Pronounced therapeutic effect of samarium 153-ethylenediaminetetramethylene phosphonate in an orthotopic human osteosarcoma tibial tumor model

Beyond Palliation: Therapeutic Applications of 153Samarium-EDTMP

Primary and metastatic malignant bone lesions result in significant pain and disability in oncology patients. Targeted bone-seeking radioisotopes including ¹⁵³Samarium ethylene-diamine-tetramethylene-phosphonic acid (¹⁵³Sm-EDTMP) have been shown to effectively palliate bone pain, often when external beam radiotherapy (EBRT) is not feasible. However, recent evidence also suggests ¹⁵³Sm-EDTMP has cytotoxic activity either alone or in combination with chemotherapy or EBRT. ¹⁵³Sm-EDTMP may be useful as anti-neoplastic therapy apart from pain palliation in a variety of malignancies. For prostate cancer patients, several phase I and II clinical trials have shown that combined ¹⁵³Sm-EDTMP and docetaxel-based chemotherapy can result in >50% decrease in prostate-specific antigen with manageable myelosuppression. In hematologic malignancies, ¹⁵³Sm-EDTMP produced clinical responses when combined with bortezomib in multiple myeloma. ¹⁵³Sm-EDTMP also can be used with myeloablative chemotherapy for marrow conditioning prior to stem cell transplant. In osteosarcoma, ¹⁵³Sm-EDTMP infusion delivers radiation to multiple unresectable lesions simultaneously and provides local cytotoxicity without soft tissue damage that can be combined with chemotherapy or radiation. Prior to routine incorporation of ¹⁵³Sm-EDTMP into therapeutic regimens, we must learn how to ensure optimal delivery to tumors, determine which patients are likely to benefit, improve our ability to assess clinical response in bone lesions and further evaluate the efficacy ¹⁵³Sm-EDTMP in combination with chemotherapy, radiation and novel targeted agents.

Studies on the synthesis and biological properties of non-carrier-added [(125)I and (131)I]-labeled arylalkylidenebisphosphonates: potent bone-seekers for diagnosis and therapy of malignant osseous lesions

Arylalkylidenebisphosphonates labeled with nca [(125)I or (131)I] have been synthesized and their biological function investigated. The label was attached to the aromatic group in high yield and under mild conditions by means of iododesilylation. The bone affinities of the radioactive compounds were investigated in normal Balb/C mice. The compound 1-hydroxy(m-iodo[(125,131)I]-phenylethylidene)-1,1-bisphosphonate was found to possess superior bone affinity compared to others, and its in vivo deiodination was insignificant. The uptake in femur 24h after injection was 850 +/- 265% and 986 +/- 118% of injected dose per gram tissue times gram body weight in mice and rats, respectively. The therapeutic potential of the compound was investigated in two tumor models in athymic (nude) rats, one model for mixed lytic/sclerotic metastatic bone-lesions originating from breast cancer and the other model simulating osseous osteosarcoma. The effects in these models compare favorably to those observed for established treatment modalities. The experiments demonstrate that radioiodinated bisphosphonates may have a potential for diagnosis and therapy of malignant osseous lesions.

High-dose samarium-153 ethylene diamine tetramethylene phosphonate: low toxicity of skeletal irradiation in patients with osteosarcoma and bone metastases

PURPOSE

Samarium-153 ethylene diamine tetramethylene phosphonate ((153)Sm-EDTMP), a bone-seeking radiopharmaceutical, provides therapeutic irradiation to osteoblastic bone metastases. Because the dose-limiting toxicity of (153)Sm-EDTMP is thrombocytopenia, a dose-escalation trial using peripheral-blood progenitor cells (PBPCs) or marrow support was conducted to treat metastatic bone cancer.

PATIENTS AND METHODS

Patients with locally recurrent or metastatic osteosarcoma or skeletal metastases avid on bone scan were treated with 1, 3, 4.5, 6, 12, 19, or 30 mCi/kg of (153)Sm-EDTMP.

