Abstract Nal-IRI, a liposomal formulation of irinotecan, is designed for extended circulation relative to non-liposomal irinotecan and to exploit leaky tumor vasculature for enhanced drug delivery to tumors. Following tumor deposition, nal-IRI is taken up by phagocytic cells followed by irinotecan release and conversion to its active metabolite, SN-38. Sustained inhibition of topoisomerase 1 (TOP1) by extended SN-38 exposure is hypothesized to enable superior anti-tumor activity compared to traditional TOP1 inhibitors. Topotecan, another TOP1 inhibitor, is an approved second-line treatment option for small cell lung cancer (SCLC). Here, we evaluate the anti-tumor activity of nal-IRI compared to irinotecan and topotecan in preclinical models of SCLC including those that have been pre-treated with therapeutics used clinically to treat SCLC. Anti-tumor activity of nal-IRI, irinotecan, or topotecan was evaluated based on tumor volume assessments in DMS-53, DMS-114 and NCI-H1048 subcutaneous xenograft models in NOD-SCID mice, as well as in a patient-derived xenograft (PDX) model in nu/nu mice. To approximate clinical dosing: Nal-IRI was dosed at 16 mg/kg (irinotecan HCl basis), q1w, equivalent to a proposed clinical dose of 90 mg/m2 free base, q2w; irinotecan was dosed at 33 mg/kg q1w, equivalent to a clinical dose of 180 mg/m2 q2w; and topotecan was dosed at 0.83 mg/kg/week, day 1-2 every 7 days, which approximates a clinical dose intensity of 1.5 mg/m2 (days 1-5 every 21 days). Additionally, the activity of these agents was evaluated after tumors progressed following prior treatment with either topotecan, irinotecan or the combination of weekly carboplatin (30 mg/kg) plus etoposide (25 mg/kg), a standard first line regimen. Nal-IRI demonstrated anti-tumor activity in xenograft models of SCLC at clinically relevant dose levels, and resulted in complete or partial responses in DMS-53, DMS-114, NCI-H1048 and a PDX model in comparison with irinotecan or topotecan, which each had limited tumor growth control. Furthermore, Nal-IRI demonstrated anti-tumor activity in tumors that progressed following treatment with topotecan, and demonstrated significantly greater anti-tumor activity than both topotecan (p<0.0001) and irinotecan (p<0.0001) in NCI-H1048 tumors (8/8 complete responses) that had progressed on prior carboplatin plus etoposide treatment. These results support the further clinical development of nal-IRI versus IV topotecan in patients with SCLC that progressed on or after prior platinum containing therapy. Citation Format: Shannon C. Leonard, Daniel Gaddy, Helen Lee, Stephan Klinz, Jonathan Fitzgerald, Bart Hendriks. Nanoliposomal irinotecan (nal-IRI, MM-398) has greater anti-tumor activity than topotecan and irinotecan in mouse models of small cell lung cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5151. doi:10.1158/1538-7445.AM2017-5151

Nal-IRI (irinotecan liposome injection, MM-398, ONIVYDE®), in combination with 5-fluorouracil and leucovorin, is currently approved by the FDA for treatment of patients with advanced pancreatic cancer who have progressed on gemcitabine-based therapies. Nal-IRI is designed for extended circulation relative to non-liposomal irinotecan and to exploit leaky tumor vasculature for enhanced drug delivery to tumors. Following tumor deposition, nal-IRI is taken up by phagocytic cells followed by irinotecan release and conversion to its active metabolite SN-38 in the tumors. Sustained inhibition of topoisomerase 1 (TOP1) by extended SN-38 delivery is hypothesized to enable superior anti-tumor activity compared to traditional TOP1 inhibitors. Topotecan, a TOP1 inhibitor, is currently a standard of care for second-line treatment of small cell lung cancer (SCLC). Here, we evaluate nal-IRI compared to topotecan in preclinical models of SCLC. Anti-tumor activity of nal-IRI as a monotherapy was evaluated in DMS-53 and NCI-H1048 xenograft models. Cells were implanted subcutaneously into right flanks of NOD-SCID mice; treatments were initiated when tumors had reached approximately 280 mm3. Nal-IRI was dosed at 16 mg/kg salt, q1w, which is equivalent to a proposed clinical dose of 90 mg/m2 free base, q2w. Topotecan was dosed at 0.83 mg/kg/week, Day 1-2 every 7 days, which approximates a clinical dose intensity of 1.5 mg/m2 (Day 1-5 every 21 days). Tumor metabolite levels were compared in mice treated with nal-IRI or non-liposomal irinotecan at 24 hours post-injection, using previously established high performance liquid chromatography methods. Carboxylesterase activity and sensitivity to SN-38 in mouse SCLC models were comparable to those measured in tumor types where either nal-IRI or irinotecan HCl has proven to be efficacious clinically (e.g. pancreatic cancer, colorectal cancer). Nal-IRI delivered irinotecan to SCLC tumors to a similar or greater extent than other tumor types including pancreatic tumors. The tumor irinotecan and SN-38 levels of nal-IRI (16 mg/kg salt) were 12 to 57-fold and 5 to 20-fold higher than non-liposomal irinotecan (30 mg/kg salt), respectively. Nal-IRI demonstrated anti-tumor activity in both xenograft models of SCLC at clinically relevant dose levels, and resulted in complete or partial responses after 4 cycles in NCI-H1048 or DMS-53 models, respectively, compared with topotecan which had limited tumor growth control. This study demonstrated that nal-IRI is more active than topotecan at clinically relevant doses in SCLC preclinical models, and thus support further clinical development of nal-IRI versus topotecan in patients with SCLC that have progressed on prior platinum-based therapy.

