Evaluation of platinum chemotherapy in combination with HER2-targeted α-particle radiation

Dual targeting with 224Ra/212Pb-conjugates for targeted alpha therapy of disseminated cancers: A conceptual approach

Metastases are the primary cause of death among cancer patients and efficacious new treatments are sorely needed. Targeted alpha-emitting radiopharmaceuticals that are highly cytotoxic may fulfill this critical need. The focus of this paper is to describe and explore a novel technology that may improve the therapeutic effect of targeted alpha therapy by combining two radionuclides from the same decay chain in the same solution. We hypothesize that the dual targeting solution containing bone-seeking 224Ra and cell-directed complexes of progeny 212Pb is a promising approach to treat metastatic cancers with bone and soft tissue lesions as well as skeletal metastases of mixed lytic/osteoblastic nature. A novel liquid 224Ra/212Pb-generator for rapid preparation of a dual targeting solution is described. Cancer cell targeting monoclonal antibodies, their fragments, synthetic proteins or peptides can all be radiolabeled with 212Pb in the 224Ra-solution in transient equilibrium with daughter nuclides. Thus, 224Ra targets stromal elements in sclerotic bone metastases and 212Pb-chelated-conjugate targets tumor cells of metastatic prostate cancer or osteosarcoma. The dual targeting solution may also be explored to treat metastatic breast cancer or multiple myeloma after manipulation of bone metastases to a more osteoblastic phenotype by the use of bisphosphonates, denosumab, bortezomib or hormone therapy prior to treatment. This may improve targeting of bone-seeking 224Ra and render an augmented radiation dose deposited within metastases. Our preliminary preclinical studies provide conceptual evidence that the dual 224Ra-solution with bone or tumor-targeted delivery of 212Pb has potential to inhibit cancer metastases without significant toxicity. In some settings, the use of a booster dose of purified 212Pb-conjugate alone could be required to elevate the effect of this tumor cell directed component, if needed, e.g., in a fractionated treatment regimen, where the dual targeting solution will act as maintenance treatment.

Bismuth nanoparticles against microbial infections

The destructive effect of infectious diseases on human life and the emergence of antibiotic-resistant strains highlight the importance of developing new and appropriate treatment strategies, one of which is the use of metals as therapeutic agents. Bismuth nanoparticles are an example of prominent metal-containing drugs. The therapeutic effects of bismuth-based drugs in the treatment of wounds have been proven. Various laboratory studies have confirmed the antimicrobial effects of bismuth nanoparticles, including the clinical treatment of ulcers caused by Helicobacter pylori. Therefore, considering the performance of this nanoparticle and its potent effect on infectious agents and its therapeutic dimensions, the present study fully investigated the properties and performance of this metal-based nanoparticle.

Why bother with alpha particles?

The approval of 223RaCl2 for cancer therapy in 2013 has heralded a resurgence of interest in the development of α-particle emitting radiopharmaceuticals. In the last decade, over a dozen α-emitting radiopharmaceuticals have entered clinical trials, spawned by strong preclinical studies. In this article, we explore the potential role of α-particle therapy in cancer treatment. We begin by providing a background for the basic principles of therapy with α-emitters, and we explore recent breakthroughs in therapy with α-emitting radionuclides, including conjugates with small molecules and antibodies. Finally, we discuss some outstanding challenges to the clinical adoption of α-therapies and potential strategies to address them.

Overview of the Most Promising Radionuclides for Targeted Alpha Therapy: The "Hopeful Eight"

Among all existing radionuclides, only a few are of interest for therapeutic applications and more specifically for targeted alpha therapy (TAT). From this selection, actinium-225, astatine-211, bismuth-212, bismuth-213, lead-212, radium-223, terbium-149 and thorium-227 are considered as the most suitable. Despite common general features, they all have their own physical characteristics that make them singular and so promising for TAT. These radionuclides were largely studied over the last two decades, leading to a better knowledge of their production process and chemical behavior, allowing for an increasing number of biological evaluations. The aim of this review is to summarize the main properties of these eight chosen radionuclides. An overview from their availability to the resulting clinical studies, by way of chemical design and preclinical studies is discussed.

