Therapeutic efficacy and toxicity of 225Ac-labelled vs. 213Bi-labelled tumour-homing peptides in a preclinical mouse model of peritoneal carcinomatosis

General overview of radioimmunotherapy of solid tumors

Radioimmunotherapy (RIT) represents an attractive tool for the treatment of local and/or diffuse tumors with radiation. In RIT, cytotoxic radionuclides are delivered by monoclonal antibodies that specifically target tumor-associated antigens or the tumor microenvironment. While RIT has been successfully employed for the treatment of lymphoma, mostly with radiolabeled antibodies against CD20 (Bexxar(®); Corixa Corp., WA, USA and Zevalin(®); Biogen Idec Inc., CA, USA and Schering AG, Berlin, Germany), its use in solid tumors is more challenging and, so far, few trials have progressed beyond Phase II. This review provides an update on antibody-radionuclide conjugates and their use in RIT. It also discusses possible optimization strategies to improve the clinical response by considering biological, radiobiological and physical features.

Gold coated lanthanide phosphate nanoparticles for targeted alpha generator radiotherapy

Targeted radiotherapies maximize cytotoxicty to cancer cells. In vivo α-generator targeted radiotherapies can deliver multiple α particles to a receptor site dramatically amplifying the radiation dose delivered to the target. The major challenge with α-generator radiotherapies is that traditional chelating moieties are unable to sequester the radioactive daughters in the bioconjugate which is critical to minimize toxicity to healthy, non-target tissue. The recoil energy of the ²²⁵Ac daughters following α decay will sever any metal-ligand bond used to form the bioconjugate. This work demonstrates that an engineered multilayered nanoparticle-antibody conjugate can deliver multiple α radiations and contain the decay daughters of ²²⁵Ac while targeting biologically relevant receptors in a female BALB/c mouse model. These multi-shell nanoparticles combine the radiation resistance of lanthanide phosphate to contain ²²⁵Ac and its radioactive decay daughters, the magnetic properties of gadolinium phosphate for easy separation, and established gold chemistry for attachment of targeting moieties.

Enhanced efficacy of combined 213Bi-DTPA-F3 and paclitaxel therapy of peritoneal carcinomatosis is mediated by enhanced induction of apoptosis and G2/M phase arrest

PURPOSE

Targeted therapy with α-particle emitting radionuclides is a promising new option in cancer therapy. Stable conjugates of the vascular tumour-homing peptide F3 with the α-emitter (213)Bi specifically target tumour cells. The aim of our study was to determine efficacy of combined (213)Bi-diethylenetriaminepentaacetic acid (DTPA)-F3 and paclitaxel treatment compared to treatment with either (213)Bi-DTPA-F3 or paclitaxel both in vitro and in vivo.

METHODS

Cytotoxicity of treatment with (213)Bi-DTPA-F3 and paclitaxel, alone or in combination, was assayed towards OVCAR-3 cells using the alamarBlue assay, the clonogenic assay and flow cytometric analyses of the mode of cell death and cell cycle arrest. Therapeutic efficacy of the different treatment options was assayed after repeated treatment of mice bearing intraperitoneal OVCAR-3 xenograft tumours. Therapy monitoring was performed by bioluminescence imaging and histopathologic analysis.

RESULTS

Treatment of OVCAR-3 cells in vitro with combined (213)Bi-DTPA-F3 and paclitaxel resulted in enhanced cytotoxicity, induction of apoptosis and G2/M phase arrest compared to treatment with either (213)Bi-DTPA-F3 or paclitaxel. Accordingly, i.p. xenograft OVCAR-3 tumours showed the best response following repeated (six times) combined therapy with (213)Bi-DTPA-F3 (1.85 MBq) and paclitaxel (120 μg) as demonstrated by bioluminescence imaging and histopathologic investigation of tumour spread on the mesentery of the small and large intestine. Moreover, mean survival of xenograft mice that received combined therapy with (213)Bi-DTPA-F3 and paclitaxel was significantly superior to mice treated with either (213)Bi-DTPA-F3 or paclitaxel alone.

CONCLUSION

Combined treatment with (213)Bi-DTPA-F3 and paclitaxel significantly increased mean survival of mice with peritoneal carcinomatosis of ovarian origin, thus favouring future therapeutic application.