336 Background: Nanoliposomal irinotecan (nal-IRI, MM-398) recently gained approval in combination with 5-fluorouracil/leucovorin (5-FU/LV) in post-gemcitabine metastatic pancreatic ductal adenocarcinoma (PDAC) based on the extended survival and manageable safety profile observed in the Phase 3 NAPOLI-1 trial. Preclinically, we have previously demonstrated the anti-tumor activity of nal-IRI with 5-FU and oxaliplatin, standard of care agents in first-line PDAC, and are currently investigating this combination in patients with previously untreated metastatic PDAC in a Phase 2 clinical trial (NCT02551991). Herein, we further evaluate nal-IRI as a potential backbone of first-line metastatic PDAC by assessing the preclinical anti-tumor activity of nal-IRI relative to, and in combination with, gemcitabine and nanoparticle albumin-bound-paclitaxel (nab-P). Methods: Nal-IRI tumor metabolite (CPT-11 and SN-38) levels were measured in mice treated with nal-IRI in combination with gemcitabine or nab-P. Anti-tumor activity and tolerability of nal-IRI, 5-FU, gemcitabine and nab-P monotherapies and combinations were evaluated using pancreatic cancer cell line (ASPC-1 and CFPAC-1)-derived xenograft models, as well as a panel of five patient-derived xenograft models. Results: Administration of gemcitabine or nab-P prior to or simultaneously with nal-IRI resulted in unchanged or increased nal-IRI deposition, as measured by tumor CPT-11 and SN-38 levels at 24 hours post-injection. Moreover, in both cell line-derived and patient-derived xenograft models of PDAC, nal-IRI monotherapy demonstrated comparable or improved anti-tumor activity relative to gemcitabine or nab-P monotherapies. Further, nal-IRI consistently improved tumor growth inhibition and survival when used in combination with either 5-FU, gemcitabine and/or nab-P, relative to the combination of gemcitabine plus nab-P. All treatments were well-tolerated in these preclinical models. Conclusions: These findings illustrate the compatibility and therapeutic potential of nal-IRI as a foundation of first-line PDAC combination regimens, and warrant clinical evaluation.

