Houston founder shares how he's using tech to make digital media more effective and equitable

houston innovators podcast episode 173

This month, Mark Walker is celebrating his company's one year anniversary of going public — only the ninth Black-founded business to accomplish this feat on a U.S. stock exchange. Photo courtesy

After working in both sides of the advertising world, Mark Walker thought he could reimagine a platform that would be more efficient and equitable.

Walker co-founded his company, Direct Digital Holdings, an adtech platform, after serving in several roles — from an early hire at Houston digital media startup Questia to business development director at NRG Energy and COO of EBONY Media. He shares on the Houston Innovators Platform how he took this experience in tech, advertising, and media to create his company's platform.

"NRG Energy gave me a top-down view of the value chain, and Ebony gave me a bottoms-up view of the value chain of how media is purchased," Walker says on the show. "At Direct Digital Holdings, we help companies buy and sell media — and we leverage technology to do it. It's really the culmination of both of those experiences."

With over 30,000 publishers on its platform, Direct Digital makes it easier for its core customers — middle market companies looking to buy into the digital media ecosystem — to tap into these opportunities without the tech know-how they might otherwise need. Walker explains that at EBONY, he saw how small to midsize publications — especially the multicultural ones — were being left out on the ad selling side of the equation. The Direct Digital platform bridges the gap on each end.

Founded in 2018 in partnership with Keith Smith, who went through similar professional experiences, Direct Digital went public exactly one year ago after growing the company through strategic M&A activity. Walker says the decision to IPO made the most sense for his company — though it wasn't an easy process. Direct Digital is only the ninth company founded by a Black entrepreneur to go public on a US stock exchange.

"If you think the process is hard — it actually is," Walker says on the journey to IPO. "We were a privately held company, and we knew we had a good growth trajectory and we looked a couple different options. We decided to go public in a very traditional way."

Walker explains there were some risks involved, but the co-founders ultimately decided to shy away from adding in investors who might not have the same ideas for the company's future.

Direct Digital has been a Houston company from the star — despite the city not being home to a booming adtech ecosystem. Instead, Houston — with its collection of Fortune 500 companies and rich diversity — has allowed the business to stand out.

"If you look at and reflect on how our company has been built — from our board of directors to our leadership and management team — we're a majority minority organization all the way across the board," Walker says. "Diversity is very important to us. It's the lifeblood of our business — especially because we're serving publishers in those communities in big way. And moreso, we think you get the best product, thoughts, and ideas from a diverse workforce, and Houston fits right into that mold for us."

Walker shares more about his company's future, advice on IPO, and what all he's watching in adtech — from AI to streaming — on the podcast. Listen to the interview below — or wherever you stream your podcasts — and subscribe for weekly episodes.


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Play it back: Houston home tech startup begins 2025 with fresh funding

HOUSTON INNOVATORS PODCAST EPISODE 272

One of the dozen or so Houston startups kicking of the new year with fresh funding is SmartAC.com, a company that's designed a platform that enables contractors in the HVAC and plumbing industries to monitor, manage, and optimize their maintenance memberships through advanced sensors, AI-driven diagnostics, and proactive alerts.

Last month, the SmartAC.com raised a follow-on round with support from local investor Mercury to continue growth and expansion of the product, which has evolved on many ways since the company launched in 2020, emerging from stealth with $10 million raised in a series A. In a May 2023 interview for the Houston Innovators Podcast, Founder and CEO Josh Teekell explained how he embraced the power of a pivot.

The company's sensors can monitor all aspects of air conditioning units and report back any issues, meaning homeowners have quicker and less costly repairs. While SmartAC.com started with providing the service and tech to homeowners directly, Teekell says he's had a greater interest in working with plumbers and HVAC companies who then deploy the technology to their customers.

"It became quite evident that homeowners don't care about air conditioning really at all until their system breaks," Teekell says on the show. "The technology is really built around giving those contractors as another way to gain a customer relationship and keep it."

Revisit the podcast episode below where Teekell talks about SmartAC.com's last raise.

SmartAC.com's previous round in 2023 — a $22 million series B — was used grow its team that goes out to deploy the technology and train the contractors on the platform.

"We've been very fortunate to get some of the biggest names in Houston on our cap table," Teekell says in the May 2023 conversation. "Since we're raising a bunch of money locally, everyone understands what a pain air conditioning can be."

