Preclinical evaluation of VAX-IP, a novel bacterial minicell-based biopharmaceutical for nonmuscle invasive bladder cancer

摘要

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. prs.rt("abs_end"); Introduction Bladder cancer is the second most common urothelial carcinoma worldwide, the sixth leading cause of cancer death, and the fourth most common malignancy of men in developed countries. 1 An estimated 70% of bladder cancer patients present with nonmuscle invasive disease (NMIBC), with tumors confined to the mucosal surface of the uroepithelium (Ta), tumors invading the lamina propria but not yet the underlying muscle (T1) and carcinoma in situ (CIS), which can occur concomitant with TaT1 disease. 2 Currently, NMIBC patients are stratified into low-, intermediate- and high-risk disease based on tumor stage and grade in addition to other prognostic factors. 3 Treatment begins with transurethral resection of bladder tumor (TURBT) followed by risk level-appropriate post-TURBT adjuvant therapy. In intermediate and high-risk NMIBC, including those patients suffering from localized CIS, intravesical immunotherapy with the live bacterial tuberculosis vaccine Bacillus Calmette-Guerin (BCG) is the most effective adjuvant therapy treatment option. While initial responses to BCG have led to its establishment as the standard-of-care, an estimated 50% will recur and face cystectomy. 4 , 5 Adverse side effects with BCG range from local toxicity (occurs in 90% of patients) to more rare ( 6 ; 7 ; 8 ; 9 Taken together, there remains great need for less toxic alternatives to BCG as well as for bladder-sparing second line salvage therapies for use in high-risk NMIBC patients. Bacterial minicells may provide an intriguing therapeutic option for the intravesical treatment of NMIBC as they represent an emerging class of targeted molecular delivery vehicles for therapeutic use in oncology with promising applications for tumor-specific targeted delivery of antineoplastic agents including small molecule drugs, nucleic acids and protein-based payloads. 10 ; 11 ; 12 Minicells are spherical, nano-sized particles best described as miniature versions of the bacterial cells from which they are produced, complete with all parental bacterial components except the bacterial chromosome. 13 Lacking a chromosome, minicells are inherently incapable of division, replication and persistence, and by definition, are noninfectious. Nonetheless, minicells are as amenable to recombinant engineering as proto-typical bacteria and easily designed to encapsulate specific macromolecular and small molecule therapeutic agents. This work describes the characterization and the in vitro and in vivo evaluation of VAX-IP minicells as a recombinant bacterial minicell-based therapeutic for the intravesical treatment of NMIBC. VAX-IP minicells are designed to selectively target and deliver the cholesterol-dependent membrane pore-forming protein toxin, perfringolysin O (PFO) to cancer cells expressing unligated α5 β1 (α5β1) or α3 β1 (α3β1) integrin heterodimers and results presented here demonstrate rapid, selective tumoricidal effects across a representative panel of human and murine urothelial cell carcinoma (UCC) cell lines in vitro . 14 , 15 Other in vitro work characterizes novel target cell plasma membrane permeabilization effects elicited by the PFO component of VAX-IP minicells, occurring in parallel with the initiation of apoptosis. The ability of VAX-IP minicells to prevent tumor growth and prolong survival after intravesical administration in vivo was evaluated using two clinically