Abstract 4934: CAPAC: a modular platform that can improve the safety and efficacy of existing cancer therapies

Click chemistry is a Nobel Prize winning technology that has been widely used in research across the life sciences. Shasqi’s Click Activated Protodrugs Against Cancer (CAPACTM) platform is pioneering the therapeutic application of click chemistry reactions in humans. The 1st gen CAPAC technology enables activation of potent anti-cancer agents at the tumor site while reducing systemic exposure and is comprised of a tetrazine-modified biopolymer (tumor targeting agent) injected intratumorally and a systemically administered trans-cyclooctene-modified payload, named a protodrug. Our lead clinical candidate SQ3370 (SQL70 biopolymer + SQP33, doxorubicin protodrug), is being evaluated in a Phase 2a study in solid tumors (NCT04106492). CAPAC platform is highly modular and can be applied to multiple cancer drugs especially those with narrow therapeutic index(s) due to toxicity. Because the tumor targeting agent (i.e., biopolymer) is separate from the protodrug, it enables the flexibility of interchanging different protodrugs with different mechanism of actions such as tubulin inhibitors (e.g., paclitaxel), topoisomerase inhibitors (e.g., exatecan), immune activators (e.g., TLR agonists), and others. This benefit can be translated in the clinic with tailored combinations for individual patients. Here we will present data on protodrugs of paclitaxel, exatecan, and TLR7/8a agonist. These therapeutics have shown considerable safety concerns either alone or in combination with other therapies in the clinic and may benefit from the precise activation at the tumor site that can be achieved by the CAPAC platform. In vitro cytotoxicity assays showed ≥20 fold-attenuation of both paclitaxel and exatecan protodrugs in various cancer lines. In a proliferation assay using mouse splenocytes we observed ≥100-fold attenuation of a TLR7/8a protodrug. These results suggest that the protodrugs may exhibit higher therapeutic indeces with enhanced safety profile. We tested the anti-tumor efficacy of paclitaxel protodrug in combination with SQL70 biopolymer in NCI-N87 gastric cancer xenograft tumor model. The doses of paclitaxel protodrug were 4x or 10x molar equivalent to the MTD of conventional paclitaxel. We observed significant reduction of tumor growth compared to vehicle (p<0.0001) and minimal body weight loss suggesting enhanced safety profile. In vivo studies to determine the safety and efficacy of these protodrugs are ongoing and will be presented. The data presented illustrates how the CAPAC platform is modular and expands the therapeutic window of different cancer therapies to achieve greater effect. This modularity enables the rapid access of therapeutic combinations. Moreover, as the click chemistry activation is independent of biological characteristics of tumors, CAPAC payloads are highly translatable across species and accelerate the path to the clinic.

Citation Format: George Coricor, Jesse M. McFarland, Masa Aleckovic, Sangeetha Srinivasan, John Lee, Leslie Priddy, Matthew Tso, Tri-Hung Nguyen, Jose M. Mejia Oneto. CAPAC: a modular platform that can improve the safety and efficacy of existing cancer therapies. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 4934.

Abstract B43: Combining SQ3370, a doxorubicin-based therapeutic, with TLR and STING agonists enhances antitumor effects in murine tumor models

