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Significant Inputs and Assumptions Used in Binomial Lattice Model for Derivative Liability (Detail)

v3.3.0.814
Significant Inputs and Assumptions Used in Binomial Lattice Model for Derivative Liability (Detail) - $ / shares
1 Months Ended
Jun. 24, 2015
Apr. 30, 2015
Feb. 06, 2015
Sep. 26, 2014
May. 31, 2015
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]          
Adjusted conversion price   $ 0.675      
Derivative Liability          
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]          
Quoted market price on valuation date $ 0.90   $ 0.96 $ 0.79 $ 0.99
Contractual conversion rate 1.00   1.00 1.00 1.00
Adjusted conversion price [1] $ 0.6750   $ 1.0000 $ 0.9759 $ 0.6750
Contractual term to maturity (years) 1 month 13 days   5 months 27 days 2 years  
Expected volatility 48.00%   124.00% 123.00%  
Contractual interest rate 1.20%   2.00% 5.00%  
Risk-free rate 0.001%   0.045% 0.59%  
Risk adjusted rate 2.80%   2.78% 2.69% 2.80%
Probability of event of default 5.00%   5.00% 5.00% 5.00%
Derivative Liability | Minimum          
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]          
Contractual term to maturity (years)         2 months 5 days
Expected volatility         90.00%
Contractual interest rate         1.50%
Risk-free rate         0.041%
Derivative Liability | Maximum          
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]          
Contractual term to maturity (years)         1 year 3 months 29 days
Expected volatility         114.00%
Contractual interest rate         5.00%
Risk-free rate         0.48%
[1] The adjusted conversion price input used in the Binomial Lattice Model considers both i) the reduction of the conversion price to $0.675 on April 30, 2015, as result of the short-term convertible notes offering in which Common Stock was sold for a weighted average price of $0.75 and ii) potential adjustment to the stated conversion price due to a future dilutive issuance. This input was calculated using a probability-weighted approach which considered the likelihood of various scenarios occurring including (i) potential success or failure of various phases for PRO 140, (ii) the probability the Company will enter into a future financing and (iii) and the potential price of a future financing.