Abstract P6-11-05: Tumor priming with cyclophosphamide for enhanced tumor delivery, penetration and anti-tumor activity of MM-302, HER2-targeted liposomal doxorubicin
Authors: Geretti Elena , Leonard Shannon C , Dumont Nancy , Espelin Christopher W , Gaddy Daniel F , Wickham Thomas J , Hendriks Bart S 
Published: May 2015

MM-302, HER2-targeted PEGylated liposomal doxorubicin, is a liposomal antibody drug conjugate designed to target doxorubicin to HER2-overexpressing cancer cells, while limiting uptake into non-target cells. Effective tumor delivery and penetration are critical barriers to the clinical activity of nanomedicines, including liposomes. Cyclophosphamide has been successfully combined with both doxorubicin and liposomal doxorubicin in breast cancer therapy, with the two drugs being administered on the same day to patients. We have evaluated a novel sequential combination regimen of cyclophosphamide with MM-302 with the goal of improving tumor delivery and penetration of MM-302.

Methods: Biodistribution studies were carried out in multiple tumor xenograft models to assess the delivery of MM-302 and free doxorubicin, either as single agents or in combination with cyclophosphamide at different dosing schedules. The total doxorubicin within tumors was quantified by HPLC and microscopically by determining the number of doxorubicin-positive nuclei within frozen tumor sections. Induction of DNA damage/repair, tumor cell apoptosis, and changes in the tumor architecture in response to drug treatment (tumor cell density and vascular parameters) were quantified by automated image analysis. Interstitial fluid pressure measurements were carried out to evaluate changes in the tumor physiology upon cyclophosphamide treatment. Anti-tumor activity studies in BT474-M3 tumor-bearing mice were performed to evaluate the ability of the different dosing regimens to inhibit tumor growth.

Results: Pre-dosing of tumors with cyclophosphamide enhanced subsequent MM-302 delivery to tumor xenografts (2-3-fold) without affecting delivery to non-target tissues, such as the heart and skin. We demonstrate that this effect is critically dependent on the timing of cyclophosphamide administration. Analysis of cyclophosphamide-treated tumors suggests that the mechanism for improved MM-302 delivery involves the induction of tumor cell apoptosis, reduction of overall tumor cell density, substantial lowering of interstitial fluid pressure and increase in vascular perfusion. Finally, treatment of tumors xenografts with cyclophosphamide followed by MM-302 resulted in a significantly greater tumor growth inhibition compared to either single agent alone.

Conclusions: Rational combination of MM-302 with cyclophosphamide results in an active and tolerable regimen in preclinical models that enhances the tumor delivery and activity of MM-302, without affecting doxorubicin exposure to non-target organs. This novel sequential dosing strategy represents an advance in addressing the critical challenge for tumor delivery of nanomedicines. This work provided data supporting the initiation of a clinical evaluation of the effect of cyclophosphamide on MM-302 delivery as part of an on-going Phase 1 clinical trial of MM-302 in HER2-positive metastatic breast cancer (http://clinicaltrials.gov/show/NCT01304797).

Citation Format: Elena Geretti, Shannon C Leonard, Nancy Dumont, Christopher W Espelin, Daniel F Gaddy, Thomas J Wickham, Bart S Hendriks. Tumor priming with cyclophosphamide for enhanced tumor delivery, penetration and anti-tumor activity of MM-302, HER2-targeted liposomal doxorubicin [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P6-11-05.