Abstract Background: MM-302 is an antibody drug conjugated HER2-targeted liposomal doxorubicin in development by Merrimack Pharmaceuticals. MM-302 is designed to deliver doxorubicin to HER2-overexpressing cancer cells with minimal exposure to healthy cardiomyocytes. Results of the MM-302 phase I study as a monotherapy, in combination with trastuzumab and trastuzumab plus cyclophosphamide, are presented. Methods: 69 patients with HER2-positive metastatic breast cancer (mBC) were treated with either MM-302 alone (8, 16, 30, 40 and 50 mg/m2, Q4W) (Arm 1), MM-302 (30 and 40 mg/m2, Q4W) plus trastuzumab (4 mg/kg, Q2W) (Arm 2), MM-302 (30 mg/m2, Q3W) plus trastuzumab (6 mg/kg, Q3W) (Arm 3), MM-302 (30 mg/m2, Q3W) plus trastuzumab (6 mg/kg, Q3W) and cyclophosphamide (450 mg/m2, Q3W) (Arm 4). Patients on Arms 3 and 4 received a single 3-7 mg/m2 (approximately 10.8 mCi) dose of 64Cu-MM-302 followed by PET/CT to assess for MM-302 tumor deposition. Results: Patients received a median of 4 prior regimens for mBC. The most common Grade 3/4 side effect was neutropenia observed in 8 patients with 1 patient experiencing febrile neutropenia. Adverse events of any grade occurring in >20% of the population were constipation, cough, decreased appetite, diarrhea, dyspnea, fatigue, nausea, neutropenia, stomatitis and vomiting. Alopecia and hand foot syndrome were observed in 10% and 4% of patients respectively. 1 patient experienced a dose limiting toxicity DLT (febrile neutropenia) and a MTD was not reached at 50 mg/m2. 11 patients received cumulative anthracycline (previous exposure plus MM-302) exposure >550 mg/m2. LVEF reductions below 50% or a >10 percentage point drop in LVEF from baseline occurred in 6 patients. 1 patient experienced Grade 1 cardiac failure resulting in treatment discontinuation. In patients treated with ≥30 mg/m2 MM-302 (n = 49), alone or in combination with trastuzumab, the response rate (RR) was 12% and median progression free survival (mPFS) was 7.6 months (95% CI: 3.6-11.0). mPFS was 10.6 months (95% CI: 1.8-10.6) in the 13 patients receiving MM-302 plus trastuzumab and cyclophosphamide in Arm 4. Conclusions: MM-302 had a manageable safety profile in this study as a monotherapy, in combination with trastuzumab and with trastuzumab and cyclophosphamide. RR and mPFS in this heavily pretreated mBC population suggest further study is warranted. MM-302 at a dose of 30 mg/m2 Q3W in combination with trastuzumab is currently being evaluated in a randomized phase II trial (HERMIONE) in anthracycline naïve HER2-positive locally advanced/mBC patients previously treated with trastuzumab, pertuzumab and T-DM1. Citation Format: Patricia LoRusso, Ian Krop, Kathy Miller, Cynthia Ma, Barry A. Siegel, Anthony F. Shields, Istvan Molnar, Thomas Wickham, Joseph Reynolds, Karen Campbell, Bart Hendriks, Ty McClure, Victor Moyo, Pamela Munster. A phase I study of MM-302, a HER2-targeted PEGylated liposomal doxorubicin, in patients with HER2+ metastatic breast cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr CT234. doi:10.1158/1538-7445.AM2015-CT234

Abstract Background: Liposomal encapsulation of doxorubicin has addressed the cardiotoxicity of free doxorubicin, but has not achieved an improvement in anti-tumor activity in metastatic breast cancer. MM-302 is a HER2-targeted liposomal doxorubicin, specifically designed to target tumor cells overexpressing HER2 and minimize uptake into normal cells such as cardiomyocytes, which express low levels of HER2. MM-302 and MM-302 plus trastuzumab are being studied in patients as part of an ongoing Phase 1 clinical trial. Published reports indicate that deposition into solid tumors is a rate-limiting step in liposome-mediated delivery of drug to tumor cells. In order to understand drug deposition into solid tumors, we have radiolabeled MM-302 with 64Cu for imaging by PET/CT. Further, preclinical work has demonstrated that pretreatment with cyclophosphamide has the ability to improve liposomal drug delivery by making the tumor microenvironment permissive for deposition and retention of liposomes. This Phase 1 study evaluates the delivery of 64Cu-MM-302 to solid tumors and the ability of cyclophosphamide pretreatment to increase delivery of 64Cu-MM-302 to tumors. Methods: Patients aged ≥ 18 years with histologically confirmed HER2-positive advanced breast cancer that has progressed or recurred on standard therapy or for which no standard therapy exists, who have adequate performance status, bone marrow reserve and organ function, were eligible for the study. Patients received 30 mg/m2 of MM-302 plus 6 mg/kg trastuzumab, q3w and 400 MBq (10.8 mCi; 3-5 mg/m2, doxorubicin basis) of 64Cu-MM-302 (cycle 1 only) with or without pretreatment of 450 mg/m2 