Often, the best investments are the ones most of the market isn't paying attention to. With all eyes focused on coronavirus stocks, it may be a good time for investors to look at the possibilities for progress on other diseases that have plagued us for a lot longer.

Alzheimer's, for example, has proven one of the hardest diseases to treat. At least 400 clinical trials of treatments for it have been conducted over the past 17 years, and not one candidate has shown enough of an impact to earn regulatory approval.

Right now, the number of people across the world with Alzheimer's is estimated to be about 44 million, and that figure is expected to triple by 2050. So as I consider the best biotech stocks to buy in November, I'm focusing on those that are targeting neurological diseases, based on my belief that all of the money pouring into research and development could lead to breakthroughs for companies such as Roche Holdings (OTC:RHHBY), Cassava Sciences (NASDAQ:SAVA), and Denali Therapeutics (NASDAQ:DNLI).

A gold metallic puzzle of the brain with a center piece missing and set aside.

Image source: Getty Images

1. Roche Holdings

Roche's drug candidate semorinemab targets the tau protein. This is a key component of the microtubes that transport nutrients from one part of a brain cell to another, but it builds up abnormally in the brains of Alzheimer's patients.

In September, the results of a phase 2 trial of semorinemab were published, showing that it failed to improve patients' scores on a clinical dementia rating scale. A second Phase 2 trial with the drug is ongoing. The company is also pursuing other potential treatments. Gantenerumab is a monoclonal antibody that binds to and neutralizes certain amyloid plaques that form in the brains of Alzheimer's patients. It, too, failed to show benefits in a 2015 clinical trial, but management isn't giving up on the drug yet, because some data suggested that at higher doses, it may have an impact.

There are three Roche clinical trials for investors to keep an eye on at the moment -- two for gantenerumab and one for crenezumab. The gantenerumab studies are in phase 1 and phase 3, respectively. The phase 1 trial aims to see how well the drug crosses the blood-brain barrier (composed of highly selective cells that prevent most detrimental substances from entering the brain), and the phase 3 trial will gauge whether it measurably helps Alzheimer's patients. The results of that study are expected in 2022.

The final Alzheimer's drug, crenezumab, is for patients with a specific genetic mutation; results from that clinical study are expected no earlier than 2023.

2. Cassava Sciences

Cassava Sciences' oral drug candidate sumifilam recently achieved a first in Alzheimer's studies by both decreasing levels of a dangerous protein associated with the disease and improving blood-brain barrier integrity (its ability to control molecular exchanges between the blood and the brain). Malfunctions in this mechanism have been recognized as a key factor in Alzheimer's disease. This month, Cassava released data from a phase 2b trial of sumifilam; the study tested two dose levels, and participants taking both showed significant improvements on both metrics.

The company took advantage of those encouraging results to announce a secondary stock offering last week, through which it is raising $75 million to fund a phase 3 clinical trial of sumifilam. Given that it only had $24 million in cash on the balance sheet at the end of the third quarter -- not enough to cover the costs of a larger study -- management needed to raise cash, sell the company, or license the drug to a better-funded partner; they chose the first of these.

Also worth noting: In September, a company director and the CFO added a total of nearly 225,000 shares to their holdings, which suggests that those who know the most about Cassava Sciences are confident about its future.

3. Denali Therapeutics

Denali, too, is working toward solutions for neurodegenerative diseases. Management paused a study it was running with Sanofi (NASDAQ:SNY) in June after the Alzheimer's drug they were jointly developing produced disappointing results, but the company still has three other drug candidates in early stages of development. For two of them, it is working in partnership with Takeda (NYSE:TAK); for the other, it teamed up with Biogen (NASDAQ:BIIB), the beleaguered company that has garnered headlines for its on-again, off-again Alzheimer's candidate aducanumab

In addition, Denali Therapeutics has partnered with Biogen to develop a drug that mitigates the most common genetic risk factor for Parkinson's disease. The companies recently agreed to a deal for that drug under which Biogen made an upfront payment of $560 million to Denali and purchased $465 million worth of its shares. Denali could also pocket more than $1.1 billion in milestone payments.

The deal will accelerate the clinical study and strengthen ties between the two companies. It's also the type of business relationship that could develop into a buyout offer if things go well. For investors, Denali shares could prove the best of both worlds, offering the potential upside of an Alzheimer's breakthrough with the safety of a big pharma partner shouldering much of the financial burden of its development.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.