Combination of [177Lu]Lu-DOTA-TATE Targeted Radionuclide Therapy and Photothermal Therapy as a Promising Approach for Cancer Treatment: In Vivo Studies in a Human Xenograft Mouse Model

Abstract

Peptide receptor radionuclide therapy (PRRT) relies on α- and β-emitting radionuclides bound to a peptide that commonly targets somatostatin receptors (SSTRs) for the localized killing of tumors through ionizing radiation. A Lutetium-177 (¹⁷⁷Lu)-based probe linked to the somatostatin analog octreotate ([¹⁷⁷Lu]Lu-DOTA-TATE) is approved for the treatment of certain SSTR-expressing tumors and has been shown to improve survival. However, a limiting factor of PRRT is the potential toxicity derived from the high doses needed to kill the tumor. This could be circumvented by combining PRRT with other treatments for an enhanced anti-tumor effect. Photothermal therapy (PTT) relies on nanoparticle-induced hyperthermia for cancer treatment and could be a useful add-on to PRRT. Here, we investigate a strategy combining [¹⁷⁷Lu]Lu-DOTA-TATE PRRT and nanoshell (NS)-based PTT for the treatment of SSTR-expressing small-cell lung tumors in mice. Our results showed that the combination treatment improved survival compared to PRRT alone, but only when PTT was performed one day after [¹⁷⁷Lu]Lu-DOTA-TATE injection (one of the timepoints examined), showcasing the effect of treatment timing in relation to outcome. Furthermore, the combination treatment was well-tolerated in the mice. This indicates that strategies involving NS-based PTT as an add-on to PRRT could be promising and should be investigated further.

Keywords: [177Lu]Lu-DOTA-TATE; cancer; nanoshells (NS); peptide receptor radionuclide therapy (PRRT); photothermal therapy (PTT); somatostatin receptor (SSTR).

Figure 1

SSTR2 expression and [⁶⁴Cu]Cu-DOTA-TATE tumor uptake in the NCI-H69 model. (A) Flow cytometric analysis of NCI-H69 cells to confirm SSTR2 expression (in triplicates). VD = viability dye. (B) Histological analysis to detect SSTR2 expression in NCI-H69 tumors and HE staining. (C) Representative PET/CT images of mice to observe [⁶⁴Cu]Cu-DOTA-TATE distribution 1 h and 24 h after injection. Arrows point to the tumors. (D,E) Mean (D) and maximum (E) [⁶⁴Cu]Cu-DOTA-TATE uptake in the tumor presented as percentage of injected dose per gram of tissue (% ID/g) 1 h and 24 h after injection. Data shown as mean ± standard error of the mean (SEM; n = 3). (F) Autoradiography of the [⁶⁴Cu]Cu-DOTA-TATE tumor distribution (each tissue slice belongs to a different mouse).

Figure 2

[¹⁷⁷Lu]Lu-DOTA-TATE and NS-based PTT for the treatment of NCI-H69 tumors and SPECT/CT imaging. (A) Timeline for the treatment study for all groups. For the groups receiving PRRT, the [¹⁷⁷Lu]Lu-DOTA-TATE injection was done on day 0. For the groups receiving PTT, the NS injection was done either on day 0 or day 5. NIR irradiation was performed a day after NS injection (day 1 or day 6). Tumor growth was followed with a caliper until endpoint (tumor volume of ~1500 mm³). (B) Representative SPECT/CT images from mice injected with [¹⁷⁷Lu]Lu-DOTA-TATE (PRRT group) at 1, 4, and 24 h after injection. (C) SPECT/CT images from mice undergoing PRRT and PTT. Mice were scanned before and after PTT to evaluate the effect of therapy on tumor uptake. Arrows point to the tumors for both the axial and coronal images. The signal intensity is comparable at different timepoints in the same mouse but not between animals (n = 2 per group).

Figure 3

Evaluation of the treatment effect of [¹⁷⁷Lu]Lu-DOTA-TATE PRRT and NS-based PTT in NCI-H69 tumor-bearing mice. (A) Tumor volume at day −1 for all groups. Data shown as mean ± SEM. (B) Representative thermal images of a mouse undergoing NS-based PTT. (C) Maximum surface temperatures on the tumors recorded with a thermal camera during the five-minute irradiation. Data shown as mean ± SEM. Temperatures at t = 300 s for all PTT mice vs. all laser mice were compared. *** represents p < 0.001. (D–J) Tumor growth curves for all mice in each of the groups. Animals were euthanized when tumors reached humane endpoints. (Control group; n = 7, PRRT group; n = 6, PTT group; n = 5, PRRT + PTT day 1 group; n = 5, PRRT + laser day 1 group; n = 7, PRRT + PTT day 6 group; n = 6, and PRRT + laser day 6 group; n = 6). (K) Survival curves for all groups.

Figure 4

Blood cell analysis after combined [¹⁷⁷Lu]Lu-DOTA-TATE and PTT. (A) Red blood cells (M/μL) at day −1, day 7, and day 14 for all groups (Control, PRRT, PTT, PRRT + PTT day 1, PRRT + laser day 1, PRRT + PTT day 6, and PRRT + PTT day 6). (B) Platelets (K/μL). (C) White blood cells (K/μL). (D) Weight (g) measured every other day for all groups, and plotted until day 21 to ensure sufficient representation of mice from all groups. Data shown as mean ± SEM. (n = 4–7 per group).