Perspectives on metals-based radioimmunotherapy (RIT): moving forward

Radioimmunotherapy (RIT) is FDA-approved for the clinical management of liquid malignancies, however, its use for solid malignancies remains a challenge. The putative benefit of RIT lies in selective targeting of antigens expressed on the tumor surface using monoclonal antibodies, to systemically deliver cytotoxic radionuclides. The past several decades yielded dramatic improvements in the quality, quantity, recent commercial availability of alpha-, beta- and Auger Electron-emitting therapeutic radiometals. Investigators have created new or improved existing bifunctional chelators. These bifunctional chelators bind radiometals and can be coupled to antigen-specific antibodies. In this review, we discuss approaches to develop radiometal-based RITs, including the selection of radiometals, chelators and antibody platforms (i.e. full-length, F(ab')2, Fab, minibodies, diabodies, scFv-Fc and nanobodies). We cite examples of the performance of RIT in the clinic, describe challenges to its implementation, and offer insights to address gaps toward translation.

First-in-human phase 0 study of 111In-CHX-A"-DTPA trastuzumab for HER2 tumor imaging

Introduction:

Tumors over-expressing the human epithelial receptor 2 (HER2) or exhibiting amplification or mutation of its proto-oncogene have a poorer prognosis. Using trastuzumab and/or other HER2 targeted therapies can increase overall survival in patients with HER2(+) tumors making it critical to accurately identify patients who may benefit. We report on a Phase 0 study of the imaging agent, ¹¹¹In-CHX-A”-DTPA trastuzumab, in patients with known HER2 status to evaluate its safety and biodistribution and to obtain preliminary data regarding its ability to provide an accurate, whole-body, non-invasive means to determine HER2 status.

Methods:

¹¹¹In-CHX-A”-DTPA trastuzumab was radiolabeled on-site and slowly infused into 11 patients who underwent single (n=5) or multiple (n=6) ɣ-camera (n=6) and/or SPECT (n=8) imaging sessions.

Results:

No safety issues were identified. Visual and semi-quantitative imaging data were concordant with tissue HER2 expression profiling in all but 1 patient. The biodistribution showed intense peak liver activity at the initial imaging timepoint (3.3h) and a single-phase clearance fit of the average time-activity curve (TAC) estimated t_1/2=46.9h (R²=0.97; 95%CI 41.8 to 53h). This was followed by high gastrointestinal (GI) tract activity peaking by 52h. Linear regression predicted GI clearance by 201.2h (R² =0.96; 95%CI 188.5 to 216.9h). Blood pool had lower activity with its maximum on the initial images. Non-linear regression fit projected a t_1/2=34.2h (R² =0.96; 95%CI 25.3 to 46.3h). Assuming linear whole-body clearance, linear regression projected complete elimination (x-intercept) at 256.5hr (R²=0.96; 95%CI 186.1 to 489.2h).

Conclusion:

¹¹¹In-CHX-A”-DTPA trastuzumab can be safely imaged in humans. The biodistribution allowed for visual and semiquantitative analysis with results concordant with tissue expression profiling in 10 of 11 patients. Advances in Knowledge and Implications for Patient Care Using readily available components and on-site radiolabeling ¹¹¹In-CHX-A”-DTPA trastuzumab SPECT imaging may provide an economical, non-invasive means to detect HER2 over-expression.

Therapeutic Effect of α-Emitting 224Ra-Labeled Calcium Carbonate Microparticles in Mice with Intraperitoneal Ovarian Cancer

BACKGROUND: Ovarian cancer patients with chemotherapy-resistant residual microscopic disease in the peritoneal cavity have a considerable need for new treatment options. Alpha-emitting radionuclides injected intraperitoneally may be an attractive therapeutic option in this situation as they are highly cytotoxic, while their short range in tissues can spare surrounding radiosensitive organs in the abdomen. Herein we evaluate the therapeutic efficacy of a novel α-emitting compound specifically designed for intracavitary radiation therapy. METHODS: The α-emitter ²²⁴Ra was absorbed on calcium carbonate microparticles. Immunodeficient, athymic nude mice with human ovarian cancer cells growing intraperitoneally were treated with different activity levels of ²²⁴Ra-microparticles. Tumor growth, survival, and tolerance of the treatment were assessed. Two tumor models based on the cell lines, ES-2 and SKOV3-luc, with different growth patterns were studied. RESULTS: In both models, intraperitoneal treatment with ²²⁴Ra-microparticles gave significant antitumor effect with either considerably reduced tumor volume or a survival benefit. An advantageous discovery was that only a few kilobecquerels per mouse were needed to yield therapeutic effects. The treatment was well tolerated up to a dose of 1000 kBq/kg with no signs of acute or subacute toxicity observed. CONCLUSIONS: Intraperitoneal α-therapy with ²²⁴Ra-microparticles demonstrated a significant potential for treatment of peritoneal micrometastases in ovarian carcinoma.

