Radiopeptides for Targeted Tumour Therapy and the Kidney

One of the main causes of morbidity and mortality in the modern world is cancer. According to World Health Organization (WHO) reports the worldwide mortality rate due to malignant neoplasms is 12.5%, but in the Western world this is about 30% in the 45-75 year age group. In The Netherlands the prevalence of different types of cancer varies between sexes; amongst men prostate cancer (21%) and

The monoclonal antibody ER-BMDM1 recognizes a macrophage and dendritic cell differentiation antigen with aminopeptidase activity

Abstract Here we describe the reactivity of monoclonal antibody (mAb) ER-BMDM1, directed against a 160-kDa cell membrane-associated antigen (Ag) with aminopeptidase activity. The aminopeptidase recognized by ER-BMDM1 is present on various mouse macrophage (MΦ) and dendritic cell (DC) subpopulations as well as on microvillous epithelia. Analysis of ER-BMDM1 Ag expression in in vitro models of MΦ maturation revealed that the Ag is expressed at increasing levels upon maturation of MΦ. In vivo, high level expression of the ER-BMDM1 Ag occurs after thmonocytic stage of maturation, since bone marrow cells and peripheral blood monocytes are essentially ER-BMDM1 negative. Analysis of isolated-resident and elicited MΦ populations showed that ER-BMDM1 recognizes a specific subpopulation of mature MΦ: only some resident peritoneal and alveolar MΦ are ER-BMDM1 positive, whereas virtually all thioglycollate-elicited peritoneal exudate MΦ bind the mAb. In lymphoid organs, a subpopulation of MΦ is recognized as well as interdigitating cells (IDC) located in T cell areas. Phenotypic analysis of isolated DC- the in vitro equivalents of IDC - from spleen and lymph nodes confirmed that the majority of this important antigen-presenting cell population expresses the ER-BMDM1 aminopeptidase. The molecular characteristics of the ER-BMDM1 Ag suggest that it may represent the mouse homolog of human CD13

Differential inhibition of macrophage proliferation by anti-transferrin receptor antibody ER-MP21: correlation to macrophage differentiation stage

Abstract Monoclonal antibodies (mAbs) directed against the transferrin receptor are known to inhibit proliferation of cells due to iron deprivation. Some cell types, however, escape from growth inhibition by a mechanism which is unclear at present. This mechanism is the subject of the present study. We investigated the differential growth inhibition caused by anti-transferrin receptor mAb ER-MP21 in connection with the differentiation of murine macrophages (Mφ). Therefore, we applied two models of Mφ differentiation, namely, culture of bone marrow cells in the presence of M-CSF and a panel of Mφ cell lines ordered in a linear differentiation sequence. In both models we observed that proliferation of Mφ precursors was strongly inhibited by ER-MP21. In contrast, proliferation of more mature stages of Mφ differentiation was hardly affected. Remarkably, iron uptake by Mφ precursor and mature Mφ cell lines was inhibited by ER-MP21 to the same extent. However, mature Mφ cell lines showed an iron uptake two-to threefold higher than that of Mφ precursor cell lines. These observations strongly suggest that mature Mφ escape from ER-MP21-mediated growth inhibition, because these cells take up more iron than is actually needed for proliferation. Furthermore, we found that enhanced iron uptake by mature Mφ is not necessarily accompanied by a higher cell surface expression of transferrin receptors, thus suggesting an increased recycling of transferrin receptors in mature Mφ

Optimization of combined temozolomide and peptide receptor radionuclide therapy (PRRT) in mice after multimodality molecular imaging studies

Background: Successful treatments of patients with somatostatin receptor (SSTR)-overexpressing neuroendocrine tumours (NET) comprise somatostatin-analogue lutetium-177-labelled octreotate (177Lu-TATE) treatment, also referred to as peptide receptor radionuclide therapy (PRRT), and temozolomide (TMZ) treatment. Their combination might result in additive effects. Using MRI and SPECT/CT, we studied tumour characteristics and therapeutic responses after different (combined) administration schemes in a murine tumour model in order to identify the optimal treatment schedule for PRRT plus TMZ. Methods: We performed molecular imaging studies in mice bearing SSTR-expressing H69 (humane small cell lung cancer) tumours after single intravenous (i.v.) administration of 30 MBq 177Lu-TATE or

Therapeutic application of CCK2R-targeting PP-F11: influence of particle range, activity and peptide amount

