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.

Positron Emission Tomography (PET) using [18F]-fluoro-deoxyglucose (FDG) is rapidly gaining acceptance in the clinics for the follow-up of anticancer therapies. Similarly in preclinical studies FDG-μPET could enable non-invasive monitoring of orthotopic or disseminated tumor models. The aim of this study was to assess the suitability of FDG-μPET imaging for the evaluation of the humanized anti-CD38 antibody SAR650984, currently in development, in mice bearing disseminated human lymphoma Daudi. Methods: Female SCID mice were implanted via the tail vein with human lymphoma Daudi cells. In the treatment groups, SAR650984 was administered by the IV route at 40mg/kg in a “prevention” protocol (e.g. before appearance of quantifiable PET signal) or in an “intervention” protocol (e.g. with quantifiable PET signal at baseline). In the vehicle (n=8) and in the SAR650984 groups (n=6), the treatment was given on a q2w schedule for 3 weeks. Serial FDG-PET imaging was performed regularly from day 11-32, 11-56 and 25-133 for control, prevention and intervention groups, respectively. Antitumor efficacy was determined by evaluating the increase in lifespan (ILS) calculated as the delay for median day of death in the treated group relative to the control. Results: SAR650984 was well tolerated at the highest dose tested of 40 mg/kg/adm x 6 adm with 6% and 12% body weight loss at nadir for prevention and intervention protocols, respectively. In the prevention group, SAR650984 was active with 131% ILS and significant delayed tumor glucose uptake: whereas signal could be detected in the PET experiment on day 25 in 8/8 control animals in kidney and ovary target organs, no significant FDG uptake occurred for mice in the prevention before day 39. The signal being quantifiable from day 39 onwards, the delay in FDG uptake between treated and control group was estimated to be 14 days. In the intervention group in which animals were treated with SAR650984 at an advanced stage of disease according to PET (e.g. with measurable FDG signal in target organ Region Of Interest [ROI]), 2 of 6 animals outlived the control group. FDG-PET imaging of the first mouse showed stable tracer uptake within ROI during treatment with an increase in the ovarian region at the end of treatment correlating with the presence of tumors at necropsy (day 88). The second mouse exhibited complete regression of the signal with no resurgence in concordance with the gross necropsy on day 133 showing no hints of tumor invasion in the target organs. Conclusion: The data demonstrates that SAR650984 therapy affects tumor metabolic activity in the disseminated Daudi lymphoma model. FDG-PET imaging thus appears as a valuable functional readout for longitudinal monitoring of anti-CD38 mAb SAR650984 pharmacological activity in the preclinical setting and may provide a mean to follow SAR650984 efficacy in clinic. Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 714.

The Merck-Serono MEK1/2 allosteric inhibitor MSC1936369B (formerly known as AS703026) was combined with the sanofi-aventis pan-PI3K inhibitor SAR245408 (also known as XL147) or the pan-PI3K/mTOR inhibitor SAR24540 (also know as XL765) in mice bearing colon carcinoma HCT116 xenograft tumors. These tumors harbor both KRAS (G13D) and PIK3CA (H1047R) mutations. Apoptosis induction was monitored non-invasively in vivo using fluorescence molecular tomography (FMT) after injection of fluorescent Annexin-V. Ex vivo apoptosis was assessed on tumor lysates using assays for cleaved caspase-3 and cleaved PARP detection. Suboptimal doses of SAR245408, SAR245409, and MSC1936369B were administered orally on a daily schedule as single agents or in combination. Single agent treatments showed marginal or no activity on HCT116 tumor growth inhibition. In contrast, robust enhanced anti-tumor activity was observed with the combination treatments, resulting in sustained tumor stasis and regression for both SAR245408/MSC1936369B (p<0.0001) and SAR245409/MSC1936369B (p=0.0009) combination regimens. This therapeutic synergy was associated with clear induction of tumor apoptosis after four days of treatment, as evidenced by markedly increased levels of cleaved caspase-3 and cleaved PARP proteins in the tumor lysates. Apoptosis monitored in vivo by FMT was induced for the SAR245408/MSC1936369B combination, with p=0.005 and p<0.0001 after three and seven days of therapy respectively. In conclusion, the combination between the MEK1/2 inhibitor MSC1936369B with the pan-PI3K inhibitor SAR245408 or the pan-PI3K/mTOR SAR245409 resulted in significantly enhanced anti-tumor activity in a KRAS/PIK3CA mutated tumor xenograft model, with synergistic induction of tumor apoptosis as demonstrated ex vivo for both combinations and in vivo using longitudinal FMT imaging for the SAR245408/MSC1936369B combination. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr LB-295. doi:10.1158/1538-7445.AM2011-LB-295