Optimal timing of administration of hyperthermia in combined radioimmunotherapy

p53 dynamics in single cells are temperature-sensitive

Cells need to preserve genome integrity despite varying cellular and physical states. p53, the guardian of the genome, plays a crucial role in the cellular response to DNA damage by triggering cell cycle arrest, apoptosis or senescence. Mutations in p53 or alterations in its regulatory network are major driving forces in tumorigenesis. As multiple studies indicate beneficial effects for hyperthermic treatments during radiation- or chemotherapy of human cancers, we aimed to understand how p53 dynamics after genotoxic stress are modulated by changes in temperature across a physiological relevant range. To this end, we employed a combination of time-resolved live-cell microscopy and computational analysis techniques to characterise the p53 response in thousands of individual cells. Our results demonstrate that p53 dynamics upon ionizing radiation are temperature dependent. In the range of 33 °C to 39 °C, pulsatile p53 dynamics are modulated in their frequency. Above 40 °C, which corresponds to mild hyperthermia in a clinical setting, we observed a reversible phase transition towards sustained hyperaccumulation of p53 disrupting its canonical response to DNA double strand breaks. Moreover, we provide evidence that mild hyperthermia alone is sufficient to induce a p53 response in the absence of genotoxic stress. These insights highlight how the p53-mediated DNA damage response is affected by alterations in the physical state of a cell and how this can be exploited by appropriate timing of combination therapies to increase the efficiency of cancer treatments.

Cancer radioimmunotherapy

Targeting of radionuclides with antibodies, or radioimmunotherapy, has been an active field of research spanning nearly 50 years, evolving with advancing technologies in molecular biology and chemistry, and with many important preclinical and clinical studies illustrating the benefits, but also the challenges, which all forms of targeted therapies face. There are currently two radiolabeled antibodies approved for the treatment of non-Hodgkin lymphoma, but radioimmunotherapy of solid tumors remains a challenge. Novel antibody constructs, focusing on treatment of localized and minimal disease, and pretargeting are all promising new approaches that are currently under investigation.

Microscopic intratumoral dosimetry of radiolabeled antibodies is a critical determinant of successful radioimmunotherapy in B-cell lymphoma

Radioimmunotherapy is a highly effective treatment for some hematologic malignancies; however, the underlying mechanisms of tumor clearance remain poorly understood. We have previously shown that both targeted radiation using (131)I-labeled anti-MHC class II (MHCII) monoclonal antibody (mAb) plus mAb signaling with unlabeled anti-idiotype are required for the long-term clearance of tumor in syngeneic murine lymphoma models. In this study, we have investigated how the microdistribution of the targeted radiation component of this combination affects the long-term clearance of lymphoma. (131)I-labeled mAb targeting CD45 and MHCII antigens was found to deliver similar doses of radiation to tumor-bearing organ using conventional dosimetry ( approximately 1.0 Gy per MBq when (131)I was labeled to 500 mug mAb and given i.v. per mouse), but when used as radiation vectors in combination therapy only, (131)I-anti-MHCII plus anti-idiotype produced long-term survival. The profound differences in therapy did not seem to be dependent on levels of (131)I-mAb tumor-binding or antibody-dependent cytotoxicity. Instead, the microscopic intratumoral dosimetry seemed to be critical with the (131)I-anti-MHCII, delivering more concentrated and therefore substantially higher radiation dose to tumor cells. When the administered activity of (131)I-anti-CD45 was increased, a radiation dose response was shown in the presence of anti-idiotype and long-term survival was seen. We believe that these new insights should influence the selection of new antigen targets and the design of dosimetric methods in radioimmunotherapy of lymphoma.

Optimization of radioimmunotherapy interactions with hyperthermia

The efficacy of radioimmunotherapy (RIT) employing radiolabelled monoclonal antibodies (MAb) is currently limited in most solid tumours. The combination of local hyperthermia (HT) with RIT has the potential to enhance tumour targeting of MAb; moreover, this approach may add an antitumour effect to radioresistant hypoxic and S-phase cells and may inhibit the cells from repairing sublethal damage or potentially lethal damage caused by ionizing radiation. There are distinct types of protocols in this combination. Hyperthermic temperature and timing relative to RIT administration appear to affect the efficacy of the combination therapy. Responses to heating at any particular condition are not always the same among different tumour types. There are many papers describing influence of HT on the biodistribution of radiolabelled MAb, but only limited information is currently available on 'therapeutic' outcomes regarding the dependency of combination protocols. A previous study suggested that the best therapeutic improvement would be achieved when HT was combined immediately after the administration of MAb, which significantly increases the radiation absorbed dose to tumours and produces a uniform intratumoural dose distribution. Further therapeutic investigation should be required to reach the optimal protocol of combining these two modalities.