Translation of New Molecular Imaging Approaches to the Clinical Setting: Bridging the Gap to Implementation

Translational strategy using multiple nuclear imaging biomarkers to evaluate target engagement and early therapeutic efficacy of SAR439859, a novel selective estrogen receptor degrader

PURPOSE

Preclinical in vivo nuclear imaging of mice offers an enabling perspective to evaluate drug efficacy at optimal dose and schedule. In this study, we interrogated sufficient estrogen receptor occupancy and degradation for the selective estrogen receptor degrader (SERD) compound SAR439859 using molecular imaging and histological techniques.

MATERIAL AND METHODS

[¹⁸F]FluoroEstradiol positron emission tomography (FES-PET), [¹⁸F]FluoroDeoxyGlucose (FDG) PET, and [¹⁸F]FluoroThymidine (FLT) PET were investigated as early pharmacodynamic, tumor metabolism, and tumor proliferation imaging biomarkers, respectively, in mice bearing subcutaneous MCF7-Y537S mutant ERα+ breast cancer model treated with the SERD agent SAR439859. ER expression and proliferation index Ki-67 were assessed by immunohistochemistry (IHC). The combination of palbociclib CDK 4/6 inhibitor with SAR439859 was tested for its potential synergistic effect on anti-tumor activity.

RESULTS

After repeated SAR439859 oral administration over 4 days, FES tumoral uptake (SUVmean) decreases compared to baseline by 35, 57, and 55% for the 25 mg/kg qd, 12.5 mg/kg bid and 5 mg/kg bid treatment groups, respectively. FES tumor uptake following SAR439859 treatment at different doses correlates with immunohistochemical scoring for ERα expression. No significant difference in FDG uptake is observed after SAR439859 treatments over 3 days. FLT accumulation in tumor is significantly decreased when palbociclib is combined to SAR439859 (- 64%) but not different from the group dosed with palbociclib alone (- 46%). The impact on proliferation is corroborated by Ki-67 IHC data for both groups of treatment.

CONCLUSIONS

In our preclinical studies, dose-dependent inhibition of FES tumoral uptake confirmed target engagement of SAR439859 to ERα. FES-PET thus appears as a relevant imaging biomarker for measuring non-invasively the impact of SAR439859 on tumor estrogen receptor occupancy. This study further validates the use of FLT-PET to directly visualize the anti-proliferative tumor effect of the palbociclib CDK 4/6 inhibitor alone and in combination with SAR439859.

Magnetic Resonance Imaging for Translational Research in Oncology

The translation of results from the preclinical to the clinical setting is often anything other than straightforward. Indeed, ideas and even very intriguing results obtained at all levels of preclinical research, i.e., in vitro, on animal models, or even in clinical trials, often require much effort to validate, and sometimes, even useful data are lost or are demonstrated to be inapplicable in the clinic. In vivo, small-animal, preclinical imaging uses almost the same technologies in terms of hardware and software settings as for human patients, and hence, might result in a more rapid translation. In this perspective, magnetic resonance imaging might be the most translatable technique, since only in rare cases does it require the use of contrast agents, and when not, sequences developed in the lab can be readily applied to patients, thanks to their non-invasiveness. The wide range of sequences can give much useful information on the anatomy and pathophysiology of oncologic lesions in different body districts. This review aims to underline the versatility of this imaging technique and its various approaches, reporting the latest preclinical studies on thyroid, breast, and prostate cancers, both on small laboratory animals and on human patients, according to our previous and ongoing research lines.

Advanced PET imaging in oncology: status and developments with current and future relevance to lung cancer care

PURPOSE OF REVIEW

This review highlights the status and developments of PET imaging in oncology, with particular emphasis on lung cancer. We discuss the significance of PET for diagnosis, staging, decision-making, monitoring of treatment response, and drug development. The PET key advantage, the noninvasive assessment of functional and molecular tumor characteristics including tumor heterogeneity, as well as PET trends relevant to cancer care are exemplified.

RECENT FINDINGS

Advances of PET and radiotracer technology are encouraging for multiple fields of oncological research and clinical application, including in-depth assessment of PET images by texture analysis (radiomics). Whole body PET imaging and novel PET tracers allow assessing characteristics of most types of cancer. However, only few PET tracers in addition to F-fluorodeoxyglucose have sufficiently been validated, approved, and are reimbursed for a limited number of indications. Therefore, validation and standardization of PET parameters including tracer dosage, image acquisition, post processing, and reading are required to expand PET imaging as clinically applicable approach.

SUMMARY

Considering the potential of PET imaging for precision medicine and drug development in lung and other types of cancer, increasing efforts are warranted to standardize PET technology and to provide evidence for PET imaging as a guiding biomarker in nearly all areas of cancer treatment.

Imaging Cobalamin Uptake within Malignant Breast Tumors In Vivo

PURPOSE

To image the uptake of cobalamin (Cbl) within malignant breast tumors in vivo.

