Shares of MannKind Corp. jumped Thursday as the Valencia-based developer of diabetes and cancer therapies said it plans a public sale of 20 million common shares in a new offering priced at $17.42 apiece.

The company’s largest stockholder, founder and Chief Executive Alfred E. Mann, and other officers and directors have committed to purchasing about 5.8 million shares. Trading volume was about 10 times the average after the announcement, adding 38 cents, or 2 percent, to reach $17.80 in midday trading.

In addition, MannKind said it will sell $100 million in senior convertible notes at 3.75 percent interest in an underwritten public offering. None of these notes, due 2013, will be sold to Mann or other company officers or directors, the company said.

JPMorgan Securities Inc. and Merrill Lynch & Co. are the joint lead managers of both offerings. The underwriters have a 30-day option to buy up to another 3 million shares to cover overallotments.

MannKind’s lead product candidate is an inhaled insulin system that is in late stage clinical trials. The company has a public float of 23.5 million shares, with roughly another 26.5 million held by Mann and other insiders.