Imaging of HER2 may improve the outcome of external irradiation therapy for prostate cancer patients

Trastuzumab cotreatment improves survival of mice with PC-3 prostate cancer xenografts treated with the GRPR antagonist 177 Lu-DOTAGA-PEG2 -RM26

Gastrin‐releasing peptide receptors (GRPRs) are overexpressed in prostate cancer and are suitable for targeted radionuclide therapy (TRT). We optimized the bombesin‐derived GRPR‐antagonist PEG₂‐RM26 for labeling with ¹⁷⁷Lu and further determined the effect of treatment with ¹⁷⁷Lu‐labeled peptide alone or in combination with the anti‐HER2 antibody trastuzumab in a murine model. The PEG₂‐RM26 analog was coupled to NOTA, NODAGA, DOTA and DOTAGA chelators. The peptide‐chelator conjugates were labeled with ¹⁷⁷Lu and characterized in vitro and in vivo. A preclinical therapeutic study was performed in PC‐3 xenografted mice. Mice were treated with intravenous injections (6 cycles) of (A) PBS, (B) DOTAGA‐PEG₂‐RM26, (C) ¹⁷⁷Lu‐DOTAGA‐PEG₂‐RM26, (D) trastuzumab or (E) ¹⁷⁷Lu‐DOTAGA‐PEG₂‐RM26 in combination with trastuzumab. ¹⁷⁷Lu‐DOTAGA‐PEG₂‐RM26 demonstrated quantitative labeling yield at high molar activity (450 GBq/μmol), high in vivo stability (5 min pi >98% of radioligand remained when coinjected with phosphoramidon), high affinity to GRPR (K_D = 0.4 ± 0.2 nM), and favorable biodistribution (1 hr pi tumor uptake was higher than in healthy tissues, including the kidneys). Therapy with ¹⁷⁷Lu‐DOTAGA‐PEG₂‐RM26 induced a significant inhibition of tumor growth. The median survival for control groups was significantly shorter than for treated groups (Group C 66 days, Group E 74 days). Trastuzumab together with radionuclide therapy significantly improved survival. No treatment‐related toxicity was observed. In conclusion, based on in vitro and in vivo characterization of the four ¹⁷⁷Lu‐labeled PEG₂‐RM26 analogs, we concluded that ¹⁷⁷Lu‐DOTAGA‐PEG₂‐RM26 was the most promising analog for TRT. Radiotherapy using ¹⁷⁷Lu‐DOTAGA‐PEG₂‐RM26 effectively inhibited tumor growth in vivo in a murine prostate cancer model. Anti‐HER2 therapy additionally improved survival.

What's new?

Targeted radionuclide therapy (TRT) using radiolabeled peptides seeking gastrin‐releasing peptide receptors (GRPRs) in tumors is a promising approach to treat disseminated prostate cancer. The possibility to improve the therapeutic index via combination therapies also warrants further investigation. Here, the authors developed and characterized a promising GRPR‐targeting radioligand and demonstrated its therapeutic efficacy in prostate cancer xenografts. Moreover, this study using the anti‐HER2 antibody trastuzumab presents the first in vivo proof‐of‐principle that the effects of anti‐GRPR radiotherapy can be amplified by co‐administration of anti‐HER2 treatment leading to prolonged survival.

Combinatorial Microenvironments Impose a Continuum of Cellular Responses to a Single Pathway-Targeted Anti-cancer Compound

Tumor microenvironments are a driver of resistance to anti-cancer drugs. Dissecting cell-microenvironment interactions into tractable units of study presents a challenge. Here, we assess the impact of hundreds of tumor-inspired microenvironments, in parallel, on lapatinib responses in four cancer cell lines. Combinations of ECM and soluble factors were printed on stiffness-tunable substrata to generate a collection of controlled microenvironments in which to explore cell-based functional responses. Proliferation, HER2 protein expression and phosphorylation, and morphology were measured in single cells. Using dimension reduction and linear modeling, the effects of microenvironment constituents were identified and then validated empirically. Each of the cell lines exhibits unique microenvironment-response patterns. Fibronectin, type IV collagen, and matrix rigidity are significant regulators of lapatinib resistance in HER2-amplified breast cancer cells. Small-molecule inhibitors were identified that could attenuate microenvironment-imposed resistance. Thus, we demonstrate a strategy to identify resistance- and sensitivity-driving microenvironments to improve the efficacy of anti-cancer therapeutics.

Molecularly targeted radiosensitization chances towards gene aberration-due organ confined/regionally advanced prostate cancer radioresistance

Considering that the prostate cancer radioresistance occurs in a significant percentage--as 20-40% of prostate cancer (PCa) patients undergone external beam radiation therapy developing, within ten years, recurrent and more aggressive tumor--the resort to customized radiosensitizer measures, focusly targeting PCa radioresistance-linked individual molecular aberrations, can increase the successful outcomes of PCa radiotherapy.