212Pb-labeled B7-H3-targeting antibody for pancreatic cancer therapy in mouse models

INTRODUCTION

We recently validated monoclonal antibody (mAb) 376.96 as an effective carrier for targeted α-particle radioimmunotherapy (RIT) with ²¹²Pb in ovarian cancer mouse models. In this study, we tested the binding of radiolabeled mAb 376.96 to human pancreatic ductal adenocarcinoma (PDAC) cells and localization in xenografts in immune-deficient mice and evaluated ²¹²Pb-labeled 376.96 (²¹²Pb-376.96) for PDAC therapy.

METHODS

In vitro Scatchard assays assessed the specific binding of ²¹²Pb-376.96 to human PDAC3 adherent differentiated cells and non-adherent cancer initiating cells (CICs) dissociated from tumorspheres. In vitro clonogenic assays were used to measure the proliferation of adherent PDAC3 cells and CIC-enriched tumorspheres treated with ²¹²Pb-376.96 or the irrelevant isotype-matched ²¹²Pb-F3-C25. Mice bearing patient derived pancreatic cancer Panc039 xenografts were i.v. injected with 0.17-0.70 MBq ²¹²Pb-376.96 or isotype control ²¹²Pb-F3-C25, and used for biodistribution and tumor growth inhibition studies. Mice bearing orthotopic PDAC3 xenografts were i.v. co-injected with ^99mTc-376.96 and ¹²⁵I-F3-C25 and used for biodistribution studies.

RESULTS

²¹²Pb-376.96 specifically bound to PDAC3 adherent and dissociated tumorsphere CICs; K_d values averaged 9.0 and 21.7 nM, respectively, with 10⁴-10⁵ binding sites/cell. ²¹²Pb-376.96 inhibited the clonogenic survival of PDAC3 cells or CICs dissociated from tumorspheres 3-6 times more effectively than isotype-matched control ²¹²Pb-F3-C25. Panc039 s.c. tumors showed significantly higher uptake of ²¹²Pb-376.96 (14.0 ± 2.1% ID/g) compared to ²¹²Pb-F3-C25 (6.5 ± 0.9% ID/g, p < .001) at 24 h after dosing. Orthotopic PDAC3 tumors showed significantly higher uptake of ^99mTc-376.96 (6.4 ± 1.8% ID/g) compared to ¹²⁵I-F3-C25 (3.9 ± 0.9% ID/g, p < .05) at 24 h after dosing. Panc039 tumor growth was significantly inhibited by ²¹²Pb-376.96 compared to ²¹²Pb-F3-C25 or non-treated control tumors (p < .05).

CONCLUSION

Our results provide evidence for the efficacy of B7-H3 targeted RIT against preclinical models of pancreatic ductal adenocarcinoma (PDAC) and support future studies with ²¹²Pb-376.96 in combination with chemotherapy to potentiate efficacy against PDAC.

Targeted α-Particle Radiation Therapy of HER1-Positive Disseminated Intraperitoneal Disease: An Investigation of the Human Anti-EGFR Monoclonal Antibody, Panitumumab

Identifying molecular targets and an appropriate targeting vehicle, i.e., monoclonal antibodies (mAb) and their various forms, for radioimmunotherapy (RIT) remains an active area of research. Panitumumab, a fully human and less immunogenic mAb that binds to the epidermal growth factor receptor (Erb1; HER1), was evaluated for targeted α-particle radiation therapy using ²¹²Pb, an in vivo α generator. A single dose of ²¹²Pb-panitumumab administered to athymic mice bearing LS-174T intraperitoneal (i.p.) tumor xenografts was found to have greater therapeutic efficacy when directly compared with ²¹²Pb-trastuzumab, which binds to HER2. A dose escalation study determined a maximum effective working dose of ²¹²Pb-panitumumab to be 20 μCi with a median survival of 35 days versus 25 days for the untreated controls. Pretreatment of tumor-bearing mice with paclitaxel and gemcitabine 24 hours prior to injection of ²¹²Pb-pantiumumab at 10 or 20 μCi resulted in the greatest enhanced therapeutic response at the higher dose with median survivals of 106 versus 192 days, respectively. The greatest therapeutic impact, however, was observed in the animals that were treated with topotecan 24 hours prior to RIT and then again 24 hours after RIT; the best response from this combination was also obtained with the lower 10-μCi dose of ²¹²Pb-panitumumab (median survival >280 days). In summary, ²¹²Pb-panitumumab is an excellent candidate for the treatment of HER1-positive disseminated i.p. disease. Furthermore, the potentiation of the therapeutic impact of ²¹²Pb-pantiumumab by chemotherapeutics confirms and validates the importance of developing a multimodal therapy regimen.