Houston biotech company tests hard-to-fight cancer therapeutics

fighting cancer

A Houston-based, female-founded biotech company has developed a treatment that could prove to be an effective therapy for a rare blood cancer.

Cellenkos Therapeutics has completed promising Phase 1b testing of its Treg cell therapy, CK0804, in the fight against myelofibrosis. According to a news release from the Cellenkos team, the use of its cord-blood-derived therapeutics could signal a paradigm shift for the treatment of this hard-to-fight cancer.

Cellenkos was founded by MD Anderson Cancer Center physician and professor Simrit Parmar. Her research at the hospital displayed the ability of a unique subset of T cells’ capability to home in on a patient’s bone marrow, restoring immune balance, and potentially halting disease progression.

Myelofibrosis has long been treated primarily with JAK (Janus Kinase) inhibitors, medications that help to block inflammatory enzymes. They work by suppressing the immune response to the blood cancer, but don’t slow the progression of the malady. And they’re not effective for every patient.

“There is a significant need for new therapeutic options for patients living with myelofibrosis who have suboptimal responses to approved JAK inhibitors,” Parmar says. “We are greatly encouraged by the safety profile and early signs of efficacy observed in this patient cohort and look forward to continuing our evaluation of the clinical potential of CK0804 in our planned expansion cohort.”

The expansion cohort is currently enrolling patients with myelofibrosis. What exactly are sufferers dealing with? Myelofibrosis is a chronic disease that causes bone marrow to form scar tissue. This makes it difficult for the body to produce normal blood cells, leaving patients with fatigue, spleen enlargement and night sweats.

Myelofibrosis is rare, with just 16,000 to 18,500 people affected in the United States. But for patients who don’t respond well to JAKs, the prognosis could mean a shorter span than the six-year median survival rate outlined for the disease by Cleveland Clinic.

Helping myelofibrosis patients to thrive isn’t the only goal for Cellenkos right now.

The company seeks to aid people with rare conditions, particularly inflammatory and autoimmune disorders, with the use of CK0804, but also other candidates including one known as CK0801. The latter drug has shown promising efficacy in aplastic anemia, including transfusion independence in treated patients.

The company closed its $15 million series A round led by BVCF Management, based in Shanghai, in 2021. Read more here.

Pioneering Houston biotech startup expands to Brazil for next phase

On the Move

Houston biotech company Cemvita has expanded into Brazil. The company officially established a new subsidiary in the country under the same name.

According to an announcement made earlier this month, the expansion aims to capitalize on Brazil’s progressive regulatory framework, including Brazil’s Fuel of the Future Law, which was enacted in 2024. The company said the expansion also aims to coincide with the 2025 COP30, the UN’s climate change conference, which will be hosted in Brazil in November.

Cemvita utilizes synthetic biology to transform carbon emissions into valuable bio-based chemicals.

“For decades Brazil has pioneered the bioeconomy, and now the time has come to create the future of the circular bioeconomy,” Moji Karimi, CEO of Cemvita, said in a news release. “Our vision is to combine the innovation Cemvita is known for with Brazil’s expertise and resources to create an ecosystem where waste becomes opportunity and sustainability drives growth. By joining forces with Brazilian partners, Cemvita aims to build on Brazil’s storied history in the bioeconomy while laying the groundwork for a circular and sustainable future.”

The Fuel of the Future Law mandates an increase in the biodiesel content of diesel fuel, starting from 15 percent in March and increasing to 20 percent by 2030. It also requires the adoption of Sustainable Aviation Fuel (SAF) and for domestic flights to reduce greenhouse gas emissions by 1 percent starting in 2027, growing to 10 percent reduction by 2037.

Cemvita agreed to a 20-year contract that specified it would supply up to 50 million gallons of SAF annually to United Airlines in 2023.

"This is all made possible by our innovative technology, which transforms carbon waste into value,” Marcio Da Silva, VP of Innovation, said in a news release. “Unlike traditional methods, it requires neither a large land footprint nor clean freshwater, ensuring minimal environmental impact. At the same time, it produces high-value green chemicals—such as sustainable oils and biofuels—without competing with the critical resources needed for food production."

In 2024, Cemvita became capable of generating 500 barrels per day of sustainable oil from carbon waste at its first commercial plant. As a result, Cemvita quadrupled output at its Houston plant. The company had originally planned to reach this milestone in 2029.

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This story originally appeared on our sister site, EnergyCapitalHTX.

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