cyclophosphamide. Patients underwent PET/CT on the day of administration and on day 2, day 3 or both. The primary goal of this analysis was to study delivery of 64Cu-MM-302 and the effect of cyclophosphamide pretreatment. Other endpoints being studied include safety, dosimetry, and treatment response. Results: Combination of MM-302 with cyclophosphamide was well tolerated and no issues were reported related to 64Cu-MM-302 administration or imaging. Uptake of 64Cu-MM-302 in tumor lesions increased over time with significant deposition at 24 and 48 h while activity in the blood decreased over time. Median lesion deposition of 64Cu-MM-302 (as % i.d./kg) in the patients with cyclophosphamide pretreatment was higher than in those without pretreatment: 6.0 (n=5 patients/20 lesions) vs. 4.4 (n=7 patients/36 lesions) at 24 h and 7.6 (n=4 patients/16 lesions) vs. 4.0 (n=4 patients/17 lesions) at 48 h. Conclusions: PET/CT imaged 64Cu-MM-302 deposition into diverse tumor lesions, including liver, brain and bone metastases. Our preliminary data thus far suggest that cyclophosphamide pretreatment increases delivery of 64Cu-MM-302 to patient tumors, as predicted by preclinical models. Correlation between 64Cu-MM-302 tumor deposition and lesion/patient response is currently being investigated. Citation Format: Kathy Miller, Patricia M LoRusso, Pamela Munster, Ian Krop, Cynthia Ma, Helen Lee, Joe Reynolds, Karen Campbell, Victor Moyo, Bart Hendriks, Thomas Wickham, Barry A Siegel, Anthony F Shields. Effect of pre-treatment with cyclophosphamide on MM-302 (HER2-targeted liposomal doxorubicin) deposition in HER2-positive metastatic breast cancer patients assessed by 64Cu-MM-302 PET/CT [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 P4-15-04.

Abstract Introduction: Despite improvements in treatment with newly approved HER2-targeted therapies, safe and effective treatments are still needed, not only for HER2-positive metastatic breast cancer (MBC), but also for MBC expressing intermediate levels of HER2 that are still considered HER2-negative (e.g. IHC 2+, FISH-negative). MM-302 is a liposomal antibody drug conjugate (ADC) designed to target doxorubicin to HER2-overexpressing cancer cells. MM-302 is currently being evaluated in HER2-positive locally advanced breast cancer (LABC)/MBC patients in the registration-directed HERMIONE trial. The objective of this study was to compare the relative efficacy of MM-302 and PLD in treating HER2-intermediate MBC (corresponding to 1+/2+ by IHC) using models that closely mimic how HER2-overexpressing metastatic tumors are established in humans. Methods: To establish metastatic disease, the murine 4T1-HER2 cell line engineered to express intermediate levels of Her2 (median of ∼1×105 HER2 receptors/cell), and the human MDA-MB-453 cells that endogenously express intermediate levels of Her2 (2+ by IHC and median of ∼3×105 HER2 receptors/cell), were inoculated orthotopically into the right and left mammary fat pads of immunocompromised mice. Primary tumors then spontaneously seed cancer cells in distant visceral organs such as the lung. When primary tumor volumes reached ∼150 mm3 (4T1-Her2) or ∼270 mm3 (MDA-MB-453), mice were randomized and treated with vehicle control, PLD or MM-302. At the end of the study, primary tumors and lungs were harvested to assess liposome delivery and quantify pulmonary metastatic burden. Results: MM-302 was more effective than PLD at reducing total pulmonary metastatic burden in both HER2-intermediate models as evidenced by the lower number of surface metastases in the 4T1-Her2 model and the lower number of human cytokeratin positive cells per lung in the MDA-MB-453 model. MM-302 and PLD were equally effective at slowing (4T1-Her2) and inhibiting (MDA-MB-453) primary tumor growth. Mechanisms responsible for differences in efficacy are being explored. To date, better distribution of liposomes in metastatic lesions than in primary tumors has been observed where liposome delivery appears to be restricted to the tumor periphery in the 4T1-Her2 model. Conclusion: MM-302 was more effective than PLD at reducing pulmonary metastatic tumor burden in both HER2-expressing models. The superiority of MM-302 over PLD was unique to metastatic lesions where there was better distribution of liposomes than in the primary tumor. These results support the rationale for evaluating MM-302 in patients with HER2-intermediate MBC. Citation Format: Nancy Dumont, Elena Geretti, Shannon Curtis Leonard, Christopher Espelin, Daniel Gaddy, Bart Hendriks, Ulrik Nielsen, Thomas Wickham. MM-302 is more effective than PEGylated liposomal doxorubicin (PLD) at reducing pulmonary metastatic burden in breast cancer models expressing intermediate levels of HER2. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4134. doi:10.1158/1538-7445.AM2015-4134