SQ3370, the lead investigational asset of the CAPACTM (Click Activated Protodrugs Against Cancer) platform, is a therapeutic based on doxorubicin which can induce immunogenic cell death in mouse tumors making it a suitable candidate for combination approaches with immunotherapies that target antigen-presenting cells. Here, we show the effects of SQ3370 combined with either TLR9 or STING agonists. Immunocompetent mice were inoculated with MC38 tumors. Once tumors reached ~100mm3, SQ3370 was administered in two parts: 1) a tetrazine-modified biopolymer was injected into the tumor and 2) a protodrug of doxorubicin modified with a trans-cyclooctene (TCO) was given intravenously as five daily doses. Efficient reaction between the biopolymer and protodrug releases the active drug in situ, delivering higher drug concentrations specifically to the tumor site compared to conventional doxorubicin, which leads to increased efficacy and reduced systemic toxicity. TLR9 and STING agonists were administered intratumorally either as monotherapies or in combination with SQ3370 by co-injection with the biopolymer. Tumor immune composition was assessed by flow cytometry and multiplex immunofluorescent analysis. Combining SQ3370 with either TLR9 or STING agonists led to a significant reduction in tumor growth and prolonged survival of MC38 tumor-bearing mice compared to any monotherapy. Higher doses of either immune adjuvant increased the effect on tumor growth inhibition, suggesting a dose-dependent effect. Complete regression of tumors was observed occasionally in mice treated with a single agent, most commonly with the TLR9 agonist. However, both combination treatments with SQ3370 increased the number of complete responses. Assessment of immune cell infiltration of tumors treated with SQ3370 suggested an increase in antitumor immune responses that were consistent with a doxorubicin-driven induction of immunogenic cell death, including an increase in tumor-infiltrating T-cells. The addition of the TLR9 agonist to SQ3370 further elevated this antitumor immune response. In line with these results, we observed regression of distal, non-injected tumors using a MC38 dual tumor model. A higher fraction of animals treated with SQ3370 + TLR9 agonist (5 out of 10) showed complete tumor regression (absence of both tumors) compared to animals receiving the SQ3370 monotherapy (1 out of 10). Tumor rechallenge of animals with complete regressions revealed a sustained response in line with T-cell mediated antitumor immunity. Previous studies have shown that SQ3370 improves safety and efficacy as compared to conventional doxorubicin. Here, we show that SQ3370 also activates an antitumor immune response and modulates several immune cell populations, particularly T-cells, to mount a lasting antitumor immune response. SQ3370 is currently being evaluated in a clinical trial in advanced solid tumors (NCT04106492) as a monotherapy. Combination strategies of SQ3370 with immunotherapies may further increase its efficacy and provide enhanced benefit to cancer patients.

Citation Format: Masa Aleckovic, Sangeetha Srinivasan, Jesse M McFarland, Leslie Priddy, Matthew Tso, Jose M Mejia Oneto. Combining SQ3370, a doxorubicin-based therapeutic, with TLR and STING agonists enhances antitumor effects in murine tumor models [abstract]. In: Proceedings of the AACR Special Conference: Tumor Immunology and Immunotherapy; 2022 Oct 21-24; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2022;10(12 Suppl):Abstract nr B43.

Abstract A029: SQ3370: CAPAC platform enables tumor-localized therapy and minimizes systemic toxicities

Conventional chemotherapies lack specificity for tumor tissue, have a low therapeutic index, and induce systemic toxicities including cardiomyopathy. SQ3370 utilizes the Click Activated Protodrugs Against Cancer (CAPAC) platform to localize doxorubicin (Dox) to tumor tissue while minimizing systemic exposure. SQ3370 consists of an intratumoral injection of a biopolymer followed by 5 daily intravenous doses of an attenuated protodrug of Dox. The tumor-localized activation of Dox is enabled by mutually reactive click chemistry groups on the biopolymer and protodrug, and is therefore agnostic to tumor characteristics that can vary from patient to patient. This allows the CAPAC platform to be readily applicable to diverse tumor types, including heterogeneous sarcoma subtypes. The lead candidate, SQ3370 is currently being evaluated in a Phase I study in patients with advanced solid tumors (NCT04106492). In preclinical studies, SQ3370 treatment showed reduced toxicity, enabling doses of 19.1-fold and 8.9-fold the maximum tolerated dose of conventional Dox in mice and dogs, respectively. Further, there was no evidence of cardiotoxicity in dogs at this dose. In syngeneic dual-tumor mouse models of MCA205 fibrosarcoma, MC38 colon carcinoma, and B16-F10 melanoma, only one tumor was injected with the biopolymer. Following 5 daily intravenous doses of the protodrug, dose-dependent antitumor responses were seen in the injected and non-injected lesions across all syngeneic models. Furthermore, T-cell infiltration was observed in both lesions of the MC38 dual-tumor model, suggesting activation of an antitumor immune response by SQ3370. The combination of SQ3370 with an immune adjuvant (TLR9 agonist) further prolonged overall survival, improved the antitumor response, and increased the number of complete responses compared to the monotherapy, likely by enhancing the immune activation effects of SQ3370. Conventional Dox can induce cardiomyopathy at incidences of 1-20% for cumulative doses from 300-500 mg/m2 in humans. In the Phase I trial, SQ3370 was well tolerated in patients receiving more than 1000 mg/m2 Dox in cumulative doses. Treated tumors included sarcoma (73%), breast cancer (7.7%), gyne (7.7%), and others (11.5%). Dose escalation is ongoing. Most frequent adverse events (AEs), included nausea, fatigue, and anemia. Ejection fraction (LVEF), indicative of cardiac function, remained normal during the study period. No AEs that led to discontinuation or death were related to SQ3370 by investigator assessment.In summary, SQ3370 facilitates localization of Dox at the tumor with minimal systemic toxicity and demonstrates the first proof of concept of the click chemistry-based CAPAC platform. The CAPAC Platform represents a new therapeutic modality to treat solid tumors by using a drug with known efficacy, such as Dox, and expanding its pharmacological capabilities.