Background: Targeted radionuclide therapy with high-energy beta-emitters is generally considered suboptimal to cure small tumours (90Y, 177Lu or 213Bi, accounting for the radionuclide specific activities (SAs), the tumour absorbed doses and tumour (radio) biology. Methods: Tumour uptake of 111In-PP-F11 was determined in nude mice bearing CCK2 receptor-transfected A431 xenografts at 1 and 4 h post-injection for escalating peptide masses of 0.03 to 15 nmol/mouse. The absorbed tumour dose was estimated, assuming comparable biodistributions of the 90Y, 177Lu or 213Bi radiolabelled peptides. The linear-quadratic (LQ) model was used to calculate the tumour control probabilities (TCP) as a function of tumour mass and growth. Results: Practically achievable maximum SAs for PP-F11 labelled with 90Y and 177Lu were 400 MBq 90Y/nmol and 120 MBq177Lu/nmol. Both the large elution volume from the 220 MBq 225Ac generator used and reaction kinetics diminished the maximum achieved 213Bi SA in practice: 40 MBq 213Bi/nmol. Tumour uptakes decreased rapidly with increasing peptide amounts, following a logarithmic curve with ED50 = 0.5 nmol. At 0.03 nmol peptide, the (300 mg) tumour dose was 9 Gy after 12 MBq 90Y-PP-F11, and for 111In and 177Lu, this was 1 Gy. A curative dose of 60 Gy could be achieved with a single administration of 111 MBq 90Y labelled to 0.28 nmol PP-F11 or with 4 × 17 MBq 213Bi (0.41 nmol) when its α-radiation relative biological effectiveness (RBE) was assumed to be 3.4. Repeated dosing is preferable to avoid complete tumour receptor saturation. Tumours larger than 200 mg are curable with 90Y-PP-F11; the other radionuclides perform better in smaller tumours. Furthermore, 177Lu is not optimal for curing fast-growing tumours. Conclusions: Receptor saturation, specific radiopharmaceutical activities and absorbed doses in the tumour together favour therapy with the CCK2 receptor-binding peptide PP-F11 labelled with 90Y, despite its longer β-particle range in tissue, certainly for tumours larger than 300 mg. The predicted TCPs are of theoretical nature and need to be compared with the outcome of targeted radionuclide experiments

Peptide receptor radionuclide therapy (PRRT) with [177Lu-DOTA0,Tyr3]octreotate in combination with RAD001 treatment: further investigations on tumor metastasis and response in the rat pancreatic CA20948 tumor model

Background Previously, we reported on the unexpected development of distant metastases in the subcutaneous rat pancreas CA20948 tumor model after 4.5 weeks of treatment with RAD001-only or in combination with [177Lu-DOTA0,Tyr3]octreotate (177Lu-DOTATATE) (Cancer Res. 73:12-8, 2013). Moreover, the combination therapy was less effective compared to 177Lu-DOTATATE-only. In the current study, we address the following questions: (1) Why was the combination therapy less effective? Is 177Lu-DOTATATE tumor uptake affected by pretreatment with RAD001? (2) Could sudden cessation of RAD001 therapy cause the development of distant metastases? (3) Is 177Lu-DOTATATE an effective treatment option for these metastases? Methods Lewis rats (HanHsd or SsNHsd substrain with a slight difference in immune response) bearing subcutaneous CA20948 tumors were treated with either 125 or 275 MBq 177Lu-DOTATATE, RAD001, or their combination. RAD001 was given twice a week for 4.5 or 12 weeks, whereas 177Lu-DOTATATE was given as a single injection. When combined, RAD001 was started either 3 days prior to or 3 days post administration of 177Lu-DOTATATE. SPECT/CT was performed to quantify 177Lu-DOTATATE tumor uptake. Where indicated, primary tumors were surgically removed when tumor size is >6,000 mm3 to enable monitoring for possible metastasis. If metastases were suspected, an 111In-DTPA-octreotide SPECT/CT scan was performed. Seven rats with metastases were treated with 400 MBq 177Lu-DOTATATE. Results Lu-DOTATATE tumor uptake was not significantly affected by RAD001 pretreatment. The occurrence of metastases after RAD001 treatment was not dose dependent in the dose range tested, nor was it related to the duration of RAD001 treatment. In the experiment in which the LEW/SsNsd substrain was used, only 12.5% of RAD001-treated rats showed complete response (CR), compared to 50% tumor regression in the control group. Re-treatment with a high dose of 177Lu-DOTATATE resulted in CR in only two out of seven animals. Conclusion Less effective anti-tumor effects after the combination of RAD001 + 177Lu-DOTATATE could not be explained by reduced 177Lu-DOTATATE tumor uptake after RAD001. Our current data support RAD001-induced immune suppression as the reason for this observation. No evidence was found that cessation of RAD001 treatment caused development of metastases. Metastases appeared to be less sensitive to 177Lu-DOTATATE treatment than primary tumors

Peptide receptor radionuclide therapy using radiolabeled somatostatin analogs: Focus on future developments

