Stock Incentive Plans

As of July 31, 2018, we had an aggregate of 5,005,142 shares of our common stock reserved for issuance under our stock incentive plans, of which, 3,088,084 shares were subject to outstanding options and restricted stock rights and 1,917,058 shares were available for future grants of stock-based awards.

Stock Options

The following summarizes our stock option transaction activity for the three months ended July 31, 2018:

Restricted Stock Rights

On June 15, 2018, the Compensation Committee of the Board of Directors granted an aggregate of 128,050 restricted stock right (“RSR”) awards to substantially all of our employees, excluding executive officers, which entitles the employee the right to be issued a share of our common stock upon vesting of the RSR. The RSR’s were granted under our 2011 Stock Incentive Plan and vest annually in equal installments over a four-year period. The RSR’s have an aggregate grant date fair value of $464, based on the closing market price of our common stock on the date of grant, which is amortized as stock-based compensation expense on a straight-line basis over the period of vesting.

The following summarizes our restricted stock right transaction activity for the three months ended July 31, 2018:

Employee Stock Purchase Plan

We have reserved a total of 2,142,857 shares of our common stock to be purchased under our Employee Stock Purchase Plan (“ESPP”), of which 1,271,409 shares remained available to purchase at July 31, 2018, and are subject to adjustment as provided in the ESPP for stock splits, stock dividends, recapitalizations and other similar events. Under the ESPP, we sell shares to participants at a price equal to the lesser of 85% of the fair market value of our common stock at the (i) beginning of a six-month offering period, or (ii) end of the six-month offering period. The ESPP provides for two six-month offering periods each year; the first offering period begins on the first trading day on or after each May 1; the second offering period begins on the first trading day on or after each November 1. No shares of our common stock were purchased under the ESPP during the three months ended July 31, 2018 as the current six-month offering period ends on October 31, 2018.

Stock-Based Compensation

Total stock-based compensation expense related to stock-based awards issued under our equity compensation plans is included in the accompanying unaudited condensed consolidated statements of operations and comprehensive loss as follows:

As of July 31, 2018, the total estimated unrecognized compensation cost related to non-vested employee stock options and non-vested restricted stock rights was $2,370 and $449, respectively. These costs are expected to be recognized over a weighted average vesting periods of 2.81 years and 3.87 years, respectively, based on current assumptions.