseline demographic profile of the patients, tumour characteristics, previous and ongoing cancer-related treatments, and the analgesics consumed are outlined in Tables 1 and 2. Among the patients treated, breast cancer (23/40, 57.5%) accounted for the maximum number of cases followed by prostate cancer (11/40, 27.5%). The remaining 6 patients had lung cancer (Table 1). Except eight patients with prostate cancer who were on concomitant hormonal therapy, no other patients were on any anti-cancer treatment during the treatment. While 15 (37.5%) patients were on morphine medications at the baseline, the remaining patients (62.5%) were either on atypical opioids, non-morphine opioids, or other NSAIDs. Before being referred to our department for bone pain palliation, all the patients had undergone a minimum of two lines of prior treatment.
The median time for the initiation of pain relief was ≤ 7 days (IQR 6-9 days) (Fig. 3). The median time of sustained response after the last cycle of the [ 177 Lu] Lu-DOTA-ZOL is 3 months (IQR 2-4 months). Only one patient observed the most prolonged duration of sustained response, which was 10 months.

Survival analysis
Among the entire series, 28 patients died during the follow-up. The median survival from treatment was 13 months (95% CI 10-14 months), with a 1-year survival probability of 55.4% (Fig. 4a). On subgroup analysis, in patients with CR, PR, MR, and NR, the median overall survival was 13, 13, 8, and 5 months, respectively (Fig. 4b). Sub-categorical analysis based on the type of cancer revealed patients with breast and prostate cancer to depict a similar median overall survival duration of 13 months, while patients with lung cancer demonstrated a median overall survival of 10 months. However, the logrank test did not prove significant (P 0.1431) (Fig. 5).

Toxicity
The laboratory parameters were tested and analysed for toxicity post-treatment (Table 6). Haematological serious adverse events (SAE) [grade III/IV toxicity] were not observed in any patient despite completing two cycles of [ 177 Lu]Lu-DOTA-ZOL treatment. Though the difference in the haemoglobin levels post-second cycle was significant (P < 0.0001), only two patients in the series experienced grade II anaemia after the [ 177 Lu]Lu-DOTA-ZOL therapy; nadir was around 4 weeks and subsequently recovered (Fig. 6). None of the patients had shown renal toxicity and other side effects like hypercalcemia.