TPS663 Background: Anthracyclines have been an effective backbone of breast cancer therapies for decades. However, cardiotoxicity issues associated with free anthracyclines have limited their effective use in the clinic and led to the exploration of anthracycline-free regimens, particularly with HER2-positive cancers that require treatment with another cardiotoxic agent, trastuzumab. While liposomal doxorubicin formulations have succeeded in reducing cardiotoxicity, they have failed to demonstrate clear-cut efficacy advantages and can involve other toxicities. To address the safety and efficacy limitations of currently available anthracyclines, we have designed a new liposomal formulation, MM-302, that targets doxorubicin to HER2-overexpressing tumor cells. Antibody fragments that bind to HER2 without blocking HER2-mediated signaling are coupled to the outer surface of pegylated liposomal doxorubicin. MM-302 specifically binds and enters tumor cells overexpressing HER2 with minimal uptake into normal cells such as cardiomyocytes which express low levels of HER2. This first-in-human phase I study evaluates the safety of MM-302 in patients and provides preliminary efficacy data in HER-2+ advanced breast cancer (ABC). Methods: Patients aged > 18 years with histologically confirmed HER-2+ advanced breast cancer that have progressed or recurred on standard therapy or for which no standard therapy exists who have adequate performance status, bone marrow reserve, and organ function, are eligible for the study. Following a standard 3 + 3 dose escalation design, the maximum tolerated dose (MTD) or maximum feasible dose (MFD) is determined and up to 25 additional patients with HER-2+ ABC will be enrolled for a planned total of 40-49 patients. The primary endpoint is determination of the MTD/MFD. Secondary endpoints include determination of dose-limiting toxicity, adverse event(s), and pharmacokinetic and immunogenicity profiles of MM-302, as well as overall response and clinical benefit rates of MM-302. MM-302 is administered intravenously weekly in 4-week cycles. At the time of this submission, 8 patients have been enrolled in the dose escalation portion.

Abstract MM-398 is a stable nanotherapeutic encapsulation of the prodrug irinotecan with an extended plasma half-life and higher intratumoral deposition compared with free-irinotecan. MM-398 is currently in multiple clinical trials, including a phase 3 trial for patients with advanced gemcitabine-resistant pancreatic cancer (NAPOLI-1). Pancreatic cancer has been described as being notoriously difficult to treat, potentially due to inadequate drug penetration through the dense stroma, or because the hypoxic tumor microenvironment suppresses cytotoxic activity. We sought to better understand how MM-398, a relatively large (100nm) liposomal nanotherapeutic, could potentially treat pancreatic cancer by determining the relative roles of systemic vs. local tumor activation of irinotecan in contributing to the activity of MM-398. Using a systems pharmacology approach, we developed a mechanistic pharmacokinetic (PK) model of MM-398 and free-irinotecan to predict both plasma and intratumoral levels of irinotecan and SN-38. The model was trained with PK and biodistribution data from mice bearing HT-29 xenografts, which were administered intravenously with varying doses of MM-398 or free-irinotecan. Model simulations predicted that MM-398 resulted in equivalent SN-38 exposure (area under curve, AUC) in tumor at a fivefold lower dose than free-irinotecan. However, an in vivo animal activity study showed that 15-fold lower dose of MM-398 was sufficient to yield equal growth inhibition of HT-29 xenografts, which reveals the limit of relating simple AUC-based exposure to in vivo tumor response. While intratumoral SN-38 exposure from free-irinotecan was limited to the first 48 hours after dosing, MM-398 maintained high levels of SN-38 throughout the week-long time window. Further analysis of the exposure-response identified that the duration of intratumoral SN-38 levels above the threshold was a valid predictive marker for xenograft tumor response. Identifying the source of intratumoral SN38 is confounded by the fact that the mouse species has an additional carboxylesterase (CES) that can convert irinotecan to SN-38 in serum. The serum SN-38/irinotecan ratio in mice is tenfold higher than that observed in humans. In order to translate this preclinical observation into the clinic, it is critical to identify the role of mouse-specific serum CES on intratumoral SN-38 exposure. Thus, we performed a PK study with knockout mice lacking the Ces1c gene, which encodes serum CES, and