Cabozantinib in genitourinary malignancies

Trial Watch: combination of tyrosine kinase inhibitors (TKIs) and immunotherapy

The past decades witnessed the clinical employment of targeted therapies including but not limited to tyrosine kinase inhibitors (TKIs) that restrain a broad variety of pro-tumorigenic signals. TKIs can be categorized into (i) agents that directly target cancer cells, (ii) normalize angiogenesis or (iii) affect cells of the hematologic lineage. However, a clear distinction of TKIs based on this definition is limited by the fact that many TKIs designed to inhibit cancer cells have also effects on immune cells that are being discovered. Additionally, TKIs originally designed to target hematological cancers exhibit bioactivities on healthy cells of the same hematological lineage. TKIs have been described to improve immune recognition and cancer immunosurveillance, providing the scientific basis to combine TKIs with immunotherapy. Indeed, combination of TKIs with immunotherapy showed synergistic effects in preclinical models and clinical trials and some combinations of TKIs normalizing angiogenesis with immune checkpoint blocking antibodies have already been approved by the FDA for cancer therapy. However, the identification of appropriate drug combinations as well as optimal dosing and scheduling needs to be improved in order to obtain tangible progress in cancer care. This Trial Watch summarizes active clinical trials combining TKIs with various immunotherapeutic strategies to treat cancer patients.

Intraoperative assessment and postsurgical treatment of prostate cancer tumors using tumor-targeted nanoprobes

Successful visualization of prostate cancer (PCa) tumor margins during surgery remains a major challenge. The visualization of these tumors during surgery via near infrared fluorescence (NIRF) imaging would greatly enhance surgical resection, minimizing tumor recurrence and improving outcome. Furthermore, chemotherapy is typically administered to patients after surgery to treat any missed tumor tissue around the surgical area, minimizing metastasis and increasing patient survival. For these reasons, a theranostics fluorescent nanoparticle could be developed to assist in the visualization of PCa tumor margins, while also delivering chemotherapeutic drug after surgery.

Methods: Ferumoxytol (FMX) conjugated to the fluorescent dye and PCa targeting agent, heptamethine carbocyanine (HMC), yielded the HMC-FMX nanoprobe that was tested in vitro with various PCa cell lines and in vivo with both subcutaneous and orthotopic PCa mouse models. Visualization of these tumors via NIRF imaging after administration of HMC-FMX was performed. In addition, delivery of chemotherapeutic drug and their effect on tumor growth was also assessed.

Results: HMC-FMX internalized into PCa cells, labeling these cells and PCa tumors in mice with near infrared fluorescence, facilitating tumor margin visualization. HMC-FMX was also able to deliver drugs to these tumors, reducing cell migration and slowing down tumor growth.

Conclusion: HMC-FMX specifically targeted PCa tumors in mice allowing for the visualization of tumor margins by NIRF imaging. Furthermore, delivery of anticancer drugs by HMC-FMX effectively reduced prostate tumor growth and reduced cell migration in vitro. Thus, HMC-FMX can potentially translate into the clinic as a nanotheranostics agent for the intraoperative visualization of PCa tumor margins, and post-operative treatment of tumors with HMC-FMX loaded with anticancer drugs.

Modulation of cabozantinib efficacy by the prostate tumor microenvironment

The tumor microenvironment (TME) is increasingly recognized as the arbiter of metastatic progression and drug resistance in advanced prostate cancer (PCa). Cabozantinib is a potent tyrosine kinase inhibitor (TKI) with reported biological activity in the PCa epithelia, but failed to provide an overall survival benefit in phase 3 clinical trials. However, the promising biologic efficacy of the drug in early trials warranted a better understanding of the mechanism of action, with the goal of improving patient selection for TKI-based therapy such as cabozantinib. We found a 100-fold lower cabozantinib IC50 in macrophages, PCa associated fibroblasts, and bone marrow fibroblasts compared to PCa epithelia. In PCa mouse models, pre-treatment with cabozantinib potentiated osseous and visceral tumor engraftment, suggesting a pro-tumorigenic host response to the drug. We further found that the host effects of cabozantinib impacted bone turnover, but not necessarily tumor expansion. Cabozantinib affected M1 macrophage polarization in mice. Analogously, circulating monocytes from PCa patients treated with cabozantinib, demonstrated a striking correlation of monocyte reprograming with therapeutic bone responsivity, to support patient selection at early stages of treatment. Thus, a re-evaluation of TKI-based therapeutic strategies in PCa can be considered for suitable patient populations based on TME responses.