XTX301, a Tumor-Activated Interleukin-12 Has the Potential to Widen the Therapeutic Index of IL12 Treatment for Solid Tumors as Evidenced by Preclinical Studies

IL12 is a proinflammatory cytokine, that has shown promising antitumor activity in humans by promoting the recruitment and activation of immune cells in tumors. However, the systemic administration of IL12 has been accompanied by considerable toxicity, prompting interest in researching alternatives to drive preferential IL12 bioactivity in the tumor. Here, we have generated XTX301, a tumor-activated IL12 linked to the human Fc protein via a protease cleavable linker that is pharmacologically inactivated by an IL12 receptor subunit beta 2 masking domain. In vitro characterization demonstrates multiple matrix metalloproteases, as well as human primary tumors cultured as cell suspensions, can effectively activate XTX301. Intravenous administration of a mouse surrogate mXTX301 demonstrated significant tumor growth inhibition (TGI) in inflamed and non-inflamed mouse models without causing systemic toxicities. The superiority of mXTX301 in mediating TGI compared with non-activatable control molecules and the greater percentage of active mXTX301 in tumors versus other organs further confirms activation by the tumor microenvironment-associated proteases in vivo. Pharmacodynamic characterization shows tumor selective increases in inflammation and upregulation of immune-related genes involved in IFNγ cell signaling, antigen processing, presentation, and adaptive immune response. XTX301 was tolerated following four repeat doses up to 2.0 mg/kg in a nonhuman primate study; XTX301 exposures were substantially higher than those at the minimally efficacious dose in mice. Thus, XTX301 has the potential to achieve potent antitumor activity while widening the therapeutic index of IL12 treatment and is currently being evaluated in a phase I clinical trial.

Abstract 587: A half-life extended, tumor-activated IL-12 increased the infiltration of effector immune cells into the tumor microenvironment and demonstrated anti-tumor activity in syngeneic mouse models

Interleukin-12 (IL-12) is a proinflammatory cytokine, which bridges innate and adaptive immunity via induction of T helper 1 differentiation and promotes cytolytic activity of natural killer and T cells. IL-12 has demonstrated potent antitumor activity in syngeneic mouse models and promising anti-tumor efficacy in humans. However, development of IL-12-based treatments has been limited by severe systemic toxicities in the clinical setting. To overcome toxicity and potentially improve the therapeutic index of IL-12 in a clinical setting, XTX301 was engineered as a half-life extended and masked IL-12. The masking domain of XTX301 is designed to pharmacologically inactivate IL-12 in circulation and non-tumor tissue, while enabling generation of an active IL-12 moiety upon cleavage of a linker sequence by matrix metalloproteinases that are enriched in the tumor microenvironment. To confirm the ability of human tumor associated proteases to activate XTX301, cleavage was assessed in primary human tumor samples and in plasma from cancer patients. We observed cleavage of XTX301 in the majority of human tumors samples tested, but no activation was observed in plasma from cancer patients. Human IL-12 does not bind and signal through the mouse IL-12 receptors, hence three murine surrogates were created for in vivo studies: mXTX301, a non-cleavable control, and an unmasked control molecule. Tumor growth inhibition was observed after a single dose of mXTX301 as low as 0.039 mg/kg. The non-cleavable form of mXTX301 was less potent than mXTX301, demonstrating that the anti-tumor activity of mXTX301 is dependent on protease activation. The unmasked control was not well tolerated, with a > 20% body weight loss observed by Day 6, resulting in 75% of animals being euthanized by Day 11. Unlike the unmasked control, mXTX301 was well-tolerated at all tested doses, as evidenced by no loss in animals’ body weights, and demonstrated minimal pharmacodynamic activity in non-tumor tissues. In tumors, mXTX301 stimulated the infiltration of cytotoxic CD8+ T cells and induced the expression of several immune-related genes including those associated with IFN-γ cell signaling, antigen processing and presentation, and defense response as well as enrichment of gene signatures for T cells, natural killer (NK) cells, macrophages and dendritic cells as determined by RNA sequencing. In non-human primates, the highest non-severely toxic dose of XTX301 was 2mg/kg dosed weekly for a total of 4 doses. In summary, a half-life extended tumor-activated IL-12 molecule, mXTX301, demonstrated anti-tumor activity in preclinical mouse models with improved tolerability compared to a systemically active IL-12 molecule suggesting that XTX301 has potential for exerting potent anti-tumor activity while widening the therapeutic index of IL-12 treatment.

Citation Format: Natalia Malkova, Ekta Patel, Sallyann Vu, Damiano Fantini, Rebekah O'Donnell, Manoussa Fanny, Justin Greene, Wilson Guzman, David Crowe, Stephanie Hsiao, Parker Johnson, Megan McLaughlin, Oleg Yerov, Kurt Jenkins, Katarina Halpin-Veszeleiova, Hanumantha Rao Madala, Caitlin O'Toole, Jake Taylor, Magali Pederzoli-Ribeil, Benjamin Nicholson, Carl Uli Bialucha, Jennifer E. O'Neil. A half-life extended, tumor-activated IL-12 increased the infiltration of effector immune cells into the tumor microenvironment and demonstrated anti-tumor activity in syngeneic mouse models [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 587.