Citation Format: Jose M. Mejia Oneto, Sangeetha Srinivasan, Jesse M. McFarland, Matthew Tso, Masa Aleckovic. SQ3370: CAPAC platform enables tumor-localized therapy and minimizes systemic toxicities [abstract]. In: Proceedings of the AACR Special Conference: Sarcomas; 2022 May 9-12; Montreal, QC, Canada. Philadelphia (PA): AACR; Clin Cancer Res 2022;28(18_Suppl):Abstract nr A029.

Interim phase 1 results for SQ3370 in advanced solid tumors

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Background: SQ3370, a novel therapy, utilizes Shasqi’s proprietary Click Activated Protodrugs Against Cancer (CAPAC) platform where mutually-reactive click chemistry groups release Doxorubicin (Dox) at the tumor site minimizing systemic exposure. In animals, SQ3370 enhanced survival, T-cell infiltration and antitumor responses in injected and non-injected tumors. Minimal to no toxicity, including no cardiotoxicity was seen in up to 9-fold dose increases in animals. Conventional Dox can induce cardiomyopathy at incidences of 1-20% for cumulative doses from 300-500 mg/m2 in humans and re-treatment with Dox is less effective in heavily pre-treated patients (pts). Here we report interim results of the Phase 1 ( NCT04106492 ). Methods: SQ3370 has 2 components: 1) Intratumoral injection of a protodrug-activating biopolymer (SQL70: 10 mL or 20 mL); 2) 5 consecutive daily IV infusions of an attenuated protodrug of Dox (SQP33). Key eligibility includes locally advanced or metastatic solid tumors, ≤300 mg/m2 prior exposure to Dox, ECOG 0-1 and no limit to prior systemic therapies. Primary objectives include safety and determining Phase 2 dose. Dose escalation was assessed in 2 stages: 1) accelerated titration; 2) 3+3 design. Results: As of 31JAN2022 data cut, 26 pts were treated, 21 with 10 mL biopolymer (bp) and 5 with 20 mL bp over 9 dose escalation protodrug cohorts. MTD has not been reached. Median age was 61 years (26-84), 62% were females, and 69% were ECOG 1. Prior procedures included surgery (89%) and radiation (62%). At study entry, 77% of pts had metastases with a median number of metastatic sites being 2 (1-5); most frequently lung (50%). Tumors were sarcoma (73%), breast cancer (7.7%), gyne (7.7%) and other (11.5%). Twenty-four of 26 (92%) pts received prior systemic therapies with 50% receiving prior Dox. Median number of prior systemic therapies was 2 (1-7). Of the 26 pts, 62% received > 500 mg/m2 cumulative Dox given as SQP33. Median duration of treatment was 2 cycles (1-12). Most frequent AEs, regardless of causality, for the 10 mL bp group included nausea (n = 11), fatigue (n = 9) and anemia (n = 6), and for the 20 mL bp group included anemia (n = 3) and nausea (n = 2). Ejection fraction (LVEF) remained normal during the study period. No AEs that led to discontinuation or death were related to SQ3370 by investigator. At a median follow-up of 9.2 wks (3-37), 21 pts were evaluable. SD was best response in 71%. Median duration of SD was 80-dys (37-186) corresponding to an overall disease control rate (CR+ PR+ SD x 30-dys) of 71% (68% in 10 mL bp; 100% in 20 mL bp). The remainder of pts had PD as best response. Over 38% of pts remain on drug. Conclusions: SQ3370 with 10 mL or 20 mL biopolymer was well tolerated in pts with half being re-treated with Dox. Although > 60% of pts received > 500 mg/m2 cumulative Dox given as SQP33, LVEF remained normal. Preliminary evidence of disease control was observed in pts despite heavy prior pre-treatment and high cancer burden. Dose escalation is ongoing. Clinical trial information: NCT04106492.

