Hyperthermia and thermochemotherapy

Integrating Loco-Regional Hyperthermia Into the Current Oncology Practice: SWOT and TOWS Analyses

Moderate hyperthermia at temperatures between 40 and 44°C is a multifaceted therapeutic modality. It is a potent radiosensitizer, interacts favorably with a host of chemotherapeutic agents, and, in combination with radiotherapy, enforces immunomodulation akin to “in situ tumor vaccination.” By sensitizing hypoxic tumor cells and inhibiting repair of radiotherapy-induced DNA damage, the properties of hyperthermia delivered together with photons might provide a tumor-selective therapeutic advantage analogous to high linear energy transfer (LET) neutrons, but with less normal tissue toxicity. Furthermore, the high LET attributes of hyperthermia thermoradiobiologically are likely to enhance low LET protons; thus, proton thermoradiotherapy would mimic ¹²C ion therapy. Hyperthermia with radiotherapy and/or chemotherapy substantially improves therapeutic outcomes without enhancing normal tissue morbidities, yielding level I evidence reported in several randomized clinical trials, systematic reviews, and meta-analyses for various tumor sites. Technological advancements in hyperthermia delivery, advancements in hyperthermia treatment planning, online invasive and non-invasive MR-guided thermometry, and adherence to quality assurance guidelines have ensured safe and effective delivery of hyperthermia to the target region. Novel biological modeling permits integration of hyperthermia and radiotherapy treatment plans. Further, hyperthermia along with immune checkpoint inhibitors and DNA damage repair inhibitors could further augment the therapeutic efficacy resulting in synthetic lethality. Additionally, hyperthermia induced by magnetic nanoparticles coupled to selective payloads, namely, tumor-specific radiotheranostics (for both tumor imaging and radionuclide therapy), chemotherapeutic drugs, immunotherapeutic agents, and gene silencing, could provide a comprehensive tumor-specific theranostic modality akin to “magic (nano)bullets.” To get a realistic overview of the strength (S), weakness (W), opportunities (O), and threats (T) of hyperthermia, a SWOT analysis has been undertaken. Additionally, a TOWS analysis categorizes future strategies to facilitate further integration of hyperthermia with the current treatment modalities. These could gainfully accomplish a safe, versatile, and cost-effective enhancement of the existing therapeutic armamentarium to improve outcomes in clinical oncology.

Novel temperature-sensitive liposomes with prolonged circulation time

Hyperthermia increases the efficiency of various chemotherapeutic drugs and is administered as an adjunct to chemotherapy for the treatment of cancer patients. The temperature-dependent effect can be strongly increased by the use of temperature-sensitive liposomes in combination with regional hyperthermia, which specifically releases the entrapped drug in the heated tumor tissue. The novel lipid 1.2-dipalmitoyl-sn-glycero-3-phosphoglyceroglycerol (DPPGOG), which is closely related to the naturally occurring 1.2-dipalmitoyl-sn-glycero-3-phosphoglycerol, in combination with 1.2-dipalmitoyl-sn-glycero-3-phosphocholine and 1.2-distearoyl-sn-glycero-3-phosphocholine provides long-circulating temperature-sensitive liposomes with favorable properties under mildly hyperthermic conditions (41-42 degrees C). DPPGOG facilitates temperature-triggered drug release from these liposomes (diameter, 175 nm) and leads to a substantially prolonged plasma half-life for the encapsulated drug with t(1/2) = 9.6 h in hamsters and t(1/2) = 5.0 h in rats. Quantitative fluorescence microscopy of amelanotic melanoma grown in the transparent dorsal skin fold chamber of hamsters demonstrated a favorable drug accumulation in heated tissue after i.v. application of these liposomes (42 degrees C for 1 h). The mean area under the curve for tissue drug concentration was increased by more than sixfold by application of the new liposomes compared with nonliposomal drug delivery. In summary, we present a new DPPGOG-based liposomal formulation enabling long circulation time combined with fast and efficient drug release under mild hyperthermia. This adds positively to the results with lipid-grafted polyethylenglycol used thus far in temperature sensitive liposomes and widens the possibilities for clinical applications.

P53-independent thermosensitization by mitomycin C in human non-small-cell lung cancer cells

PURPOSE

To elucidate the relationship between p53 functions and the interactive effects of the combined treatment with mild hyperthermia and mitomycin C.

METHODS AND MATERIALS

p53-deficient human non-small-cell lung cancer H1299 cells were transfected with a vector carrying a neomycin-resistant gene (neo) or together with a wild-type or mutant p53 gene. Sensitivities of these transfectants to mild hyperthermia at 42 degrees C, mitomycin C (0.05 microg/mL) at 37 degrees C, or the combination treatment were determined by colony formation assay. After these treatments, the induction of apoptosis, the changes in cell cycle distribution, and the accumulation of Hsp72 were examined.

RESULTS

The combined treatment resulted in an enhanced cell killing effect in H1299 cells in a p53-independent manner, which was partially the result of an enhancement of heat-induced apoptosis. The treatment also caused a marked G(2)/M arrest in the neo and the mutant p53 cells, but not in the wild-type p53 cells. The subsequent release of G(2)/M arrest was accompanied with an increase in the sub-G(1) fractions. Mitomycin C did not affect the accumulation of Hsp72 induced by hyperthermia in H1299 cells regardless of their p53 gene status.

CONCLUSION

Our findings demonstrate a p53-independent mechanism for an interactively cytotoxic enhancement by combined treatment with mild hyperthermia and mitomycin C.