The development of new therapies that can prevent recurrence and progression of nonmuscle invasive bladder cancer remains an unmet clinical need. The continued cost of monitoring and treatment of recurrent disease, along with its high prevalence and incidence rate, is a strain on healthcare economics worldwide. The current work describes the characterization and pharmacological evaluation of VAX-IP as a novel bacterial minicell-based biopharmaceutical agent undergoing development for the treatment of nonmuscle invasive bladder cancer and other oncology indications. VAX-IP minicells selectively target two oncology-associated integrin heterodimer subtypes to deliver a unique bacterial cytolysin protein toxin, perfringolysin O, specifically to cancer cells, rapidly killing integrin-expressing murine and human urothelial cell carcinoma cells with a unique tumorlytic mechanism. The in vivo pharmacological evaluation of VAX-IP minicells as a single agent administered intravesically in two clinically relevant variations of a syngeneic orthotopic model of superficial bladder cancer results in a significant survival advantage with 28.6% (P = 0.001) and 16.7% (P = 0.003) of animals surviving after early or late treatment initiation, respectively. The results of these preclinical studies warrant further nonclinical and eventual clinical investigation in underserved nonmuscle invasive bladder cancer patient populations where complete cures are achievable.
Abstract. Background/Aim: VAX014 minicells (VAX014) Bladder cancer ranks second amongst newly diagnosed urothelial carcinomas worldwide, is the sixth leading cause of cancer death and the fourth most common malignancy of men in developed countries (1). Current estimates suggest that as many as 75-80% of patients with bladder cancer present for the first time with localized non-muscle invasive bladder cancer (NMIBC). It is further estimated that of those newly diagnosed NMIBC cases, 70% present with what the European Association of Urologists classifies as low-risk disease (2).Current recommended clinical practice for the treatment of low-risk NMIBC is cystoscopic transurethral resection of bladder tumor (TURBT) followed by an immediate postoperative intravesical instillation of a chemotherapeutic agent. Without adjuvant treatment, as many as 35.8% of patients treated for low-risk NMIBC will suffer recurrence within 2 years (3). There have been several studies and meta-analyses published indicating that the immediate postoperative instillation of adjuvant therapy may lead to a decrease in the overall risk of recurrence of up to 39%, with absolute reduction in recurrence rates as high as 17% (4). While clearly effective in reducing recurrence, several recently conducted surveys have revealed that immediate single-dose post-operative adjuvant therapy is not consistently administered (5, 6). A prominently cited reason among those clinicians who do not administer immediate post-operative chemotherapy is that the potential for systemic exposure and agent-associated toxicity outweighs the clinical benefit, especially in cases where bladder perforation is suspected. The perceived clinical benefit-torisk ratio argument seems justified given that while patients with low-and intermediate-risk NMIBC have a high rate of recurrence, the initial risk of progression is low (0.8% and 6% at 5 years, respectively) (2). However, the risk of progression increases with the number and interval of recurrences, so any initial prevention or delay of recurrence would be of clear benefit (2). Moreover, because of the high rate of recurrence, frequent monitoring and treatment are required, making NMIBC one of the most expensive cancer types to treat over the course of the disease (7). Therefore, an effective agent for use in the immediate post-operative setting would impart considerable pharmacoeconomic benefit. Recent failures in mid-and late-stage clinical trials highlight the unmet clinical need for the development of new agents that can be safely administered in the immediate post-operative setting (8).
Emerging clinical evidence indicates that the combination of local administration of immunotherapy with systemic immune checkpoint blockade targeting the PD-1/PD-L1 pathway improves response rates in select solid tumor indications; however, limited clinical experience with this approach exists in advanced bladder cancer patients. VAX014 is a novel bacterial minicell-based, integrin-targeted oncolytic agent undergoing clinical investigation for intravesical (IVE) treatment of non-muscle invasive bladder cancer. Here, we demonstrated that the antitumor activity of VAX014 following IVE administration was dependent upon CD4+ and CD8+ T cells in two syngeneic orthotopic bladder tumor models (MB49 and MBT-2). PD-L1 upregulation was found to be an acquired immune-resistance mechanism in the MB49 model, and the combination of VAX014 with systemic PD-L1 blockade resulted in a significant improvement in bladder tumor clearance rates and development of protective antitumor immunologic memory. Combination treatment also led to enhanced systemic antitumor immune responses capable of clearing distal intradermal tumors and controlling pulmonary metastasis. Distal tumors actively responding to combination therapy demonstrated a phenotypic shift from Treg to Th1 in intratumoral CD4+ T cells, which was accompanied by a higher percentage of activated CD8+ T cells and higher IFNγ. Finally, VAX014’s target integrins α3β1 and α5β1 were overexpressed in tumor biopsies from advanced stage bladder cancer patients, as well as in both the MB49 and MBT-2 orthotopic mouse models of bladder cancer. These collective findings provide rationale for clinical investigation of VAX014 and systemic PD-1/PD-L1 blockade in advanced stage bladder cancer.
BackgroundImmunologically cold tumors with an ‘immune desert’ phenotype lack tumor-infiltrating lymphocytes (TILs) and are typically impervious to systemic immune checkpoint blockade (ICB). Intratumoral treatment of tumors with immunomodulatory agents can promote local tumor inflammation leading to improved T cell responses in injected tumors. Addition of systemic ICB increases response frequency and immune-mediated clearance of injected and distal non-injected lesions, and this promising approach is being widely investigated clinically. In this work, we evaluate and characterize the local and systemic antitumor immunotherapeutic activity of VAX014, a novel non-viral targeted oncolytic agent based on recombinant bacterial minicells, following intratumoral administration and in combination with systemic ICB.MethodsThe immunotherapeutic activity of VAX014 following weekly intratumoral administration was investigated in multiple preclinical tumor models with B16F10 murine melanoma serving as the primary model for evaluation of immune desert tumors. Mice bearing a single intradermal tumor were used to evaluate tumor response and overall survival (OS), assess changes in immune cell populations, and explore global changes to immunotranscriptomes of injected tumors. Mice bearing bilateral intradermal tumors were then used to evaluate non-injected tumors for changes in TIL populations and phenotypes, compare immunotranscriptomes across treatment groups, and assess distal non-injected tumor response in the context of monotherapy or in combination with ICB.ResultsVAX014 demonstrated strong immune-mediated tumor clearance of injected tumors coinciding with significantly elevated CD8+TILs and upregulation of multiple immune pathways essential for antitumor immune responses. Modest activity against distal non-injected immune desert tumors was observed despite elevated levels of systemic antitumor lymphocytes. Combination with systemic CTLA-4 blockade improved survival and elevated TILs but did not improve clearance rates of non-injected tumors. Immunotranscriptomes of non-injected tumors from this treatment combination group exhibited upregulation of multiple immune pathways but also identified upregulation of PD-1. Further addition of systemic PD-1 blockade led to rapid clearance of non-injected tumors, enhanced OS, and provided durable protective immunological memory.ConclusionsIntratumoral administration of VAX014 stimulates local immune activation and robust systemic antitumor lymphocytic responses. Combination with systemic ICB deepens systemic antitumor responses to mediate clearance of injected and distal non-injected tumors.
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