Preparation of 212Pb-labeled monoclonal antibody using a novel 224Ra-based generator solution

INTRODUCTION

Alpha-emitting radionuclides have gained considerable attention as payloads for cancer targeting molecules due to their high cytotoxicity. One attractive radionuclide for this purpose is ²¹²Pb, which by itself is a β-emitter, but acts as an in vivo generator for its short-lived α-emitting daughters. The standard method of preparing ²¹²Pb-labeled antibodies requires handling and evaporation of strong acids containing high radioactivity levels by the end user. An operationally easier and more rapid process could be useful since the 10.6h half-life of ²¹²Pb puts time constraints on the preparation protocol. In this study, an in situ procedure for antibody labeling with ²¹²Pb, using a solution of the generator nuclide ²²⁴Ra, is proposed as an alternative protocol for preparing ²¹²Pb-radioimmunoconjugates.

METHODS

Radium-224, the generator radionuclide of ²¹²Pb, was extracted from its parent nuclide, ²²⁸Th. Lead-212-labeling of the TCMC-chelator conjugated monoclonal antibody trastuzumab was carried out in a solution containing ²²⁴Ra in equilibrium with progeny. Subsequently, the efficiency of separating the ²¹²Pb-radioimmunoconjugate from ²²⁴Ra and other unconjugated daughter nuclides in the solution using either centrifugal separation or a PD-10 desalting size exclusion column was evaluated and compared.

RESULTS

Radiolabeling with ²¹²Pb in ²²⁴Ra-solutions was more than 90% efficient after only 30min reaction time at TCMC-trastuzumab concentrations from 0.15mg/mL and higher. Separation of ²¹²Pb-labeled trastuzumab from ²²⁴Ra using a PD-10 column was clearly superior to centrifugal separation. This method allowed recovery of approximately 75% of the ²¹²Pb-antibody-conjugate in the eluate, and the remaining amount of ²²⁴Ra was only 0.9±0.8% (n=7).

CONCLUSIONS

The current work demonstrates a novel method of producing ²¹²Pb-based radioimmunoconjugates from a ²²⁴Ra-solution, which may be simpler and less time-consuming for the end user compared with the method established for use in clinical trials of ²¹²Pb-TCMC-trastuzumab.

Radioimmunotherapy of cancer with high linear energy transfer (LET) radiation delivered by radionuclides emitting α-particles or Auger electrons

Radioimmunotherapy (RIT) aims to selectively deliver radionuclides emitting α-particles, β-particles or Auger electrons to tumors by conjugation to monoclonal antibodies (mAbs) that recognize tumor-associated antigens/receptors. The approach has been most successful for treatment of non-Hodgkin's B-cell lymphoma but challenges have been encountered in extending these promising results to the treatment of solid malignancies. These challenges include the low potency of β-particle emitters such as ¹³¹I, ¹⁷⁷Lu or ⁹⁰Y which have been commonly conjugated to the mAbs, due to their low linear energy transfer (LET=0.1-1.0keV/μm). Furthermore, since the β-particles have a 2-10mm range, there has been dose-limiting non-specific toxicity to hematopoietic stem cells in the bone marrow (BM) due to the cross-fire effect. Conjugation of mAbs to α-particle-emitters (e.g. ²²⁵Ac, ²¹³Bi, ²¹²Pb or ²¹¹At) or Auger electron-emitters (e.g. ¹¹¹In, ⁶⁷Ga, ¹²³I or ¹²⁵I) would increase the potency of RIT due to their high LET (50-230keV/μm and 4 to 26keV/μm, respectively). In addition, α-particles have a range in tissues of 28-100μm and Auger electrons are nanometer in range which greatly reduces or eliminates the cross-fire effect compared to β-particles, potentially reducing their non-specific toxicity to the BM. In this review, we describe the results of preclinical and clinical studies of RIT of cancer using radioimmunoconjugates emitting α-particles or Auger electrons, and discuss the potential of these high LET forms of radiation to improve the outcome of cancer patients.

