Matthew VanBrocklin

My research program has four major areas of focus: (1) Utilizing our RCAS/TVA model in order to identify novel drivers of melanoma (e.g., NF-1, KIT, RAC1, PDGFRA), identify resistance mechanisms, and to develop more effective therapeutic strategies.  (2) Developing CRISPR/Homology Directed Repair (HDR) for in vivo cancer and disease modeling. (3) Characterizing immune checkpoint ligands and evaluating their role in immune evasion in melanoma with long term goals of developing therapeutic agents. (4) Oncolytic Immunotherapy, focusing on developing/evaluating novel oncolytic viruses in combination with immune checkpoint blockade in vivo.

1) RCAS-TVA Model

We are currently evaluating a role for RAC1^P29S in melanoma initiation and progression in BRAF or NRAS driven melanomas. Preliminary data suggests that RAC1 is insufficient as a melanoma driver in the context of Cdkn2a and/or Pten loss, but may enhance metastatic progression of BRAF driven tumors. We are assessing a role for RAC1 in promoting metastatic dissemination in our NRAS and Nf-1 melanomas as these alterations co-occur in patients (13-14%). Utilizing in vivo CRISPR targeting Nf-1 (exon 2 or 4) we were successful in inducing tumors in our mouse model in the context of Cdkn2aand/or Pten loss with high penetrance. We are expanding this model to assess pharmacologic and immunotherapeutic intervention strategies.

2) CRISPR/HDR Modeling

We have developed a novel method for single vector CRISPR mediated homology directed repair (HDR) that has high potential in developing novel disease models and gene therapy applications. As proof of principle, we have evaluated the ability of our CRISPR/Cas9-HDR vector to correct altered GFP (possessing an early termination codon) in vitro. We observed a 23% repair rate with our single vector design comparable to current state of the art approaches requiring multiple factors including a ssDNA oligo (17.7%). We have also observed similar results with another CRISPR nuclease hAsCpf1 (15%). We are in the process of applying our technology to developing preclinical models of cancer (e.g., NSCLC, melanoma) and correcting monogenic diseases (e.g., CTFR).

3) Evaluating B7-H3 and B7-H4

We have observed that each of these immune checkpoint ligands is vital for immune evasion in a murine syngeneic tumor  model where loss of either (via CRISPR) results in a 0% (B7-H3, 0/51 - B7-H4 0/37) take rate compared to parental melanoma cells with a 60% take rate in these immune competent mice. We are characterizing their role in immune evasion and utilizing novel methods to identify their receptors on CD8+ T cells. We have also begun to develop antibodies that block the interaction of these immune checkpoint ligands with their receptors in order to block immunosuppressive signaling.

 4) Oncolytic Immunotherapy

We have developed several novel oncolytic viruses and are evaluating them in several preclinical cancer models. These are wild type RNA viruses that utilize cellular receptors often overexpressed on many tumor types. Therefore, their tropism is largely limited to specific tumor cells enhancing viral infection and spread while limiting toxicity. We are evaluating these as single agents and in combination with immune checkpoint blockade. We are generating modified viruses with expanded tropism by altering capsid genes. We are also developing replication competent viruses encoding small immunomodulatory factors that may enhance host antitumor immunity. In addition, in collaboration with Dr Robert Andtbacka we are evaluating longitudinal patient samples treated with oncolytic viruses (HF10, CVA21) in order to identify biomarkers of response and/or resistance.