then retrained our mechanistic PK model. Serum SN-38 levels in the Ces1c knockout mice were measurably decreased by ˜85% in the central compartment. In contrast, simulating the effect of knock-out of either serum CES or tumor CES, predicts that the duration of intratumoral residence of SN-38 is significantly affected by tumor CES, rather than serum CES. This suggests that local activation to SN-38 by tumor CES as the main driver for SN-38 tumor residence, which in turn drives response. In summary, we applied a systems pharmacology approach to identify the importance of tumor CES (local SN-38 generation) as one of the determinants of MM-398 response. Liposomal encapsulation of irinotecan dramatically alters the pharmacokinetic profile of SN-38 in the tumor, as well as tumor response, by maintaining SN-38 levels above the response threshold. Local, sustained activity of this active irinotecan metabolite could result in prolonged cytotoxic and tumor microenvironment modifications with beneficial effects on treatment of pancreatic cancer and other solid tumors. Citation Format: Jaeyeon Kim, Eliel Bayever, Peter Laivins, Clet Niyikiza, Ulrik Nielsen, Jonathan Fitzgerald, Ashish Kalra, Milind Chalishazar, Stephan Klinz, Nancy Paz, Bart Hendriks, Daryl Drummond, Dmitri Kirpotin, Victor Moyo. Sustained intratumoral activation of MM-398 results in superior activity over irinotecan demonstrated by using a systems pharmacology approach [abstract]. In: Proceedings of the AACR Special Conference on Chemical Systems Biology: Assembling and Interrogating Computational Models of the Cancer Cell by Chemical Perturbations; 2012 Jun 27-30; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2012;72(13 Suppl):Abstract nr A6.

Abstract For the chemotherapeutic, doxorubicin, liposomal encapsulation simultaneously (i) protects the heart from doxorubicin-induced cardiotoxicity, (ii) results in passive tumor accumulation via the enhanced permeability and retention effect and (iii) increases its circulation life-time. Clinically, pegylated-liposomal doxorubicin (PLD) shows a dramatic benefit to Kaposi sarcoma (KS) patients relative to free doxorubicin. In contrast, PLD does not show any survival benefit relative to free doxorubicin in patients with metastatic breast cancer. We hypothesized that the differential efficacy observed might be explained by differences in tumor cell exposure to drug. To better understand the effects of liposomal encapsulation on drug exposure, we developed a mechanism-based PK model of liposome biodistribution. The model consists of superimposed PK models for free and liposomal doxorubicin with a common central blood compartment which are then connected to a physiologically-based tumor tissue compartment. The tumor tissue compartment includes vascular, interstitial and cell space and captures rates of blood flow, tumor deposition into the interstitial space, doxorubicin release from the liposomes and the trafficking of free doxorubicin into and out of cells. The model parameters were extensively validated against literature data from in vitro studies, mouse xenografts and human clinical data. With our model we are able to simulate total tumor doxorubicin and DNA-bound doxorubicin in tumors, reproducing observed mouse xenograft data for free vs. liposomal doxorubicin. Analysis of the model revealed dramatically different dynamics in tumor exposure for free vs. liposomal doxorubicin delivery. Further, rates of tumor deposition were rate-limiting for overall tumor cell exposure for liposomally-delivered doxorubicin. Upon scaling the model to reflect human physiology, we demonstrate that the clinically observed liposome accumulation in KS tumors can quantitatively explain the dramatic increase in efficacy relative to free doxorubicin. Furthermore, the model indicates that the lower rates of liposome tumor deposition seen in breast cancer patients result in no survival benefit relative to free doxorubicin, consistent with clinical trial results. 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 4915. doi:10.1158/1538-7445.AM2011-4915