PROCEDURES

Prior to surgery 20 female patients with clinically suspected breast tumors were intravenously administered 0.25 μg of an In-111 labeled 5-deoxyadenosylcobalamin (AC) analog ([¹¹¹In]AC) and sequentially imaged with whole-body planar (WBP) and single-photon emission computed tomography (SPECT) between 2-5 h and 20-24 h post-injection (P.I.). The tumor to background (T/B) ratio for [¹¹¹In]AC in breast tumors at 2-5 h was correlated to its expression of estrogen (ER), progesterone (PR), and human epidermal growth factor 2 (HER2) receptors. Subsequent pulse chase (PC) experiments in nude mice burdened with the MDA-MB-231 triple-negative (TN) breast tumor xenograft measured the effect that pulses of AC or dexamethasone (DEX) had on [¹¹¹In]AC uptake in both normal murine tissue and the TN breast tumor.

RESULTS

The mean [¹¹¹In]AC T/B ratio of the patients' 18 resected tumors was 5.8. Comparing ER- and PR-positive tumors (n = 11) to TN and HER2-positive tumors (n = 7), the mean [¹¹¹In]AC T/B ratios at 2-5 h P.I. were 3.2 (range 1.8-5.6) and 10.4 (range 3.3-22.5), respectively. Pulses of 2.0 μg of AC at 2, 8, or 24 h; or 40.0 μg of DEX at 24 h prior to injecting 0.5 μg of [¹¹¹In]AC, increased mean tracer uptake in the MDA-MB-231 tumors by 26.4, 71.5, 92.6, and 49.1 %, respectively. Only the 2- and 24-h PC intervals concomitantly suppressed [¹¹¹In]AC uptake in normal murine tissue while enhancing [¹¹¹In]AC uptake in MDA-MB-231 tumors.

CONCLUSION

The uptake of Cbl within malignant breast tumors can be imaged clinically. Cbl uptake is greatest in TN and HER2-positive breast tumors. A solitary bolus of AC or DEX increases the [¹¹¹In]AC uptake within a breast tumor in vivo. Investigating the cytogenetic mechanisms controlling the endocytosis of Cbl in malignant breast tumors is warranted.

Response Detection of Castrate-Resistant Prostate Cancer to Clinically Utilised and Novel Treatments by Monitoring Phospholipid Metabolism

Androgen receptor (AR) activation is the primary driving factor in prostate cancer which is initially responsive to castration but then becomes resistant (castration-resistant prostate cancer (CRPC)). CRPC cells still retain the functioning AR which can be targeted by other therapies. A recent promising development is the use of inhibitors (Epi-1) of protein-protein interaction to inhibit AR-activated signalling. Translating novel therapies into the clinic requires sensitive early response indicators. Here potential response markers are explored. Growth inhibition of prostate cancer cells with flutamide, paclitaxel, and Epi-1 was measured using the MTT assay. To simulate choline-PET scans, pulse-chase experiments were carried out with [³H-methyl]choline and proportion of phosphorylated activity was determined after treatment with growth inhibitory concentrations of each drug. Extracts from treated cells were also subject to ³¹P-NMR spectroscopy. Cells treated with flutamide demonstrated decreased [³H-methyl]choline phosphorylation, whilst the proportion of phosphorylated [³H-methyl]choline that was present in the lipid fraction was increased in Epi-1-treated cells. Phospholipid breakdown products, glycerophosphorylcholine and glycerophosphoethanolamine levels, were shown by 31P-NMR spectroscopy to be decreased to undetectable levels in cells treated with Epi-1. LNCaP cells responding to treatment with novel protein-protein interaction inhibitors suggest that ³¹P-NMR spectroscopy may be useful in detecting response to this promising therapy.

In vitro cytotoxic and genotoxic evaluation of peptides used in nuclear medicine (DOTATATE and Ubiquicidin29-41) in CHO-K1 cells

Micronucleus (MN) assay constitutes a valuable surrogate to the chromosome aberration technique for in vitro testing of the genotoxicity of substances. As test substances, two peptidic compounds (DOTATATE and Ubiquicidin_29-41) used in nuclear medicine, were tested for in vitro cytotoxicity and genotoxicity in CHO-K1 cells. None of the compounds showed detectable cytotoxicity (0.5-7.3 ng/mL for DOTATATE and 0.3-4.5 ng/mL for UBI_29-41), genotoxicity (0.72, 7.2 and 72.0 ng/ml for DOTATATE and 0.45, 4.5 and 45.0 ng/mL for UBI_29-41) or cell cycle changes as compared to untreated controls at the concentrations tested. Statistical analysis showed good concordance between two independent analysts. The results corroborate the notion of the safety of the compounds and present improvements of the in vitro MN assay when performed in a pre-clinical trial context that increase the throughput of small-to-medium testing facilities as an alternative to high content screening systems.