Discussion
Three independent randomised, placebo-controlled trials on zoledronic acid in about 3000 patients demonstrating hormone-resistant metastatic prostate cancer [33], breast cancer [34], have demonstrated a reduction in skeletalrelated events (SREs) and proved it clinically effective. Subsequently, zoledronate received regulatory approval for the prevention of SREs and treating bone metastases. The labelling of zoledronate to beta-and alpha-emitting radionuclides like 177 Lu and 225 Ac, respectively, was a logical development [19,20]. Though EDTMP has been proved effective for bone pain palliation [8], [ 177 Lu]Lu-DOTA-ZOL proves superior to the former agent in certain aspects. In comparison with EDTMP, zoledronate demonstrates higher osteoclastic bone affinity and excellent anti-resorptive  Well, in line with the literature [1], 85% of the patients treated comprised of skeletal metastases from breast and prostate cancer. Interestingly, a significant component of our patients (70%) managed had an ECOG performance state of 3 or 4, and 35% of patients presented with either diffuse or super-scan reflecting the high tumour burden and poor ECOG status, which is a real-life scenario at the clinics. These sets of patients were refractory to the ongoing therapy options, including strong analgesics.
Khawar et al. [21] reported an estimated maximum tolerable dose (MTD) of [ 177 Lu]Lu-DOTA-ZOL to be 3.6-5.0 GBq can be administered based on the 2 Gy bone marrow limit. In the present study, we administered a mean cumulative dose of 2.1 ± 0.6 GBq and ranged 1.3-2.7 GBq over a median of 2 cycles at three-monthly intervals; these administered activities were well within the prescribed limits. According to Khawar et al. [21], if the administered activities do not exceed MTD, the threshold adsorbed doses for the critical organ, namely kidneys, shall be within the predicted limit. Patients who responded from the first cycle of [ 177 Lu]Lu-DOTA-ZOL were counselled or self-consented for the second cycle, while patients who were not willing to undergo the next cycle of treatment or those who did not experience any relief in pain after the first cycle of [ 177 Lu]Lu-DOTA-ZOL were not treated further. Another interesting find observed was that those patients who experienced minimal response from the 1st cycle of [ 177 Lu]Lu-DOTA-ZOL treatment when re-challenged with the 2nd cycle did not encounter further reduction in the pain.
The current study reports an ORR of 90%, which is well within the range of response rate with other bone-seeking pain palliating agent [ 177 Lu]Lu-EDTMP ranging between 83 and 86% [8,9]. Interestingly, pain relief was initiated within ≤ 7 days after the [ 177 Lu] Lu-DOTA-ZOL treatment and lasted up to 10 months. In a previous study using [ 177 Lu]Lu-EDTMP, we had reported response durations that varied from 2 weeks to 4 months from the onset of pain relief [8]. Detailed analysis revealed a similar ORR of 82% in prostate cancer patients when compared to the historic [ 177 Lu] Lu-EDTMP study (ORR 84%) [8]. However, a remarkably high ORR of 100% was observed in the breast cancer cohort of the present study in contrast to 92% in the historic [ 177 Lu]Lu-EDTMP study [8]. Though data regarding the response pattern in bone metastases from lung cancer are limited, Ye et al. [35] reported a treatment efficacy rate of 75.4% in the lung cancer group, but with 2.22 MBq/kg 89 SrCl 2 . In agreement with our results, they reported efficacy was lower in patients with bone metastases from the lung cancer sub-group than in those with bone metastasis from breast and prostate cancer [35].
The 1-year survival rate was 55.4% and was significantly higher when compared to that of the [ 177 Lu]Lu-EDTMP historical data set [35% and 38% in the two-level dose group] [8], but drastically dropped to 26% at 13 months. This drop of overall survival is not clearly understood; however, it could be attributed to the aggressive biology of the tumour and the extent of spread. Among the cancer types, similar overall survival was noted in patients with breast and prostate cancer (13 months) and a slightly decreased survival in bone metastases patients with primary lung cancer. Attributed to the superior radiobiological properties of the alpha emitter, radium-223 chloride, Parker et al. [4] in their RCT, involving 921 patients with bone metastases from prostate cancer, outlined an OS of 14.9 months. Nilsson et al. [36] performed a survival follow-up of the phase-II RCT in which bone metastases patients from prostate cancer were treated with radium-223 chloride, and their study findings suggested a survival benefit of 65 weeks versus 46 weeks in patients treated with a single dose of radium-223 chloride and placebo group, respectively.
Analgesic consumption was recorded according to the analgesic scoring of EORTC protocol. Among our recruited patients, 15 patients were on opioid analgesic morphine before radionuclide therapy out of whom 12 responded to [ 177 Lu]Lu-DOTA-ZOL treatment and thus were weaned off morphine. It is these set of patients whom the pain palliation was most beneficial as they have exhausted the available pain relief options. Interestingly, reassuring results were obtained with [ 177 Lu] Lu-DOTA-ZOL in patients demonstrating extensive skeletal metastases and those presenting with superscan or diffuse involvement of the bone. The relief in pain was also reflected in their KPS and ECOG performance status. Toxicity related to [ 177 Lu]Lu-DOTA-ZOL therapy was minimal, and no grade III/IV toxicities were documents.

Limitations
The significant limitations of this cohort study are the non-randomised study, and no parallel arm was used. Although the results of [ 177 Lu]Lu-DOTA-ZOL were comparable to historical data of [ 177 Lu]Lu-EDTMP, a randomised control trial to compare the efficacy and safety of two bone-seeking palliative agents is urgently desired to take this agent further.

Conclusion
[ 177 Lu]Lu-DOTA-ZOL is safe, effective, and an ideal agent in the treatment of metastatic bone pain. Thanks to its characteristics as theranostics, it allows for patientindividual therapies and perfectly matches the expectations for precision oncology. Interestingly, [ 177 Lu] Lu-DOTA-ZOL is not only effective in addressing bone metastases derived from breast cancer; it shows clear evidence also for prostate and lung cancers. [ 177 Lu] Lu-DOTA-ZOL pain palliation treatment demonstrated an ORR of 90% with 27.5% of complete response and 50% of partial response.