Enhancing Neoadjuvant Virotherapy's Effectiveness by Targeting Stroma to Improve Resectability in Pancreatic Cancer

Abstract

About one-fourth of patients with pancreatic ductal adenocarcinoma (PDAC) are categorized as borderline resectable (BR) or locally advanced (LA). Chemotherapy and radiation therapy have not yielded the anticipated outcomes in curing patients with BR/LA PDAC. The surgical resection of these tumors presents challenges owing to the unpredictability of the resection margin, involvement of vasculature with the tumor, the likelihood of occult metastasis, a higher ratio of positive lymph nodes, and the relatively larger size of tumor nodules. Oncolytic virotherapy has shown promising activity in preclinical PDAC models. Unfortunately, the desmoplastic stroma within the PDAC tumor microenvironment establishes a barrier, hindering the infiltration of oncolytic viruses and various therapeutic drugs-such as antibodies, adoptive cell therapy agents, and chemotherapeutic agents-in reaching the tumor site. Recently, a growing emphasis has been placed on targeting major acellular components of tumor stroma, such as hyaluronic acid and collagen, to enhance drug penetration. Oncolytic viruses can be engineered to express proteolytic enzymes that cleave hyaluronic acid and collagen into smaller polypeptides, thereby softening the desmoplastic stroma, ultimately leading to increased viral distribution along with increased oncolysis and subsequent tumor size regression. This approach may offer new possibilities to improve the resectability of patients diagnosed with BR and LA PDAC.

Keywords: borderline resectable; locally advanced; oncolytic virus; pancreatic ductal adenocarcinoma; proteolytic enzymes; resection margin; stroma degradation; surgical resection.

Figure 1

(a) A male patient with PDAC. (b) The edge of the surgically removed tissue is free of cancer lesions, indicating R0 resection. (c) The edge of the surgically removed tissue contains cancerous lesions, resulting in R1 resection.

Figure 2

PDAC tumor microenvironment is composed of immunosuppressive intricate structures of cellular and acellular components like TAMs, CAFs, PSCs, Tregs, MDSCs, collagen, hyaluronic acid, fibronectin, and laminin. This complex structure establishes a dense stromal barrier, obstructing the entry of drug molecules like chemotherapy or immunotherapies, along with anti-tumor immune cells.

Figure 3

Schematic of molecular engineering of oncolytic VSV virus expressing proteolytic enzymes. (a) Cloning of VSV plasmid (p-VSV′) is done by inserting transgene (encoding an enzyme) in between VSV G and L genes, giving rise to a plasmid of engineered VSV variant (p-VSV) containing a gene that expresses proteolytic enzyme. (b) Producer cells (example: BHK21, Vero) are infected with vaccinia virus with T7 polymerase along with transfection with p-VSV vector and helper plasmids (pVSV-P, pVSV-N, pVSV-L). This step is called viral rescue. The supernatant is filtered and is used to infect a new batch of cells that ultimately yields VSV particles capable of expressing stroma-depleting proteolytic enzyme.

Figure 4

(a) The increased size of a BR or LA PDAC tumor raises the probability of a cancerous lesion persisting even post-surgery, a condition referred to as R1 resection. Further complicating the situation, the vascular involvement also increases the risk of metastasis. (b) Intratumoral injection of OV expressing proteolytic enzyme in BR/LA PDAC tumors decreases the stromal rigidity and increases drug/immune cell infiltration, thereby increasing tumor cell death and boosting the immune response against the tumor. Consequently, these events may lead to the likelihood of R0 resection with no vascular involvement, metastasis, or tumor recurrence.