B7-H3-targeted 212Pb radioimmunotherapy of ovarian cancer in preclinical models

INTRODUCTION

Novel therapies that effectively kill both differentiated cancer cells and cancer initiating cells (CICs), which are implicated in causing chemotherapy-resistance and disease recurrence, are needed to reduce the morbidity and mortality of ovarian cancer. These studies used monoclonal antibody (mAb) 376.96, which recognizes a B7-H3 epitope expressed on ovarian cancer cells and CICs, as a carrier molecule for targeted α-particle radioimmunotherapy (RIT) in preclinical models of human ovarian cancer.

METHODS

mAb 376.96 was conjugated to the chelate 2-(4-isothiocyanotobenzyl)-1,4,7,10-tetraaza-1,4,7,10-tetra-(2-carbamoylmethyl)-cyclododecane (TCMC) and radiolabeled with ²¹²Pb, a source of α-particles. In vitro Scatchard assays determined the specific binding of ²¹²Pb-376.96 to adherent differentiated or non-adherent CIC-enriched ES-2 and A2780cp20 ovarian cancer cells. Adherent ovarian cancer cells and non-adherent CIC-enriched tumorspheres treated in vitro with ²¹²Pb-376.96 or the irrelevant isotype-matched ²¹²Pb-F3-C25 were assessed for clonogenic survival. Mice bearing i.p. ES-2 or A2780cp20 xenografts were injected i.p. with 0.17-0.70MBq ²¹²Pb-376.96 or ²¹²Pb-F3-C25 and were used for in vivo imaging, ex vivo biodistribution, and therapeutic survival studies.

RESULTS

²¹²Pb-376.96 was obtained in high yield and purity (>98%); K_d values ranged from 10.6-26.6nM for ovarian cancer cells, with 10⁴-10⁵ binding sites/cell. ²¹²Pb-376.96 inhibited the clonogenic survival of ovarian cancer cells up to 40 times more effectively than isotype-matched control ²¹²Pb-F3-C25; combining ²¹²Pb-376.96 with carboplatin significantly decreased clonogenic survival compared to either agent alone. In vivo imaging and biodistribution analysis 24h after i.p. injection of ²¹²Pb-376.96 showed high peritoneal retention and tumor tissue accumulation (28.7% ID/g in ES-2 ascites, 73.1% ID/g in A2780cp20 tumors); normal tissues showed lower and comparable uptake for ²¹²Pb-376.96 and ²¹²Pb-F3-C25. Tumor-bearing mice treated with ²¹²Pb-376.96 alone or combined with carboplatin survived 2-3 times longer than mice treated with ²¹²Pb-F3-C25 or non-treated controls.

CONCLUSION

These results support additional RIT studies with ²¹²Pb-376.96 for future evaluation in patients with ovarian cancer.

Imaging, biodistribution, and toxicology evaluation of (212)Pb-TCMC-trastuzumab in nonhuman primates

INTRODUCTION

The biodistribution and toxicology of a radiotherapeutic (212)Pb-trastuzumab conjugate were evaluated in nonhuman primates to meet the investigational new drug requirements prior to a phase I clinical trial in human subjects.

METHODS

Male cynomolgus monkeys (n=3/group) were injected intraperitoneally with the (212)Pb-trastuzumab conjugate and terminated at 8h, 10d, and 90d post-injection. Quantitative imaging studies in phantoms and monkeys were conducted using a planar gamma camera and a high purity germanium (HPGe) detector out to 48h following injection. Biodistribution analyses were conducted at 8h; all tissues and time points were evaluated for macroscopic and microscopic pathology. Blood samples were taken throughout the 90d study period for assessment of hematology parameters and serum chemistry parameters.

RESULTS

Quantitative gamma camera imaging and region-of-interest analyses of phantoms and monkeys indicated that 95.5±5.0% of the decay-corrected (212)Pb activity was retained in the peritoneal region up to 48h following administration of the (212)Pb-trastuzumab. Gamma-ray spectroscopy analyses confirmed that 87.6±4.5% of the decay-corrected (212)Bi activity was also retained in the peritoneal cavity during this time. Serum chemistry parameters for all groups always fell within normal ranges. Gross and histopathology evaluations showed no radiation-related toxicity in any tissue at any time.

