The potential of a-particle emitters to treat cancer has been recognized since the early 1900s. Advances in the targeted delivery of radionuclides and radionuclide conjugation chemistry, and the increased availability of a-emitters appropriate for clinical use, have recently led to patient trials of radiopharmaceuticals labeled with a-particle emitters. Although a-emitters have been studied for many decades, their current use in humans for targeted therapy is an important milestone. The objective of this work is to review those aspects of the field that are pertinent to targeted a-particle emitter therapy and to provide guidance and recommendations for human a-particle emitter dosimetry.

a-Particle-emitting radionuclides, such as 211 At, with a 7.2-h half-life, may be optimally suited for the molecularly targeted radiotherapy of strategically sensitive tumor sites, such as those in the central nervous system. Because of the much shorter range and more potent cytotoxicity of a-particles than of b-particles, 211 At-labeled agents may be ideal for the eradication of tumor cells remaining after surgical debulking of malignant brain tumors. The main goal of this study was to investigate the feasibility and safety of this approach in patients with recurrent malignant brain tumors. Methods: Chimeric antitenascin monoclonal antibody 81C6 (ch81C6) (10 mg) was labeled with 71-347 MBq of 211 At by use of N-succinimidyl 3-[ 211 At]astatobenzoate. Eighteen patients were treated with 211 At-labeled ch81C6 ( 211 At-ch81C6) administered into a surgically created resection cavity (SCRC) and then with salvage chemotherapy. Serial g-camera imaging and blood sampling over 24 h were performed. Results: A total of 96.7% 6 3.6% (mean 6 SD) of 211 At decays occurred in the SCRC, and the mean blood-pool percentage injected dose was #0.3. No patient experienced dose-limiting toxicity, and the maximum tolerated dose was not identified. Six patients experienced grade 2 neurotoxicity within 6 wk of 211 At-ch81C6 administration; this neurotoxicity resolved fully in all but 1 patient. No toxicities of grade 3 or higher were attributable to the treatment. No patient required repeat surgery for radionecrosis. The median survival times for all patients, those with glioblastoma multiforme, and those with anaplastic astrocytoma or oligodendroglioma were 54, 52, and 116 wk, respectively. Conclusion: This study provides proof of concept for regional targeted radiotherapy with 211 At-labeled molecules in oncology. Specifically, the regional administration of 211 At-ch81C6 is feasible, safe, and associated with a promising antitumor benefit in patients with malignant central nervous system tumors.

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The purpose of this study is to determine the maximum tolerated dose (MTD), dose-limiting toxicity (DLT), and intracerebral distribution of a recombinant toxin (TP-38) targeting the epidermal growth factor receptor in patients with recurrent malignant brain tumors using the intracerebral infusion technique of convection-enhanced delivery (CED). Twenty patients were enrolled and stratified for dose escalation by the presence of residual tumor from 25 to 100 ng/ml in a 40-ml infusion volume. In the last eight patients, coinfusion of (123)I-albumin was performed to monitor distribution within the brain. The MTD was not reached in this study. Dose escalation was stopped at 100 ng/ml due to inconsistent drug delivery as evidenced by imaging the coinfused (123)I-albumin. Two DLTs were seen, and both were neurologic. Median survival after TP-38 was 28 weeks (95% confidence interval, 26.5-102.8). Of 15 patients treated with residual disease, two (13.3%) demonstrated radiographic responses, including one patient with glioblastoma multiforme who had a nearly complete response and remains alive >260 weeks after therapy. Coinfusion of (123)I-albumin demonstrated that high concentrations of the infusate could be delivered >4 cm from the catheter tip. However, only 3 of 16 (19%) catheters produced intraparenchymal infusate distribution, while the majority leaked infusate into the cerebrospinal fluid spaces. Intracerebral CED of TP-38 was well tolerated and produced some durable radiographic responses at doses

Median survival achieved with (131)I-labeled 81C6 exceeds that of historical controls treated with conventional radiotherapy and chemotherapy, even after accounting for established prognostic factors including age and Karnofsky performance status. The median survival achieved with (131)I-labeled 81C6 compares favorably with either (125)I interstitial brachy-therapy or stereotactic radiosurgery and is associated with a significantly lower rate of reoperation for radionecrosis. Our results confirm the efficacy of (131)I-labeled 81C6 for patients with newly diagnosed malignant glioma and suggest that a randomized phase III study is indicated.

In this single-institution phase II study, administration of 100 mCi of 131I-m81C6 to recurrent malignant glioma patients followed by chemotherapy is associated with a median survival that is greater than that of historical controls treated with surgery plus iodine-125 brachytherapy. Furthermore, toxicity was acceptable. Administration of a fixed millicurie dose resulted in a wide range of absorbed radiation doses to the SCRC. We are now conducting a phase II trial, approved by the US Food and Drug Administration, using patient-specific 131I-m81C6 dosing, to deliver 44 Gy to the SCRC followed by standardized chemotherapy. A phase III multicenter trial with patient-specific dosing is planned.

The MTD for administration of 131I-labeled 81C6 into the SCRCs of previously irradiated patients with recurrent primary or metastatic brain tumors was 100 mCi. The dose-limiting toxicity was neurologic toxicity. We are encouraged by the minimal toxicity and survival in this phase I trial. Radiolabeled mAbs may improve the current therapy for brain tumor patients.

Although nanomedicines have been pursued for nearly 20 years, fundamental chemical strategies that seek to optimize both the drug and drug carrier together in a concerted effort remain uncommon yet may be powerful. In this work, two block polymers and one dimeric prodrug molecule were designed to be coassembled into degradable, functional nanocarriers, where the chemistry of each component was defined to accomplish important tasks. The result is a poly(ethylene glycol) (PEG)-protected redox-responsive dimeric paclitaxel (diPTX)-loaded cationic poly(d-glucose carbonate) micelle (diPTX@CPGC). These nanostructures showed tunable sizes and surface charges and displayed controlled PTX drug release profiles in the presence of reducing agents, such as glutathione (GSH) and dithiothreitol (DTT), thereby resulting in significant selectivity for killing cancer cells over healthy cells. Compared to free PTX and diPTX, diPTX@CPGC exhibited improved tumor penetration and significant inhibition of tumor cell growth toward osteosarcoma (OS) lung metastases with minimal side effects both in vitro and in vivo, indicating the promise of diPTX@CPGC as optimized anticancer therapeutic agents for treatment of OS lung metastases.