San Diego-based Tocagen Inc. has raised $8.5 million of a planned $15.75 million investment round, according to a filing with the U.S. Securities and Exchange Commission.

Seventy-Seven investors participated in the equity financing, with a minimum investment of $210,000, according to the SEC filing.

The company has raised nearly $70 million in eight equity financings dating back to June 2009, filings show. Most recently, it raised a little less than $9.1 million from 32 investors in December 2012.

Tocagen is working to create therapeutics to treat cancer using immunotherapeutic products that are based on gene therapy technology. The company is focusing initially on developing a treatment for an aggressive type of brain cancer, namely recurrent high-grade glioma, according to its website.

Harry Gruber is the company’s CEO.