CONCLUSION

In vivo imaging and biodistribution analyses showed that about 90% of both (212)Pb and decay product (212)Bi remained in the monkey peritoneal cavity. The imaging methods could also be applied to human subjects. The lack of toxicity observed in monkeys following intraperitoneal injection of the (212)Pb-trastuzumab conjugate supports its clinical assessment in humans.

Evaluation of cetuximab as a candidate for targeted α-particle radiation therapy of HER1-positive disseminated intraperitoneal disease

Although the epidermal growth factor receptor (EGFR), also known as HER1, has been studied for over a decade, it continues to be a molecule of great interest and focus of investigators for development of targeted therapies. The marketed monoclonal antibody cetuximab binds to HER1, and thus might serve as the basis for creation of imaging or therapies that target this receptor. The potential of cetuximab as a vehicle for the delivery of α-particle radiation was investigated in an intraperitoneal tumor mouse model. The effective working dose of 10 μCi of (212)Pb-cetuximab was determined from a dose (10-50 μCi) escalation study. Toxicity, as indicated by the lack of animal weight loss, was not evident at the 10 μCi dose of (212)Pb-cetuximab. A subsequent study demonstrated (212)Pb-cetuximab had a therapeutic efficacy similar to that of (212)Pb-trastuzumab (p = 0.588). Gemcitabine given 24 h prior to (212)Pb-cetuximab increased the median survival from 174 d to 283 d, but carboplatin suppressed the effectiveness of (212)Pb-cetuximab. Notably, concurrent treatment of tumor-bearing mice with (212)Pb-labeled cetuximab and trastuzumab provided therapeutic benefit that was greater than either antibody alone. In conclusion, cetuximab proved to be an effective vehicle for targeting HER1-expressing tumors with α-radiation for the treatment of disseminated intraperitoneal disease. These studies provide further evidence that the multimodality therapy regimens may have greater efficacy and benefit in the treatment of cancer patients.

Application of 212Pb for Targeted α-particle Therapy (TAT): Pre-clinical and Mechanistic Understanding through to Clinical Translation

Targeted α-particle therapy (TAT), in which an α-particle emitting radionuclide is specifically directed to a biological target, is gaining more attention to treat cancers as new targets are validated. Bio-vectors such as monoclonal antibodies are able to selectively transport α-particles to destroy targeted cancer cells. TAT has the potential for an improved therapeutic ratio over β-particle targeted conjugate therapy. The short path length and the intense ionization path generated render α-emitters suitable for treatment and management of minimal disease such as micrometastases or residual tumor after surgical debulking. ²¹²Pb is the longer-lived parent radionuclide of ²¹²Bi and serves as an in vivo generator of ²¹²Bi. ²¹²Pb has demonstrated significant utility in both in vitro and in vivo models. Recent evaluation of ²¹²Pb-TCMC-trastuzumab in a Phase I clinical trial has demonstrated the feasibility of ²¹²Pb in TAT for the treatment of ovarian cancer patients. This review highlights progress in radionuclide production, radiolabeling chemistry, molecular mechanisms, and application of ²¹²Pb to targeted pre-clinical and clinical radiation therapy for the management and treatment of cancer.

Toxicological Studies of 212Pb Intravenously or Intraperitoneally Injected into Mice for a Phase 1 Trial

Faced with the novelty of a ²¹²Pb-labeled monoclonal antibody (mAb) for clinical translation, concerns were expressed by the Food and Drug Administration (FDA) regarding ²¹²Pb prematurely released from the mAb-chelate conjugate. The objective of this study was to simulate the worst case scenario of such a failure. Groups of Balb/c mice (n = 9–20) were administered ²¹²Pb by intraperitoneal (0.0925–1.85 MBq) or intravenous (0.0925–1.11 MBq) injection and then euthanized at 7 or 90 days to assess acute or chronic effects. Weights were recorded prior to injection of the ²¹²Pb and at the end of the observation periods. Blood samples were collected for clinical chemistry and blood cell analysis. Thirty tissues were harvested and formalin fixed for histopathological examination. Treatment related effects of the ²¹²Pb were observed in the bone marrow, spleen, kidneys and the liver. Histological alterations in these organs were considered mild to moderate, indicating low grade toxicity, and not considered severe enough to affect function. This data was presented to the FDA and determined to be acceptable. The clinical trial with ²¹²Pb-TCMC-trastuzumab was approved in January 2011 and the trial opened at the University of Alabama at Birmingham (UAB) in July.

