68Ga-PSMA PET/CT imaging in recurrent prostate cancer: Where are we now?

64Cu-DOTHA2-PSMA, a Novel PSMA PET Radiotracer for Prostate Cancer with a Long Imaging Time Window

Prostate cancer imaging and late-stage management can be improved with prostate-specific membrane antigen (PSMA)-targeting radiotracers. We developed a PSMA positron emission tomography (PET) radiotracer, DOTHA2-PSMA radiolabeled with 64Cu (T1/2: 12.7 h), to leverage its large imaging time window. This preclinical study aimed to evaluate the biological and imaging properties of 64Cu-DOTHA2-PSMA. Its stability was assessed in plasma ex vivo and in mice. Cellular behavior was studied for up to 48 h in LNCaP cells. Biodistribution studies were performed in balb/c mice for up to 48 h. Dynamic (1 h) and static (4 h and 24 h) PET imaging was completed in LNCaP tumor-bearing mice. 64Cu-DOTHA2-PSMA was stable ex vivo in plasma and reached cellular internalization up to 34.1 ± 4.9% injected activity (IA)/106 cells at 48 h post-injection (p.i.). Biodistribution results showed significantly lower uptake in kidneys than 68Ga-PSMA-617, our reference PET tracer (p < 0.001), but higher liver uptake at 2 h p.i. (p < 0.001). PET images showed 64Cu-DOTHA2-PSMA’s highest tumoral uptake at 4 h p.i., with a significant difference between blocked and non-blocked groups from the time of injection to 24 h p.i. The high stability and tumor uptake with a long tumor imaging time window of 64Cu-DOTHA2-PSMA potentially contribute to the prostate cancer theranostic approach and its local recurrence detection.

18F-choline positron emission tomography/computed tomography guided laparoscopic salvage lymph node dissection in patients after radical prostatectomy

Introduction

Salvage lymph node dissection (sLND) using novel imaging methods is an interesting alternative to treat lymph node (LN) metastasis after radical prostatectomy (RP); however, recommendations for using sLND as such are still being developed.

Aim

To assess the clinical outcomes of prostate cancer (PCa) after fluorine-18-choline (18F-choline) positron emission tomography/computed tomography (PET/CT) guided sLND.

Material and methods

Ten patients who had undergone sLND under 18F-choline PET/CT guidance (positive nodes: median 1, range 1-3) and had biochemical recurrence or persistence of prostate-specific antigen (PSA: median PSA 2.05 ng/ml, range: 0.8–8.4) after RP were enrolled in this retrospective study. Complete biochemical response (cBCR) after salvage surgery was defined as PSA < 0.2 ng/ml.

Results

The median follow-up time after salvage surgery was 33 months. The median PSA level 6 weeks after sLND and at the end of follow-up was 0.93 and 2.95 ng/ml, respectively. At 6 weeks after targeted sLND only 1 patient had cBCR, whereas a PSA decrease was noted in 7 patients. No patient had cBCR at the end of follow-up.

Conclusions

Laparoscopic sLND in cases of LN metastatic PCa after RP is a feasible option with low morbidity. However, an initial cBCR occurs in a negligible proportion of patients, and a long-term response is unlikely to be achieved.

Positron Emission Tomography/Computed Tomography with Gallium-68-labeled Prostate-specific Membrane Antigen Detects Relapse After Vascular-targeted Photodynamic Therapy in a Prostate Cancer Model

BACKGROUND

Evaluating the efficacy of focal therapy for prostate cancer is limited by current approaches and may be improved with biological imaging techniques.

OBJECTIVE

We assessed whether positron emission tomography/computed tomography with gallium-68-labeled prostate-specific membrane antigen (⁶⁸Ga-PSMA PET/CT) can be used to predict relapse after vascular-targeted photodynamic therapy (VTP).

DESIGN, SETTING, AND PARTICIPANTS

A total of 1×10⁶ LNCaP cells were grafted subcutaneously in the flanks of 6-8-wk-old SCID mice. Of 24 mice with measurable tumors 6 wk after tumor implantation, 20 were treated with VTP (150mW/cm²) to ablate the tumors. Blood prostate-specific antigen (PSA) levels were assessed, and ⁶⁸Ga-PSMA PET/CT images were performed 1 d before VTP and 1 and 4 wk after.

OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS

Local tumor relapse was evaluated by histology, and tumors were analyzed by prostate-specific membrane antigen (PSMA) and PSA immunohistochemistry. T tests and Kruskal-Wallis tests were used to determine significance.

RESULTS AND LIMITATIONS

Four weeks after VTP, 11 (65%) mice had complete responses and six (35%) had tumor relapses confirmed by histology (hematoxylin and eosin, and PSMA immunohistochemistry). All mice with local relapse had positive ⁶⁸Ga-PSMA PET/CT findings 4 wk after VTP; all complete responders did not. One week after VTP, the relapse detection sensitivity of ⁶⁸Ga-PSMA PET/CT was 75%, whereas the sensitivity of PSA was only 33%. Compared with controls, relapsed tumors had a three-fold reduction in the number of cells with strong PSA staining by immunohistochemistry (1.5% vs 4.5%; p=0.01).

CONCLUSIONS

In a preclinical prostate cancer model, we show that ⁶⁸Ga-PSMA PET/CT can identify and predict relapse earlier than blood PSA level. These findings support further testing in clinical trials.

PATIENT SUMMARY

Positron emission tomography/computed tomography with gallium-68-labeled prostate-specific membrane antigen may be used to follow and evaluate treatment outcomes in men who receive focal therapy for prostate cancer.

Review of Gallium-68 PSMA PET/CT Imaging in the Management of Prostate Cancer

Over 90% of prostate cancers over-express prostate specific membrane antigen (PSMA) and these tumor cells may be accurately targeted for diagnosis by 68Ga-PSMA-positron emission tomography/computed tomography (68Ga-PSMA-PET/CT) imaging. This novel molecular imaging modality appears clinically to have superseded CT, and appears superior to MR imaging, for the detection of metastatic disease. 68Ga-PSMA PET/CT has the ability to reliably stage prostate cancer at presentation and can help inform an optimal treatment approach. Novel diagnostic applications of 68Ga-PSMA PET/CT include guiding biopsy to improve sampling accuracy, and guiding surgery and radiotherapy. In addition to facilitating the management of metastatic castrate resistant prostate cancer (mCRPC), 68Ga-PSMA can select patients who may benefit from targeted systemic radionuclide therapy. 68Ga-PSMA is the diagnostic positron-emitting theranostic pair with the beta emitter Lutetium-177 PSMA (177Lu-PSMA) and alpha-emitter Actinium-225 PSMA (225Ac-PSMA) which can both be used to treat PSMA-avid metastases of prostate cancer in the molecular tumor-targeted approach of theranostic nuclear oncology.