RESULTS

Thirty patients were treated with (153)Sm-EDTMP. Transient symptoms of hypocalcemia were seen at 30 mCi/kg. Estimates of radioisotope bound to bone surfaces and marrow radiation dose were linear with injected amount of (153)Sm-EDTMP. Cytopenias also occurred in all subjects and were dose-related. At day +13 after (153)Sm-EDTMP, residual whole-body radioactivity was 1% to 65% of whole-body radioactivity considered safe for PBPC infusion, 3.6 mCi. After PBPC or marrow infusion on day +14 after (153)Sm-EDTMP, recovery of hematopoiesis was problematic in two patients at the 30 mCi/kg dose infused with less than 2 x 10(6) CD34(+)/kg on day +14, but not in other patients. Reduction or elimination of opiates for pain was seen in all patients. Patients had no adverse changes in appetite or performance status.

CONCLUSION

(153)Sm-EDTMP with PBPC support can provide bone-specific therapeutic irradiation (estimates of 39 to 241 Gy). Hematologic toxicity at 30 mCi (153)Sm-EDTMP/kg requires PBPC grafts with more than 2 x 10(6) CD34(+)/kg to overcome myeloablative effects of skeletal irradiation. Nonhematologic side effects are minimal.

Current treatment of osteosarcoma

A comprehensive multidisciplinary approach has transformed osteosarcoma from a disease with a modest long-term survival to one in which at least two-thirds of patients will be cured. Surgery remains the vital modality for treating the primary tumor, whereas adjuvant chemotherapy plays an essential role in the control of subclinical metastatic disease. Complete surgical excision of the primary tumor remains an essential element of treatment. For many patients, a combination of advances in surgical technique, improved imaging modalities to accurately document tumor extent, and the effect of neoadjuvant chemotherapy has made limb salvage procedures a safe alternative to amputation. In some patients for whom complete surgical excision is impossible, the addition of radiation therapy may allow local tumor control. The most effective chemotherapy agents currently in use include high-dose methotrexate, doxorubicin, cisplatin, and ifosfamide/etoposide. The optimal schedule of therapy is still being investigated, as is the role of dose intensification. Unfortunately, some groups of patients remain at high risk of eventual relapse. Those whose tumors show relatively low degrees of necrosis after administration of chemotherapy have poorer survival than patients with more chemotherapy-responsive tumors. Similarly, patients who present with overt metastatic disease (particularly bone metastases), as well as patients with tumors that recur after treatment, continue to have an unsatisfactory outcome. These groups, in particular, may benefit from future investigations into novel agents, such as biological response modifiers, antiangiogenesis factors, and growth receptor modulation.

Radiotherapeutic efficacy of (153)Sm-CMDTPA-Tyr(3)-octreotate in tumor-bearing rats

A number of radiolabeled somatostatin analogs have been evaluated in animal tumor models for radiotherapeutic efficacy. The majority of the agents tested have used either high-energy beta-emitters, such as Y-90 or Re-188, or the Auger electron-emitting radionuclide, In-111. Because a medium-energy beta-emitter might have equivalent efficacy compared to high-energy emitters, and lower toxicity to non-target tissues, we have evaluated the therapeutic potential of the beta-emitting nuclide, Sm-153, chelated to the somatostatin analog, CMDTPA-Tyr(3)-octreotate. Using an in vitro binding assay, this octreotate derivative was shown to have high affinity for the somatostatin subtype-2 receptor (IC(50) = 2.7 nM). Biodistribution studies in CA20948 tumor-bearing Lewis rats demonstrate that the Sm-153 labeled compound has high uptake and retention in tumor tissue (1.7% injected dose/g tissue, 4 hrs post injection) and has rapid overall clearance properties from non-target tissue. Radiotherapy studies were carried out using (153)Sm-CMDTPA-Tyr(3)-octreotate and CA20948 tumor bearing Lewis rats at 7 days post implant. Dose regimens consisting of single and multiple i.v. injections of 5.0 mCi/rat (185 MBq) were employed over a time span of 7 days. Suppression of tumor growth rate was observed in all treated animals compared to untreated controls. Greater inhibition of tumor growth was observed in animals that received multiple doses. These studies indicate that medium-energy beta-emitting isotopes have considerable potential for the treatment of somatostatin receptor-positive tumors.