Insider buying can be an encouraging signal for potential investors.

Insiders at some small-cap biotechs have made notable share purchases.

At two of them, the shares were sold in recent secondary offerings.

Conventional wisdom says that insiders and 10% owners really only buy shares of a company for one reason — they believe the stock price will rise and they want to profit. So insider buying can be an encouraging signal for potential investors, particularly with markets near all-time highs and during periods of uncertainty.

The following are a few of significant insider purchases reported last week, all small-cap biotechs. Also note that with earnings season in full swing, buy windows for many insiders are closed.

Aptinyx

A director at Aptinyx Inc (NASDAQ: APTX) purchased over 3.33 million shares of this clinical-stage biopharmaceutical company focused on brain and nervous system disorders. At $3 per share, that totaled just shy of $10 million and far outstripped the prior week's insider purchases in the same common stock offering.

Aptinyx stock saw about a 9% gain in the past week, and shares were last seen trading at $4.60 apiece, above the director's purchase price and a multimonth high.

The stock still is down more than 12% year-over-year. The consensus analyst recommendation is to buy the shares, and on average they see the share price going to $11.

La Jolla Pharmaceutical

A La Jolla Pharmaceutical Company (NASDAQ: LJPC) director stepped up to the buy window last week and picked up more than 1.25 million shares of this San Diego-based biopharma company at between $6.01 and $7 each. An executive also purchased 3,000 shares at about $8.23 each. Altogether, that totaled more than $8.37 million.

Kevin Tang of Tang Capital Management recently disclosed a more than 30% stake in La Jolla. The stock closed most recently at $7.73 a share, after starting the year at $3.93. Analysts currently anticipate the share price will go to $12.50 and recommend buying La Jolla stock.

Osmotica Pharmaceuticals

Osmotica Pharmaceuticals PLC (NASDAQ: OSMT) reported that two directors and three 10% owners each purchased 1.25 million shares in a public offering of ordinary shares. At $5 per share, that cost each of them $6.25 million. Shares surged on the news of the purchases.

The fourth-quarter earnings report is scheduled for Feb. 13. The shares of this New Jersey-based integrated biopharma company were trading at $5.85 each on last look, above the secondary offering purchase price. The stock has traded as high as $8.45 in the past year, and the consensus price target is $8.25.