Abstract Introduction: MM-302 is an ErbB2/HER2-targeted liposomal doxorubicin formulation designed to target doxorubicin to HER2-overexpressing cancer cells while limiting uptake into non-target cells. The characterization of the binding and uptake of MM-302 as a function of HER2 surface levels on various cell lines and in tumor models will help determine the minimum HER2 receptor levels required for MM-302 patient selection. Methods: Cellular models included 16+ established human tumor cell lines as well as 4T1 murine breast cancer and HeLa human cervical cancer cells engineered to overexpress HER2 from 1E05-1E06 receptors/cell. Cells were incubated with MM-302, untargeted liposomes or free doxorubicin and binding/uptake was measured by HPLC or flow cytometry. In vivo efficacy was determined in select mouse xenograft models. Tumors were mechanically and enzymatically dissociated, followed by flow cytometry to quantify the uptake of targeted and untargeted liposomes into HER2-expressing tumor cells, macrophages and other cell types. Results: Binding and uptake of MM-302 increased with rising HER2 surface levels in cells of common parental origin (4T1, HeLa), with significant uptake into cells with >2E05 HER2/cell. Further, total cell binding/uptake of MM-302 also increased with rising HER2 expression across a panel of 16+ cell lines. There was negligible uptake of untargeted liposomes under all conditions that showed no dependence on HER2 expression. Improved anti-tumor efficacy of MM-302 was observed in BT474-M3 and NCI-N87 mouse xenograft models relative to untargeted liposomal doxorubicin and free doxorubicin. Further, using disaggregated tumors, the relationship between HER2 expression and MM-302 uptake was confirmed in vivo in both models. Conclusions: Our studies identified a HER2 threshold for uptake of MM-302 of approximately 2E05 receptors/cell, and suggest a role for MM-302 not only in HER2 3+ cancers, but also in HER2 2+ cancers as well. The ability to treat HER2 2+ tumors offers an exciting opportunity to serve a major unmet clinical need. 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 3637. doi:10.1158/1538-7445.AM2011-3637

Abstract Introduction: Anthracyclines have historically been the backbone of anticancer therapy for decades; however, the clinical observation of permanent cardiotoxicity has limited their broader use. In the HER2 positive breast cancer setting, the combination of trastuzumab with anthracyclines was associated with an unacceptable risk of clinical cardiotoxicity. This appears to be related to 1) doxorubicin-induced cardiomyocyte stress and 2) inability of the cardiomyocytes to respond to the stress due to the trastuzumab-related impairment of HER2 signaling. Encapsulation of doxorubicin into liposomes (Doxil®) has been associated with a reduced risk of doxorubicin-associated cardiotoxicity relative to free doxorubicin. MM-302 is a HER2-targeted liposomal doxorubicin-based agent designed to target doxorubicin to HER2-overexpressing cancer cells, while limiting uptake into non-target cells. Since HER2-mediated signaling plays an important role in cardiac repair, the purpose of this work was to support clinical development of MM-302 by investigating whether HER2-targeting of liposomal doxorubicin would adversely affect the cardiac safety profile relative to untargeted liposomal doxorubicin. Methods: MM-302, untargeted liposomal doxorubicin and free doxorubicin were compared for their uptake into HER2-overexpressing cancer cells and two models of human stem cell-derived cardiomyocytes. High-content microscopy was used to determine the effects of exposure to specific cellular targets in cardiomyocytes. Mouse biodistribution studies were used to assess the total and nuclear accumulation of doxorubicin in mouse cardiac tissue upon treatment with either MM-302, untargeted liposomes or free doxorubicin. Quantitative immunofluorescence was used to quantify the HER2 expression on human normal and diseased heart specimens. Kinetic computational modeling was applied to interpret study results and to make predictions on human heart exposure to doxorubicin based on the experimental mouse data. Results: Human stem cell-derived cardiomyocytes showed nuclear accumulation of doxorubicin followed by cell death upon free doxorubicin treatment but not upon MM-302 or untargeted liposomes treatment. Similarly, MM-302 resulted in a significantly lower nuclear accumulation of doxorubicin compared to free doxorubicin treatment in mouse cardiac tissue. HER2 expression levels on normal and diseased human heart tissue were shown to be ≤100,000 receptors/cell, in concordance with the HER2 levels on the stem cell-derived cardiomyocytes found in vitro. Computational modeling predicts liposomal encapsulation to significantly protect the human heart from exposure to doxorubicin, consistent with clinical findings. Conclusions: MM-302 is not taken up by human cardiomyocytes via HER2, but selectively increases doxorubicin delivery to human HER2-overexpressing tumor cells. MM-302 can potentially improve the clinical efficacy demonstrated by conventional anthracyclines and maintain the cardiac safety profile of untargeted liposomal doxorubicin in patients with HER2 overexpressing cancers. Clinical evaluation of this patient population is currently in Phase I. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr C90.

