PeptiDream Inc. (Tokyo:4587) jumped over 400% in its first week of trading, but due to rules on daily price limits, there's no telling what investors are really willing to pay for the company.

The preclinical but profitable cyclic peptide specialist soared even higher than an equal price-weighted index of 25 Japanese biotechs, which jumped 22% last week amid a rollercoaster ride for the broader Japanese market.