Development of Novel Cell Fate Control Gene Therapy for Applications in Cancer and Immune Disorders

Cellular therapies rely on the delivery of therapeutic cells into patients, but their safety can be compromised by the manipulation of cells ex vivo or their placement outside of their natural context in vivo. Cell Fate Control Gene Therapy (CFCGT) offers the possibility of establishing pharmacological controls over gene-modified cells (GMCs) with regards to their proliferation, differentiation, or function. In its simplest form, 'suicide' gene therapy (SGT), stable introduction of a 'suicide' gene that can activate a non-toxic prodrug establishes control over the survival of GMCs. Current SGT modalities are sub-optimal in clinical setting. To overcome the many limitation of current strategies, we have developed a next-generation CFCGT approach based on the active site-engineered variants of human deoxyCytidine Kinase (dCK), which enable robust activation of multiple Nucleoside Analogue (NA)-based prodrugs, act early in the pathway enabling rapid accumulation of activated NAs in target cells, and also provide the capabilities for the direct imaging of GMCs. Stable introduction of dCK variants into target cells by means of Lentiviral (LV) gene transfer significantly increases their sensitivity to multiple prodrugs. Our dCK variant with only two active site amino acid substitutions is expected to be non-immunogenic yet capable of specifically activating deoxythymidine- and deoxyuridine-based NAs that are not substrates for the wild-type enzyme, such as bromovinyldeoxyuridine (BVdU) and L-deoxythymidine (LdT). We show here that dCK can be used for controlling the survival of GMCs, in cell lines and primary cells in vitro and in a murine xenogeneic transplant models in vivo. To characterize dCK/prodrug-mediated killing mechanisms in GMCs, we have examined the levels of active metabolites in cells and the cellular pathways they antagonize. We describe here the experimental basis for the application of this novel CFCGT in bone marrow transplantation for management of Graft-versus-Host Disease (GvHD) and in enhancing chemotherapy in direct treatment of tumors. In summary, we have developed a novel and robust strategy for effective CFCGT that addresses the many shortcomings of existing modalities. Future studies will validate this novel system in a variety of primary cells and animal disease models, including models of hematopoietic transplantation and ES/iPS-based cell therapies.Ph

The engineered thymidylate kinase (TMPK)/AZT enzyme-prodrug axis offers efficient bystander cell killing for suicide gene therapy of cancer.

We previously described a novel suicide (or 'cell fate control') gene therapy enzyme/prodrug system based on an engineered variant of human thymidylate kinase (TMPK) that potentiates azidothymidine (AZT) activation. Delivery of a suicide gene sequence into tumors by lentiviral transduction embodies a cancer gene therapy that could employ bystander cell killing as a mechanism driving significant tumor regression in vivo. Here we present evidence of a significant bystander cell killing in vitro and in vivo mediated by the TMPK/AZT suicide gene axis that is reliant on the formation of functional gap-junctional intercellular communications (GJICs). Potentiation of AZT activation by the engineered TMPK expressed in the human prostate cancer cell line, PC-3, resulted in effective bystander killing of PC-3 cells lacking TMPK expression--an effect that could be blocked by the GJIC inhibitor, carbenoxolone. Although GJICs are mainly formed by connexins, a new family of GJIC molecules designated pannexins has been recently identified. PC-3 cells expressed both connexin43 (Cx43) and Pannexin1 (Panx1), but Panx1 expression predominated at the plasma membrane, whereas Cx43 expression was primarily localized to the cytosol. The contribution of bystander effects to the reduction of solid tumor xenografts established by the PC-3 cell line was evaluated in an animal model. We demonstrate the contribution of bystander cell killing to tumor regression in a xenograft model relying on the delivery of expression of the TMPK suicide gene into tumors via direct intratumoral injection of recombinant therapeutic lentivirus. Taken together, our data underscore that the TMPK/AZT enzyme-prodrug axis can be effectively utilized in suicide gene therapy of solid tumors, wherein significant tumor regression can be achieved via bystander effects mediated by GJICs

Bystander cell killing mediated by TMPK-F105Y/AZT therapy drives a significant tumor mass reduction in a prostate cancer xenograft model.

<p>(A) Magnitude of bystander cell killing was evaluated following the delivery of the TMPK-F105Y suicide gene by direct intratumoral injection of LV/TMPK into established tumors in NOD/SCID mice (n=6). Reduction in tumor mass was assessed at the end of 6-day AZT treatment regimen (at 50mg/kg/day) by extraction of tumors and measurement of wet tumor weight. Statistical significance is indicated by an asterisk (* p<0.05). (B) Weight of individual extracted tumors is shown for each animal in the AZT-treated and vehicle-untreated groups.</p

PC-3 cells express functional GJICs.

<p>(A) Expression of GJIC components, connexin43 and pannexin1, was confirmed by Western blot on whole-cell lysates of non-transduced, LV/TMPK-transduced, and LV/eGFP-transduced PC-3 cells. GAPDH expression was evaluated as an equal loading control. (B) Expression of TMPK was confirmed by Western blot on whole-cell lysates of non-transduced, LV/TMPK-transduced, and LV/TMPK-F105Y-transduced PC-3 cells. GAPDH expression was evaluated as an equal loading control. (C) Expression pattern of connexin43 (left panel) and pannexin1 (right panel) GJIC components (green fluorescence) was assessed by confocal immunofluorescent microscopy. Cytoskeleton (F-actin) was visualized with rhodamine phalloidin (red fluorescence) staining. (D) Dye transfer of calcein into adjacent PKH26-labelled cells was measured by flow cytometry in direct (normal) or transwell co-cultures of PC-3 cells as percentage of cells double-positive for calcein and PKH26 fluorescence (n=3). (E) Dye transfer of calcein into adjacent PKH26-labelled cells was significantly inhibited by carbenoxolone (CBX) (n=3). Statistical significance is indicated (p<0.0001).</p