Current and potential applications of bismuth-based drugs

: Bismuth compounds have been used extensively as medicines and in particular for the treatment of gastrointestinal ailments. In addition to bismuth's well known gastroprotective effects and efficacy in treating H. pylori infection it also has broad anti-microbial, anti-leishmanial and anti-cancer properties. Aspects of the biological chemistry of bismuth are discussed and biomolecular targets associated with bismuth treatment are highlighted. This review strives to provide the reader with an up to date account of bismuth-based drugs currently used to treat patients and discuss potential medicinal applications of bismuth drugs with reference to recent developments in the literature. Ultimately this review aims to encourage original contributions to this exciting and important field.

Dose escalation and dosimetry of first-in-human α radioimmunotherapy with 212Pb-TCMC-trastuzumab

Our purpose was to study the safety, distribution, pharmacokinetics, immunogenicity, and tumor response of intraperitoneal (212)Pb-TCMC-trastuzumab (TCMC is S-2-(4-isothiocyanatobenzyl)-1,4,7,10-tetraaza-1,4,7,10-tetra(2-carbamoylmethyl)cyclododecane) in patients with human epidermal growth factor receptor type 2 (HER-2)-expressing malignancy.

METHODS

In a standard 3 + 3 phase 1 design for dose escalation, (212)Pb-TCMC-trastuzumab was delivered intraperitoneally less than 4 h after administration of trastuzumab (4 mg/kg intravenously) to patients with peritoneal carcinomatosis who had failed standard therapies.

RESULTS

Five dosage levels (7.4, 9.6, 12.6, 16.3, and 21.1 MBq/m(2)) showed minimal toxicity at more than 1 y for the first group and more than 4 mo for others. The lack of substantial toxicity was consistent with the dosimetry assessments (mean equivalent dose to marrow, 0.18 mSv/MBq). Radiation dosimetry assessment was performed using pharmacokinetics data obtained in the initial cohort (n = 3). Limited redistribution of radioactivity out of the peritoneal cavity to circulating blood, which cleared via urinary excretion, and no specific uptake in major organs were observed in 24 h. Maximum serum concentration of the radiolabeled antibody was 22.9% at 24 h (decay-corrected to injection time) and 500 Bq/mL (decay-corrected to collection time). Non-decay-corrected cumulative urinary excretion was 6% or less in 24 h (2.3 half-lives). Dose rate measurements performed at 1 m from the patient registered less than 5μSv/h (using portable detectors) in the latest cohort, significantly less than what is normally observed using nuclear medicine imaging agents. Antidrug antibody assays performed on serum from the first 4 cohorts were all negative.

CONCLUSION

Five dose levels of intraperitoneal (212)Pb-TCMC-trastuzumab treatment of patients with peritoneal carcinomatosis showed little agent-related toxicity, consistent with the dosimetry calculations.

Dose escalation and dosimetry of first-in-human α radioimmunotherapy with 212Pb-TCMC-trastuzumab

Our purpose was to study the safety, distribution, pharmacokinetics, immunogenicity, and tumor response of intraperitoneal (212)Pb-TCMC-trastuzumab (TCMC is S-2-(4-isothiocyanatobenzyl)-1,4,7,10-tetraaza-1,4,7,10-tetra(2-carbamoylmethyl)cyclododecane) in patients with human epidermal growth factor receptor type 2 (HER-2)-expressing malignancy.

METHODS

In a standard 3 + 3 phase 1 design for dose escalation, (212)Pb-TCMC-trastuzumab was delivered intraperitoneally less than 4 h after administration of trastuzumab (4 mg/kg intravenously) to patients with peritoneal carcinomatosis who had failed standard therapies.