719 XTX301, a protein-engineered IL-12, exhibits tumor-selective activity in mice without peripheral toxicities and is well tolerated in non-human primates

Background

Interleukin-12 (IL-12) is a proinflammatory cytokine which bridges innate and adaptive immunity via induction of T helper 1 differentiation and promoting cytolytic activity of natural killer and T cells. IL-12 has demonstrated potent antitumor activity in syngeneic mouse models and promising anti-tumor efficacy in humans. However, development of IL-12 has been limited by severe systemic toxicities. To overcome toxicity and improve the therapeutic index of IL-12, we employed protein engineering to generate XTX301, a highly potent, half-life extended and masked IL-12. The masking domain of XTX301 is designed to pharmacologically inactivate IL-12 systemically and render an active IL-12 moiety upon cleavage by proteases that are enriched in the tumor microenvironment.

Methods

We conducted experiments to assess the binding, bioactivity, safety, and anti-tumor efficacy of XTX301. Binding interactions were measured via SPR, bioactivity was measured using STAT-4 phosphorylation in a reporter cell line, and IFN-g production was assessed in human PBMCs via ELISA. Anti-tumor efficacy and pharmacodynamics were assessed in MC38 and B16F10 syngeneic tumor mouse models using a XTX301 murine surrogate, mXTX301. Safety and pharmacokinetics of XTX301 were evaluated in non-human primates (NHP).

Results

XTX301 showed no detectable binding to the high affinity IL12RB2 demonstrating that the masking domain indeed prevents interaction with the receptor. Upon cleavage of the masking domain by relevant proteases, binding was observed and was comparable to XTX300 unmasked control. Likewise, restoration of activity upon proteolytic cleavage was observed in an IL-12-dependent reporter gene assay and in primary human PBMCs. Human IL-12 does not cross react with mouse IL-12 receptors; hence a murine surrogate (mXTX301) was created for in vivo anti-tumor efficacy evaluation. A single dose of mXTX301 demonstrated up to 90% tumor growth inhibition in an inflamed MC38 and non-inflamed B16F10 syngeneic mouse models. mXTX301 induced a ~3 fold increase in IFN-g in tumors compared to vehicle control and ~150 fold less peripheral IFN-g compared to mXTX300. XTX301 exhibits minimal elevation in liver enzymes and a 50-fold improvement in tolerability compared to XTX300, in a repeat dose NHP safety study.

Conclusions

Our data demonstrates that both XTX301 and mXTX301 are inactive when in masked form and become activated upon proteolytic cleavage to exert bioactivity comparable to recombinant IL-12. For efficacy, mXTX301 demonstrated tumor selective activity in syngeneic mouse models. XTX301 was well tolerated in repeat dose NHP safety study. In conclusion, XTX301 has potential for exerting potent anti-tumor activity with a favorable tolerability profile.

Tumor-selective activity of XTX202, a protein-engineered IL-2, in mice without peripheral toxicities in nonhuman primates

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Background: High-dose recombinant human interleukin-2 (aldesleukin) elicits anti-tumor immunity and is approved for the treatment of renal cell carcinoma and melanoma based on durable complete remissions. However, use of aldesleukin is limited due to treatment-related life-threatening toxicities. Recent second-generation efforts to alleviate toxicities have largely focused on eliminating binding to IL-2Rα, often with half-life extension. We have determined that mice and non-human primates (NHPs) treated with a second generation IL-2 surrogate still experience characteristic dose-limiting toxicities, including vascular leak syndrome. To overcome these toxicities and improve the therapeutic index (TI) of IL-2 as an anti-tumor immunotherapy, we employed protein engineering to generate XTX202, a highly potent third generation masked IL-2. XTX202 is unmasked in the tumor microenvironment by proteolytic activation resulting in full restoration of binding to IL-2Rβ without binding to IL-2Rα. The current study characterizes the therapeutic index of XTX202 versus aldesleukin and a second generation IL-2 surrogate. Methods: XTX202 bioactivity was measured using STAT-5 phosphorylation in human PBMCs and reporter cell lines. Anti-tumor efficacy and peripheral immune activation were evaluated in mice bearing syngeneic tumor models. Safety was evaluated in rodents and Cynomolgus monkeys. XTX200, an unmasked half-life extended IL-2 that does not bind to IL-2Rα, was used as a surrogate second generation IL-2. Results: Masked XTX202 showed limited IL-2R-dependent STAT-5 signaling in vitro. Proteolytic activation of XTX202 resulted in CD8+ T and NK cell activation and over 1000-fold reduction in Treg activation as compared to WT IL-2. XTX202 achieved potent tumor growth inhibition in syngeneic mouse models as a single agent with no evidence of toxicity or peripheral immune activation, thus demonstrating tumor selective activity. XTX202 efficacy in mice at 2 mg/kg dose was equivalent to that achieved with the MTD dose of 0.5 mg/kg of a second generation IL-2 surrogate. XTX202 was well tolerated in NHPs in a 4-week repeat dose study at doses up to 30 mg/kg QW whereas a second generation IL-2 surrogate was not tolerated beyond 0.7 mg/kg QW. Based on these data, XTX202 has a 10 fold improvement in TI vs second generation IL-2. Based on comparative efficacy studies with aldesleukin and literature NHP tolerability data, XTX202 is projected to have a ≥150 fold greater TI than aldesleukin. Conclusions: XTX202, a third generation, tumor-selective IL-2, inhibits tumor growth and is well tolerated in repeat dose studies in NHPs at high doses. GLP toxicity studies with XTX202 are underway and first-in-human studies are expected to initiate this year. XTX202 has the potential to be a best-in-class IL-2 immunotherapy by expanding the curative anti-tumor activity of IL-2 while minimizing dose-limiting toxicities.