Peptide receptor radionuclide therapy (PRRT) has been shown to be an effective treatment for neuroendocrine tumors (NETs) if curative surgery is not an option. A majority of NETs abundantly express somatostatin receptors. Consequently, following administration of somatostatin (SST) analogs labeled with γ-emitting radionuclides, these tumors can be imaged for diagnosis, staging or follow-up purposes. Furthermore, when β-emitting radionuclides are used, radiolabeled peptides (radiopeptides) can also be used for the treatment for NET patients. Even though excellent results have been achieved with PRRT, complete responses are still rare, which means that there is room for improvement. In this review, we highlight some of the directions currently under investigation in pilot clinical studies or in preclinical development to achieve this goal. Although randomized clinical trials are still lacking, early studies have shown that tumor response might be improved by a

Reduction of renal uptake of radiolabeled octreotate by amifostine coadministration

Megalin-mediated renal retention of radiolabeled somatostatin analogs may lead to nephrotoxicity during peptide receptor radionuclide therapy (PRRT). The cytoprotective agent amifostine protected rats from long-term nephrotoxicity after PRRT with 177Lu-DOTA,Tyr3-octreotate. This study describes the direct effect of amifostine on kidney and tumor uptake of 111In- DOTA,Tyr3-octreotate. Methods: In vivo biodistribution studies were performed using CA20948 tumor-bearing rats, with or without amifostine coadministration, via several routes. In vitro uptake was studied in somatostatin receptor-expressing CA20948 and megalin or cubilin receptor-expressing BN-16 cells, in the absence or presence of amifostine or its active metabolite WR-1065. Results: Coadministration of amifostine decreased renal uptake of radiolabeled octreotate in vivo, whereas tumor uptake was not affected. In agreement, amifostine and WR-1065 coincubation reduced uptake in BN-16 but not in CA20948 cells. Conclusion: Amifostine may provide renal protection during PRRT using somatostatin analogs, both by mitigation of radiation damage and the currently observed reduction of absorbed kidney radiation dose. Copyrigh

Heterogeneity in a mouse model of histiocytosis: Transformation of Langerin+ dendritic cells, macrophages, and precursors

Neoplastic diseases of macrophages (Mφ) and dendritic cells (DC), collectively called histiocytoses, are relatively rare. The etiology of most forms of histiocytosis is poorly understood, and the development of animal models is crucial for further research in this field. Previously, an animal model for malignant histiocytosis (MH), involving transformed histiocytic cells, has been generated by infecting mice with malignant histiocytosis sarcoma virus (MHSV). However, increased insight into the heterogeneity of Mφ and DC, and the associated reappraisal of human proliferative diseases involving these cells inspired us to re-evaluate the mouse model. We analyzed spleen, bone marrow, and lymph nodes of susceptible mice at various time points after infection. From day 11 onwards, a heterogeneous population of cells, consisting of CD8α+ Langerin+ DC, ER-MP58+ CD11b+ myeloid precursor cells, CD169+ metallophilic Mφ, and CD71hi erythroblasts, was affected by viral transformation. In different mice, these subsets expanded at different rates in different organs, causing a variable disease profile in terminal stages. Cell lines, which were generated from MHSV-transformed tumors, showed a DC-like morphology and phenotype, and appeared to be arrested in different stages of maturation. Upon injection into healthy mice, different preferential homing patterns were observed for the various cell lines, and the cells acquired distinct phenotypes depending on the organ of homing. This indicates that these transformed cells adapt to their microenvironment by switching between precursor, DC/Langerhans cell, and Mφ phenotypes. Our results demonstrate that the MHSV model represents a heterogeneous neoplastic disease with characteristics of Mφ/DC sarcomas

mTOR inhibitor RAD001 promotes metastasis in a rat model of pancreatic neuroendocrine cancer

Inhibition of mTOR is commonly considered a valid target in cancer treatment, but this assertion does not address effects on the immune microenvironment that may be detrimental to cancer treatment. Here we show how administration of the mTOR inhibitor RAD001 (everolimus) results in the occurrence of distant metastasis in a rat model of pancreatic cancer. RAD001 was administered twice weekly for 4.5 weeks as a single treatment or combined with [177Lu-DOTA,Tyr3]octreotate (177Lu-DOTATATE), where the latter targets the somatostatin receptor-2. The hypothesized synergistic therapeutic effect of RAD001 combined with 177Lu-DOTATATE was, however, not observed in our experiments. The combination was shown to be less effective than 177Lu-DOTATATE alone. Unexpectedly, tumor metastasis was observed in 77% of the subjects treated with RAD001, either alone or as part of the combination treatment. This was a striking effect, because metastasis did not occur in control or 177Lu-DOTATATE-treated animals, including those where the primary tumor was surgically removed. These findings may be important clinically among noncompliant patients or patients that discontinue RAD001 therapy because of adverse effects