Abstract BS03-1: Tumor-derived exosomes promote pre-metastatic niche formation and organotropism

Metastasis is the most deadly aspect of cancer due to a lack of appropriate therapies. Tumor-secreted factors have been recently recognized to be one of the main culprits for metastatic progression. Tumor-secreted factors such as VEGF-A, PlGF, TGFb, TNF-a, and LOX have been shown to play active roles in the recruitment of bone marrow (BM)-derived cells to the primary tumor microenvironment and pre-metastatic niches. We have found that tumor-derived exosomes are abundantly secreted into the circulation in highly metastatic murine models and in patients with stage IV metastatic disease. Tumor-derived exosomes induce vascular leakiness, and hypoxic and pro-inflammatory changes at pre-metastatic sites. Moreover, tumor-derived exosomes preferentially fuse and “educate” BM-derived progenitor cells to a pro-vasculogenic phenotype characterized by upregulation of Tie-2, VEGF-A, VEGFR2, TSP1 and ADAM10. We found that B16-F10 melanoma-derived exosomes help establish pre-metastatic niches, including the recruitment of “educated” BM cells, in specific organs destined to be involved in future metastasis whereas LLC lung cancer-derived exosomes predominant in the lung as the main organ of metastasis. These results suggest that tumor-derived exosomes may have a role in metastatic organotropism, whereby cancer metastasizes to specific organs, as proposed by Stephen Paget's ‘seed and soil’ hypothesis more than a 100 years ago. We believe that the identification of exosomes proteins, with their prognostic and therapeutic potential, may also partially explain the specific receptor-ligand binding of exosomes to a pre-metastatic niche defining an organotropic site for future metastasis.

Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr BS03-1.

Phosphoglycerate mutase 1 coordinates glycolysis and biosynthesis to promote tumor growth

It is unclear how cancer cells coordinate glycolysis and biosynthesis to support rapidly growing tumors. We found that the glycolytic enzyme phosphoglycerate mutase 1 (PGAM1), commonly upregulated in human cancers due to loss of TP53, contributes to biosynthesis regulation in part by controlling intracellular levels of its substrate, 3-phosphoglycerate (3-PG), and product, 2-phosphoglycerate (2-PG). 3-PG binds to and inhibits 6-phosphogluconate dehydrogenase in the oxidative pentose phosphate pathway (PPP), while 2-PG activates 3-phosphoglycerate dehydrogenase to provide feedback control of 3-PG levels. Inhibition of PGAM1 by shRNA or a small molecule inhibitor PGMI-004A results in increased 3-PG and decreased 2-PG levels in cancer cells, leading to significantly decreased glycolysis, PPP flux and biosynthesis, as well as attenuated cell proliferation and tumor growth.