RESULTS

Five dosage levels (7.4, 9.6, 12.6, 16.3, and 21.1 MBq/m(2)) showed minimal toxicity at more than 1 y for the first group and more than 4 mo for others. The lack of substantial toxicity was consistent with the dosimetry assessments (mean equivalent dose to marrow, 0.18 mSv/MBq). Radiation dosimetry assessment was performed using pharmacokinetics data obtained in the initial cohort (n = 3). Limited redistribution of radioactivity out of the peritoneal cavity to circulating blood, which cleared via urinary excretion, and no specific uptake in major organs were observed in 24 h. Maximum serum concentration of the radiolabeled antibody was 22.9% at 24 h (decay-corrected to injection time) and 500 Bq/mL (decay-corrected to collection time). Non-decay-corrected cumulative urinary excretion was 6% or less in 24 h (2.3 half-lives). Dose rate measurements performed at 1 m from the patient registered less than 5μSv/h (using portable detectors) in the latest cohort, significantly less than what is normally observed using nuclear medicine imaging agents. Antidrug antibody assays performed on serum from the first 4 cohorts were all negative.

CONCLUSION

Five dose levels of intraperitoneal (212)Pb-TCMC-trastuzumab treatment of patients with peritoneal carcinomatosis showed little agent-related toxicity, consistent with the dosimetry calculations.

Radioimmunotherapy with α-particle-emitting radionuclides

α-particle-emitting radionuclides are highly cytotoxic and are thus promising candidates for use in targeted radioimmunotherapy of cancer. Due to their high linear energy transfer (LET) combined with a short path length in tissue, α-particles cause severe DNA double-strand breaks that are repaired inaccurately and finally trigger cell death. For radioimmunotherapy, α-emitters such as 225Ac, 211At, 212Bi/212Pb, 213Bi and 227Th are coupled to antibodies via appropriate chelating agents. The α-emitter immunoconjugates preferably target proteins that are overexpressed or exclusively expressed on cancer cells. Application of α-emitter immunoconjugates seems particularly promising in treatment of disseminated cancer cells and small tumor cell clusters that are released during the resection of a primary tumor. α-emitter immunoconjugates have been successfully administered in numerous experimental studies for therapy of ovarian, colon, gastric, blood, breast and bladder cancer. Initial clinical trials evaluating α-emitter immunoconjugates in terms of toxicity and therapeutic efficacy have also shown positive results in patients with melanoma, ovarian cancer, acute myeloid lymphoma and glioma. The present problems in terms of availability of therapeutically effiective α-emitters will presumably be solved by use of alternative production routes and installation of additional production facilities in the near future. Therefore, clinical establishment of targeted α-emitter radioimmunotherapy as one part of a multimodal concept for therapy of cancer is a promising, middle-term concept.

Targeted chemoradiation in metastatic colorectal cancer: a phase I trial of 131I-huA33 with concurrent capecitabine

huA33 is a humanized antibody that targets the A33 antigen, which is highly expressed in intestinal epithelium and more than 95% of human colon cancers but not other normal tissues. Previous studies have shown huA33 can target and be retained in a metastatic tumor for 6 wk but eliminated from normal colonocytes within days. This phase I study used radiolabeled huA33 in combination with capecitabine to target chemoradiation to metastatic colorectal cancer. The primary objective was safety and tolerability of the combination of capecitabine and (131)I-huA33. Pharmacokinetics, biodistribution, immunogenicity, and tumor response were also assessed.

METHODS

Eligibility included measurable metastatic colorectal cancer, adequate hematologic and biochemical function, and informed consent. An outpatient scout (131)I-huA33 dose was followed by a single-therapy infusion 1 wk later, when capecitabine was commenced. Dose escalation occurred over 5 dose levels. Patients were evaluated weekly, with tumor response assessment at the end of the 12-wk trial. Tumor targeting was assessed using a γ camera and SPECT imaging.

RESULTS

Nineteen eligible patients were enrolled. The most frequently observed toxicity included myelosuppression, gastrointestinal symptoms, and asymptomatic hyperbilirubinemia. Biodistribution analysis demonstrated excellent tumor targeting of the known tumor sites, expected transient bowel uptake, but no other normal tissue uptake. (131)I-huA33 demonstrated a mean terminal half-life and serum clearance suited to radioimmunotherapy (T1/2β, 100.24 ± 20.92 h, and clearance, 36.72 ± 8.01 mL/h). The mean total tumor dose was 13.8 ± 7.6 Gy (range, 5.1-26.9 Gy). One patient had a partial response, and 10 patients had stable disease.

CONCLUSION

(131)I-huA33 achieves specific targeting of radiotherapy to colorectal cancer metastases and can be safely combined with chemotherapy, providing an opportunity to deliver chemoradiation specifically to metastatic disease in colorectal cancer patients.