Abstract In HER2+ (ErbB2+) breast cancer, the ability to combine anthracyclines, such as doxorubicin, with anti-HER2 targeted therapies is limited clinically due to potential synergistic cardiotoxicity: doxorubicin directly damages heart cells and HER2 is an important mediator of cardiac repair signaling. Herein we detail findings for MM-302, a novel HER2-targeted liposomal doxorubicin formulation. The liposomal encapsulation is designed to protect the heart from doxorubicin exposure and the HER2-targeting component mediates uptake in HER2-positive cells without blocking HER2 signaling. In order to study the potential effects of MM-302 on the heart, we performed studies using Embryonic Stem Cell (ESC)-derived cardiac cells. Total cell uptake of free doxorubicin and MM-302 into ESC-derived cardiac cells was measured using HPLC. We found that, despite expressing low levels of HER2, the ESC-derived cardiac cells do not take up MM-302, whereas doxorubicin freely enters the cells in a time and dose-dependent manner over a 3 hour time course. Subsequent to delivery, cell viability was assessed in response to free doxorubicin or MM-302 at 24 hours post 3-hour exposure. Doxorubicin resulted in cell death in a dose-dependent manner, whereas MM-302 had no effect on cardiac cell viability. To understand the mechanism underlying the cardiotoxicity associated with doxorubicin exposure, and to differentiate MM-302 from existing therapies, we measured cell functional responses in ESC-derived cardiac cells, including cell stress (phopsho-p53), DNA damage (gamma-H2AX) and apoptosis (cleaved-PARP) with high-content microscopy. We demonstrated that, while doxorubicin treatment results in DNA damage, cell stress, apoptosis, and ultimately cell death in a dose-dependent manner, MM-302 does not. Our findings demonstrate that MM-302 provides a means to deliver doxorubicin to high HER2-expressing cancer cells, while sparing exposure, accumulation, and toxicity in non-target (low HER2-expressing) cells, such as cardiomyocytes. This opens an exciting avenue for potentially introducing a novel anthracycline product for the treatment of HER2+ breast cancer. 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 3638. doi:10.1158/1538-7445.AM2011-3638

Abstract MM-398 (aka PEP02) is a stable, nanotherapeutic encapsulation of the pro-drug CPT-11 (irinotecan) that is currently in clinical development. In preclinical experiments, treatment with MM-398 resulted in significantly higher intratumoral concentrations of both irinotecan (142-fold) and its major metabolite, SN-38 (9-fold) and exhibited superior anti-tumor activity compared to free irinotecan in multiple tumor xenografts. Subsequently, multiple phase 1 and 2 studies have established a pharmacokinetic and safety profile that supports continued clinical development, including in pancreatic, gastric, colorectal and potentially other cancers. Because current evidence suggests that resistance to pancreatic cancer is driven largely by inadequate drug penetration into these often poorly vascularized, stromally dense and hypoxic tumors, we sought to better understand how this relatively large (100nm) liposomal nanotherapeutic could potentially result in increased efficacy in very advanced gemcitabine-resistant pancreatic cancer and other cancer types. We developed a mechanism-based PK model of MM-398 and free irinotecan designed to predict intratumor SN-38 levels. Sensitivity analysis revealed that for MM-398 local activation of irinotecan to SN-38 was a far more important parameter than systemic activation. Through cellular uptake studies, we demonstrated in vitro that MM-398 was preferentially internalized by phagocytic macrophage/monocyte cell lines and, to a far lesser extent, by tumor cell lines. Furthermore, tumor microdistribution studies by flow cytometry and IHC showed uptake of MM-398 liposomes in both tumor cells and tumor-associated macrophages with more liposomal material being present in the macrophages. This distribution also suggests that macrophages may contribute to the postulated rate limiting process of irinotecan activation. The sensitivity analysis also suggested that tumor permeability and vascularization are important determinants of tumor-associated SN-38 levels for both free irinotecan and MM-398. To determine the effect of MM-398 on these parameters we treated mice bearing HT29 (colorectal cancer) xenografts with a single dose of MM-398 and measured hypoxic markers (CAIX) and microvessel density (CD31) by IHC. Tumors treated with MM-398 showed a greater degree of CD31 staining and lower CAIX staining, indicating that MM-398 may be able to affect tumor characteristics that traditionally have contributed to therapy resistance and limited the delivery of cancer therapeutics and resistance. In summary, encapsulation of irinotecan alters rate-limiting processes that determine tumoral SN-38 levels. Delivery of MM-398 is believed to alter tumor microvessel density and decrease hypoxia. These intriguing mechanisms of action findings support the continued clinical development of MM-398 as a differentiated therapeutic for several cancer types. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr C207.